Cu–Zn Catalysts Derived From ZIF-8 Applied in Ethynylation of Formaldehyde for 1,4-Butynediol Synthesis: The Positive Effect of Carbon Layers

Cu-based catalysts applied in ethynylation reaction of formaldehyde for 1,4-butynediol synthesis has been widely concerned. The activity and stability of Cu-based catalyst is still a challenging task in this field. Here, Cu–Zn catalysts derived from ZIF-8 are prepared by a coprecipitation method and applied in ethynylation reaction of formaldehyde. All catalysts were characterized through thermogravimetric, x-ray diffraction, N₂ physical adsorption–desorption, transmission electron microscopy, H₂-temperture-programmed reduction, x-ray photoelectron spectroscopy, and Raman and Fourier transform infrared analysis. The effect of calcination temperature of ZIF-8 on the catalyst structures and ethynylation performances are all investigated. The results show that CuO_5h-ZnO₄₀₀ catalyst has the best catalytic activity, with a formaldehyde conversion of 98% and 1,4-butynediol selectivity of 100%. It is mainly due to the presence of highly dispersed and small particle CuO. Moreover, CuO_3h-ZnO₄₀₀ catalyst prepared by optimized conditions can further improve the stability in ethynylation reaction due to more carbon species on the surface of ZnO. The more carbon contents in Cu–Zn catalyst contribute to the ethynylation activity and stability due to the interaction between Cu and C species favoring Cu₂C₂ formed. In addition, the ethynylation reaction mechanism catalyzed by Cu–Zn catalyst is illustrated carefully. The Cu–Zn catalysts derived from ZIF-8 can provide some ideas for the application in ethynylation reaction of formaldehyde for 1,4-butynediol synthesis.