(509bf) Hydrocarbon-Based Selective Catalytic Reduction of NO over Ag/?-Al2O3 Catalysts:the Effect of Preparation Method

Nitrogen oxides (NOx) emission adversely impacts the environment and human health. Hydrocarbon-based selective catalytic reduction (HC-SCR) is a new catalytic system that is capable of operation in excess of oxygen, has great potential for control of automotive NOx in future applications. The γ-alumina supported silver catalysts (Ag/γ-Al₂O₃) are effective for such HC-SCR. In this study, we employed impregnation and single-step sol-gel methods to prepare 5wt% Ag/γ-Al₂O₃ catalyst. The prepared catalysts were systematically characterized by various analytical, spectroscopic and imaging techniques, and well-characterized catalysts were used to carry out the titled reaction.

Packed-bed reactor experiments are performed with 1000 ppm each of nitric oxide and propylene, 7.0 vol% of oxygen, and rest nitrogen at a total flow rate of 0.6 slpm, with a catalyst loading of 1.0 g. The catalytic activities were shown in Fig. 1(a). With the impregnated catalyst, Ag/γ-Al₂O₃(Imp), there is maximum NOx conversion of 85% obtained at higher temperature of 500℃ while the catalyst prepared by single-step sol-gel method, Ag/γ-Al₂O₃(S-G), exhibits excellent activity (99% NOx conversion), see Fig. 1a, owing to high surface area and highly dispersed silver nanoparticles as evidenced from HR-TEM results (Fig. 1b).

The catalytic activity obtained over a fairly broad range of temperature window (380-600℃) with NOx conversion of more than 80% for HC-SCR in excess of O₂. Further, the method is highly reliable with good reproducibility, thus shows promise. In order to improve the performance of the catalyst, in particular to lower the temperature, we have planned to modify the Ag/γ-Al₂O₃ catalyst with metals such as bismuth, molybdenum and vanadium. In addition, kinetics information for both systems will be developed.