| The process of low-temperature CO catalytic oxidation has become an important research topic due to its potential applications in many areas, including air-purification devices for respiratory protection, carbon monoxide gas sensors, closed-cycle carbon dioxide lasers, and removing trace quantities of CO from the ambient air in sealed cabins. In addition, the CO oxidation has been regarded as a probe reaction to show the relationship between the structure and catalytic performance, and also to investigate the reaction mechanism.Noble metal catalyst is considered to be the preferred catalyst for CO oxidation at low temperature due to its high catalytic activity, but the high cost, poor stability and complicated preparation procesure of noble metal catalyst limit its application in practice. Thus, the development for low cost non-noble metal catalyst with high activity has attracted great attentions in recent years. Here, we prepared two kinds of non-noble metal catalysts Co3O4/SiO2 and CuO/CeO2, and tested in CO oxidation to investigate the catalytic activity. The catalysts were characterized by BET, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).Co3O4/SiO2 catalysts were prepared by incipient-wetness impregnation of silica support with Co(NO3)2·6H2O in aqueous solution. The silica support was pretreated by ethylene glycol (EG) at room temperature which modified the surface properties of SiO2, enhanced the interaction between silica support and cobalt oxide species, contributing to higher catalytic activity in CO oxidation. According to the results of XRD and TEM, the pretreatment of silica support by EG remarkably modified the properties of silica support, leading to the formation of smaller Co3O4 particles, thus giving high CO oxidation activity. For the catalyst prepared by modified silica support using 10 vol% EG, the Co3O4 particle size was 4 times smaller and the temperature of 100% CO conversion was 140 K lower than those of the catalyst prepared from unmodified silica support. In addition, the XPS study was carried out to determine the chemical composition and valence state of the elements on the surface of support cobalt oxide. It was showed that the atomic ratio of Co3+ on the subsurface was increased from 47% to 63% after the silica support was pretreated by 10 vol% EG. It was reported that Co3+ species were the active site of CO oxidation on Co3O4 catalysts. Thus the pretreatment of silica support favored to forming more Co3+ species on the surface of Co3O4, contributing higher CO oxidation activity. In short, the modification of silica support significantly improved the dispersion of supported cobalt oxide and formed more Co3+ species on the surface of Co3O4 particles, resulting in very high catalytic activity in CO oxidation.CuO/CeO2 catalysts were prepared by homogeneous precipitation method using urea as the precipitating agent in ethylene glycol (EG) solution instead of water, which decreased the particle size of precipitate, leading to high catalytic activity. The temperature of 100% CO conversion was lowered by 40 K compared to catalysts prepared in water solution. A novel method using hexamethylenetetramine (HMT) in conjunction with hydrogen peroxide (H2O2) to prepared CuO/CeO2 catalysts was proposed for the first time. We studied the influence of heating conditions and calcination temperature on catalytic activity, it was showed that the mixed solution reacted at 50℃for 6 hours and calcined the precipitate at 200℃gave the highest CO catalytic activity. |
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