Preparation Of Cobalt Carbide/Zeolite Functional Catalyst And Its Catalytic Performance

Syngas conversion is an extremely important step to increase the utilization of carbon resources,and its downstream products have high added value.Fischer-Tropsch synthesis is a classic pathway of syngas conversion,but the product selectivity of Fischer-Tropsch synthesis is limited by the Anderson-Schulz-Flory（ASF）distribution,and the product selectivity is difficult to control.Recent years,the reaction coupling strategies based on functional catalysts,which are composed of metal oxide nanoparticles and zeolites,have shined in the selective regulation of synthesis gas conversion products.However,the lower ability of metal oxides to dissociate CO limits the CO conversion rate,resulting in a CO-rich environment.The relationship between CO and selectivity is still unclear.This article focuses on the challenges faced by the selective regulation of traditional Fischer-Tropsch synthesis reaction and the unknown role of CO in the coupling reaction.The main research contents are as follows:（1）Aiming at the difficulty in controlling the selectivity of the Fischer-Tropsch synthesis reaction product,the Co₂C/Zeolite catalyst was designed based on the coupling strategy to directly obtain hydrocarbons from the syngas conversion reaction.Combining the zeolite pore structure and acidity to explore product selectivity,it was successfully realized highly selective production of isoparaffins,in which isobutane selectivity is as high as 43.5%,and the methane selectivity seems to be related to the chemical environment of the Al site of the zeolite.Proper acidity and porous structure are conducive to the stability of the catalyst.（2）In view of such high isobutane selectivity,covering of Br（?）nsted acid sites to react by Na-modified zeolite proves that Br（?）nsted acid sites can promote the production of isobutane.The zeolite is modified by citric acid to improve its pore structure and acidity,and the selectivity of isoparaffin products is increased to 73.5%,and the selectivity of single product isobutane is increased to 61.2%.The olefin model reaction with MZ-H-βcatalyst proves that CO can increase the reaction rate and contribute to the formation of isomerized products.The ¹H NMR technique combined with py-IR characterization proved that the adsorption of CO on the zeolite can increase the density ratio of Br（?）nsted acid and Lewis acid sites to affect the selectivity of isobutane.In-situ diffuse reflection Infrared spectroscopy characterizes the conversion process of CO with ethylene on zeolites,and proves that CO can promote the formation of isobutane by stabilizing the key intermediate,allyl carbocation.The construction of the model reaction explains the key role of CO in the ethylene conversion process.Therefore,the synthesis gas conversion reaction under different H₂/CO is found that the selectivity of isobutane products decreases significantly as the CO content decreases,while the selectivity of C₅,C₆,and C₇ isoparaffin products gradually increases.Indicating the selectivity of isoparaffin products can be controlled by simply changing H₂/CO.These conclusions provide ideas for the selective regulation of synthesis gas conversion reaction products.