Applied Catalysis B: Environmental 21 (1999) 203–213 Ce-ZSM-5 catalysts for the selective catalytic reduction of NO x in stationary diesel exhaust gas W.E.J. van Kooten a,∗ , B. Liang a,b , H.C. Krijnsen a , O.L. Oudshoorn a , H.P.A. Calis a , C.M. van den Bleek a a Delft University of Technology, Faculty of Applied Sciences, Section Chemical Reactor Engineering, Julianalaan 136, 2628 BL Delft, The Netherlands b Department of Chemical Engineering, Sichuan Union University, Chengdu 610065, PR China Received 18 December 1998; received in revised form 24 February 1999; accepted 27 February 1999 Abstract This paper describes the preparation of Ce-ZSM-5 SCR catalysts for stationary diesel engine applications, such as marine diesels, and the performance of these catalysts with ammonia as a reducing agent in both simulated and real diesel exhaust gas. Catalysts prepared by ion exchange in aqueous solution, show an increasing NO x conversion with increasing cerium ion-exchange level at all temperatures tested (NO x conversion > 80% in the temperature range 350–500 ◦ 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 excess 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 ratios of at least 1.1. With diesel exhaust gases of a three-cylinder, 10 kW diesel engine, Ce-ZSM-5 can reach about 70% NO x conversion at 500 ◦ C at a GHSV of 50.000 h −1 . Deactivation of the catalysts in real diesel exhaust occurs mainly in the first 60 h of operation resulting in stable catalysts which show about 40% NO x conversion at 450 ◦ 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. ©1999 Elsevier Science B.V. All rights reserved. Keywords: ZSM-5; Cerium; SCR; NO x removal; Ammonia; Diesel; Deactivation; Solid-state ion exchange 1. Introduction Since the successful introduction of the three way catalyst for Otto-engines, the emission of hazardous compounds originating from diesel engines, especially soot and nitrogen oxides (NO x ) has attracted much attention. A large—but not yet very successful— ∗ Corresponding author. Tel.: +31-15-2786-733; fax: +31-15- 2784-452; e-mail: c.m.vandenbleek@stm.tudelft.nl research effort is being put into development of ze- olite NO x reduction catalysts using hydrocarbons as reducing agents for mobile applications (reviewed by e.g. Gilot et al. [1]). One of the most promising NO x removal techniques for stationary diesel engines, such as on ships, is selective catalytic reduction (SCR). In this technique, ammonia (NH 3 ) or an aqueous urea (HN 2 CONH 2 ) solution is injected in the exhaust gas stream. At T > 300 ◦ C, in the presence of water vapor, urea mainly decomposes into ammonia and carbon 0926-3373/99/$ – see front matter ©1999 Elsevier Science B.V. All rights reserved. PII:S0926-3373(99)00023-5