Process for manufacturing a catalyst optimized for maximized catalytic combustion of dihydrogen from room temperature

Abstract

The present invention relates to a method for manufacturing a catalyst suitable for the catalytic combustion of dihydrogen, this catalyst comprising a catalytically active phase of platinum (Pt) and an alumina support (Al2O3), the method comprising the successive steps of: - S1) providing an aluminum hydroxide support (Al(OH)3); - S2) dispersing in said support a platinum precursor, the decomposition of which by calcination forms the catalytically active phase; and - S3) treating the support in which the platinum precursor is dispersed at the end of step S2), comprising a sub-step S31) of drying followed by a sub-step S32) of calcination at a target temperature of between 250°C and 1000°C to jointly: -- transform the aluminum hydroxide (Al(OH)3) of the support into alumina (Al2O3); and-- obtaining the catalytically active phase from the precursor dispersed in the support in step S2). Figure for abstract: Fig.1

Description

Title of the invention: Method for manufacturing a catalyst optimized for maximized catalytic combustion of di-hydrogen from room temperature TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of catalytic combustion, and more particularly to a method for synthesizing a catalyst particularly suitable for equipping a domestic catalytic combustion device for the diffusion of perfume and / or active substances, for the destruction of odorous or non-odorous molecules, and / or for air purification. TECHNICAL BACKGROUND

[0002] Certain devices for the diffusion of perfume and / or active substances, for the destruction of odorous or non-odorous molecules, and / or for air purification, operate on the so-called catalytic combustion of a perfumed solution based on alcohol derived from petrochemicals, commonly propan-2-ol also called isopropyl alcohol.

[0003] Such devices, some of which are referred to as "catalytic lamps", generically comprise a bottle containing the solution, a wick immersed in the solution, and a catalytic head comprising a burner. The latter ensures the diffusion of the product by catalysis from the solution rising by capillarity along the wick.

[0004] The catalytic reaction is a flameless chemical oxidation reaction, which is facilitated at low temperature by the presence of the catalyst. In practice, the catalyst is a component which accelerates the rate of a chemical transformation and remains unchanged at the end of the reaction. The catalytic action results from the lowering of the activation energy level through which the transformation must be carried out.

[0005] Generally speaking, a so-called impregnated catalyst comprises a catalytically active phase and a porous support, in which the active phase is diluted, which gives the whole the desired textural (specific surface area, porosity) and mechanical properties.

[0006] Although perfectly functional, the catalytic combustion of isopropyl alcohol generates carbon dioxide and volatile organic compounds which participate in the formation of ozone, which therefore contributes to the greenhouse effect.

[0007] In a context of ecological transition, dihydrogen appears to be a particularly promising candidate to replace petroleum and its derivatives, and in particular to replace isopropyl alcohol in this case of use of catalytic lamps. In fact, the combustion of dihydrogen does not as such emit volatile organic compounds, nor even carbon dioxide, in that it essentially produces water and heat in its expression: H2 4- % 02• H2 O — 286 mol-1

[0008] There are a number of research works on catalytic reactors, catalysts and the identification of the different factors having an impact on the kinetics of catalytic combustion of dihydrogen, such as: - “Pt-impregnated catalysts on powdered SiC and other commercial supports for hydrogen combustion under oxidation conditions”, Jongho Kim a, Jianglong Yu, Soonho Lee, Arash Tahmasebi,

[0009] Chung-Hwan Jeon, John Lucas, International Journal of Hydrogen RGY 46 (2021) 400 73e40104, October 2021; - “Monolithic supports based on biomorphic SiC for the catalytic combustion of hydrogen”, GM Arzac, J. Rarmrez-Rico, Gutiérrez-Pardo, MC Jiménez de Haro, D. Hufschmidt, J. Martinez-Fernandez, The Royal Society of Chemistry 2016, RSC Adv., 2016, 6, 66373.

[0010] This work highlights the interest in forming catalysts whose active phase is based on platinum, as a noble reactive metal probably the most appropriate for reactions linked to dihydrogen.

[0011] Also, it is known from the literature, in particular from documents KR100522435 and KR100823929, to synthesize so-called Pt-alumina catalysts by means of a dispersion of platinum salt in alumina. The term alumina is used very generally to designate materials of the aluminum oxide type conventionally obtained by calcination of a precursor of the aluminum oxo-hydroxide or alumina monohydrate type (A1OOH) or of the aluminum hydroxide tri-hydrate alumina type also called alumina tri-hydrate (A1(OH)3]).

[0012] Through the test, it appears that the catalysts prepared according to these methods known from the prior art do not make it possible to satisfactorily meet all of the criteria of the specific specifications of a catalytic lamp, including in particular the major criteria of allowing: - the initiation of catalytic combustion in air at room temperature; and - a substantially total conversion of hydrogen at 100°C.

[0013] In continuation of the development of Pt-alumina type catalysts, the invention aims to propose a process for synthesizing a catalyst making it possible to ensure maximum catalytic activity at 100°C with initiation in air at room temperature to be transposable to a catalytic lamp, or other domestic devices with catalytic combustion for the diffusion of perfume and / or substances active, for the destruction of odorous or non-odorous molecules, and / or for air purification. Such a catalyst can also be used for other applications such as domestic heating. Statement of the invention

[0014] To this end, the invention relates to a method for manufacturing a catalyst suitable for the catalytic combustion of dihydrogen, this catalyst comprising a catalytically active phase of platinum (Pt) and an alumina (A12O3) support, the method comprising the successive steps of: - SI) provision of an aluminum hydroxide support (A1(OH)3); - S2) dispersion in said support of a platinum precursor, the decomposition of which by calcination forms the catalytically active phase; and - S3) treatment of the support in which the platinum precursor is dispersed at the end of step S2), comprising a sub-step S31) of drying followed by a sub-step S32) of calcination at a target temperature between 250°C and 1000°C for jointly: — transforming the aluminum hydroxide (A1(OH)3) of the support into alumina (A12O3); and — obtain the catalytically active phase from the precursor dispersed in the S2 phase support).

[0015] The invention also relates to a process thus defined, in which the aluminum hydroxide constituting the support provided in step S1) is Bayerite (A1(OH)3).

[0016] The invention also relates to a process thus defined, in which the calcination temperature in sub-step S32) of the Bayerite (A1(OH)3) support is between 550°C and 650°C.

[0017] The invention also relates to a process thus defined, in which the aluminum hydroxide constituting the support is Gibbsite (A1(OH)3).

[0018] The invention also relates to a method thus defined, in which the calcination temperature in sub-step S32) of the Gibbsite support is set at substantially 550°C.

[0019] The invention also relates to a method thus defined, in which: - sub-step S31) of drying the impregnated support includes freezing at a temperature of -18°C for 12 hours followed by freeze-drying for 12 hours; and - sub-step S32) of calcining the support is ensured by a gradual increase in temperature until the target temperature is reached, followed by maintenance at the target temperature for two hours.

[0020] The invention also relates to a method thus defined, in which step S2) of dispersing the precursor in the support provided in step S1) is carried out by im- pregnancy or by exchange.

[0021] The invention also relates to a process thus defined, in which the platinum precursor used in step S2) is a solution of hexachloroplatinic acid (H2PtCl6) or a solution of tetraammineplatinum dichloride (Pt(NH3)4Cl2).

[0022] The invention also relates to a catalyst comprising a catalytically active phase of platinum (Pt) and an alumina support (A12O3) manufactured in accordance with the process thus defined.

[0023] The invention also relates to a catalyst thus defined, comprising a platinum (Pt) content of between 0.3 and 1% by weight.

[0024] The invention also relates to the use of a catalyst thus defined in a device for the diffusion of perfume and / or active substances, for the destruction of odorous or non-odorous molecules, and / or for air purification. Brief description of the drawings

[0025] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which reference will be made to the appended drawings in which: - [Fig.l] is a flowchart schematically illustrating the method according to the invention; - [Fig.2] illustrates the results of catalytic activity between room temperature and 100°C of a (Pt / Bayerite)-550°C catalyst obtained by impregnation of 0.5%Pt on Bayerite followed by calcination at 550°C in accordance with the process according to the invention, and of a control catalyst (Pt / Al2O3eXBayerite)-550°C obtained by calcination at 550°C of an alumina support derived from Bayerite and impregnated with 0.5%Pt according to a process different from that of the invention; - [Fig.3] illustrates the catalytic activity results of three batches of catalysts (0.5Pt / Bayerite)-550°C obtained by impregnation of 0.5%Pt on Bayerite followed by calcination at 550°C in accordance with the process according to the invention; - [Fig.4] illustrates the catalytic activity results of catalysts (0.5Pt / A12O3ex Bayerite)-550°C and (0.5Pt / Al2O3exBayerite)-550°C bis obtained by calcination at 550°C of alumina supports from Bayerite and impregnated with 0.5%Pt according to a process different from that of the invention; - [Fig.5] illustrates the results by dark field transmission electron microscopy (ADF STEM) of a catalyst (0.5Pt / Bayerite)-550°C obtained by impregnation of 0.5%Pt on Bayerite followed by calcination respectively at 550°C in accordance with the process according to the invention; - [Fig.6] illustrates the results by dark field transmission electron microscopy (ADF STEM) of a catalyst (0.5Pt / Al2O3exBayerite)-550°C obtained by calcination at 550°C of an alumina support from Bayerite and is impregnated with 0.5%Pt according to a method different from that of the invention; - [Fig.7] illustrates the catalytic activity results of four catalysts (0.3%Pt / Bayerite)-550°C, (0.5%Pt / Bayerite)-550°C, (0.8%Pt / Bayerite)-550°C and (1%Pt / Bayerite)-550°C obtained by impregnation of respectively 0.3%, 0.5%, 0.8% and 1% by weight content of platinum on Bayerite followed by calcination at 550°C in accordance with the process according to the invention; - [Fig.8] illustrates the catalytic activity results of eight catalysts (0.5Pt / Bayerite)-T°C obtained by impregnation of 0.5%Pt on Bayerite by the incipient humidity impregnation method followed by calcination at different temperatures between 250 and 1000°C; - [Fig.9] illustrates the catalytic activity results of six catalysts manufactured by dispersing platinum in Bayerite (A1(OH)3) by the anion exchange method before calcination at 550°C; - [Fig. 10] illustrates the catalytic activity results of a catalyst (0.5Pt / Bayerite)-550°C: H2PtCl6 obtained by impregnation of the Bayerite support with a solution of hexachloroplatinic acid H2PtCl6, and of a catalyst (0.5Pt / Bayerite)-550°C: Pt(NH3)4Cl2 obtained by impregnation of the Bayerite support with a solution of tetraammineplatinum dichloride Pt(NH3)4Cl2; - [Fig. 11] illustrates the catalytic activity results of a catalyst (0.5Pt / Gibbsite)-550°C obtained by impregnation of 0.5%Pt on Gibbsite followed by calcination at 550°C in accordance with the process according to the invention, and of a catalyst (0.5Pt / Al2O3eXGibbsite)-550°C obtained by calcination at 550°C of an alumina support derived from Gibbsite and impregnated with 0.5%Pt according to a process different from that of the invention; - [Fig. 12] illustrates the catalytic activity results of a catalyst (0.5Pt / Boehmite)-550°C obtained by impregnation of 0.5%Pt on Boehmite followed by calcination at 550°C, and of a catalyst (0.5Pt / Al2O3eXBOehmite)-550°C obtained by calcination at 550°C of an alumina support derived from Boehmite and impregnated with 0.5%Pt according to a process different from that of the invention; - [Fig. 13] shows pictures of: 1) Bayerite, Gibbsite and Boehmite; 2) catalysts (0.5Pt / Bayerite) -550°C, (0.5Pt / Gibbsite) -550°C and (0.5Pt / Gibbsite) -550°C obtained by impregnation of 0.5%Pt on Bayerite, Gibbsite and Boehmite respectively, followed by calcination at 550°C; 3) aluminas Al2O3eXBayerite, Al2O3eXGibbsite and Al2 O3eXBoehmite obtained by calcination at 550°C of Bayerite, Gibbsite and Boehmite respectively; and 4) catalysts (0.5Pt / Al2O3exBayerite) -550°C, (0.5Pt / Al2O3eXGibbsite) -550°C and (0.5Pt / Al2O3exBoehmite) -550°C obtained after impregnation of 0.5%Pt on alumina Al2 O3exBayerite, Al2O3exGibbsite and Al2O3exBoehmite respectively, followed by calcination at 550°C. DETAILED DESCRIPTION OF THE INVENTION

[0026] Within the framework of the invention, it is aimed to propose a catalyst active in the combustion of dihydrogen from room temperature and providing substantially total combustion at 100°C, so as to authorize its use in a catalytic lamp for safe domestic use.

[0027] It is known from the state of the art to form Pt-Alumina type catalysts, namely catalysts whose active phase is platinum and the support is formed from transition alumina, to ensure catalytic combustion of dihydrogen.

[0028] These Pt-Alumina type catalysts known from the state of the art are formed by impregnation of a transition alumina (A12O3) support with a solution of hexachloroplatinic acid (H2PtCl6), called platinum precursor salt, followed by drying and calcination steps. In practice, in solution, the hexachloroplatinic acid (H2 PtCl6) is dissociated into protons H+ and anions [PtCl62 ], and the anions attach to the alumina dispersed in this acidic solution, the surface of the alumina being positively charged at acidic pH. The chlorine (Cl) is then partially or totally eliminated subsequently by means of calcination which decomposes the PtCl6 species, thus obtaining the Pt-Alumina catalyst.

[0029] So-called transition alumina (A12O3), also called aluminum oxide, is a crystalline structure resulting from the dehydration of precursors of the alumina hydrate type: aluminum hydroxides of formula A1(OH)3 and aluminum oxo-hydroxides A10(0H). In practice, alumina (A12O3) is metastable, i.e., it varies irreversibly according to the dehydration of the precursor until it reaches its final thermodynamically stable form, called alumina α.

[0030] One of the most commonly used forms of alumina used to form the support before its impregnation with platinum salt is so-called gamma alumina (y-Al2O3) obtained by calcination of Boehmite (A1OOH) which is an aluminum oxo-hydroxide.

[0031] Although these Pt-alumina catalysts are recognized as particularly suitable for the purposes of catalytic combustion of dihydrogen, their action at room temperature is insufficient while their maximum activity is observed at temperatures significantly above 100°C. This results in a risk that the residual part of the unconsumed dihydrogen, from room temperature up to 100°C, accumulates and leads to the formation of explosive combustible mixtures, which is not admissible from an operational safety point of view for equipping a catalytic lamp in a domestic application.

[0032] The invention is part of a study aimed at evaluating the opportunities for improving Pt-alumina type catalysts to meet the aforementioned criteria, in particular by carrying out variations in the synthesis process.

[0033] It was surprisingly observed during this study that dispersing a platinum precursor on aluminum hydroxide (A1(OH)3), before calcining to obtain both alumina (A12O3) from aluminum hydroxide (A1(OH)3) and platinum (Pt) from the platinum precursor, makes it possible to obtain Pt-alumina catalysts whose response in catalytic combustion of di-hydrogen is significantly improved.

[0034] In particular, the effectiveness of the process according to the invention has been demonstrated within the framework of the invention regardless of the polymorph, Bayerite and Gibbsite, of aluminum hydroxide (A1(OH)3) considered.

[0035] The process for manufacturing a Pt-alumina type catalyst thus defined within the framework of the invention requires overall: - a step SI) of providing an aluminum hydroxide support (A1(OH)3); - a step S2) of dispersing a platinum precursor in said support; - a step S3) of treating the support in which the platinum precursor is dispersed at the end of step S2), comprising a sub-step S31) of drying followed by a sub-step S32) of calcination at a temperature between 250° and 1000°C. The process according to the invention is shown diagrammatically in [Fig.l].

[0036] It is advantageously recommended that the calcination applied to the impregnated Bayerite or Gibbsite support in step c) be carried out at a temperature of 550° or 650°C to result in the most optimized catalyst.

[0037] As understood, the major feature of the invention lies in the use of an aluminum hydroxide as a support to which a platinum precursor is added before co-calcining both the support and the platinum precursor embedded in this support to result in a Pt-alumina catalyst which is particularly efficient from room temperature.

[0038] In the following, examples of test results on the basis of which the method according to the invention was formulated will be presented. Example 1

[0039] This first example corresponds to a comparative analysis of catalytic activity obtained between: - a Pt-alumina catalyst with a platinum content of the order of 0.5% by weight, synthesized in accordance with the process according to the invention, by impregnating the platinum salt directly onto a Bayerite (A1(OH)3) support as aluminum hydroxide, the calcination of which results in the formation of alumina (A12O3); and - a Pt-Alumina catalyst called “control” with a platinum content by weight of the order of 0.5%, which is manufactured in the manner recommended in the state of the art, namely by impregnating the platinum salt on the alumina (A12O3) obtained in this case after the calcination of the Bayerite (A1(OH)3).

[0040] In the context of this first comparative study, two Pt-alumina catalysts were manufactured. Test Matrix - Example 1

[0041] Among these two catalysts listed in Table 1 below, we distinguish: - a first catalyst referenced (Pt / Bayerite)-550°C manufactured in accordance with the process according to the invention by directly impregnating the Bayerite (A1(OH)3) with the platinum salt, followed by calcination at 550°C transforming the Bayerite (A1(OH)3) into alumina (A12O3); and - a second catalyst referenced (Pt / Al2O3eXBayerite 550) -550°C not in accordance with the invention, manufactured by calcining Bayerite (A1(OH)3) at 550°C to transform it into alumina (A12O3) before being impregnated with the platinum salt; followed by calcination at 550°C.

[0042] [Tables 1] Support ACTIVE PHASE CATALYST Nomenclature Nature / Calcination temperature Nature Content (% wt) Post-impregnation treatment (Pt / (support))-T°C Bayerite (A1(OH)3) Pt 0.5 Calcination at 550°C (Pt / Bayerite)-550°C Alumina (A12O3) (ex-Bayerite calcined at 550°C) (Pt / A12O3 exBayerite-55û) 550°C Manufacturing - example 1

[0043] In detail, each catalyst was manufactured in a quantity of 5g on the same base of commercial Bayerite (A1(OH)3) ((A1(OH)3 - PURAL BT, SASOL Chemicals) and hexachloroplatinic acid (H2PtCl6) in aqueous solution comprising 1.45% by weight of platinum.

[0044] For the preparation of the catalyst (Pt / Al2O3eXBayerite 550) -550°C called “control”, i.e. not in accordance with the invention, a calcination at 550°C of the Bayerite (A1(OH)3) was first carried out to obtain the transition alumina (A12O3) intended to serve as an impregnation support. This support is designated by Al203eXBayerite-55o-

[0045] This calcination of Bayerite (A1(OH)3) before impregnation in the context of the production of the control catalyst was carried out in hot air, at 550°C, remaining 2 hours at maximum temperature in a muffle furnace having a heating rate of 5°C / min.

[0046] Once the alumina was thus obtained, 5g was taken in order to form the Al2 support. O3exBayerite-550 corresponding.

[0047] Regarding the preparation of the catalyst (Pt / Bayerite)-550°C, 6.68 g of Bayerite (A1(OH)3) were used as the impregnation support. This peculiarity arises from the fact that Bayerite is subject to a mass variation during its calcination after impregnation due to water losses by dehydroxylation. The value of 6.68 g of Bayerite was determined on the basis of a mass loss quantification, as follows: _^iipwrf^cstaà-vseiïr 4 «na# _» na ----- 100 m. = x 100 1 Wte 1

[0048] Once all the impregnation supports have been produced, they have undergone a so-called "incipient humidity" impregnation. This type of impregnation consists of bringing the support into contact with an aqueous solution containing hexachloroplatinic acid (H2PtCl6) in a quantity slightly greater than the pore volume of the support in order to fill all the available pores of this support.

[0049] This technique thus required first determining for each of the supports the quantity of aqueous solution containing hexachloroplatinic acid (H2PtCl6) to be produced to achieve a Pt impregnation of the order of 0.5% on this basis:

[0050] For 5g of catalyst at 0.5% by weight of platinum to be formed, the following was thus produced: - 6.23g of aqueous solution of hexachloroplatinic acid containing 0.025g of platinum to impregnate the 6.68g support of Bayerite (A1(OH)3) associated with the synthesis of the catalyst (Pt / Bayerite)-550°C.

[0051] - 7.42 g of aqueous solution of hexachloroplatinic acid (H2PtCl6) containing 0.025 g of platinum to impregnate the alumina support resulting from the calcination of 5 g of Bayerite (A1(OH)3), in order to prepare the synthesis of the catalyst (Pt / Al2O3eXBayerite 550) -550°C.

[0052] The supports were then each placed in a Pyrex flask and impregnated drop by drop with the corresponding aqueous hexachloroplatinic acid solution, before being placed in a rotary evaporator and left stirring for two hours at atmospheric pressure and room temperature.

[0053] The supports now impregnated with the aqueous solution of hexachloroplatinic acid were then dried and then calcined.

[0054] The drying step was carried out by means of freezing the impregnated supports at a temperature of -18°C for 12 hours, followed by freeze-drying of the mass. solid obtained for 12 hours to achieve complete drying.

[0055] The impregnated and dry supports were finally calcined under hot air at 550°C in a muffle furnace with a heating rate of 5°C / min, remaining two hours at maximum temperature.

[0056] Validation of the composition and catalytic tests - example 1

[0057] With reference to Table 2, the percentage of platinum deposited on the different supports was verified by inductively coupled plasma spectrometry, commonly referred to as “ICP” from the English “Inductively Coupled Plasma”.

[0058] [Tables2] Catalyst Theoretical Pt content (wt%) Actual Pt content (wt%) (Pt / bayerite) -550°C 0.5 0.51 (Pt / Al2O3 exBayerite-55o) -550°C 0.5 0.47

[0059] As observed, the effective amount of platinum deposited by incipient humidity impregnation varies between 0.47 and 0.51% by weight, which is very close to the theoretical target content. On this basis, the reproducibility of this incipient moisture impregnation method is validated. It follows that the behavior of catalysts manufactured according to the manufacturing process can be validly compared with that of catalysts manufactured in the usual way, based on the same common denominator {Bayerite - Pt content - calcination temperature}.

[0060] The catalytic combustion performance of dihydrogen was evaluated under the following standard operating conditions: - a quantity of 50 mg of each catalyst is diluted in 5 g of silicon carbide (SiC) then loaded into a fixed-bed Pyrex© glass tubular reactor operating at atmospheric pressure; - the reactor is subjected for 30 minutes to pretreatment at room temperature (20-22°C) under a synthetic air flow of 50 mL / min; - the catalytic activity is controlled at room temperature (20-22 °C) for 30 minutes and for 1 hour of heating from room temperature to 100°C under a gas flow comprising synthetic air and 2% dihydrogen.

[0061] Monitoring of the catalytic conversion of hydrogen was based on gas chromatographic analysis using a TCD detector, for "Thermal Conductivity Detector". The hydrogen conversion rate is expressed as the ratio between the difference in hydrogen concentrations before and after the reaction and the hydrogen concentration before the reaction. The hydrogen concentration before the The start of the reaction was measured in particular via a bypass circuit of the catalytic bed during the pretreatment period of the catalytic bed under air at the start of the test. Analysis of the results - example 1

[0062] [Fig.2], which compiles the catalytic activity results of the two catalysts manufactured, highlights that the catalyst (Pt / bayerite) -550°C, namely the catalyst based on 0.5% Pt impregnated on Bayerite then calcined at 550°C in accordance with the process according to the invention, is active in catalytic combustion of dihydrogen from room temperature, with a stable conversion around 37%. Also, the conversion into hydrogen of this catalyst increases progressively with the increase in the temperature of the furnace: of the order of 50% conversion of dihydrogen is obtained at 40°C and more than 90% from 65°C.

[0063] Conversely, it appears that the control catalyst (Pt / Al2O3 exBayente-550) -550°C, the manufacture of which differs only from that of the catalyst (Pt / bayerite) -550°C in that the support was calcined before impregnation with platinum, is inactive at room temperature and remains so up to 75°C. At 97°C, the conversion of dihydrogen by this catalyst (Pt / Al 2O3 exBayerite 550) -550°C remains less than 20%.

[0064] [Fig.2] thus provides information that the Pt / alumina (A12O3) type catalyst manufactured at from Bayerite impregnated with 0.5% platinum then calcined at 550°C, in accordance with the process according to the invention, presents a substantial gain in performance in catalytic combustion compared to a Pt / alumina catalyst (A12O3) of the same type but whose Bayerite is calcined before impregnation. Example 2

[0065] To verify the repeatability of the catalytic activity results of the catalyst (Pt / bayerite) -550°C demonstrated in example 1, satisfying in particular the criteria sought within the framework of the invention, three other batches of catalysts (Pt / bayerite) -550°C were manufactured. Manufacturing - example 2

[0066] These catalysts, designated Batch 1, Batch 2 and Batch 3, were manufactured in exactly the same way as that described in Example 1, namely by means of: - the contribution of 6.68 g of Bayerite (A1(OH)3) to form each impregnation support; - impregnation by nascent humidity of these impregnation supports with 6.23g of aqueous solution of hexachloroplatinic acid (H2PtCl6) containing 0.025g of platinum; then - drying followed by calcination at 550°C of the impregnated supports.

[0067] Catalytic tests and analysis of results - example 2

[0068] The reaction performance in catalytic combustion of dihydrogen of batches 1, 2 and 3 was evaluated under the same operating conditions as in Example 1.

[0069] As visible in [Fig.3], the catalytic activity results of batches 1, 2 and 3 are substantially the same and superimposable on those obtained on the basis of the catalyst (Pt / bayerite) -550°C of example 1.

[0070] It can be observed in particular that the catalysts (Pt / bayerite) -550°C of batches 1, 2 and 3: - convert dihydrogen at room temperature to 38% to 43%; - reach 50% conversion of dihydrogen at around 40°C; and - ensure total conversion of dihydrogen from 90°C.

[0071] The results obtained in the context of this example 2 thus validate the reproducibility of the synthesis process according to the invention and the performances that they allow to be granted by impregnation on Bayerite. Example 3

[0072] Based on Example 2, uniformity of catalytic performance of (Pt / bayerite) type catalysts -550°C with a platinum content of 0.5% manufactured in accordance with the process according to the invention was observed.

[0073] This example 3 aims to ensure a real gain in performance of these catalysts (Pt / bayerite) -550°C manufactured using the process according to the invention compared to catalysts formed in the usual manner.

[0074] In this regard, another so-called "bis" catalyst of type (Pt / Al2O3 eXBayerite-55o) -550°C not in accordance with the invention was manufactured in the same way as in example 1 and its catalytic activity was evaluated under the same operating conditions.

[0075] As can be seen in [Fig.4], which compiles the test results of the catalyst (Pt / Al2O3 exBayerite-550) -550°C bis with those of the catalyst (Pt / Al2O3 exBayerite-550) -550°C of Example 1, these catalysts not in accordance with the invention are indeed inactive up to a temperature of 75°C. At 97°C the conversion of hydrogen is less than 20% in the presence of (0.5% Pt / Al2O3exBayerite)-550°C, while it is less than 10% in the presence of (0.5% Pt / Al2O3exBayerite)-550°C-biS.

[0076] Example 3 thus makes it possible to validate the observations made in the context of example 1, and to confirm the real gain of the synthesis process according to the invention. Example 4

[0077] With reference to figures 5 and 6, the differences in morphology between a catalyst (Pt / bayerite) -550°C in accordance with the invention and a catalyst (Pt / Al2O3exBayerite) -550°C not in accordance were assessed by dark field transmission electron microscopy (ADF STEM).

[0078] The catalyst (Pt / bayerite) -550°C is characterized by polydisperse Pt particle sizes with a significant population of nanoparticles between 5 and 20 nm, small (l-2nm) metal nanoparticles (NPs) and isolated platinum atoms(ions) / clusters. The control catalyst (Pt / Al2O3exBayerite)-550°C, synthesized in the usual way, presents a homogeneous dispersion of platinum particles with the presence of only two populations, small (l-2nm) metal nanoparticles (NPs) and isolated atoms(ions) / clusters.

[0079] The formation of a significant population of the largest platinum nanoparticles, between 5 and 20 nm, observed on the catalyst (Pt / bayerite) -550°C suggests sintering of the platinum particles made possible by the water generated during calcination, by dehydroxylation of the support. Example 5

[0080] In order to assess the robustness of the catalyst synthesis process according to the invention, the behavior of the (Pt / bayerite) type catalysts was evaluated by modifying the mass content of platinum in the catalytic phase.

[0081] The objective of this analysis is to verify that the recorded performances of the catalysts manufactured in accordance with the process according to the invention are not limited to the case for which the impregnated platinum content is fixed at 0.5% by weight.

[0082] In this regard, four catalysts were manufactured and then tested in the same way as in Example 1, except that they differ from each other in their platinum content. In more detail, we distinguish: - a catalyst (0.3% Pt / bayerite)-550°C containing 0.3% platinum; - a catalyst (0.5% Pt / bayerite)-550°C containing 0.5% platinum; - a catalyst (0.8% Pt / bayerite)-550°C containing 0.8% platinum; and - a catalyst (1% Pt / bayerite)-550°C containing 1% platinum.

[0083] With reference to [Fig.7], the results show that the more the platinum content is increased, the more the conversion rates are improved.

[0084] In detail, the conversion of hydrogen at room temperature is recorded: - of the order of 20-30% for the catalyst (0.3%Pt / bayerite)-550°C; - of the order of 30-40% for the catalyst (0.5%Pt / bayerite)-550°C; - of the order of 55-65% for the catalyst (0.8%Pt / bayerite)-550°C; and - of the order of 65-85% for the catalyst (1%Pt / bayerite)-550°C.

[0085] It is thus clear from this example that the higher the mass content of platinum in the catalytic phase, the greater the activity in catalytic combustion of dihydrogen. The performance of the catalysts manufactured by the process according to the invention logically aligns with the platinum content, the observations made in Example 1 therefore do not result from a particular exception.

[0086] It follows that the process according to the invention is not strictly limited to forming Pt / alumina type catalysts from Bayerite loaded with 0.5% platinum by weight. In other words, the platinum content is not a limiting factor of the process according to the invention. Example 6

[0087] In this example, the aim is to quantify the influence of the calcination temperature on the activity of the catalysts obtained by the process according to the invention. Concretely, it is a question of determining a range of calcination temperatures for which the process according to the invention allows the production of catalysts active in catalytic combustion of dihydrogen from room temperature. Test and manufacturing matrix - example 6

[0088] On this basis, eight (Pt / Bayerite)-T°C catalysts were manufactured in accordance with the process according to the invention by impregnating Bayerite (A1(OH)3) with the aqueous solution of hexachloroplatinic acid (H2PtCl6), to achieve a platinum content of 0.5% by weight, before calcining at distinct T°C temperatures between 250°C and 1000°C, as follows:

[0089] [Tables3] Support ACTIVE PHASE CATALYST Nomenclature Nature Nature Content (% wt) Post-impregnation treatment (Pt content / (support))-T°C Bayerite (A1(OH)3) Pt 0.5 Calcination at 250 °C (0.5% Pt / bayerite)-250°C Calcination at 350 °C (0.5% Pt / bayerite)-350°C Calcination at 450 °C (0.5% Pt / bayerite)-450°C Calcination at 550 °C (0.5% Pt / bayerite)-550°C Calcination at 650 °C (0.5% Pt / bayerite)-650°C Calcination at 750 °C (0.5% Pt / bayerite)-750°C Calcination at 850 °C (0.5% Pt / bayerite)-850°C Calcination at 1000°C (0.5% Pt / bayerite)-1000°C

[0090] Catalytic tests and analysis of results - example 6

[0091] Once these (Pt / Bayerite)-T°C catalysts were manufactured, their catalytic activities were measured while respecting the operating conditions of example 1.

[0092] With reference to [Fig.8], it is observed that: - all the catalysts (Pt / Bayerite)-T°C manufactured are active from room temperature; - the conversion to dihydrogen is greater than 20% at room temperature for catalysts whose calcination temperature is in the range [350°C-850°C]; - the (Pt / Bayerite)-250°C and (Pt / Bayerite)-1000°C catalysts, whose calcination temperatures correspond to the extreme values of the batch of (Pt / Bayerite)-T°C catalysts manufactured, are the least efficient, displaying conversion rates of the order of 10% at room temperature; - catalytic activity is optimal, with a dihydrogen conversion equal to or greater than 40%, following calcination at 550°C or 650°C.

[0093] In view of the above, it appears that the process according to the invention guarantees the manufacture of high-performance (Pt / Bayerite)-T°C type catalysts from room temperature regardless of the calcination temperature T chosen in the range [250°C-1000°C]. It is thus demonstrated that the process according to the invention is not limited to the calcination temperature T value of 550°C of example 1.

[0094] Calcination between 550° and 650°C will be chosen to obtain the highest performance. Example 7

[0095] Examples 1 to 6 made it possible to validate the performance of Pt-Alumina type catalysts manufactured in accordance with the process according to the invention by means of incipient humidity impregnation of a Bayerite support with a solution of hexachloroplatinic acid (H2PtCl6).

[0096] In this example 7, it is aimed to quantify the influence of the dispersion method in the Bayerite support of the platinum precursor, and more specifically to verify whether the process according to the invention is limited or not to the method of impregnation with nascent humidity of hexachloroplatinic acid (H2PtCl6). Test Matrix - Example 7

[0097] For the purpose of this example, six catalysts were made by dispersing hexachloroplatinic acid (H2PtCl6) in Bayerite (A1(OH)3) by the anion exchange method before calcination at 550°C. The catalysts, each made with a distinct platinum content, are referenced (x%Pt / bayerite)-550 where x is the mass content of platinum (determined by ICP) as follows:

[0098] [Tables4] Support ACTIVE PHASE CATALYST Nomenclature Nature Nature Content (% wt) Post-dispersion treatment by exchange (Content Pt / (support))-T°C Bayerite (A1(OH)3) Pt 0.22 Calcination at 550 °C (0.22% Pt / bayerite)-550°C 0.41 (0.41% Pt / bayerite)-550°C 0.45 (0.45% Pt / bayerite)-550°C 0.48 (0.48% Pt / bayerite)-550°C 0.49 (0.49% Pt / bayerite)-550°C 0.59 (0.59% Pt / bayerite)-550°C Manufacturing - example 7

[0099] Anion exchange synthesis consists of suspending the bayerite support in an aqueous solution of the platinum salt H2PtCl6. In aqueous solution, the salt is completely dissociated (2 H+, PtCl62).

[0100] The suspension is left stirring for a determined period to allow the anionic PtCl62 species to exchange with the surface of the bayerite. The suspended solid is then separated by filtration; this solid corresponds to the bayerite enriched with PtCl62 species retained on its surface. Several exchange preparations are carried out using hexachloroplatinic acid solutions of increasing concentrations so as to vary the quantities of platinum species retained and to reach saturation of the surface. The catalysts were then dried by lyophilization and calcined at 550°C, in the same way as in the manufacture of the catalysts prepared by impregnation of Example 1.

[0101] In detail, each catalyst was manufactured in a quantity of 3g on the same base of commercial Bayerite (A1(OH)3) ((A1(OH)3 - PURAL BT, SASOL Chemicals) and hexachloroplatinic acid (H2PtCl6).

[0102] The initial mass of bayerite used for the exchange was taken in excess in order to obtain the desired quantity of catalyst at the end of the calcination step. Indeed, the loss of mass of the support during calcination at 550°C is 25.2% (water losses by dehydroxylation during calcination).

[0103] The bayerite support, suspended in an aqueous solution of hexachloroplatinic acid, is left stirring in a rotary evaporator for two hours at atmospheric pressure and room temperature to allow the exchange between the bayerite and platinum species in solution.

[0104] To achieve the desired platinum content for each of the catalysts, 20g of hexachloroplatinic acid solutions of increasing concentrations were prepared, containing: - 0.0075g of platinum to obtain the 0.22%Ptech / bayerite-550 catalyst; - 0.015g of platinum for the 0.41%Ptech / bayerite-550 catalyst; - 0.0225g of platinum for the 0.45%Ptech / bayerite-550 catalyst - 0.03g of platinum for the 0.48%Ptech / bayerite-550 catalyst; - 0.0375g of platinum for the 0.49%Ptech / bayerite-550 catalyst; and - 0.06g of platinum for the 0.59%Ptech / bayerite-550 catalyst.

[0105] The supports thus enriched in platinum were then dried and then calcined following the same protocol as that described in example 1.

[0106] The wet solids, separated by centrifugation, were frozen at a temperature of -18°C for 12 hours, before being freeze-dried for 12 hours to achieve complete drying, then calcined.

[0107] The calcination was carried out in hot air at 550°C in a muffle furnace with a heating rate of 5°C / min, remaining at maximum temperature for two hours.

[0108] Catalytic tests and analysis of results - example 7

[0109] The catalytic combustion performance of dihydrogen was evaluated under the same standard operating conditions as in Example 1, and compiled in [Fig.9],

[0110] [Fig.9] shows that the catalysts prepared by exchange are active in catalytic combustion of dihydrogen at room temperature, of the order of 5% to 10% conversion, for a platinum content greater than 0.4%. A dihydrogen conversion of 50% is notably achieved for these catalysts when the furnace temperature reaches 70°C-80°C.

[0111] On this basis, it is thus justified to conclude that the method according to the invention is not not limited to the technique chosen to disperse the platinum salt (H2PtCl6), as a platinum precursor, in the Bayerite support. Example 8

[0112] The preceding examples have made it possible to validate the performance of Pt-Alumina type catalysts manufactured in accordance with the process according to the invention using different dispersion techniques of the same platinum precursor, namely hexachloroplatinic acid (H2PtCl6).

[0113] In this example 8, it is aimed to verify whether or not the process is constrained to the use of hexachloroplatinic acid (H2PtCl6), and more generally to a specific nature of platinum precursor. Test Matrix - Example 8

[0114] In this example, two catalysts were manufactured following the same protocol, with the difference that two different platinum precursors were used, each being associated with a corresponding catalyst: hexachloroplatinic acid (H2PtCl6) and Tetraammineplatinum Dichloride (Pt(NH3)4Cl2).

[0115] Among these two catalysts listed in table 5 below, we distinguish: - a first catalyst referenced (0.5%Pt / Bayerite)-550°C: H2PtCl6 manufactured by impregnation with nascent humidity directly of Bayerite (A1(OH)3) with a solution of hexachloroplatinic acid, followed by calcination at 550°C to jointly obtain alumina (A12O3) from Bayerite (A1(OH)3) and the active platinum phase from hexachloroplatinic acid; and - a second catalyst referenced (0.5%Pt / Bayerite)-550°C: Pt(NH3)4Cl2 manufactured by incipient humidity impregnation directly of Bayerite (A1(OH)3) with an aqueous solution of Tetraammineplatinum Dichloride (Pt(NH3)4Cl2), followed by calcination at 550°C to jointly obtain alumina (A12O3) from Bayerite (A1(OH)3) and the active platinum phase from Tetraammineplatinum Dichloride.

[0116] [Tables5] Support ACTIVE PHASE CATALYST Nomenclature Nature Nature (Precursor) Content (%wt) Post-impregnation treatment (%Pt / (support))-T°C: precursor Bayerite (A1(OH)3) Pt (H2PtCl6) 0.5 Calcination at 550 °C (0.5%Pt / Bayerite)-550 °C: H2PtCl6 Pt (Pt(NH3)4Cl2) (0.5%Pt / Bayerite)-550 °C: Pt(NH3)4Cl2 Manufacturing - example 8

[0117] In the case of the catalyst (0.5%Pt / Bayerite)-550°C: H2PtCl6, the preparation of its support and its impregnation were carried out in the same way as that described in example 1 in order to obtain 5g of catalyst.

[0118] Regarding the preparation of 5g of the catalyst (0.5%Pt / Bayerite)-550°C: Pt(NH3)4Cl2, 6.68g of commercial Bayerite (PURAL BT, SASOL Chemicals) were used as inorganic support. The initial mass of Bayerite used for impregnation was taken in excess in order to obtain the desired quantity of catalyst at the end of the synthesis. Indeed, the loss of mass in support during calcination at 550°C is 25.2% (water losses by dehydroxylation during calcination, after impregnation).

[0119] For the impregnation of the support, 6.23 g of an aqueous solution of Pt(NH3)4C12 containing 0.025 g of platinum was prepared. The impregnation of the support with the solution was carried out dropwise in a Pyrex flask, before being placed in a rotary evaporator and left stirring for two hours at atmospheric pressure and room temperature.

[0120] The now impregnated supports were then dried and then calcined in the same way as in the case of example 1, namely: - freeze them at a temperature of -18°C for 12 hours before freeze-drying them for 12 hours until completely dry; then - calcine them in air for 2 hours at 550°C in a muffle furnace using a heating rate of 5°C / min.

[0121] Catalytic tests and analysis of results - example 8

[0122] The catalytic combustion performance of dihydrogen was evaluated under the same standard operating conditions as in Example 1, and compiled in [Fig.10],

[0123] [Fig.10] shows that both catalysts are very active in catalytic combustion of dihydrogen from room temperature, with a conversion greater than 40%.

[0124] On this basis, it is understood that the process according to the invention makes it possible to obtain Pt-Alumina catalysts which perform well in the catalytic combustion of dihydrogen at any temperature, whatever the nature of the Pt precursor dispersed in the Bayerite support.

[0125] Examples 1 to 8 thus made it possible to validate the performance of Pt-Alumina type catalysts manufactured in accordance with the process according to the invention by dispersing a platinum precursor in a Bayerite support which is an aluminum hydroxide.

[0126] In the following examples 9 and 10, it is intended to evaluate whether the process is applicable for other alumina hydrates, precursors of the alumina-based support of the aluminum hydroxide or aluminum oxo-hydroxide type. Example 9

[0127] This example 9 aims to verify whether a generalization of the process to any form of aluminum hydroxide (Al(OH)3) is possible. Test Matrix - Example 9

[0128] In this sense, this example is based on a comparative analysis of catalytic activities obtained between two Pt-Alumina catalysts manufactured from Gibbsite as listed in Table 6, including: - a Pt-Alumina catalyst referenced (Pt / Gibbsite)-550°C, with a platinum content of the order of 0.5% by weight, synthesized in accordance with the process according to the invention by directly impregnating the platinum salt onto a Gibbsite (A1(OH)3) support, followed by calcination at 550°C transforming the Gibbsite (A1(OH)3) into alumina (A12O3); and - a “control” Pt-Alumina catalyst referenced (Pt / Ai203exGibbsite55o°c), with a platinum content of the order of 0.5% by weight, manufactured in the manner recommended in the state of the art, namely by impregnating the platinum salt onto the alumina obtained after calcination of the Gibbsite (A1(OH)3) at 550°C.

[0129] [Tableauxô] Support ACTIVE PHASE CATALYST Nomenclature Nature / Calcination temperature Nature Content (% wt) Post-impregnation treatment (Pt / (support))-T°C Gibbsite (A1(OH)3) Pt 0.5 Calcination at 550°C (Pt / Gibbsite)-550°C A12O3 (ex-gibbsite calcined at 550°C) (Pt / A12O3 exGibbsite-55o) " 550°C Manufacturing - example 9

[0130] Each catalyst was manufactured in a quantity of 5g on the same base of commercial Gibbsite (A1(OH)3 - Hydrargillite EMPLURA from Sigma-Alfrich) and hexachloroplatinic acid (H2PtCl6).

[0131] For the preparation of the catalyst (Pt / Al2O3eXGibbsite 550) -550°C called “control”, i.e. not in accordance with the invention, a calcination at 550°C of the Gibbsite (A1(OH)3) was first carried out to obtain the transition alumina (A12O3) intended to serve as an impregnation support. This impregnation support is designated Al2O3ex Gibbsite-550-

[0132] This calcination of Gibbsite (A1(OH)3) before impregnation in the context of the production of the control catalyst was carried out in hot air, at 550°C, remaining 2 hours at maximum temperature in a muffle furnace having a heating rate of 5°C / min, in the same way as in example 1.

[0133] The impregnation step was carried out in a similar manner to Example 1, as follows: - 5 g of transition alumina Al2O3eXGibsite taken after calcination of the Gibsite (A1(OH)3 were impregnated by nascent humidity with 3.40 g of aqueous solution of hexachloroplatinic acid containing 0.025 g of platinum, in order to manufacture 5 g of catalyst (Pt / Al2O3exGibsite)-550°; and - 6.56g of Gibsite (A1(OH)3) were used as an impregnation support for 3.97g of aqueous hexachloroplatinic acid solution containing 0.025g of platinum, in the manufacture of the catalyst (Pt / Gibbsite)-550°C.

[0134] The supports now impregnated with the aqueous solution of hexachloroplatinic acid were then dried and then calcined at 550°C following the protocol described in example 1.

[0135] Validation of the composition and catalytic tests - example 9

[0136] With reference to Table 7 below, the percentage of platinum deposited on the different supports was verified by ICP.

[0137] As observed, the effective amount of platinum deposited by incipient humidity impregnation varies between 0.46 and 0.55% by weight, which is very close to the theoretical target content.

[0138] On this basis, the reproducibility of the incipient moisture impregnation method is validated also in the context of the use of Gibbsite. It follows that the behavior of the (Pt / Gibbsite) -550°C catalyst manufactured according to the manufacturing method can be validly compared with that of the (Pt / Al2O3ex Gibbsite 550) -550°C catalyst manufactured in the usual manner, on the basis of the same common denominator {Gibbsite - Pt content - calcination temperature}.

[0139] [Tables7] Catalyst Theoretical Pt content (wt%) Actual Pt content (wt%) (Pt / Gibbsite) -550°C 0.5 0.46 (Pt / Al2O3 exGibbsite-55o) -550°C 0.5 0.55 Counting the results - example 9

[0140] The reaction performances in catalytic combustion of dihydrogen were evaluated under the same stable operating conditions of Example 1 and reported in [Fig.II],

[0141] [Fig. 11] shows that the catalyst (Pt / Gibbsite) -550°C manufactured in accordance with the process according to the invention is active from room temperature with an average conversion of 23%. Also, the conversion into dihydrogen increases progressively with the increase in the temperature of the furnace, of the order of 50% conversion at the temperature of 53°C and to more than 70% at 85°C.

[0142] In comparison, the control catalyst (Pt / Al2O3 exBayente-550) -550°C, the manufacture of which differs only from that of the catalyst (Pt / Gibbsite) -550°C in that the support was calcined before platinum impregnation, is inactive at room temperature and the rest up to 75°C. At 95°C, the conversion of dihydrogen by the catalyst (Pt / Al2O3 exBayente 550) -550°C remains below 20%.

[0143] Based on this example 9, it appears that the process according to the invention is also suitable for manufacturing Pt-alumina catalysts which meet the targeted performance criteria from Gibbsite. Thus, the process according to the invention does not appear to be limited to the use of a particular form of aluminum hydroxide.

[0144] Even if in example 9 the catalysts manufactured from Gibbsite underwent calcination only at 550°C, the observation results reasonably lead us to admit that the performance results of Bayerite are generally transposable to those of Gibbsite and, more generally, to any form of aluminum hydroxide (A1(OH)3). Example 10

[0145] This example aims to verify whether the scope of the process extends to another type of alumina hydrate, a precursor of alumina, different from aluminum hydroxide (Al(OH)3) which is an alumina trihydrate. Test Matrix - Example 10

[0146] In this regard, this example 10 is based on a comparative analysis of catalytic activity between two Pt-alumina catalysts as listed in table 8, which are manufactured from alumina monohydrate, Boehmite which is an aluminum oxo-hydroxide A10(0H), of which: - a Pt-Alumina catalyst referenced (Pt / Boehmite)-550°C, with a platinum content of around 0.5%, obtained by directly impregnating the platinum salt onto a Boehmite A10(0H) support, followed by calcination at 550°C transforming the Boehmite A10(OH) into alumina (A12O3); and - a Pt-Alumina catalyst referenced (Pt / Al2O3eXBoehmite)-550oC, with a platinum content of around 0.5%, which is manufactured in the manner recommended in the state of the art, namely by impregnating the platinum salt on the alumina (A12O3) obtained after the calcination of Boehmite AIO(OH) at 550°C.

[0147] [Tables8] Support ACTIVE PHASE CATALYST Nomenclature Nature / Calcination temperature Nature Content (% wt) Post-impregnation treatment (Pt / (support))-T°C Boehmite AIO(OH) Pt 0.5 Calcination at 550°C (Pt / Boehmite )-550°C A12O3 (ex-Boehmite calcined at 550°C) (Pt / AI2O3 exBoehmite-55û) 550°C Manufacturing - example 10

[0148] Each catalyst was manufactured in a quantity of 5g on the same base of commercial Boehmite (A1OOH-PURAL SB1, SASOL Chemicals) and hexachloroplatinic acid (H2PtCl6).

[0149] For the preparation of the catalyst (Pt / Al203exBoehmite-55o) -550°C, a calcination at 550°C of Boehmite (AIO(OH)) was first carried out to obtain the transition alumina (A12O3) intended to serve as an impregnation support. This impregnation support is designated Al203exBoehmite_55o-

[0150] This calcination of Boehmite (AIO(OH)) before impregnation in the context of the production of the catalyst was carried out in hot air, at 550°C, remaining 2 hours at maximum temperature in a muffle furnace having a heating rate of 5°C / min, in the same way as in example 1.

[0151] The impregnation step was carried out in a similar manner to Example 1, using: - a nascent humidity impregnation of 5.83 g of aqueous solution of hexachloroplatinic acid containing 0.025 g of platinum on 5 g of transition alumina Al2O3exBoeh mite 550, obtained by calcination at 550°C, in order to manufacture 5 g of catalyst (Pt / A12O3 exBoehmite-550)-550°; and - an impregnation with nascent humidity of 5.80g of aqueous solution of hexachloroplatinic acid containing 0.025g of platinum on 5.89g of Boehmite (AIO(OH)) as part of the manufacture of the catalyst (Pt / Boehmite)-550°C.

[0152] The supports now impregnated with the aqueous solution of hexachloroplatinic acid were then dried and then calcined at 550°C following the same protocol as in example 1. Validation of the composition - example 10

[0153] With reference to Table 9, the percentage of platinum deposited on the different supports has been verified by ICP.

[0154] As observed, the effective amount of platinum deposited by moisture impregnation is 0.51 and 0.57% by weight, which is very close to the theoretical target content.

[0155] On this basis, the reproducibility of the incipient moisture impregnation method is validated also in the context of the use of Boehmite. It follows that the behavior of the catalyst (Pt / Boehmite) -550°C can be validly compared with that of the catalyst (Pt / Al2O3eXBOehmite 55o)-55O°C on the basis of the same common denominator {Boehmite - Pt content - calcination temperature}.

[0156] [Tables9] Catalyst Theoretical Pt content (wt.%) Actual Pt content (wt.%) (Pt / Boehmite) -550°C 0.5 0.51 (Pt / Al2O3 exBoehmite-55()) -550°C 0.5 0.57

[0157] Catalytic tests and analysis of results - example 10

[0158] The reaction performances in catalytic combustion of dihydrogen were thus evaluated under the same stable operating conditions of example 1 and reported in [Fig. 10].

[0159] [Fig. 12] shows that the catalyst (Pt / Boehmite) -550°C and the catalyst (Pt / Al2 O3exBoehmite 550) -550°C both have no activity in catalytic combustion of dihydrogen from room temperature up to 80°C. At 95°C, the observed dihydrogen conversion remains below 10%.

[0160] Example 10 thus made it possible to exclude Boehmite, which is an aluminium oxo-hydroxide (otherwise known as alumina monohydrate), from the alumina hydrates which are precursors of alumina for which the process according to the invention provides real added value in terms of the catalytic activity of the catalysts which it can be used to manufacture. Characterization

[0161] In order to explain such a gain in catalytic activity of the catalysts resulting from a dispersion of platinum precursor on aluminum hydroxide before calcination to form alumina in accordance with the invention, compared to the catalysts whose platinum impregnation is carried out either on aluminum oxo-hydroxide (namely on alumina monohydrate) or in a known manner on alumina, a preliminary characterization study was carried out.

[0162] This characterization study focused on the six catalysts, listed in Tables 2, 4 and 6, manufactured from Bayerite, Gibbsite and Boehmite with an iso-content of 0.5% by weight of platinum and a support calcination temperature of 550°C.

[0163] With reference to [Fig. 13], it is visually observable in photo 1) that initially, Gibbsite, Bayerite and Boehmite have the same pale yellow hue.

[0164] Following the impregnation of platinum directly onto Gibbsite, Bayerite and Boehmite followed by a freeze-drying step and calcination at 550°C, photo 2) reveals that: - the catalysts (Pt / Gibbsite) -550°C and (Pt / Bayerite) -550°C, each derived from an aluminium hydroxide in accordance with the process according to the invention, have a light grey tint; while - the catalyst (Pt / Boehmite) -550°C, non-compliant in that it is derived from an aluminum oxo-hydroxide, conversely retains the same pale yellow tint.

[0165] Photos 3) and 4) show that the aluminas formed by calcination of Gibbsite, Bayerite and Boehmite, as well as the catalysts obtained following the impregnation of these aluminas with platinum followed by calcination at 550°C, all have approximately the same white color.

[0166] This preliminary study suggests a correlation between the light grey colour of the (Pt / Bayerite) -550°C and (Pt / Gibbsite) -550°C catalysts, manufactured from aluminium hydroxide in accordance with the process according to the invention, and their substantial gain in catalytic activity observed compared to: - to the corresponding “control” catalysts, (Pt / Al2O3exBayerite 550) -550°C and (Pt / Al2O3 exGibbsite 550) -550°C respectively; as well as - catalysts formed from Boehmite which is not an aluminum hydroxide (A1(OH)3).

[0167] This feature suggests a strong interaction between the PtCl62 anions of hexachloroplatinic acid and the surface of the aluminum hydroxides impregnated with the hexachloroplatinic acid solution, leading to increased dispersions and inclusions of platinum in the aluminas formed after calcination. Method according to the invention and applications

[0168] On the basis of the various examples 1 to 10, it was surprisingly observed by the test that the dispersion of platinum precursor on an aluminum hydroxide support, followed by post-drying calcination of the assembly {support + platinum precursor impregnated in the support] makes it possible to obtain more efficient Pt-alumina catalysts with iso-platinum content than in the case of a dispersion of platinum precursor on alumina followed by drying and calcination.

[0169] In particular, a calcination of the aluminum hydroxide supports, in which the platinum precursor is dispersed, in the temperature range [250°C-1000°C] with catalysts: - active in the combustion of dihydrogen from room temperature; and - ensuring substantially complete combustion at 100°C.

[0170] Calcination at a temperature in the range [350°C-850°C], and more spec specifically in the reduced range [550°C-650°C] allows to arrive at the most efficient Pt-alumina catalysts.

[0171] It is thus recommended to equip the burner with a catalytic combustion lamp of dihydrogen with a Pt-alumina type catalyst manufactured on this basis, to achieve active and efficient combustion of dihydrogen from room temperature. This arrangement thus makes it possible to avoid an accumulation of dihydrogen after passing over the burner, which otherwise could lead to a risk of explosion.

[0172] It will be advantageous to integrate into such a catalytic lamp a catalyst manufactured in accordance with the process according to the invention for a calcination temperature belonging to the range [550°C -650°C], retained as the most efficient.

[0173] It should be noted, however, that the manufacturing method according to the invention is not limited to providing catalysts for such an application of a catalytic lamp, or other domestic device with catalytic combustion for the diffusion of perfume and / or active substances, for the destruction of odorous or non-odorous molecules, and / or for air purification. Given that such Pt-alumina type catalysts ensure greater heat release due to the fact that the dihydrogen is better consumed, they can thus find an application, for example, in domestic or commercial heating, gas turbines, the nuclear industry or even in fuel cells.

Claims

Claims

1. A method of manufacturing a catalyst suitable for the catalytic combustion of dihydrogen, this catalyst comprising a catalytically active phase of platinum (Pt) and an alumina (A12O3) support, the method comprising the successive steps of: - S1) providing an aluminum hydroxide (A1(OH)3) support; - S2) dispersing in said support a platinum precursor, the decomposition of which by calcination forms the catalytically active phase; - S3) treating the support in which the platinum precursor is dispersed at the end of step S2), comprising a sub-step S31) of drying followed by a sub-step S32) of calcination at a target temperature of between 250°C and 1000°C to jointly: — transform the aluminum hydroxide (A1(OH)3) of the support into alumina (A12O3); and — obtaining the catalytically active phase from the precursor dispersed in the support in step S2).

2. A method of manufacturing a catalyst according to claim 1, wherein the aluminum hydroxide constituting the support provided in step S1) is Bayerite (A1(OH)3).

3. A method of manufacturing a catalyst according to claim 2, wherein the calcination temperature in sub-step S32) is between 550°C and 650°C.

4. A method of manufacturing a catalyst according to claim 1, wherein the aluminum hydroxide constituting the support is Gibbsite (A1(OH)3).

5. A method of manufacturing a catalyst according to claim 5, wherein the calcination temperature in substep S32) is set at substantially 550°C.

6. A method of manufacturing a catalyst according to any one of the preceding claims, wherein: - sub-step S31) of drying the impregnated support includes freezing at a temperature of -18°C for 12 hours followed by freeze-drying for 12 hours; and - sub-step S32) of calcination is ensured by a gradual increase in temperature until the target temperature is reached, followed by maintenance at the target temperature for two hours.

7. A method of manufacturing a catalyst according to any one of the re-

8.

9.

10.

11. preceding claims, in which step S2) of dispersing the precursor in the support provided in step S1) is carried out by impregnation or by exchange. A method of manufacturing a catalyst according to any one of the preceding claims, wherein the platinum precursor used in step S2) is a solution of hexachloroplatinic acid (H2PtCl6) or a solution of tetraammineplatinum dichloride (Pt(NH3)4Cl2). Catalyst comprising a catalytically active platinum (Pt) phase and an alumina (A12O3) support manufactured in accordance with the method according to any one of the preceding claims. Catalyst according to claim 9, comprising a platinum (Pt) content of between 0.3 and 1% by weight. Use of a catalyst according to claim 9 or 10 in a device for the diffusion of perfume and / or active substances, for the destruction of odorous or non-odorous molecules, and / or for air purification.

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