The morphological impact of siliceous porous carriers on copper-catalysts for selective direct CO2 hydrogenation to methanol

Abstract

A series of copper-catalysts, Cu-ZnO-MnO (CZM), supported on morphologically distinct siliceous porous carriers (SBA-15, MCF, KIT-6) were synthesized and applied in direct CO2 hydrogenation to methanol. The morphological impact of porous carriers on the formation and growth of copper crystallites and the molecular pore diffusion of the porous catalysts were investigated. Among the synthesized catalysts, KIT-6 supported catalyst (CZM/KIT-6) presented the most superior properties. The morphology of KIT-6 deterred mesopore plugging and favored the formation of small copper crystallites. CZM/KIT-6 also possessed greater resistance to copper crystallite growth and loss of copper surface area during reaction due to the pore-confining effect of the porous carrier and the larger inter-crystallites spacing among copper crystallites. The high effective diffusivity (catalyst pore-geometry dependent coefficient) of CO2 molecules in CZM/KIT-6 could indicate efficient transfer of reactant molecules to active sites and the removal of reaction products. The superior characteristics of CZM/KIT-6 contributed to the high CO2 conversion (8.2%) and high methanol production rate (105.3 mol/kgcat.h) at low reaction temperature (180 °C). The methanol selectivity attained was ≥99% in all the experiments.