Reactor based XPS and other in-situ studies on the Effect of Substitution of Bismuth for Indium in Defect Laden Indium Oxide Hydroxide BizIn2-zO3-x(OH)y on the Photocatalytic Hydrogenation of Carbon Dioxide

Abstract

The photocatalytic activity of nanostructured In2O3-x(OH)y for the Reverse Water Gas Shift (RWGS) Reaction CO2 + H2 -> CO + H2O can be greatly enhanced by substitution of Bi(III) for In(III) in the lattice of BizIn2-zO3-xOHy. This behavior was hypothesized as the effect of the population and location of Bi(III) on the Lewis acidity and Lewis basicity of proximal hydroxide and coordinately unsaturated metal surface sites in BizIn2-zO3-xOHy acting synergistically as a Frustrated Lewis Acid-Base Pair reaction. Reported herein, XPS interrogates this photochemical RWGS reaction transiting from vacuum state to similar conditions in a photocatalytic reactor, under dark and ambient temperature, 150 degC, and 150 degC with photoillumination. Binding energy shifts were used to correlate the material system's Lewis basicity response to these acidic probe gases. In-situ gas electronic sensitivity and in-situ UV-Vis derived band gap trends confirm the trends shown in the XPS results. The enhanced photo-catalytic reduction rate of CO2 with H2 with low doped 0.05% a.t Bi system is thus associated with an increased gas sensitivity in H2+CO2, a greater increase in the OH shoulder than that of the undoped system under heat and light conditions. The photo-induced expansion of the OH shoulder and the increased positive binding energy shifts shows the important role of photoillumination over that of thermal conditions. The poor catalytic performance of the high doped system can be attributed to a competing H2 reduction of In3+. The results provide new insight into how methodical tuning of the Lewis acidity and Lewis basicity of surface Frustrated Lewis Acid Base Pair sites by varying z amount in BizIn2O3-xOHy enables optimization of the rate of the photochemical RWGS.