Synergistic Coupling of Photo and Thermal Conditions for Enhancing CO Reduction Rates in the Reverse Water Gas Shift Reaction.

The photocatalytic activity of nanostructured InO(OH) for the reverse water gas shift (RWGS) reaction CO + H → CO + HO can be greatly enhanced by substitution of Bi(III) for In(III) in the lattice of BiInO(OH). 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 BiInO(OH) acting synergistically as a frustrated Lewis acid-base pair reaction. Nonetheless, such photocatalytic activity is usually optimized in a specific batch reactor setup sequence, with H as an initial gas input under photo and thermal conditions before introducing CO. Hence, the chemical interplay between environment parameters such as photoillumination, thermal input, and gas reactant components with the effects of Bi substitution is unclear. Reported herein, glovebox-protected X-ray photoelectron spectroscopy (XPS) interrogates this photochemical RWGS reaction transiting from vacuum state to similar conditions in a photocatalytic reactor, under dark and ambient temperatures, 150°C in dark and 150 °C under 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, hence showing its equivalency with in situ methods. The enhanced photocatalytic reduction rate of CO with H with a low doped 0.05% a.t Bi system is thus associated with an increased gas sensitivity in H + CO, a greater expansion in the OH shoulder than that of the undoped system under heat and light conditions, as well as a greater thermal stability of dissociated H adatoms. The photoinduced expansion of the OH shoulder and the increased positive binding energy shifts show 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 H reduction of In. The results provide new insight into how pairing photo and thermal conditions with the methodical tuning of the Lewis acidity and Lewis basicity of surface frustrated Lewis acid-base pair sites by varying z amount in BiInO(OH) enables optimization of the rate of the photochemical RWGS.