Study On The Catalytic Properties And Mechanism Of Co Containing AlPO-5Catalysts For Selective Catalytic Reduction Of NO With Methane

NO, which is responsible for ozone hole, acid rain and optical smoke, is an important pollutant in the atmosphere. In recent years, the concentrations of NO in the atmosphere increased rapdly. Thus, removal of NO becomes one of the main tasks of environmental protection. Because methane is present in most combustion exhausts and could lead to greenhouse effect, the selectivecatalytic reduction of NO with methane has been considered as a promising NO removal method and attracted the attention of researchers from home and abroad.Aluminophosphate zeolite possesses fine hydrothermal stability, thus believed to be a favorable way to obviate the problem of deactivation in hydrothermal conditions in conventional CH4-SCR catalysts. Cobalt, a transition metal, can catalyze the selective reduction of NO with methane. Previous studies by our group have confirmed that FeAlPO-5have good activity and hydrothermal stability in catalytic reduction of N2O with CH4. In this article, the catalytic performance and reaction mechanism of CoAlPO-5catalysts for selective catalytic reduction of NO with methane were investigated. Basing on this mechanism, the modification of CoAlPO-5catalyst has been studied. Several conclusions were reached as follows:(1) CoAlPO-5and Co/ZSM-5were prepared by hydrothermal and ion exchange method. X-ray diffraction results confirmed that CoAlPO-5has a typical framework structure of A1PO-5zeolite. The catalytic activity of CoAlPO-5is significantly lower than Co/ZSM-5. After the treatment with CH4, NO and CH4, XPS and UV-visible spectroscopy results showed that the Co species in CoZSM-5can form Co2+/Co3+cycle while CoAlPO-5can not, and Co2+/Co3+cycle is based on the cobalt oxide species outside of the skeleton of the zeolites.(2) Basing on the catalytic mechanism mentioned above, we loaded a small amount of Co by impregnation method in CoAlPO-5catalyst, which exibited good catalytic activity. CoZSM-5prepared by hydrothermal method had relatively low catalytic activity. Characterization results of H2-TPR evinced that, the impregnated cobalt in CoAlPO-5is cobalt oxide species which have catalytic activity, yet there are no presence of cobalt oxide species in CoZSM-5.(3) In order to further improve the catalytic activity, we have evaluated the catalytic performance of Ce loaded CoAlPO-5catalysts and found a small amount of Ce can substantially increase the catalytic activity of CoAlPO-5. H2-TPR results indicated that the load of Ce improved the reduction performance of CoAlPO-5catalysts and thus promoted its catalytic activity.