A catalyst for alkane isomerization reaction, its preparation method and application

Abstract

This invention belongs to the field of catalytic materials, and particularly relates to a catalyst for alkane isomerization reactions, its preparation method, and its application. The preparation method provided by this invention includes the following steps: a) heat-treating an acidic support under vacuum conditions to obtain a treated acidic support; b) immobilizing a metal compound onto the surface of the treated acidic support using surface chemistry methods to obtain a catalyst precursor; the metal compound includes first and second metal compounds, the first metal compound being a Pt source and / or a Pd source compound, and the second metal compound being one or more of a Cu source, Ga source, Ni source, and Sn source compound; c) reducing the catalyst precursor in a hydrogen atmosphere to obtain the catalyst. The catalyst prepared by this invention has the advantages of small active metal particle size and high dispersion, and exhibits excellent catalytic synergy between the metal center and the acidic center in the catalyst, demonstrating excellent conversion rate, selectivity, and stability in alkane isomerization reactions.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials, and particularly relates to a catalyst for alkane isomerization reaction, its preparation method and application. Background Technology

[0002] Isomerized gasoline contains no sulfur, aromatics, or olefins, and is a high-octane, clean gasoline blending component. The process of producing isomerized gasoline from light alkane isomerization is expected to see significant future development. Currently, the alkane isomerization catalysts widely used in industry are all noble metal-supported solid acid catalysts. The isomerization reaction of alkane follows a "metal-acid" bifunctional catalytic mechanism, where the noble metal active center is responsible for catalyzing the dehydrogenation of n-alkane molecules to olefin molecules and the hydrogenation of isoolefin molecules to obtain isoalkanes, while the acidic center is responsible for the carbon chain skeleton isomerization of olefin molecules. Therefore, the catalytic synergy between the metal center and the acidic center is crucial for the effectiveness of the alkane isomerization reaction. The placement and occurrence form of the metal center on the surface of the acidic support determine the extent of the synergistic effect of the two types of active centers in catalytic isomerization.

[0003] Currently, the commonly used metal loading process in the preparation of isomerization catalysts is the impregnation method. The impregnation method involves immersing an acidic support in a solution containing a metal component. Under capillary pressure, the liquid penetrates into the pores of the acidic solid support, and the metal component adheres to the solid surface. However, existing impregnation techniques struggle to achieve controllable loading of the metal component on the support surface. This is mainly due to several issues: the metal particles on the catalyst surface prepared by this method are prone to agglomeration and sintering at high temperatures, resulting in poor stability. This leads to larger particle sizes, uneven distribution, and even pore blockage of the metal component, resulting in low metal component utilization efficiency, low catalytic conversion of alkane isomerization, and poor selectivity for isoolefins. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a catalyst for alkane isomerization reaction, its preparation method and application. The catalyst prepared by the method of the present invention has the advantages of small active metal particle size and high dispersion. The catalytic synergy between the metal center and the acidic center in the catalyst is good, and it can exhibit excellent conversion rate, selectivity and stability in alkane isomerization reaction.

[0005] This invention provides a method for preparing a catalyst for alkane isomerization reactions, comprising the following steps:

[0006] a) The acidic support is heat-treated under vacuum conditions to obtain the treated acidic support;

[0007] b) A metal compound is immobilized onto the surface of the treated acidic support using a surface chemistry method to obtain a catalyst precursor;

[0008] The metal compound includes a first metal compound and a second metal compound, wherein the first metal compound is a Pt source compound and / or a Pd source compound, and the second metal compound is one or more of a Cu source compound, a Ga source compound, a Ni source compound, and a Sn source compound;

[0009] c) The catalyst precursor is reduced in a hydrogen atmosphere to obtain the catalyst.

[0010] Preferably, in step a), the acidic support is an acid-treated oxide support and / or an acidic molecular sieve.

[0011] Preferably, the acid-treated oxide support is a product of an oxide support modified by an acid treatment reagent, wherein the oxide support is one or more selected from SiO2, Al2O3, ZrO2, Nb2O5, La2O3, CeO2 and kaolin, and the acid treatment reagent is one or more selected from phosphoric acid, ammonium phosphate, hydrochloric acid, ammonium chloride, sulfuric acid, ammonium sulfate, metatungstic acid, ammonium metatungstate, phosphomolybdic acid and ammonium phosphomolybdate.

[0012] The acidic molecular sieve is one or more of HZSM-5 molecular sieve, HBeta molecular sieve, HMOR molecular sieve, HY molecular sieve and SAPO-11 molecular sieve.

[0013] Preferably, in step a), the temperature of the heat treatment is 200–600°C; the absolute pressure of the heat treatment is 0.001–0.1 MPa; and the time of the heat treatment is 2–24 h.

[0014] Preferably, in step b), the Pt source compound is one or more of trimethylcyclopentadienylplatinum, tetra(triphenylphosphine)platinum, tri(dibenzylideneacetone)platinum, dichloro(dicyclopentadienyl)platinum, and diphenyl(1,5-cyclooctadienyl)platinum;

[0015] The Pd source compound is one or more of bis(dibenzylacetone)palladium, (1,5-cyclooctadiene)palladium dichloride, and tris(dibenzylacetone)palladium;

[0016] The Cu source compound is one or more of the following: hexafluoroacetylacetone-cyclooctadiene copper, (ethylcyclopentadienyl) (triphenylphosphine) copper, tri(triphenylphosphine) chloride copper, bis(triphenylphosphine)borohydride cuprous, bis(triphenylphosphine) copper nitrate, and (1,10-phenanthroline)(trifluoromethyl)(triphenylphosphine) copper;

[0017] The Ga source compound is one or more selected from gallium trifluoromethanesulfonate, gallium acetylacetonate, gallium isopropoxide, tris(2,2,6,6-tetramethyl-3,5-heptanoic acid) gallium, and tris(2-methyl-3-hydroxy-4-pyranone) gallium;

[0018] The Ni source compound is one or more of the following: bis(cyclopentadienyl)nickel, bis(pentamethylcyclopentadienyl)nickel, bis(ethylcyclopentadienyl)nickel, chloro(cyclopentadienyl)(triphenylphosphine)nickel, tetra(triphenylphosphine)nickel, bis(triphenylphosphine)nickel chloride, bis(triphenylphosphine)dicarbonylnickel, dichlorobis(tributylphosphine)nickel, chlorobis(triphenylphosphine)phenylnickel, and [1,2-bis(diphenylphosphine)ethane]dichloride nickel;

[0019] The Sn source compound is one or more of tetra-n-butyltin, dibutyltin maleate, tri-n-butyltin hydride, phenylacetylenytributyltin, dibutyltin dilaurate, tetraphenyltin, hexaphenylditin, and triphenyltin acetate.

[0020] Preferably, in step b), the specific process of immobilizing the metal compound using the surface chemical method includes:

[0021] Under anaerobic and anhydrous conditions, the treated acidic support is immersed in an organic solution of a metal compound for immobilization reaction, followed by heating to evaporate the solvent, to obtain a catalyst precursor.

[0022] Preferably, in step c), the reduction temperature is 80–500°C, and the reduction time is 1–24 h.

[0023] This invention provides a catalyst for alkane isomerization reactions, which is prepared according to the preparation method described in the above technical solution.

[0024] Preferably, the catalyst support is immobilized with a first metal element corresponding to a first metal compound and a second metal element corresponding to a second metal compound, wherein the first metal element accounts for 0.01 to 0.5 wt% of the total mass of the catalyst and the second metal element accounts for 0.1 to 5 wt% of the total mass of the catalyst.

[0025] This invention provides a method for alkane isomerization, comprising the following steps:

[0026] Alkanes undergo isomerization reactions in the presence of the catalyst described in the above technical solution.

[0027] Compared with existing technologies, this invention provides a catalyst for alkane isomerization reactions, its preparation method, and its application. The preparation method provided by this invention includes the following steps: a) heat-treating an acidic support under vacuum conditions to obtain a treated acidic support; b) immobilizing a metal compound onto the surface of the treated acidic support using a surface chemistry method to obtain a catalyst precursor; the metal compound includes a first metal compound and a second metal compound, wherein the first metal compound is a Pt source compound and / or a Pd source compound, and the second metal compound is one or more of a Cu source compound, a Ga source compound, a Ni source compound, and a Sn source compound; c) reducing the catalyst precursor in a hydrogen atmosphere to obtain the catalyst. The preparation method provided by this invention utilizes surface chemical immobilization to directionally anchor metal components to defect sites on the surface of an acidic support, thereby controllably preparing small and uniformly distributed metal nanoclusters on the support surface. This achieves effective control over the synthesis process, structural properties, and catalytic performance of the "metal-acid" bifunctional catalyst, enhancing the catalytic synergy between the metal center and the acidic center in the catalyst during the alkane isomerization reaction. Ultimately, this enables the catalyst to exhibit excellent conversion rate, selectivity, and stability in the alkane isomerization reaction. More specifically, the preparation method provided by this invention first uses a vacuum high-temperature operation to dehydrate and dehydroxylate the acidic support, completely desorbing the water that exists in the pores of the support through physical adsorption. At the same time, some of the weakly adsorbed hydroxyl groups on the support surface undergo condensation and dehydration reactions, exposing more defect sites on the support surface that are conducive to the loading of metal components. During the surface chemical immobilization process, the metal components preferentially undergo strong chemical adsorption with the defect sites on the support surface and are thus anchored to the support surface, making them less prone to migration and agglomeration during subsequent heat treatment. In contrast, the traditional impregnation method for metal loading relies on the surface tension of the liquid on the solid surface as the driving force, resulting in weak interaction between the metal and the support. During drying and calcination, the metal components are prone to agglomeration, leading to poor dispersion and uneven particle size of the active metal. Therefore, the catalyst prepared by the method provided by this invention has a more uniform dispersion of metal components on the surface and a more uniform grain size. The metal components can provide more catalytically active surfaces, thereby improving the utilization efficiency of the metal components, especially the noble metal components. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1This is a STEM image of the Pt-CuGa / HBeta-1 catalyst prepared in Example 1 of this invention;

[0030] Figure 2 This is a STEM image of the Reference-1 catalyst prepared in Comparative Example 1 provided by the present invention. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a method for preparing a catalyst for alkane isomerization reactions, comprising the following steps:

[0033] a) The acidic support is heat-treated under vacuum conditions to obtain the treated acidic support;

[0034] b) A metal compound is immobilized onto the surface of the treated acidic support using a surface chemistry method to obtain a catalyst precursor;

[0035] c) The catalyst precursor is reduced in a hydrogen atmosphere to obtain the catalyst.

[0036] In the preparation method provided by the present invention, in step a), the acidic support is preferably an acid-treated oxide support and / or an acidic molecular sieve; wherein, the acid-treated oxide support is preferably a product of an oxide support modified by an acid treatment reagent, the oxide support is preferably one or more of SiO2, Al2O3, ZrO2, Nb2O5, La2O3, CeO2 and kaolin, the acid treatment reagent is preferably one or more of phosphoric acid, ammonium phosphate, hydrochloric acid, ammonium chloride, sulfuric acid, ammonium sulfate, metatungstic acid, ammonium metatungstate, phosphomolybdic acid and ammonium phosphomolybdate; the acidic molecular sieve is preferably a hydrogen-type silica-alumina molecular sieve and / or silica-alumina phosphate molecular sieve, more preferably one or more of HZSM-5 molecular sieve, HBeta molecular sieve (H-type Beta molecular sieve), HMOR molecular sieve, HY molecular sieve and SAPO-11 molecular sieve.

[0037] In the preparation method provided by the present invention, in step a), the temperature of the heat treatment is preferably 200-600℃, more preferably 260-550℃, and specifically can be 300℃, 350℃, 400℃, 450℃ or 500℃; the absolute pressure of the heat treatment is preferably 0.001-0.1MPa, more preferably 0.001-0.02MPa; the time of the heat treatment is preferably 2-24h, more preferably 6-12h, and specifically can be 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0038] In the preparation method provided by the present invention, in step a), the acidic carrier is subjected to vacuum heat treatment to obtain a dehydrated, dehydroxylated, and surface-cleaned acidic carrier.

[0039] In the preparation method provided by the present invention, in step b), the metal compound includes a first metal compound and a second metal compound; wherein, the first metal compound is a Pt source compound and / or a Pd source compound; the Pt source compound is preferably one or more of trimethylcyclopentadiene platinum, tetra(triphenylphosphine)platinum, tri(dibenzylacetone)platinum, dichloro(dicyclopentadienyl)platinum, and diphenyl(1,5-cyclooctadiene)platinum; the Pd source compound is preferably one or more of bis(dibenzylacetone)palladium, (1,5-cyclooctadiene)palladium dichloride, and tri(dibenzylacetone)dipalladium; the second metal compound is one or more of Cu source compound, Ga source compound, Ni source compound, and Sn source compound; the Cu source compound is preferably hexafluoroacetylacetone-cyclooctadiene copper, (ethylcyclopentadienyl)(triphenylphosphine)copper, tri(triphenylphosphine)copper chloride, bis(triphenylphosphine)copper borohydride, bis(triphenylphosphine)copper nitrate, and (1,1) One or more of 0-phenanthroline)(trifluoromethyl)(triphenylphosphine)copper; the Ga source compound is preferably one or more of gallium trifluoromethanesulfonate, gallium acetylacetonate, gallium isopropoxide, tris(2,2,6,6-tetramethyl-3,5-heptanoic acid)gallium and tris(2-methyl-3-hydroxy-4-pyranone)gallium; the Ni source compound is preferably bis(cyclopentadienyl)nickel, bis(pentamethylcyclopentadienyl)nickel, di(ethylcyclopentadienyl)nickel, chloro(cyclopentadienyl)(triphenylphosphine)copper, etc. The Sn source compound is preferably one or more of the following: nickel bis(triphenylphosphine) chloride, nickel tetra(triphenylphosphine) chloride, nickel bis(triphenylphosphine)dicarbonyl chloride, nickel dichlorobis(tributylphosphine) chloride, nickel chlorobis(triphenylphosphine)phenylene, and nickel [1,2-bis(diphenylphosphine)ethane]dichloride; the Sn source compound is preferably one or more of the following: tetrabutyltin, tin dibutylmaleate, tin tributylhydride, tin phenylacetylenide, tin dibutyldilaurate, tetraphenyltin, hexaphenylditin, and tin triphenylacetate.

[0040] In the preparation method provided by the present invention, step b) preferably includes the following specific process of immobilizing the metal compound using the surface chemical method:

[0041] Under anaerobic and anhydrous conditions, the treated acidic support is immersed in an organic solution of a metal compound for immobilization reaction. Then, the solvent is evaporated by heating, and the metal compound is immobilized on the surface of the support to obtain a catalyst precursor.

[0042] In the above-mentioned immobilization process provided by the present invention, the solvent in the organic solution is a volatile organic solvent, preferably tetrahydrofuran or n-hexane; the temperature of the immobilization reaction is preferably 25-300℃, more preferably 50-200℃, specifically 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃ or 200℃; the time of the immobilization reaction is preferably 1-24h, more preferably 1-12h, specifically 1h, The heating and volatilization temperature is preferably 50–300°C, more preferably 50–200°C, and specifically can be 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C; the heating and volatilization time is preferably 1–24 hours, more preferably 2–6 hours, and specifically can be 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0043] In the above-mentioned fixation process provided by the present invention, the metal compound can be fixed in one step or in stages (i.e., one metal compound is fixed each time), preferably in stages. In the process of staged fixation, the fixation reaction temperature, fixation reaction time, heating volatilization temperature and heating volatilization time for each metal compound can be referred to the above description and will not be repeated here.

[0044] In the preparation method provided by the present invention, in step c), the reduction temperature is preferably 80-500℃, more preferably 120-300℃, and specifically can be 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃ or 300℃; the reduction time is preferably 1-24h, more preferably 2-6h, and specifically can be 2h, 3h, 4h, 5h or 6h.

[0045] The present invention also provides a catalyst for alkane isomerization reaction prepared according to the preparation method described above; the catalyst comprises: an acidic support and a first metal element and a second metal element immobilized on the acidic support, wherein the first metal element is the metal element corresponding to the first metal compound after reduction reaction (i.e., Pt and / or Pd), and the second metal element is the metal element corresponding to the second metal compound after reduction reaction (i.e., one or more of Cu, Ga, Ni and Sn).

[0046] In the catalyst provided by this invention, the first elemental metal serves as the active component of the catalyst, and it is highly dispersed on the support surface in the form of small crystallite nanoclusters. In this invention, the first elemental metal preferably accounts for 0.01 to 0.5 wt% of the total mass of the catalyst, specifically 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, or 0.5 wt%.

[0047] In the catalyst provided by this invention, the second metallic element acts as a metal promoter, diluting and isolating the active sites of the first metallic element, promoting the high dispersion of the first metallic element in the form of small crystallite nanoclusters on the support surface, forming a single active site, and significantly improving catalytic performance. In one embodiment of this invention, the second metallic element is Cu and Ga, and the mass ratio of Cu to Ga is preferably 1:(0.5-2), more preferably 1:1; in another embodiment of this invention, the second metallic element is Ni and Sn, and the mass ratio of Ni to Sn is preferably 1:(0.5-2), more preferably 1:1. In this invention, the second metallic element preferably accounts for 0.1-5 wt% of the total mass of the catalyst, specifically 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt%.

[0048] In the catalyst provided by this invention, the acidic support serves to disperse the first and second elemental metals. In this invention, the total mass of the three components—the first elemental metal, the second elemental metal, and the acidic support—is 100%, and the remaining portion of the catalyst, excluding the first and second elemental metal components, is the acidic support.

[0049] The present invention also provides a method for alkane isomerization, comprising the following steps:

[0050] Alkanes undergo isomerization reactions in the presence of the catalyst described in the above technical solution.

[0051] In the alkane isomerization method provided by this invention, the alkane is preferably a light n-alkanes, more preferably C4-C8 straight-chain alkanes; the isomerization reaction is preferably carried out in a fixed-bed reactor; the temperature of the isomerization reaction is preferably 120-400℃, specifically 120℃, 140℃, 160℃, 180℃, 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 320℃, 340℃, 360℃, 380℃, or 400℃; the pressure of the isomerization reaction is preferably 0.1-3 MPa, specifically 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.7 MPa, 1 MPa, 1.2 MPa, 1.5 MPa, 1.7 MPa, 2 MPa, 2.3 MPa, 2.5 MPa, 2.7 MPa, or 3 MPa; the mass hourly space velocity of the isomerization reaction is preferably 0.5-3 h⁻¹. -1 Specifically, it can be 0.5h. -1 0.7h -1 1h -1 1.2h -1 1.5h -1 1.7h -1 2h -1 2.3h -1 2.5h -1 2.7h -1 or 3h -1 The hydrogen-to-oil molar ratio in the isomerization reaction is preferably 0.06 to 1, specifically 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0052] In the alkane isomerization method provided by the present invention, if the catalyst support is an acid-treated oxide, it is preferable to chlorinate the catalyst before the isomerization reaction to increase the density and strength of acidic sites on the catalyst surface.

[0053] The technical solution provided by this invention utilizes a surface chemical immobilization method to directionally anchor metal components onto defect sites on the surface of an acidic support, thereby controllably preparing small and uniformly distributed metal nanoclusters on the support surface. This achieves effective control over the synthesis process, structural properties, and catalytic performance of "metal-acid" bifunctional catalysts, enhancing the catalytic synergy between metal centers and acidic centers in the catalyst during alkane isomerization reactions. Ultimately, this enables the catalyst to exhibit excellent conversion rate, selectivity, and stability in alkane isomerization reactions.

[0054] For clarity, the following examples and comparative models will be used to provide a detailed description.

[0055] Example 1

[0056] (1) Place 50g of H-type Beta molecular sieve (SiO2 / Al2O3=25) in a quartz tube and vacuum treat it at 500℃ and 0.001MPa absolute pressure for 12h to obtain a dehydrated and dehydroxylated surface-clean HBeta molecular sieve carrier for later use.

[0057] (2) In a glove box, 6.97 g of tris(triphenylphosphine)copper chloride, 2.63 g of gallium acetylacetonate, and 0.26 g of (1,5-cyclooctadiene)dimethylplatinum were dissolved in tetrahydrofuran to obtain the corresponding metal compound solutions. The vacuum-treated HBeta molecular sieve support was immersed in the solution of tris(triphenylphosphine)copper chloride for immobilization reaction. Then, the solvent was evaporated by heating to immobilize the copper source onto the surface of the support. The immobilization reaction temperature was 50 °C and the time was 4 h, and the solvent evaporation temperature was 80 °C and the time was 4 h. The above process was repeated to immobilize the gallium source and the platinum source in sequence to obtain the catalyst precursor.

[0058] (3) Finally, the catalyst precursor was reduced in a hydrogen atmosphere at 140℃ for 2 hours to obtain the Pt-CuGa / HBeta-1 catalyst.

[0059] Example 2

[0060] The preparation steps and synthesis conditions of Example 1 are the same, except that in step (2), 6.97g of tris(triphenylphosphine)copper chloride, 2.63g of gallium acetylacetonate and 0.26g of (1,5-cyclooctadiene)dimethylplatinum are simultaneously immobilized on the surface of the HBeta molecular sieve support, and the resulting catalyst is called Pt-CuGa / HBeta-2 catalyst.

[0061] Example 3

[0062] The preparation steps and synthesis conditions are the same as in Example 1, except that the absolute pressure of HBeta pretreatment in step (1) is 0.1 MPa, and the resulting catalyst is denoted as Pt-CuGa / HBeta-3 catalyst.

[0063] Example 4

[0064] The preparation steps and synthesis conditions of Example 1 are the same, except that: 0.26g of (1,5-cyclooctadiene) dimethylplatinum in step (2) is replaced with 0.41g of (1,5-cyclooctadiene) palladium dichloride in equal molar amounts, the fixed reaction temperature is increased to 70°C, and the fixed reaction time is shortened to 1h. The resulting catalyst is called Pd-CuGa / HBeta-1 catalyst.

[0065] Example 5

[0066] (1) Place 50g of acidic alumina (Al2O3) in a quartz tube and vacuum heat treat it for 12h at 500℃ and 0.002MPa absolute pressure in a heating furnace under nitrogen atmosphere to obtain dehydrated and dehydroxylated Al2O3 support for later use.

[0067] (2) In a glove box, 2.41 g of bis(cyclopentadiene)nickel, 2.70 g of tetraphenyltin and 0.26 g of (1,5-cyclooctadiene)dimethylplatinum were sequentially immobilized onto the surface of an Al2O3 support; the immobilization reaction temperature was 60 °C and the immobilization reaction time was 3 h; the solvent evaporation temperature was 70 °C and the reaction time was 4 h, to obtain the catalyst precursor;

[0068] (3) Finally, the catalyst precursor was reduced in a hydrogen atmosphere at 160℃ for 2h to obtain the Pt-NiSn / Al2O3-1 catalyst.

[0069] Example 6

[0070] The preparation steps and synthesis conditions of Example 5 are the same, except that in step (2), 2.41 g of bis(cyclopentadiene)nickel, 2.70 g of tetraphenyltin and 0.26 g of (1,5-cyclooctadiene)dimethylplatinum are simultaneously immobilized on the surface of Al2O3 support, and the resulting catalyst is called Pt-NiSn / Al2O3-2 catalyst.

[0071] Example 7

[0072] The preparation steps and synthesis conditions of Example 5 are the same, except that the absolute pressure of Al2O3 pretreatment in step (1) is 0.1 MPa, and the resulting catalyst is denoted as Pt-NiSn / Al2O3-3 catalyst.

[0073] Example 8

[0074] The preparation steps and synthesis conditions of Example 5 are the same, except that: 0.26g of (1,5-cyclooctadiene) dimethylplatinum in step (2) is replaced with 0.41g of (1,5-cyclooctadiene) palladium dichloride in equal molar amounts, the fixed reaction temperature is increased to 70°C, the reaction time is shortened to 1h, and the resulting catalyst is called Pd-NiSn / Al2O3-1 catalyst.

[0075] Comparative Example 1

[0076] 50g of H-type Beta molecular sieve (SiO2 / Al2O3 = 25) was dried at 120℃ for 2h, and its water absorption rate was determined to be 120%. 1.90g of copper nitrate trihydrate, 1.82g of gallium nitrate, and 0.40g of platinum nitrate hexahydrate were dissolved in water to prepare 60g aqueous solutions of metal salts. The dried Beta molecular sieve support was sequentially immersed in aqueous solutions of Cu, Ga, and Pt, ensuring the impregnation solution completely entered the pores. After each equal-volume impregnation, the sample was dried at 120℃ for 2h and then calcined in a muffle furnace at 500℃ for 2h. After the sample cooled to room temperature, the next metal was impregnated. The final catalyst, Reference-1, was obtained.

[0077] Comparative Example 2

[0078] 50g of acidic alumina (Al₂O₃) was dried at 120℃ for 2h, and its water absorption rate was determined to be 45%. 3.71g of nickel nitrate hexahydrate, 1.19g of stannous chloride, and 0.40g of platinum nitrate hexahydrate were dissolved in water to prepare 60g aqueous solutions of metal salts. The dried acidic alumina support was sequentially immersed in aqueous solutions of Cu, Ga, and Pt, ensuring the impregnation solution just completely entered the pores. After each equal-volume impregnation, the sample was dried at 120℃ for 2h and then calcined in a muffle furnace at 500℃ for 2h. After the sample cooled to room temperature, the next metal was impregnated. The final catalyst, Reference-2, was obtained.

[0079] Comparative evaluation of catalysts in the examples and comparative examples

[0080] (1) Comparison of physical property parameters:

[0081] The metal component content, specific surface area, and pore volume of the catalysts in the examples and comparative examples are shown in Table 1:

[0082] Table 1. Catalyst product physical properties

[0083]

[0084]

[0085] As can be seen from Table 1, compared with the conventional equal-volume impregnation method for loading metal components, the catalyst prepared by the surface chemical immobilization method used in the examples has a larger specific surface area and pore volume, and can provide more accessible active sites for alkane isomerization reactions.

[0086] (2) Comparison of microscopic morphology:

[0087] The STEM characterization results of the catalysts in Example 1 and Comparative Example 1 are as follows: Figure 1 and Figure 2 As shown, Figure 1This is a STEM image of the Pt-CuGa / HBeta-1 catalyst prepared in Example 1 of this invention. Figure 2 This is a STEM image of the Reference-1 catalyst prepared in Comparative Example 1 provided by the present invention.

[0088] pass Figure 1 and Figure 2 It can be seen that, under the same metal composition and loading conditions, the catalyst prepared by the surface chemical immobilization method exhibits a more uniform distribution of metal components and a more uniform grain size. This is mainly because, during the catalyst preparation process using the surface chemical immobilization method, the support is dehydrated and dehydroxylated through vacuum high-temperature heat treatment. This completely desorbs the water existing in the pores of the support through physical adsorption, and simultaneously causes some of the weakly adsorbed hydroxyl groups on the support surface to undergo condensation and dehydration reactions, exposing more defect sites on the support surface that are conducive to the loading of metal components. During the surface chemical immobilization process, the metal components preferentially undergo strong chemical adsorption with the defect sites on the surface of the support pores, thus anchoring them to the support surface and making them less prone to migration and aggregation during subsequent heat treatment. Therefore, the catalyst prepared by the immobilization method provided by this invention has a more uniform dispersion of metal components and a more uniform grain size, allowing the metal components to provide more catalytically active surfaces, thereby improving the utilization efficiency of the metal components, especially the noble metal components.

[0089] (3) Catalytic performance test:

[0090] (3.1) Catalytic performance tests of the catalysts prepared in Examples 1-4 and Comparative Example 1:

[0091] The catalyst was evaluated using n-heptane as a raw material in a 20 mL small fixed-bed reactor. 10 mL of catalyst was loaded into the fixed-bed reactor, and the air in the pipeline was replaced by nitrogen purging for 30 min. The catalyst was reduced for 4 h at 2.0 MPa and 450 °C under a hydrogen atmosphere. The temperature was then lowered to 280 °C, and n-heptane and hydrogen were introduced to initiate the reaction. Reaction conditions: temperature 280 °C, pressure 2.0 MPa, space velocity 1.0 h⁻¹. -1 The hydrogen-to-oil molar ratio was 0.6, and samples were taken after 24 hours of reaction. The reaction period was 240 hours. The experimental results are shown in Table 2.

[0092] Table 2 Effects of n-Heptane Isomerization Reaction

[0093]

[0094]

[0095] As shown in Table 2, both the example and comparative catalysts exhibited good catalytic stability for n-heptane isomerization during the 240-hour evaluation. The Beta-based catalyst prepared by the surface chemical immobilization method showed higher n-heptane conversion and selectivity for isoalkanes, especially for bibranched isoalkanes. In the "metal-acid" bifunctional catalyst, the occurrence form and placement state of the metal center within the pores of the acidic support are the decisive factors in the catalytic synergistic effect mechanism of the two types of active centers. Compared with Comparative Example 1, the metal active component was loaded onto the acidic Beta-based catalyst using a conventional impregnation method. Compared to the surface of eta molecular sieves, the particle size of the metal components in the catalysts prepared by the surface chemical immobilization method in Examples 1-4 is significantly smaller than that of the catalysts prepared by the impregnation method. This reduces the clogging of the molecular sieve micropores by the metal components, better preserves the connectivity of the molecular sieve channels, and thus significantly reduces the probability of cracking reactions caused by pore blockage by the metal components, thereby improving the selectivity of isomerization reactions. The Pd-CuGa / HBeta-4 catalyst exhibits the optimal "metal-acid" catalytic isomerization synergy, and under the highest n-heptane conversion conditions, the selectivity of high-octane dibranched isoalkanes is as high as 26.0%.

[0096] (3.2) Catalytic performance tests of the catalysts prepared in Examples 5-8 and Comparative Example 2:

[0097] Using n-butane as a raw material, the catalyst was evaluated in a 20 mL small fixed-bed reactor. 10 mL of the prepared catalyst was packed into the fixed-bed reactor. After purging the pipeline with N2 for 30 min to replace the air, AlCl3 was added as a carrier gas for the first step of chlorination. The carrier gas flow rate was 20 mL / min, the chlorination temperature was 550 °C, and the chlorination time was 4 h. After the chlorination process, the gas was switched to high-purity N2 to purge the catalyst surface. AgNO3 solution was passed through the tail gas until no more white precipitate was formed. The temperature was lowered to 400 °C, and CCl4 was added as a carrier gas for the second step of supplementary chlorination. The carrier gas flow rate was 20 mL / min, and the chlorination time was 1 h. After the chlorination process, the reactor was purged with N2 until the tail gas no longer caused precipitation of AgNO3 solution, yielding the chlorinated catalyst. The temperature was lowered to 140 °C, and n-butane and hydrogen were introduced to start the reaction. The reaction conditions were: temperature 160 °C, pressure 3.0 MPa, and space velocity 1.0 h⁻¹. -1 The hydrogen-to-oil molar ratio was 0.08, and samples were taken after 24 hours of reaction, with a reaction cycle of 240 hours. The experimental results are shown in Table 3.

[0098] Table 3 Effects of n-Butane Isomerization Reaction

[0099]

[0100] As shown in Table 3, both the example and comparative catalysts exhibited good stability in catalytic n-butane isomerization during the 240-hour evaluation process. Compared with the conventional impregnation method used in Comparative Example 2 to load the metal active component onto the Al2O3 surface, the Al2O3-based catalyst prepared by the chemical surface immobilization method also showed higher n-butane conversion and isobutane selectivity in the n-butane isomerization reaction, which is also due to the uniformity and high dispersion of the metal active component.

[0101] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for the preparation of a catalyst for the isomerization of alkanes, characterized in that, The method comprises the following steps: a) heat-treating an acidic carrier under vacuum conditions to obtain a dehydrated and dehydroxylated treated acidic carrier; The acidic carrier is an acid-treated oxide carrier and / or an acidic molecular sieve; the temperature of the heat treatment is 200-600°C; the absolute pressure of the heat treatment is 0.001-0.1 MPa; and the time of the heat treatment is 2-24 h; b) immobilizing metal compounds onto the surface of the treated acidic carrier by a surface chemical method to obtain a catalyst precursor; The metal compounds comprise a first metal compound and a second metal compound, the first metal compound is a Pt source compound and / or a Pd source compound, and the second metal compound is one or more of a Cu source compound, a Ga source compound, a Ni source compound and a Sn source compound; The specific process of immobilizing metal compounds by the surface chemical method comprises: under oxygen-free and water-free conditions, immersing the treated acidic carrier into an organic solution of metal compounds to perform an immobilization reaction, and then heating and volatilizing the solvent to obtain a catalyst precursor; c) reducing the catalyst precursor in a hydrogen atmosphere to obtain a catalyst.

2. The production method according to claim 1, characterized by, The acid-treated oxide carrier is a product obtained by modifying an oxide carrier with an acid treatment reagent, the oxide carrier is one or more of SiO2, Al2O3, ZrO2, Nb2O5, La2O3 and CeO2, and the acid treatment reagent is one or more of phosphoric acid, hydrochloric acid, sulfuric acid, metatungstic acid and phosphomolybdic acid; The acidic molecular sieve is one or more of HZSM-5 molecular sieve, HBeta molecular sieve, HMOR molecular sieve, HY molecular sieve and SAPO-11 molecular sieve.

3. The production method according to claim 1, characterized by, In step b), the Pt source compound is one or more of trimethylcyclopentadienyl platinum, tetrakis(triphenylphosphine) platinum, tris(dibenzylideneacetone) platinum, dichlorobis(cyclopentadienyl) platinum and diphenyl(1,5-cyclooctadiene) platinum; The Pd source compound is one or more of bis(dibenzylideneacetone)palladium, (1,5-cyclooctadiene)palladium dichloride and tris(dibenzylideneacetone)dipalladium; The Cu source compound is one or more of hexafluoroacetylacetonatocopper, (ethylcyclopentadienyl)(triphenylphosphine)copper, chlorotris(triphenylphosphine)copper, bis(triphenylphosphine)borohydrido cuprous, bis(triphenylphosphine)copper nitrate and (1,10-phenanthroline)(trifluoromethyl)(triphenylphosphine)copper; The Ga source compound is one or more of gallium triflate, gallium acetylacetonate, gallium isopropyl alcohol, gallium tris(2,2,6,6-tetramethyl-3,5-heptanedioate) and gallium tris(2-methyl-3-hydroxy-4-pyrone); The Ni source compound is one or more of bis(cyclopentadiene)nickel, bis(pentamethylcyclopentadiene)nickel, di(ethylcyclopentadienyl)nickel, chloro(cyclopentadienyl)(triphenylphosphine)nickel, tetrakis(triphenylphosphine)nickel, bis(triphenylphosphine)nickel chloride, bis(triphenylphosphine)dicarbonylnickel, dichlorobis(triphenylphosphine)nickel, chlorobis(triphenylphosphine)benzene nickel and [1,2-bis(diphenylphosphino)ethane]nickel dichloride; The Sn source compound is one or more of tetra-n-butyl tin, dibutyl tin maleate, tri-n-butyl tin hydride, phenylacetylene tributyl tin, dibutyl tin dilaurate, tetraphenyl tin, hexaphenyl di-tin and tributyl tin acetate.

4. The production method according to claim 1, characterized by, In step c), the temperature of the reduction is 80-500 DEG C; the time of the reduction is 1-24 hours.

5. A catalyst for isomerization of an alkane, characterized in that, The catalyst is prepared according to the preparation method of any one of claims 1-4.

6. The catalyst of claim 5, wherein The first metal element corresponding to the first metal compound and the second metal element corresponding to the second metal compound are supported on the carrier of the catalyst, the first metal element accounts for 0.01-0.5 wt% of the total mass of the catalyst, and the second metal element accounts for 0.1-5 wt% of the total mass of the catalyst.

7. A process for isomerization of an alkane, characterized in that The process comprises the following steps: The alkane is subjected to isomerization in the presence of the catalyst of claim 5 or 6.

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