One-step conversion of syngas to hydrocarbons and ethers over ZIF-8 derived ZnO coupling HZSM-5

Zeolitic imidazolate frameworks (ZIF-8) were synthesized by solvothermal method. Used as precursor, ZIF-8 was decomposed into nanoparticles ZnO at different pyrolysis temperature in air atmosphere. The composition, structure and crystal size of ZnO were characterized by XRD, TEM, XPS, and Raman methods. The ZnO nanoparticles were coupled with HZSM-5 to form bifunctional catalysts. The catalytic performances of bifunctional catalysts in the syngas conversion were investigated in a fixed-bed tubular reactor. The results demonstrate that the pyrolysis temperature has an important influence on the particle size of ZnO. The temperature affects the rate of grain formation. High temperature promotes the aggregation of ZnO. The ZnO grain size by changing the temperature plays a role in changing the product distribution. When the pyrolysis temperature is near or below 450℃, carbon-coated ZnO nanoparticles are obtained, and the ZnO grain size is less than 20 nm. The carbon-coated ZnO coupled with HZSM-5 catalyzes syngas mainly into dimethyl ether (DME). When the temperature is higher than 450℃, pure phase ZnO nanoparticles are obtained, and the ZnO grain size is larger than 20 nm. The pure ZnO coupled with HZSM-5 catalyzes syngas mainly into hydrocarbons. Obviously, the coupling modes of ZnO and HZSM-5 have a significant effect on the product selectivity of bifunctional catalysts.