Iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalysts, their preparation methods and applications

Abstract

This invention relates to the field of catalysis technology, and discloses an iridium-molybdenum bimetallic titanium dioxide-modified molecular sieve catalyst, its preparation method, and its application. The catalyst of this invention uses titanium dioxide-modified ZSM-22 molecular sieve as a support, and iridium nanoparticles and molybdenum oxide clusters as bimetallic active components. The titanium dioxide particles in the support confine the iridium nanoparticles and molybdenum oxide clusters, which can reduce the amount of precious metals used while ensuring catalytic activity, thereby achieving low-cost catalyst preparation. When applied to the reaction of methyl palmitate hydrodeoxygenation-hydroisomerization to prepare hexadecane and its isomers, the catalyst exhibits high activity, high selectivity, high stability, and good product isomerization ability.

Description

Technical Field

[0001] This invention relates to the field of catalysis technology, and in particular to an iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] With the increasing depletion of global fossil resources, the development of technologies for converting renewable biomass resources into high-value-added fuels and chemicals has attracted much attention. Biomass, as the only renewable organic carbon source in nature, produces biomass oil through rapid pyrolysis, which, while possessing a high octane number, suffers from drawbacks such as a high oxygen content (20-40%), high acid value, high viscosity, and poor stability, making it unsuitable for direct use as fuel. Therefore, upgrading biomass and its platform molecules through methods such as hydrodeoxygenation (HDO) is a crucial step in improving its quality and utilization value.

[0003] The core of hydrotreating processes lies in the development of highly efficient supported metal catalysts. Traditional single-metal hydrogenation catalysts often face challenges such as harsh reaction conditions and insufficient selectivity for target products, making it difficult to meet the needs of large-scale applications. Research shows that developing bifunctional supported metal catalysts that can regulate both hydrogenation activity and C-O bond breaking / C-C bond isomerization selectivity is an effective way to overcome these bottlenecks. Such catalysts typically couple a hydrogenation-active metal (such as Pt, Pd, Ni, etc.) with a variable-valence transition metal oxide (ReO2). x WO x Transition metal-based catalysts are supported on supports with acidic sites (such as zeolite molecular sieves and alumina). Utilizing the synergistic effect of the acidity between the metal and the support, efficient hydrogenation conversion of oxygen-containing compounds is achieved under mild conditions. While transition metal-based catalysts are inexpensive, they exhibit low catalytic activity and poor selectivity; noble metal catalysts typically possess good reactivity and selectivity, but their stability is low, their cost is high, and they are difficult to prepare on a large scale.

[0004] Therefore, effectively reducing the loading of precious metals in bifunctional catalysts while maintaining excellent hydrodeoxygenation / hydroisomerization performance, and developing catalyst systems that combine low cost, high activity, high selectivity, and high stability are of great significance for achieving the efficient conversion of biomass platform methyl palmitate to high-quality fuels such as hexadecane / isohexadecane. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides an iridium-molybdenum bimetallic titanium dioxide-modified molecular sieve catalyst, its preparation method, and its applications. The catalyst uses titanium dioxide-modified ZSM-22 molecular sieve as a support, with iridium nanoparticles and molybdenum oxide clusters as the bimetallic active components. The titanium dioxide particles in the support confine the iridium nanoparticles and molybdenum oxide clusters, reducing the amount of precious metals required while ensuring catalytic activity, thus achieving low-cost catalyst preparation. When applied to the hydrodeoxygenation-hydroisomerization of methyl palmitate to prepare hexadecane and its isomers, the catalyst exhibits high activity, high selectivity, high stability, and good product isomerization ability.

[0006] The specific technical solution of this application includes: First, this invention provides an iridium-molybdenum bimetallic titanium dioxide-modified molecular sieve catalyst, comprising a ZSM-22 molecular sieve as a support, titanium dioxide particles deposited on the surface of the ZSM-22 molecular sieve via a deposition method, and iridium nanoparticles and molybdenum oxide clusters formed sequentially via a stepwise impregnation method. During the preparation process, the iridium nanoparticles preferentially enrich and anchor to the surface of the titanium dioxide particles due to the strong titanium-iridium interaction, while the molybdenum oxide clusters mainly adhere to the surface of the iridium nanoparticles.

[0007] The catalyst of this invention uses titanium oxide-modified ZSM-22 molecular sieve as a support, and iridium nanoparticles and molybdenum oxide clusters as bimetallic active components. By utilizing the titanium oxide particles in the support to confine the iridium nanoparticles and molybdenum oxide clusters, the amount of precious metals used can be reduced while ensuring catalytic activity, thus achieving low-cost catalyst preparation. This invention also reveals that applying the catalyst to the hydrodeoxygenation-hydroisomerization of methyl palmitate to prepare hexadecane and its isomers exhibits high activity, high selectivity, high stability, and good product isomerization ability.

[0008] The specific reasons are as follows: Firstly, the titanium oxide particles deposited on the surface of ZSM-22 molecular sieve effectively confine the iridium-molybdenum bimetallic compound, forming Ir-MoO. x The specific catalyst structure of TiO2 utilizes the noble metal Ir as a site for activating hydrogen gas, forming active hydrogen species through adsorption and dissociation; Ir-MoO x MoO at the interface xThe clusters (molybdenum oxide clusters) are responsible for adsorbing and activating methyl palmitate molecules. Under the reaction conditions, the active hydrogen at the interface preferentially attacks the carbon-oxygen bonds of the ester group, resulting in hydrogenolysis and hydrodeoxygenation reactions, converting the feedstock into n-hexadecane. Based on this, the product is further isomerized using acidic sites on the ZSM-22 molecular sieve and promptly desorbed from the catalyst surface, yielding n / isohexadecane. The above catalyst effectively inhibits further cracking of n / isohexadecane, ensuring that the liquid alkanes meet the low-temperature flowability requirements of biofuels. Ir-MoO confined on titanium oxide particles... x The synergistic effect between the two (provided that the molybdenum oxide clusters must be mainly attached to the surface of the iridium nanoparticles rather than directly dispersed on the surface of the ZSM-22 molecular sieve or titanium oxide particles) can improve the reaction activity and product selectivity, achieving highly efficient catalytic hydrodeoxygenation of methyl palmitate to hexadecane, with the proportion of hexadecane isomers ≥40 mol% and the carbon chain cleavage product selectivity less than 3 mol%. Furthermore, the effective confinement of the iridium-molybdenum bimetallic compound in the catalyst of this invention on the titanium oxide particles can inhibit the loss and aggregation of metal components, thus significantly improving the stability of the catalyst. Further, this invention also discovers that titanium oxide particles are formed on the surface of the ZSM-22 molecular sieve by selective deposition. The titanium oxide particles formed by this method are more uniform than those obtained by the general impregnation method, thus providing a unique confined environment for subsequent metal loading.

[0009] Furthermore, the main reason for choosing titanium oxide instead of other conventional oxides (such as cerium oxide) to modify ZSM-22 molecular sieve in this invention is that the active metal iridium and titanium oxide can form a stronger interaction (stronger than the interaction between iridium and ZSM-22 molecular sieve). Therefore, the iridium species after calcination (the component before reduction treatment is iridium oxide) will preferentially accumulate on the surface of titanium oxide rather than ZSM-22 molecular sieve. If it is replaced with metal oxides such as cerium oxide, the catalytic effect in hydrodeoxygenation and isomerization reactions will be significantly reduced.

[0010] In summary, this invention selects titanium oxide-modified ZSM-22 molecular sieve as a support. Compared with unmodified ordinary ZSM-22 molecular sieve and common acidic silica-alumina molecular sieves such as SAPO-11, ZSM-5, and Beta, the prepared iridium-molybdenum bimetallic catalyst has higher hydrodeoxygenation activity, as well as product selectivity and isomer ratio. Furthermore, the loading of the noble metal iridium on ZSM-22 molecular sieve is significantly lower than that on other supports.

[0011] Furthermore, the loading of titanium is 3-12 wt% (numerator is titanium content, denominator is the total amount of titanium oxide modified ZSM-22 molecular sieve), preferably 6-10 wt%, and most preferably 8 wt%; the loading of iridium is 0.1-4 wt% (numerator is iridium content, denominator is the total amount of iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst), preferably 0.1-0.3 wt%, and most preferably 0.2 wt%; the molar ratio of molybdenum to iridium is (0.6-1.8):1; preferably (0.8-1.2):1, and most preferably 1:1.

[0012] The reason why the loading of titanium and iridium and the molar ratio of iridium to molybdenum are limited to the above range in this invention is that: (1) if the titanium loading is too high, it will easily lead to the aggregation of titanium oxide particles (>10nm), which is not conducive to the uniform dispersion of iridium and molybdenum in the future; (2) the iridium loading needs to be controlled within a reasonable range. When the iridium loading is too low, although the particle size of iridium nanoparticles can be controlled to <1nm, molybdenum oxide is not easy to adhere to the surface of iridium particles, the synergistic effect of iridium-molybdenum bimetal is reduced, resulting in poor hydrogenation deoxygenation performance of the catalyst; while when the iridium loading is high, the particle size of iridium nanoparticles is >5nm, which is not conducive to the uniform dispersion of iridium and molybdenum in the future. The effective confinement of the catalyst is on the surface of titanium oxide (which will be dispersed in large quantities on the surface of ZSM-22 molecular sieve). Under high temperature reaction conditions, it is very easy to migrate and agglomerate (sinter), which will lead to a sharp reduction in the number of active sites, which is also unfavorable to the reaction and also increases the preparation cost of the catalyst; (3) If the molybdenum loading is too high, the molybdenum oxide cannot form clusters of <1nm; Excessive molybdenum will also cause the iridium nanoparticles to be over-covered, the catalyst's ability to activate hydrogen is insufficient, and it is also easy to introduce too many acidic sites, leading to an increase in by-products such as carbon-carbon bond breakage, which reduces the selectivity of the target product.

[0013] Furthermore, the titanium oxide particles have a particle size of 2-10 nm, the iridium nanoparticles have a particle size of 1-5 nm (preferably 1-3 nm), and the molybdenum oxide clusters have a size of <1 nm.

[0014] Furthermore, the precursor of the titanium oxide particles is TiCl3, the precursor of the iridium nanoparticles is chloroiridium acid, and the precursor of the molybdenum oxide clusters is ammonium molybdate.

[0015] This invention reveals that, compared to other iridium and molybdenum source precursors such as iridium nitrate, molybdenum nitrate, molybdenum chloride, and molybdenum acetate, the use of iridium chloroacid and ammonium molybdate results in stronger interactions between the iridium nanoparticles and molybdenum oxide, higher hexadecane yield, and better catalytic performance in the stepwise impregnation method. TiCl3 was chosen as the titanium salt in this invention because other titanium salts readily precipitate.

[0016] Secondly, this invention provides a method for preparing the above-mentioned iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst, which includes the following steps: 1) Add TiCl3 solution dropwise to the ZSM-22 molecular sieve dispersion, then add ammonia water and stir evenly to carry out hydrolysis reaction. After separation, washing, drying and calcination, titanium oxide modified ZSM-22 molecular sieve is obtained.

[0017] This invention utilizes the rapid hydrolysis of TiCl3 in ammonia water to prepare titanium oxide-modified ZSM-22 molecular sieves. Compared with the conventional impregnation method, this method yields more uniform titanium oxide particles, providing a unique confined environment for subsequent metal loading.

[0018] 2) The titanium oxide modified ZSM-22 molecular sieve was dispersed in an aqueous solution of chloroiridium acid, allowed to stand and age, and then separated and dried to obtain the iridium-loaded titanium oxide modified ZSM-22 molecular sieve.

[0019] 3) The iridium-loaded titanium dioxide modified ZSM-22 molecular sieve was dispersed in an ammoniacal molybdate aqueous solution, allowed to stand for aging, and then separated, dried, and calcined to obtain the iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst.

[0020] Preferably, step 1) specifically includes: dispersing ZSM-22 molecular sieve in water, ultrasonically dispersing, and stirring at room temperature; adding TiCl3 solution dropwise, then adding ammonia water, and continuing to stir to carry out the hydrolysis reaction; filtering, washing with water until neutral, drying, and calcining to obtain titanium oxide modified ZSM-22 molecular sieve.

[0021] More preferably, in step 1), the concentration of the ammonia solution is 1-6 mol / L; the molar ratio of the ammonia solution to TiCl3 is 1-6:1. Preferably, in step 2) and / or step 3): the static aging time is 10-20 hours; the drying temperature is 85-95°C, and the time is 10-20 hours; More preferably, in step 1), the roasting temperature is 400-700℃ and the time is 10-20h; in step 3), the roasting temperature is 450-600℃ and the time is 2-4h.

[0022] This invention reveals that the calcination temperature during catalyst preparation significantly affects the size of the active metal in the catalyst. In step 1), if the calcination temperature is too low, the chlorine in the precursor cannot be completely decomposed, affecting the catalytic performance; while if the calcination temperature is too high, the size of the titanium oxide particles will increase sharply, leading to a weakening of their metal confinement function. In step 3), the calcination temperature directly affects the interaction between the bimetals. An appropriate calcination temperature is beneficial for forming smaller and more uniformly distributed iridium-molybdenum active sites, thereby improving the activity and selectivity of hydrodeoxygenation.

[0023] Third, this invention provides the application of the above-mentioned iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst in the preparation of hexadecane and its isomers by the hydrogenation deoxygenation-hydroisomerization of methyl palmitate.

[0024] Preferably, the application includes the following steps: S1: The iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst is granulated and then subjected to reduction treatment.

[0025] S2: The reduced iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst is mixed with a reaction solution consisting of methyl palmitate and solvent, loaded into a reactor, and reacted in a hydrogen atmosphere. During the reaction, the iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst is used to catalyze the hydrogenation and deoxygenation of methyl palmitate and to inhibit the carbon-carbon bond breaking side reaction, so as to obtain a product with hexadecane and its isomers as the main components.

[0026] Preferably, during the reaction, the selectivity of hexadecane is ≥90 mol%, and the selectivity of hexadecane isomers ( i / n The proportion of isomers (to normal) is ≥40 mol, and the selectivity of carbon chain pyrolysis products is less than 3 mol.

[0027] Preferably, in S1, the reduction treatment includes: placing the iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst in a closed container, and passing H2 at a rate of 20-40 mL / min under normal pressure for reduction treatment. The temperature of the reduction treatment is 300-550ºC, and the time is 60-180 min.

[0028] Preferably, in step S2, the concentration of methyl palmitate in the reaction solution is 5-20 wt%. Preferably, in S2, the solvent includes one or more of methanol, cyclopentane, and dodecane; Preferably, in S2, the reaction conditions are: pressure 1-3 MPa, temperature 180-300℃, and stirring speed 300-600 r / min.

[0029] Compared with the prior art, the beneficial effects of the present invention are: (1) The catalyst of the present invention uses ZSM-22 molecular sieve as a support and uses the deposition method to modify the surface of the molecular sieve with titanium oxide nanoparticles to form a composite support with nano-confined function, which can provide a unique environment for the anchoring and loading of active metals (iridium and molybdenum).

[0030] (2) This invention uses a stepwise impregnation method to sequentially load iridium and molybdenum onto titanium oxide-modified molecular sieves. Utilizing the confinement function of titanium oxide, iridium nanoparticles are anchored onto the titanium oxide particles, further resulting in iridium-molybdenum interfacial active centers partially covered by molybdenum oxide clusters. This preparation method effectively reduces the noble metal loading of bimetallic catalysts while ensuring catalyst performance, resulting in significant economic benefits in catalyst preparation costs.

[0031] (3) This invention provides a method for preparing hexadecane and its isomers by catalyzing the hydrogenation deoxygenation-hydroisomerization of methyl palmitate using an iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst. This method has high atom economy, high selectivity for hexadecane (≥90%), high proportion of hexadecane isomers (≥40%), and few byproducts such as carbon-carbon bond breaking (selectivity of carbon chain cracking products is less than 3%). Attached Figure Description

[0032] Figure 1 X-ray diffraction (XRD) patterns of ZSM-22 molecular sieve and titanium oxide-modified ZSM-22 molecular sieve prepared in Example 1; Figure 2 The image shows a scanning transmission electron microscope (STEM) image of the titanium oxide-modified ZSM-22 molecular sieve prepared in Example 1 (the yellow circles in the image represent titanium oxide particles). Figure 3 The image shows a STEM image of the iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst prepared in Example 1 after hydrogen reduction (the yellow dashed circle represents titanium oxide particles, and the yellow solid circle represents iridium nanoparticles). Figure 4 The images show the STEM and EDX spectra of the iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst prepared in Example 1 after hydrogen reduction. Figure 5 The image shows a gas chromatogram of the product obtained by catalytic hydrogenation deoxygenation-hydroisomerization using the iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst prepared in Example 1. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to specific embodiments. The reactions in the following examples and comparative examples were all carried out in a batch reactor. These examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0034] First, an iridium-molybdenum bimetallic titanium dioxide-modified molecular sieve catalyst is disclosed, comprising a ZSM-22 molecular sieve as a support, titanium dioxide particles deposited on the surface of the ZSM-22 molecular sieve via a deposition method, and iridium nanoparticles and molybdenum oxide clusters formed sequentially via a stepwise impregnation method. During the preparation process, the iridium nanoparticles preferentially enrich and anchor to the surface of the titanium dioxide particles due to the strong titanium-iridium interaction, while the molybdenum oxide clusters mainly adhere to the surface of the iridium nanoparticles.

[0035] In some embodiments, the loading of titanium is 3-12 wt% (numerator is titanium content, denominator is the total amount of titanium oxide modified ZSM-22 molecular sieve), preferably 6-10 wt%, and most preferably 8 wt%; the loading of iridium is 0.1-4 wt% (numerator is iridium content, denominator is the total amount of iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst), preferably 0.1-0.3 wt%, and most preferably 0.2 wt%; the molar ratio of molybdenum to iridium is (0.6-1.8):1; preferably (0.8-1.2):1, and most preferably 1:1.

[0036] In some embodiments, the precursor of the titanium oxide particles is TiCl3, the precursor of the iridium nanoparticles is chloroiridium acid, and the precursor of the molybdenum oxide clusters is ammonium molybdate.

[0037] In some embodiments, the titanium oxide particles have a particle size of 2-10 nm, the iridium nanoparticles have a particle size of 1-5 nm, preferably 1-3 nm, and the molybdenum oxide clusters have a size of <1 nm.

[0038] Secondly, a method for preparing an iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst includes the following steps: 1) Add TiCl3 solution dropwise to the ZSM-22 molecular sieve dispersion, then add ammonia water and stir evenly to carry out hydrolysis reaction. After separation, washing, drying and calcination, titanium oxide modified ZSM-22 molecular sieve is obtained.

[0039] In some implementations, step 1) specifically includes: dispersing ZSM-22 molecular sieve in water, ultrasonically dispersing, and stirring at room temperature; adding TiCl3 solution dropwise, then adding ammonia water, and continuing to stir to carry out the hydrolysis reaction; filtering, washing with water until neutral, drying, and calcining to obtain titanium oxide modified ZSM-22 molecular sieve.

[0040] In some preferred embodiments, in step 1), the concentration of the ammonia water is 1-6 mol / L; the molar ratio of the ammonia water to TiCl3 is 1-6:1.

[0041] In some preferred embodiments, in step 1), the calcination temperature is 400-700°C and the time is 10-20 hours.

[0042] 2) The titanium oxide modified ZSM-22 molecular sieve was dispersed in an aqueous solution of chloroiridium acid, allowed to stand and age, and then separated and dried to obtain the iridium-loaded titanium oxide modified ZSM-22 molecular sieve.

[0043] In some preferred embodiments, in step 2), the aging time is 10-20 hours; the drying temperature is 85-95°C and the time is 10-20 hours.

[0044] 3) The iridium-loaded titanium dioxide modified ZSM-22 molecular sieve was dispersed in an ammoniacal molybdate aqueous solution, allowed to stand for aging, and then separated, dried, and calcined to obtain the iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst.

[0045] In some preferred embodiments, in step 3), the aging time is 10-20 hours; the drying temperature is 85-95°C and the time is 10-20 hours.

[0046] In some preferred embodiments, in step 3), the calcination temperature is 450-600°C and the time is 2-4 hours.

[0047] Third, the application of the above-mentioned iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst in the preparation of hexadecane and its isomers by the hydrogenation deoxygenation-hydroisomerization of methyl palmitate.

[0048] In some implementations, the application includes the following steps: S1: The iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst is granulated and then subjected to reduction treatment.

[0049] In some more preferred embodiments, in S1, the reduction treatment includes: placing the iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst in a closed container, and passing H2 at a rate of 20-40 mL / min under normal pressure for reduction treatment, with a temperature of 300-550ºC and a time of 60-180 min.

[0050] S2: The reduced iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst is mixed with a reaction solution consisting of methyl palmitate and solvent, loaded into a reactor, and reacted in a hydrogen atmosphere. During the reaction, the iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst is used to catalyze the hydrogenation and deoxygenation of methyl palmitate and to inhibit the carbon-carbon bond breaking side reaction, so as to obtain a product with hexadecane and its isomers as the main components.

[0051] In some preferred embodiments, during the reaction process, the selectivity of hexadecane is ≥90 mol%, the proportion of hexadecane isomers is ≥40 mol%, and the selectivity of carbon chain cleavage products is less than 3 mol.

[0052] In some more preferred embodiments, in S2, the concentration of methyl palmitate in the reaction solution is 5-20 wt%.

[0053] In some more preferred embodiments, in S2, the solvent includes one or more of methanol, cyclopentane, and dodecane.

[0054] In some more preferred embodiments, in S2, the reaction conditions are: pressure 1-3 MPa, temperature 180-300°C, and stirring speed 300-600 r / min.

[0055] Example 1 (Iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst, the molecular sieve is TiO2) x -ZSM-22 (45), iridium content approximately 0.2 wt%, iridium-molybdenum molar ratio 1:1) Preparation of TiO by deposition method x -ZSM-22 (45) molecular sieve ("(45)" indicates the silicon-aluminum molar ratio): 3g of ZSM-22 molecular sieve (45) was dispersed in 200mL of deionized water, sonicated for 30min, and then vigorously stirred at room temperature; 2.4g of titanium chloride solution (titanium content of 1wt%, the same in subsequent cases) was added dropwise, followed by rapid addition of 4.3g of ammonia solution (concentration of 2mol / L, the same in subsequent cases), and stirring was continued for 20min; after filtration and repeated washing with water until neutral, it was dried and calcined at 550℃ for 12h to prepare titanium oxide modified ZSM-22 molecular sieve (i.e., TiO2). x -ZSM-22 (45) molecular sieve), with a titanium loading of about 8wt% and a titanium oxide particle size of about 2-5nm. Figure 1 X-ray diffraction (XRD) pattern of titanium oxide modified ZSM-22 molecular sieve prepared in Example 1; Figure 2 The image shows a scanning transmission electron microscope (STEM) image of the titanium oxide-modified ZSM-22 molecular sieve prepared in Example 1.

[0056] Preparation of iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst by stepwise equal-volume impregnation method: 0.1967 g of chloroiridium acid precursor solution (iridium content 1 wt%, the same in subsequent cases) was weighed into a beaker and dispersed in 2 mL of deionized water, and shaken evenly; then 0.997 g of TiO2 was weighed... x-ZSM-22 (45) molecular sieve was added to a beaker, and the diluted precursor solution was slowly added dropwise. After adding 4 mL of water, the mixture was ultrasonically dispersed for 20 min and allowed to stand for aging at room temperature for 12 h. The sample was further dried overnight in a 90 °C oven and then ground into powder. 0.1 g of ammonium molybdate precursor solution (molybdenum content of 1 wt%, the same for subsequent cases) was weighed and dispersed in 2 mL of deionized water. The ground powder was added to the solution, and the above dissolution, standing, drying, and grinding steps were repeated. The sample powder was then calcined in a muffle furnace at 500 °C for 3 h to obtain Ir-MoO x @TiO x / ZSM-22 catalyst. In this catalyst, iridium nanoparticles are preferentially anchored on the surface of titanium oxide particles due to their strong interaction with titanium oxide particles, while molybdenum oxide clusters are attached to the surface of iridium nanoparticles. The iridium loading is approximately 0.2 wt%, the iridium-molybdenum molar ratio is approximately 1:1, the particle size of the iridium nanoparticles is approximately 1-3 μm, and the size of the molybdenum oxide clusters is <1 nm. Figure 3 and Figure 4 Image a is a STEM image of the iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst prepared in Example 1 after hydrogen reduction. Figure 4 The image bf is the EDX spectrum analysis of the iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst prepared in Example 1 after hydrogen reduction.

[0057] Example 2 (The difference from Example 1 is that the iridium content is approximately 0.1 wt%) Preparation of iridium-molybdenum bimetallic silicon-based catalyst by stepwise equal-volume impregnation method: 0.0988 g of chloroiridium acid precursor solution was weighed into a beaker and dispersed in 2 mL of deionized water, and shaken evenly; then 0.997 g of TiO2 was weighed... x -ZSM-22 (45) molecular sieve (same as in Example 1) was added to a beaker, and the diluted precursor solution was slowly added dropwise. After adding 4 mL of water, it was ultrasonically dispersed for 20 min and aged at room temperature for 12 h. The sample was further dried overnight in a 90 °C oven and then ground into powder. 0.05 g of ammonium molybdate precursor solution was weighed and dispersed in 2 mL of deionized water. The ground powder was added to the solution, and the above dissolution, standing, drying, and grinding steps were repeated. Then the sample was calcined in a muffle furnace at 500 °C for 3 h to obtain Ir-MoO x @TiO x / ZSM-22 catalyst. In this catalyst, iridium nanoparticles are preferentially anchored on the surface of titanium oxide particles due to their strong interaction with the titanium oxide particles, while molybdenum oxide clusters are attached to the surface of the iridium nanoparticles; the iridium loading is approximately 0.1 wt%, and the iridium-molybdenum molar ratio is approximately 1:1.

[0058] Example 3 (The difference from Example 1 is that the iridium content is approximately 2 wt%) Preparation of iridium-molybdenum bimetallic silicon-based catalyst by stepwise equal-volume impregnation method: 1.966 g of chloroiridium acid precursor solution was weighed into a beaker and dispersed in 2 mL of deionized water, and shaken evenly; then 0.97 g of TiO2 was weighed... x -ZSM-22 (45) molecular sieve (same as in Example 1) was added to a beaker, and the prepared precursor solution was slowly added dropwise. After adding 4 mL of water, it was ultrasonically dispersed for 20 min and aged at room temperature for 12 h. The sample was further dried overnight in a 90 °C oven and then ground into powder. 0.9983 g of ammonium molybdate precursor solution was weighed and dispersed in 2 mL of deionized water. The ground powder was added to the solution, and the above dissolution, standing, drying, and grinding steps were repeated. Then, the sample powder was calcined in a muffle furnace at 500 °C for 3 h to obtain Ir-MoO x @TiO x The / ZSM-22 catalyst has an iridium loading of approximately 2 wt% and an iridium-molybdenum molar ratio of approximately 1:1.

[0059] Example 4 (The difference from Example 3 is that TiO2) x -ZSM-22(45) contains approximately 10 wt% titanium and approximately 0.2 wt% iridium, with an iridium-molybdenum molar ratio of approximately 1:1. Preparation of TiO by deposition method x -ZSM-22 (45) molecular sieve (titanium content approximately 10wt%): 3g ZSM-22 molecular sieve was dispersed in 200mL deionized water, sonicated for 30min, and then vigorously stirred at room temperature; 3g titanium chloride solution was added dropwise, followed by rapid addition of 5.35g ammonia solution, and stirring continued for 20min; after filtration and repeated washing with water until neutral, the solution was dried and calcined at 550℃ for 12h to prepare titanium oxide modified ZSM-22 molecular sieve (i.e., TiO2). x -ZSM-22(45)), with a titanium loading of about 10wt% and a titanium oxide particle size of about 2-5nm.

[0060] Preparation of iridium-molybdenum bimetallic silicon-based catalyst by stepwise equal-volume impregnation method: 0.1967 g of chloroiridium acid precursor solution was weighed into a beaker and dispersed in 2 mL of deionized water, and shaken evenly; then 0.997 g of TiO2 was weighed... x -ZSM-22 (45) molecular sieve (titanium content approximately 10wt%) was added to a beaker, and the prepared precursor solution was slowly added dropwise. After adding 4mL of water, the mixture was ultrasonically dispersed for 20min and aged at room temperature for 12h. The sample was further dried overnight in a 90℃ oven and then ground into powder. 0.1g of ammonium molybdate precursor was weighed and dispersed in 2mL of deionized water. The ground powder was added to the solution, and the above steps of dissolution, standing, drying, and grinding were repeated. Subsequently, the sample powder was calcined in a muffle furnace at 500℃ for 3h to obtain Ir-MoO. x @TiOx / ZSM-22 catalyst. In this catalyst, iridium nanoparticles are preferentially anchored on the surface of titanium oxide particles due to their strong interaction with the titanium oxide particles, while molybdenum oxide clusters are attached to the surface of the iridium nanoparticles; the iridium loading is approximately 0.2 wt%, and the iridium-molybdenum molar ratio is approximately 1:1.

[0061] Example 5 (The difference from Example 1 is that the iridium-molybdenum molar ratio is approximately 1:1.5) Preparation of iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst by stepwise equal-volume impregnation method: 0.1967 g of chloroiridium acid precursor solution was weighed into 2 mL of deionized water and dispersed, and shaken evenly; then 0.997 g of TiO2 was weighed... x -ZSM-22 (45) molecular sieve was added to a beaker, and the diluted precursor solution was slowly added dropwise. After adding 4 ml of water, the mixture was ultrasonically dispersed for 20 min and aged at room temperature for 12 h. The sample was further dried overnight in a 90℃ oven and then ground into powder. 0.15 g of ammonium molybdate precursor solution was weighed and dispersed in 2 ml of deionized water. The ground powder was added to the solution, and the above dissolution, settling, drying, and grinding steps were repeated. The sample powder was then calcined in a muffle furnace at 500℃ for 3 h to obtain Ir-MoO x @TiO x / ZSM-22 catalyst. In this catalyst, iridium nanoparticles are preferentially anchored on the surface of titanium oxide particles due to their strong interaction with the titanium oxide particles, while molybdenum oxide clusters are attached to the surface of the iridium nanoparticles; the iridium loading is approximately 0.2 wt%, and the iridium-molybdenum molar ratio is approximately 1:1.5.

[0062] Comparative Example 1 (the difference from Example 1 is that the iridium content is about 0.05 wt%, and the iridium-molybdenum molar ratio is about 1:1) Preparation of iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst by stepwise equal-volume impregnation method: 0.05 g of chloroiridium acid precursor solution was weighed into 2 mL of deionized water and shaken evenly; then 0.9993 g of TiO2 was weighed... x -ZSM-22 (45) molecular sieve was added to a beaker, and the prepared precursor solution was slowly added dropwise. After adding 4 mL of water, the mixture was ultrasonically dispersed for 20 min and allowed to stand for aging at room temperature for 12 h. The sample was further dried overnight in a 90 °C oven and then ground into powder. 0.025 g of ammonium molybdate precursor solution was weighed and dispersed in 2 mL of deionized water. The ground powder was added to the solution, and the above dissolution, standing, drying, and grinding steps were repeated. Subsequently, the sample powder was calcined in a muffle furnace at 500 °C for 3 h to obtain Ir-MoO x @TiO x / ZSM-22 catalyst. Iridium loading is approximately 0.05 wt%, and the iridium-molybdenum molar ratio is approximately 1:1.

[0063] Comparative Example 2 (The difference from Example 1 is that the iridium-molybdenum molar ratio is approximately 1:0, which is a single metal catalyst) Preparation of iridium monometallic titanium oxide modified molecular sieve catalyst by equal volume impregnation method: 0.1967 g of chloroiridium acid precursor solution was weighed into a beaker and dispersed in 2 mL of deionized water, and shaken evenly; then 0.9993 g of TiO2 was weighed... x -ZSM-22 (45) molecular sieve was added to a beaker, and the prepared precursor solution was slowly added dropwise. After adding 4 mL of water, the mixture was ultrasonically dispersed for 20 min and aged at room temperature for 12 h. The sample was then further dried in a 90 °C oven overnight and then ground into powder. Subsequently, the sample powder was calcined in a muffle furnace at 500 °C for 3 h to obtain Ir@TiO x / ZSM-22 catalyst, with an iridium loading of approximately 0.2 wt%.

[0064] Comparative Example 3 (The difference from Example 1 is that the carrier is ZSM-22 (45) without titanium oxide modification) Preparation of Ir-MoO2 bimetallic titanium dioxide modified molecular sieve catalyst by stepwise equal-volume impregnation method: 0.1967 g of chloroiridium acid precursor solution was weighed into a beaker and dispersed in 2 mL of deionized water and shaken evenly; then 0.9993 g of ZSM-22 (45) molecular sieve was weighed and added to the beaker, the prepared precursor solution was slowly added dropwise, 4 mL of water was added, and ultrasonic dispersion was performed for 20 min. The sample was then aged at room temperature for 12 h. The sample was further dried overnight in a 90 °C oven and then ground into powder. 0.1 g of ammonium molybdate precursor solution was weighed and dispersed in 2 mL of deionized water. The ground powder was added to the solution, and the above steps of dissolution, standing, drying, and grinding were repeated. The sample powder was then calcined in a muffle furnace at 500 °C for 3 h to obtain Ir-MoO2. x / The ZSM-22 catalyst has an iridium loading of approximately 0.2 wt% and an iridium-molybdenum molar ratio of approximately 1:1.

[0065] Comparative Example 4 (the difference from Comparative Example 3 is that the vector is Beta (13)) Preparation of iridium-molybdenum bimetallic catalyst: The molecular sieve ZSM-22 (45) in Comparative Example 3 was replaced with Beta (13), and the other conditions were the same as in Comparative Example 3.

[0066] Comparative Example 5 (the difference from Comparative Example 3 is that the carrier is ZSM-5 (50)) Preparation of iridium-molybdenum bimetallic catalyst: The molecular sieve ZSM-22 (45) in Comparative Example 3 was replaced with ZSM-5 (50), and the other conditions were the same as in Comparative Example 3.

[0067] Comparative Example 6 (The difference from Comparative Example 3 is that the carrier is SAPO-11) Preparation of iridium-molybdenum bimetallic catalyst: The molecular sieve ZSM-22 (45) in Comparative Example 3 was replaced with SAPO-11, and the other conditions were the same as those in Comparative Example 3.

[0068] Comparative Example 7 (The difference from Example 1 is that the second roasting temperature is 350°C) Preparation of iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst: The second calcination temperature in Example 1 was replaced from 500℃ to 350℃, and other conditions were the same as in Example 1.

[0069] Comparative Example 8 (The difference from Example 1 is that the iridium source is iridium nitrate) Preparation of iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst: The chloroiridium acid precursor solution in Example 1 was replaced with iridium nitrate precursor solution (iridium content 1wt%), and other conditions were the same as in Example 1.

[0070] Comparative Example 9 (The difference from Example 1 is that the molybdenum source is phosphomolybdic acid) Preparation of iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst: The ammonium molybdate precursor solution in Example 1 was replaced with a phosphomolybdic acid precursor solution (molybdenum content was 1 wt%), and other conditions were the same as in Example 1.

[0071] Comparative Example 10 (the difference from Example 1 is that: TiO2) x The titanium loading in ZSM-22 (45) molecular sieve is approximately 15 wt%. Preparation of TiO by deposition method x -ZSM-22 (45) molecular sieve: 3g of ZSM-22 molecular sieve was dispersed in 200mL of deionized water, sonicated for 30min, and then stirred vigorously at room temperature; 4.5g of titanium chloride solution was added dropwise, followed by 5.7g of ammonia solution, and stirring was continued for 20min; after filtration and repeated washing with water until neutral, the solution was dried and then calcined at 550℃ for 12h to prepare titanium oxide modified ZSM-22 molecular sieve with a titanium loading of about 15wt%.

[0072] Preparation of iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst: The TiO2 catalyst from Example 1 was prepared... x -ZSM-22 (45) molecular sieve (Ti content approximately 8 wt%) was replaced with 15% TiO2. x -ZSM-22 (45) (Ti content approximately 15wt%), other conditions are the same as in Example 1.

[0073] Comparative Example 11 (The difference from Example 1 is that the active metal molybdenum is replaced with tungsten, the iridium content is about 0.2 wt%, and the iridium-tungsten molar ratio is about 1:1) Preparation of iridium-tungsten bimetallic molecular sieve composite supported catalyst by stepwise equal-volume impregnation method: 0.197 g of chloroiridium acid precursor solution was weighed into a beaker and dispersed in 2 mL of deionized water, and shaken evenly; then 0.996 g of TiO2 was weighed... x -ZSM-22 (45) molecular sieve was added to a beaker, and the prepared precursor solution was slowly added dropwise. After adding 4 mL of water, it was ultrasonically dispersed for 20 min and aged at room temperature for 12 h. The sample was further dried in a 90℃ oven overnight and then ground into powder. 0.256 g of ammonium metatungstate precursor solution (tungsten content of 1 wt%) was weighed and dispersed in 2 mL of deionized water. The ground powder was added to the solution, and the above steps of dissolving, settling, drying, and grinding were repeated. Then the sample powder was calcined in a muffle furnace at 500℃ for 3 h to obtain Ir-WO x @TiO x The / ZSM-22 catalyst has an iridium loading of approximately 0.2 wt% and an iridium-tungsten molar ratio of approximately 1:1.

[0074] Comparative Example 12 (The difference from Example 1 is that the active metal molybdenum is replaced with rhenium, the iridium content is about 0.2 wt%, and the iridium-rhenium molar ratio is about 1:1) Preparation of iridium-rhenium bimetallic molecular sieve composite supported catalyst by stepwise equal-volume impregnation method: 0.197 g of chloroiridium acid precursor solution was weighed into 2 mL of deionized water and dispersed, then shaken evenly; subsequently, 0.996 g of TiO2 was weighed... x -ZSM-22 (45) molecular sieve was added to a beaker, and the prepared precursor solution was slowly added dropwise. After adding 4 mL of water, it was ultrasonically dispersed for 20 min and aged at room temperature for 12 h. The sample was further dried in a 90℃ oven overnight and then ground into powder. 0.278 g of ammonium perrhenate precursor solution (rhenium content of 1 wt%) was weighed and dispersed in 2 mL of deionized water. The ground powder was added to the solution, and the above steps of dissolving, settling, drying, and grinding were repeated. Then the sample powder was calcined in a muffle furnace at 500℃ for 3 h to obtain Ir-ReO. x @TiO x The / ZSM-22 catalyst has an iridium loading of approximately 0.2 wt% and an iridium-rhenium molar ratio of approximately 1:1.

[0075] Comparative Example 13 (the difference from Example 1 is that the iridium-molybdenum molar ratio is approximately 1:0.5) In a stepwise equal-volume impregnation method, 0.1967 g of chloroiridium acid precursor solution was weighed and dispersed in 2 mL of deionized water, and shaken thoroughly. Then, 0.997 g of TiO₂ was weighed... x-ZSM-22 (45) molecular sieve was added to a beaker, and the prepared precursor solution was slowly added dropwise. After adding 4 mL of water, the mixture was ultrasonically dispersed for 10-30 min and aged at room temperature for 12 h. The sample was further dried overnight in a 90℃ oven and then ground into powder. 0.05 g of ammonium molybdate precursor solution was weighed and dispersed in 2 mL of deionized water. The ground powder was added to the solution, and the above steps were repeated. The sample powder was then calcined in a muffle furnace at 500℃ for 3 h to obtain Ir-MoO x @TiO x The / ZSM-22 catalyst has an iridium loading of approximately 0.2 wt% and an iridium-molybdenum molar ratio of approximately 1:0.5.

[0076] Comparative Example 14 (The difference from Example 1 is that the iridium-molybdenum molar ratio is approximately 1:2) Preparation of iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst by stepwise equal-volume impregnation method: 0.197 g of chloroiridium acid precursor solution was weighed into a beaker and dispersed in 2 mL of deionized water, and shaken evenly; then 0.997 g of TiO2 was weighed... x -ZSM-22 (45) molecular sieve was added to a beaker, and the prepared precursor solution was slowly added dropwise. After adding 4 mL of water, the mixture was ultrasonically dispersed for 10-30 min and aged at room temperature for 12 h. The sample was further dried overnight in a 90℃ oven and then ground into powder. 0.2 g of ammonium molybdate precursor solution was weighed and dispersed in 2 mL of deionized water. The ground powder was added to the solution, and the above steps were repeated. Subsequently, the sample powder was calcined in a muffle furnace at 500℃ for 3 h to obtain Ir-MoO x @TiO x The / ZSM-22 catalyst has an iridium loading of approximately 0.2 wt% and an iridium-molybdenum molar ratio of approximately 1:2.

[0077] Comparative Example 15 (the difference from Example 1 is that TiO2 was prepared by deposition method) x -ZSM-22 (45) was roasted at 800℃ during the process. Preparation of iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalysts: TiO x -ZSM-22 (45) was calcined at 800℃ for 12h to obtain high-temperature calcined titanium oxide modified ZSM-22 molecular sieve.

[0078] The TiO in Example 1 x -ZSM-22 (45) molecular sieve (deposition method, calcination at 550℃, titanium loading 8wt%) replaced with TiO x -ZSM-22 (45) (deposition method, calcination at 800°C, titanium loading of 8wt%), other conditions are the same as in Example 1.

[0079] Comparative Example 16 (the difference from Example 1 is that: TiO2) x -ZSM-22 (45) was prepared by impregnation method) TiO x Preparation of ZSM-22 (45) (impregnation): 3g of ZSM-22 (45) molecular sieve was dispersed in 200mL of deionized water, sonicated for 30min, and then vigorously stirred at room temperature to form a stable suspension; then 2.4g of titanium trichloride solution (titanium content of 1wt%) was slowly added dropwise, and the mixture was stirred vigorously for 30min; the mixture was placed in a water bath and slowly evaporated to near dryness, placed indoors for 12h of static aging, and then further placed in a 90℃ oven for overnight drying; the dried sample was calcined at high temperature for 3h to decompose titanium trichloride into titanium oxide, and finally titanium oxide modified ZSM-22 molecular sieve prepared by impregnation method was obtained with a titanium loading of about 8wt%.

[0080] The TiO in Example 1 x -ZSM-22 (45) molecular sieve (deposition method, calcination at 550℃, titanium loading of 8%) was replaced with TiO2. x -ZSM-22 (45) (impregnation method, firing at 550°C, titanium loading of 8%), other conditions are the same as in Example 1.

[0081] Comparative Example 17 (the difference from Example 1 is that TiO₂ is used) x -ZSM-22(45) is replaced with CeO x -ZSM-22(45)) CeO x Preparation of ZSM-22 (45) (cerium loading of 8 wt%): 3 g of ZSM-22 molecular sieve (45) was dispersed in 200 mL of deionized water, sonicated for 30 min, and then stirred vigorously at room temperature; 2.4 g of cerium nitrate (cerium content 1 wt%) solution was added dropwise, followed by the rapid addition of 4.3 g of ammonia solution, and stirring was continued for 20 min; after filtration and repeated washing with water until neutral, the solution was dried and then calcined at 550 °C for 12 h to prepare cerium oxide modified ZSM-22 molecular sieve (i.e., CeO2). x -ZSM-22(45)).

[0082] Replace the titanium oxide-modified ZSM-22 molecular sieve with cerium oxide-modified ZSM-22 molecular sieve, and keep the other conditions the same as in Example 1.

[0083] Comparative Example 18 (The difference from Example 1 is that the iridium-molybdenum molar ratio is approximately 0:1, which is a single metal catalyst) Preparation of molybdenum monometallic titanium oxide modified molecular sieve catalyst by equal volume impregnation method: 0.1 g of ammonium molybdate precursor solution was weighed into a beaker and dispersed in 2 mL of deionized water, and shaken evenly; then 0.9993 g of TiO2 was weighed... x-ZSM-22 (45) molecular sieve was added to a beaker, and the prepared ammonium molybdate precursor solution was slowly added dropwise. After adding 4 mL of water, the mixture was ultrasonically dispersed for 20 min and aged at room temperature for 12 h. The sample was then further dried in a 90 °C oven overnight and then ground into powder. Subsequently, the ground sample powder was calcined in a muffle furnace at 500 °C for 3 h to obtain Mo@TiO x / ZSM-22 catalyst.

[0084] Performance Comparison The catalysts prepared in the above examples and comparative examples were subjected to online reduction and catalytic performance evaluation, as follows: 0.3 g of catalyst was weighed and placed in a glass quartz tube, and H2 was introduced at 30 mL / min under normal pressure for reduction at 350 °C for 1 h. After reduction, 0.15 g of the reduced catalyst, 8.5 g of dodecane (solvent), and 1.5 g of methyl palmitate (reactant) were weighed and placed in a glass liner. A high-temperature rotor was added, and then the glass liner was placed in a batch reactor. Hydrogen gas was introduced to replace the air in the reactor three times, and after sealing, 3 MPa of hydrogen gas was introduced. The reactor was then placed on a magnetic stirrer at a speed of 500 r / min for 3 h at a temperature of 280 °C, and the concentration of methyl palmitate was 15 wt%. After condensation and gas-liquid separation, the reaction products were analyzed by gas chromatography, and the conversion rate of methyl palmitate, hexadecane selectivity, and isomerization rate were calculated. The results are as follows: Figure 5 As shown in Table 1.

[0085] Table 1: Catalytic performance data of methyl palmitate hydrodeoxygenation to hexadecane

[0086] A comparison of the data in Table 1 shows that: As demonstrated in Example 1 and Comparative Example 2, iridium alone cannot efficiently catalyze the directional conversion of methyl palmitate; the introduction of molybdenum species can significantly improve catalytic performance, which is closely related to the iridium-molybdenum bimetallic interface formed on the molecular sieve. Similarly, as demonstrated in Comparative Example 18, molybdenum alone cannot efficiently catalyze the directional conversion of methyl palmitate.

[0087] As shown in Example 1 and Comparative Example 3, the methyl palmitate conversion rate of the ZSM-22 molecular sieve in Comparative Example 3 was only 5.3% without titanium dioxide modification, indicating that a highly efficient iridium-molybdenum bimetallic active interface could not be formed on the unmodified ZSM-22 molecular sieve. This is mainly because the molecular sieve has a large specific surface area, and with a low iridium loading, molybdenum has difficulty forming a strong interaction with iridium, resulting in iridium and molybdenum being dispersed separately on the molecular sieve surface. When the molecular sieve surface is modified with titanium dioxide, the titanium dioxide particles provide a unique confined environment, and the strong interaction between iridium and titanium dioxide promotes iridium to preferentially anchor on the titanium dioxide surface, which is beneficial for the subsequent formation of an iridium-molybdenum bimetallic interface with molybdenum.

[0088] As can be seen from Example 1 and Comparative Example 1, when the iridium loading is further reduced to 0.05 wt%, the catalyst activity will decrease significantly. This is mainly because the molybdenum oxide cannot effectively cover the surface of the iridium particles. Compared with Examples 2 and 3, when the iridium loading is reduced, the catalytic performance such as conversion rate decreases. This is because the iridium nanoparticles cannot be fully dispersed, reducing the active sites. When the iridium loading is increased, the catalytic performance such as methyl palmitate conversion rate decreases. This is mainly because the aggregation of iridium nanoparticles reduces the active sites. Therefore, the iridium content is preferably 0.2 wt%.

[0089] Comparative Examples 4-6 compared the effects of different acidic molecular sieves, such as Beta, ZSM-5, and SAPO-11, on catalyst performance. The results showed that, under the same iridium loading, the methyl palmitate conversion, hexadecane selectivity, and isomerization rate of the investigated catalysts were significantly lower than those using TiO2. x -ZSM-22 (45) is used as the support for the catalyst. Furthermore, when a strongly acidic Beta molecular sieve is used as the support, the number of small molecule alkanes with broken carbon-carbon bonds on the catalyst increases significantly, indicating that excessively strong catalyst acidity is not conducive to the formation of the target product, hexadecane. Using TiO2... x -ZSM-22 (45) can meet the requirements of high conversion rate and high selectivity. At the same time, the catalyst also has a certain degree of isomerization ability, which is closely related to the unique molecular sieve composite support that confines the metal.

[0090] As can be seen from Example 1 and Comparative Example 7, Comparative Example 7 reduced the calcination temperature, and the yield decreased from 83.5% to 25.6%. The lower calcination temperature caused the precursor to not decompose completely, and the residual chloride ions would poison the catalyst, resulting in a significant decrease in both conversion rate and isomerization rate.

[0091] As shown in Example 1 and Comparative Example 8, when the iridium precursor was replaced with iridium nitrate, the conversion rate, selectivity, and isomerization rate all decreased to some extent. The likely reason is that the iridium nanoparticles obtained using iridium nitrate as a precursor were unevenly distributed, leading to a weakened interaction between iridium and molybdenum, which is detrimental to the reaction. Similarly, as shown in Example 1 and Comparative Example 9, when the molybdenum precursor was replaced with molybdenum phosphate, the catalytic performance also decreased significantly. This may be because the molybdenum oxide clusters produced by the decomposition of molybdenum phosphate cannot effectively interact with iridium, resulting in decreased catalytic activity.

[0092] Through Example 1 and Comparative Examples 11-12, when the transition metal molybdenum was replaced with tungsten and rhenium respectively; the performance of rhenium was similar to that of molybdenum, but rhenium was prone to causing further cracking of the reactants. In addition, the high cost of rhenium did not meet the requirements of economic efficiency and large-scale production; while the catalytic performance of tungsten was lower than that of molybdenum.

[0093] The comparison of Examples 1, 13, and 14 shows that the molar ratio of molybdenum to iridium has a significant impact on catalyst performance. As the molar ratio increases from 0.5:1 to 2:1, the catalyst performance initially increases and then decreases. When the relative molybdenum content is too low, an iridium-molybdenum interface cannot be formed, weakening the bimetallic synergistic effect; conversely, when the relative molybdenum content is too high, it excessively covers the iridium nanoparticles, leading to insufficient catalyst activation and hydrogenation capacity. Furthermore, the introduction of excessive acidic sites also increases byproducts. Therefore, a molybdenum-iridium molar ratio of 1:1 results in the optimal bimetallic synergistic performance.

[0094] The comparison between Example 1 and Comparative Examples 10 and 15 shows that titanium dioxide on the ZSM-22 molecular sieve also has a significant impact on catalyst performance. Excessive titanium dioxide content (Comparative Example 10) and excessively high calcination temperature (Comparative Example 15) can lead to the aggregation of iridium nanoparticles, weakening the synergistic effect of the bimetallic compounds and thus affecting catalyst performance.

[0095] A comparison of Example 1 with Comparative Examples 16 and 17 shows that, compared to the deposition method, the catalyst prepared by the impregnation method also leads to a decrease in catalytic performance. The impregnation method cannot achieve uniform dispersion of titanium oxide particles on the surface of the ZSM-22 molecular sieve, resulting in the agglomeration of the noble metal iridium, which weakens the synergistic effect of the bimetallic catalyst and is therefore detrimental to the reaction. Replacing the titanium oxide modified with cerium oxide in the ZSM-22 molecular sieve also results in a decrease in catalytic performance, which is related to the basicity of cerium oxide, leading to a reduction in catalyst activity and isomerization ability. Therefore, appropriate titanium oxide content and calcination temperature are beneficial for improving catalytic performance.

[0096] In summary, the catalyst prepared in Example 1, with an iridium loading of approximately 0.2 wt% and a molar ratio of 1:1 for molybdenum to iridium, exhibits the best catalytic effect.

[0097] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of this invention should be considered within the scope of protection of this invention.

Claims

1. An iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst, characterized in that: include: ZSM-22 molecular sieve, First, titanium dioxide particles are deposited on the surface of ZSM-22 molecular sieve using a deposition method. Then, iridium nanoparticles and molybdenum oxide clusters were formed sequentially by a stepwise impregnation method; The iridium nanoparticles preferentially anchor to the surface of the titanium oxide particles due to their strong interaction with the titanium oxide particles, and the molybdenum oxide clusters are attached to the surface of the iridium nanoparticles; wherein: The precursor of the titanium oxide particles is TiCl3, the precursor of the iridium nanoparticles is chloroiridium acid, and the precursor of the molybdenum oxide clusters is ammonium molybdate.

2. The iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst as described in claim 1, characterized in that: The loading of titanium is 3-12 wt%; the loading of iridium is 0.1-4 wt%; the molar ratio of molybdenum to iridium is (0.6-1.8):1; the particle size of the titanium oxide particles is 2-10 nm; the particle size of the iridium nanoparticles is 1-5 nm; and the size of the molybdenum oxide clusters is <1 nm.

3. A method for preparing the iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst as described in claim 1 or 2, characterized in that: Includes the following steps: 1) Add TiCl3 solution dropwise to ZSM-22 molecular sieve dispersion, then add ammonia water and stir evenly to carry out hydrolysis reaction. After separation, washing, drying and calcination, titanium oxide modified ZSM-22 molecular sieve is obtained. 2) The titanium oxide modified ZSM-22 molecular sieve was dispersed in an aqueous solution of chloroiridium acid, allowed to stand and age, and then separated and dried to obtain iridium-loaded titanium oxide modified ZSM-22 molecular sieve; 3) The iridium-loaded titanium oxide modified ZSM-22 molecular sieve was dispersed in an ammoniacal molybdate aqueous solution, allowed to stand for aging, separated, dried, and calcined to obtain an iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst.

4. The preparation method according to claim 3, characterized in that: Step 1) specifically includes: dispersing ZSM-22 molecular sieve in water, ultrasonically dispersing, stirring at room temperature; adding TiCl3 solution dropwise, then adding ammonia water, and continuing stirring to carry out the hydrolysis reaction; filtering, washing with water until neutral, drying, and calcining to obtain titanium oxide modified ZSM-22 molecular sieve.

5. The preparation method according to claim 3 or 4, characterized in that: In step 1), The concentration of the ammonia solution is 1-6 mol / L; The molar ratio of ammonia to TiCl3 is 1-6:1; The roasting temperature is 400-700℃ and the time is 10-20h.

6. The preparation method according to claim 3, characterized in that: In step 2) and / or step 3): the static aging time is 10-20 hours; the drying temperature is 85-95°C and the time is 10-20 hours; In step 3): the roasting temperature is 450-600℃ and the time is 2-4h.

7. The application of the iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst as described in claim 1 or 2, or the iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst obtained by the preparation method described in any one of claims 3-6, in the preparation of hexadecane and its isomers by the hydrodeoxygenation-hydroisomerization of methyl palmitate.

8. The application as described in claim 7, characterized in that: Includes the following steps: S1: The iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst is granulated and then subjected to reduction treatment; S2: The reduced iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst is mixed with a reaction solution consisting of methyl palmitate and solvent, loaded into a reactor, and reacted in a hydrogen atmosphere. During the reaction, the iridium-molybdenum bimetallic titanium dioxide modified molecular sieve catalyst is used to catalyze the hydrogenation and deoxygenation of methyl palmitate and to inhibit the carbon-carbon bond breaking side reaction, so as to obtain a product with hexadecane and its isomers as the main components.

9. The application as described in claim 8, characterized in that: During the reaction, the selectivity of hexadecane is ≥90 mol%, the proportion of hexadecane isomers is ≥40 mol%, and the selectivity of carbon chain cleavage products is less than 3 mol.

10. The application as described in claim 8, characterized in that: In S1, the reduction treatment includes: placing the iridium-molybdenum bimetallic titanium oxide modified molecular sieve catalyst in a closed container, and passing H2 at a rate of 20-40 mL / min under normal pressure for reduction treatment. The temperature of the reduction treatment is 300-550ºC, and the time is 60-180 min. In S2, the concentration of methyl palmitate in the reaction solution is 5-20 wt%. In S2, the solvent includes one or more of methanol, cyclopentane, and dodecane; In S2, the reaction conditions are: pressure 1-3 MPa, temperature 180-300℃, and stirring speed 300-600 r / min.

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