PRODUCING THE SAME

BACKGROUND

[001 ] Silica (Si0 ₂ ) is a chemical compound that is most commonly found in nature as sand or quartz. Manufactured forms of silica include fused quartz, colloidal silica, silica gel, and aerogel, among others. Silica is used in glass for windows, drinking glasses, optical fibers for telecommunications and in ceramics, among others.

SUMMARY OF THE DISCLOSURE

[002] Broadly, th present patent application relates to improved porous silicon-metal silicide products and methods for making the same, The porous silicon-metal silicide products may be useful, for instance, as catalysts, absorbents, adsorbents, filters, and fillers, among other potential applications. The porous silicon-metal silicide products are generally produced by contacting porous precursor products with magnesium (e.g., gaseous magnesium). The porous precursor products comprise silicon and metal, and with at least some of the silicon being bonded to oxygen (Si-O). Due to the contacting step, the magnesium may reduce at least some of the Si-0 bonds to elemental silicon. Concomitantly, one or more of the metals may react with at least one of a silicon or a Si-0 compound to produce a metal silicide. After the contacting step, a porous silicon-metal silicide product may be recovered. The magnesium contacting step may not materially degrade the initial form of the porous precursor product, and, thus, the recovered silicon-metal silicide product may correspond to the initial form of the porous precursor product. Likewise, the average pore size, average pore volumes and/or specific surface area of the recovered porous silicon- metal silicide product may also correspond to the porous precursor product. Furthermore, the amount, type and size of the silicides may be tailored. Thus, production of silicon-metal silicide products having tailored product forms, pore sizes, pore volumes, specific surface areas, metal silicide amounts, metal silicide types, and/or metal silicide sizes, among other properties, may be facilitated.

[003] One embodiment of a method of producing porous silicon-metal silicide products is illustrated in FIGS. 1 -3. In the illustrated embodiment, the method includes contacting (100) a porous precursor product (I) with a magnesium-containing material (30). in the iilustrated embodiment of FIG. 2, the precursor product (1) includes a porous precursor base (10) in the form of a silica base that has been loaded with at least some metal oxide (MO), thereby placing the metal oxide (MO) in contact with the silica base. For example, the one or more metal oxides (MO) may be within one or more pores of the porous precursor base, on one or more outer surface of the porous precursor base (10), or otherwise located on, within, or partially within the porous precursor base (10), In the illustrated embodiment of FIG. 2, the base ( 0) consists essentially of is silica, but, as described below, other Si-0 materials can be used as the porous precursor product (1).

[004] The contacting step (100) generally includes reducing at least some of the Si-0 bonds of the porous precursor product (1) to silicon (Si) via the magnesium-containing material (30) and/or reducing at least some of the meta! oxide (MO) of the porous precursor product (1 ) to metal (M) via at least one of the silicon, the Si-0 material, and the magnesium- containing material. Concomitant to the contacting step (100), at least some of the metal oxide (MO) or the metal (M) reacts (150) with at least a portion of at least one of the Si-0 material and the silicon, thereby producing at least one silicide (M _x Si _y ). in turn, a porous silicon-metal Si product (2) having a porous silicon-containing base (12) and having the at least one silicide (M _x Si _y ) may be recovered (200), where the at least one silicide (M _x Si _y ) is located on, within, or partially within the porous silicon-containing base (12) (see, e.g., FIG. 3).

[005] As described above, the porous precursor product (1) may have a porous precursor base (10), A "porous precursor base" (10) is a base (a) having a silicon material with at least some silicon-oxygen bonding, (b) having pores, (c) having a specific surface area of at least 1 m"7gram, and (d) is suited for use as a base for another material, such as a base for metal(s), a metal oxides, and combinations thereof. By way of example, the porous precursor base (10) may be a material that is comprised of (and in some instances consist essentially of) porous versions of any of silica, glass (e.g., VYCOR), silicates, silicon monoxide, clays, aluniinosilicates, silica fibers, silica aerogels, silica fume, fumed silica, and silica metallates (e.g., titanates, zirconates), and combinations thereof, among others. In one embodiment, at least 25 wt. % of the porous precursor base includes silicon-oxygen bonding. In another embodiment, at least 50 wt. % of the porous precursor base includes silicon-oxygen bonding. In yet another embodiment, at least 75 wt. % of the porous precursor base includes silicon- oxygen bonding. In another embodiment, at least 90 wt. % of the porous precursor base includes silicon-oxygen bonding, in yet another embodiment, at least 95 wt. % of the porous precursor base includes silicon-oxygen bonding. In another embodiment the porous precursor consists essentially of silicon-oxygen bonding (e.g., essentially pure silica is used as the porous precursor base). [006] The porous precursor base (10) may be microporous, mesoporous and/or macroporous, Microporous means having an average pore size of less than 2 nanometers. Mesoporous means having an average pore size of from 2 nanometers to 50 nanometers, Macroporous means having an average pore size of greater than 50 nanometers.

[007] in one embodiment, the porous precursor base (10) is predominately composed of silica (e.g., contains at least 24 wt. % Si). In one embodiment, the porous precursor base (10) consists essentially of silica. As used herein, "silica" means silicon dioxide (Si0 ₂ ), and irrespective of its crystalline or amorphous structure. In one embodiment, the porous precursor base (10) is mesoporous silica, in another embodiment, the porous precursor base (10) is microporous silica, in yet another embodiment, the porous precursor base (10) is macroporous silica.

[008] in other embodiments, the porous precursor product (1) does not have a distinct base, such as in naturally occurring porous products having metal and silicon therein, Examples include clays and minerals (natural or synthetic).

[009] in one approach, the porous precursor product (1) is a porous particulate. The porous particulate may be of any size suitable for use in producing a porous silicon-metal silicide product. In one embodiment, the porous particulate has a median particle size (DO.5) of from 20 nanometers to 4 mesh. DO.5 is the volume (v) median diameter, in another embodiment, the porous particulate has a median particle size of from 100 nanometers to 100 microns, in yet another embodiment, the porous particulate has a median particle size of from 1 micron to about 50 microns. If required, particle size can be tailored, for example, by- ball milling. Also, since the magnesium contacting step may not materially degrade the initial product form of the porous precursor product (1 ), the recovered product may realize a median particulate size that corresponds to the median particulate size of the porous precursor product (1 ). Particle size may be measured by light diffraction particle size analysis.

[0010] In other embodiments, the porous precursor product may be a porous film, a porous disk, a porous monolith, a hollow sphere, a porous rod, a porous wire, and/or a porous tube (e.g., nano, micro, macro), among others.

[001 1 ] The porous precursor product (1) may have any surface area suitable for production of a porous silicon-metal silicide product (1), but generally has a specific surface area of at least 1 m ² /gram. Higher surface areas may be useful for some applications, In one embodiment, the porous precursor product (1 ) may have a specifi c surface area of at least 25 m ² /gram. In another embodiment, the porous precursor product may have a specific surface area of at least 100 or /grain, Since the magnesium contacting step may not materially degrade the initial product form of the porous precursor product (1 ), the recovered product may realize a surface area that corresponds to the surface area of the porous precursor product (1). The final specific surface area of the final product may be higher than an intermediate product, such as when MgO is removed from the intermediate product (e.g., via an etch, described below), thereby potentially causing an increase in specific surface area. Surface area is measured by BET analysis.

[0012] The porous precursor product (1) may have any suitable pore size, in one embodiment, the porous precursor product (1) has an average pore size of from 2 nanometers (run) to 1 micron (μηι). in one embodiment, the average pore size is from 3 nanometers to 500 nanometers. In another embodiment, the average pore size is from 4 nanometers to 250 nanometers. In yet another embodiment, the average pore size is from 5 nanometers to 125 nanometers. In another embodiment, the average pore size is from 6 nanometers to 60 nanometers. In yet another embodiment, the average pore size is from 6 nanometers to 30 nanometers, in another embodiment, the average pore size is from 7 nanometers to 30 nanometers. Since the magnesium contacting step may not materially degrade the initial product form of the porous precursor product (1), the recovered product may have a pore size that corresponds to the pore size of the porous precursor product (1). The average pore size of a product may be measured by BET analysis.

[0013] The porous precursor product (1) may have any suitable pore volume. In one embodiment, the porous precursor product (1) has a pore volume of at least 0.01 mL/gram. Since the magnesium contacting step may not materially degrade the initial product form of the porous precursor product (1), the recovered product may have a pore volume that corresponds to the pore volume of the porous precursor product (1). Pore volume may he measured by BET analysis.

[0014] As it relates to the phrase "metal silicides", the term "metal" means a metal that can be converted into a silicide. Examples of some useful metals that may be used include Li, Na, K, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Sr, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ba, La, Hf, Ta, Re, Os, Ir, W, P Bi, U, rare earth elements, and mixtures thereof. In one embodiment, the metal is a transition metal that is capable of forming a silicide. In another embodiment, the metal is copper. In yet another embodiment, the metal is titanium. In another embodiment, the metal is vanadium. In yet another embodiment, the metal is chromium. In another embodiment, the metal is manganese. In yet another embodiment, the metal is iron. In another embodiment, the metal is cobalt. In yet another embodiment, the metal is molybdenum. In another embodiment, the metal is tungsten. In yet another embodiment, the metal is platinum, in another embodiment, the metal is palladium. In yet another embodiment, the metal is rhodium, in another embodiment, the metal is ruthenium. In yet another embodiment, the metal is nickel.

[0015] As illustrated in FIGS. 1-2, prior to the contacting step (100) the metal may be in the form of a metal oxide (MO). In other embodiments, the metal may be in metallic or non- metallic forms, such as metal nitrates, carbonates, sulfates, sulfonates, phosphates, amines, and acetylacetonates, among others.

[0016] As described above, the contacting step (100) comprises contacting the porous precursor product (1) with a magnesium containing material (30). The "magnesium- containing material" may be a solid, liquid and/or gas that contains magnesium. As used herein, "magnesium-containing fluid" and the like means a fluid (liquid and/or gas) containing magnesium. In one embodiment, the magnesium-containing material contains a predominate amount of magnesium. In one embodiment, the magnesium-containing material contains more than 50% magnesium. In another embodiment, the magnesium-containing material contains at least 75% magnesium. In yet another embodiment, the magnesium- containing material contains at least 90% magnesium. In another embodiment, the magnesium-containing material contains at least 95% magnesium. In yet another embodiment, the magnesium-containing material contains at least 99% magnesium. In one embodiment, the magnesium-containing material is a fluid and consists essentially of magnesium optionally with one or more other inert fluids. In one embodiment, the magnesium-containing material is a gas,

[0017] The contact step ( 100) may occur for a time and at a temperature suitable to reduce at least some of (e.g., a majority of) the silicon-oxygen bonds, thereby producing at least a portion of the silicon-metal silicide product (2). The silicon-metal silicide product (2) generally contains a similar amount of silicon as the porous precursor product (1), but the amount of silicon-oxygen bonding is less than in the porous precursor product (1). This silicon of the silicon-metal silicide product (2) may be in the form of elemental silicon, or in the form of other silicon compounds, such as in the form of metal silicides, but with fewer silicon-oxygen bonds as compared to its porous precursor product,

[0018] After the contacting step (100), the si!icon-metal silicide product (2) may include silicide portion(s) and non-silicide portion(s). In one embodiment, the amount of silicon in the non-silicide portions is at least 25 wt. %. In another embodiment, the amount of silicon in the non-silicide portions is at least 50 wt. %. In yet another embodiment, the amount of silicon in the non-silicide portions is at least 75 wt. %, In another embodiment, the amount of silicon in the non-silicide portions is at least 90 wt. %. In yet another embodiment, the amount of silicon in the non-silicide portions is at least 95 wt. %. In another embodiment, the amount of silicon in the non-silicide portions is at least 99 wt. %. In yet another embodiment, the non-silicide portions consist essentially of silicon.

[001 ] In one embodiment, the non-silicide portions comprise less than 90 wt. % silicon material having Si-0 bonds. In another embodiment, the non-silicide portions comprise less than 75 wt. % silicon material having Si-0 bonds. In yet another embodiment, the non- silicide portions comprise less than 50 wt. % silicon material having Si-0 bonds. In another embodiment, the non-silicide portions comprise less than 25 wt. % silicon material having Si- O bonds. In yet another embodiment, the non-silicide portions comprise less than 10 wt. % silicon material having Si-0 bonds. In another embodiment, the non-silicide portions comprise less than 5 wt. % silicon material having Si-0 bonds. In yet another embodiment, the non-silicide portions comprise less than 1 wt. % silicon material having Si-0 bonds. In another embodiment, the non-silicide portions is substantially free of any Si-0 bonding (trace amounts or less of Si-0 bonding are measured). The amount of silicon material having Si-0 bonds in the non-silicide portions is a function of the amount of Si-0 bonds In the porous precursor product (1) and the magnesium exposure time and conditions. The amount of Si-0 bonding may be determined by, for example, mass loss via HP etching, accounting for the amount of silicide in the end product.

[0020] In one embodiment, the silicon-metal silicide product (2) contains at least 50 wt. % of at least one of (a) elemental silicon, (b) metal silicides, (c) silicates, and (d), SiOz, wherein Z is less than 2, and (e) combinations of the foregoing, In one embodiment, the silicon-metal silicide product includes at least 50% wt. % elemental silicon, in another embodiment, the silicon-metal silicide product includes at least 50 wt. % silicides. In yet another embodiment, the silicon-metai silicide product includes at least 50 wt. % silicates, As used herein, "silicates" (Si0 ₄ ^4" ) and the like is a compound containing a silicon bearing anion. Silicates includes aluminosiiicates, such as zeolites, titanates, zirconates and the like. In another embodiment, the silicon-metal silicide product includes at least 50 wt. % SiOz, wherein Z is less than 2, [0021] In one embodiment, the silicon-metal silicide product (2) consists essentially of silicides. To produce a silicon-metal silicide product (2) that consists essentially of silicides, a porous precursor base (10) may be used, and the porous precursor product may include high metal loading, In turn, the Si-0 bonds of the porous precursor base may be substantially converted to metal silicides (i.e., trace amounts or less of elemental silicon and silica are measured). In this regard, the base may comprise a first metal silicide, and optionally with one or more other metal silicides being located on, within, or partially within the porous silicide base. The other metal silicides may comprise a different metal and/or a different silicide formula relative to the first metal silicide. For example, the base may comprise monosilicide(s) (e.g., CrSi), and disilicides(s) (e.g., CrSi ₂ ) may be located on, within, or partially within the monosilicide(s) base, in other embodiments, the product consists essentially of a homogenous mixture of silicide(s). Any of the silieide-forming metals described herein may be used to form such silicon-metal silicide products consisting essentially of silicides.

[0022] The silicon-metal silicide product (2) may comprise a distinct porous silicon- containing base (12), such as in embodiments when a porous precursor base (10) is used, and/or where the product (2) is not folly converted to a metal silicide. The porous silicon- containing base may comprise any of the silicon-containing materials described above.

[0023] The contacting step (100) may occur in any environment that facilitates reduction of silicon-oxygen bonds via the magnesium-containing material. The contacting step may occur in a batch or a continuous process. The contacting step may be repeated, as necessary, to achieve one or more preselected properties in the recovered silicon-metal silicide product.

[0024] In one embodiment, the contacting step (100) occurs in an inert environment, such as a sealed vessel having an input and optionally an output. The input may be used to deliver the magnesium-containing material (e.g., a magnesium-containing fluid) into the vessel, the vessel holding porous precursor product. In one embodiment, the magnesium-containing material is magnesium-containing gas, which may be used with or without a carrier gas (e.g., argon as the carrier gas). The output may be used to remove effluent, such as a carrier gas, so as to maintain the pressure within the sealed vessel. Thus, the contacting step (100) may comprise flowing a magnesium-containing gas into a vessel, wherein the vessel comprises a porous precursor product. In turn, the contacting step (100) may also comprise purging gas from the vessel Other configurations may be used to facilitate contacting the porous precursor product with the magnesium-containing material. Similar arrangements may be used when the magnesium-containing material is magnesium-containing liquid, As an example of a solid-to-solid reduction, solid silica and magnesium may be mixed (e.g., at elevated temperature, but below the melting point of the magnesium-containing material).

[0025] The contacting step (100) may occur at any temperature that facilitates reduction of silicon-oxygen bonding by the magnesium-containing material. As may be appreciated, the thermodynamics and kinetics surrounding reduction of the silicon-oxygen bonding and production of metal silicides may be more favorable at higher temperatures. In one embodiment, the temperature of at least one of the porous precursor product and the magnesium-containing material is at least 200°C during at least a portion of the contacting step. In another embodiment, the temperature is at least 400°C. In yet another embodiment, the temperature is at least 600°C, In another embodiment, the temperature is at least 800°C. In yet another embodiment, the temperature is at least 900°C. Higher temperatures may be more useful when the magnesium-containing material is a magnesium-containing gas.

[0026] In one embodiment, the contacting step (100) comprises agitating (not illustrated) the porous precursor product (1). Agitating may facilitate mass transfer so that the magnesium-containing material may more readily reach the silicon-oxygen bonding of the porous precursor product and/or a more homogeneous end product is realized. The agitating may occur via any suitable agitation method and/or apparatus, such as via stirring, a rotary furnace, fl idized bed, vibratory apparatus, and the like.

[0027] Referring now to FIGS, 1-2, concomitant to the contacting step (100) one or more silicides may be produced from the metal of the porous precursor product (1), In this regard, and as described above, the contacting step (100) may include reducing at least some of the silicon-oxygen bonding of the porous silica-metal oxide product to silicon (Si) via the magnesium-containing material (30), For instance, when silica is used, the reaction is (1):

(1) 2Mg + Si<¾→ 2MgO + Si

Concomitantly, some of the metal is in the form of a metal oxide (MO), at least some of the metal oxide (MO) of the porous precursor product may be reduced to metal (M) via at least one of the silicon and the magnesium-containing material, as shown in equations (2) and (3), below.

(2) 2MO + Si > 2M + Si0 ₂

(3) MO + Mg→ M + MgO Concomitantly, the metal (M) may react with the silica and/or the silicon to produce one or more metal silicides, as shown in equations (4) and (5), below.

(4) M + Si→ MxSi _y

(5) M + Si0 ₂ + 2Mg→ M _x Siy + 2MgO

Similar reactions may occur when the metal is not in oxide form.

[0028] As used herein, ''silicides" and the like means a compound that includes at least one metal (M) and silicon, and having the chemical formula M _x Si _y . In one embodiment, the silicides comprise at least one of a monosilicide, a disilicides and a combination thereof. In one embodiment, a monosilicide may be represented by the empirical formula M _x Si where "y" is 1, and "x" is an integer. In another embodiment, a monosilicide may be represented by the formula M _x Si where "y" is 1, and "x" is > 0. In one embodiment, a disilicide may be represented by the empirical formula M _x Si ₂ where "y" is 2, and ^,! x" is an integer. In another embodiment, a disilicide may be represented by the formula M _x Si ₂ where "y" is 2, and "x" is > 0. The silicides may comprises higher order silicides (trisilicides and higher) and/or multiple metals (Ml, M2, or more), and may or may not have an empirical formula.

[0029] As described above, a porous silicon-metal silicide product may be produced and recovered (200), one embodiment of which is shown in FIG. 3. Any number of different metal oxides can be used to produce a porous silicon-metal silicide product (2). In one embodiment, one metal element (Ml) is selected for and/or used as the metal oxide (MI O), and thus, in this embodiment, the final porous silicon-metal silicide product would include silicides of the formula Ml _x Si _y . For instance, if a porous precursor base (10) is used and only chromium (Cr) is selected for and used as the metal element (Ml) of the metal oxide, a final porous silicon-metal silicide product may consist essentially of a porous silicon base and chromium silicides. In another embodiment, two or more metal elements are selected for and/or used as the metal oxides (MIO; M20, etc.), and thus, in this embodiment, the final porous silicon-metal silicide product may include silicides of the formula Ml _x Si _y , M2 _x Si _y , Ml _xi M2 _X 2Siy, and/or (Ml (s _-X) M2 _(X) )Si _yi among others potential compounds / materials, and depending upon metals selected and the contacting (100) and the reaction (150) conditions, among others. As described above, such metal silicides may be monosilicides, disilicides, trisilicides, other higher order silicides, and combinations thereof. As described in further detail below, one or more of the contacting (100) and reacting (150) steps may be controlled in order to produce final porous silicon-metal silicide products (2) having a predetermined amount of monosilicides, disilicides, trisilicides, other higher order other silicides, and combinations thereof.

[0030] In one embodiment, the metal silicides of the porous silicon-metal silicide product (2) comprise at least some monosilicides. In one embodiment, at least 1 wt. % of the metal silicides are monosilicides. In another embodiment, at least 5 wt. % of the metal silicides are monosilicides. In yet another embodiment, at least 10 wt. % of the metal silicides are monosilicides. in another embodiment, at least 20 wt. % of the metal silicides are monosilicides In yet another embodiment, at least 30 wt. % of the metal silicides are monosilicides. In another embodiment, at least 40 wt. % of the metal silicides are monosilicides. in yet another embodiment, at least 50 wt. % of the metal silicides are monosilicides. In another embodiment, at least 60 wt. % of the metal silicides are monosilicides. In yet another embodiment, at least 70 wt. % of the metal silicides are monosilicides. In another embodiment, at least 80 wt. % of the metal silicides are monosilicides. In yet another embodiment, at least 90 wt. % of the metal silicides are monosilicides. In another embodiment, at least 95 wt. % of the metal silicides are monosilicides. In yet another embodiment, at least 99 wt. % of the metal silicides are monosilicides. In another embodiment, the metal silicides of the porous silicon-metal silicide product consist essentially of monosilicides. As described in further detail below, one or more of the contacting (100) and reacting (150) steps may be controlled in order to produce final porous silicon-metal silicide products having a predetermined amount of monosilicides.

[0031] In one embodiment, the metal silicides of the porous silicon-metal silicide product (2) comprise at least some disilicides. In one embodiment, at least I wt. % of the metal silicides are disilicides. In another embodiment, at least 5 wt. % of the metal silicides are disilicides. In yet another embodiment, at least 10 wt. % of the metal silicides are disilicides. In another embodiment, at least 20 wt. % of the metal silicides are disilicide. in yet another embodiment, at least 30 wt. % of the metal silicides are disilicides. In another embodiment, at least 40 wt. % of the metal silicides are disilicides. In yet another embodiment, at least 50 wt. % of the metal silicides are disilicides. In another embodiment, at least 60 wt. % of the metal silicides are disilicides. In yet another embodiment, at least 70 wt. % of the metal silicides are disilicides. In another embodiment, at least 80 wt. % of the metal silicides are disilicides. In yet another embodiment, at least 90 wt, % of the metal silicides are disilicides. In another embodiment, at least 95 wt. % of the metal silicides are disilicides. In yet another embodiment, at least 99 wt. % of the metal silicides are disilicides. In another embodiment. the metal silicides of the porous silicon-metal silicide product consist essentially of disi!icides. As described in further detail below, one or more of the contacting (100) and reacting (150) steps may be controlled in order to produce final porous silicon-metal silicide products having a predetermined amount of disilicides. Similar methodologies may be used to produce final porous silicon-metal silicide products (2) having a predetermined amount of trisilicides or other higher order silicides.

[0032] The silicides may be in the form of crystallites, one embodiment of which is illustrated in FIGS. 4a~4b. As shown in FIG. 4a, the product 2 includes a porous silicon- containing base 12 having a plurality of crystallite silicides 20 disposed thereon. As used herein, "crystallite silicides disposed on a silicon-containing base" and the like means that the crystallite silicides are physically connected to a silicon-containing base, and irrespective of whether the crystallite silicides are fully within the silicon-containing base (encapsulated by), are partially within the silicon-containing base (the crystallites are partially outside of the silicon base), or are disposed on an outer surface of the silicon-containing base, among other possibilities. In cases where the porous precursor base is fully converted to silicides, i.e., consists essentially of silicides, the crystallite silicides are still disposed on the silicon- containing base even though the base and the silicides are the same.

[0033] The crystallite silicides 20 may be in single crystallite form (e.g., crystallite 21) or may be agglomerated to form a larger crystalline structure (e.g., agglomerate 22), The crystallite silicides 20 may be include any of the silicide compounds describe above. As shown in FIG. 4b, the crystallite silicides 20 may be located within (crystallites 20a, which are within pores 26 of the silicon base 12), partially within (crystallite 20b), on (crystallite 20c), or otherwise in contact with the base 12. Although not illustrated, the crystallite silicides may be located beneath surfaces of the base 12, such as via diffusion and/or via reactions ( 150) that may occur during the contacting step (100), and such crystallite silicides 20 may be "within" the base 12.

[0034] The crystallite silicides 20 may have an average crystallite size of from about 5 nanometers to about 500 nanometers. In one embodiment, the crystallite silicides have an average crystallite size of from about 7 nanometers to about 250 nanometers. In another embodiment, the crystallite silicides have an average crystallite size of from about 8 nanometers to about 100 nanometers. In yet another embodiment, the crystallite silicides have an average crystallite size of from about 9 nanometers to about 50 nanometers. Crystallite size may be measured using the Scherrer Equation (1) that relates crystallite size and powder XRD peak widths (FWHM), where Β(2Θ) is the mean size of the crystalline domains, K is the Scherrer constant, λ is the X-ray wavelength, L is the line broadening at half the maximum intensity (FWHM), and Θ is the Bragg angle. See, the examples section, below, equation (7) in subsection (iV)(a).

[0035] After the contacting step (100), the porous silicon-metal silicide product (2) may comprise at least some magnesium. In one approach, a recovered porous silicon-metal silicide product (2) comprises at least some MgO, such as at least 0.1 wt. % MgO. in another embodiment, a porous silicon-metal silicide product (2) comprises at least 1.0 wt. % MgO. In one embodiment, a porous siiicon-metal silicide product (2) comprises not greater than 75 wt. % MgO. In another embodiment, a porous silicon-metal silicide product (2) comprises not greater than 60 wt. % MgO.

[0036] In embodiments where MgO is produced and is contained in a porous silicon- metal silicide product (2), the MgO may be removed. Thus, a method may comprise removing at least, some MgO from a porous silicon-metal silicide product (removing step not illustrated). In one embodiment, the method comprises removing at least some MgO from a porous silicon-metal silicide product via an acid (e.g., via HC1). In one embodiment, substantially ail of the MgO is removed from a porous siiicon-metal silicide product. In other embodiments, tailored or preselected amounts of MgO may be removed via the removing step. Thus, a final porous silicon-metal silicide product may comprise substantially no MgO (e.g. trace amounts or less), or ma comprise tailored or preselected amounts of MgO.

[0037] In another embodiment, a porous silicon-metal silicide product (2) comprises at least some magnesium silicates (e.g., M&SiC ). In one approach, a recovered porous silicon- metal silicide product (2) comprises at least some magnesium silicates, such as at least 0.1 wt. % of magnesium silicates. In another embodiment, a porous silicon-metal silicide product (2) comprises at least some magnesium si licates, such as at least 1.0 wt. % magnesium silicates. In one embodiment, a porous silicon-metal silicide product (2) comprises less than 50 wt. % magnesium silicates (e.g., not greater than 49,5 wt. % magnesium silicates). In some embodiments, tailored or preselected amounts of magnesium silicates may be in the final product due to processing conditions and/or starting materials used. Thus, a final porous silicon-metal silicide product may comprise substantially no magnesium silicates (e.g. trace amounts or less), or may comprise tailored or preselected amounts of magnesium silicates. [0038] in one embodiment, and as described in further detail below, the amount of magnesium in the final porous silicon-metal silicide product is tailored or preselected, such as via control of one or more of the contacting step (100) and the reacting step (150).

[0039] Another embodiment of a method for producing porous silicon-metal silicide products is illustrated in FIG. 5. In this embodiment, one or more of the contacting step (100) and the reacting step (150) may be controlled (45) so as to recover (200) a silicon-metal silicide product having one or more preselected silicide characteristics. In this embodiment, the method may include selecting (40) one or more predetermined silicide characteristic(s) of the silicides of the porous silicon-metal silicide product, and controlling (45) at least one of the contacting step (100) and the reacting step (150) to achieve the predetermined silicide characteristic(s). In turn, the recovering step (200) may comprise recovering a porous silicon-metal silicide product, wherein the porous silicon-metal silicide product realizes the predetermined silicide characteristic(s). When the method includes a producing step (5) (see, FIG. 6, described in further detail below), the controlling step (45) may also include controlling this producing step (5). For instance, to realize more monosilicides, metal-to- silicon stoichiometry and/or magnesium-to-oxygen stoichiometry and/or processing time and/or temperature and/or pressure may be controlled (45) to be in an appropriate range of a phase diagram, which facilitates production of monosilicides. Similarly, more disilicides may be realized by controlling (45) metal-to-silicon stoichiometry and/or magnesium-to- oxygen stoichiometry and/or processing time and/or temperature and/or pressure to be in an appropriate range of a phase diagram.

[0040] The predetermined silicide characteristic may be an amount of silicides and/or a type of silicides and/or a size of silicides of the porous silicon-metal silicide product. In one aspect, the predetermined silicide characteristic is a predetermined amount of silicides, such as a predetermined amount of monosilicides and/or a predetermined amount of disilicides, such as any of the monosilicides and/or disilicides amounts described above.

[0041] In one aspect, the predetermined silicide characteristic is a predetermined amount of monosilicides, In one approach, the predetermined amount of monosilicides exceeds the amount of all other silicides produced via the contacting (100) and reacting (150) steps. In some embodiments, the amount of disilicides may be less than the amount of monosilicides. Thus, the ratio of monosilicides to disilicides (by wt) may be greater than 1.0 (MS DS > 1 .0). In one embodiment, the ratio of monosilicides to disilicides is at least 1.05 (MS/DS > 1.05). in another embodiment, the ratio of monosilicides to disilicides is at least 1.3. In yet another embodiment, the ratio of monosilicides to disilicides is at least 1.7. In another embodiment, the ratio of monosilicides to disilicides is at least 2.0. In yet another embodiment, the ratio of monosilicides to disilicides is at least 2.3, or higher. Thus, this approach may also involve (explicitly or implicitly) selecting a predetermined amount of disilicides via the selection of a predetermined amount of monosilicides.

[0042] In a related aspect, the predetermined silicide characteristic may be a predetermined amount of disilicides. In one approach, the amount of disilicides is controlled so that low amounts of disilicides or no disilicides are produced. In one embodiment, the porous silicon-metal silicide product contains not greater than 10 wt. % disilicides. In another embodiment, the porous silicon-metal silicide product contains not greater than 5 wt. % disilicides. In yet another embodiment, the porous silicon-metal silicide product contains not greater than 1 wt. % disilicides. In another embodiment, the porous silicon-metal silicide product contains not greater than 0.5 wt. % disilicides. In yet another embodiment, the porous silicon-metal silicide product contains not greater than 0.1 wt. % disilicides. In another embodiment, the porous silicon-metal silicide product contains no measureable disilicides. Thus, the ratio of monosilicides to disilicides may be at least 3.0 (MS/DS > 3.0). In one embodiment, the ratio of monosilicides to disilicides is at least 5.0. In another embodiment, the ratio of monosilicides to disilicides is at least 10,0. In yet another embodiment, the ratio of monosilicides to disilicides is at least 20.0. In another embodiment, the ratio of monosilicides to disilicides is at least 50,0. In yet another embodiment, the ratio of monosilicides to disilicides is at least 100.0, or higher. Thus, this approach may also involve (explicitly or implicitly) selecting a predetermined amount of monosilicides via the selection of a predetermined amount of disilicides.

[0043] In another approach, the predetermined silicide characteristic may be a predetermined amount of disilicides and the predetermined amount of disilicides exceeds the amount of all other silicides produced via the contacting (100) and reacting (150) steps, In some embodiments, the amount of monosilicides may be less than the amount of disilicides. Thus, the ratio of disilicides to monosilicides (by wt.) may be greater than 1.0 (DS/MS > 1.0). in one embodiment, the ratio of disilicides to monosilicides is at least 1.05 (MS/DS > 1.05). In another embodiment, the ratio of disilicides to monosilicides is at least 1.3. In yet another embodiment, the ratio of disilicides to monosilicides is at least 1.7. In another embodiment, the ratio of disilicides to monosilicides is at least 2.0. In yet another embodiment, the ratio of disilicides to monosilicides is at least 2.3, or higher. Thus, this approach may also involve (explicitly or implicitly) selecting a predetermined amount of monosilicides via the selection of a predetermined amount of disilicides.

[0044] in a related aspect, the amount of monosilicides is controlled so that low amounts of monosilicides or no monosilicides are produced, in one embodiment, the porous silicon- metal siiicide product contains not greater than 10 t. % monosilicides. In another embodiment, the porous silicon-metal siiicide product contains not greater than 5 wt. % monosilicides. In yet another embodiment, the porous silicon-metal siiicide product contains not greater than 1 wt. % monosilicides. In another embodiment, the porous silicon-metal siiicide product contains not greater than 0.5 wt. % monosilicides. In yet another embodiment, the porous silicon-metal siiicide product contains not greater than 0.1 wt. % monosilicides. In another embodiment, the porous silicon-metal siiicide product contains no rneasureab!e monosilicides. Thus, the ratio of disilicides to monosilicides may be at least 3.0 (MS/DS > 3.0). In one embodiment, the ratio of disilicides to monosilicides is at least 5.0. In another embodiment, the ratio of disilicides to monosilicides is at least 10.0. In yet another embodiment, the ratio of disilicides to monosilicides is at least 20,0, In another embodiment, the ratio of disilicides to monosilicides is at least 50.0. In yet another embodiment, the ratio of disilicides to monosilicides is at least 100.0, or higher. Thus, this approach may also involve (explicitly or implicitly) selecting a predetermined amount of monosilicides via the selection of a predetennined amount of disilicides.

[0045] In one approach the predetermined siiicide characteristic is a predetennined type of monosilicides, and the predetennined type of monosilicides is selected from the group consisting of MSi, M _? Si and combinations thereof. In one embodiment, the predetermined type of monosilicides is MSi. In another embodiment, the predetermined type of monosilicides is M ₂ Si. The type of predetermined monosilicides may be preselected in combination with an amount of monosilicides, such as any of the monosilicides amounts described above. Thus, tailored or preselected porous silicon-monosilicide products may be fabricated.

[0046] in another approach the predetermined siiicide characteristic is a predetermined type of disilicides, and the predetermined type of disilicides is selected from the group consisting of MSi;?, M ₃ Si ₂ MgSi? and combinations thereof. In one embodiment, the predetermined type of monosilicides is MSi?. The type of predetermined disilicides may be preselected in combination with an amount of disilicides, such as any of the disilicides amounts described above. Thus, tailored or preselected porous silicon-disilicide products may be fabricated. Similar methodologies may be used to produce final porous silicon- trisilieide products (or other higher order silicon-metal silicide products).

[0047] In another approach, the predetermined silicide characteristic is a predetermined size of the si!icides. For instance, high temperature processing (e.g., annealing) may be used to produce silicides having a larger average crystallite size. Smaller average crystallite sizes may be produced by using shorter contacting step (100) durations and/or lower temperatures, for instance.

[0048] Referring now to FIG. 6, a method may include producing (5) a porous precursor product. As described above, this porous precursor product may be loaded with metals (e.g., metal oxides), and which metals may be all the same element or which may be different metal(s) of the periodic table, including the metals capable of forming silicides, described above. Other metals may also be used to form metal-to-metal-silicide composites. In one approach, the silica-based precursor is contacted (15) with a metal precursor, in one embodiment, the metal precursor is a metal-precursor liquid, and the metal precursor liquid comprises at least one decomposable metal complex. As used herein, "metal-precursor liquid" and the like means a liquid having at least one decomposable metal complex, the decomposable metal complex being a precursor to a decomposed metal version of the decomposable metal complex. A decomposable metal complex is a metal complex that can be changed to two separate compounds / elements (e.g., a metal nitrate solution being heated and then decomposing to a metal oxide and a nitrous / nitric oxide (e.g., in the presence of air)).

[0049] Examples of metal -precursor solutions suitable for use in impregnating pores of a porous product include metal salt solutions, metal nitrate solutions, chelated solutions, and/or organomeiallics, among others. In one embodiment, the decomposable metal complex is a metal nitrate. As used herein, a metal nitrate is one or more compounds of die formula M(N03)x.(H20)a where x is the valency of the metal M. and 'a' may be 0 or a number > 0, and also partial decomposition products of such compounds formed for example during a previous drying step, such as metal hydroxy nitrates.

[0050] The producing (5) a porous precursor product may be completed in a batch process or in a continuous process. In one embodiment, multiple producing steps (5) are used to achieve a preselected metal loading level for the porous precursor product.

[0051] In some embodiments, the contacting step (15) may include impregnating (17) at least some pores of the porous product with at least some of the decomposable metal- complex. As used herein, "impregnating pores" and the like means to at least partially place a material into at least one pore of a porous product. The impregnating may occur by capillary action, diffusion, and/or any other type of movement that facilitates placing the material into at least a portion of the at least one pore of the porous product. In one embodiment, the impregnating comprises capillary action, such as when incipient wetness impregnation is used, where a liquid moves into at least a portion of the pore via capillary action. In another embodiment, the impregnating comprises diffusion. Other methods of impregnation may be used (e.g., grafting, sol-gel processing, co-precipitation). In one embodiment, the contacting step (15) comprises incipient wetness impregnation.

[0052] After or concomitant to the contacting step (15), the method may include decomposing (20) at least some of the metal precursor to a metal, optionally followed by oxidizing at least some of the metal to a metal oxide. The decomposing step may comprise heating the metal precursor at elevated temperature, such as at a temperature of 200°C, or higher (e.g., when metal nitrates are used). Similarly, the method may comprise oxidizing at least some of the metal to a metal oxide. For instance, a metal-loaded porous precursor product may be heated at elevated temperature (e.g., calcined), for instance, so as to remove any residual metal-precursor liquid and/or other liquids. In oxygen-containing atmospheres, this heating operation may oxidize at least some of the metal of the metal-loaded precursor product to one or more metal oxides.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIG, 1 is a flow chart illustrating one embodiment of a new method for producing porous silicon-metal silicide products.

[0054] FIG. 2 is a schematic, cut-away view of one embodiment of a porous silica-metal oxide product.

[0055] FIG. 3 is a schematic, cut-away view of a porous silicon-metal silicide product produced from the porous silica-metal oxide product of FIG. 2.

[0056] FIG. 4a is a schematic, perspective view of a porous silicon-metal silicide product.

[0057] FIG. 4b is a schematic, cut-away view of a portion of a porous silicon-metal silicide product.

[0058] FIG. 5 is a flow chart illustrating one embodiment of a new method for producing porous silicon-metal silicide products having one or more predetermined silicide characteristics. [0059] FIG. 6 is a flow chart illustrating one embodiment of a new method for producing porous silicon-metal silicide products, including a step for producing a porous precursor product.

DETAILED DESCRIPTION

Example 1

[0060] Example 1 - Production of Silicon-Silicide Particulates Via Incipient Wetness Impregnation and Magnesiotbermic Reduction

[0061] I. Production of silica-metal particulate precursor products

[0062] Various different silica-metal particulate products were prepared from silica particles and various metals (e.g., Fe, Co, Ni. Cu, and Gd). Specifically, the silica particles were DAVISIL 633, DAVISIL 636, and SBA-15. DAVIS1L products are available from SIGMA ALDRICH, and SBA-15 is available from ACS Materials, LLC.

[0063] The DAVISIL 633 had a particle size of 35-75 μηι, an average pore size of 60 A, an average pore volume of 0.75 cm /g, and a speci c surface area of 480 m7g. The DAVISIL 636 had a particle size of 250-500 μιη, an average pore size of 60 A, an average pore volume of 0.75 cm /g, and a specific surface area of 480 m7g. The SBA-15 had a particle size of 500 run to 5 μτη, an average pore size of 77 A, an average pore volume of 1.1 cnrVg, and a specific surface area of 571 m7'g.

[0064] The silica particulates were prepared for incipient wetness impregnation by heating to about 400 °C in air and at a rate of about 1 °C mm ^"1 . This heating step facilitates removal of any physisorbed water in the silica. The silica was then allowed to cool to ambient temperature, placed under vacuum, and stored in an Ar-fllled glovebox.

[0065] Next, silica-metal oxide particulates were prepared by incipient wetness impregnation. As an example of a typical impregnation, an aqueous metal nitrate solution (e.g., Fe(NG3)2 ^« 9H20 (2.653 M), available from Sigma-AIdrich) was added dropwise to stirred silica to the point of incipient wetness. The particulates are then heated to thermally decompose the metal nitrate into its corresponding metal oxide (e.g., by heating at about 200°C (1 °C miii-1) in air). In these experiments, the decomposed metal nitrate forms a metal oxide due to the use of air as the heating medium. The metal oxide content of the final silica-metal product was then calculated based on the amount of metal added to the silica.

[0066] II. Magnesiothermic Reduction [0067] The silica-metal oxide products from Section I, above, were then separately contacted via a magnesium containing fluid. Specifically, a silica-metal oxide product (e.g., a silica-iron oxide product) was placed into a steel canister under an inert atmosphere (argon gas for these experiments). A magnesium-powder (99%) from Strem Chemicals was also placed in the steel canister. The steel canister was then placed in a rotary furnace. The rotary furnace was heated to about 950°C (about 300 °C above the melting temperature of the magnesium) and the steel canister was rotated at a rate of about 8 rpm for 6.5 hours (starting when the furnace reached about 950°C), Next, the steel canister was removed from the rotary furnace, and allowed to cool to ambient temperature, The reactor was then cut open and the silicon-silicide products were then recovered. The recovered products were contacted with HC1 (6M) for a period of time (e.g., 3 hours, with stirring) to remove residual MgO. The product was then washed and filtered, producing final silicon-silicide particulate products.

[0068] Specific silicon-silicide particulate production processes and products are provided in Section III, below. Properties of the recovered silicon-silicide products are provided in Section IV, below,

[0069] III. Specific silicon-silicide products and process.

[0070] a. Preparation and Reduction of 9.7 at% CoO/Davisil 636, (ID 24855-53). 9,7 at% CoO/Si02 (Davisil 636) was prepared via standard incipient wetness impregnation using a 2.54M aqueous solution of Co(N03)2 ^» 6H20 and Davisil 636 that was previously dried at 400 °C to remove any physisorbed water. An amount of 14.35 n L of the Co(N03)2*6H20 solution was added to 20.4792 g of Davisil 636 which afforded a calculated loading of 9,7 at% Co(N03)2/Si02. The 9.7 at% Co(N03)2-impregnated silica was then decomposed to 9.7 at CoO-impregnated silica by heating in air (1 °Cmin-l) to 400 °C. Under Ar, a steel reactor was loaded with 4.0020 g of 9.7 at% CoO/Si02 and 2.9995 g of Mg powder (Mg:0 total = 1.0). The steel reactor was then sealed and placed inside an alumina tube and inserted into a rotary furnace. The rotation was then engaged (8 rpm) and the furnace was heated rapidly to 950 °C and held for 6.5 h. After cooling to room temperature, the steel reactor was opened in air and the contents were washed with 6M HC1 overnight with stirring. After etching, the dark brown/black solid was isolated via centrifuge. Powder XRD results show the etched product contains about (wt%) 42% CoSi2 (61.2 nm crystallite size), 51 % Si (81.1 nm crystallite size), 7% Si02 (>100 nm). BET surface area measurements showed the etched product had a pore size of about 7.2 nanometers, a pore volume of about 0,10 cm /gram and a specific surface area of about 57 m /gram. [0071] b. Preparation and Reduction of 30.2 at% CoO/Davisil 636 (ID 24855-57). 30.2 at% CoO/Si02 (Davisil 636) was prepared and reduced similar to 24855-53 with the following changes. In order to increase the CoO loading, multiple incipient wetness impregnations were performed with ~2.5 M aqueous solutions of Co(NQ3)2 ^» 6H20. Magnesiothermic reduction conditions were Mg:0 total ^::: 1.0, 950 °C, 6.5 h. Powder XRD results show the etched product contains about (wt%) 30% Mg2Si04 (121.8 nm crystallite size), 34% CoSi (55.7nm crystallite size), and 34% CoSi2 (86,5 nm crystallite size). BET surface area measurements showed the etched product had a pore size of about 10 nanometers, a pore volume of about 0.14 em ^' Vgram and a specific surface area of about 54 m ^' /gram.

[0072] c. Preparation and Reduction of 30.2 at% CoO Davisil 636 (ID 24855-41). 30.2 at% CoO/Si02 (Davisil 636) was prepared and reduced similar to 24855-53 with the following changes. In order to increase the CoO loading, multiple incipient wetness impregnations were performed with --2.5 M aqueous solutions of Co(N03)2 ^» 6H20. Magnesiothermic reduction conditions were Mg:0 total = 0.93, 800 °C, 6.5 h. Powder XRD results show the etched product contains (wt%) 21% CoSi (72.8 nm crystallite size), 37% CoSi2 (56,7 nm crystallite size), 31% Mg2Si04 (69.8 nm crystallite size), 1 1% Co2Si (58.1 nm crystallite size). BET surface area measurements show the etched product has a pore size of 6.2 nm, a pore volume of 0.094 cm ³ /g, and a specific surface area of 60 m ² /g.

[0073] d. Preparation and Reduction of 30.2 at% CoO/Davisil 636 (ID 24855-35). 30.2 at% CoO/Si02 (Davisil 636) was prepared and reduced similar to 24855-53 with the following changes. In order to increase the CoO loading, multiple incipient wetness impregnations were performed with -2.5 M aqueous solutions of Co(N03)2 ^» 6H20. Magnesiothermic reduction conditions were Mg:0 total = 0.93, 950 °C, 22 h. Powder XRD results show the etched product contains about (wt%) 27% CoSi (152.7 nm crystallite size), 17% CoSi2 (121.6 nm crystallite size), 46% Mg ₂ Si0 ₄ (127.6 nm crystallite size), 8% Co ₂ Si (230.7 nm crystallite size), 2.1% MgO (7.5 nm crystallite size). BET surface area measurements show the etched product has a pore size of 8.6 nm, a pore volume of 0.055 cm g, and a specific surface area of 25 m /g.

[0074] e. Preparation and Reduction of 30.2 at% CoO/Davisil 636 (ID 24855-67), 30.2 at% CoO/Si02 (Davisil 636) was prepared and reduced similar to 24855-53 with the following changes. In order to increase the CoO loading, multiple incipient wetness impregnations were performed with -2.5 M aqueous solutions of Co(N03)2 ^» 6H20. agnesiotheraiic reduction conditions were Mg:0 total ^:::: 2.0, 950 °C, 6.5 h. Powder XRD results show the etched product contains (wt%) >99% CoSi (34.8 nm crystallite size). BET surface area measurements showed the etched product had a pore size of about 7.2 nanometers, a pore volume oi about 0,064 cm /gram and a specific surface area of about 36 m7gram.

[0075] f. Preparation and Reduction of 10.2 at% Mo03/Davisil 636 (ID 24855-47). 10.2 at% Mo03/Si02 (Davisii 636) was prepared and reduced similar to 24855-53 with the following changes. Incipient wetness impregnations were carried out using 0.342 M aqueous solutions of ammonium molybdate tetrahydrate, (ΝΗ4)6Μο7024·4Η20, impregnated samples were decomposed to Mo03/Si02 by heating to 500 °C (l °Cmin-l) Magnesiothermic reduction conditions were Mg:0 total = 1 ,0, 950 °C, 6.5 h, Powder XRD results show the etched product contains about (wt%) 45% Si (31.4 nm crystallite size), 45% a-MoSi2 (29,4 nm crystallite size), and 6% β- ο812 (5,9 nm crystallite size), 4% Mg2Si04 (25.3 nm crystallite size), and < 1% Mo (34.2 nm crystallite size). BET surface area measurements show the etched product has a pore size of 8,8 nm, a pore volume of 0,09 cm3/g, and a specific surface area of 41 m2/g. Light diffraction particle analysis on the raw and etched product showed particle size ranges of 1 .2 - 209 μηι with a DO.5 particle size of about 38.5 um.

[0076] g. Preparation and Reduction of 6.6 at% Ti02/Davisil 636 (ID 24855-68). 6.6 at% Ti02/Si02 (Davisii 636) was prepared and reduced similar to 2.4855-53 with the following changes, Incipient wetness impregnations were carried out using 1.453 M isopropanol solutions of tetrakisisopropoxytitanium(IV), Ti(OiPr)4. Impregnated samples were dried and then decomposed to Ti02/Si02 by heating to 500 °C (l °Cmin-l) Magnesiothermic reduction conditions were Mg:0 total = 1.0, 950 °C, 6.5 h. Powder XRD results show the etched product contains Si (66.8 nm crystallite size) and TiSi2 (39,2 m crystallite size). BET surface area measurements show the etched product has a pore size of 8.6 nm, a pore volume of 0.17 cnrVg, and a specific surface area of 77 m /g.

[0077] h. Preparation and Reduction of 1 1.5 at% Mn02/DavisiS 633 (ID 24855-5). 1 1.5 at% Mn02/Si02 (Davisii 633) was prepared and reduced similar to 24855-53 with the following changes. Incipient wetness impregnations were carried out using 2.536 M aqueous solutions of Μη(Ν03)2·χΗ20. Impregnated samples were decomposed to MnQ2/Si02 by heating to 300 °C (l °Cmin-l) Magnesiothermic reduction conditions were Mg:0 total = 1.0, 950 °C, 8 h. Powder XRD results show the etched product contains about (wt%) 16% Si (80,0 nm crystallite size), 12% Mn4Si7 (69.3 nm crystallite size), 44% Mg ₂ Si0 ₄ (64.1 run crystallite size), and 28% MgO (62.0 nm crystallite size). BET surface area measurements show the etched product has a pore size of 3.1 nm, a pore volume of 0.027 cnr/'g, and a specific surface area of 35 m ² /g.

[0078] i. Preparation and Reduction of 7.9 at% Fe203/Davisil 633 (ID 24441-101). 7.9 at% Fe203/Si02 (Davisil 633) was prepared and reduced similar to 24855-53 with the following changes, incipient wetness impregnations were carried out using 2.653 M aqueous solutions of Fe(N03)3*9H20. Impregnated samples were decomposed to Fe203/Si02 by heating to 200 °C (l °Cmin-l) Magnesiothermic reduction conditions were Mg:0 totai ^::: 1.1, 950 °C, 8 h. Powder XRD results show the etched product contains about (wt%) 31% Si (50,6 nm crystallite size), 45% Fe0.82Si2 (57.3 nm crystallite size), 2% γ-Fe ( 1.3 nm crystallite size), < 1% Fe (50.1 nm crystallite size), 17% FeSi2 (.30.9 nm crystallite size) and 5% Fe304 (9.5 nm crystallite size). BET surface area measurements showed the etched product has a pore size of 12 nm, a pore volume of 0.27 cm3/g, and a specific surface area of 89 m2/g.

[0079] j. Preparation and Reduction of 5.9 at% Cr2G3/Davisil 633 (ID 24441-144). 5.9 at% Cr203/Si02 (Davisil 633) was prepared and reduced similar to 24855-53 with the following changes. Incipient wetness impregnations were carried out using 2.49 M aqueous solutions of Cr(N03)3 ^» 9H20. Impregnated samples were decomposed to Cr203/Si02 by heating to 550 °C (l°Cmin-l) Magnesiothermic reduction conditions were Mg:0 total = 1.1, 950 °C, 6.5 h. Powder XRD results show the etched product contains about (wt%) 46% Si (126.3 nm crystallite size) and 54% CrSi2 (73,2 nm crystallite size).

[0080] k. Preparation and Reduction of 5.6 at% Gd203/Davisil 633 (24441 -1 1 1), 5.6 at% Gd203/Si02 (Davisil 633) was prepared and reduced similar to 24855-53 with the following changes. Incipient wetness impregnations were carried out using 2.23 M aqueous solutions of Gd(NQ3)3*5H20. Impregnated samples were decomposed to Gd203/Si02 by heating to 367 °C (l °Cmin-l) Magnesiothermic reduction conditions were Mg:0 total = 1 , 1, 950 °C, 8 h. Powder XRD results show the raw product contains about (wt%) 17% Si (14.9 nm crystallite size), 6% GdSiI .4 (22.6 nm crystallite size). 4% GdSil .85 (52.8 nm crystallite size), 69% MgO (15.9 nm crystallite size), 2% Mg2Si04 (74.8 nm crystallite size), 2% Gd (9.4 nm crystallite size), <1% Gd0.75Mg0.25 (37,3 nm crystallite size). Powder XRD results show the etched product contains (wt%) >99% Si (21 ,3 nm crystallite size). BET surface area measurements show the etched product has a pore size of 9 nm, a pore volume of 0,32 cm3/g, and a specific surface area of 131 m2/g,

[0081 ] I. Preparation and Reduction of 8.2 at% CoO/SBA-15 (TO 24441-106). 8.2 at% CoO/Si02 (SBA-15) was prepared and reduced similar to 24855-53 with the following changes. Incipient wetness impregnations were carried out using 2.50 M aqueous solutions of Co(N03)2 ^» 6H20. Impregnated samples were decomposed to CoO/Si02 by heating to 242 °C (i °Cmin-l) Magnesiothermic reduction conditions were Mg:0 total = 1.1, 950 °C, 8 h. Powder XRD results show the etched product contains about (wt%) 40% Si (28.2 nm crystallite size), 60% CoSi2 (41.5 nm crystallite size). BET surface area measurements show the etched product has a pore size of 12 nm, a pore volume of 0.29 cm3/g, and a specific surface area of 92 m2/g.

[0082] m. Preparation and Reduction of 7.7 at% CuO/Davisil 633 (ID 24441-108). 7.7 at% CoO/Si02 (Davisil 633) was prepared and reduced similar to 24855-53 with the following changes, incipient wetness impregnations were carried out using 2.50 M aqueous solutions of Cu(N03)2 ^» 3H20. Impregnated samples were decomposed to CuO/Si02 by heating to 200 °C (l°Cmin-l) Magnesiothermic reduction conditions were Mg:0 total 1.1, 950 °C, 8 h. Powder XRD results show the raw product contains about (wt%) 64% MgO (32.7 nm crystallite size), 17% Si (37.5 nm crystallite size), 4%€«3.1781 (38.6 nm crystallite size), 15% g SiOi (66.9 nm crystallite size).

[0083] n. Preparation and Reduction of 10.0 at% Ta205/Davisil 633 (ID 24441-80). 10.0 at% Ta205/Si02 (Davisil 633) was prepared and reduced similar to 24855-53 with the following changes. Incipient wetness impregnations were carried out using 6.79 M ethanoi solutions of tetraethoxytantalum(V), Ta(OEt)5, Impregnated samples were dried under flowing Ar and were then decomposed to Ta205/Si02 by heating to 500 °C (l°Cmin-l) Magnesiothermic reduction conditions were Mg:0 total = 1.0, 950 °C, 8 h. Powder XRD results show the etched product contains about (wt%) 48% Si (10.1 nm crystallite size), 52% TaSi2 (17.7 nm crystallite size). BET surface area measurements show the etched product has a pore size of 11 nm, a pore volume of 0,20 cm3/g, and a specific surface area of 71 m2/g.

[0084] 0. Preparation and Reduction of 10.2 at% NiO/Davisil 633 (ID 24441-75). 10.2 at% NiO/Si02 (Davisil 633) was prepared and reduced similar to 24855-53 with the following changes. Incipient wetness impregnations were carried out using 2.52 M aqueous solutions of Ni(N03)2 ^» 3H20. Impregnated samples were decomposed to NiO/Si02 by heating to 100 °C in a vacuum oven overnight. Magnesioihennic reduction conditions were carried out in a stainless steel tube with no rotation. Mg:0 total = 1.1, 950 °C, 8 h. Powder XRD results show the raw product contains about (wt%) 19% NiSi2 (39.7 nm crystallite size), 1% Si02 (30.2 nm crystallite size), 74% MgO (34.4 nm crystallite size), 4% Mg2Si04 (42.1 nm crystallite size), 15% Si (38.7 nm crystallite size). BET surface area measurements show the etched product has a pore size of 15 nm. a pore volume of 0,34 cm3/g, and a specific surface area of 86 m2/g.

[0085] p. Preparation and Reduction of 4.2 at% Mo03/4.4 at% Ti02/Davisil 636 (ID 24595-56). 4.2 at% Mo03/4.4 at% Ti02/Davisil 636 was prepared and reduced similar to 24855-53 with the following changes. Incipient wetness impregnations were carried out using subsequent impregnation/calcinations steps using 0.991 M isopropanol solutions of tetrakisisopropoxytitanium(IV), Ti(OiPr)4, and 0.136 M aqueous solutions of ammonium niolybdate tetrahydrate, (ΝΗ4)6Μο7024·4Η20. The silica was impregnated with the Ti solution first, then the sample was decomposed to Ti02/Si02 by heating to 500 °C (l°Cmin- 1). The impregnated Ti02/Si02 sample was then impregnated with Mo solution and was calcined by heating to 500 °C (l°Cmin-l ) for 24 h. Magnesioihennic reduction conditions were Mg:0 total - 1.1 , 950 °C, 6.5 h. Powder XRD results show the etched product contains about (wt%) 57% Si (107.5 nm crystallite size), 43% (MoTi2)Si6 (43.9 nm crystallite size).

[0086] IK Properties

[0087] a. Measurement Techniques

[0088] XRD: X-ray diffraction (XRD) patterns were collected in Bragg-Brentano geometry from 10 to 80° 2Θ in 0.02° increments at 0.4 second per step with a Cu anode operating at 40 kV and 44 mA. An open height limiting slit, 0.6 mm divergence slit, 22.92 mm scattering slit, 37.77 mm receiving slit were used, and intensity data were collected with a high speed detector. Crystallite sizes were acquired using the Scherrer Equation (7) that relates crystallite size and powder XRD peak widths (FWHM), where Β(2Θ) is the mean size of the crystalline domains, K is the Scherrer constant, λ is the X-ray wavelength, L is the line broadening at half the maximum intensity (FWHM), and Θ is the Bragg angle.

(7) [0089] SEM: Scanning electron microscopy (SECM) was performed using a Hitachi 3400N. Samples were analyzed in variable pressure mode, and images and spectra were collected using a 15 kV accelerating voltage,

[0090] EDS: EDS (Energy-dispersive X-ray spectroscopy) spectra were collected in spot mode for 5 seconds per analysis location,

[0091 ] TEM: Transmission electron microscopy (ΊΈΜ) was performed using a JEOL JEM2100F instrument operated at 200 kV, Samples for TEM imaging were prepared by placing the powder samples in methanol (roughly 20x by volume) and were sonicated for ] 0 minutes, One droplet of the suspension was then placed on a standard TEM Cu grid with a holey carbon film. The specimen was analyzed following air-drying. The micrographs were obtained using a G atari CCD camera below the TEM column.

[0092] BET ^" ' and Pore Characteristics: BET surface area and pore characteristics were acquired using a Micromeritics ASAP 2020 model surface area analyzer with nitrogen gas using manufacturer recommended settings.

[0093] Particle Size Determination: Light diffraction particle analysis was run on the Microtrac S3500. Method development was completed for this request as per manufacturer's instruction. The samples were run in isopropanol. The refractive indexes used were based on a weighted average of the phases identified via powder XRD. Experiments were run in triplicate. Samples were stirred and roiled for 2 minutes in a glass sample jar to redistribute material. Sample preparation before analysis consisted of weighing out ~20 grams of isopropanol and ~0.2 grams of sample in a 1 ounce glass jar. No surfactants were added. The mixture was then mixed quickly with a small spatula to get material off the bottom and sides of the jar for two minutes. Immediately after mixing the mixture was sonicated for 2 minutes to evenly disperse the sample in the solvent, the sample was then loaded into the S3500 sample cell to collect data.