Hydrogen production from ethanol steam reforming over cerium and nickel based oxyhydrides

Hydrogen production from ethanol steam reforming (H2O/C2H5OH = 3) was investigated over cerium–nickel CeNixOY (0 < x ≤ 5) mixed oxide catalysts. The influence of different parameters was analysed, such as reaction temperature, Ni content and in-situ pre-treatment in H2. While an ethanol conversion of 100% is reached at 400 °C, a stable activity i.e., ethanol conversion, and H2 selectivity can be obtained at very low temperature (200 °C) when the solid is previously in-situ treated in H2 in a temperature range between 200 °C and 300 °C. After such a treatment, the solids studied are hydrogen reservoirs, called oxyhydrides, with the presence of hydrogen species of hydride nature in the anionic vacancies of the solid. Different physicochemical techniques, including XPS, ion sputtering, XRD, TPR were used to characterize the catalysts. Depending on the composition and metal loading, a solid solution and/or a highly dispersed nickel oxide in ceria can be obtained. Ion sputtering followed by XPS analysis allowed estimating the size of NiO nanoparticles (2–3 nm) present in the compounds, too small to be detected by XRD. The characterization of CeNixOY solids, evidenced the existence of high interactions between Ce and Ni cations located either in the solid solution of cerium–nickel or at the interface between NiO and CeO2 (or solid solution). The active nickel species belonging to the small particles and/or to the solid solution, participating actively in the catalytic reaction, present the characteristic of being able to be reduced and reoxidized easily and reversibly (redox process), allowed by their close interaction with Ce species. Finally, correlations among the species present in the solid, and the catalytic performances are discussed, and an active site based on the formation of anionic vacancies and a mechanism involving a heterolytic abstraction of a hydride species from ethanol are envisaged.