Effect of alkaline earth metal oxide (MO) Cu/MO/Al2O3 catalysts on methanol synthesis activity and selectivity via CO2 reduction

Abstract

Heterogeneous copper/alumina catalysts with MgO, CaO, SrO, and BaO were prepared by co-precipitation synthesis method and characterized by means of N2-sorption, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and subsequent H2 temperature-programmed reduction (H2 TPR) and H2/CO2 temperature-programmed desorption (H2 and CO2 TPD). The incorporation of oxides increases the metallic Cu surface area, as follows: Mg > Sr > Zn > Ca > Ba. These metal oxides thus increased the interaction between CuO and Al, resulting weaker reducibility of CuO. MgO increased the number of carbon dioxide and hydrogen adsorption active sites, whereas Ba augmented the basicity of the material. The activity with respect to methanol production matched the increase of Cu surface. As CH3OH selectivity monotonically decreased with the temperature, CO increased proportionally. Among the examined catalytic materials, Cu/MgO/Al2O3 exhibited a higher reactant conversion than the pelletized commercial analogues. Hydrogenation performance of the catalysts thus depended on both, the Cu surface site availability and the interaction between copper–metal oxides. While the industrial Cu/ZnO/Al2O3 has been extensively employed for quite some time, it is demonstrated herein that even upon the application of inexpensive non-critical raw material resources, such as MgO, an increment in bifunctional catalysis performance is attained. The Cu/Mg/Al catalyst showed a turnover frequency of 11.9 × 10−4 s−1, which is higher than the commercial HFR120 and LURGI catalysts.