Dependence of Copper Species on the Nature of the Support for Dispersed CuO Catalysts Antonella Gervasini* Dipartimento di Chimica Fisica ed Elettrochimica & Centro di Eccellenza CIMAINA, UniVersita ` degli Studi di Milano, Via C. Golgi 19, 20133 Milano, Italy Maela Manzoli and Gianmario Martra Dipartimento di Chimica I.F.M. & NIS Centre of Excellence, UniVersita ` di Torino, Via P. Giuria 7, I-10125 Torino, Italy, and UdR Torino 1 InteruniVersity Consortium INCA Alessandro Ponti Istituto di Scienze e Tecnologie Molecolari, Consiglio Nazionale delle Ricerche, Via Golgi 19, I-20133 Milano, Italy, and UdR Milano UniVersita ` , INSTM, Via Giusti 9, 50121 Firenze, Italy Nicoletta Ravasio* and Laura Sordelli Istituto di Scienze e Tecnologie Molecolari, Consiglio Nazionale delle Ricerche, Via Golgi 19, I-20133 Milano, Italy Federica Zaccheria Dipartimento di Chimica Inorganica, Metallorganica e Analitica (CIMA), UniVersita ` degli Studi di Milano, Via Venezian 21, I-20133 Milano, Italy ReceiVed: NoVember 15, 2005; In Final Form: February 20, 2006 Copper catalysts prepared by chemisorption-hydrolysis technique over silica (Cu/Si) and silica-alumina (Cu/SiAl) supports were studied to understand the role of the support on the nature and surface properties of the copper species stabilized on their surfaces. The morphological and surface properties of the copper phases have been characterized by complementary techniques, such as HRTEM, EXAFS-XANES, EPR, XPS, and FTIR. For the FTIR investigation, molecular probes (CO and NO) were also adsorbed on the surfaces to test the reactivity of the copper species. Moreover, the catalytic performances of the two catalysts have been compared in the HC-SCR reaction (NO reduction by C 2 H 4 ) performed in highly oxidant conditions. The superior activity and selectivity of the supported silica-alumina catalyst with respect to that supported on silica could be related with the different nature of the copper species stabilized on the two supports, as emerged from the results obtained from the spectroscopic investigations. Small and well-dispersed CuO particles were present on silica, whereas isolated copper ions predominated on silica-alumina, likely in regions rich in alumina that made some exchangeable sites available, as indicated by FTIR spectra of adsorbed CO. The less positive global charge of copper species on Cu/SiAl than in Cu/Si has been confirmed by EPR, XPS, and EXAFS-XANES analyses. Introduction In the past few years, the number of patents and scientific papers dealing with the use or the preparation of copper catalysts has been growing continuously. This is mainly due to the activity and the selectivity exhibited by these catalysts in a wide series of reactions suitable to be used, on one hand, in pollutants abatement processes, such as the direct decomposition of NO 1-3 and the selective lean reduction of NO x to N 2 by hydrocarbons in excess of O 2, 4,5 and, on the other hand, in hydrogenation or oxidative coupling in liquid media. 6,7 However, the activity in some of these reactions needs to be improved. Copper dispersion, depending in turn from the catalyst preparation method, has been shown to be one of the key factors for the catalytic activity. 8-10 That is why we focused our attention on the chemisorption- hydrolysis technique, allowing a higher dispersion of the metallic phase in supported copper catalysts. By comparing two sets of Cu/TiO 2 samples with copper loading ranging from 2 to 8%, one obtained by the conventional wet impregnation technique and the other by the so-called “chemisorption-hydrolysis” method, some of us found that samples obtained with the latter technique show much higher Cu(0) specific surface areas. Moreover, we could show that on both samples, highly dispersed two-dimensional (2D) copper aggregates rendered partially electropositive by interaction with the support are present, whereas small and well-dispersed three-dimensional (3D) copper metallic particles are only present on samples prepared by chemisorption-hydrolysis. 11 The same morphological and surface properties of the copper phase were also found on Cu/SiO 2 and two Cu/SiO 2 -TiO 2 * To whom correspondence should be addressed. E-mail: antonella.gervasini@unimi.it (A.G.), n.ravasio@istm.cnr.it (N.R.). 7851 J. Phys. Chem. B 2006, 110, 7851-7861 10.1021/jp056604c CCC: $30.25 © 2006 American Chemical Society Published on Web 03/25/2006