Acid-Base Reactivity of Perovskite Catalysts Probed via Conversion of 2-Propanol over Titanates and Zirconates

Although perovskite catalysts are well-known for their excellent redox property, their acid base reactivity remains largely unknown. To explore the potential of perovskites in acid-base catalysis, we made a comprehensive investigation in this work on the acid base properties and reactivity of a series of selected perovskites, SrTiO3, BaTiO3, SrZrO3, and BaZrO3, via a combination of various approaches including adsorption microcalorimetry, in situ FTIR spectroscopy, steady state kinetic measurements, and density functional theory (DFT) modeling. The perovskite surfaces are shown to be dominated with intermediate and strong basic sites with the presence of some weak Lewis acid sites, due to the preferred exposure of SrO/BaO on the perovskite surfaces as evidenced by low energy ion scattering (LEIS) measurements. Using the conversion of 2-propanol as a probe reaction, we found that the reaction is more selective to dehydrogenation over dehydration due to the dominant surface basicity of the perovskites. Furthermore, the adsorption energy of 2-propanol (Delta H-ads,H-2-propanol) is found to be related to both a bulk property (tolerance factor) and the synergy between surface acid and base sites. The results from in situ FTIR and DFT calculations suggest that both dehydration and dehydrogenation reactions occur mainly through the E-1cB pathway, which involves the deprotonation of the alcohol group to form a common alkoxy intermediate on the perovskite surfaces. The results obtained in this work pave a path for further exploration and understanding of acid-base catalysis over perovskite catalysts.