Evaluation of Al2O3 and ZrO2 addition to reduced graphene oxide (rGO) supports and their interplay with Cu sites in the catalyst surface

Abstract

In this contribution it is reported the synthesis of Cu-based catalysts supported on reduced graphene oxide (rGO) and its hybrids (Al-rGO and Zr-rGO), aiming at the tailoring of the surface properties for application in the CO2 hydrogenation. With the purpose of gaining more insight about the preparation method and nature of the rGO promoter (Al2O3, ZrO2) the catalysts were prepared by the hydrothermal and wetness impregnation methods. The hydrothermal catalyst Cu@Zr-rGO led to highest methanol space time yield (STY), envisaging an interaction between ZrO2 and GO (graphene oxide) during synthesis, promoting the formation of ZrO2 nanostructures and allowing the stabilization of Cu species at the nanoscale. X-Ray diffraction indicated distinct interactions of Cu and the catalysts components, with Cu0 and Cu2+ predominantly present in the hydrothermal catalysts whereas Cu1+ was only detected in the impregnated samples. Furthermore, Cu/Zr-rGO also exhibited feature corresponding to Cu2+, denoting a significant role of the promoter over the Cu species distribution. Raman spectroscopy indicated highly defective structures for all the samples, with Zr promoted catalysts appearing with the richest in defects, possibly due to the presence of oxygen vacancies. Thus, there is a fine interplay among rGO, promoter and synthesis route over the Cu oxidation and particle size and, thus, over the catalytic properties.