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Published online: 15 April 2009 | doi:10.1038/nchina.2009.73

Catalysis: Coming to the surface

Felix Cheung

Introduction

© (2009) Nature

Carbon monoxide (CO) oxidation is becoming an increasingly important research topic as more people are encouraged to lower their car emissions. Among the oxidation catalysts known, metal oxides are active at ambient temperatures but can easily be deactivated by moisture. Wenjie Shen at the Chinese Academy of Sciences in Dalian and co-workers¹ have discovered a nanorod version of tricobalt tetraoxide (Co₃O₄) that not only has enhanced catalytic activity, but also is water tolerant. The discovery should aid the future development of highly efficient oxidation catalysts.

The use of Co₃O₄ for the low-temperature oxidation of CO is not new. The catalyst has been known to be active at temperatures as low as -54 °C. However, in normal feed gas, most of the active sites of Co₃O₄ are covered by moisture, which considerably hinders the adsorption and catalytic oxidation of CO.

The researchers prepare Co₃O₄ nanorods from the precipitation of cobalt acetate with sodium carbonate in ethylene glycol. Each nanorod has a diameter of 10–20 nm and a length of 200–300 nm. Subsequent thermal treatment of the nanorods at 450 °C in air causes their diameters to shrink to 5–15 nm and their surface morphology to change (see top image).

Tests show the Co₃O₄ nanorods not only catalyse CO oxidation at temperatures as low as -77 °C, but also remain stable in a moist stream of normal feed gas. The researchers attribute this improvement to the high density of catalytically active cobalt ion sites exposed on the nanorod surface (see bottom image).

Although Co₃O₄ nanorods might not necessarily be useful for air purification (cobalt can cause lung disease), the findings nevertheless demonstrate how a change in surface morphology can improve the performance of metal-oxide catalysts.

The authors of this work are from:
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, China; Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China; Department of Applied Chemistry, Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, Tokyo, Japan; Japan Science and Technology Agency, CREST, Saitama, Japan.

Reference

1. Xie, X., Li, Y., Liu, Z. Q., Haruta, M. & Shen, W. Low-temperature oxidation of CO catalysed by Co₃O₄ nanorods. Nature 458, 746–749 (2009).
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