In Situ Generation of the Cu@3D-ZrO_<i>x</i> Framework Catalyst for Selective Methanol Synthesis from CO₂/H₂

Abstract

Cu-based catalysts have been widely studied for direct hydrogenation of CO2 to methanol. Their activities quite depend on the amount of exposed active sites (e.g., Cu-oxide interfaces), which can be tuned by the particle size as well as porosity. Here, we report an active, selective, and stable Cu@ZrOx catalyst with a three-dimensional (3D) porous framework structure via the in situ reconstruction of size-confined Cu@UiO-66. The optimized CU-0.5-300 catalyst shows a high methanol selectivity of 78.8% at a conversion of 13.1% at 260 °C, 4.5 MPa, giving a methanol space-time yield of 796 g·kgcat–1·h–1. It also shows long-term stability for 105 h in a time-on-stream test. Such good performance benefits from abundant Cu–ZrOx interfaces and a stable 3D ZrOx framework. During the reaction, ZrOx species in situ evolves from the unstable Zr-oxide cluster (the building unit of UiO-66) or amorphous ZrO2 to a stable tetragonal ZrO2 phase, but strong metal–support interaction (SMSI) at Cu–ZrOx interfaces retains. The SMSI enables the formation of Cu+ at the ZrO2 surface, which is strongly associated with the active sites for methanol synthesis. In situ diffuse-reflectance infrared Fourier transform spectroscopy studies reveal methanol synthesis which follows a HCOO-intermediated pathway. It is believed that this work provides an “in situ reconstruction” strategy to fabricate a practical Cu@ZrOx framework catalyst for methanol production.