NOx Adsorption and Decomposition over H3PW12O40/CNTs and the Effect of Microwave Irradiation

A series of HPW/CNTs catalysts was prepared by impregnation and mechanical grinding methods. For this purpose, CNTs was pretreated separately by nitric acid vapor, mixture of nitric acid and sulphuric acid, and subsequently calcined. The performances of catalysts on NOx adsorption-decomposition were studied. The 0.5 g catalyst was used to adsorb 1696 mg/m(3) NOx under the space velocity of 1000 h(-1) at 200 degrees C and the results showed that the catalyst prepared by mechanical grinding methods supporting HPW on CNTs pretreated by nitric acid vapor and calcined at 300 degrees C had the highest NOx adsorption efficiency and capacity of 54% and 16.6 mg NOx/(g . h). Temperature-programmed desorption-mass spectroscopy(TPD-MS) was carried out on the catalyst adsorbed NOx and the result showed that N-2, O-2 and N2O were formed during rapid heating, among which O-2 was observed for the first time. Two modes of decomposition were adopted, one is by electric oven at a ramping rate of 150 degrees C/min, and the other, by microwave oven. Compared to the mode of the former, the latter has higher N-2 yield with a N-2 yield upto 33.3% corresponding to the power of microwave oven being 700 W. The catalyst used can be reused by water vapor reactivation, and the recycling results showed that there were no significant performance degradation on NOx adsorption and catalytic decomposition.