Indium-doped Co 3 O 4 nanorods for catalytic oxidation of CO and C 3 H 6 towards diesel exhaust (original) (raw)

Applied Catalysis B: Environmental, 2018

Abstract

Abstract Platinum-group metals are widely used as diesel oxidation catalysts (DOCs) for exhaust control. It is a challenge to improve performance and reduce the cost of DOCs, while also to avoid interference of hydrocarbons and sintering of platinum metals at high temperatures. We present here an indium-doped Co 3 O 4 uniform nanorod catalyst whose catalytic performance in CO, C 3 H 6 , and even NO oxidation is comparable to platinum-group DOCs in diesel exhaust. No obvious deactivation was observed in long-term stability tests under simulated diesel exhaust conditions. These indium-doped Co 3 O 4 nanorods might open a promising pathway towards low-cost efficient diesel exhaust control systems. Characterization results indicated that lattice oxygen could be much more easily abstracted by hydrogen or carbon monoxide from indium-doped Co 3 O 4 than from Co 3 O 4 and the physical mixture Co 3 O 4 and In 2 O 3 . The presence of indium with its large cation radius could influence the chemical status of surface/chemisorbed oxygen in Co 3 O 4 -In 2 O 3 nanorods, thereby increasing the mobility of lattice oxygen involved in the catalytic oxidation reaction. The reaction mechanism of catalytic oxidation of CO and C 3 H 6 were evaluated based on kinetic and FTIR studies. For CO oxidation, activated CO 3 * reduced by adsorbed CO* in an irreversible step to generate the final product of CO 2 could be considered as the kinetically-relevant step. DRIFT spectroscopy confirmed that only stable carbonate species were observed over Co 3 O 4 -In 2 O 3 nanorods that might be further reduced by CO to form CO 2 . For C 3 H 6 oxidation, the incorporation of activated oxygen (O*) into anion vacancy of catalyst surface was the kinetically-relevant step, while the active sites on catalyst surface should be totally covered by the intermediates of C 3 H 6 or its generated species, which actually acted as the most abundant surface intermediates (MASI). DRIFT spectroscopy confirmed that C 3 H 6 and its related intermediates like formate, acetate, and acetone species would be formed over Co 3 O 4 -In 2 O 3 nanorods.

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