CH704017B1 - A process for preparing a oxyhydride containing at least one rare earth and its use to catalyze a partial oxidation of an alkane. - Google Patents

Abstract

A process for preparing the mixed oxyhydride comprising the following steps: A. producing a mixture of hydroxides of at least one rare earth and at least one metallic element other than rare earth; B. subjecting the hydroxide mixture of step A to drying and then heat treatment; and C. contacting the solid from Step B with hydrogen; and using such mixed oxyhydride to catalyze a partial oxidation reaction of an alkane to a mixture of H 2 and CO at a temperature below 200 ° C.

Description

Object and technical field:

The present invention relates to the use of a material based on a mixed oxyhydride of at least one rare earth and at least one metal element other than a rare earth, to catalyze an oxidation reaction partial methane or alkane in H2 and CO at low temperature.

Description of the invention

The present invention completes the processes for converting methane or an alkane into a mixture of H 2 and CO by a partial oxidation reaction at low temperature. This oxidation reaction is possible for natural gas but also for alkanes.

For this purpose, the invention consists in the use of a material based on mixed oxyhydride of at least one rare earth and at least one metal element, other than zirconium and a ground rare to catalyze a partial oxidation reaction of methane or an alkane to a synthesis gas (H2 and CO) at a temperature between 15 ° C and 200 ° C with conversion rates never reached under these conditions .

disadvantages:

The conversion of an alkane type fuel into synthesis gas may be the reforming process, with the following endothermic reactions: CnH2n + 2 + n CO2 → (n + 2) H2 + 2nCO (dry reforming) CnH2n + 2 + n H2O → 2 (n + 1) H2 + nCO (steam reforming)

Given their endothermic character, these reforming processes have the major disadvantage of requiring the implementation of a significant amount of energy, with its impact in terms of cost.

The partial oxidation requires high temperatures, higher than 500 ° C and the conversion rate of the alkane is insufficient for the formation of hydrogen when using materials based on mixed oxyhydrides to catalyze a low temperature partial oxidation reaction.

Technical problem:

The object of the present invention is to provide a process for converting methane and alkanes to H2 and CO which is economically interesting and is more effective than current processes in terms of alkane conversion and selectivity hydrogen formation, but at room temperature.

Solution:

The inventor's work has made it possible to demonstrate that the materials based on mixed oxyhydride of at least one rare earth is at least one metal element, judiciously chosen, other than a rare earth element. aforementioned type particularly effective for the partial oxidation reaction of an alkane in H2 + CO, and this at low temperature.

Advantages:

Thus, these catalysts make it possible to obtain very interesting results both in terms of the conversion rate of the alkane and selectivity for hydrogen formed at temperatures below 200 ° C. but also at room temperature.

Enumeration of formulas:

The balance equation of this partial oxidation reaction of an alkane is as follows: <tb> formula (1): <sep> CnH2n + 2 + (n / 2) O2 → (n + 1) H2 + nCO <tb> <sep> (COH2n + (n / 2) O2 → nH2 + nCO, for a cycloalkane)

Realization of the invention:

This partial oxidation reaction is used to obtain hydrogen from methane which is the most interesting alkane insofar as its H / C ratio is the highest. The conversion of natural gas, rich in methane, into synthesis gas (H2 and CO) is interesting in this respect.

For this reaction many types of catalysts have been proposed, including catalysts based on supported metals or even catalysts of the metal oxide type. These catalysts are interesting in terms of alkane conversion and selectivity to hydrogen formed but have the disadvantage of requiring often high temperatures.

The conversion of an alkane type fuel into synthesis gas may also be the reforming process, with the following endothermic reactions: CnH2n + 2 + n CO2 → (n + 2) H2 + 2nCO (dry reforming) CnH2n + 2 + n H2O → 2 (n + 1) H2 + nCO (steam reforming)

Given their endothermic character, these reforming processes have the major disadvantage of requiring the implementation of a significant amount of energy, with its impact in terms of cost.

[0015] Thus, partial exothermic fuel oxidation processes are preferred, which requires a lower energy input. However, when the partial oxidation does not require high temperatures, well above 500 ° C, the conversion rate of the alkane may be disappointing for the formation of hydrogen.

In addition, high temperatures can lead to the formation of carbon or (coking phenomenon), which can block the catalyst. For temperatures of the order of 500 ° C at most, most of the currently known alkane partial oxidation catalysts have poor catalytic activities and the technical difficulties encountered with the reactor components are particularly severe.

It is therefore necessary to achieve for catalytic activities really interesting temperatures of the order of 700 ° C to 800 ° C.

A particular use is the partial oxidation reaction of the alkanes in a mixture of H 2 and CO (synthesis gas).

An important issue is to achieve the partial oxidation reaction of methane or alkanes at even lower temperatures, between 15 and 200 ° C, and preferably at ambient temperatures (between 15 and 30 ° C) the catalysts currently used for the partial oxidation reaction of alkanes do not provide with good efficiency.

The contribution of the present invention is to provide a process for converting methane and alkanes to H2 and CO which is economically interesting and is more efficient than current processes in terms of conversion of the alkane and selectivity of hydrogen formation, but at room temperature. The object of the invention is in particular to provide a process for converting methane or alkanes into an effective hydrogen, possibly for obtaining a synthesis gas, a step that can be prolonged by the storage of H 2 easier than biogas or implementation within a fuel cell.

Publications:

For more details concerning this reaction, reference may be made to Science, Volume 259, page 343 (1993) or to nature, volume 344, page 319 (1990).

[0022] There are rare documents describing catalysts made at less than 500 ° C. For example, U.S. Patent 5,411,927 discloses partial oxidation conducted between 200 ° C and 1000 ° C as well as FR 2,876,996-A1.

The catalyst:

By "rare earth" is meant, in the sense of the present description, an element selected from the group consisting of scandium, yttrium and lanthanides, the lanthanides being the elements of atomic number between 57 and 71 , namely elements ranging from lanthanum to lutetium, inclusively.

Furthermore, within the meaning of the present description the term "mixed oxyhydride of at least one rare earth is at least one metal element other than a rare earth" means a solid which comprises metal cathions of a or more rare earths, metal cathions of one or more metal elements other than rare earth, O 2 - anions and hydride ions.

According to a first embodiment, this mixed oxyhydride has the structure of an intermetallic oxide of the rare earth (s) and of the metallic element (s) and comprises in addition, hydride ions within anionic gaps of the crystal lattice of this intermetallic oxide.

Alternatively, the oxyhydride used according to the invention may also be a mixture of several distinct metal oxides based on the rare earth (s) and the (or) element (s). ) metal (s), where all or part of these oxides comprises hydride ions within anionic gaps in their crystal lattice. Where appropriate, the mixed oxyhydride preferably contains at least one oxyhydride of the rare earth (s), namely an oxide of the rare earth (s) including hydride ions within anionic gaps of its crystal lattice.

Thus, according to one variant, the mixed oxyhydride may consist of a mixture of several oxyhydrides, this mixture being, for example, in the form of oxyhydride crystallite based on (or) metal element (s) ( s) other than rare earths dispersed within a matrix based on an oxyhydride of the rare earth (s).

According to another possible variant, the mixed oxyhydride may also be based on a mixture comprising on the one hand oxyhydrides and on the other hand oxides not comprising hydride ions. Where appropriate, the oxyhydrides advantageously comprise one or more oxyhydrides based on the rare earth (s) and a base oxide of the metal element (s). According to this particular embodiment, the catalyst may for example comprise oxide crystallites based on the metal element (s) other than rare earths dispersed in a matrix based on oxyhydride. rare earth (s).

The inventor's work has made it possible to demonstrate that the materials based on mixed oxyhydride of at least one rare earth is at least one metal element, judiciously chosen, other than a rare earth element. aforementioned type particularly effective for the partial oxidation reaction of an alkane in H2 + CO, and this at low temperature.

Thus, these catalysts make it possible to obtain very interesting results both in terms of the conversion rate of the alkane and selectivity for hydrogen formed, at temperatures below 200 ° C. but also at room temperature.

By "conversion rate of the alkane" in a partial oxidation reaction of an alkane is meant, within the meaning of the present description, the following ratio C (expressed in%): C = (Ni-alkane-N-alkane) / Ni-alkane Or: Ni alkane represents the number of moles of alkane introduced, Nf alkane represents the number of moles of alkane remaining after the reaction.

Furthermore, by "hydrogen selectivity formed" in a partial oxidation reaction of an alkane is meant the following ratio S (expressed in%): S = Nf H2 / 2 (Ni alkane - Nf alkane) Or: Ni alkane represents the number of moles of alkane introduced, Nf alkane represents the number of moles of alkane remaining after the reaction; and Nf H2 represent the number of moles of hydrogen formed during the reaction.

The use of a mixed oxyhydride of at least one rare earth is at least one metal element, other than a rare earth, provides alkane conversion rates that can be greater than 50%. Achieving a level greater than 70%, with a hydrogen selectivity of at least 70%, is obtained at temperatures below 200 ° C, or even below 100 ° C.

These properties are far superior to those of the partial oxidation of alkanes at high temperatures. Even more unexpectedly, the inventors have demonstrated that mixed oxyhydrides of at least one rare earth is at least one metal element other than a rare earth generally have a catalytic activity of interest on a wide range of temperatures. Oxyhydrides make it possible to obtain an excellent conversion of the alkane and a good selectivity for formed hydrogen at room temperature (ie at temperatures of 15 to 30 ° C., for example of the order of 20 ° C.).

Thus, it turns out that a mixed oxyhydride of at least one rare earth is at least one metal element other than a rare earth and such as palladium, can be used to catalyze a reaction of partial oxidation of an alkane to a mixture of H 2 and CO at a temperature between 10 ° C and 100 ° C, with high values of alkane conversion and selectivity of the hydrogen formed. Thus, very advantageous properties are obtained for example at temperatures between 15 and 100 ° C.

The inventors work has established that these advantageous results are particularly observed when the oxyhydride used is obtained by treating with hydrogen a calcined mixture of oxide and / or hydroxide. rare earth (s) and (or) metallic element (s) other than rare earth and zirconium.

Thus, according to a particularly advantageous embodiment, it is advantageous for the mixed oxide used according to the invention to be obtained according to a process comprising the following steps: <tb> (A) <sep> make a mixture of hydroxide of the rare earth (s) and metal element (s) other than rare earths; <b> (B) <sep> subjecting the hydroxide mixture of step (A) to a heat treatment; and <tb> (C) <sep> contact the solid from step (B) with hydrogen.

The "hydroxide mixture" formed in step (A) may, in general, be any mixture comprising one of the four metal ions of the rare earth (s) and the or metal element (s) other than rare earths and OH- ions, this mixture may for example be an internal mixed metal hydroxide or a physical mixture of several metal hydroxides. Advantageously, the hydroxide mixture produced in step (A) is an internal metal hydroxide of the rare earth (s) and metal element (s) (s) ( s) other than rare earths.

Preferably, step (A) is carried out by performing a coprecipitation of metal salts of the rare earth (s) and metal element (s) (s). ) other than rare earths in a basic medium, in general, by adding an aqueous or aqueous solution of metal salts corresponding to a base, in particular of the amine type (for example triethylamine). In this context, the metal salts used are advantageously nitrates.

As a general rule, especially when the hydroxide mixture of step (A) is obtained by coprecipitation in a basic medium, the hydroxide mixture obtained is most often recovered by filtration, and it is then advantageously washed, for example by water and an alcohol (methanol or ethanol for example), this washing being optionally carried out beforehand with a water-alcohol mixture (for example a methanol mixture).

Step (B) comprises a heat treatment of the hydroxide mixture. If appropriate, this heat treatment is advantageously preceded by a step of drying the hydroxide mixture, in particular to allow a homogeneous temperature rise during the heat treatment.

For the heat treatment implemented in step (B), it is preferably carried out at a temperature at least equal to 300 ° C., advantageously at least 400 ° C., this temperature preferably remaining however preferably <50.degree. 700 ° C, and more preferably below 600 ° C.

In a particularly advantageous manner, it is preferred that this temperature be of the order of 500 ° C. Preferably, this heat treatment carried out carrying the hydroxide mixture of step (A) to the calcination temperature with a controlled temperature rise gradient, this temperature rise gradient being advantageously between 10 ° C. per hour. and 500 ° C per hour, and preferably between 25 ° C per hour and 100 ° C per hour.

With regard to step (C), the inventor's work has shown that the solid obtained at the end of step (B) behaves like a "hydrogen reservoir" particularly suitable to incorporate hydride ions into its crystalline structure when it is contacted with hydrogen. Without wishing to be bound to a particular theory, the inventor's work makes it possible to state that the catalytic properties obtained for oxyhydride are all the more interesting as the quantity of hydrides incorporated in the solid during step (C ) was high. In this context, it has been demonstrated that there is an optimum treatment temperature of step (C), making it possible to obtain maximum incorporation of the hydride ions. This optimal temperature depends on the nature of the rare earth (s) and the choice of other metallic elements other than rare earths. It can easily be determined for a given solid by observing the amount of hydrogen absorbed by the solid at different temperatures as a rule, this optimum temperature is between 25 ° and 1000 ° C, and most often between 150 and 350 ° C .

It is advantageous that the treatment of step (C) is carried out at a temperature of the order of the above-mentioned optimum temperature permitting maximum incorporation of the hydride ions into the catalyst. For this purpose, step (C) is typically conducted at a temperature between 25 ° C and 500 ° C, for example between 150 ° C and 350 ° C, for example between 180 and 250 ° C (typically at a temperature of the order of 200 ° C).

According to another conceivable embodiment, the mixed oxide used according to the invention may also be obtained according to a process comprising the following steps: <tb> (A) <sep> depositing a hydroxide-based mixture of the rare earth (s) on a support based on an oxide of said metal element (s) other than rare earth; <b> (B) <sep> subjecting the supported hydroxide mixture of step (A) to a heat treatment; and <tb> (C) <sep> contact the solid from step (B) with hydrogen.

Where appropriate, steps (B) and (C) are advantageously carried out under the same temperature conditions as steps (B) and (C) above.

Whatever its exact mode of production, the mixed oxyhydride used according to the invention advantageously has a molar ratio rare earths / other metal elements between 1: 0.01 and 1:10, this ratio preferably being between 1: 0.05 and 1: 6.

Thus, according to a particularly advantageous embodiment, the mixed oxyhydride used according to the invention corresponds to the general formula (1) below: TMaOxHy (I) in which: T represents a rare earth, or a mixture of rare earths, T being advantageously cerium or a mixture of rare earths comprising cerium; M denotes a metallic element, or a mixture of metallic elements, other than a rare earth, M being advantageously chosen from Al, Ni, Pt, Pd, Cu, Mn, Fe, Cr, Co, Rh elements; Ru, Ir, Os, Mo, V, Ti, W, Au, Zn, Nb, and mixtures of these elements; a is between 0.01 and 10, for example between 0.02 and 8 (typically between 0.05 and 6); x is from 1 to 10; and y is between 0.1 and 100.

Even more advantageously, the mixed hydroxide used corresponds to the general formula (II) below: TM1a1M2a2OxHy (ll) in which: T represents a rare earth, or a mixture of rare earth; M1 denotes a metal chosen from Al or Pd M2 denotes a metallic element, or a mixture of metallic elements, other than zirconium, aluminum and rare earths, for example Ni, Pt, Pd, Cu, Mn, Fe, Cr, Co, Rh, Ru, Ir, Os, Mo, V, Ti, W, Au, Zn, Nb, or a mixture of two or more elements, M2 being advantageously nickel, or alternatively platinum, palladium (where nickel is preferred because less expensive); a1 is between 0 and 1; a2 is between 0.01 and 10, where a2 is generally less than or equal to 8, where a2 is most often between 0.05 and 5; X is from 1 to 10; and Y is between 0.1 and 100.

Thus, according to a first variant of the invention, the mixed oxyhydride used corresponds to the general formula (IIa) below: TPda1M2a2OxHy (IIa) in which: T, M2, a2, x and y have the aforementioned meanings; and a1 is between 0.1 and 1.

In the context of its first variant, T advantageously represents cerium. Thus, the mixed oxyhydride advantageously corresponds to the following formula (IIa-1): CePda1M2a2OxHy (lla-1) wherein M2, a1, a2, x and y have the aforementioned meanings.

Even more preferentially, the mixed oxyhydride has the following formula (Ila-2): CePda1Nia2OxHy (lla-2) wherein a1, a2, x and y have the abovementioned meanings, a1 being preferably between 0.4 and 0.6, and a2 being preferably between 1 and 5.

For example, the recycled oxyhydride may advantageously be a ternary oxyhydride of cerium, palladium and nickel corresponding to the following general formula (Ila-3): CePd0.5Nia2OxHy (lla-3) in which a2, x and y have the abovementioned meanings, a2 being preferably between 1 and 5 are particularly interesting oxyhydrides of formula (IIIa-3) in which a2 = 1 or 3.

According to a second variant of the invention, the mixed oxyhydride used corresponds to the general formula (IIb) TPda1M2a2OxHy (llb) in which: T, M2, a2, x and y have the abovementioned meanings with the exception of palladium for M2; and a1 is between 0.1 and 1.

Here again, T advantageously represents cerium and the mixed oxyhydride (IIb) according to this second variant preferably corresponds to the following formula (IIb-1): CePda1M2a2OxHy (llb-1) wherein M2, a1, a2, x and y have the aforementioned meanings.

More advantageously, the mixed oxyhydride has the following formula (IIb-2): CePda1Nia2OxHy (IIb-2) wherein a1, a2, x and y have the abovementioned meanings, a1 being for example between 0.4 and 0.6 and a2 being preferably between 0.5 and 5.

Thus, for example, the oxyhydride reused according to this variant may advantageously be a ternary oxyhydride of cerium, palladium and nickel, corresponding to the following formula (IIb-3): CePd0.5Nia2OxHy (IIb-3) wherein a2, x and y have the aforementioned meanings, a2 being preferably between one and 5.

According to a third variant of the invention, the mixed oxyhydride used corresponds to the general formula (IIc) below: TM2a2OxHy (IIc) wherein T, M2, a2, x and y have the aforementioned meanings.

More advantageously, the mixed oxyhydride has the following formula (IIc-1): CeM2a2OxHy (IIc-1) wherein M2, a2, x and y have the aforementioned meanings.

Thus, for example, the oxyhydride used according to this variant may advantageously be a binary oxyhydride of cerium and nickel corresponding to the following general formula (IIc-2): CeNia2OxHy (llc-2) wherein a2, x and y have the abovementioned meanings, a2 being preferably between 0.05 and 2, for example between 0.1 let 1 and typically between 0.2 and 0.8.

Whatever their exact nature, the oxyhydrides of the present invention are particularly useful for converting alkanes to a mixture of CO and H 2 at low temperatures.

In this context, according to a particular aspect, the present invention specifically relates to the use of the oxyhydride of the invention to achieve the conversion of methane, for example methane contained in natural gas, into a CO mixture. and H 2, in the aforementioned temperature ranges, advantageously between 10 and 200 ° C, and preferably at a temperature below 180 ° C, more preferably at a temperature below 150 ° C, and typically between 15 and 100 ° C, for example between 50 and 100 ° C.

According to another particular aspect, the subject of the present invention is also the use of the oxyhydrides of the invention for carrying out the conversion of a cycloalkane, for example cyclohexane or a mixture containing it, into a mixture of CO and H2 in the aforementioned temperature ranges, and preferably at a temperature below 200 ° C, for example a temperature between 15 and 100 ° C.

The characteristics and various advantages of the present invention will appear even more clearly in view of the illustrative examples set out below.

Examples

Example 1

Preparation of catalysts based on ternary oxyhydride of cerium, palladium and nickel.

It was prepared several catalyst (1A to 1C) based on ternary oxyhydrides of cerium, palladium and nickel having a palladium / cerium molar ratio of 0.5 different nickel / cerium molar ratios. In other words, these catalysts are based on an oxyhydride of formula.

CePd0.5Nia2OxHy (formula IIIa-3), having different values of a2 which are shown in Table 1 below. These catalysts 1A to 1C were prepared according to the following steps 1.1 to 1.3:

1.1 Preparation of a mixture of hydroxides of cerium, palladium and nickel by coprecipitation of the corresponding metallic nitrates in a basic medium

A solution of nitrates of cerium, palladium and nickel was prepared by mixing: <tb> (i) <sep> 20 ml of an aqueous solution of 0.5 M cerium nitrates; <tb> (ii) <sep> 10 ml of a 0.5 M aqueous solution of palladium nitrate; and <tb> (iii) <sep> a volume V1 of (20 X a2) ml of an aqueous solution of nickel nitrates of concentration 0.5 M, where a2 is the desired nickel / cerium molar ratio for the oxyhydride of catalyst. The volumes of aqueous nickel nitrate solution used in each case are reported in Table 1 below. <tb> (iv) <sep> The resulting mixture was stirred for 10 minutes. <tb> (v) <sep> The solution obtained at the end of the mixture was added dropwise to a volume V2 of a solution of 1.5M triethylamine in methanol. The volume V 2 used in each case is reported in Table 1 below. During this addition, the formation of a precipitate of metal hydroxides was observed. <tb> (vi) <sep> The hydroxide mixture thus formed was recovered by filtration (porosity filter 3), then washed and rinsed by a total volume equivalent to the volume recovered, and this time, by water and methanol.

1.2 Drying then calcination under air at 500 ° C

The washed hydroxide mixture obtained at the end of the previous one was dried at 120 ° C in an oven for 12 hours. The solid was then obtained which was then ground in a mortar in the form of a fine powder.

The powder obtained after the previous grinding was then heated to 500 ° C in air, with a temperature rise rate of 30 ° C per hour. The solid was kept at 500 ° C for 4 hours, after which it was allowed to cool to room temperature.

The catalysts subjected to the calcination step will be referred to herein as "calcined" catalysts.

1.3 Hydrogen treatment

The solid resulting from step 1.2 was then treated under a flow of hydrogen at a temperature of 200 ° C for 12 hours, whereby the catalyst was obtained in the activated state, ready for use. implemented in the partial oxidation reaction of an alkane.

The various characteristics of the catalysts 1A to 1C and their preparation process are reported in Table 1 below.

Table 1: Catalysts 1A to 1C (of Ce type Pd0.5Nia2)

[0075] <Tb> Catalyst <September> 1A <September> 1E <September> 1F <tb> Values of a2 <sep> 3 <sep> 4 <sep> 5 <tb> Catalyst Type <sep> Calcined <sep> Calcined <sep> Calcined <tb> Volume V1 of nickel nitrate solution used in the mixture of step 1.1 <sep> 60 ml <sep> 80 ml <sep> 100 ml <tb> Volume V2 of triethylamine solutions used for coprecipitation <sep> 112 ml <sep> 138 ml <sep> 163 ml

Example 2

Preparation of catalyst based on a binary oxyhydride of cerium and nickel.

It has been prepared several catalysts (2A to 2B) based on binary oxyhydrides of cerium and nickel having different molar ratios nickel / cerium. Thus, these catalysts are based on an oxyhydride of the formula CeNia2OxHy (formula IIc-2), with different values of a2, indicated in Table 2 below. These catalysts 2A to 2B were prepared according to the following steps 2.1 to 2.3:

2.1 Preparation of a mixture of hydroxides of cerium and nickel by coprecipitation of the corresponding metallic nitrates in a basic medium

It was realized a solution of nitrates of cerium, palladium and nickel by mixing: <tb> (i) <sep> 20 ml of a 0.5 M aqueous solution of cerium nitrate; and <tb> (ii) <sep> a volume V1 of (20 X a2) ml an aqueous solution of nickel nitrate of concentration 0.5 M, where a2 the desired nickel / cerium molar ratio for the oxyhydride of the catalyst. The volumes of aqueous solutions of nickel nitrate used in each case are reported in Table 2 below. <tb> <sep> The resulting mixture was stirred for 10 minutes. <tb> <sep> The solution obtained at the end of the mixture was added dropwise to a volume V2 of a solution of triethylamine at 1.5 M in methanol. The volume V2 used in each is reported in Table 2 below. During this addition, the formation of a precipitate of metal hydroxides was observed. <tb> <sep> The hydroxide mixture thus formed was recovered by filtration (porosity filter 3), and then washed and rinsed with a total volume equivalent to the volume recovered, and this time with water and methanol.

2.2 Drying then calcination under air at 500 ° C.

The washed hydroxide mixture obtained at the end of the previous step was dried at 120 ° C in an oven for 12 hours. A solid was then obtained which was then ground in a mortar in the form of a fine powder.

The powder obtained after the preceding grinding was then heated to 500 ° C in air, with a temperature rise rate of 30 ° C per hour. The solid was kept at 500 ° C for 4 hours, after which it was allowed to cool to room temperature.

2.3 Hydrogen treatments

The solid resulting from step 2.2 was then treated under a stream of hydrogen at a temperature of 200 ° C for 12 hours, whereby the catalyst was obtained ready for its implementation in the reaction. partial oxidation of an alkane.

The different characteristics of the catalysts 2A to 2B and their preparation processes are reported in Table 2 below.

Table 2 Catalysts 2A to 2B (CeNia2 type)

[0083] <Tb> Catalyst <September> 2A <September> 2B <tb> Value of a2 <sep> 0.2 <sep> 0.9 <tb> Catalyst Type <sep> Calcined <sep> Calcined <tb> Volume V1 of nickel nitrate solution used in the mixture of step 2.1 <sep> 4 ml <sep> 18 ml <tb> Volume V2 of triethylamine solutions used for coprecipitation <sep> 30 ml <sep> 47.5 ml

Example 3

Using the catalysts of Examples 1 to 2 for the partial oxidation reaction of methane.

The catalysts 1A to 1C, 2A and 2B, obtained in the preceding examples, were used to catalyze the partial oxidation reaction of methane into a mixture of H 2 and CO 2.

In each case, the reaction was carried out by circulating, in a stainless steel fixed-bed tubular reactor containing 200 mg of catalyst, a gaseous flow based on a mixture of CH.sub.4, O.sub.2 and N.sub.2, with a molar ratio CH4 / 02 / N2 of 3/1/3. In each case, the catalyst is deposited in the reactor on a bed of inert carborundum (SiC) organized in a succession of layers of decreasing grain diameter (bed of about 5 cm 3 volume, comprising a first layer of diameter of grain equal to 2.38 mm (volume: 2 cm <3>), a second layer grain diameter equal to 1.19 mm (volume: 1.5 cm <3>) and a third layer grain diameter equal to 0.48 mm (this third layer contains an inert volume of carborundum equal to that of the catalyst, mixed with the catalyst).

In practice, the hydrogen treatment steps 1.3 and 2.3 of Examples 1 to 2 are carried out within the tubular reactor which is used for the partial oxidation reaction. Following the hydrogen treatment, the reactor is purged with a stream of helium for 30 minutes before the introduction of the reactive gas mixture for the partial oxidation reaction.

Once equilibrium reached for the partial oxidation reaction, the gas flow leaving the reactor is analyzed by gas chromatography using a chromatograph of "Shimatdzu GC 9" type associated with an interface allowing FID and katharometer signal processing using data software to establish and process the chromatograph. This analysis reveals the presence of H2, CO, N2, O2, CH4 and CO at the reactor outlet. On the basis of the quantitative data from the chromatography, the conversion of CH4 and oxygen as well as the selectivity into the different products formed are calculated at equilibrium by the following formulas: methane conversion rate (expressed as a percentage): CH4 = (dICH4-dfCH4) / dl CH oxygen conversion rate (expressed as a percentage): SO2 = (d102-dfO2) / d102 hydrogen selectivity formed (expressed as a percentage) SH2 = dlH2 / 2 (dlCH4-dfCH4) CO selectivity formed (expressed as a percentage) SCO = DFCO / (dlCH4-dfCH4) CO2 selectivity formed (expressed as a percentage): SCO2 = dfCO2 / (dlCH4-dfCH4) with the following meanings: dlCH4 and dIO2 respectively represent the flows of methane and O2 entering the reactor; and dfCH4, dfH2, dfO2, cfCO and dfCO2 respectively represent the flow rates of methane, H2, O2, CO and CO2 at the reactor outlet.

The results obtained for the various catalysts at temperatures between 50 ° and 200 ° C and with different flow rates of the reactive gas (CH4 + O2 + N2) are reported in Table 3 below.

In the reaction, great care was taken in regulating the temperature. In particular, a thermocouple is used in particular for controlling the effective temperature of the catalytic bed.

Table 3: Catalytic Activities

[0091] <tb> Catalyst <sep> Reaction temperature <sep> Reactant gas flow <sep> Conversion rate <sep> Conversion rate <sep> Selectivity in formed products <sep> Selectivity in formed products <sep> Selectivity in formed products <tb> <sep> <sep> <sep> CH4% <sep> 02% <sep> H2% <sep> CO% <sep> CO2% <tb> 1A <sep> 50 ° C <sep> 1.2 L / h <sep> 75 <sep> 84 <sep> 32 <sep> 28 <sep> 0 <tb> <sep> 100 ° C <sep> 1.2 L / h <sep> 71 <sep> 84 <sep> 41 <sep> 32 <sep> 0 <tb> <sep> 100 ° C <sep> 3 L / h <sep> 38 <sep> 68 <sep> 82 <sep> 68 <sep> 0 <tb> <sep> 200 ° C <sep> 1.2 L / h <sep> 69 <sep> 86 <sep> 44 <sep> 35 <sep> 0 <tb> <sep> 200 ° C <sep> 3 L / h <sep> 42 <sep> 70 <sep> 100 <sep> 69 <sep> 0 <tb> 1B <sep> 100 ° C <sep> 3 L / h <sep> 41 <sep> 56 <sep> 72 <sep> 100 <sep> 0 <tb> <sep> 100 ° C <sep> 3 L / h <sep> 41 <sep> 57 <sep> 93 <sep> 97 <sep> 0 <tb> 1C <sep> 100 ° C <sep> 2.6 L / h <sep> 55 <sep> 42 <sep> 15 <sep> 9 <sep> 0 <tb> <sep> 100 ° C <sep> 2.6 L / h <sep> 55 <sep> 42 <sep> 23 <sep> 10 <sep> 0 <tb> <sep> 100 ° C <sep> 2.6 L / h <sep> 55 <sep> 44 <sep> 65 <sep> 9 <sep> 0 <tb> 2A <sep> 100 ° C <sep> 1 L / h <sep> 70 <sep> 90 <sep> 33 <sep> 32 <sep> 0.03 <tb> <sep> 100 ° C <sep> 1 L / h <sep> 70 <sep> 90 <sep> 49 <sep> 32 <sep> 0.12 <tb> 2B <sep> 100 ° C <sep> 3 L / h <sep> 26 <sep> 46 <sep> 49 <sep> 19 <sep> 0 <tb> <sep> 100 ° C <sep> 1 L / h <sep> 69 <sep> 75 <sep> 14 <sep> 30 <sep> 0.08 <tb> <sep> 100 ° C <sep> 3 L / h <sep> 41 <sep> 57 <sep> 61 <sep> 9 <sep> 0 <tb> <sep> 100 ° C <sep> 1 L / h <sep> 70 <sep> 75 <sep> 24 <sep> 30 <sep> 0.1 <tb> <sep> 100 ° C <sep> 3 L / h <sep> 41 <sep> 64 <sep> 64 <sep> 10 <sep> 0

Claims (9)

A process for preparing the mixed oxyhydride comprising the following steps: <tb> A. <sep> Making a mixture of hydroxides of at least one rare earth and at least one metallic element other than a rare earth; <b> B. <sep> subjecting the hydroxide mixture of step A to pubic drying to a heat treatment; and <tb> C. <sep> bring the solid from step B into contact with hydrogen. 2. Use of a material based on a mixed oxyhydride of at least one rare earth and at least one metal element other than a rare earth, prepared according to claim 1, for catalyzing a partial oxidation reaction an alkane to a mixture of H 2 and CO at a temperature below 200 ° C. 3. Use of a material based on a mixed oxyhdride of at least one rare earth and at least one metal element other than a rare earth prepared according to claim 1, for catalyzing a partial oxidation reaction of an alkane to a mixture of H 2 and CO at a temperature of between 15 and 200 ° C. 4. Use according to claim 3, wherein in the mixed oxyhydride, the molar ratio of rare earth and metal element other than a rare earth is between 1: 0.01 and 1:10. 5. Use according to any one of claims 2 to 4, wherein the mixed oxyhydride has the general formula (I) below: TMaOxHy (I) in which; T represents a rare earth or a mixture of rare earths; M denotes a metallic element, or a mixture of metallic elements other than zirconium and a rare earth; A is between 0.01 and 10; X is between 1 and 10; - is between 0.1 and 100. 6. Use according to claim 5, wherein the mixed oxyhydride has the general formula (II) below: TM1a1M2a2OxHy (II) in which: - T represents a rare earth; M1 denotes the metal Pd or Al; M2 designates a metallic element, or a mixture of metallic elements other than zirconium, aluminum, palladium and a rare earth; - a1 is between 0 and 1; - a2 is between 0.01 and 10; X is between 1 and 10; and - is between 0.1 and 100. 7. Use according to claim 6, wherein the mixed oxyhydride has the following formula (11a-3): CePd0.5Nia2OxHy (lla-3) in which: - a2, x and y have the meanings given in claim 6. 8. Use according to claim 6, wherein the mixed oxyhydride has the following formula (IIb): TPda1M2a2OxHy (IIb) in which: T, M2, a2, x and y have the meanings given in claim 6; - a1 is between 0.1 and 1. 9. Use according to any one of claims 2 to 8 for carrying out the conversion of methane to a mixture of CO and H 2 at a temperature below 200 ° C.