Probing into the multifunctional role of copper species and reaction pathway on copper-cerium-zirconium catalysts for CO2 hydrogenation to methanol using high pressure in situ DRIFTS

Abstract

A series of ternary copper-cerium-zirconium catalysts containing two kinds of copper species, surface CuO and Cu-Ce-Zr solid solution, are prepared and studied for catalytic properties of CO2 hydrogenation to methanol. The copper-cerium- zirconiumcatalyst calcined at 450 °C (CCZ-450) is much more favorable for improving the nature of surface CuO species and forming Cu-Ce-Zr solid solution than others. The best catalytic behavior in terms of methanol selectivity (T = 280 °C, SCH3OH = 71.8%), turnover frequency (TOFCO2 = 13.4 × 10−2 s−1) and activation energy (Ea = 28.5 kJ/mol) are achieved using CCZ-450. The excellent catalytic performance of CCZ-450 is attributed to the stronger H2 adsorption ability arising from highly dispersed surface CuO specie with higher copper surface area and higher concentration of active bi/m-HCOO* intermediate caused by the formation of Cu-Ce-Zr solid solution. Both the dispersion and surface area of active sites and the activation abilities of CO2 are critical for catalyst activity and product selectivity. In situ diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) experiments at 3 MPa confirm that both bi-HCOO* and m-HCOO* are the active intermediates for CO2 hydrogenation to methanol. The accumulation of m-HCOO* on the catalyst surface is the crucial step of CO2 hydrogenation to methanol.