Reduction of nitrogen dioxide by propene over acidic mordenites: influenceof acid site concentration, formation of by-products and mechanism

The reduction of nitrogen dioxide to nitrogen by propene was studied over a variety of acidic mordenite zeolites differing in their Si:AI ratio and th us, in their concentration of acid sites. The formation of by-products was monitored applying an ion-molecule reaction (IMR) mass spectrometer. It was found that at fixed conditions the yield of nitrogen increases with increa sing concentration of acid sites, confirming that acid sites are the active catalytic centres in the reaction. Apart from nitrogen and nitric oxide, a crylonitrile and ammonia are formed as nitrogen containing gas-phase produc ts in the reaction. In separate experiments, it was shown that acrylonitril e is hydrolysed by water over the acidic zeolites to yield ammonia and acry lic acid. When acrylonitrile is used as reducing agent for nitrogen dioxide , formation of nitrogen is strongly enhanced in the presence of water. Wate r also has a promoting effect on the formation of nitrogen in the reaction between nitrogen dioxide and propene. Acrylonitrile and its product of hydr olysis, ammonia, are considered to be intermediates of nitrogen dioxide red uction to nitrogen by propene over acidic zeolites. (C) 1999 Elsevier Scien ce B.V. All rights reserved.