Abstract: 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 NO_x adsorption-decomposition were studied. The 0.5 g catalyst was used to adsorb 1696 mg/m³ NO_x under the space velocity of 1000 h^-1 at 200℃, 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℃ had the highest NO_x adsorption efficiency and capacity of 54% and 16.6 mg NO_x/(g\5h). Temperature-programmed desorption-mass spectroscopy(TPD-MS) was carried out on the catalyst adsorbed NO_x, and the result showed that N₂, O₂ and N₂O were formed during rapid heating, among which O₂ was observed for the first time. Two modes of decomposition were adopted, one is by electric oven at a ramping rate of 150℃/min, and the other, by microwave oven. Compared to the mode of the former, the latter has higher N₂ yield with a N₂ 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 NO_x adsorption and catalytic decomposition.

Key words: NO_x, Tungstophosphoric acid, Carbon nanotubes, Microwave radiation, Adsorption-decomposition