Atomic Structural Origin of the High Methanol Selectivity over In<sub>2</sub>O<sub>3</sub>–Metal Interfaces: Metal–Support Interactions and the Formation of a InO<sub><i>x</i></sub> Overlayer in Ru/In<sub>2</sub>O<sub>3</sub> Catalysts during CO<sub>2</sub> Hydrogenation
Ning Rui, Xuelong Wang, Kaixi Deng, Jorge Moncada, Rina Rosales, Feng Zhang, Wenqian Xu, Iradwikanari Waluyo, Adrian Hunt, Eli Stavitski, Sanjaya D. Senanayake, Ping Liu, José A. Rodríguez
Abstract
CO 2 hydrogenation to methanol is of great environmental and economic interest due to its potential to reduce carbon emissions and produce valuable chemicals in one single reaction. Compared with the unmodified traditional Cu/ZnO/Al 2 O 3 catalyst, an indium oxide (In 2 O 3 )-based catalyst can double the methanol selectivity from 30–50 to 60–100%. It is worth noting that over catalysts involving various active metals dispersed on indium oxide (M/In 2 O 3, M = Pd, Ni, Au, etc.), although the methanol yield is boosted, the selectivity remains similar to that of plain In 2 O 3 despite the distinct chemical properties of the added metals. To investigate the phenomena behind this behavior, here we used RuO 2 /In 2 O 3 as a test catalyst. The results of ambient pressure photoelectron spectroscopy, in situ X-ray absorption fine structure, and time-resolved X-ray diffraction indicate that the structure of the RuO 2 /In 2 O 3 catalyst is highly dynamic in the presence of a reactive environment. Specifically, under CO 2 hydrogenation conditions, Ru clusters facilitate the reduction of In 2 O 3 to generate In 2 O 3– x aggregates, which encapsulate the Ru systems in a migration driven by thermodynamics. In this way, the Ru 0 sites for CH 4 production are blocked while creating RuO x –In 2 O 3– x interfacial sites with tunable metal–oxide interactions for selective methanol production. In an inverse oxide/metal configuration, indium oxide has properties not seen in its bulk phase that are useful for the binding and conversion of CO 2 . This work reveals the dynamic nature of In 2 O 3 -based catalysts, providing insights for a rational design of materials for the selective synthesis of methanol.