Ce-ZSM-5 catalysts for the selective catalytic reduction of NOx in stationary diesel exhaust gas

This paper describes the preparation of Ce-ZSM-5 SCR catalysts for stationa ry diesel engine applications, such as marine diesels, and the performance of these catalysts with ammonia as a reducing agent in both simulated and r eal diesel exhaust gas. Catalysts prepared by ion exchange in aqueous solut ion, show an increasing NOx conversion with increasing cerium ion-exchange level at all temperatures tested (NOx conversion > 80% in the temperature r ange 350-500 degrees C at a gas hourly space velocity (GHSV) of 40.000 h(-1 ) with simulated diesel exhaust). Ce-ZSM-5 does not convert nitric oxide or ammonia into the greenhouse gas nitrous oxide. Moreover, Ce-ZSM-5 does not exhibit ammonia slip up to ammonia/nitric oxide feed ratios of 1.4, the ex cess ammonia being converted to nitrogen. Ce-ZSM-5 extrudates with 50 wt.% alumina binder do not show ammonia slip up to ammonia/nitric oxide feed rat ios of at least 1.1. With diesel exhaust gases of a three-cylinder, 10 kW d iesel engine, Ce-ZSM-5 can reach about 70% NOx conversion at 500 degrees C at a GHSV of 50.000 h(-1). Deactivation of the catalysts in real diesel exh aust occurs mainly in the first 60 h of operation resulting in stable catal ysts which show about 40% NOx conversion at 450 degrees C, at a GHSV of 32. 000 h(-1). The preparation of Ce-ZSM-5 via solid-state ion exchange results in a remarkably active catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.