Preparation And Catalytic Performance Of Bifunctional Catalyst For Direct Conversion Of Syngas To Aromatics

Light aromatics are important basic organic chemical raw materials.More than 97%of traditional aromatics production comes from petroleum routes.However,with Chinese increasing dependence on foreign oil and the rapid increase in demand for aromatics,traditional petroleum routes to aromatics faces huge challenges.Therefore,according to the resource endowment characteristics of China——"rich coal,lean oil,and less gas",development of coal-to-aromatic technology which uses coal as raw material,has important strategic significance for achieving oil substitution and improving the level of efficiency and clean in coal utilization in China.In recent years,breakthrough progress has been made in the direct conversion of syngas to aromatics.One of the key is the design and development of oxide-zeolite bifunctional catalyst.At present,in the study of the oxide-zeolite bifunctional catalyst applying to one-step synthesis of aromatics from syngas,the zeolite chosen is mainly ZSM-5 zeolite with a ten-membered ring cross-channel structure.It is worth noting that,MCM-22 zeolite?MWW topology?has similar acid strength and distribution as ZSM-5,and the unique two-dimensional sinusoidal ten-membered ring channel and twelve-membered ring supercage structure with ten-membered ring as the opening,and it shows good catalytic performance in methanol to aromatics.In addition,the precursor of MCM-22 zeolite——MCM-22?P?can be pillared and peeled to obtain MCM-36 zeolite with micro-mesoporous structure and ITQ-2 zeolite with single-layer MWW structure,respectively.Therefore,combined with the previous work foundation of the research group in the synthesis of MWW zeolite,this paper proposes to use the zeolite of MWW structure for the construction of bifunctional catalyst,and systematically studied its catalytic performance in the synthesis of aromatics from syngas,the main research content and conclusions are as follows:?1?Using MCM-22 zeolite as the aromatized catalyst component,the effects of metal oxide types,zeolite SiO₂/Al₂O₃,metal oxide to zeolite mass ratio,reaction temperature,pressure,space velocity,and syngas hydrogen-carbon ratio on CO conversion and aromatic selectivity were systematically studied.The results show that the Zn Cr O_x-MCM-22 bifunctional catalyst exhibits excellent overall performance.Among them,when the zeolite SiO₂/Al₂O₃ is 100,the metal oxide to zeolite mass ratio is 2:1,the temperature is 350?,the pressure is 2.0 MPa,the syngas flow rate is 1500 h^-1,and the H₂/CO is 1,the highest CO conversion and aromatic selectivity are obtained.However,its aromatic selectivity is significantly lower than the results reported in the literature when using ZSM-5 as aromatization component in a bifunctional catalyst.?2?In order to improve the aromatic selectivity of the bifunctional catalyst,MCM-22 zeolite was modified with metals having aromatization activity such as Zn²⁺?Zr⁴⁺?Ga³⁺,and the effect of metal type and loading on its catalytic performance was systematically studied.The results show that the bifunctional catalyst composed of 3%Zn/MCM-22 and Zn Cr O_x exhibits high CO conversion and aromatic selectivity.?3?Using MCM-36 zeolite with micro-mesoporous structure and ITQ-2 zeolite with single-layer MWW structure instead of MCM-22 zeolite as aromatized catalytic functional component,and loaded with 3%Zn mixed with ZnCrO_x catalyst to prepare bifunctional catalyst,under the same reaction conditions,their catalytic performance in the synthesis of aromatics from syngas was studied.And the effect of zeolite structure on catalytic performance was explored.The results show that ZnCrO_x-Zn/MCM-36 and ZnCrO_x-Zn/ITQ-2 exhibit higher CO conversion and aromatic selectivity compared to Zn Cr O_x-Zn/MCM-22 bifunctional catalyst.This may be attributed to the more open pore structure of MCM-36 and ITQ-2 zeolites,which reduces the diffusion limitation of intermediate species and products,drives the rapid reaction and diffusion of intermediate species,thereby improving the final CO conversion and aromatic selectivity.