How oxide carriers control the catalytic functionality of the Cu-ZnO system in the hydrogenation of CO2 to methanol

摘要

The reactivity pattern of Al2O3 (CuZnAl), CeO2 (CuZnCe) and ZrO2 (CuZnZr) supported Cu-ZnO systems in the synthesis of methanol via CO2 hydrogenation in the range of 453-513 K at 3.0-5.0 MPa has been addressed. The CuZnCe system shows superior surface methanol productivity, though textural and chemical effects of zirconia carrier account for the better performance of CuZnZr catalyst. Characterization data of "steady-state" catalysts show significant surface coverage by CO2 irrespective of metal surface area (MSA). Direct relationships among activity, CO2 uptake and oxides surface area (OSA) point out a dual-site Langmuir-Hinshelwood reaction mechanism, involving hydrogenation and CO2 adsorption sites at the surface of both metal and oxide phases. The influence of space-velocity on selectivity signals the occurrence of a parallel-consecutive path leading to methanol and CO, while higher reaction rate and methanol selectivity with lowering contact time signal a negative influence of water formation on the catalyst performance.