"Catalyst element and system, method of manufacturing such element"

[0001] The present invention relates to a system for the catalytic oxidation of uncombusted methane in vehicles with natural gas powered engines, a method for manufacturing and a use of such a system for the at least partial abatement of methane, preferably to legislative tolerance levels.

[0002] In recent years, the steady and inexorable increase in excise duties on fuels such as unleaded petrol or diesel, and the environmental problem related to the use of such fuels have encouraged the development of vehicles fitted with gas systems (e.g. LPG, methane, propane) , possibly combined - in hybrid mode - with the traditional power systems.

[0003] Although the efficiency of the combustion of the above gases or mixtures is lower than that of traditional liquid fuels, it is undeniable that the increased diffusion of gas systems is mainly due to a significant economic benefit to the end user.

[0004] This increased diffusion offers a new type of environmental problem, which concerns the incomplete oxidation of the components more difficult to combust, in particular of natural gas, which are discharged into the atmosphere through the exhaust pipes of vehicles.

[0005] As a result, since methane is a gas which has a power to generate greenhouse effects even greater than carbon dioxide in the medium and long term, it is unthinkable for a rational environmental policy not to involve a reduction of emissions of such gas into the atmosphere.

[0006] The present invention falls within the above context, setting out to provide a catalytic system capable of drastically reducing the emission levels of the natural gas already at relatively low temperatures, and designed to be chemically and mechanically durable.

[0007] This objective is achieved by means of an element according to claim 1, using a system according to claim 10 and by a method according to claim 11. The dependent claims refer to advantageous or preferred embodiment variants.

[0008] The invention according to the present invention will now be described with reference to the appended drawings, wherein:

[0009] - figures 1, 2 and 3 show catalytic elements, and in particular support bodies, which the present invention relates to according to possible embodiments;.

[0010] - Figure 4 is a perspective view of a catalytic system according to the present invention, containing a plurality of catalytic elements according to Figure 1 or 3 ;

[0011] - Figures 5 to 10 show experimental diagrams pertaining to the examples 1-11 provided with reference to this description.

[0012] With reference to the appended drawings, reference numeral 1, 1', 1" globally indicates an element for the catalytic oxidation of uncombusted methane in natural gas powered vehicles.

[0013] Consequently, the present invention is aimed both at completing the oxidation in so-called "pure" methane systems, and the oxidation of such gas as one of the possible components of a gaseous mixture, for example LPG, hydromethane (mixture of hydrogen and methane) or dual fuel (mixture of diesel and methane or petrol and methane) .

[0014] Such element 1, 1', 1" comprises a support body 2 which defines a plurality of inner channels 4, for example longitudinal. In particular, these channels are oriented in the body 2 so as to allow crossing of a gaseous flow comprising the methane. Advantageously, the support body is chemically inert.

[0015] With reference for example to the embodiments in Figures 1, 2 and 3, other embodiments provide that the support body has a polygonal, circular or - in variations not shown - ellipsoidal, triangular, or any other cross-sectional shape.

[0016] According to a further embodiment, said body 2 extends in a substantially cylindrical manner along a reference axis X, wherein the inner channels are preferably oriented along or parallel to such axis X.

[0017] Consequently, this variant provides that the inner channels 4 extend completely across the support body 2, and that they fluidically communicate outside the body through a plurality of openings positioned on a first front surface 6 and on an opposite front surface 8 delimited by said body.

[0018] Optionally, an outer tubular wall 12 of the support body 2 may peripherally enclose the plurality of inner channels 4, and possibly promote conveying of the gaseous flow inside the latter.

[0019] According to a preferred embodiment, the support body 2 is a chemically inert body.

[0020] According to a further variant, the support body comprises - mainly or exclusively - a honeycomb structure .

[0021] According to yet a further variant, the body 2 comprises a monolith, advantageously a ceramic monolith, preferably a monolith made of cordierite.

[0022] Further embodiments provide that the monolith is not made of ceramic, but of a metallic and/or plastic material .

[0023] The walls 14 which delimit the aforesaid inner channels 4 are at least partially coated with a silica selected from the group consisting of SBA-15, KIT-6 and mixtures thereof. In particular, the materials marked SBA-15 and KIT-6 are specific mesoporous silicas which are characterised by a high degree of crystalline order, respectively, of the two-dimensional (SBA-15) and three-dimensional (KIT-6) type.

[0024], Within the present description, the term "mesoporous silica" shall mean a silica having pores of a mean diameter between about 2 nm and about 100 nm, and in particular such as to allow the reversible passage of molecules of a comparable size or of a smaller size.

[0025] Advantageously the , pores of the silica fluidically communicate . with the inner channels of the support body, so as to receive the gaseous flow to be catalysed through such channels.

[0026] As regards the conformation of the aforementioned walls 14, they could for example be positioned in the form of a grid as shown schematically in Figures 1 and 2.

[0027] According to a possible embodiment, inside the silica matrix a percentage of silicon (IV) is exchanged with aluminium ions (III), in particular to generate ionic charges in the matrix. This way, it was surprisingly found that silica of any type among those discussed constitutes an optimal support for enhancing the performance of the active ingredient of the catalyst (palladium) , even in the presence of very low concentration levels of the latter.

[0028] Preferably, the ratio of silicon atoms and aluminium atoms in the silica matrix is comprised between 10 and 30, preferably between 15 and 25, advantageously between 18 and 22, for example substantially 20.

[0029] In addition, the walls 14 are also at least partially coated with a palladium-based catalyst, at least partially dispersed on said silica. Preferably, such palladium-based catalyst comprises mainly or consists of palladium oxide.

[0030] This way, the catalytic element described is innovatively capable of efficiently catalysing the oxidation of the methane residue coming, from the combustion chamber of the vehicle, such activity being carried out in a substantially quantitative manner over a wide range of operating temperatures, and advantageously with dramatically reduced amounts of palladium compared to conventional commercial applications .

[0031] In fact, in motor vehicles, the temperature of the catalyst when starting is usually ambient temperature, but after the passage of a certain amount of hot gas, such temperature increases dramatically.. Consequently, an efficient catalytic element must be able to operate in an extremely wide range of temperatures .

[0032] According to various embodiments, the percentage in weight of dispersed palladium is less than or equal to about 2%wt relative to the weight of silica, for example equal to or less than about l%wt, in particular less than or equal to 1.8 %wt, 1.7 %wt, 1.6 %wt, 1.5 %wt, 1.4 %wt, 1.3 %wt, 1.2 %wt, 1.1 %wt, 0.9 %wt, 0.8 %wt, 0.7 %wt.

[0033] According to a further embodiment, the percentage in weight is equal to or greater than about 0.4 %wt - 0.5 %wt.

[0034] According to a preferred embodiment, the BET surface of the silica with the palladium-based catalyst dispersed thereover is in the range 600-900 m ² /g, preferably in the range 670-830 m ² /g, optionally in the range 680-750 m ² /g for example approximately 700 m ² /g.

[0035] Optionally, the mean volume of the pores in the silica matrix could be in the range 0.50 - 0.90 cm ³ /g, optionally in the range 0.60- 0.80 cm ³ /g, said volume being preferably 0.70 cm ³ /g.

[0036] A catalyst system 10 according to the present invention comprises a casing 16 defining an inner chamber 18 fluidically connected upstream (for example by means of a duct - not shown - connected to a first portion 20 of the casing 16) with a combustion chamber of a motor vehicle, and connected downstream (e.g. via a second portion 22 of the casing 16) with an exhaust pipe (not shown) . Consequently, the flow of the mixture of combusted gases proceeds in the direction of arrow 26 according to the orientation in figure 4.

[0037] Optionally, the casing may be at least partially insulated. For example, a thermo-insulating material 24 may be inserted into a shell of such casing.

[0038] Furthermore, at least one element 1 according to any of the embodiments discussed above is inserted in the inner chamber 18. For example a series of such elements may be positioned in series along the flow direction of the gas mixture. Alternatively, an element 1 or a plurality of such elements could be juxtaposed with at least a further element 28 suitable to abate other types of components.

[0039] For example, the further element 28 could be designed for the catalytic oxidation of other components of natural gas, or for the abatement of NOx and/or SOx.

[0040] The present invention also relates to a method for the manufacture of a catalytic element according to any of the previous variants. Such method comprises the steps of:

[0041] i) providing the support body;

[0042] ii) producing the silica SBA-15 and/or KIT-6 by means of a hydrothermal treatment;

[0043] iii) impregnating the silica with a solution containing palladium ions;

[0044] iv) coating at least partially the inner channels of the support body with the silica produced in step iii) ;

[0045] v) calcinating the semi-finished product obtained in step iv) to convert the palladium ions into activated palladium oxide for the catalytic oxidation of methane.

[0046] Following the step v) , the palladium is preferably finely dispersed in the mesoporous structure of the silica, in such a manner that the catalytic combustion of the gas takes place at a very large number of active sites, thus with unmatched performance compared to the traditional techniques. [0047] According to one embodiment, the step ii) comprises an exchange step of a percentage of silicon (IV) of the matrix with aluminium ions (III), for example in the ratios of silicon atoms to aluminium atoms discussed previously.

[0048] According to one . embodiment, the step iii) comprises one or more stages of wetness impregnation, i.e. using a solution of palladium ions in a volume substantially equal to the volume of the pores of the material to be coated.

[0049] Advantageously, the step iv) comprises at least one stage of dip coating.

[0050] Preferably, the step v) takes place by means of a heat treatment at 550°C for a period of approximately 5 hours, with a heating speed of not more than 3°C/minute. This way, the calcination step also has the effect of making the silica adhere to at least a part of the aforesaid inner channels.

[0051] The purpose of the present invention will now be illustrated on the basis of several non-limiting examples .

[0052] Example 1 : Preparation of mesoporous silica SBA- 15. ^'

[0053], Approximately 8 g of polyethylene glycol- polypropylene glycol-polyethylene glycol is measured onto a previously calibrated plastic tray. 240. g of distilled water and 47.2 g of 37% HC1, previously dried in a beaker are kept to one side.

[0054] The acid is added to the previously measured distilled water and stirred using a magnetic stirrer with stir bar.

[0055] The HC1, water and polymer are placed in a synthetic teflon bottle containing the magnetic stir bar making the solution flow over the sample holder, so as to recover all of the polymer.

[0056] The bottle with HCl, polymer and distilled water is placed on a stirrer, until the polymer has dissolved

(time required: about an hour and a half) .

[0057] 6 g of KC1 (99% in purity) are measured out separately in a beaker, and poured into the bottle with the polymer, HCl and water.

[0058] 6 g of Mesytilene suitably pre-dosed into a beaker are poured into the bottle. The solution is left to mix for exactly 2 hours.

[0059] 17 g of TEOS are taken for pouring into the reaction bottle drop by drop.

[0060] The bottle is placed inside a basket with water heated to 35°C for 24 hours (eliminating the stir bar to reach static conditions) , and subsequently the bottle is put in the oven at 100°C for a further 24 hours .

[0061] Filtration follows, taking a hollow Pyrex cone, placing it on top of a ceramic funnel that has 2 paper filters having a diameter equal to the widest part of the funnel. Paper is wrapped around the neck of the latter to better seal the assembly.

[0062] A vacuum is obtained using a compressor, the filter is wetted with distilled water in large excess to make it stick to the ceramic, and the contents of the reaction bottle are poured inside the filter.

[0063] Washing is performed with 500 ml of distilled water, using a spatula to remove all the contents in the bottle.

[0064] A bowl in refractory material is used and placed inside the basket in which the water is kept at 70°C.

[0065] Once the powder is well dried, calcination takes place at 550°C for 5 hours: the bowl should be covered with a sheet of perforated aluminium. Heating rate to ensure: 3°C/min.

[0066] By means of the above procedure a final quantity equal to about 5 g of SBA-15 is obtained.

[0067] Example 2 : Preparation of mesoporous silica KIT-

6.

[0068] Approximately 6 g of polyethylene glycol- polypropylene glycol-polyethylene glycol is measured onto a plastic tray.

[0069] 217 g of distilled water and 11.8 g of 37% HC1, previously dried in a beaker are kept to one side.

[0070] The acid is added to the previously measured distilled water and stirred with a magnetic stirrer, and a stir bar or, alternatively, by hand.

[0071] The HC1, water and polymer are placed in a synthetic teflon bottle containing the magnetic stir bar making the solution flow over the sample holder, so as to recover all of the polymer.

[0072] The bottle with HC1, polymer and distilled water is placed on the stirrer, until the polymer has dissolved.

[0073] 6g of butanol are measured out and put into the bottle with the polymer, HC1 and water. It is left to mix for an hour .

[0074] 14.3g of TEOS are taken for pouring into the teflon bottle drop by drop.

[0075] The bottle is positioned inside a beaker containing water heated to 35°C for 24 hours. The mixing is continued in dynamic conditions.

[0076] .Subsequently the bottle is placed in the oven at 100°C for a further 24 hours, after which filtration is performed as discussed in example 1 above.

[0077] The powder is poured into a refractory bowl and dried, stirring from time to time to facilitate the gas escape. Alternatively the drying temperature may be increased, as long the water does not come to boiling.

[0078] Calcination takes place - at 550°C for 5 hours: the bowl should be covered with a sheet of perforated aluminium. Recommended speed of temperature increase: 3°C/min.

[0079] Following the above steps about 5g of KIT-6 are obtained.

[0080] Examples 3 and 4 : Replacement of silicon with aluminium in the mesoporous silica matrix.

[0081] The mesoporous silicas prepared according to examples 1 and 2 were subjected to a procedure of partial exchange of silicon (Si) with aluminium (Al) in the mesoporous matrix, using the procedure below.

[0082] In the appended tables, the mesoporous silicas modified this way will be referred to as "Al-mod-KIT- 6", "Al-KIT-6" or "Al-mod -SBA-15", "Al-SBA- 15 ".

[0083] The modification of the material for the addition of aluminium in partial replacement of the silicon in the matrix is carried out by making a conventional Si-SBA-15 - dried for one night at 200°C - react with a solution of 0.06 M A10 ₃ (i- (CH (CH ₃ ) 2) 3 (aluminium iso-propoxide ) .

[0084] The suspension is kept stirred for 24 hours at ambient temperature, then filtered, washed in distilled water, in order to obtain the solid to be dried (at a temperature of 120°C for about 2 hours) . The final calcination in air (for about 5 hours at a temperature of 550°C) permits a partial substitution of the silicon to be achieved.

[0085] Such exchange was carried out to give the matrix greater acidity and reactivity, especially given the different oxidation states of silicon (IV) and aluminium (III) . Such diversity creates a charge deficiency in the mesoporous matrix, compensated only with the entry and binding of H ⁺ protons.

[0086] The substitution levels obtained with the synthesis above are such as to bring the Si/Al ratio to a value equal to about 20.

[0087] Example 5: Deposition of palladium on the mesoporous silica matrix.

[0088] For the impregnation of the palladium in the mesoporous silica (SBA-15 or KIT-6 according to the examples 1 or 2, optionally in the presence of partial substitution with aluminium according to examples 3 and 4) the wetness impregnation technique is used.

[0089] To use this technique, a solution of palladium in distilled water of a volume equal to that of the pores of the material to be coated is used. This solution thus has the desired volume and concentration of palladium, the concentration being in particular calculated according to the palladium load to be achieved .

[0090] In such a solution a palladium salt is used, preferably palladium nitrate.

[0091] The solution is placed in contact with the powder drop by drop. The powder is then mixed so that the solution bathes all the powder and becomes homogeneous .

[0092] A heat treatment is then performed at 100°C to dry the powder and subsequently a calcination treatment to decompose the nitrate and anchor the palladium - in the form of palladium oxide - to the inner channels of the silica. This calcination is performed for 5 hours at approximately 550°C.

[0093] This way a catalytic coating is obtained for the ceramic monolith support.

[0094] Example 6: Characterisation of the catalytic coating.

[0095] XRD analysis of the mesoporous silica according to the examples 1 and 2 produced a diffractogram showing peaks of variable intensity as a function of the diffraction angle, which were then compared ' with the values contained in the database of the International Centre for Diffraction Data 2002 JCPDS using the PCDFWIN programme.

[0096] Analysing the X-rays at a low angle it can be seen that the structures are well ordered with hexagonal and cubic shaped pores, respectively.

[0097] BET analysis showed that the incorporation of palladium in the mesoporous matrix at different concentrations does not make the surface area, and consequently the shape of the hysteresis curve, vary significantly. This suggests that the shape of the pore was maintained in the sample's. The volume of the pore also remains substantially constant despite the impregnation of palladium.

[0098] However when the material is modified by partial replacement of the silicon with aluminium in the matrix (examples 3 and 4) to increase the acidity, the situation changes. In fact there is an increase of the surface area, pore volume and the mean diameter.

[0099] The surface area for samples loaded at different concentrations of Pd remained around 700 m ² /g, while as regards the values of the mean size of the pore and volume of the pore, these were respectively around 5 nm, and 0.70 cm ³ g.

[00100] As regards the sample modified with aluminium instead (examples 3 and 4) there was an increase of the surface area up to 826 m ² /g and of the average diameter of the pore, nearly 7 nm. But the most significant figure is given by the pore volume which almost doubled .

[00101] Example 7 : Catalytic activity tests in a micro- reactor.

[00102] These tests make it possible to assess the progress of the catalytic combustion reaction of methane with the varying of the temperature reached in the catalytic bed for each catalyst tested, preferably in a range of values of the W/F ratio between the quantity of catalyst used (W) and the flow speed (or flow rate) of the gas (F) of interest for applications in the automotive field.

[00103] In a _v micro-reactor loaded with a fixed amount of catalytic powder substance (in particular about 80 mg) a constant flow of reagents was introduced and the trend of the catalytic combustion reaction of methane was evaluated as the temperature reached in the catalyst bed for each catalyst tested varied.

[00104] The flow of reactants fed to the catalyst had the following composition:

[00105] The micro-reactor is fed with a flow of reagents equal to 250 Nml/min (measured in conditions of ambient temperature and pressure) consisting of: - CH ₄ at 0.400% vol. (4000 ppm) ;

- N ₂ at 97, 62% vol . ;

- 0 ₂ at 1.98% vol.

[00106] The main reaction taking place in the reactor is the oxidation of methane thanks to the presence of the catalyst which facilitates the following reaction:

CH ₄ + 0 ₂ C0 ₂ + H ₂ 0

[00107] For the purposes of ^' the analysis it was decided to consider the conversion trend as the bed temperature varied (Ti), according to the following formula:

[00108] wherein C ₀ is the initial concentration of methane at the temperature T ₀ and Ci is its concentration at the temperature T± . This way a dimensionless parameter is obtained which varies from 0% to 100%.

- [00109] The data used to compare the activities of different catalysts are the temperature at which 10%, 50% and 90% conversion of the methane takes place. These parameters are used to quantify the activity of the catalyst studied as well as to compare different catalytic systems with each other. The catalyst which has a higher catalytic activity also has lower conversion temperatures T _i0% , T ₅₀ % and T ₉₀ % . [00110] This is due to the principle that the reaction kinetics greatly decreases with decreasing temperature, so that a catalyst which - other experimental conditions being equal - has lower Ti temperatures is more effective in the oxidation activity of methane. Moreover, from the point of view of automobile applications, the goal pursued is to have, systems capable of delivering the required performance in as low a range of temperatures as possible.

[00111] In particular T _10% is a parameter which makes it possible to evaluate the speed of triggering the catalytic combustion reaction, since the catalyst with the highest catalytic activity has the lowest ΤΊ _0% .

[00112] With reference to the appended figure 5, from the activity tests carried out on KIT-6-based catalysts, it can be seen that these are very active in the process of reducing the pollutant methane, despite the small content of Pd used (≤ 1% wt . ) . The sample consisting of impregnated palladium oxide on the KIT-6 system modified with the addition of aluminium shows ^■ the best activity. This seems to be due to the increased acidity of the Al-mod-KIT-6, and a probable better interaction and dispersion of the palladium with the mesoporous silica structure.

[00113] Even for the SBA-15 based catalysts (Figure 6), the best catalytic activity was found with the material 'modified by a partial substitution of silicon in the matrix with aluminium. It should however be clarified that an excessive proportion of aluminium could run the risk of deteriorating the thermal stability of the catalyst .

[00114] Example 8 : Ageing tests of - catalytic coatings.

[00115] A further ageing test was performed on mesoporous silicas to see if their properties remain over time.

[00116] For the SBA-15 medium modified with Al (Figure 7) the test was conducted up to 800°C with the fresh material, then it was left at temperature for 12 hours, after which the catalyst system was made to cool and the test repeated subsequently. The results were extremely positive in that the catalytic system maintained its performance almost entirely in the abatement of methane.

[00117] As regards the SBA-15 with 0.6% Pd (Figure 8) the fresh sample was brought to temperature at 800°C and this temperature was maintained for 3 hours.

[00118] Once cooled the activity test was conducted to measure the degree of conversion. After the test the sample was left to cool and then the temperature was raised to 800°C in a stream of inert gas, and this temperature was maintained for 6 hours.

[00119] This type of treatment led to better results than those obtained on the fresh material. The main reason for this is due to two phenomena. The first concerns the size of the crystals of palladium oxide present in the matrix. The temperatures reached and maintained for many hours are highly critical for the catalytic ingredient which may decompose into smaller crystals increasing the number of active sites available. But the main reason is due to an improved dispersion of palladium in the pores, greatly increasing the catalytic activity. In any case, both the mesoporous structures were deemed thermally stable in the range of temperatures of interest, and hence the typical phenomena of sintering and consequent loss of activity which occurs in catalysts based on oxides systems does not occur.

[00120] Final summary values regarding the ageing tests above are shown in table I below: Table I l%Pd/Al- l%Pd/Al- 0, 6%Pd/SBA- 0, 6%Pd/SBA- SBA-15 -

SBA-15H 15n 15 'AGED ^■ 6+3J

AGEDH

Tio%« 295°Cn 297°CQ 290°Cn 305°Cn

T ₅ o%B 350°Cn 370°Cn 380°C« 332 °CH

T 0%» 425°CH 450°Ca 450°CH 380°CH [00121] As may be appreciated from the above table, the Tio% temperature values for the catalysts in the first three columns show values below 300°C, consequently extremely low triggering temperatures.

[00122] For the Al-SBA-15 system with 1% Pd such value remains below the threshold of 300 °C even after ageing, while for the Al-SBA-15 system with 0.6% Pd it slightly exceeds the threshold. This is in any case an important technical discovery.

[00123] Example 9: Preparation of the ceramic support monoliths.

[00124] The honeycomb monoliths which support the catalytic system itself are composed of an inert substrate with a plurality of longitudinal passages which completely traverse the thickness. Some examples of such monoliths are for example shown in Figures 1, 2 and 3.

[00125] A technique was therefore developed for depositing the catalytically active material, consisting of the mesoporous silica which supports small quantities of palladium (≤ l%wt.).

[00126] The preparation of the catalytically active monoliths takes place by means of dip coating, i.e. wetting the monolith in suspensions of the material to be loaded on the inner walls of the structured support, and bringing the system to 550°C in air for two hours (calcination) to achieve good adhesion of the material.

[00127] The suspension used is composed of the mesoporous silica added in various titres to a solution of distilled water, optionally at controlled pH (acidified with HN0 ₃ , or basified with NaOH/NH ₃ ) . The highest concentration of silica powders (at sub micron levels) in the suspension determines a greatest load of the catalyst deposited in the dip coating although with a highest viscosity and therefore with a reduced uniformity and risk of obstructing a certain number of channels .

[00128] Conversely, more dilute solutions produce more uniform layers of silica deposited on the channels of the monoliths, but also achieve more modest loads of catalytic material. The best compromise is achieved using quite dilute suspensions and consecutive cycles of dip-coating (bath + drying + calcination) .

[00129] Example 10: Trend of the increase in weight of monolith in repeated deposition cycles conducted at different concentrations of the suspension.

[00130] From the graphs in Figures 9a, 9b, and from table II below it may be noted that, for the same number of impregnation cycles carried out, a higher deposition level is achieved when the concentration of the suspension is greater. In Figure 9a, the increase in weight is expressed in relative terms compared to the initial weight of the monolith, whereas in figure 9b such parameter is expressed in absolute terms.

Table II

[00131] With highly concentrated suspensions, with about 8-20% of the mesoporous silica powder in water, the desired load of material is achieved in a single step, whereas with more dilute suspensions the same result is obtained with 6 or 8 cycles.

[00132] However, the obstruction of some of the channels during the dip coating procedure may be noted when more concentrated solutions are used (in this regard see the partial closing of some channels in Figure 1 ) .

[00133] Example 11: Methane abatement test of a monolithic catalyst.

[00134] The catalytic oxidation reaction (figure 10) of the monolithic catalyst obtained with 6 deposition cycles and at 6% concentration of SBA-15 in solution according to example 10 was tested. [00135] The results appear of great practical interest, since compared to the corresponding powder, no significant differences were observed. In essence, the system performs as expected.

[00136] In other words, although the mesoporous silica adheres to the surface defining the inner channels of the monolith, the catalytic activity remains substantially the same compared to the pure powder, not supported.

[00137] As a result, on the one hand the mesoporous silica is not significantly altered or compromised by the deposition process on the monolith; on the other, the diffusion phenomena of the methane molecules inside the longitudinal passages first, and in the inner channels afterwards, takes place as easily as with the free powder.

[00138,] Innovatively, the catalytic system according to the present invention makes it possible to use a low content of palladium for effective abatement,, such as to remain within the legal limits for emissions, and said content is greatly reduced compared to conventional, commercially established systems. For example, by a factor of 5:1 up to 20:1.

[00139] Advantageously, the catalytic system according to the present invention makes it possible to use reduced quantities of palladium dispersed on the surface of the silica, which is the factor having the greatest impact on the overall cost of the catalyst. In fact, in view of the improved level of dispersion achieved with the method discussed above, the presence of palladium in the system is limited to low percentage values in weight (to the order of 1 to 2 %wt relative to the weight of the mesoporous matrix) , the reason for which the present system is able to combine the remarkable, proven result of catalytic activity, at a production cost not burdened by the excessive presence of the precious metal.

[00140] Advantageously, the catalytic system according to the present invention permits the modified silica support and palladium to cooperate in a synergistic manner to achieve high yields of methane oxidation.

[00141] Advantageously, the catalytic system according to the present invention is resistant, both in mechanical and thermo-chemical terms, in the context in which the system is placed.

[00142] Furthermore, the catalyst support has a low coefficient of thermal expansion, reason for which the temperature gradients acting on it do not cause a progressive crumbling. This way, the shape and size of the inner channels are maintained in a reliable manner. [00143] Advantageously, at the operating temperatures for which the above system has been designed, the phenomenon of sintering is virtually absent, and there is also no evidence of degenerative reduction phenomena of the catalytic surface of other types.

[00144] Advantageously, the above method has proven effective and reproducible regardless of the nature of the support used. It follows that, although the effects of such a body may in some cases be synergistic with the catalyst, any material can in principle be used as a support.

[00145] Even though not previously specified, a person skilled in the art may make variations to any of the aforementioned aspects, replacing them with others technically equivalent, resorting to the expertise typical of the sector.

[00146] These variations or replacements are also contained within the sphere of protection defined by the following claims.

[00147] In addition, any alternatives illustrated in relation to a particular embodiment may be realised independently of the other variants described.