A simple and a reproducible synthetic protocol was utilized to synthesize hybrid perovskites with a nominal stoichiometry of LaCoxMn1-xO3 (x = 0.1-0.9), whose bulk B-site stoichiometry, bulk B-site oxidation states, and bulk oxygen vacancy population can be controlled in a gradual manner [1]. Structural and functional properties of these materials were investigated with: XRD, BET, ICP-MS, XPS, TEM, ex-situ and in-situ XANES, in-situ FTIR and TPD. An efficient methodology was presented to estimate the bulk stoichiometry and the bulk oxygen deficiency of the hybrid perovskites by combining average bulk-oxidation state information provided by XANES and bulk A-site and B-site atomic ratios measured in ICP-MS. Here, we demonstrate that these bulk-oxygen vacancies have a strong influence on the redox activity of the hybrid perovskites allowing them to efficiently switch between high and low B-site oxidation states in a reversible fashion under relatively moderate redox conditions without requiring elevated temperatures for regeneration, unlike LaCoO3 and LaMnO3 benchmark systems. Our former [2, 3] and current studies indicate that A-site bulk oxidation state seems to remain intact without presenting a strong influence on reactivity. Furthermore, we exploit catalytic disproportionation of NO2 (g) into surface nitrates/nitrites on the hybrid perovskite surfaces as a proof of principle, in order to illustrate that perovskites such as La1.01Co0.75Mn0.24O2.97 and La1.04Co0.65Mn0.31O2.97 with a particular bulk-oxygen vacancy population and electronically-modified hybrid B-site cations with specific oxidation states can reveal superior reactivity in transforming NO2 (g) into surface nitrates/nitrites that can surpass single B-site benchmark perovskites such as LaCoO3 and LaMnO3. This may be accomplished by the diffusion of bulk oxygen vacancies to the surface which eventually governs the surface catalytic reactivity.

Does bulk matter?: Controlling bulk oxygen vacancies enhances catalytic reactivity of perovskite surfaces

2019 Spring National Meeting

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