Spectroscopic characterization of a highly selective NiCu3/C hydrodeoxygenation catalyst†
The design of selective and active heterogeneous catalysts for the hydrodeoxygenation (HDO) of biomass-derived platform molecules requires understanding of the catalyst structure under reaction conditions. In this work, we design, build and qualify an operando X-ray absorption (XAS) cell to characterize a highly selective NiCu3 catalyst under HDO conditions. We complement XAS measurements with X-ray photoelectron spectroscopy (XPS) studies and theoretical calculations to show that in bimetallic NiCu catalysts, Ni and Cu are segregated. The as-made catalysts are mixed oxides, with a NiO shell over a NiCuOx core. The core becomes a partially reduced metal alloy after treatment with hydrogen at temperatures below 473 K, while the shell becomes fully reduced at higher treatment temperatures. The liquid-phase reaction results in gradual reoxidation of the catalyst to a core–shell mixed oxide, in which the Cu in the core is predominately Cu(I) and the Ni shell is predominately Ni(II).