The Influence of the Chemical Potential on Defects and Function of Perovskites in Catalysis

Abstract

A Sm-deficient Sm0.96MnO3 perovskite was prepared on a gram scale to investigate the influence of the chemical potential of the gas phase on the defect concentration, the oxidation states of the metals and the nature of the oxygen species at the surface. The oxide was treated at 450°C in nitrogen, synthetic air, oxygen, water vapor or CO and investigated for its properties as a catalyst in the oxidative dehydrogenation of propane both before and after treatment. After treatment in water vapor, but especially after treatment with CO, increased selectivity to propene was observed, but only when water vapor was added to the reaction gas. As shown by XRD, SEM, EDX and XRF, the bulk structure of the oxide remained stable under all conditions. In contrast, the surface underwent strong changes. This was shown by AP-XPS and AP-NEXAFS measurements in the presence of the different gas atmospheres at elevated temperatures. The treatment with CO caused a partial reduction of the metals at the surface, leading to changes in the charge of the cations, which was compensated by an increased concentration of oxygen defects. Based on the present experiments, the influence of defects and concentration of electrophilic oxygen species at the catalyst surface on the selectivity in propane oxidation is discussed.

Investigation of AFeO3 (A=Ba, Sr) Perovskites for the Oxidative Dehydrogenation of Light Alkanes under Chemical Looping Conditions

“…Perovskite (ABO 3 ) and Ruddlesden-Popper (A x + 1 B x O 3x + 1 ) oxides have shown intriguing potential as alternative ODH catalysts that can be tailored for this application due to their enormous range of tunability through A/B-site substitution and exceptional oxygen storage capacity (OSC). Within the last five years, researchers have placed their efforts on optimizing various types of perovskite materials including lanthanum-based perovskites (La 0.8 Ba 0.2 MnO 3À δ , [11] alkali metal-promoted La x Sr 2À x FeO 4À δ , [12] molten Li 2 CO 3 shell modified-La 0.8 Fe 0.2 FeO 3 , [13] LaMnO 3 [14][15] ) and other perovskites (Na 2 WO 4 -promoted CaMn 0.9 Fe 0.1 O 3 , [16] Sm 0.96 MnO 3, [17] and BaCoO 3 [2] ) for ODH coupled with chemical looping or under anaerobic conditions. Although the surface modifications have shown to significantly improve olefin selectivity by facilitating the transport of active peroxide (O 2 2À ) species, there is limited research on the robustness and cyclability of these systems, creating opportunities for developing other novel perovskite catalysts for both ethane and propane CL-ODH.…”

Energy Maps of Complex Catalyst Surfaces

“…In this work, we probe the adsorption energy distribution for C2−C4 alkanes and alkenes on metal oxides and phosphates, including V 2 O 5 , 2 8 MnWO 4 , 2 9 , 3 0 (VO) 2 P 2 O 7 , 2 8 , 3 1 SmMnO 3 , 32,33 and MoVO x , 34,35 and present a comprehensive data set for the interaction of alkanes and alkenes with oxide surfaces. The selection of materials focused on diversity in chemical composition and catalytic properties.…”