Phase speciation and surface analysis of copper phosphate on high surface area silica support by in situ XAS/XRD and DFT: Assessment for guaiacol hydrodeoxygenation

Abstract In situ characterization has become indispensable technique in the heterogeneous catalyst development because it provides insights into the composition and fundamental nature of materials in a dynamic process. In this work, in situ analysis including X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) could disclose phase transition via several intermediates during the reduction of copper phosphate precursor (CuHPO4·H2O) to copper phosphide on high surface silica support (Cu3P/SiO2). The synthesized Cu3P/SiO2 was further used as a catalyst for hydrodeoxygenation (HDO) reaction of guaiacol, a well-known representative model compound in lignin-derivatives upgrading. Many major products, such as cyclic hydrocarbons, demethylated, deoxygenated, and methylated compounds, were detected in the reaction mixture. The highest selectivity of catechol (72 mol%) was obtained at reaction condition of 300 °C and 50 bar H2 after 150 min. The density-functional theory (DFT) calculations revealed the local electronic charge nature and the different roles of Cu and P active sites towards the interaction between reactants/intermediates and the Cu3P surfaces. The findings of the phase transition during the Cu3P synthesis and its catalytic activity to the guaiacol HDO reaction, the first to be reported, is beneficial for improving the efficiency metal phosphide-based catalyst for lignin-derived bio-oil into biofuels in the future.