Catalysis Today 56 (2000) 431–441 Catalytic properties in deNO x and SO 2 –SO 3 reactions Pio Forzatti (I-3) ∗ , Isabella Nova (I-3), Alessandra Beretta (I-3) Dipartimento di Chimica Industriale, Ingegneria Chimica “G. Natta” Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan, Italy Contributors: Isabella Nova, Alessandra Beretta, Pio Forzatti (I-3); Vincenzo Palma, Paolo Ciambelli (I-4); Elena M. Slavinskaya, Bair S. Bal’zhinimaev (RU-1); Raffaele Colafato, Fiorenzo Bregani (I-6) Abstract SCR-deNO x reaction and SO 2 –SO 3 oxidation tests were carried out by different research groups over fresh and used EUROCAT oxide samples in order to characterize the reactivity of the catalysts and to compare data obtained in several laboratories (Politecnico of Milan, Università of Salerno, ENEL of Milan, Boreskov Insitute of Catalysis). Data are presented which indicate that the used EUROCAT catalyst is slightly more active both in the deNO x reaction and SO 2 –SO 3 oxidation than the fresh sample. An analyses of data collected over honeycomb catalysts by means of a 2D, single-channel model of the SCR monolith reactor has been performed to evaluate the intrinsic kinetic constant of the deNO x reaction; a satisfactory comparison has been obtained between estimation of the intrinsic kinetic constant and estimation of the intrinsic catalyst activity from data collected over powdered catalysts. A good agreement has been found in the experimental results collected in the different labs, both for the deNO x reaction and SO 2 –SO 3 oxidation. ©2000 Elsevier Science B.V. All rights reserved. Keywords: DeNO x ; SO 2 –SO 3 reactions; Selective catalytic reduction 1. Introduction The selective catalytic reduction (SCR) process is the most widely spread technology for the control of NO x emissions from stationary sources (including power-plants and incinerators), due to its efficiency and selectivity [1,2]. The deNO x process is based on the reaction be- tween NO and ammonia to produce nitrogen and wa- ter according to the reaction 4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O ∗ Corresponding author. Tel.: +39-2-23993238; fax: +39-2-70638173. E-mail address: pio.forzatti@polimi.it (P. Forzatti (I-3)). In the treatment of sulfur-containing flue gases, SO 2 is also fed to the SCR reactor; here it is partly oxidized to SO 3 which can react with water and unconverted ammonia to form sulfuric acid and am- monium sulfates. Accordingly, SO 2 oxidation repre- sents a highly undesirable side reaction of the SCR process; catalyst formulation and operating variables have to be designed in order to minimize its extent and, as a consequence, to avoid the risk of deposition of ammonium-sulfates or corrosion in the cold sec- tions of equipment of the plant downstream from the reactor. Commercial SCR catalysts are a homogeneous mixture of vanadium pentoxide, tungsten (or molyb- denum) trioxide, supported on a high-surface area anatase TiO 2 carrier. It is well accepted that tung- sten (molybdenum) trioxide acts as a promoter of the 0920-5861/00/$ – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII:S0920-5861(99)00302-8