Catalytic Oxidation Of Formaldehyde Over Co₃O₄ Catalysts At Low Temperature

Since formaldehyde is one of the most serious pollutants in the indoor environment and is harmful to human health, Indoor formaldehyde elimination has been attracting researchers’ attention. Compared with other formaldehyde elimination methods, catalytic oxidation technique can catalize HCHO to oxidize into non-toxic CO2 and H2O at low temperature and has revealed the huge development potential. In the case, a series of catalysts such as Co3O4, Co3O4/CeO2 and Pd/Co3O4/CeO2 et al,were prepared by coprecipitation or impregnation method and the relationship between the catalytic performance for formaldehyde oxidation and catalyst structure obtained by changing the promoters or precious metals contents as wll as changing the catalysts preparation conditions are investigated. The main conclusions were as follows:(1) The catalytic performace of Co3O4 catalysts prepared via the coprecipitation methods with different pretreatment temperatures or pretreatment atmospheres shows that the pretreatment conditios have a significant to catalytic activity for formaldehyde oxidation.The surface of Co3O4 catalysts as prepared was covered by the adsorbed water and carbonate species, which hindered the adsorption and activation of HCHO, and then revealed no catalytic activities.The surface species and the oxygen vacancies formed in the pretreatment processes have a great influence on the catalyst activities, furthermore Co3O4 catalysts pretreated in N2 at 200℃℃ showed the optimal catalytic activity and stability. However, the Co3O4 catalysts pretreated in O2 atmosphere showed poor catalytic activity relative to one pretreated in N2 because oxygen vacancies were healed in oxgen.(2) The Co3O4/CeO2 catalysts were prepared with impregnation method by the different proportion of Co/Ce, at the same time the catalyst activities and stabilities change trends with physical properties of the catalysts induced with tntroduction of CeO2 are also investigated. The results showed that the CeO2 could not only affect the particle size, the specific surface area and the dispersion of Co3O4 patticles significantly, but also strongly interact with Co3O4, as plays a key role in formaldehyde oxidation. Among them, Co3O4/CeO2 with Co/Ce atomic ratio of 15:1 dislayed the largest interface between Co3O4 and CeO2 and the most evident synergies, therefore, could oxidize 600 ppm of HCHO completely at room temperature without no activity loss within 23.5 h.(3) Pd element with different loadings was impregnated over Co3O4/CeO2 and the performances for formadedye oxidation were also investigated. The results showed that HCHO could be oxided to CO2 and water completely at room temperature over Pd/ Co3O4/CeO2 with Pd loadins being 2%. With uninterrupted operation for 33 h, the HCHO conversion over Pd/Co3O4/CeO2 could still maintain at 100%.