Excess oxygen moieties, which are a recurring feature in the study of bulk oxide catalysts, have been attributed a variety of roles in the effectuation of catalytic partial oxidation reactions. Ethane oxidation over bulk nickel oxide catalysts represents a prototypical example of their catalytic relevance, with excess oxygen purported to participate in the deep oxidation of ethane, but not necessarily in Mars-van Krevelen cycles that produce light olefins. Despite the widespread attribution of catalytic function to non-stoichiometric oxygen, to the best of our knowledge, no characterization technique exists that allows for the quantitative estimation of excess oxygen, and its rigorous deconvolution from the inevitable presence of lattice oxygen.<br/> <br/>In this presentation we will discuss the effect of CO<sub>2</sub> – a common side product associated with catalytic partial oxidation reactions – on the reactivity of oxide surfaces. Two types of carbonate species are formed on NiO surfaces during the oxidation of ethane, and the quantitative analysis of these species provides us access to the density of surface lattice and excess oxygen. Such dimorphic behavior of carbonates persists upon varying surface excess oxygen densities through the use of thermal treatments and aliovalent doping protocols, and can be used in the interpretation of rate data on more complex mixed metal oxides that in many cases deliver improved ethene selectivities. The differing adsorptive propensities of these two types of oxygen toward probe molecules of interest, used here in the interpretation of the frequencies of ethane partial oxidation turnovers, may be broadly applicable in the context of (reverse) Mars-van Krevelen cycles ubiquitous in the realm of bulk oxide catalysis. Our findings provide key insights into the oftentimes underappreciated effect of side products on catalyst and reactor performance.

Impact of side product-mediated carbonate formation on the catalytic oxidation of ethane over bulk nickel oxide

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