Abstract
The structure and chemical composition of the catalyst may change under reaction conditions resulting in changes of the active sites and, thereby, loss of selectivity. In this work, we investigated the reactive interaction of isopropanol with well-defined Co3O4(1 1 1)/Ir(1 0 0) and Pt/Co3O4 (1 1 1)/Ir(1 0 0) model catalysts by means of synchrotron radiation photoelectron spectroscopy (SRPES), near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), scanning tunneling microscopy (STM), and temperature programmed desorption (TPD).
We found that adsorption at 150 K yields molecularly adsorbed isopropanol on both model catalysts accompanied by small fractions of isopropoxide and enolate species on Co3O4(1 1 1) and supported Pt nanoparticles, respectively. The reactive interaction of isopropanolderived species with the model catalysts upon annealing in UHV and in 1 x10(-7) mbar and 1 mbar of isopropanol results in the reduction of Co3O4 (1 1 1) followed by its conversion to CoO(1 1 1) and, finally, to metallic Co and Pt-Co alloy.
The mechanism of isopropanol decomposition reveals remarkable sensitivity to the oxidation state and morphology of the model catalysts. On as-prepared Pt/Co3O4(1 1 1) catalyst, Pt particles densely cover the Co3O4(1 1 1) substrate steering isopropanol decomposition to acetone and hydrogen.
Selective channels towards acetone and propene, both accompanied by water, open after temperature-driven sintering of the supported Pt particles. The selectivity of these channels is controlled by the degree of reduction of the Co3O4(1 1 1) substrate and the chemical composition of the supported nanoparticles.
At high degrees of reduction of Co3O4(1 1 1), the formation of both propene and acetone through selective channels decline due to the strong preference for C-C bond scission. Under NAP conditions, the formation of acetone resumes after complete reduction of model catalysts to metallic Co and Pt-Co alloy. (C) 2021 Elsevier Inc.
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