The invention relates to a catalyst having an improved sta ^¬ bility against deactivation at high temperatures and high partial pressure of steam, which is especially suited for methanation processes, steam and oxygen reforming processes and catalytic combustion processes, as well as such pro ^¬ cesses. Substitute Natural Gas (SNG) can be produced in large scale from coal via gasification and subsequent methanation of the produced synthesis gas in one or several reactors to achieve sufficiently high CH ₄ content in the final product. The methanation step is often carried out in a series of adiabatic, fixed bed reactors, where the main reactions taking place are:

CO + H ₂ 0 = C0 ₂ + H ₂ (1)

CO + 3 H ₂ = CH ₄ + H ₂ 0(2)

In the case of methanation from C0 ₂ and H ₂ , it is believed that the mechanism of the reaction goes first via reverse water gas shift (i.e., the reverse of reaction (1)), fol ^¬ lowed by CO methanation to form CH ₄ , so that the overall reaction is:

C0 ₂ + 4 H ₂ = CH ₄ + 2 H ₂ 0 (3)

The methanation of synthesis gas is highly exothermic, which results in a large temperature increase in these re ^¬ actors. Suitable catalysts for methanation thus need to be sufficiently active at low temperatures, resistant against sintering at high temperatures and high partial pressure of steam, and resistant to other deactivation phenomena, for example carbon formation. The catalyst sintering stability is most critical in the upstream reactors where the exit temperatures are the highest. The methanation process is typically carried out at elevated pressure (above 10 barg, potentially up to more than 100 barg) and at maximum tem ^¬ peratures between 500°C and 750°C with a partial pressure of steam between 2 and 15 barg, but potentially up to 30 barg .

The reverse process steam reforming and the similar process oxygen reforming occur under similar conditions and even higher temperatures such as up to 900°C in the presence of methane (and/or other hydrocarbons) and water.

A further high temperature process for which stabilization of catalyst and catalyst support is important is catalytic combustion of fuels, which may occur at elevated pressures, at temperatures between 600°C and 1000°C, and with water as a product in the case of fuels comprising hydrogen, e.g. according to (4) below. CH ₄ + 2 0 ₂ = C0 ₂ + 2 H ₂ 0 (4)

In patent GB 1 546 774 a methanation catalyst comprising nickel and molybdenum is disclosed. It is demonstrated that the presence of molybdenum either in the metallic or oxidic state improves the catalytic activity of the methanation catalyst .

In patent application PCT/EP2014/053541 it is disclosed that a synergetic stabilization of a catalyst support com- prising transition alumina may be obtained through a combi ^¬ nation of stabilization using zirconia and lanthanoid ox ^¬ ides . It has now been identified that a surprising synergy exists between promoters providing a stabilization effect of the support, promoters providing a stabilization of the cata- lytically active metal and promotion of the catalytic ac ^¬ tivity.

Well known catalysts for methanation processes contain Ni as the active phase, which provide the highest methanation activity per unit cost, on a stabilized support containing high surface area AI ₂ O ₃ . The stabilization works by inhibi ^¬ tion of formation of low surface area alpha-alumina. One example of this is the addition of lanthania and zirconium, as disclosed in WO application PCT/EP2014/053541. Another example of a stabilized high surface area support is the [MgAl ₂ 0 ₄ ] x [ AI ₂ O ₃ ] _y solid solution in the case of so-called magnesium-alumina spinel. Without stabilization, high sur ^¬ face area AI ₂ O ₃ is converted to low surface area alpha- alumina .

The loss of surface area can be so severe that the Ni par ^¬ ticles also sinter together, leading to a loss of catalytic activity. The reduction in the mechanical strength can be so severe that the catalyst pellets crumble into dust dur ^¬ ing operation or unloading.

A further stabilization method is the stabilization of the nickel particles on the catalyst against sintering. As nickel is the catalytically active component in the cata ^¬ lyst, the sintering of nickel particles will reduce the catalytic activity. Finally some promoters are also believed to participate in the catalytic reactions and thereby increase the catalytic activity . Now, according to the present disclosure, a reforming cata ^¬ lyst and a methanation catalyst with improved stability is provided wherein the high surface area support is stabi ^¬ lized against phase transformation by introducing a nonreducible metal oxide, a metal capable of forming a hexa- aluminate stable under reducing conditions, nickel and a group VIB element. Such a catalyst was found to provide surprisingly high stability and activity, compared to what may be expected from the addition of the individual ele ^¬ ments .

As it is well known to the skilled person, a catalyst ac ^¬ tive in methanation is also active in the reverse reforming process, which is also active at elevated temperatures. Therefore a steam reforming catalyst being stabilized against deactivation will similarly be attractive.

In the following the elemental concentrations of metals designated by %, wt% or wt/wt%, including nickel, molyb ^¬ denum, magnesium, zirconium, alkaline earth metals and lan- thanoid shall be understood as the weight fractions of ele ^¬ mental metal, relative to the total mass of catalyst, irre ^¬ spectively whether the metal is present in metallic or non- metallic form. In the following the terms catalyst support and carrier shall be construed as synonyms. Both terms shall refer to the structural support of the catalyst, which has a wide range of important characteristics known to the person skilled in the art, including the provision of a high surface area for the active material (such as nickel or noble metals) dispersed on the catalyst support.

As the specific preparation methodology may influence the observed methanation activity in a manner irrelevant to the present disclosure, the effect on the methanation activity is presented as a relative intrinsic methanation activity, normalized by an appropriate corresponding baseline value, as described for the individual examples.

The term "in oxide form" as e.g. aluminum, zirconium, and one or more lanthanoid elements "in oxide form" shall be understood as non-limiting in terms of the specific oxide form, which may thus be as combinations of the individual oxides AI2O ₃ , MgO, BaO, ZrC>2, La ₂ <03, etc. as binary oxides such as LaA103 or as hexa-aluminates such as barium hexa- aluminate [BaO] · [Α1 ₂ θ3] 6·

The term non-reducible metal oxide shall in the following be construed as an oxide which is thermodynamically stable with respect to formation of the element in the metallic state under a hydrogen partial pressure of 1 bar and a wa- ter partial pressure of 10 ^~10 bar at a temperature of 700°C. Examples of such non-reducible oxides are Zr0 ₂ , MgO, La ₂ 03, Y2O ₃ and AI2O ₃ , but the skilled person may experimentally or by use of thermodynamic calculations identify further such oxides. An example of this is ZnO which is thermodynamical- ly unstable and which may be reduced to Zn. In comparison Ce0 ₂ will in a similar atmosphere be converted to Ce ₂ 03, which is thermodynamically stable under hydrogen partial pressure of 1 bar and a water partial pressure of 10 ^~ bar at a temperature of 700°C and cannot be reduced to metallic form under these conditions. For this reason Ce2<0 ₃ falls under the definition of an oxide of a metal forming a non- reducible metal oxide because metallic Ce is not formed un ^¬ der the mentioned conditions.

The thermodynamically stable oxides may even be further limited to highly thermodynamically stable oxides, which in the following shall be construed as an oxide which is ther ^¬ modynamically stable with respect to formation of the ele ^¬ ment in the metallic state under a hydrogen partial pres ^¬ sure of 1 bar and a water partial pressure of 10 ^~12 bar at a temperature of 700°C.

The term a metal oxide being an oxide of a metal forming a metal oxide being thermodynamically stable at specific con ^¬ ditions shall in the following be construed as comprising not only the stable oxide, but also any other oxides, sta- ble or unstable, comprising this metal.

The present disclosure has identified that addition of ox ^¬ ides of lanthanoid elements and/or alkaline earth metals contribute to the stability of metal oxide catalyst sup- ports. Without being bound by theory it is believed that this capability is directly or indirectly related to these oxides being capable of forming crystalline hexa-aluminates which are known to be thermally stable (Catal. Today (1995) 217), even though crystalline hexa-aluminates have not been detectable in X-ray diffraction diagram. This improved sta ^¬ bility may be related to the presence of minor amounts of amorphous hexa-aluminates or it may be related to other more indirect mechanisms of stabilization.

In a broad form the present disclosure relates to a stabi- lized catalyst comprising a stable alumina support compris ing alumina in combination with at least one non-reducible metal oxide, and one or more further metal oxides capable of forming a crystalline hexa-aluminate stable under reduc ing conditions and an active phase comprising nickel and a Group VIB element, with the associated benefit of such a catalyst having a high activity and stability at elevated temperatures .

The stabilized catalyst comprises a stable support which comprises alumina in combination with at least two further metal oxides, of which two further metal oxides at least one first metal oxide, is thermodynamically stable at a hy drogen partial pressure of 1 bar and a water partial pres ^¬ sure of 10 ^~10 bar at a temperature of 700°C, and of which two further metal oxides at least one further metal oxide is an oxide of a metal taken from a group comprising lan- thanoid elements and alkaline earth metals and said cata ^¬ lyst further having an active phase comprising nickel and Group VIB element, with the associated benefit of such a catalyst having a high activity and stability at elevated temperatures .

In a further embodiment the stabilized catalyst comprises stable support which comprises alumina in combination with at least two further metal oxides, of which two further metal oxides at least one first metal oxide, is highly thermodynamically stable at a hydrogen partial pressure of 1 bar and a water partial pressure of 10 ^~ bar at a temper ^¬ ature of 700°C, and of which two further metal oxides at least one further metal oxide is an oxide of a metal taken from a group comprising lanthanoid elements and alkaline earth metals and said catalyst further having an active phase comprising nickel and a Group VIB element, with the associated benefit of such a catalyst having a high activi ^¬ ty and stability at elevated temperatures. In a further embodiment the metal of the oxide of a metal taken from a group comprising lanthanoid elements and alka ^¬ line earth metals has an atomic mass of at least 39 or 83, with the associated benefit of such heavy atoms providing an increased stability of the support phase, in that the ionic radius is sufficiently high for forming layered alu ^¬ mina structures as is known in the art (J. Catal . 103

(1987) 385) .

In a further embodiment said alkaline earth metal is calci- urn, strontium or barium, with the associated benefit of these metals of providing a stable support phase.

In a further embodiment the one or more lanthanoid elements are taken from the group consisting of lanthanum, cerium, praseodymium, samarium, gadolinium, neodymium, europium, dysprosium and ytterbium, with the associated benefit of providing a stable support phase.

In a further embodiment the metal of the further metal ox- ide is present in a concentration from 0.1% or 0.5% to 5% or 10%, with the associated benefit of providing an attrac ^¬ tive balance between cost and promotion. In a further embodiment the Group VIB element is either mo ^¬ lybdenum or tungsten, and the concentration of the Group VIB element is from 0.5% or 1.0% to 5% or 10%, with the as- sociated benefit of providing a high stabilization of the nickel particles and the alumina based support of the cata ^¬ lyst.

In a further embodiment the concentration of the nickel is from 5%, 10% or 15% to 30%, 50% or 80%, with the associated benefit of providing a high catalytic activity.

In a further embodiment the non-reducible oxide comprises magnesium, in a concentration from 1%, 2% or 4% to 9%, 12% or 15%, with the associated benefit of stabilizing AI ₂ O ₃ in the form of an Al ₂ 03-MgAl ₂ 0 ₄ solid solution.

In a further embodiment the non-reducible oxide comprises zirconium, in a concentration from 1%, 2 to 20%, 25% or 35%, with the associated benefit of zirconium providing a stable support.

A further aspect of the present disclosure relates to a precursor for such a catalyst, with the associated benefit of providing logistic simplicity as the precursor of a cat ^¬ alyst does not have to be stabilized prior to shipment.

A further aspect of the present disclosure relates to use of such a catalyst for catalysis of one of the following reactions; methanation, steam and/or oxygen reforming and catalytic combustion, with the associated benefit of such a catalyst being highly active and stable during these reac ^¬ tions .

A further aspect of the present disclosure relates to a process for producing a gas rich in methane by reacting a synthesis gas comprising carbon oxide and hydrogen in the presence of a catalyst according to the present disclosure, with the associated benefit of such a catalyst being highly active and stable during these reactions.

In a further embodiment the process temperature of the syn ^¬ thesis gas prior to contacting the catalytically active ma ^¬ terial is from 200°C, 300°C or 400°C to 500°C, 700°C or 800°C, with the associated benefit of such a catalyst being highly active and stable under these conditions.

In a further embodiment the temperature increase of the gas comprising methane after contacting the catalytically ac ^¬ tive material is at least 50°C, with the associated benefit of a temperature stable catalyst being especially attrac ^¬ tive during highly exothermic processes.

A further aspect of the present disclosure relates to a process for producing a synthesis gas from a gas rich in hydrocarbons by steam and/or oxygen reforming, involving reacting the gas rich in hydrocarbons with water and/or oxygen in the presence of a catalyst according to the present disclosure, with the associated benefit of such a catalyst being highly active and stable during these reactions.

In a further embodiment the temperature of the gas rich in hydrocarbons prior to contacting the catalytically active material is from 350°C or 550°C to 600°C, 1000°C or 1200°C, with the associated benefit of such a catalyst being highly active and stable under these conditions. The stabilization of alumina in catalysts is made by addi ^¬ tion of various elements known to reduce the susceptibility of alumina to change phase. This includes the provision of at least one non-reducible oxide, which is thermodynamical- ly stable at a hydrogen partial pressure of 1 bar and a wa- ter partial pressure of 10 ^~10 · bar at a temperature of

700°C.

In addition alumina may be stabilized by the presence of metal oxides, which may be associated with alumina as sta- ble crystalline hexa-aluminates , as it is discussed in a.o. Catal . Today 26 (1995) 217, which lists higher alkaline earth metals (Ca, Sr and Ba) as well as lanthanoids as met ^¬ als capable of forming stable crystalline hexa-aluminates. While magnesium is also an alkaline earth metal, it does not form a well-defined crystalline hexa-aluminate

MgO- (Al ₂ 0 ₃ ) 6 but rather a (MgAl ₂ 0 ₄ ) · (A1 ₂ 0 ₃ ) solid solution.

According to the present disclosure, a catalyst with im ^¬ proved stability is provided according to which, the AI ₂ O ₃ carrier is stabilized against phase transformation by in ^¬ troducing at least one non-reducible oxide and at least one further oxide capable of forming a stable crystalline hexa- aluminate, as well as introduction of an element providing stabilization of nickel particles.

Without being bound by theory, said high surface area alu ^¬ mina based support is assumed to be stabilized by the pres- ence of a stable refractory non-reducible phase (e.g. MgO and AI ₂ O ₃ or Zr02 and AI ₂ O ₃ ) . A further stabilizing effect of the metal forming a stable hexa-aluminate is assumed to be provided by hindering the sintering of the high surface area support by inhibition of phase transformation towards larger crystalline structures such as α-Αΐ ₂ θ ₃ . This inhibi ^¬ tion effect is possibly promoted by an oxide phase compris ^¬ ing molybdenum, which is able to form binary oxides like La ₂ Mo ₂ 0 ₉ .

Also without being bound by theory, the Group VIB element is assumed to work as a stabilizer of the nickel particles, predominantly by alloy formation which hinders the sinter ^¬ ing of the nickel particles.

The manufacturing methodology for the catalysts of the pre ^¬ sent disclosure is based on creating intimate contact be ^¬ tween the components involved, either on nanometer scale or on micrometer scale. Thus, the catalysts of the present in- vention can be produced by any method known in the art which renders an effective mixture of the individual compo ^¬ nents. This may involve precipitation of a single constitu ^¬ ent, or co-precipitation of multiple constituents, which methods are described in more detail in Synthesis of Solid Catalysts, edited by Krijn de Jong, 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Alternatively, the preparation might involve mixing of constituent ( s ) followed by extru ^¬ sion or high energy milling in the dry or wet phase. High energy milling may be carried out using a range of methods, of which some are disclosed in section 2.4 of Mechanochem- istry in Nanoscience and Minerals Engineering by Peter Balaz, Springer 2008. Suitable precursors comprise water soluble salts of the constituents, in the case of (co) precipitation . Furthermore oxides, hydroxides, carbonates, basic carbonates and mix- tures thereof are suitable materials for mixing, extrusion and high energy milling. These examples should be under ^¬ stood as illustrations rather than limitations of the pre ^¬ sent inventions. The mixing steps are usually followed by drying steps, optionally preceded by filtration as in the case of (co) precipitation .

After drying, the mixtures are transformed into so-called green bodies by a shaping method such as tabletizing. Alternatively, the green bodies comprise the extrudates, which are obtained prior to the drying step. The green bod ^¬ ies may be fired under air, other O2 containing gases, ni ^¬ trogen or other inert gasses at temperatures of 600-1200°C after which the active Ni catalyst is obtained by a reduc ^¬ tion treatment using dihydrogen at elevated temperatures of 500-1000°C. As known to the person skilled in the art, transition alumina as such is unstable at temperatures above 1050°C, but if alumina is modified by a stabilizer such as a non reducible oxide, a lanthanoid, an alkaline earth metal or nickel oxide firing at higher temperatures is not a problem. Firing must also be made at elevated tem ^¬ peratures (600-1200°C) to ensure that at least one of the stabilizing components, i.e. non reducible oxides, lantha- noids, and alkaline earth metals are structurally integrat ^¬ ed in the alumina, and thereby providing a stabilized crys- tal structure. In one aspect of the present disclosure the green body con ^¬ sists of some of said components and the addition of the remaining components may be carried out by an impregnation step comprising at least one aqueous solution containing said component (s) in dissolved state. Impregnation steps are followed by thermal treatment e.g. calcination and fi ^¬ nally reduction. Optionally, the impregnation steps are preceded by calcination at 600-1200°C. Impregnation may be made with one or more component solutions of appropriate purity or a mixture of components of limited purity depend ^¬ ent on the desired catalyst quality, cost and other practi ^¬ cal issues.

The assessment of catalyst stability involved an aging pro- cedure in combination with an evaluation of the aged catalyst.

The accelerated lab aging procedure involved exposing the fresh catalyst to high temperatures and high steam partial pressures in the laboratory. Relevant catalysts were used as whole pellets and subjected to a gas consisting of steam and hydrogen in high levels, with the specific process con ^¬ ditions differing for the individual catalysts. These con ^¬ ditions are not often found in normal operation, but it al- lows a realistic investigation of the long term sintering stability in a relatively short time in the laboratory. The relevant catalysts are then analyzed for various properties after the aging procedure. The evaluation of the activity of the aged catalyst was made by determining the intrinsic methanation activity of the aged catalysts under the same operating condition: the relevant catalyst was crushed to 0.1-0.3 mm fraction and diluted with an appropriate inert also crushed to the same fraction such that the catalyst weight fraction in the mixture was approximately 4%. The reason to mix the catalyst with inert was to limit the conversion inside the catalyst bed and obtain the most representative intrinsic activity measurements. One gram of the catalyst and inert mixture was loaded in a fixed bed reactor and exposed to approxi ^¬ mately 10 L/h of a gas containing 10% CO and 90% ¾ . The exit gas was analyzed for composition using a standard gas chromatograph .

The temperature inside the reactor was monitored both in ^¬ side the catalyst bed and on the reactor wall. The catalyst activity may thus be calculated from the CH ₄ produced and the CO and ¾ consumed. The intrinsic activity was measured several times at the same temperature, and was measured from 275 to 325°C. Under these conditions, it was confirmed that there was insignificant temperature increase through the catalyst bed, as well as insignificant mass and heat transfer limitations such that the effectiveness of the catalyst particles was close to 1. This means that the measured catalyst activity was the true intrinsic methana- tion activity.

Examples

In total 25 catalysts were prepared according to various production methods to evaluate the effect of the present disclosure under various conditions and preparation meth- ods, and they were evaluated by similar accelerated meth ^¬ ods. The Ni particle size and the relative activity were evaluated after aging at 800°C (catalysts 1,2 and 3) or 750°C (catalysts 4-25) at 30 barg, in an atmosphere with a ¾():¾ ratio of 2 for 2 weeks. The Ni crystallite size is determined using the Scherrer equation which relates the line broadening of a peak in the diffraction pattern to the crystallite size. The concentrations of metals in the cata ^¬ lysts are listed together with the measured Ni crystallite size and the relative activity in Table 1.

Three catalysts containing Ni were prepared using the fol- lowing method. The methanation activity for these catalysts was normalized with the activity of catalyst 1.

Catalyst 1

Catalyst 1 according to the prior art was prepared from an aqueous suspension containing Al (as bohmite) , Zr (as hydroxide) and Ni (as basic carbonate) . The suspension was dried and the powder was pressed into tablets after addi ^¬ tion of graphite. The tablets were calcined in air at 900- 1000°C and impregnated with an aqueous La(N03)3 solution. The final catalyst was then obtained after calcination at 450°C and reduction with ¾ while increasing the tempera ^¬ ture up to 840°C.

Catalyst 1 consisted of 22.7% Ni on a high surface area transition AI ₂ O ₃ support, stabilized by 2.7% La as La ₂ 03 and 20.7% Zr as Zr0 ₂ .

Catalyst 2

Catalyst 2 according to the prior art was prepared from catalyst 1 by impregnation of the La free calcined tablets with an aqueous (ΝΗ ₄ )2Μθ2θ7 solution containing N¾ . The final catalyst was then obtained after drying at 80°C and re- duction while increasing the temperature to 840°C, as men ^¬ tioned above.

Catalyst 2 consisted of 22.8% Ni and 2.7% Mo on a high sur- face area transition AI ₂ O ₃ support, stabilized by 20.8% Zr as Zr02.

Catalyst 3

Catalyst 3 according to the present disclosure was prepared from catalyst 1 by impregnation of the La containing calcined tablets with an aqueous ( Η ₄ )2Μθ2θ7 solution contain ^¬ ing NH ₃ . The final catalyst was then obtained after drying at 80°C and reduction while increasing the temperature to 840°C, as mentioned above.

Catalyst 3 consisted of 22.1% Ni and 2.6% Mo on a high sur ^¬ face area transition AI ₂ O ₃ support, stabilized by 2.6% La as La ₂ 03 and 20.2% Zr as Zr0 ₂ . Four catalysts containing Ni on an MgO-Al ₂ 03 support were prepared according to the method below, to evaluate the ef ^¬ fect of La and Mo in this context. The methanation activity for these catalysts was normalized with the activity of catalyst 4.

Catalyst 4

A powder mixture is prepared using 859 g Bohmite, 86 g MgO and 138 g Gibbsite using a mixer such as a z-mixer. Then, a mixture of 78,5 g HNO ₃ (65%) and 839 g water is added to the powder while mixing continuously and producing a paste. Finally, the paste is extruded and the extrudates are cal ^¬ cined at 500°C. The calcined extrudates are crushed, mixed with water and magnesium stearate, and tabletized. Then, the tablets are calcined at 1000-1200°C for 4 h affording a support. The support was impregnated with aqueous Ni(N03)2, calcined at 450°C and reduced with ¾ while increasing the temperature to 600°C to afford catalyst 4.

Catalyst 4 according to the prior art consisted of 14.1% Ni on an MgAl ₂ 0 ₄ -Al ₂ 03 support. The Mg:Al atomic ratio in the support amounts to 1:6.9. Catalyst 5

Catalyst 5 according to the prior art was prepared from catalyst 4 by impregnation of the calcined tablets contain ^¬ ing Ni, with an aqueous La( 03)3 solution. The final cata ^¬ lyst was then obtained after calcination at 450°C and re- duction with hydrogen, while increasing the temperature to 600°C, as mentioned above.

Catalyst 5 consisted of 13.7% Ni on a La stabilized

MgAl ₂ 0 ₄ -Al ₂ 03 support. The Mg:Al atomic ratio in the support amounts to 1:6.9 and the amount of La was 2.1%.

Catalyst 6

Catalyst 6 according to the prior art was prepared from catalyst 4 by impregnation of the calcined tablets contain- ing Ni with an aqueous (ΝΗ ₄ )2Μθ2θ7 solution containing N¾ . The final catalyst was then obtained after drying at 80°C and reduction while increasing the temperature to 840°C.

Catalyst 6 consisted of 13.8% Ni on an Mo stabilized

MgAl ₂ 0 ₄ -Al ₂ 03 support. The Mg:Al atomic ratio in the support amounts to 1:6.9 and the amount of Mo was 1.6%. Catalyst 7

Catalyst 7 according to the present disclosure was prepared from catalyst 5 by impregnation of the calcined La contain ^¬ ing tablets with an aqueous ( Η ₄ )2Μθ2θ7 solution containing N¾ . The final catalyst was then obtained after drying at 80°C and reduction while increasing the temperature to 840°C, as mentioned above.

Catalyst 7 consisted of 13.5% Ni on a La and Mo stabilized MgAl ₂ 0 ₄ -Al ₂ 03 support. The Mg:Al atomic ratio in the support amounts to 1:6.9, the amount of La was 2.0% and the amount of Mo was 1.6%.

Three catalysts containing Ni on a spinel support were pre ^¬ pared using the following method corresponding essentially to EP 0 044 117 Bl, to evaluate the effect of Ni concentra ^¬ tion. The methanation activity for these catalysts was nor ^¬ malized with the activity of catalyst 8.

Catalyst 8

Catalyst 8 according to the prior art was prepared by pre ^¬ cipitation of an acidic solution containing Ni(N03) ₂ ,

Mg(N03)2, and La(N03)3 with basic solutions containing KAIO2 and K ₂ CO ₃ , respectively, at pH 9.1. The precipitate was filtered, washed with water and dried. The powder was pressed into tablets after addition of graphite. The tab ^¬ lets were calcined in air at 900-1000°C and reduced with ¾ while increasing the temperature to 840°C.

Catalyst 8 consisted of 29.6% Ni on a La stabilized

MgAl ₂ 0 ₄ -Al ₂ 03 support. The Mg:Al atomic ratio in the support amounts to 1:2.05 and the amount of La was 3.7%. Catalyst 9

Catalyst 9 according to the present disclosure was prepared from catalyst 8 by impregnation of the calcined tablets with an aqueous ( Η ₄ ) ₂ Μθ ₂ θ ₇ solution containing N¾ . The final catalyst was then obtained after drying at 80°C and re ^¬ duction while increasing the temperature to 840°C, as men ^¬ tioned above. Catalyst 9 consisted of 28.6% Ni on a La and Mo stabilized MgAl ₂ 0 ₄ -Al ₂ 0 ₃ support. The Mg : Al atomic ratio in the support amounts to 1:2.05, the amount of La was 3.6% and the amount of Mo was 3.3%. Catalyst 10

Catalyst 10 according to the present disclosure was pre ^¬ pared by precipitation of an acidic solution containing Ni(N0 ₃ )2, Mg(N0 ₃ )2, and La(N0 ₃ )3 with basic solutions con ^¬ taining KAIO ₂ and KOH respectively, at pH 9.5. The precipi- tate was filtered, washed with water and dried. The powder was pressed into tablets after addition of graphite. The tablets were calcined in air at 900-1000°C and impregnated with an aqueous ( Η ₄ ) ₂ Μθ ₂ θ ₇ solution containing N¾ . The final catalyst was then obtained after drying at 80°C and re- duction while increasing the temperature to 840°C, as men ^¬ tioned above.

Catalyst 10 consisted of 44.4% Ni on a La and Mo stabilized MgAl ₂ 0 ₄ -Al ₂ 0 ₃ support. The Mg : Al atomic ratio in the support amounts to 1:2.19, the amount of La was 2.5% and the amount of Mo was 5.2%. Three catalysts comprising Ni on a spinel support were pre ^¬ pared according to the following method, in order to evalu ^¬ ate the effect of Ba and Mo. The methanation activity for these catalysts was normalized with the activity of cata- lyst 11.

Catalyst 11

A powder mixture is prepared using 432.4 g Bohmite, 124.9 g MgO and 69.5 g Gibbsite using a mixer such as a z-mixer. Then, a mixture of 47.2 g HNO ₃ (65%) and 521 g water is added to the powder while mixing and producing a paste. Fi ^¬ nally, the paste is extruded and the extrudates are cal ^¬ cined at 500°C. The calcined extrudates are crushed, mixed with water and magnesium stearate, and tabletized. Then, the tablets are calcined at 1000-1200°C for 4 h affording a support. The support was impregnated with aqueous Ni(N03)2, calcined at 450°C and reduced with ¾ up to 600°C to afford catalyst 11. Catalyst 11 according to the prior art consisted of 16.3% Ni on an MgAl ₂ 0 ₄ -Al ₂ 03 support. The Mg:Al atomic ratio in the support amounts to 1:2.38.

Catalyst 12

A powder mixture is prepared using 432.4 g Bohmite, 124.9 g MgO, 22.4 g BaCC>3 and 69.5 g Gibbsite using a mixer such as a z-mixer. Then, a mixture of 47.2 g HNO ₃ (65%) and 555 g water is added to the powder while mixing and producing a paste. Finally, the paste is extruded and the extrudates are calcined at 500°C. The calcined extrudates are crushed, mixed with water and magnesium stearate, and tabletized. Then, the tablets are calcined at 1000-1200°C for 4 h af- fording a support. The support was impregnated with aqueous Ni(N0 ₃ ) ₂ , calcined at 450°C and reduced with H ₂ up to 600°C to afford catalyst 12. Catalyst 12 according to the prior art consisted of 20.7%

Ni on a Ba stabilized MgAl ₂ 0 ₄ -Al ₂ 03 support. The Mg:Al atom ^¬ ic ratio in the support amounts to 1:2.38 and the Ba con ^¬ tent was 2.4%. Catalyst 13

Catalyst 13 according to the present invention was prepared from catalyst 12 by impregnation of the Ni containing calcined tablets with an aqueous ( Η ₄ )2Μθ2θ7 solution contain ^¬ ing N¾ . The final catalyst was then obtained after drying at 80°C and reduction while increasing the temperature to 840°C.

Catalyst 13 consisted of 20.3% Ni on a Ba and Mo stabilized MgAl ₂ 0 ₄ -Al ₂ 03 support. The Mg:Al atomic ratio in the support amounts to 1:2.38, the Ba content was 2.3% and the amount of Mo was 2.4%.

Three catalysts were prepared according to the following methods, to evaluate the effect of the Zr concentration. The methanation activity for these catalysts was normalized with the activity of catalyst 14.

Catalyst 14

A mixture of 36 g HNO ₃ (65%) and 605 g water is added to 1000 g Bohmite and mixed thoroughly using a mixer such as a z-mixer. Then, the mixture is extruded and the extrudates are calcined at 500°C. The calcined extrudates are crushed, mixed with water and magnesium stearate, and tabletized. The tablets, were impregnated with an aqueous La( 03)3 so ^¬ lution to obtain a La content of 4% and calcined at 1000- 1200°C for 2 h. Then, the calcined tablets were impregnated with aqueous i( 03)2 and calcined at 450°C. The final cat- alyst was obtained by impregnation of the calcined tablets with an aqueous ( Η ₄ )2Μθ2θ7 solution containing N¾ followed by drying at 80°C and reduction with ¾ while increasing the temperature to 840°C. Catalyst 14 according to the prior art consisted of 13.8% Ni and 1.6% Mo on a high surface area transition AI ₂ O ₃ sup ^¬ port, stabilized by 3.4% La as La ₂ <03.

Catalyst 15

Catalyst 15 according to the present invention was prepared according to the procedure of catalyst 14 using 36 g HNO ₃ (65%), 617 g water, 974 g Bohmite and 26 g Zirconium hydroxide. The impregnation, calcination and reduction procedures were similar to those of catalyst 14.

Catalyst 15 consisted of 13.9% Ni and 1.6% Mo on a high surface area transition AI ₂ O ₃ support, stabilized by 3.4% La as La203 and 1.5 % Zr as Zr02. Catalyst 16

Catalyst 16 according to the present invention was prepared according to the procedure of catalyst 14 using 36 g HNO ₃ (65%), 643 g water, 753 g Bohmite and 247 g Zirconium hy ^¬ droxide. The impregnation, calcination and reduction proce- dures were similar to those of catalyst 14. Catalyst 16 consisted of 13.6% Ni and 1.6% Mo on a high surface area transition AI ₂ O ₃ support, stabilized by 3.4% La as La ₂ <03 and 14.5 % Zr as Zr0 ₂ - Three catalysts containing Ni on a La ₂ 03-Zr0 ₂ ~ l ₂ 03 support were prepared from two different La promoted bohmites, to evaluate the effect of varying the amount of La. The methanation activity for these catalysts was normalized with the activity of catalyst 17.

Catalyst 17

Catalyst 17 according to the prior art was prepared from an aqueous suspension containing Al (as bohmite) , Zr (as hydroxide) and Ni (as basic carbonate) . The suspension was dried and the powder was pressed into tablets after addi ^¬ tion of graphite. The tablets were calcined in air at 900- 1000°C and the final catalyst was then obtained after re ^¬ duction with ¾ while increasing the temperature to 840°C. Catalyst 17 consisted of 23.4% Ni on a high surface area transition AI ₂ O ₃ support, stabilized by 21.4% Zr as Zr0 ₂ -

Catalyst 18

Catalyst 18 according to the present invention was prepared from an aqueous suspension containing Al (as La promoted bohmite) , Zr (as hydroxide) and Ni (as basic carbonate) . The suspension was dried and the powder was pressed into tablets after addition of graphite. The tablets were cal ^¬ cined in air at 900-1000°C and impregnated with an aqueous (ΝΗ ₄ )2Μθ2θ7 solution containing N¾ . The final catalyst was then obtained after drying at 80°C and reduction while increasing the temperature to 840°C, as mentioned above. Catalyst 18 consisted of 22.8% Ni and 2.1% Mo on a high surface area transition AI ₂ O ₃ support, stabilized by 0.4% La as La ₂ <03 and 20.8% Zr as Zr0 ₂ .

Catalyst 19

Catalyst 19 according to the present invention was prepared from an aqueous suspension containing Al (as La promoted bohmite) , Zr (as hydroxide) and Ni (as basic carbonate) . The suspension was dried and the powder was pressed into tablets after addition of graphite. The tablets were cal ^¬ cined in air at 900-1000°C and impregnated with an aqueous ( Η ₄ )2Μθ2θ7 solution containing N¾ . The final catalyst was then obtained after drying at 80°C and reduction in the presence of hydrogen while increasing the temperature to 840°C.

Catalyst 19 consisted of 22.3% Ni and 2.1% Mo on a high surface area transition AI ₂ O ₃ support, stabilized by 2.1% La as La ₂ 0 ₃ and 20.4% Zr as Zr0 ₂ .

Catalyst 20

Catalyst 20 according to the prior art was prepared from an aqueous suspension containing Al (as bohmite) , Zr (as hy- droxide) and Ni (as basic carbonate) . The suspension was dried and the powder was pressed into tablets after addi ^¬ tion of graphite. The tablets were calcined in air at 925- 1000°C and impregnated with an aqueous Ce(N03)3 solution. The final catalyst was then obtained after calcination at 450°C and reduction with H ₂ up to 840°C. Catalyst 20 consisted of 22.7% Ni on a high surface area transition AI ₂ O ₃ support, stabilized by 2.6% Ce as Ce ₂ <03 and 20.7% Zr as Zr0 ₂ . Catalyst 21

Catalyst 21 according to the present disclosure was pre ^¬ pared from Catalyst 20 by impregnation of the Ce containing calcined tablets with an aqueous ( Η ₄ )2Μθ2θ7 solution con ^¬ taining NH ₃ . The final catalyst was then obtained after drying at 250°C and reduction up to 840°C.

Catalyst 21 consisted of 22.1% Ni and 2.6% Mo on a high surface area transition AI ₂ O ₃ support, stabilized by 2.6% Ce as Ce ₂ 0 ₃ and 20.2% Zr as Zr0 ₂ .

Catalyst 22

Catalyst 22 according to the prior art was prepared from an aqueous suspension containing Al (as bohmite) , Zr (as hydroxide) and Ni (as basic carbonate) . The suspension was dried and the powder was pressed into tablets after addi ^¬ tion of graphite. The tablets were calcined in air at 925- 1000°C and impregnated with an aqueous Pr(N03)3 solution. The final catalyst was then obtained after calcination at 450°C and reduction with H ₂ up to 840°C.

Catalyst 22 consisted of 22.6% Ni on a high surface area transition AI ₂ O ₃ support, stabilized by 2.6% Pr as Pr ₆ On and 20.7% Zr as Zr0 ₂ . Catalyst 23

Catalyst 23 according to the present disclosure was pre ^¬ pared from Catalyst 22 by impregnation of the Pr containing calcined tablets with an aqueous (ΝΗ ₄ )2Μθ2θ7 solution con- taining N¾ . The final catalyst was then obtained after drying at 250°C and reduction up to 840°C.

Catalyst 23 consisted of 22.1% Ni and 2.6% Mo on a high surface area transition AI ₂ O ₃ support, stabilized by 2.6% Pr as Pr ₆ On and 20.2% Zr as Zr0 ₂ .

Catalyst 24

Catalyst 24 according to the prior art was prepared from an aqueous suspension containing Al (as bohmite) , Zr (as hydroxide) and Ni (as basic carbonate) . The suspension was dried and the powder was pressed into tablets after addi ^¬ tion of graphite. The tablets were calcined in air at 925- 1000°C and impregnated with an aqueous Sm( 03)3 solution. The final catalyst was then obtained after calcination at 450°C and reduction with H ₂ up to 840°C.

Catalyst 24 consisted of 22.7% Ni on a high surface area transition AI ₂ O ₃ support, stabilized by 2.6% Sm as Sm ₂ 03 and 20.7% Zr as Zr0 ₂ .

Catalyst 25

Catalyst 25 according to the present disclosure was pre ^¬ pared from Catalyst 24 by impregnation of the Sm containing calcined tablets with an aqueous (ΝΗ ₄ )2Μθ2θ7 solution con ^¬ taining NH ₃ . The final catalyst was then obtained after drying at 250°C and reduction up to 840°C.

Catalyst 25 consisted of 22.1% Ni and 2.6% Mo on a high surface area transition AI ₂ O ₃ support, stabilized by 2.6% Sm as Sm ₂ 03 and 20.2% Zr as Zr0 ₂ - Table 1 indicating an embodiment of the present disclosure:

The evaluation of the catalysts reveals several tendencies. In general the methanation activity is correlated to the size of nickel crystallites. In all examples the methana ^¬ tion activity is standardized for similar materials against the methanation activity of an unstabilized material.

Catalysts 1 to 3 and 4 to 7 demonstrate that the trends for La and Mo stabilization of zirconia stabilized alumina are equivalent to those of a magnesium-alumina spinel based support, i.e. that in combination Mo, La and Zr or Mg sta ^¬ bilize the Ni crystallites and increases the activity be ^¬ yond a simple additive effect.

Catalysts 8, 9 and 10 demonstrate that an increased Ni con ^¬ tent increases methanation activity.

Catalysts 11, 12 and 13 demonstrate that Ba has an effect very similar to that of La, but that the stabilization of Ni particles is mainly obtained in the presence of Mo.

Catalysts 14, 15 and 16 demonstrate stabilization of cata ^¬ lysts comprising alumina support is improved with increased concentration of Zr.

Catalysts 17, 18 and 19 demonstrate that an increased con ^¬ centration of La in catalysts comprising alumina support improves stabilization.

Catalyst 20 vs. Catalyst 21, Catalyst 22 vs. Catalyst 23 and Catalyst 24 vs Catalyst 25 all demonstrate that the surprising synergetic stabilization effect of Mo is a general phenomenon for catalysts comprising alumina support and lanthanoids.