Catalysts containing doped sulfated zirconium oxide

Abstract

The present invention relates to a catalyst comprising: (a) an aluminium-doped sulphated zirconium oxide, in which: the aluminium content is between 0.8 and 3.0% by weight based on the weight of the catalyst; - with regard to the crystallographic phases, the proportion of zirconium oxide in the tetragonal phase is at least 80%, in particular at least 85% or at least 90%; - the crystallinity of the zirconium oxide is at least 55%, in particular at least 60%, alternatively at least 65% or at least 70%; (b) a refractory oxide selected from silica and / or alumina; (c) a group VIIIB metal.

Description

[Technical field]

[0001] The present invention relates to the field of hydrocarbon conversion, in particular the conversion of saturated hydrocarbons. The invention more particularly relates to the isomerization of light paraffins having 4 to 12 carbon atoms. The invention therefore relates to a catalyst used to promote this conversion, a method for preparing the catalyst, as well as the use of the catalyst in an isomerization process. [Background technology]

[0002] The isomerization of linear paraffins is a widely used process for improving the octane number of naphtha hydrocarbon fractions. Various catalyst compositions suitable for this type of isomerization reaction are known.

[0003] Thus, Patent Document 1 describes a catalyst for the isomerization of paraffinic hydrocarbons, which is a catalyst that is capable of isomerizing SO 4 and at least one Group VIII metal on a support consisting of oxides and hydroxides of metals from Groups IV and III. Some examples of this type of composition are PdSO 4 / ZrO 2 , PtSO 4 / ZrO 2 , or alternatively PtSO 4 / SiO 2 -Al 2 O 3 However, it has been found that this type of composition results in a less active and less stable catalyst over time.

[0004] A catalyst is also known from US Pat. No. 5,399,633 and comprises a support made of sulfated oxides or hydroxides of elements of group IVB, to which elements from the lanthanide group, in particular ytterbium and platinum, are added. Ytterbium is a rare and expensive element and this type of catalyst does not have a high activity.

[0005] Also known from the publication by GAO et al. (Non-Patent Document 1) is a study on catalysts based on sulfated zirconia containing an aluminum promoter, which are recommended in a study to increase the activity and stability of catalysts for n-butane isomerization at low temperatures in the absence of hydrogen. However, it should be noted that the performance tests were carried out on powders and not on the final catalysts after molding, and that their performance on hydrocarbons heavier than butane was not evaluated.

[0006] For the purposes of the present invention, the various embodiments presented may be used alone or in combination with one another, without any limitations on said combinations.

[0007] For purposes of the present invention, various ranges of parameters for a given process, such as pressure ranges and temperature ranges, may be used alone or in combination. For example, for purposes of the present invention, a preferred range of pressure values ​​may be combined with a more preferred range of temperature values.

[0008] In the remainder of the text, groups of chemical elements are given according to the CAS classification (CRC Handbook of Chemistry and Physics, published by CRC Press, editor DR Lide, 81st ed., 2000-2001). For example, group VIII according to the CAS classification corresponds to metals in columns 8, 9 and 10 according to the new IUPAC classification, and group VIB corresponds to metals from column 6.

[0009] In the text that follows, the expressions "of between A and B" and "between A and B" are equivalent and mean that both limits of the interval (A, B) are included in the stated range of values. If this is not the case and if both limits are not included in the stated range, a statement to that effect is provided by the present invention. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 5,036,035 [Patent Document 2] US Patent Application Publication No. 2003 / 0050523 [Non-patent literature]

[0011] [Non-Patent Document 1] GAO Zi, XIA Yongde, HUA Weiming, MIAO Changxi, “New Catalyst of SO42- / Al2O3-ZrO2of n-butane isomerization. in: Topics in Catalysis”, 1998, Volume 6, Issue 1, p.101106. DOI: 10.1023 / A:1019122608037 Summary of the Invention [Means for solving the problem]

[0012] (Summary of the invention) The object of the present invention is to provide a new, more efficient catalyst suitable for the isomerization of saturated C4-C12 hydrocarbons. In particular, the object of the present invention is to develop a catalyst which is more active while retaining stability and selectivity.

[0013] A first subject of the invention is a catalyst comprising: (a) Sulfated zirconium oxide doped with aluminum; - The aluminum content is 0.8% to 3.0% by weight based on the weight of the catalyst; - with respect to the crystallographic phase, the proportion of zirconium oxide in the tetragonal phase is at least 80%, in particular at least 85% or at least 90%; the crystallinity of the zirconium oxide is at least 55%, in particular at least 60%, or alternatively at least 65% or at least 70%; (b) a refractory oxide selected from silica and / or alumina, preferably alumina or an alumina-silica mixture and / or alumina; (c) Group VIIIB metals.

[0014] Throughout this text: The term "support" refers to a mixture of sulfated zirconium oxide (a) and at least an aluminium dopant with a refractory oxide (b), preferably chosen from silica-alumina mixtures or alumina, preferably formed by kneading / extrusion, or more generally to the oxide, to which one or more active metals, such as here the platinum group metals, have subsequently been added.

[0015] The term "catalyst" refers to a Group VIIIB metal, such as platinum(c), loaded onto a predefined support.

[0016] "Crystallinity" is defined by the ratio of the area measured between 10° and 70° 2θ for the signal corresponding to the crystalline phase to the total area including the crystalline and amorphous phases (it should be noted that this calculation is performed by calculation methods / software known to the skilled person).

[0017] The term "zirconia" should be understood to be synonymous with zirconium oxide.

[0018] The catalyst according to the invention is therefore in the form of an active phase based on sulfated zirconia of specific crystallographic characteristics, doped with a very specific content of aluminium, to which is added a refractory oxide which will act as a binder, constituting the support, and to which is finally added a metal of Group VIIIB, for example platinum, constituting the catalyst (regardless of the order and the manner in which these various compounds are introduced).

[0019] The catalyst advantageously does not contain any elements from the lanthanide group.

[0020] Such a catalyst has been shown to have high activity and high stability for the isomerization of C4-C12, especially C4-C7, and especially C5+ light paraffins: it therefore has an activity and stability that is at least comparable to those of catalysts known to the skilled artisan, especially those containing dopants that are considerably rarer and more expensive than aluminum, such as elements from the lanthanide group.

[0021] Specifically, in the context of the present invention, it has been shown that the catalytic performance for the isomerization of C4-C7 light paraffins is closely related to the balance between the dopant content, the sulfate content, the zirconia crystallinity and the proportion of tetragonal phase in the support, leading to an optimum content of surface oxygen vacancies relative to the catalytic activity of the catalyst: it is by choosing specific values ​​for these four characteristics that particularly efficient catalysts can be obtained.

[0022] According to a variant of the invention, the sulfated zirconium oxide may also be doped with yttrium, in particular with a content of 0.5% to 1.5% by weight based on the weight of the catalyst. Indeed, in some cases, depending in particular on the aluminum content used, a second dopant may be added, preferably with a lower weight content. Preferably, the total amount of doping agent added (Al+Y) is between 0.8% and 3% by weight. In this variant, the Al / Y weight ratio is preferably at least equal to 1, in particular greater than 1, preferably greater than or equal to 1.5.

[0023] According to the present invention, the SO 3 The content is preferably at least 2.5% by weight, in particular 2.5% to 8% by weight or 2.5% to 9% by weight, based on the weight of the catalyst. Below the lower limit, the catalytic activity may decrease. Above the upper limit, it may become more difficult to stabilize the sulfate in the material.

[0024] According to the invention, the sulfate content in the sulfated zirconium oxide doped with aluminum is at least 5% by weight, in particular at least 7% by weight, preferably between 7% and 11% by weight of the zirconium oxide.

[0025] Preferably, the surface density of the sulfate in the catalyst according to the invention is less than 1.0SO 4 2- / nm 2 ~6SO 4 2- / nm 2 or 1.0SO 4 2- / nm 2 ~5SO 4 2- / nm 2 It is.

[0026] Advantageously, the doped sulfated zirconium oxide superacid Zr 3+ The site content is Zr per gram of the combined weight of (a) doped sulfated zirconium oxide and (b) refractory oxide. 3+ At least 0.16 mmol, in particular Zr per gram of weight of the two oxides (a) and (b). 3+ 0.16-0.3 mmol. It will be noted that the sum of these two oxides corresponds to the support of the catalyst. As will be explained in more detail below, this content is obtained here by a measurement carried out on the support of the catalyst (a)+(b), i.e. the combination of the doped sulfated zirconia and the refractory oxide. Where appropriate, the content of Zr per gram of weight of the doped sulfated zirconia (a) is 3+ It is possible to estimate the site's content.

[0027] Super acid Zr 3+ The content of Zr sites is related to the g factor as follows, and is expressed as Zr per gram of support weight: 3+ is understood to mean the amount of vacancies, corresponding to a species: g xx =g yy = 1.9784 and g zz=1.9288, and g xx =g yy = 1.9784 and g zz = 1.9060, or g xx =g yy = 1.9768 and g zz =1.9589.

[0028] The amount of vacancies is determined by calibration methods known to those skilled in the art. The reference compound used is 2,2-diphenyl-1-picrylhydrazyl (2,2-DPPH). The g-factor is explained below.

[0029] To determine this content, the inventors used Electron Paramagnetic Resonance (EPR), a known method for characterizing and quantifying oxygen vacancies. EPR is a spectroscopic method specific for paramagnetic species, i.e. species that contain unpaired electrons, as is the case for zirconium species in the vicinity of an oxygen vacancy. It is known to those skilled in the art that EPR makes it possible to identify the nature of a paramagnetic species by measuring its resonance frequency (called the g-factor) and to quantify this species (in terms of the number of spins per gram of weight relative to a reference material analyzed under identical conditions). This technique has the advantage of being very sensitive, and therefore capable of detecting trace amounts of the order of ppm. Numerous publications (e.g. Chavez JR, Devine RAB, Koltunski L, J. Appl. Phys., 2001; 90: 4284;Foster AS, Sulimov VB, Gejo FL, Shluger AL, Nieminen RM, Phys. Rev. B, 2001; 64: 224108;Foster AS, Gejo FL, Shluger AL, Nieminen RM, Phys. Rev. B, 2002; 65: 174117), zirconium oxide ZrO 2Theoretical calculations have been performed on the oxide, showing that the main defects in this oxide are oxygen vacancies and interstitial oxygen atoms that can trap charges. According to these same publications, calculations have shown that some of these defects may contain unpaired electrons and therefore may be detectable by EPR. This unpaired electron does not remain in a vacancy, but is attached to the 4d of the zirconium ion. 1 It is noted that the defects are present at the Zr level, which is reduced to the oxidation state (III). 3+ is observed indirectly through characteristic signals.

[0030] The inventors have surprisingly found that the good performance of their catalysts is due to the presence of Zr 3+ It has thus been shown that this corresponds to a minimum content of 0.16 mmol of vacancies in the sulfated zirconium oxide, which appears to be a "translation" of the amount of vacancies in the sulfated zirconium oxide, which is highly desirable for its catalytic activity.

[0031] Preferably, the content of (b) refractory oxide, in particular aluminum oxide and / or silicon oxide, is between 10% and 40% by weight of the catalyst, highly preferably between 15% and 25% by weight of the catalyst. When the oxide comprises aluminum oxide (alumina), it is preferably incorporated into the catalyst being prepared in the form of boehmite.

[0032] Preferably, the (c) Group VIIIB metal is a platinum group element, in particular Pt or Pd, preferably Pt, and more preferably, its content is 0.15% by weight to 0.35% by weight based on the weight of the catalyst.

[0033] Advantageously, the weight of doped sulfated zirconium oxide (a) in the catalyst is at least 60% by weight, in particular chosen between 75% and 85% by weight.

[0034] Preferably, the catalyst has an S_BET specific surface area of ​​at least 130 m2 / g, especially at least 150m 2 / g, preferably 150 to 180 m 2 / g. In particular, it has been proven to be advantageous for the catalyst to have this specific surface area in order to have good catalytic activity.

[0035] Another subject of the invention is a process for preparing the catalyst described above, comprising the following steps: (1) preparing a sulfated zirconium oxide doped with aluminum and, optionally, with yttrium; (2) mixing the doped sulfated zirconium oxide prepared in step (1) with at least one refractory oxide selected from silica and / or alumina or with a precursor of at least one of these oxides; the mixing is carried out in particular by mixing the powders in a solvent, (3) shaping the mixture obtained in step (2), in particular by extrusion; (4) firing the mixture formed in step (3); (5) impregnating the calcined mixture of step (4) with a Group VIIIB metal precursor; and (6) Calcining the mixture impregnated in step (5).

[0036] According to one embodiment of the method of the invention, step (1) of preparing sulfated zirconium oxide doped with aluminium may comprise a substep (1.2) of calcining said oxide.

[0037] According to one embodiment of the method of the present invention, the mixing step (2) ends with a sub-step of calcining the pre-shaped mixture, preferably at a temperature higher than the calcination temperature of step (4) of calcining the shaped mixture.

[0038] According to one embodiment of the method of the invention, step (1) of preparing the doped sulfated zirconium oxide comprises a substep (1.1) of incorporating aluminum and, optionally, yttrium, if these are present in the catalyst, into the sulfated zirconium oxide, by mixing the oxide with an aluminum precursor and, optionally, with an yttrium precursor. The two precursors can be added simultaneously when the yttrium and aluminum are incorporated, or they can be added sequentially, one after the other.

[0039] Another subject of the invention is the use of a catalyst as defined above in a process for the isomerization of a hydrocarbon feedstock.

[0040] The present invention also provides a process for isomerizing at least one alkane or cycloalkane contained in a hydrocarbon feedstock with an end point of 230° C. or less, said process being carried out in the vapor or liquid phase at a temperature of 120° C. to 190° C., a pressure of 20 to 80 MPa, a hydrogen / hydrocarbon compound molar ratio of 0.1 to 10, an hourly space velocity HSV of 0.05 to 15 h -1 with the abovementioned catalysts, which are especially in the form of oxysulfates and contain: aluminium doped sulfated zirconium oxide; - the aluminum content is 0.8% to 3.0% by weight based on the weight of the catalyst; - with respect to the crystallographic phase, the proportion of zirconium oxide in the tetragonal phase is at least 80%, in particular at least 85% or at least 90%; the crystallinity of the zirconium oxide is at least 55%, in particular at least 60%, or alternatively at least 65% or at least 70%, (b) a refractory oxide selected from silica and / or alumina; (c) Group VIIIB metals. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] (Description of the embodiment) In the following, the invention will be described in detail using non-limiting embodiments and examples.

[0042] (definition) Weight percentages are expressed relative to the anhydrous weight of the final composite material, which is determined by measuring the loss on ignition (LOI), which corresponds to the weight change resulting from heating a sample at 1000° C. for 2 hours. Loss on ignition is expressed as a weight percentage of solids.

[0043] The specific surface area of ​​the catalyst according to the invention or of the support used for the preparation of the catalyst according to the invention is understood to mean the BET specific surface area determined by nitrogen adsorption according to the ASTM D 3663-78 standard, which is derived from the Brunauer-Emmett-Teller method described in the academic journal "The Journal of the American Society", 60, 309 (1938).

[0044] The crystallographic structure of the zirconium oxide is determined by X-ray diffraction (XRD) techniques. More specifically, the 30.2° 2θ line is associated with the tetragonal crystallographic form and the 28.2° 2θ line is associated with the monoclinic crystallographic form. The proportion of the tetragonal crystallographic phase is determined by measuring the intensity of the 30.2° 2θ line and the 28.2° 2θ line, which is corrected by the I / Ic response factor (RIR, reference intensity ratio, method known to the skilled person). The proportion is at least 0.80. The crystallinity is determined by the ratio of the area measured between 10° and 70° 2θ for the signal corresponding to the crystalline phase to the total area including the crystalline and amorphous phases (this calculation is carried out by software known to the skilled person). According to the invention, the crystallinity is preferably at least 55%, in particular 60% or more, or even 65% or more.

[0045] The sulfate coverage is the ratio of SO 2 on the surface of the zirconium oxide. 4 2- It is determined by the density of sulfate ions. This is SO4 2- It is calculated as the ratio between the number of sulfate ions and the specific surface area of ​​the support.

[0046] Super acid Zr 3+ The content of Zr sites is expressed as Zr per gram of support weight. 3+ is understood to mean the amount of vacancies associated with the g factor corresponding to a species, e.g., g xx =g yy = 1.9784 and g zz = 1.9288 and g xx =g yy = 1.9784 and g zz =1.9060 or g xx =g yy = 1.9768 and g zz = 1.9589. The amount of vacancies is determined by a calibration method well known to those skilled in the art. The reference compound used is 2,2-diphenyl-1-picrylhydrazyl (2,2-DPPH). The method is detailed above.

[0047] The present invention relates to a catalyst based on oxysulfates comprising (or consisting of) sulfated zirconium oxide doped with aluminum or with a mixture of aluminum and yttrium, an inorganic refractory oxide used as a binder selected from silica, alumina and silica-alumina, and a metal of group VIII. The inventors have shown that the catalyst according to the invention has activity and stability comparable to those of a chlorinated alumina reference catalyst prepared according to patent WO 97 / 19752, the main drawback of which is the use of chlorine, leading to corrosion problems in industrial units.

[0048] The active phase of the catalyst of the invention comprises (or consists of) an oxysulfate consisting of a sulfated zirconium oxide modified by doping with aluminium or with aluminium and yttrium.

[0049] Sulfated zirconium oxide can be prepared, for example, from sulfated zirconium hydroxide. Sulfated zirconium hydroxide sold by Luxfer MEL Technologies, Flemington, NJ, can be used in the context of the present invention. Alternatively, zirconium hydroxide can be prepared by adding concentrated ammonia solution to a zirconium salt, for example ZrOCl. 2 8H 2 O, ZrCl 4 , ZrONH 3 The zirconium hydroxide sulfation step can be carried out by precipitation of an aqueous solution of a sulfating agent, e.g., H 2 SO 4 , (NH 4 ) 2 SO 4 , H 2 S, SO 2 , C.S. 2This can be carried out in the liquid or gas phase by Mention may in particular be made of the following publications: TICHIT, D.; Coq, B.; Armendariz, H.; Figueras, F. (1996) One-step sol-gel synthesis of sulfated-zirconia catalysts. in: Catalysis Letters, vol. 38, no. 1-2, p. 109-113. DOI: 10.1007 / BF00806908, TICHIT, D.;ELALAMI, D.; Figueras, F. (1996) Preparation and anion exchange properties of zirconia. in: Applied Catalysis A: General, vol. 145, no. 1-2, p. 195-210. DOI: 10.1016 / 0926-860X(96)00171-8, Li, X.;Nagaoka, K.; Olindo, R.; Lercher, JA (2006) Synthesis of highly active sulfated zirconia by sulfation with SO 3. in: Journal of Catalysis, vol. 238, no. 1, p. 39-45. DOI: 10.1016 / j.jcat.2005.11.039.

[0050] The sulfated zirconium hydroxide can be dried before or after the step of doping with aluminum or with aluminum and yttrium, at a temperature that allows the evaporation of volatile species without modifying its performance. The XRD technique does not show the 2θ lines at 28.2° and 30.2°, which are characteristic of monoclinic and tetragonal zirconium oxide (tetragonal phase zirconia formation after calcination).

[0051] Aluminum is another important component of the catalyst of the present invention. Aluminum is added to the sulfated zirconium hydroxide before the high temperature calcination treatment, which makes it possible to obtain a crystalline zirconium oxide form. Aluminum is in the ionic form Al 3+ Preferably, the aluminum precursor is in the form of a nitrate, carbonate, acetate, chloride, hydroxide, hydroxycarbonate, oxalate, sulfate or formate, or in the form of a complex formed with a polyacid or an acid alcohol.

[0052] According to the invention, the content of Al dopant in the sulfated zirconium oxide doped with alumina is between 0.8% and 3% by weight of said oxide, preferably between 1% and 2.5% by weight of said oxide.

[0053] Furthermore, optionally, elemental yttrium may be present in the range of 0.5% to 1.5% by weight relative to the sulfated zirconium oxide, the Al / Y ratio being greater than 1, and preferably the Al / Y ratio being less than 1.5, the total amount of doping agents Al+Y being 0.8% to 3% by weight of the catalyst or 1% to 2.5% by weight of the catalyst.

[0054] Yttrium is Y 3+ Preferably, the yttrium precursor is in the form of a nitrate, carbonate, acetate, chloride, hydroxide, hydroxycarbonate, oxalate, sulfate or formate, or in the form of a complex formed with a polyacid or an acid alcohol.

[0055] The dopants (aluminum and possibly also yttrium) are incorporated into the zirconium hydroxide before or after sulfation by any method known to those skilled in the art (dry or excess impregnation, co-precipitation, etc.).

[0056] The addition of yttrium can be done simultaneously with the addition of aluminum or after the addition of aluminum, but is advantageously done prior to the high temperature calcination treatment for catalytic activity.

[0057] The shaping of the previously obtained doped sulfated zirconium hydroxide or doped sulfated zirconium oxide, for example in the form of beads or extrudates, is carried out in the presence of a refractory inorganic binder selected from silica, boehmite, alumina and silica-alumina. Preferably, the binder selected is boehmite.

[0058] In order to obtain the sulfated zirconium oxide in tetragonal form, a high-temperature heat treatment should be carried out. This high-temperature heat treatment can be carried out before or after shaping. If it is carried out before shaping, the temperature is preferentially between 650°C and 750°C, preferentially between 670°C and 725°C. The temperature is adjusted so that a minimum of 80% of zirconium oxide in tetragonal crystallographic form is obtained according to XRD characterization.

[0059] The content of aluminum element in sulfated zirconium oxide is 0.8% by weight to 3% by weight. The presence of aluminum in the crystallographic structure of sulfated zirconium oxide is verified by EPR after high-temperature calcination treatment.

[0060] The specific surface area of ​​zirconium sulfate hydroxide or oxide is 80m 2 / g~400m 2 / g, highly preferably 100m 2 / g~300m 2 / g.

[0061] According to the invention, the sulfate content in the sulfated zirconium oxide doped with aluminum is at least 5% by weight, in particular at least 7% by weight, preferably between 7% and 11% by weight of the oxide.

[0062] Zr as support 3+ The site content is Zr per weight (gram) of the support (a) + (b). 3+ 0.160~0.300mmol.

[0063] The density of structural and surface defects is calculated as follows: after determining the optimal acquisition conditions (i.e. within the linearity range of the detector), a calibration straight line is generated using various solutions of DPPH (2,2-diphenyl-1-picrylhydrazyl), the spin concentration of which is known. To do this, these solutions are 2 The EPR spectrum of zirconium oxide is then subtracted from the baseline and double integrated. The area is then plotted on a calibration line, which makes it possible to extract the number of spins per gram of sample weight. This number is then converted into the amount of vacancies, since there is only one spin per defect.

[0064] The catalyst formulation may contain organic auxiliaries, advantageously chosen from cellulose derivatives, polyethylene glycols, aliphatic monocarboxylic acids, alkylated aromatic compounds, fatty acids, polyvinyl alcohols, methylcellulose, polyacrylates, polymethacrylates, polysaccharide type polymers (such as xanthan gum), etc., used alone or in mixtures.

[0065] This organic auxiliary may be chosen from any additive known to the skilled person. Nitric acid (10M) is added to ensure an effective peptization of the boehmite. Nitric acid combined with effective kneading has the effect of breaking down aggregates on the nanoscale and dispersing them. This dispersion makes it possible to achieve a more homogeneous mixture between the boehmite and the material previously obtained in the form of doped sulfated zirconium hydroxide or doped sulfated zirconium oxide. During the preparation of the catalyst, especially with one or more calcination steps, this auxiliary disappears and is therefore no longer present as an auxiliary in the final catalyst.

[0066] The shape chosen for shaping is generally beads or extrudates, and such shape does not affect the performance or characteristics of the catalyst according to the invention. The doped sulfated zirconium hydroxide or doped sulfated zirconium oxide is in the form of beads, extrudates or tablets, according to the usual means described in the literature.

[0067] Preferably, the starting components / reactants for producing the final catalyst according to the invention may have the following characteristics / proportions: - sulfated and doped zirconium hydroxide or sulfated and doped zirconium oxide: from 1% to 99% by weight, preferably from 5% to 99% by weight, preferably from 10% to 99% by weight, highly preferably from 10% to 80% by weight, - boehmite: 1% to 99% by weight, preferably 1% to 50% by weight, preferably 10% to 40% by weight, highly preferably 15% to 25% by weight, - nitric acid (concentration range 10M): 0% to 40% by weight, preferably 0% to 25% by weight, highly preferably 3% to 15% by weight, - at least one organic auxiliary: 0% to 20% by weight, preferably 0% to 10% by weight, highly preferably 0% to 7% by weight, The weight percentages are expressed relative to the total weight of said material, the sum of the respective contents of the compounds of said material being equal to 100%.

[0068] The method for preparing the catalyst according to the invention, according to one embodiment, preferably comprises at least the following two steps: a) mixing a powder of doped sulfated zirconium hydroxide or doped sulfated zirconium oxide with a powder of a boehmite type binder and at least one solvent; obtaining a mixture; and b) shaping the mixture obtained at the conclusion of step a).

[0069] (Step a)) Step a) consists of mixing a powder of doped sulfated zirconium hydroxide or doped sulfated zirconium oxide with a powder of a boehmite type binder and at least one solvent to obtain a mixture.

[0070] Preferably, the boehmite source and optionally also the organic adjuvant are mixed during step a).

[0071] Preferably, the boehmite source and optionally at least one organic adjuvant may be mixed in the form of powders or in solution in said solvent, which is preferably water.

[0072] The order in which the mixing of at least the powders of the doped sulfated zirconium hydroxide or doped sulfated zirconium oxide, the refractory inorganic binder, and optionally the at least one organic auxiliary (if they are mixed in powder form) with the at least one solvent is carried out is not important.

[0073] The mixing of the powder and the solvent may advantageously be carried out all at once. The addition of powder and solvent may advantageously be carried out alternately.

[0074] Preferably, said powders of at least one doped sulfated zirconium hydroxide or doped sulfated zirconium oxide, the refractory inorganic binder and optionally at least one organic auxiliary, if they are mixed in powder form, are first dry premixed followed by the introduction of a solvent, optionally in the presence of nitric acid.

[0075] The premixed powders are then advantageously contacted with the solvent, optionally in the presence of nitric acid, resulting in a mixture which is then kneaded.

[0076] Preferably, said mixing step a) is carried out by batch or continuous kneading. If said step a) is carried out batchwise, it is advantageously carried out in a kneader, preferably a kneader with a Z-arm, or a cam mixer, or in any other type of known mixer. The mixing step a) makes it possible to obtain a homogeneous mixture of the powdery components.

[0077] Preferably, said step a) is carried out for a period of 5 to 60 minutes, preferably 10 to 50 minutes. The rotation speed of the kneader arms is advantageously between 10 and 75 rpm, preferably between 25 and 50 rpm. The starting compounds / reactants listed above are introduced in step a).

[0078] (Step b)) Step b) consists of shaping the mixture obtained at the end of the mixing step a).

[0079] Preferably, the mixture obtained at the end of the mixing step a) is advantageously shaped by extrusion. Step b) is advantageously carried out in a ram extruder, a single screw extruder or a twin screw extruder.

[0080] In this case, organic auxiliaries may optionally be added in the mixing step a), the presence of which facilitates shaping by extrusion, said organic auxiliaries being as described above and introduced in step a) in the proportions indicated above.

[0081] When the preparation method is carried out continuously, the mixing step a) can be connected to the step b) of shaping by extrusion in the same equipment. According to this embodiment, the extrusion of the mixture, also called "mixed paste", can be carried out either directly at the end of a twin-screw continuous kneader, for example, or by connecting one or more batch kneaders to an extruder. The geometry of the die, which gives the extrudates their shape, can be chosen from dies known to those skilled in the art. They can therefore be, for example, of cylindrical, multilobal, grooved or slotted shape.

[0082] During step b), the amount of solvent added in mixing step a) is adjusted so as to obtain, at the end of this step, a mixture or paste that, regardless of the modifications carried out, is neither runny nor too dry, allowing extrusion under appropriate pressure conditions well known to those skilled in the art and depending on the extrusion equipment used.

[0083] Preferably, said step b) of shaping by extrusion is carried out at an extrusion pressure of more than 1 MPa, preferably between 3 MPa and 10 MPa.

[0084] (Step c)) The process for preparing said material also comprises a step c) of drying the shaped material obtained at the end of step b), said drying step being advantageously carried out at a temperature between 0° C. and 300° C., preferably between 20° C. and 200° C., preferably between 20° C. and 150° C., for a period between 1 min and 72 h, preferably between 30 min and 72 h, preferably between 1 h and 48 h, more preferably between 1 h and 24 h.

[0085] (Step d)) The material obtained at the end of step c), which thus constitutes the support, can be calcined in step d) at a temperature between 600° C. and 800° C., preferably between 650° C. and 750° C., in air, for a period between 1 h and 6 h, preferably between 1 h and 2 h.

[0086] In the variant in which the doped sulfated zirconium hydroxide or the doped sulfated zirconium oxide is calcined before shaping to obtain the support, the calcination carried out on the material is carried out at a temperature below the 650-700°C temperatures indicated above: the calcination is preferably carried out at a temperature between 450°C and 600°C or between 450°C and 550°C, in air, for a period between 1 hour and 6 hours, or between 1 hour and 2 hours.

[0087] The temperature and duration of calcination of the composite product are adjusted to obtain a minimum of 80% of zirconium oxide in the tetragonal crystallographic phase in the final catalyst. The proportion of crystalline phase is monitored by XRD, where the 2θ lines at 28.2° and 30.2° are characteristic of the monoclinic and tetragonal zirconium oxide phases, respectively.

[0088] The specific surface area and sulfate content are monitored according to characterization methods well known to those skilled in the art (eg, nitrogen physisorption and CHNS analysis, respectively).

[0089] The group VIII element, preferably Pt, is added by any means known in the literature (dry impregnation or excess impregnation). The final catalyst is calcined at 400° C. to 500° C. The content of the group VIII element, preferably Pt, is between 0.15% and 0.35% by weight relative to the final catalyst.

[0090] The catalyst according to the invention may be used in a process for isomerizing at least one alkane contained in a hydrocarbon feedstock containing from 4 to 12 carbon atoms, preferably a feedstock containing from 4 to 7 carbon atoms, more preferentially a feedstock consisting of a mixture of paraffins having from 4 to 7 carbon atoms and cycloalkanes having from 5 to 7 carbon atoms. Preferentially, the feedstock contains a minimum of 50% by weight of linear paraffins. The feedstock may also contain olefins and aromatics, generally less than 15% by weight.

[0091] The process for isomerizing a hydrocarbon feedstock consisting of a mixture of paraffins having 4 to 8 carbon atoms and cycloalkanes having 5 to 8 carbon atoms is carried out in the vapour or liquid phase at a temperature between 100° C. and 250° C., preferably between 130° C. and 190° C., more preferentially between 150° C. and 180° C., at a pressure between 20 and 80 MPa, at a molar ratio of hydrogen / (paraffinic compounds to be isomerized) between 0.1 and 10, and at an hourly space velocity HSV between 0.05 and 15 h -1 It is.

[0092] In some cases, the step of drying the catalyst, once it has occurred, is carried out at a temperature below 250°C.

[0093] Advantageously, the step of heat treatment of the catalyst, once it has occurred, is carried out at a temperature below 250° C., in the presence of a reducing gas, preferably dihydrogen. Preferably, the hydrogen flow rate, expressed in L / h / gram catalyst precursor, is between 0.01 and 100 L / h / gram catalyst.

[0094] (Example) Example 1: Catalyst A (Pt / S-Zr-Al 2 O 3 Preparation of (Comparative Example) Catalyst A was prepared from commercially available sulfated zirconium hydroxide, S-Zr(OH), supplied by Luxfer MEL Technologies, Flemington, NJ, part number XZO1247.

[0095] The support A is prepared by co-kneading commercially available sulfated zirconium hydroxide S-Zr(OH) with boehmite suspended in an acidic aqueous solution, then extruding it, drying it at 120°C, and calcining it at 700°C for 2 hours. 4 )NO 3and calcination at 450° C. to obtain the final catalyst A. The volume of the impregnation solution is equal to the pore volume. This example is a comparative example because the sulfated zirconia is not doped with aluminum.

[0096] Table 1 below details the formulation and characteristics of Catalyst A.

[0097] [Table 1]

[0098] Example 2: Catalyst B (Pt / Al 1 -SZr-Al 2 O 3 Preparation of (According to the Invention) Catalyst B was prepared from commercially available sulfated zirconium hydroxide S-Zr(OH) (supplied by Luxfer MEL Technologies, Flemington, NJ, part number XZO1247) and doped with aluminum nitrate solution.

[0099] The support B is prepared by dry impregnation of commercially available sulfated zirconium hydroxide S-Zr(OH) with an aluminum nitrate solution. The concentration of aluminum in the impregnation solution is adjusted to reach 1% by weight of aluminum in catalyst B. The volume of the aluminum nitrate solution is equal to the pore volume. Aluminum-doped sulfated zirconium hydroxide Al 1 —SZr(OH) is co-kneaded with boehmite suspended in an acidic aqueous solution, which is then extruded, dried at 120° C., and calcined at 650° C. for 2 hours. 4 )NO 3 and calcined at 450° C. to obtain the final catalyst B according to the present invention. The volume of the impregnation solution is equal to the pore volume. Table 2 below details the formulation and characteristics of catalyst B.

[0100] [Table 2]

[0101] Example 3: Catalyst C (Pt / Al 1 Y 0.5 -SZr(OH)-Al 2 O 3 Preparation of (According to the Invention) Catalyst C was prepared from commercially available sulfated zirconium hydroxide, S-Zr(OH) (supplied by Luxfer MEL Technologies, Flemington, NJ, part number XZO1247) and doped with a solution of aluminum nitrate and yttrium nitrate.

[0102] The support C is prepared by dry impregnation of the commercially available sulfated zirconium hydroxide S-Zr(OH) with a solution of aluminum nitrate and yttrium nitrate. The concentrations of aluminum and yttrium in the impregnation solution are adjusted to reach 1% by weight of aluminum and 0.5% by weight of yttrium in the catalyst C. The volume of the solution of aluminum nitrate and yttrium nitrate is equal to the pore volume. Sulfated zirconium hydroxide Al doped with aluminum and yttrium 1 Y 0.5 -SZr(OH) is co-kneaded with boehmite suspended in an acidic aqueous solution, which is then extruded, dried at 120 °C, and then calcined at 650 °C for 2 h. 4 )NO 3 and calcined at 450° C. to obtain the final catalyst C according to the present invention. The volume of the impregnation solution is equal to the pore volume. Table 3 below details the formulation and characteristics of catalyst C.

[0103] [Table 3]

[0104] Example 4: Catalyst D (Pt / Al 2.5 -SZr-Al 2 O 3 Preparation of (According to the Invention) Catalyst D was prepared from commercially available sulfated zirconium hydroxide S-Zr(OH) (supplied by Luxfer MEL Technologies, Flemington, NJ, part number XZO1247) and doped with aluminum nitrate solution.

[0105] Support D is prepared by co-kneading commercial sulfated zirconium hydroxide S-Zr(OH) with boehmite suspended in an acidic aqueous solution, then extruding it, drying it at 120°C, dry impregnating it with an aluminum nitrate solution, and then calcining it at 700°C for 2 hours. The concentration of aluminum in the impregnation solution is adjusted to reach 2.5% by weight of aluminum in catalyst D. Support D is doped with Pt(NH 4 )NO 3 and calcined at 450° C. to obtain the final catalyst D. The volume of the impregnation solution is equal to the pore volume. Table 4 below details the formulation and characteristics of catalyst D.

[0106] [Table 4]

[0107] Example 5: Catalyst E (Pt / Al 0.5 -SZr-Al 2 O 3 Preparation of (Comparative Example) Catalyst E was prepared from commercially available sulfated zirconium hydroxide S-Zr(OH) (supplied by Luxfer MEL Technologies, Flemington, NJ, part number XZO1247) and doped with aluminum nitrate solution.

[0108] The support E is prepared by dry impregnation of the commercially available sulfated zirconium hydroxide S-Zr(OH) with an aluminum nitrate solution. The concentration of aluminum in the impregnation solution is adjusted to reach 0.5% by weight of aluminum in the catalyst E. The volume of the aluminum nitrate solution is equal to the pore volume. Aluminum-doped sulfated zirconium hydroxide Al 0.5—SZr(OH) is co-kneaded with boehmite suspended in an acidic aqueous solution, which is then extruded, dried at 120°C, and calcined at 650°C for 2 hours. 4 )NO 3 and calcination at 450° C. to obtain the final catalyst E according to the invention. The volume of the impregnation solution is equal to the pore volume. This example is a comparative example because it has an insufficient aminium content (and Zr 3+ This is because the site coverage is too low.

[0109] Table 5 below details the formulation and characteristics of Catalyst E.

[0110] [Table 5]

[0111] Example 6: Catalyst F (Pt / Al 2.5 -SZr-Al 2 O 3 Preparation of (According to the Invention) Catalyst F was prepared from commercially available sulfated zirconium hydroxide S-Zr(OH) (supplied by Luxfer MEL Technologies, Flemington, NJ, part number XZO1247) and doped with aluminum nitrate solution according to the protocol of Example D.

[0112] The support F is prepared by co-kneading a commercially available sulfated zirconium hydroxide doped with 2.5% by weight of aluminum and calcined at 700°C, Al-S-Zr(OH), with boehmite suspended in an acidic aqueous solution, then extruding it, drying at 120°C, and calcining at 550°C for 2 hours. The support F is doped with Pt(NH 4 )NO 3 and calcined at 450° C. to obtain the final catalyst F. The volume of the impregnation solution is equal to the pore volume. Table 6 below details the formulation and characteristics of catalyst F.

[0113] [Table 6]

[0114] Example 7: Catalyst G (Pt / Al 1 -SZr-Al 2 O 3 Preparation of (Comparative Example) Catalyst G was prepared from commercially available sulfated zirconium hydroxide S-Zr(OH) (supplied by Luxfer MEL Technologies, Flemington, NJ, part number XZO1247) and doped with aluminum nitrate solution.

[0115] The support G is prepared by co-kneading the commercially available sulfated zirconium hydroxide S-Zr(OH) with boehmite suspended in an acidic aqueous solution, then extruding it, drying it at 120°C, and calcining it at 700°C for 2 hours. The support G is then dry-impregnated with an aluminum nitrate solution. The concentration of aluminum in the impregnation solution is adjusted to reach 1 mol% of aluminum in catalyst E. The support G is doped with Pt(NH 4 )NO 3 and calcined at 450° C. to obtain the final catalyst G. The volume of the impregnation solution is equal to the pore volume. This example is a comparative example, in particular because of the too low tetragonal phase of ZrO 2 % Zr. The formulation and characteristics of Catalyst G are detailed in Table 7 below.

[0116] [Table 7]

[0117] Example 8: Catalyst H (Pt / Al 2.5 -SZr-Al 2 O 3 Preparation of (Comparative Example) Catalyst H was prepared from commercially available sulfated zirconium hydroxide S-Zr(OH) (supplied by Luxfer MEL Technologies, Flemington, NJ, part number XZO1247) and doped with aluminum nitrate solution according to the protocol of Example D.

[0118] The support H is prepared by co-kneading a commercially available sulfated zirconium hydroxide Al-S-Zr(OH) doped with 2.5 wt. % aluminum, calcined at 650° C., with boehmite suspended in an acidic aqueous solution, then extruding it, drying at 120° C., and calcining it at 550° C. for 2 hours. The support H is doped with Pt(NH 4 )NO 3 The final catalyst H is obtained by dry impregnation with the solution of Zr and then calcination at 450°C. The volume of the impregnation solution is equal to the pore volume. This example is a comparative example because Zr 3+ As with the content of zirconia sites, the crystallinity of zirconia is 50%. 3+ This is because, like the site content, it is too low.

[0119] Table 8 below details the formulation and characteristics of Catalyst H.

[0120] [Table 8]

[0121] Example 9: Catalyst I (Pt / Al 2.5 -SZr-Al 2 O 3 Preparation of (Comparative Example) Catalyst I was prepared from commercially available sulfated zirconium hydroxide, S-Zr(OH) (obtained from Luxfer MEL Technologies, Flemington, NJ, part number XZO1247) and doped with aluminum nitrate solution according to the protocol of Example D.

[0122] Support I is prepared by co-kneading a commercially available sulfated zirconium hydroxide Al-S-Zr(OH) doped with 2.5 wt. % aluminum, calcined at 800° C., with boehmite suspended in an acidic aqueous solution, then extruding it, drying at 120° C., and calcining it at 550° C. for 2 hours. Support I is doped with Pt(NH 4 )NO 3 solution and then calcined at 450° C. to obtain the final catalyst I. The volume of the impregnation solution is equal to the pore volume.

[0123] This example is a comparative example because the residual sulfur content is too low.

[0124] Table 9 below details the catalyst formulation and characteristics.

[0125] [Table 9]

[0126] Example 10: Catalyst J (Pt / Al 2.5 -SZr-Al 2 O 3 Preparation of (Comparative Example) Catalyst J was prepared from commercially available sulfated zirconium hydroxide S-Zr(OH) (obtained from Luxfer MEL Technologies, Flemington, NJ, part number XZO1247) and doped with aluminum nitrate solution according to the protocol of Example D.

[0127] The support J is prepared by co-mixing the commercially available sulfated zirconium hydroxide Al-S-Zr(OH) doped with 2.5% by weight of aluminum, calcined at 700° C., with boehmite suspended in an acidic aqueous solution, then extruding it, drying at 120° C., and then calcining for 2 hours at 700° C. In this example, the support is therefore: pre-calcined (for powder), shaped (extruded), dried and then post-calcined.

[0128] Support J is Pt(NH 4 )NO 3 is dry impregnated with the solution of 1.0 g of 100% sucrose, followed by calcination at 450° C. to obtain the final catalyst J. The volume of the impregnation solution is equal to the pore volume.

[0129] This example is a comparative example because the residual sulfur content is too low, which has been found to be related to two high-temperature calcinations of the support, more specifically to a post-calcination (after extrusion and drying) at too high a temperature. In the case of two calcinations, it is therefore preferable to choose a lower temperature for the second calcination than for the first calcination.

[0130] Table 10 below details the catalyst formulation and characteristics.

[0131] [Table 10]

[0132] Example 11: Isomerization of C5 / C6 / C7 fraction Approximately 20 g of the prepared catalysts A to J are loaded into a fixed-bed reactor. The catalysts are dried at 400° C. under nitrogen flow, and then the feedstock is loaded into the glove box in the reactor. The catalysts are dried at 400° C. under nitrogen flow, and then the feedstock is loaded into the glove box in the reactor. 2 The mixture is reduced under a stream of 160° C. for 2 hours.

[0133] 40bar, temperature 160℃, H 2 The test was carried out with a molar ratio of 4 / hydrocarbon. The feedstock was a mixture containing 29.5 wt% n-pentane, 33.9 wt% n-hexane, 5.6 wt% n-heptane, 5.5 wt% C5 naphthenes, and 25.2 wt% C6 naphthenes. The mass flow rate was 1.3 g feedstock (g catalyst) / g. -1 h -1 It is.

[0134] Table 11 below summarizes the catalytic activity results for Examples 1 to 8 corresponding to Catalysts A to H. The catalytic activities are expressed as follows: - %iC5 / C5: weight ratio of isopentane to the sum of all pentanes (iC5 / C5) - %22DMB / C6: ratio of 2,2-dimethylbutane to the sum of paraffins having 6 carbon atoms (22DMB / C6); obtained at the conversion of the synthetic feedstock in a fixed bed at the set operating conditions.

[0135] Increasing these ratios represent increases in octane number (also known as RON or Research Octane Number).

[0136] It should be noted that the accuracy of the measurement of the iC5 / C5 ratio is ±2% (absolute value) at iC5 / C5=65% and ±4% at iC5 / C5=45%.

[0137] To assess the stability of the catalyst, these two ratios are compared after 5 hours and 160 hours under feed. If the catalyst is stable, these two ratios do not decrease significantly over time.

[0138] [Table 11]

[0139] It can be seen from these results that the results for %iC5 / C5 at 5 hours are at least 61.5 (catalyst D according to the invention) up to 75.3 (catalyst C according to the invention), while these same results are at most 53 (comparative example catalyst G): the invention therefore makes it possible to improve the activity of the catalyst by at least 23%.

[0140] The results expressed in terms of %(22DMB / C6) at 5 hours follow a similar trend.

[0141] The remarkable stability of the %(iC5 / C5) and %(22DMB / C6) values ​​for the examples consistent with the present invention should be noted, with the values ​​measured at 160 hours being substantially unchanged relative to the values ​​measured at 5 hours.

Claims

1. A catalyst comprising: (a) sulfated zirconium oxide doped with aluminum; the aluminum content is between 0.8% and 3.0% by weight of the catalyst; - with respect to the crystallographic phase, the proportion of zirconium oxide in the tetragonal phase is at least 80%, in particular at least 85% or at least 90%; the crystallinity of the zirconium oxide is at least 55%, in particular at least 60%, or at least 65% or at least 70%; (b) a refractory oxide selected from silica and / or alumina, preferably alumina or an alumina-silica mixture; (c) Group VIIIB metals.

2. Catalyst according to claim 1, characterized in that (a) the sulfated zirconium oxide is also doped with yttrium, the content of which is in particular between 0.5% and 1.5% by weight of the catalyst.

3. Catalyst according to claim 2, characterized in that the Al / Y weight ratio is at least equal to 1, in particular greater than 1, preferably greater than or equal to 1.

5.

4. Catalyst according to claim 1, characterized in that the sulfate content of the catalyst is at least 2.5 wt. %, in particular 2.5 wt. % to 9 wt. % or 2.5 wt. % to 8 wt. % based on the weight of the catalyst.

5. Catalyst according to claim 1, characterized in that (a) the sulfate content in the sulfated zirconium oxide doped with aluminium is at least 5 wt. %, in particular at least 7 wt. %, preferably between 7 wt. % and 11 wt. % by weight of the oxide.

6. Doped sulfated zirconium oxide superacid Zr ３＋ The content of Zr per gram of the combined weight of (a) doped sulfated zirconium oxide and (b) refractory oxide is ３＋ at least 0.16 mmol, in particular Zr per gram of combined weight of (a) doped sulfated zirconium oxide and (b) refractory oxide; ３＋ The catalyst according to claim 1, characterized in that the amount is 0.16 to 0.3 mmol.

7. Catalyst according to claim 1, characterized in that the content of (b) refractory oxide, in particular aluminium oxide, is between 10% and 40% by weight, in particular between 15% and 25% by weight, based on the weight of the catalyst.

8. Catalyst according to claim 1, characterized in that (c) the Group VIIIB metal is a platinum group element, in particular Pt or Pd, preferably Pt, the content of which is preferably between 0.15% and 0.35% by weight of the catalyst.

9. Catalyst according to claim 1, characterized in that the weight of (a) doped sulfated zirconium oxide in the catalyst is at least 60% by weight, in particular 75% to 85% by weight.

10. The specific surface area S_BET of the catalyst is at least 130 m ２ / g, especially at least 150 m ２ / g, preferably 150 to 180 m ２ 2. The catalyst according to claim 1, wherein the average molecular weight of the catalyst is 1.0g.

11. A process for preparing the catalyst according to any one of claims 1 to 10, characterized in that it comprises the following steps: (1) preparing a sulfated zirconium oxide doped with aluminum and, optionally, with yttrium; (2) mixing the doped sulfated zirconium oxide prepared in step (1) with at least one refractory oxide selected from silica and / or alumina, preferably alumina or an alumina-silica mixture, or with a precursor of at least one of these oxides; the mixing is carried out in particular by mixing the powders in a solvent; (3) shaping the mixture obtained in step (2), in particular by extrusion; (4) firing the mixture formed in step (3); (5) impregnating the calcined mixture of step (4) with a precursor of a Group VIIIB metal; (6) Calcining the mixture impregnated in step (5).

12. 12. The method according to claim 11, wherein the step (1) of preparing sulfated zirconium oxide doped with aluminum comprises the substep (1.2) of calcining said oxide.

13. 12. The method according to claim 11, wherein the mixing step (2) ends with a sub-step of calcining the pre-shaped mixture, preferably at a temperature higher than the calcination temperature of the step (4) of calcining the shaped mixture.

14. 12. The method according to claim 11, wherein step (1) of preparing doped sulfated zirconium oxide comprises a substep (1.1) of incorporating aluminum and optionally yttrium into sulfated zirconium oxide, which substep (1.1) is carried out by mixing said oxide with an aluminum precursor and optionally also with an yttrium precursor.

15. Use of a catalyst according to any one of claims 1 to 10 in a process for the isomerization of a hydrocarbon feedstock.

16. A process for isomerizing at least one alkane contained in a hydrocarbon feedstock, the end point of which is 230°C or less, characterized in that it is carried out catalytically in the vapor or liquid phase, the temperature being 120°C to 190°C, the pressure being 20 to 80 MPa, the hydrogen / paraffinic compound molar ratio being 0.1 to 10, and the hourly space velocity HSV being 0.05 to 15 h －１ wherein the catalyst comprises: (a) sulfated zirconium oxide doped with aluminum; the aluminum content is between 0.8% and 3.0% by weight of the catalyst, preferably between 1% and 2.5% by weight of the catalyst; - with respect to the crystallographic phase, the proportion of zirconium oxide in the tetragonal phase is at least 80%, in particular at least 85% or at least 90%; the crystallinity of the zirconium oxide is at least 55%, in particular at least 60%, or at least 65% or at least 70%; (b) a refractory oxide selected from silica and / or alumina; (c) Group VIIIB metals.