Catalyst and microsystem investigations for the selective detection of carbon monoxide in concentrated hydrogen fuels using mixed copper cerium oxide catalysts

Rong Zhang, Purdue University

Abstract

Copper cerium oxide catalysts are known for their high CO oxidation selectivity in concentrated H2, for applications both in CO preferential oxidation (CO-PROX) and in selective catalytic microthermal CO sensors. Fundamental insights were provided with newly developed methods to (1) understand the catalyst surface requirements as well as (2) identify the local coordination of the active redox sites for selective CO oxidation, for the purpose of designing catalysts with better CO selectivity and better sensor sensitivity. Reactive titration and steady-state isotopic transient kinetic analysis (SSITKA) were used to quantify surface adsorbed reactive CO and H2 under reaction conditions to further describe the competitive redox mechanism between CO and H2, and the observed CO2 selectivity decrease with decreasing CO pressure. CO oxidation is kinetically preferred over the oxidized active sites. The relative reactive CO coverage is the determiner of CO2 selectivity. The further depiction of selectivity parameters provides a useful principle for the design of selective PROX catalysts. The local coordination of the active redox site in Cu0.08Ce 0.92O2 for CO-PROX in concentrated H2 was investigated using in-situ X-ray absorption spectroscopy (XAS) at both Cu K-edge and Ce L3-edge during anaerobic reaction. The active redox oxygen was identified to be bridging oxygen between Cu and Ce in a mixed copper ceria oxide phase with isolated Cu ions. The active phase of the catalyst is the topmost 1–2 nm of the catalyst surface. For the first time, direct and solid experimental evidence has been provided to identify the local coordination of the active oxygen site under reaction conditions. Broad applications of in-situ XAS during anaerobic reaction will have great impact on heterogeneous catalysis. These understandings about the catalyst as well as the competitive redox mechanism provide fundamental insight into designing catalysts with higher CO rate, leading to enhanced CO sensor sensitivity and CO selectivity (operated at low temperature). Moreover, the two newly developed methods, reactive titration and in-situ XAS during anaerobic reaction, will have broad applications in heterogeneous catalysis.

Degree

Ph.D.

Advisors

Varma, Purdue University.

Subject Area

Chemical engineering

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