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Abstract

Catalytic performance is known to be influenced by several factors, with the catalyst surface oxidation state being the most prominent of all. However, in the great majority of industrial heterogeneous catalytic reactions the oxidation state of the active sites is a subject of intense debate. Preferential oxidation of carbon monoxide in hydrogen-rich mixtures (COPrOx) is an important heterogeneous catalytic reaction involved in the purification of hydrogen. In the search for an economically affordable catalyst for this reaction, cobalt appears as one of the most promising materials. Therefore, it is essential to distinguish if a certain surface state of cobalt exists that favors the reaction more than the others. Here we directly compare the activity of CoO and Co3O4 phases by combining ex situ and operando analytical methods with first-principles modeling. CoO is identified as the most favored cobalt surface oxidation state for the COPrOx process, providing a critical element for the rational design of efficient and durable COPrOx catalysts.