Low temperature catalytic oxidation of volatile organic compounds: a review

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Abstract

Volatile organic compounds (VOCs) are toxic and recognized as one of the major contributors to air pollution.

Abstract

Volatile organic compounds (VOCs) are toxic and recognized as one of the major contributors to air pollution. The development of efficient processes to reduce their emissions is highly required. Complete catalytic oxidation is a promising way to convert VOCs, especially with low concentration, into harmless CO ₂ and water. This reaction is highly desirable to proceed at low temperature for the consideration of safety, energy savings, low cost and environmental friendliness. Great efforts have been devoted to develop efficient catalysts in order to reduce the temperature of catalytic oxidation of VOCs. The present review highlights recent important progress in the development of supported noble metal and metal oxide catalysts in this field. We examined several typical metals that are widely adopted as essential components for catalytic oxidation of VOCs and explored the effect of some important influencing factors such as the properties of metal and support, dispersion, particle size and morphology of metals. The specific mechanism that leads to superior catalytic activity towards low temperature VOC oxidation was discussed too.

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Low-temperature oxidation of CO catalysed by Co(3)O(4) nanorods.

Xiaowei Xie, Yong Li, Zhi-Quan Liu … (2009)

Low-temperature oxidation of CO, perhaps the most extensively studied reaction in the history of heterogeneous catalysis, is becoming increasingly important in the context of cleaning air and lowering automotive emissions. Hopcalite catalysts (mixtures of manganese and copper oxides) were originally developed for purifying air in submarines, but they are not especially active at ambient temperatures and are also deactivated by the presence of moisture. Noble metal catalysts, on the other hand, are water tolerant but usually require temperatures above 100 degrees C for efficient operation. Gold exhibits high activity at low temperatures and superior stability under moisture, but only when deposited in nanoparticulate form on base transition-metal oxides. The development of active and stable catalysts without noble metals for low-temperature CO oxidation under an ambient atmosphere remains a significant challenge. Here we report that tricobalt tetraoxide nanorods not only catalyse CO oxidation at temperatures as low as -77 degrees C but also remain stable in a moist stream of normal feed gas. High-resolution transmission electron microscopy demonstrates that the Co(3)O(4) nanorods predominantly expose their {110} planes, favouring the presence of active Co(3+) species at the surface. Kinetic analyses reveal that the turnover frequency associated with individual Co(3+) sites on the nanorods is similar to that of the conventional nanoparticles of this material, indicating that the significantly higher reaction rate that we have obtained with a nanorod morphology is probably due to the surface richness of active Co(3+) sites. These results show the importance of morphology control in the preparation of base transition-metal oxides as highly efficient oxidation catalysts.