Effect of alkali metals on the performance of CoCu/TiO2 catalysts for CO2 hydrogenation to long-chain hydrocarbons

CoCu/TiO2 catalysts promoted using alkali metals (Li, Na, K, Rb, and Cs) were prepared by the homogeneous deposition-precipitation method followed by the incipient wetness impregnation method. The influences of the alkali metals on the physicochemical properties of the CoCu/TiO2 catalysts and the catalytic performance for CO2 hydrogenation to long-chain hydrocarbons (Cs.) were investigated in this work. According to the characterization of the catalysts based on X-ray photoelectron spectroscopy, X-ray diffraction, CO2 temperature-programmed desorption (TPD), and H-2-TPD, the introduction of alkali metals could increase the CO2 adsorption and decrease the H-2 chemisorption, which could suppress the formation of CH4, enhance the production of C5+, and decrease the hydrogenation activity. Among all the promoters, the Na-modified CoCu/TiO2 catalyst provided the maximum Cs. yield of 5.4%, with a CO2 conversion of 18.4% and Cs. selectivity of 42.1%, because it showed the strongest basicity and a slight decrease in the amount of H-2 desorption; it also exhibited excellent catalytic stability of more than 200 h. (C) 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.