Local structural evolutions of CuO/ZnO/Al2O3 catalyst for methanol synthesis under operando conditions studied by in situ quick X-ray absorption spectroscopy

Abstract

In situ quick X-ray absorption spectroscopy (QXAFS) at the Cu and Zn K-edge under operando conditions has been used to unravel the Cu/Zn interaction and identify possible active site of CuO/ZnO/Al2O3 catalyst for methanol synthesis. In this work, the catalyst, whose activity increases with the reaction temperature and pressure, was studied at calcined, reduced, and reacted conditions. TEM and EDX images for the calcined and reduced catalysts showed that copper was distributed uniformly at both conditions. TPR profile revealed two reduction peaks at 165 and 195 °C for copper species in the calcined catalyst. QXAFS results demonstrated that the calcined form consisted mainly of a mixed CuO and ZnO, and it was progressively transformed into Cu metal particles and dispersed ZnO species as the reduction treatment. It was demonstrated that activation of the catalyst precursor occurred via a Cu+ intermediate, and the active catalyst predominantly consisted of metallic Cu and ZnO even under higher pressures. Structure of the active catalyst did not change with the temperature or pressure, indicating that the role of the Zn was mainly to improve Cu dispersion. This indicates the potential of QXAFS method in studying the structure evolutions of catalysts in methanol synthesis.