1744
Langmuir 1992,8, 1744-1749
Characterization of Tungsta-Titania Catalysts G. Ramis,+G. Busca,*v+C. Cristiani,$L. Lietti,* P. Forzatti,$ and F. Breganis Istituto di Chimica, Facolth di Ingegneria, Uniuersith P. le J. F. Kennedy, I-16129 Genova, Italy, Dipartimento di Chimica Industriale e Ingegneria Chimica "G. Natta", Politecnico di Milano, P. le L. Da Vinci 33, I-20132 Milano, Italy, and ENEL, DSR, Centro di Ricerca Termica e Nucleare, via Rubattino 54, I-20134 Milano, Italy Received December 5, 1991. In Final Form: March 18, 1992 The structural, morphological, and surface properties of a W03-TiOz catalyst (W = 6% (wlw)) have been investigated and compared with those of TiOz. X-ray diffraction, differential thermal analysis, porosity, and surface area measurements indicated that WOSinhibits the initial sintering of anatase and ita phase transformation to rutile. Fourier transform infrared spectra of adsorbed water, pyridine, ammonia and carbon dioxide show that W03-Ti02 is a very strong Lewis acid, displays also a Bronsted acid behavior, and lacks significant surface basicity. Surface tungsten oxide speciesconsist of wolframyl groups (W-0) that are coordinatively unsaturated on dry surfaces. The different properties of W03-TiOz and VpOs Ti02 are discussed in relation to their use as catalysts for the selective catalytic reduction of NO,.
Introduction pure V2O5,l2and pure WO3l3have already been considered. The evolution with temperature of the morphological Among flue gas treatment methods for the control of properties of Ti-W-0 samples with different W loadings the emission of nitrogen oxides from stationary sources has been discussed e1~ewhere.l~ In this paper we report the selective catalytic reduction (SCR) of NO, by NH3 is on the bulk, surface, and redox properties of a WO3-TiO2 the best developed and the most widely used due to its catalyst which is representative of other similar materials efficiency, selectivity, and favorable economics.lV2 CataSCR catalysts. with different W content and of commercial lysts based on noble metals: zeolites: and transition-metal mixed oxides5 have been considered for this reaction. Experimental Section Commercial catalysts are made of homogeneous mixtures of high surface area Ti02 anatase as support (-80% (w/ Preparation. Pure Ti02 was prepared by neutralization at w)), V205 (
