Preparation Of Mo₂C/SAPO-11 Catalytic Material And Study On Its 1-hexene Isomerization Properties

The directional isomerization process of olefins in catalytically cracked gasoline is an important way to produce high-octane clean gasoline blending components,and metal-acid bifunctional catalysts are usually used.After a lot of research,it is found that SAPO-11 molecular sieve with special pore structure and suitable acidity is one of the most commonly used catalysts and catalyst supports in the isomerization reaction.Significance.Precious metals Pt and Pd are often used as active metals in bifunctional catalysts,but their industrial applications are greatly limited due to their small reserves and high prices.Studies have shown that molybdenum carbide has electronic and catalytic properties similar to those of noble metals,especially in some hydrogen-related reactions,the catalytic activity of molybdenum carbide is close to or even surpasses that of noble metal catalysts,which has practical significance for solving the problem of fossil fuel consumption.In this paper,SAPO-11 molecular sieves were synthesized by hydrothermal method,and the effects of different modulation mechanisms on the physicochemical properties and 1-hexene isomerization properties of SAPO-11 molecular sieves were investigated.Then,the Mo₂C/SAPO-11 catalyst was prepared by temperature-programmed reduction method with solid polyvinylpyrrolidone（PVP）as carbon dopant,and the effect of different carbonization conditions on the physicochemical properties of the catalyst was investigated.Using the hydroisomerization reaction of 1-hexene as the evaluation method,the catalytic activity and isomer selectivity of each catalyst were investigated.The hydrodesulfurization performance of Mo₂C/SAPO-11 catalyst was investigated with thiophene as the probe molecule.The details are as follows:1.Synthesis of SAPO-11 molecular sieve and research on its olefin isomerization properties.In the synthesis system for the hydrothermal synthesis of SAPO-11 molecular sieves,the effects of synthetic raw material ratio,template agent,seed crystal effect and crystallization conditions on the phase state,morphology,acidity and pore structure of SAPO-11 molecular sieves were investigated.The characterization results show that increasing the silicon/aluminum ratio of SAPO-11 molecular sieve within a certain range will increase the acid content and acid strength of the product.Properly increasing the water/aluminum ratio can make SAPO-11 zeolite crystallize preferentially,thereby exposing more pores and improving the catalytic performance of the zeolite.When di-n-propylamine（DPA）is used as the template agent and the mold/aluminum ratio is 1.0,the crystal form of the product is pure and the crystallinity is high.Adding heterogeneous seeds to the precursor mixture can effectively improve the crystallinity of the product molecular sieve,shorten the crystallization time,reduce the crystal size of the product molecular sieve,increase the mesopore volume and external surface area,and significantly improve the product molecular sieve.The acid strength and the concentration of Br?nsted acid centers greatly enhanced the catalytic activity of the product molecular sieves.The 1-hexene hydroisomerization reaction test was carried out on all synthesized sample molecular sieves.It was found that the SAPO-11 molecular sieve synthesized at high water/aluminum ratio,adding heterogeneous seed crystals,and high crystallization temperature had the smallest crystallite size.size,the largest mesopore volume and external specific surface area,and the highest acid content,so its catalytic activity and skeletal isomer selectivity for the hydroisomerization reaction of 1-hexene are the best,and its skeletal isomer selectivity is the highest was 66.1%.2.Preparation of Mo₂C/SAPO-11 catalyst and its olefin isomerization performance.In the process of preparing Mo₂C/SAPO-11 catalyst by temperature-programmed reduction method using cheap and readily available solid polyvinylpyrrolidone（PVP）as carbon doping agent,the physicochemical effects of precursor molybdenum source,carbonization conditions and Mo impregnation amount on the product catalyst were investigated.The effects of the properties and catalytic performance are discussed as follows:In the process of preparing Mo₂C/SAPO-11 catalyst with（NH₄）₆Mo₇O₂₄·4H₂O as the molybdenum source,the carbonization time will affect the surface species content of molybdenum carbide,and prolonging the carbonization time is beneficial to the Mo₂C/SAPO-11 catalyst.Species are stabilized and Mo²⁺content increases.The introduction of more Mo components would increase the catalyst acid content,especially the medium-strong Br?nsted acid content,but also affect the long-range order of the mesoporous structure of SAPO-11 and decrease the specific surface area and pore volume of the samples.In the process of preparing Mo₂C/SAPO-11 catalyst by using Mo（CO）₆ as metal molybdenum source,the carbonyl complex is easily decomposed and other characteristics,the carbonization final temperature and carbonization time are significantly reduced,and the reaction energy consumption is saved.The evaluation results of the catalytic performance of the above catalysts in the hydroisomerization of 1-hexene show that among a series of catalysts prepared with ammonium molybdate as the molybdenum source,the Mo impregnation amount is 10%,and the catalysts were synthesized by carbonization at 700°C for 18h.The Mo₂C/SAPO-11 catalyst exhibits excellent 1-hexene isomerization rate and hydroisomerization selectivity due to the highest total acid content and Br?nsted acid content,among which the hydroisomerization selectivity is the highest of 32.1%.However,the selectivity of cracked products on this catalyst is as high as 30%.Among a series of Mo₂C/SAPO-11 catalysts prepared with molybdenum hexacarbonyl as molybdenum source,the Mo₂C/SAPO-11 catalysts synthesized by carbonization at 600℃for 5h have suitable Br?nsted acid and Lewis acid contents with 10%Mo impregnation amount.In the hydroisomerization of 1-hexene,the selectivity of hydroisomerization can reach up to 38.9%,and there is no cracking side reaction.3.Study on catalytic performance of Mo₂C/SAPO-11 catalyst after post-treatment.The Mo₂C/SAPO-11 catalyst was subjected to high-temperature hydrogen treatment to remove carbon on the surface of the catalyst to reduce the real catalytic performance of the catalyst.The effects of reaction temperature and space velocity on the catalytic performance of 1-hexene hydroisomerization by reduction passivation Mo₂C/SAPO-11 catalyst were investigated,and the hydrodesulfurization reaction of thiophene was used as a probe reaction.The conversion of thiophene on the reductively passivated Mo₂C/SAPO-11 catalyst was investigated.The results are discussed as follows:Mo₂C/SAPO-11 catalysts with different impregnation amounts prepared with ammonium molybdate as molybdenum source were significantly improved in the hydroisomerization performance of 1-hexene after high temperature hydrogen treatment,and the hydroisomerization selectivity increased from The highest 32.1%increased to the highest 51.4%.In contrast,the isomerization performance of Mo₂C/SAPO-11 catalysts with different impregnation amounts prepared with molybdenum hexacarbonyl as molybdenum source did not change significantly.By studying the laws of hydroisomerization of 1-hexene under different reaction temperature and space velocity,it is found that within a certain temperature range,increasing the reaction temperature is beneficial to improve the isomerization rate and hydroisomerization selectivity of 1-hexene.If the temperature is too high,it will be accompanied by the occurrence of cracking side reactions and reduce the product selectivity of the isomerization reaction.With the increase of the feed space velocity,the contact time between the reactant molecules and the catalyst is shortened,the side reactions of cracking are suppressed,and the isomerization selectivity is improved.In addition,the reduction passivation Mo₂C/SAPO-11 catalyst has excellent thiophene HDS catalytic performance,and its thiophene conversion rate can reach up to 99.0%.It is worth noting that the reduction passivation state Mo₂C/SAPO-11 catalyst also has anti-sulfur poisoning effect.In the reaction system with a sulfur content of 500 ppm,the hydroisomerization selectivity of 1-hexene can reach up to 40.8%.