Recent years have seen extensive research on catalysts that promote the reduction of NOx by ammonia. Of particular interest are those catalytic systems that exhibit selective reduction. Commerical scale installations of a process based on Norton Zeolon 200H are successfully operating in the United States for the removal of NOx from nitric acid plant tail gas. Data on a new zeolitic catalyst NC-300 with higher activity than Zeolon 200H are discussed. Effects of operating temperature, concentration of NH3, S02, H20, N02, 02, and space velocity are discussed. Advantages and disadvantages of various types of SCR catalyst are reviewed. As reported by others over Zeolon 200H we find that NC-300 does not catalyze the reaction of NO and NH3 in the absence of 02. A mechanism of NO, reduction by ammonia involving the reaction of N02 as the reactive species to form N20 is proposed.
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