Enhancing the anti-K poisoning performance of Co3O4 catalyst for toluene oxidation by modifying MnOx

Abstract

A series of cobalt-based catalysts (Co3O4, Mn/Co3O4, K-Co3O4, and K-Mn/Co3O4) were prepared for toluene catalytic combustion and anti-K poisoning experiments. Co3O4 catalyst has exhibited good performance in toluene oxidation, but it has poor anti-K poisoning performance. The Mn/Co3O4 catalyst has shown excellent low-temperature catalytic activity, good resistance to K poisoning at T90 of 226 °C, and achieved a complete toluene conversion at about 235 °C; the activity after the addition of K slightly reduced at T90 of 237 °C. A series of characterizations indicated that adding Mn can effectively promote the Co2+↔Co3+ cycle, increase the Co3+ content on the catalyst surface, and enhance the redox performance of the catalyst. On the other hand, MnOx intercepts K species and generates Mn-O-K, blocking most of the poisonous effects of K on cobalt oxide, thereby protecting the active species (Co3+ and surface-adsorbed oxygen) and acidic sites on the Co3O4 surface. Finally, GC-MS and in-situ infrared characterization were adopted to investigate the reaction mechanism of the catalysts. Two reaction paths of the Co3O4 catalyst may co-occur. Still, the reaction path of the Mn/Co3O4 catalyst is relatively simple; that is, the chemically adsorbed toluene molecules are oxidized through surface-active oxygen, after which various intermediate by-products are formed successively. Finally, they are completely degraded into CO2.