WO2025068040A1 - Method for dehydrogenating paraffins and/or naphthenes in the presence of a catalyst based on a support containing a medium density of macropores - Google Patents

Abstract

The invention relates to a method for dehydrogenating a hydrocarbon feedstock comprising paraffins and/or naphthenes, in which the feedstock is placed in contact with a catalyst comprising an active phase based on at least one group VIII metal; at least one element M1 selected from tin, germanium, lead, gallium, indium and thallium; and at least one element M2 selected from the alkali or alkaline-earth elements, and a support comprising at least one refractory oxide, characterised in that the mean density of the macropores of the support is greater than or equal to 900 kpores/mm² and less than 2000 kpores/mm² and in that the tapped density (TD) is between 0.50 and 0.68 g/ml.

Description

PROCESS FOR THE DEHYDROGENATION OF PARAFFINS AND/OR NAPHTHENES IN THE PRESENCE OF A CATALYST BASED ON A SUPPORT CONTAINING AN AVERAGE DENSITY OF MACROPORES

Field of invention

The present invention relates to the field of the conversion of hydrocarbon compounds, more specifically to the dehydrogenation of a hydrocarbon feedstock comprising paraffinic compounds and/or naphthenic compounds, and more particularly to the dehydrogenation of propane in the presence of a catalyst to produce olefins and more particularly propylene.

State of the art

Paraffin and/or naphthenes dehydrogenation processes are interesting routes for the dedicated production of unsaturated compounds and particularly olefins, for which the demand for global production is growing. Indeed, among the possible routes for olefin production, such as thermal or catalytic cracking, metathesis as well as alcohol dehydration, paraffin and/or naphthenes dehydrogenation processes have higher yields and are very selective. Propylene production in particular is of particular interest in a context of increased demand for polypropylene and propylene derivatives such as acrylic acid or acrylonitrile. The need for optimization of catalysts and processes is therefore always present.

Paraffin and/or naphthenes dehydrogenation reactions are highly endothermic and reversible. Conversion rates are limited by thermodynamic equilibrium conditions. In the case of propane dehydrogenation (AH = - 125 kJ/mol), a high temperature above 600°C is typically used and the equilibrium conversion under these conditions is around 30% under industrial conditions. Since the separation of olefin from paraffin is a costly step in terms of investment and energy, it is essential to work towards maximum conversion of the feedstock to maximize process productivity.

The harsh conditions that allow this are thus very favorable to the secondary reactions of deep dehydrogenation, olefin oligomerization, hydrogenolysis, cracking and coke formation. These secondary products and this coke formation are at the origin of the deactivation of dehydrogenation catalysts and involve the regeneration of the catalyst, and in particular of the metallic phase, by at least one combustion step. The challenge is therefore to succeed in developing an active but also selective and stable catalyst for an economically viable process. Among the catalysts suitable for the dehydrogenation of paraffins and more particularly for dehydrogenation implemented in a moving bed process known as CCR ("Continuous Catalytic Reforming" in English terminology), we can notably cite platinum (Pt)-based catalysts and more particularly PtSnK type catalysts.

Numerous prior art works describe this type of dehydrogenation catalyst and the means implemented to improve its activity, selectivity and stability. In particular, certain patents recommend increasing the average diameter of the mesopores and/or introducing macropores.

To adapt the catalyst to the dehydrogenation of propane, US patent 4,914,075 teaches that it is essential to carry out a high-temperature calcination, i.e. between 1000°C and 1200°C, of the alumina support containing tin in order to increase the average diameter of the pores of said support and thus promote the diffusion of heavy species and limit deactivation. This results in a reduction in the specific surface area of the support, an increase in density and a modification of the crystalline phase of the alumina from gamma to a predominantly theta alumina (> 75% by weight relative to the total weight of the alumina).

US Patent 8,993,474 discloses a catalyst whose tin-containing alumina support is obtained by a calcination step carried out for 6 hours at 1050°C, allowing the production of a support with a theta crystallinity greater than 90% by weight relative to the total weight of the alumina and having average mesopore and macropore diameters of between 5 and 100 nm and between 0.1 and 20 pm, respectively. Such a type of catalyst has improved performance compared to those whose supports have not undergone a high-temperature calcination step.

The Applicant, in its research into improving the performance of heterogeneous catalysts for the dehydrogenation of paraffins and/or naphthenes, has surprisingly identified that the performance of the catalysts, in terms of activity, selectivity and stability, is increased by selecting a catalyst comprising a specific support having a compromise between its macropore density and its packed filling density (DRT) value.

Objects of the invention

The subject of the present invention is a process for dehydrogenating a hydrocarbon feedstock comprising paraffins and/or naphthenes in which said feedstock is brought into contact with a catalyst, at a pressure of between 0.1 MPa and 4 MPa, at a temperature of between 200°C and 800°C, and with a liquid volumetric space velocity of between 0.5 h' ¹ and 50 h' ¹ , said catalyst comprising an active phase based on at least one of the following: at least one metal from group VIII, at least one element M1 chosen from tin, germanium, lead, gallium, indium and thallium, and at least one element M2 chosen from alkali or alkaline-earth elements, and a support comprising at least one refractory oxide, characterized in that the average density of the macropores of said support is greater than or equal to 900 kpores/mm ² (kilo pores/mm ² ) and less than 2000 kpores/mm ² (kilo pores/mm ² ) and in that its packed filling density (DRT) value is between 0.50 g/mL and 0.68 g/mL.

It has been surprisingly shown that the use of a catalyst comprising a macroporous texture support having a specific macropore density associated with a well-defined packed filling density (DRT) value, makes it possible to obtain, by synergistic effect, an activity, a selectivity and a stability in dehydrogenation of a hydrocarbon feedstock comprising paraffinic and/or naphthenic compounds which are superior to those obtained by using catalysts not simultaneously having all of these combinations of characteristics.

According to one or more embodiments, the support is an alumina.

According to one or more embodiments, the specific surface area of the support is between 170 m ² /g and 250 m ² /g.

According to one or more embodiments, the average macroporous diameter of said support is between 0.20 μm and 0.80 μm.

According to one or more embodiments, the specific surface area of said support is between 195 m ² /g and 210 m ² /g.

According to one or more embodiments, the average density of the macropores of said support is between 1000 kpores/mm ² and 1950 kpores/mm ² .

According to one or more embodiments, the content of group VIII metal is between 0.02% and 2% by elemental weight of group VIII metal relative to the total weight of the catalyst.

According to one or more embodiments, the group VIII metal is platinum.

According to one or more embodiments, the content of element M1 is between 0.01% and 10% by elemental weight of element M1 relative to the total weight of the catalyst.

According to one or more embodiments, element M1 is tin.

According to one or more embodiments, the surface density of element M2 is between 0.5 atoms and 2 atoms of element M2/nm ² . According to one or more embodiments, the element M2 chosen from the alkali or alkaline-earth elements is potassium.

13 According to one or more embodiments, the potassium content, expressed as an element, is between 0.5% and 3% by weight relative to the total weight of the catalyst.

According to one or more embodiments, the hydrocarbon feedstock comprises paraffinic and/or naphthenic compounds containing from 2 to 30 carbon atoms per molecule, taken alone or as a mixture.

According to one or more embodiments, the hydrocarbon feedstock comprises paraffinic compounds comprising 2 to 5 carbon atoms per molecule and/or naphthenic compounds comprising from 5 to 12 carbon atoms.

List of figures

Fig. 1 is a snapshot of support A1 according to example 1 taken by Scanning Electron Microscopy (SEM) on polished section with a magnification of x2500 and a resolution of 2048x1536 pixels.

Fig. 2 is a snapshot of support B1 according to example 1 taken by Scanning Electron Microscopy (SEM) on polished section with a magnification of x2500 and a resolution of 2048x1536 pixels.

Fig. 3 is a snapshot of the C1 support according to example 1 taken by Scanning Electron Microscopy (SEM) on a polished section with a magnification of x2500 and a resolution of 2048x1536 pixels.

Fig. 4 is a snapshot of the D1 support according to example 1 taken by Scanning Electron Microscopy (SEM) on a polished section with a magnification of x2500 and a resolution of 2048x1536 pixels.

Detailed description of the invention

1. Definitions

In the following, the groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, publisher CRC press, editor-in-chief DR Lide, ^81st edition, 2000-2001). For example, group VIII according to the CAS classification corresponds to the metals of columns 8, 9 and 10 according to the new IUPAC classification.

In the present description, according to the IUPAC convention, micropores are understood to mean pores whose diameter is less than 2 nm, i.e. 0.002 pm, mesopores are understood to mean pores whose diameter is greater than or equal to 2 nm, i.e. 0.002 pm and less than 50 nm, i.e. 0.05 μm, and by macropores the pores whose diameter is greater than or equal to 50 nm, i.e. 0.05 μm.

Specific surface area means the BET specific surface area (SBET in ^m2 /g) determined by nitrogen adsorption in accordance with ASTM D 3663-78 established from the BRUNAUER-EMMETT-TELLER method described in the periodical "The Journal of American Society", 1938, 60, 309.

The total pore volume of the catalyst or support used for catalyst preparation is defined as the volume measured by mercury porosimeter intrusion according to ASTM D4284 at a maximum pressure of 4000 bar (400 MPa), using a surface tension of 484 dyne/cm and a contact angle of 140°, for example with a Microméritics® Autopore III model device.

The wetting angle was taken as 140° following the recommendations of the book "Techniques de l'ingénieur, traité analyse et caractérisation", pages 1050-1055, written by Jean Charpin and Bernard Rasneur. In order to obtain better precision, the value of the total pore volume corresponds to the value of the total pore volume measured by intrusion with a mercury porosimeter measured on the sample at 4000 bars (400 MPa) minus the value of the total pore volume measured by intrusion with a mercury porosimeter measured on the same sample for a pressure corresponding to 2 bars (0.2 MPa).

The average macropore diameter and the average density of macropores within the support are determined from the processing of scanning electron microscopy (SEM) images by considering all pores with a diameter between 0.05 μm and 30 μm. Scanning microscopy is used to quantify the number and average diameter of macropores, for example on a ZEISS Supra40® microscope. These samples are observed on polished section in backscattered electrons (chemical contrast). The images were taken using Multi SP software at magnifications of x30, x250 and x1000 to observe the support, for example in the form of beads, in its entirety and at x2500 for image analysis. Image analysis, to determine the distribution of the average macropore diameter, was carried out using Plug im! from 10 images, taken at a magnification of x2500, on 5 samples of different support, for example 5 different beads, and at a resolution of 2048*1536 pixels. The quantification method makes it possible to determine the number and average diameter of macropores between 0.2 and 30 pm from images taken at magnification of x500. This method of determining macropores is generally supplemented or substituted by the so-called "quantification of small macropores" method making it possible to determine the number and average diameter of macropores between 0.05 and 0.5 pm at from images taken at x2500 magnification. The total surface area of the macropores is reduced to the surface of the image to obtain the macroporosity rate. This apparent macroporosity rate on the image is considered identical to the volumetric macroporosity rate of the support. A person skilled in the art knows how to analyze enough images to obtain an average density of macropores representative of the entire support.

The tapped filling density (TFD) is measured as described in the book "Applied Heter G. Martino, J. Miquel, R. Montarnal, A. Sugier, H. Van Landeghem, Technip, Paris, 1987, chapter 6.2.4, pages 167-168. A graduated cylinder of acceptable dimensions is filled by successive additions and, between two successive additions, the catalyst is packed by shaking the cylinder until a constant volume is reached. This measurement is generally carried out on 1000 cm ³ of catalyst or support packed in a cylinder whose height to diameter ratio is close to 5:1. The bulk density of the packed product is calculated by dividing the mass introduced and the volume occupied after packing. The uncertainty on the measurement is generally of the order of ± 0.01 g/mL. This measurement can preferably be carried out on automated devices such as Autotap® commercially available by Quantachrome®.

The contents of metals, halogens and alkali or alkaline-earth elements are measured by X-ray fluorescence.

By paraffinic compound (also called indifferently paraffinic hydrocarbon or more simply paraffin), we mean hydrocarbon compounds of general empirical formula C _n H2n+2-

By naphthenic compound (also called indifferently naphthenic hydrocarbon or more simply naphthene), we mean hydrocarbon compounds comprising at least one non-aromatic saturated cycle.

Activity means the mass of converted paraffin expressed in grams of converted paraffin per gram of active metal per hour.

Selectivity means the mass of olefins formed relative to the mass of all the products formed by conversion of the paraffin.

Stability means the stability of activity which is generally measured by a percentage drop in activity compared to activity between 1 hour and at least 9 hours of testing.

Surface density means the quantity of atoms of the element considered per unit of surface expressed in square nanometers calculated from the mass content given by an X-ray fluorescence analysis and the BET specific surface area of the catalyst. It is expressed in atoms/nm ² (or at/nm ² ).

2. Catalyst

The catalyst used in the process according to the invention comprises, preferably consists of, an active phase based on at least one metal from group VIII, at least one element M1 chosen from tin, germanium, lead, gallium, indium and thallium, and at least one element M2 chosen from alkali or alkaline-earth elements, and a support comprising at least one refractory oxide, characterized in that the average density of the macropores of said support is greater than or equal to 900 kpores/mm ² and less than 2000 kpores/mm ² and in that the packed filling density value of said support is between 0.50 g/mL and 0.68 g/mL.

Thanks to the combination of these very specific characteristics, namely an average macropore density associated with a specific packed filling density (DRT) value of the support, the catalyst presents improved performances in terms of activity, selectivity and stability for the dehydrogenation of paraffins and/or naphthenes and more particularly for the dehydrogenation of propane.

Advantageously, the content of metal from group VIII, expressed as an element, is between 0.02% and 2% by weight relative to the total weight of the catalyst, preferably between 0.05% and 1.5% by weight, even more preferably between 0.1% and 0.8% by weight.

Advantageously, the group VIII metal is chosen from platinum (Pt) or palladium (Pd), preferably platinum.

The group VIII metal can be present in the final catalyst in oxide, sulfide, halide, oxyhalide form, in chemical combination with one or more of the other catalyst components or in elemental metal form.

Advantageously, the content of element M1, chosen from tin, germanium, lead, gallium, indium and thallium, expressed as an element, in the catalyst according to the invention is between 0.01% and 10% by weight relative to the total weight of the catalyst, more preferably between 0.05% and 5% by weight and very preferably between 0.1% and 1% by weight.

Preferably, element M1 is tin (Sn).

Element M1 can exist in the catalyst in oxide, sulfide, halide, oxyhalide form, in chemical combination with one or more of the other components of the catalyst or in elemental metal form. Advantageously, the content of element M2, chosen from alkali or alkaline-earth elements, expressed as an element, in the catalyst according to the invention is between 0.4% and 8% by weight relative to the total weight of the catalyst, more preferably between 0.45% and 6.0% by weight, and very preferably between 0.5% and 3% by weight.

Preferably, element M2 is potassium (K) or cesium (Cs), and more preferably potassium.

When the element M2 is potassium, the potassium content, expressed as an element, in the catalyst according to the invention is advantageously between 0.5% and 3% by weight relative to the total weight of the catalyst, more preferably between 0.5% and 2.5% by weight, and very preferably between 0.5% and 2.25% by weight, and even more preferably between 0.65% and 0.95% by weight.

Advantageously, the surface density of element M2 in the catalyst according to the invention is between 0.5 atoms and 2 atoms of element M2/nm ² , more preferably between 0.55 atoms and 1.2 atoms of element M2/nm ² and very preferably between 0.65 atoms and 1 atom of element M2/nm ² .

In one embodiment according to the invention, the catalyst comprises a halogen element (hereinafter referred to as X). The halogen content is advantageously between 0.75% and 5.5% by weight of halogen element relative to the total weight of the catalyst, more preferably between 0.85% and 4% by weight and very preferably between 1% and 3.5% by weight.

Preferably, the halogen element is selected from the group consisting of fluorine, chlorine, bromine and iodine. Preferably, the halogen element is chlorine (Cl).

Advantageously, the surface density of halogen element in the catalyst is between 0.75 atoms and 5.5 atoms of element X/nm ² , preferably between 0.85 atoms and 4 atoms of element X/nm ² , more preferably between 1 atom and 3.5 atoms of element X/nm ² and very preferably between 1 atom and 2.45 atoms of element X/nm ² .

Advantageously, the atomic ratio between the halogen element and the element M2 chosen from alkali or alkaline-earth compounds is between 1.5 and 3, and preferably between 1.5 and 2.5. Preferably, the halogen is chlorine and the alkali or alkaline-earth is potassium.

In one embodiment according to the invention, the catalyst may further comprise phosphorus. The phosphorus may be present in the final catalyst as an oxide or mixed oxide compound, phosphate, polyphosphate, sulfide, halide, oxyhalide, hydride, in chemical combination with one or more of the other components of the catalyst. In this embodiment, the phosphorus content, expressed as an element, in the catalyst is between 0.4% and 1% by weight relative to the total weight of the catalyst, preferably between 0.4% and 0.8% by weight.

All elements (group VIII metal, element M1, element M2, element X, optionally phosphorus) are preferably distributed uniformly in the support. This distribution is characterized by a Castaing microprobe analysis by determining a distribution coefficient between 0.8 and 1.1 for all elements and preferably between 0.9 and 1.0 for all elements.

The specific surface area of the catalyst according to the invention is advantageously between 170 m ² /g and 250 m ² /g, preferably between 180 m ² /g and 220 m ² /g, preferentially between 190 m ² /g and 220 m ² /g, more preferentially between 195 m ² /g and 215 m ² /g, and even more preferentially between 195 m ² /g and 210 m ² /g.

The catalyst advantageously has a total pore volume measured by mercury porosimetry of between 0.1 cm ³ /g and 1.5 cm ³ /g, preferably between 0.4 cm ³ /g and 0.8 cm ³ /g, and very preferably between 0.4 cm ³ /g and 0.7 cm ³ /g.

Advantageously, the catalyst has a tapped filling density (TFD) value of between 0.50 g/mL and 0.68 g/mL, preferably between 0.55 g/mL and 0.65 g/mL.

3. Support

The catalyst support comprises at least one refractory oxide. Preferably, said porous support is based on alumina, silica, or silica-alumina, more preferably based on alumina.

When the support is based on alumina, it is understood that it comprises at least 95% by weight, preferably at least 98% by weight, and particularly preferably at least 99% by weight of alumina relative to the weight of the support. The alumina generally has a crystallographic structure of the delta, gamma or theta alumina type, alone or in a mixture, more preferably of the gamma type.

Even more preferably, the support is made of an alumina.

The specific surface area of the support is advantageously between 170 m ² /g and 250 m ² /g, preferably between 180 m ² /g and 220 m ² /g, preferentially between 190 m ² /g and 220 m ² /g, more preferentially between 195 m ² /g and 215 m ² /g, and even more preferentially between 195 m ² /g and 210 m ² /g. The support advantageously has a total pore volume measured by mercury porosimetry of between 0.1 cm ³ /g and 1.5 cm ³ /g, preferably between 0.4 cm ³ /g and 0.8 cm ³ /g, and very preferably between 0.4 cm ³ /g and 0.7 cm ³ /g.

Advantageously, the support has a packed filling density (DRT) value of between 0.50 g/mL and 0.65 g/mL, preferably between 0.55 g/mL and 0.65 g/mL.

Advantageously, the catalyst support according to the invention comprises an average density of macropores greater than or equal to 900 kpores/mm ² (kilo pores/mm ² ) and less than 2000 kpores/mm ² , preferably between 1000 kpores/mm ² and 1950 kpores/mm ² , and even more preferably between 1000 kpores/mm ² and 1400 kpores/mm ² .

Advantageously, the catalyst support comprises macropores with an average diameter of between 0.20 pm and 0.80 pm, preferably between 0.25 pm and 0.65 pm, and more preferably between 0.25 pm and 0.55 pm.

The support is advantageously in the form of beads, extrudates, pellets or powder. Preferably, the support is in the form of beads. When the support is in the form of beads, its diameter is generally between 0.5 mm and 5 mm, preferably between 1 mm and 2 mm. When the support is in the form of extrudates, the diameter of the extrudates is between 0.5 mm and 5 mm, preferably with a length-to-diameter ratio of 1:1 to 5:1.

The support can be obtained by any technique known to those skilled in the art. The shaping can be carried out for example by extrusion, by pelletizing, by the oil-drop method, by granulation on a rotating plate or by any other method well known to those skilled in the art. Preferably, the support is obtained by the drop coagulation method, as described in document FR3035798 A1.

4. Process for preparing the catalyst

The catalyst according to the invention may be prepared using any technique known to those skilled in the art. When the catalyst support is an alumina, the catalyst may be prepared by depositing its various constituents on said alumina support. The deposition of each constituent may be carried out on the alumina support before or after shaping thereof. The constituents may be introduced successively in any order, from a solution or separate solutions. In the latter case, intermediate drying and/or calcination may be carried out. In a particular embodiment, the catalyst is prepared according to a preparation method comprising the following successive steps: a) a support comprising the element M1 chosen from tin, germanium, lead, gallium, indium and thallium is prepared to obtain a first catalyst precursor; b) the first catalyst precursor obtained in step a) is dried under a flow of a neutral gas or under a flow of a gas containing oxygen at a temperature less than or equal to 250°C, then calcined at a temperature between 350°C and 750°C to obtain a first dried and calcined catalyst precursor; c) the first dried and calcined catalyst precursor obtained in step b) is impregnated with an impregnation solution comprising at least one precursor of at least one metal from group VIII, and optionally at least one precursor of an element X, and optionally phosphorus to obtain a second catalyst precursor; d) the second catalyst precursor obtained in step c) is dried under a flow of a neutral gas or under a flow of a gas containing oxygen at a temperature less than or equal to 250°C, then calcined at a temperature between 350°C and 750°C to obtain a second dried and calcined catalyst precursor; e) the second dried and calcined catalyst precursor obtained in step d) is impregnated with an impregnation solution comprising a precursor of at least one element M2, and optionally at least one precursor of an element X, to obtain a third catalyst precursor; f) the third catalyst precursor obtained in step e) is dried under a flow of a neutral gas or under a flow of a gas containing oxygen at a temperature less than or equal to 250°C, then calcined at a temperature between 350°C and 750°C; g) optionally, an oxychlorination step is carried out at a temperature between 350°C and 550°C and under a pressure between 0.1 MPa and 1.5 MPa, then calcination is carried out at a temperature between 350°C and 750°C.

Group VIII metal

Advantageously, the group VIII metal is supplied to the support in any suitable manner, such as coprecipitation, ion exchange or impregnation. Preferably, it is introduced by impregnation of the support, for example by excess or dry impregnation (the volume of solution containing the element to be introduced corresponding to the pore volume of the support), and preferably by excess impregnation. For this, the support is impregnated with an impregnation solution, aqueous or organic or consisting of a mixture of water and at least one organic solvent, comprising at least one precursor of the group VIII metal. In general, hydrogen chloride or another similar acid may also be added to the impregnation solution to further facilitate the incorporation or attachment to the surface of the support of the Group VIII metal and promote uniform distribution of the Group VIII metal in the support.

When the group VIII metal is platinum, the platinum precursors are part of the following group, but this list is not exhaustive: hexachloroplatinic acid, bromoplatinic acid, ammonium chloroplatinate, platinum chlorides, such as PtCh or PtCl, platinum dichlorocarbonyl dichloride, platinum tetraamine chloride or even dihydroxyplatindiammine. Organic platinum complexes, such as platinum (II) diacetyl acetonate, can also be used. These precursors can be used alone or in a mixture. Preferably, the precursor used is hexachloroplatinic acid.

Element M1

The element M1 selected from tin, germanium, lead, gallium, indium and thallium can be supplied in any suitable manner, such as coprecipitation, ion exchange or impregnation, at any stage of the catalyst preparation process.

According to a first variant, the element M1 can be introduced into the support, for example during the synthesis of the support or during the shaping of the support. Without being exhaustive, the techniques of addition before or during the dissolution of the oxide precursors of the support during the synthesis of the support, with or without ripening, may be suitable. The introduction can therefore be simultaneous or successive to the mixing of the precursors of the support. The element M1 can be introduced during the synthesis of the support using a sol-gel technique or even be added to an alumina sol. The element M1 can also be introduced during the implementation of the support using prior art techniques for shaping the support such as extrusion or oil-drop shaping procedures.

According to a second variant, the element M1 can be introduced onto the support, for example by impregnation of the previously shaped support. The impregnation of the support with a solution, aqueous or organic or consisting of a mixture of water and at least one organic solvent, comprising one or more precursors of elements M1 can be carried out by excess solution or dry. The impregnation of the support with a solution containing one or more precursors of element M1 can be carried out before, after or at the same time as the impregnation of the group VIII metal. The impregnation can be carried out in the presence of species acting on the interaction between the precursor of element M1 and the support. These species may be, for example, and without being limiting, mineral acids (HCl, HNO3) or organic acids (carboxylic or polycarboxylic acid types), and organic compounds of the complexing type, as described for example in patents US 6,872,300 and US 6,291,394. Preferably, the impregnation is carried out according to any technique known to those skilled in the art making it possible to obtain a homogeneous distribution of the element M1 within the support.

According to a third variant, the element M1 can also be introduced partly during the synthesis or shaping of the support and partly by deposition on the shaped support.

Preferably, the element M1 is introduced into the support, i.e. during the synthesis of the support or during the shaping of the support. In the case of an alumina-based support in the form of beads prepared by the draining technique, the precursor of the element M1 is introduced into the suspension to be drained.

The precursors of element M1 may be inorganic or of organometallic type, possibly of water-soluble organometallic type. The precursor of element M1 may be chosen from the group formed by halogenated compounds, hydroxides, carbonates, carboxylates, sulfates, tartrates and nitrates. These forms of element M1 may be introduced into the catalyst preparation medium as such or generated in situ (for example by introduction of tin and carboxylic acid). When the element M1 is tin, the tin-based organometallic precursors may be chosen, for example, from the following list: SnF t, where R represents an alkyl group, for example the butyl group, MeaSnCl, MeaSnCh, EtaSnCl, EtaSnCh, EtSnCh, iPrSnCh and the hydroxides MeaSnOH, Me2Sn(OH)2, EtaSnOH, Et2Sn(OH)2, the oxides (BuaSn^O, the acetate Bu3SnOC(O)Me. Preferably, halogenated species of tin, in particular chlorinated, are used. Even more preferably, the precursor of element M1 is SnCh or SnCk

Element M2

The element M2 selected from the alkali or alkaline-earth elements can be supplied in any suitable manner, such as coprecipitation, ion exchange or impregnation and this at any stage of the catalyst preparation process. It can in particular be introduced according to the three variants described in the case of the element M1. Preferably, it is introduced by impregnation, dry or in excess, preferably in excess and particularly preferably it is introduced after having introduced the metal of group VIII as described above.

The precursor(s) of element M2 chosen from alkali or alkaline-earth elements may be chosen from hydroxides, halides, nitrates, carbonates. When element M2 is potassium, the precursors can be chosen from KOH, KCI, KNO3, K2CO3, or ^PtCle-

Element X (optional)

The element X selected from halogens can be supplied in any suitable manner, such as coprecipitation, ion exchange or impregnation, and this at any stage of the catalyst preparation process. It can in particular be introduced according to the three variants described in the case of element M1.

In a preferred embodiment, element X is chlorine. Chlorine is introduced by impregnation, and particularly preferably it is introduced by impregnation at the same time as the group VIII metal or before the impregnation of the group VIII metal. As a possible counter anion of the compounds comprising element M1, group VIII metal and element M2, chlorine can also be introduced simultaneously with these elements, for example by the use of precursors of the type hhPtCl, SnCh or KCl or by treatment of the support in one of the preparation steps with hydrochloric acid. Chlorine can also be supplied in the preparation process by an additional oxychlorination step.

Phosphorus (optional)

Phosphorus can be supplied in any suitable manner, such as coprecipitation, ion exchange or impregnation, at any stage of the catalyst preparation process. In particular, it can be introduced according to the three variants described in the case of element M1.

According to a variant, the phosphorus is introduced into the support, that is to say during its shaping, for example simultaneously with the element M1.

According to another variant, the phosphorus is introduced by impregnation, and particularly preferably it is introduced by impregnation at the same time as the group VIII metal. In this case, the impregnation solution contains the precursor of the group VIII metal and the precursor of the phosphorus.

The phosphorus precursors may be acids or salts, and may be selected from the following compounds: H3PO4, H3PO3, H3PO2, NH4H2PO4, or (NhL^HPCU.

Order of introduction of precursors

As described above, the process for preparing the catalyst according to the invention comprises several modes of implementation which are distinguished in particular by the order of introduction of the metal from group VIII, of the element M1, of the element M2, of the element X and optionally phosphorus on the shaped support and/or in the support, i.e. during the synthesis of the support or during the shaping of the support. The process for preparing the catalyst comprises the introduction, simultaneously or successively, in any order, of the metal of group VIII, of the element M1, of the element M2, and optionally of the phosphorus and/or of the element X on the shaped support and/or in the support.

When element M1 and/or element M2 and/or optionally phosphorus and/or element X are introduced into the support, i.e. during the synthesis of the support or during the shaping of the support, the preparation process generally comprises a drying step and a calcination step before the deposition of the group VIII metal. The drying is generally carried out at a temperature less than or equal to 250°C, preferably between 50°C and 250°C, more preferably between 70°C and 200°C, in air or under an inert atmosphere. The calcination is preferably carried out at a temperature between 350°C and 750°C and preferably between 400°C and 650°C and even more preferably between 500°C and 600°C. The temperature rise can be steady or include intermediate temperature steps, these steps being reached with fixed or variable temperature rise rates. These temperature rises can therefore be identical or differ in their speed (in degrees per minute or per hour). The gas atmosphere used during calcination contains oxygen. Air can therefore also be used during this calcination step. The calcination gas may optionally contain water.

When one or more elements from among the metal of group VIII, the element M1, the element M2, the element X and/or optionally phosphorus, are introduced onto the shaped support, preferably by dry or excess impregnation, the introduction of said elements can be simultaneous by a single impregnation solution or take place separately by several impregnation solutions containing one or more of the components and this in any order.

Any impregnation solution described in the present invention may comprise any polar solvent known to those skilled in the art. Said polar solvent used is advantageously chosen from the group formed by methanol, ethanol, water, phenol, cyclohexanol, taken alone or as a mixture. Said polar solvent may also be advantageously chosen from the group formed by propylene carbonate, DMSO (dimethyl sulfoxide), N-methylpyrrolidone (NMP) or sulfolane, taken alone or as a mixture. Preferably, a polar protic solvent is used. A list of common polar solvents and their dielectric constant can be found in the book "Solvents and Solvent Effects in Organic Chemistry", C. Reichardt, Wiley-VCH, 3rd edition, 2003, pages 472-474. Very preferably, the solvent used is water or ethanol, and particularly preferably, the solvent is water. After each impregnation step, the catalyst precursor obtained is preferably dried in order to remove all or part of the solvent introduced during the impregnation, preferably at a temperature below 250°C, more preferably between 50°C and 250°C, and more preferably between 70°C and 200°C. The drying is advantageously carried out for a period of between 1 and 24 hours, preferably between 1 and 20 hours. The drying is carried out in air, or under an inert atmosphere (nitrogen for example). After the drying step, the catalyst is preferably calcined, generally in air. The calcination is preferably carried out at a temperature of between 350°C and 750°C and preferably between 400°C and 650°C and even more preferably between 500°C and 600°C. The temperature ramp may optionally contain temperature steps. The calcination time is generally between 0.5 hours and 16 hours, preferably between 1 hour and 5 hours. The gas atmosphere used during calcination contains oxygen. Air can therefore also be used during this calcination step. The calcination gas may optionally contain water.

In a particular embodiment, the catalyst is prepared according to a preparation method comprising the following successive steps: a) a support comprising the element M1 chosen from tin, germanium, lead, gallium, indium and thallium is prepared to obtain a first catalyst precursor; b) the first catalyst precursor obtained in step a) is dried under a flow of a neutral gas or under a flow of a gas containing oxygen at a temperature less than or equal to 250°C, then calcined at a temperature between 350°C and 750°C to obtain a first dried and calcined catalyst precursor; c) the first dried and calcined catalyst precursor obtained in step b) is impregnated with an impregnation solution comprising at least one precursor of at least one metal from group VIII, and optionally at least one precursor of an element X, and optionally phosphorus to obtain a second catalyst precursor; d) the second catalyst precursor obtained in step c) is dried under a flow of a neutral gas or under a flow of a gas containing oxygen at a temperature less than or equal to 250°C, then calcined at a temperature between 350°C and 750°C to obtain a second dried and calcined catalyst precursor; e) the second dried and calcined catalyst precursor obtained in step d) is impregnated with an impregnation solution comprising a precursor of at least one element M2, and optionally at least one precursor of an element X, to obtain a third catalyst precursor; f) the third catalyst precursor obtained in step e) is dried under a flow of a neutral gas or under a flow of a gas containing oxygen at a temperature less than or equal to 250°C, then calcined at a temperature between 350°C and 750°C; g) optionally, an oxychlorination step is carried out at a temperature between 350°C and 550°C and under a pressure between 0.1 MPa and 1.5 MPa, then calcined at a temperature between 350°C and 750°C.

In one embodiment according to the invention, when element X is chlorine, said chlorine element is supplied at least once either in step c) and/or in step e), and/or in step g).

Preferably, the introduction of the element M2 chosen from the alkali or alkaline-earth elements, and more particularly potassium, is carried out on a catalyst precursor comprising the metal of group VIII, more particularly platinum, previously dried and calcined. Indeed, the fact of introducing the potassium after the platinum makes it possible to avoid a leaching effect of the platinum during the impregnation of the metal of group VIII.

In step a), a support is prepared comprising the element M1, preferably tin. The element M1, preferably tin, can be introduced at any time during the preparation of the support, and preferably during shaping, or by impregnation on an already formed support. Preferably, the element M1 is introduced during the shaping of the support.

Similarly, the phosphorus can be introduced at any time during the preparation of the support, and preferably during shaping, or by impregnation on an already formed support. According to one variant, the phosphorus is introduced into the support, i.e. during the shaping of the support, preferably with the element M1, preferably tin. According to another variant, the phosphorus is introduced by impregnation, and particularly preferably it is introduced by impregnation at the same time as the group VIII metal.

The introduction of the group VIII metal can advantageously be carried out by one or more excess impregnations of solution on the support, or by one or more dry impregnations, and, preferably, by a single excess impregnation of said support (preferably containing the element M1, preferably tin, and optionally phosphorus), using solution(s), preferably aqueous, containing the precursor of the group VIII metal and optionally the phosphorus precursor (when the support does not contain or partially contains phosphorus).

In step e) the second dried and calcined catalyst precursor obtained in step d) is impregnated with an impregnation solution comprising at least one precursor of an element M2 chosen from alkali or alkaline-earth elements. The introduction of the element(s) alkali or alkaline-earth elements can advantageously be carried out by one or more excess solution impregnations on the support, or by one or more dry impregnations, and, preferably, by a single dry or excess impregnation of said precursor, using solution(s), preferably aqueous, containing at least one precursor of the alkali or alkaline-earth element, and preferably at least one potassium precursor.

In optional step g), the chlorine is supplied by means of an oxychlorination treatment. Such a treatment may for example be carried out at a temperature between 350°C and 550°C and under a pressure between 0.1 MPa and 1.5 MPa, for a duration preferably between 30 minutes and 10 hours, and under a flow of air containing the desired quantity of chlorine and possibly containing water.

According to another variant, the catalyst according to the invention can be prepared by preparing a support comprising tin by introducing the tin precursor during the shaping of the support, followed by one or more excess solution impregnations on the support, or by one or more dry impregnations, using solution(s), preferably aqueous, containing a precursor of a metal from group VIII, a phosphorus precursor and a precursor of an alkali or alkaline-earth element and preferably a potassium precursor, alone or as a mixture, then drying and calcining under the conditions described above.

When the various precursors used in the preparation of the catalyst according to the invention do not contain halogen or contain halogen in insufficient quantity, it may be necessary to add a halogenated compound during the preparation. Any compound known to those skilled in the art may be used and incorporated into any of the steps of preparation of the catalyst according to the invention. In particular, it is possible to use organic compounds such as methyl or ethyl halides, for example dichloromethane, dichloroethane, dichloropropane, chloroform, methylchloroform or carbon tetrachloride.

Halogen can also be added by impregnation with an aqueous solution of the corresponding acid, e.g., hydrochloric acid, at any time during preparation. A typical protocol is to impregnate the solid to introduce the desired amount of halogen. The catalyst is kept in contact with the aqueous solution for a time long enough to deposit this amount of halogen. Additional reduction step (optional)

In one embodiment according to the invention, prior to the use of the catalyst in the catalytic reactor and the implementation of a dehydrogenation process, a reducing treatment step is carried out in the presence of a reducing gas so as to obtain a catalyst comprising said metal from group VIII and said element M1 at least partially in metallic form. This step is advantageously carried out in situ, that is to say after the loading of the catalyst into a dehydrogenation reactor. Carrying out the reducing treatment of the catalyst in situ makes it possible to dispense with an additional step of passivation of the catalyst by an oxygenated compound or by CO2, which is necessarily the case when the catalyst is prepared by carrying out a reducing treatment ex situ, that is to say outside the reactor used for the dehydrogenation. Indeed, when the reducing treatment is carried out ex-situ, it is necessary to carry out a passivation step in order to preserve the metallic phase of the catalyst in the presence of air (during the operations of transporting and loading the catalyst into the hydrogenation reactor), then to carry out a new step of reducing the catalyst in-situ.

The reducing gas is preferably hydrogen. Hydrogen can be used pure or in a mixture (e.g., hydrogen/nitrogen, hydrogen/argon, hydrogen/methane). When hydrogen is used in a mixture, any proportion is possible.

Preferably, said reducing treatment is carried out at a temperature between 100°C and 600°C, and preferably between 200°C and 580°C, under a stream of hydrogen, pure or diluted, up to the maximum reduction temperature, followed by maintenance for example for 30 minutes to 6 hours at this temperature. The rise in temperature up to the desired reduction temperature is generally slow, for example set between 0.1 and 10°C/min, preferably between 0.3 and 7°C/min.

The hydrogen flow rate, expressed in L/hour/gram of catalyst precursor, is between 0.01 and 100 L/hour/gram of catalyst, preferably between 0.05 and 10 L/hour/gram of catalyst precursor, even more preferably between 0.1 and 5 L/hour/gram of catalyst precursor.

Passivation step (optional)

The process according to the invention can advantageously comprise a passivation step using a sulfur compound which makes it possible to improve the selectivity of the catalysts and to avoid thermal runaways during the start-up of new catalysts ("run-away" according to the The passivation step is carried out by implementing methods known to those skilled in the art.

The passivation step with a sulfur compound is generally carried out at a temperature between 20 and 350°C, preferably between 40 and 200°C, for 10 minutes to 240 minutes. The sulfur compound is for example chosen from the following compounds: thiophene, thiophane, alkylmonosulfides such as dimethylsulfide, diethylsulfide, dipropylsulfide and propylmethylsulfide or an organic disulfide of formula HO-R1-S-S-R2-OH such as di-thio-di-ethanol of formula HO-C2H4-S-S-C2H4-OH (often called DEODS). The sulfur content is generally between 0.1 and 2% by weight of said element relative to the total weight of the catalyst.

5. Process for the dehydrogenation of paraffins and/or naphthenes

The invention also relates to a process for dehydrogenation of a hydrocarbon feedstock comprising paraffinic and/or naphthenic compounds in the presence of the catalyst according to the invention.

Paraffin and/or naphthenes dehydrogenation processes enable the selective production of olefins and contribute to the production of significant quantities of hydrogen essential for the hydrogenation and hydrotreatment processes of a petrochemical complex or refinery.

The hydrocarbon feedstock generally comprises paraffinic and/or naphthenic compounds containing from 2 to 30 carbon atoms per molecule, taken alone or in a mixture. More particularly, the hydrocarbon feedstock comprises paraffinic and/or naphthenic compounds containing from 2 to 15 carbon atoms per molecule, preferably paraffinic compounds containing from 2 to 5 carbon atoms per molecule, such as propane, n-butane, n-pentane, isomers of butane and pentane or their mixture, and/or preferably naphthenic compounds containing from 5 to 12 carbon atoms such as cyclohexane, methylcyclohexane, decalin or their mixture. The feedstock may also comprise unsaturated hydrocarbons containing from 2 to 15 carbon atoms per molecule.

Typically, the dehydrogenation catalyst is loaded into a unit and previously subjected to a reduction treatment as described above. It can be implemented in any manner known to those skilled in the art. It can, for example, be implemented in a fixed bed or in a moving bed, preferably in a moving bed. According to a variant of the invention, the dehydrogenation catalyst is implemented in several reactors installed in series. The various processes for the dehydrogenation of paraffins and naphthenes differ in the choice of operating conditions and the composition of the feedstock. The adjustment of the operating conditions, depending on the nature of the feedstock to be treated, is done in such a way as to obtain the best pressure-temperature-yield and activity match in a manner known to those skilled in the art.

Generally speaking, the process for dehydrogenating a hydrocarbon feedstock comprising paraffins and/or naphthenes is carried out at a pressure of between 0.1 MPa and 4 MPa, at a temperature of between 200°C and 800°C and with a liquid hourly space velocity (LHSV) of between 0.5 h' ¹ and 50 h' ¹ .

More particularly, the paraffin dehydrogenation reaction is carried out at a pressure of between 0.1 MPa and 4 MPa and more preferably between 0.25 MPa and 3.0 MPa and at a temperature of between 400°C and 800°C depending on the nature of the feedstock, the temperature being advantageously between 560°C and 700°C for a feedstock comprising mainly propane, between 450°C and 600°C for a feedstock comprising mainly isobutane, and between 400°C and 550°C for a feedstock comprising mainly isopentane. It may be advantageous to use hydrogen as a diluent. The hydrogen/hydrocarbon molar ratio of the feedstock is generally between 0.1 and 10, preferably between 0.5 and 8. The liquid volumetric space velocity of the hydrocarbon feedstock (LHSV or Liquid Hourly Space Velocity according to English terminology), the unit of which is in liters of hydrocarbon feedstock per liter of catalyst and per hour, is preferably between 0.5 h' ¹ to 50 h' ¹ , more preferably between 1.5 h' ¹ to 15 tr 1

More particularly, the naphthenes dehydrogenation reaction is carried out at a pressure of between 0.1 MPa and 2 MPa, preferably between 0.1 MPa and 1 MPa, and at a temperature of between 200°C and 400°C. The liquid volumetric space velocity of the hydrocarbon feedstock (LHSV or Liquid Hourly Space Velocity according to English terminology), the unit of which is in liters of hydrocarbon feedstock per liter of catalyst and per hour, is generally between 0.5 h' ¹ and 50 h' ¹ .

The catalyst according to the invention can be regenerated by at least one combustion step in an oxidizing medium.

Catalyst regeneration is carried out in a cyclic or continuous system. It can consist of a simple combustion of the coke deposits. This combustion operation is usually carried out by injecting air into an inert mixture. The oxygen content in the gas at the regeneration inlet is preferably between 0.1% and 2% by volume. Combustion is usually carried out at a temperature between 350°C and 550°C and under pressure between 0.1 MPa and 1.5 MPa.

Combustion may possibly be preceded by an operation to strip the sulphur contained in the catalyst in the case where the catalyst includes sulphur introduced by injection of DM DS for example.

The regeneration may also include, at the end of the coke combustion step, a catalyst oxyhalogenation step, preferably oxychlorination. To this end, the oxygen content in the gas entering the regeneration is increased by at least 10% compared to the value of the previous combustion step. At least one halogenated derivative is introduced simultaneously, i.e. at least one halogen and/or one halogenated compound. Chlorine and/or a chlorinated compound are preferably used. The proportion of halogen and/or halogenated compound used is such that 0.2% to 3.5% by weight of a halogenated alumina derivative can be formed relative to the catalyst subjected to regeneration. The oxyhalogenation is carried out at a temperature between 350°C and 550°C and under a pressure between 0.1 MPa and 1.5 Mpa. A catalyst calcination step is generally carried out after oxyhalogenation during which the oxygen content in the gas at the regeneration inlet is between 3% and 20% by volume, the average temperature is between 350°C and 550°C and the pressure is between 0.1 MPa and 1.5 MPa.

Before subjecting the regenerated catalyst to the reaction conditions, it undergoes a preliminary reduction under a gas containing hydrogen, preferably under pure hydrogen. This reduction can be carried out in the regeneration chamber if this is separate from the reaction chamber, in the reaction chamber itself or in an intermediate zone separate from the regeneration and reaction zones. This reduction, if it has not been carried out prior to the reaction, can also take place in the reaction chamber after the reaction has started: the first stages of the reaction then serve to transform the catalyst into a catalytically active form for dehydrogenation. The reduction is carried out under a stream of gas containing hydrogen, preferably under pure hydrogen, at a temperature between 100°C and 600°C and at a pressure between 0.2 MPa and 2.5 MPa, preferably between 0.4 MPa and 1.5 MPa.

Possible sulfurization of the catalyst can follow this reduction step and therefore precede the dehydrogenation reaction itself.

All or part of the hydrogen produced can be recycled to the inlet of the dehydrogenation reactor. All or part of the unconverted propane can be recycled to the inlet of the dehydrogenation reactor. Examples

The following examples illustrate the invention without limiting its scope.

Example 1: Preparation of catalysts A, B, C and D with supports A1, B1, C1 and D1

Catalysts A to D are all prepared with the same method from supports A1, B1, C1 and D1 whose textural properties are described in Table 1 below.

Table 1

The Scanning Electron Microscopy (SEM) images on Polished Section are shown in Figures 1, 2, 3 and 4 corresponding respectively to supports A1, B1, C1, and D1. The images were taken at a magnification of x2500 and at a resolution of 2048x1536 pixels.

To 100 grams of alumina support A1, B1, C1 and D1 containing tin, 400 cm ³ of an aqueous solution of hexachloroplatinic acid and hydrochloric acid are added by excess impregnation. The mixture is left in contact for 4 hours and then drained. It is dried at 120°C for 15 hours and then calcined at 500°C under an air flow of 100 liters per hour for 3 hours, with a temperature rise rate of 7°C per minute.

To 100 grams of this calcined solid, 75 cm ³ of a potassium carbonate solution of suitable concentration is added by dry impregnation. It is left to mature, dried at 120°C for 15 hours and then calcined at 500°C under an air flow of 100 liters per hour for 3 hours, with a temperature rise rate of 7°C per minute.

Catalysts A, B, C and D obtained after calcination all contain 0.30% by weight of platinum, 0.29% by weight of tin relative to the total weight of the catalyst, 1.33 atCl/nm ² and 0.75 atK/nm ² . Their characteristics are described in Table 2 below. Table 2

Example 2: Propane dehydrogenation process using catalysts A to D

10 ^cm3 of catalyst are introduced into a reactor equipped with an electrically heated shell. The gas flows are sent in downflow, i.e. from top to bottom relative to the catalytic bed.

The reduction step is carried out with the following protocol: the catalyst is heated under inert gas to 150°C with a ramp of 5°C/min then maintained at 150°C for 1 h 30. The inert gas is replaced by hydrogen and the temperature is raised to 635°C with a ramp of 5°C/min then maintained at 635°C for 9 h 30. The reduction step is then completed and the hydrogen flow rate is set at 28 L/h.

The propane flow rate is in turn set to 28 L/h, i.e. a LHSV of 10.8 h' ¹ . The setting of this flow rate corresponds to the initial reaction time. The gaseous effluent is analyzed by gas chromatography by calculating the volume and mass proportions of each compound. The major products formed participating in the calculation of selectivity are methane, ethane, ethylene, propylene and benzene.

The conversion is calculated by calculating the ratio of the mass quantity of products formed analyzed in the effluent to the mass quantity of propane injected.

Activity is calculated by determining the mass quantity of propane converted per gram of platinum per hour.

Propylene selectivity is calculated by dividing the mass quantity of propylene formed by the sum of the mass quantities of all the reaction products at a propane conversion level of 28% by weight.

Benzene selectivity is calculated by taking the ratio of the mass quantity of benzene formed to the sum of the mass quantities of all the products of the reaction at a propane conversion level of 28% by weight. The benzene selectivity is particularly informative regarding the catalyst's propensity to produce coke and to deactivate: the higher this selectivity, the more easily the catalyst cokes.

Stability is determined by comparing the initial catalyst activity with the activity at 9 hours TOS (Time on Stream): % activity loss = ((activity at 1 hour TOS) - (activity at 9 hours TOS)) / (activity at 1 hour TOS).

Table 3 below reports the activities after 1 and 9 hours of “Time On Stream”, the percentage of loss of activity between 1 hour and 9 hours of TOS and the maximum selectivities obtained in propylene and benzene.

Table 3

The performance of non-compliant catalysts A and B, which do not meet the macropore number density and DRT conditions, clearly shows a deficit in activity, propylene selectivity and a high value of benzene selectivity compared to the catalysts according to the invention. The deactivation of these catalysts is also increased compared to the catalysts according to the invention.

The performances of catalysts C and D according to the invention respecting the conditions of macropore number density and DRT are the best both in terms of activity, propylene selectivity and stability with low values of benzene selectivity compared to non-compliant catalysts.

Claims

1. Process for the dehydrogenation of a hydrocarbon feedstock comprising paraffins and/or naphthenes, in which said feedstock is brought into contact with a catalyst, at a pressure of between 0.1 MPa and 4 MPa, at a temperature of between 200°C and 800°C, and with a liquid volumetric space velocity of between 0.5 h' ¹ and 50 h' ¹ , said catalyst comprising an active phase based on at least one metal from group VIII, at least one element M1 chosen from tin, germanium, lead, gallium, indium and thallium, and at least one element M2 chosen from alkali or alkaline-earth elements, and a support comprising at least one refractory oxide, characterized in that the average density of the macropores of said support is greater than or equal to 900 kpores/mm ² and less than 2000 kpores/mm ² and in that the density value compacted filling (DRT) of said support is between 0.50 g/mL and 0.68 g/mL. 2. Method according to claim 1, characterized in that the support is an alumina. 3. Method according to one of claims 1 or 2, characterized in that the specific surface area of the support is between 170 m ² /g and 250 m ² /g. 4. Method according to any one of the preceding claims, characterized in that the average macroporous diameter of said support is between 0.20 μm and 0.80 μm. 5. Method according to any one of the preceding claims, characterized in that the specific surface area of said support is between 195 m ² /g and 210 m ² /g. 6. Method according to any one of the preceding claims, characterized in that the average density of the macropores of said support is between 1000 kpores/mm ² and 1950 kpores/mm ² . 7. Process according to any one of the preceding claims, characterized in that the content of group VIII metal is between 0.02% and 2% by elemental weight of group VIII metal relative to the total weight of the catalyst. 8. Method according to any one of the preceding claims, characterized in that the group VIII metal is platinum. 9. Method according to any one of the preceding claims, characterized in that the content of element M1 is between 0.01% and 10% by elementary weight of element M1 relative to the total weight of the catalyst. 10. Method according to any one of the preceding claims, characterized in that the element M1 is tin. 11. Method according to any one of the preceding claims, characterized in that the surface density of element M2 is between 0.5 atoms and 2 atoms of element M2/nm ² . 12. Method according to any one of the preceding claims, characterized in that the element M2 chosen from the alkali or alkaline-earth elements is potassium. 13. Method according to claim 12, characterized in that the potassium content, expressed as an element, is between 0.5% and 3% by weight relative to the total weight of the catalyst. 14. Process according to any one of the preceding claims, in which the hydrocarbon feedstock comprises paraffinic and/or naphthenic compounds containing from 2 to 30 carbon atoms per molecule, taken alone or as a mixture. 15. Process according to claim 14, in which the hydrocarbon feedstock comprises paraffinic compounds comprising 2 to 5 carbon atoms per molecule and/or naphthenic compounds comprising from 5 to 12 carbon atoms.