Strontium titanate (SrTiO3, STO) is an extensively investigated perovskite for various applications due to its optical, electrical and chemical properties. Our group has studied 2-propanol and ethanol conversions over STO nanocrystals. One major finding is that surface reconstruction of STO occurs readily and depends heavily on the pretreatment, posing a significant effect on catalysis. These studies showed obvious surface reconstruction but the facet effect of STO on alcohol conversion remains unclear. Furthermore, there is a lack of information on 1) the true nature of the active sites for alcohol conversion, and 2) the true reaction rate in terms of turn over frequency (TOF) after the surface reconstruction. Recently, our work on methane combustion over a series of STO catalysts unveiled step sites at the surface after surface reconstruction as the active sites for methane activation and conversion. This finding inspires us to re-visit alcohol conversion in order to understand the nature of active sites for acid-base reactions over STO perovskites. In this work, we further explore the effects of both surface facet and reconstruction of the shape-controlled SrTiO3 on the nature and quantity of active site using the 2-propanol conversion as a probe reaction. Both XPS and low energy ion scattering analysis reveal that the surface reconstruction of all STO samples depends on both the pretreatment temperature and the shape of STO, leading to the different rate in IPA conversion. The reconstruction-resulted step sites were quantified by the steady-state isotopic transit kinetic analysis study to be a minor portion of all surface sites and are proposed responsible for the acid-base catalysis in IPA conversion over STO. The role of STO facet is to control the degree of surface reconstruction: more step sites occur on less stable (110) facets, leading to higher overall reaction rate than the (100) facets. The reaction mechanism for isopropanol dehydrogenation is proposed based on the in situ FTIR investigation and verified by DFT calculations to go through an isopropoxy intermediate adsorbed on the Lewis acid sites present at the surface steps.

Interplay between surface facet and reconstruction on 2-propanol conversion over SrTiO3 nanocrystals

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.