Investigation of Binary and Ternary Cu-V-Ce Oxides by X-ray Diffraction, Thermal Analysis, and Electron Paramagnetic Resonance R. Cousin, S. Capelle, E. Abi-Aad,* D. Courcot, and A. Aboukaı ¨s Laboratoire de Catalyse et Environnement, EA 2598, Universite ´ du Littoral-Co ˆ te d’Opale, MREID, 145 Avenue Maurice Schumann, F-59140 Dunkerque, France Received January 18, 2000. Revised Manuscript Received June 15, 2001 The influence of vanadyl and copper precursors, impregnated on ceria, was evaluated by X-ray diffraction (XRD), thermal analysis (TG-DSC), and electron paramagnetic resonance (EPR) of binary and ternary oxides. The formation of a copper oxalate phase from copper nitrate and vanadyl oxalate was revealed during the preparation of the ternary oxide (1Cu1V10Ce). Three types of Cu(II) species in the dried copper containing solids were evidenced: (i) Cu(II) cations with an elongated octahedral symmetry attributed to the copper nitrate precursor, (ii) a copper oxalate phase with a compressed octahedral symmetry and (iii) well-dispersed Cu 2+ ions on the ceria surface, located in a tetragonally distorted octahedral crystal field and surrounded by less than six ligands. The dispersion of the copper- (II) cations over the ceria support surface was facilitated by the copper nitrate precursor. The EPR intensities clearly show that the increase of the oxalate precursor content induces a large fraction of copper that escapes detection by EPR and could be consistent with the presence of large Cu(II) agglomerates. After the calcination of the solids at 300 °C, only one copper species was evidenced and assigned to Cu 2+ ions located in octahedral sites tetragonally distorted. The distortion was more pronounced in the presence of vanadium than in the case of the copper cerium oxide samples. The high dispersion of the copper(II) cations over the ceria support surface, owing to the copper nitrate precursor, was confirmed even after its thermal decomposition. Introduction Catalytic performances of the metal oxide catalysts are highly dependent on several parameters, such as the type of support, the active phase dispersion, the structural properties, the thermal treatments, the ac- tivation conditions, and it is undeniable that the prepa- ration method and the precursors have a major effect on the previous parameters and on the performances of the catalytic materials. 1-5 It has been recently demonstrated 5 that during the preparation of alumina as a catalyst support from aluminum nitrates, NO 2 • radicals have been formed in the catalyst after calcina- tion of the solid under air at different temperatures. These radicals remained stable until a calcination temperature of 800 °C. When the calcined catalyst was degassed under vacuum above 300 °C, the NO 2 • was reduced to give NO • and O - species, which were both tightly trapped in the solid. 5 The formation of such unexpected radicals could affect the catalytic properties of solids in the case where they were not previously evidenced. Cerium(III) hydroxide is commonly prepared by pre- cipitation from cerium(III) nitrate and sodium hydrox- ide. In presence of oxygen in air, at room temperature, Ce(OH) 3 leads to the formation of Ce(OH) 4 . After calcination of this hydroxide at high temperatures (>400 °C), ceria (CeO 2 ) is mainly formed, and EPR reveals some Ce 3+ ions, 6 which are paramagnetic species char- acterized by the presence of a simple electron in the 4f orbital. Ceria exhibits a large deviation from its CeO 2 stoichiometric composition by the creation of oxygen vacancies. 7-10 This property is the main reason that ceria is widely used as a support in catalysis. When Cu 2+ ions were added to CeO 2 and calcined under air at different temperatures, monomers, dimers, and clusters of Cu 2+ were formed in the solid. 11-13 Cu 2+ * Corresponding author: E-mail: abiaad@univ-littoral.fr. (1) Bond, G. C.; Perez Zurita, J.; Flamerz, S. Appl. Catal. 1986, 27, 353. (2) Haller, G. L.; Resasco, D. E. Adv. Catal. 1987, 108, 364. (3) Wainwright, M. S.; Trimm, D. L. Catal. Today 1995, 23, 29. (4) Boccuzzi, F.; Chiorino, A.; Martra, G.; Gargano, M.; Ravasio, N.; Corrozzini, B. J. Catal. 1997, 165, 129 and references therein. (5) Decarne, C.; Abi-Aad, E.; Aboukaı¨s, A. Catal. Lett. 1999, 62, 45. (6) Abi-Aad, E.; Bechara, R.; Grimblot, J.; Aboukaı ¨s A. Chem. Mater. 1993, 5, 6, 793. (7) Harrison, P. G.; Creaser, D. A.; Wolfindale, B. A.; Waugh, K. C.; Morris, M. A.; Mackrodt, W. C. In Catalytic Surface Characterisa- tion; Dines, T. J., Rochester, C. H., Thomson, T., Eds.; Royal Society of Chemistry: Cambridge, 1992; 76. (8) Otsuka, K.; Hatano, M.; Morikawa, A. J. Catal. 1983, 79, 493. (9) Ko ¨ rner, R.; Ricken, N.; No ¨ lting, J.; Riess, I. J. Solid State Chem. 1989, 78, 136. (10) Brauer, G.; Gingerich, A.; Holtzchmidt, U. J. Inorg. Nucl. Chem. 1960, 16, 77. (11) Soria, J.; Conesa, J. C.; Martinez-Arias, A.; Coronado, J. M. Solid States Ionics 1993, 63-65, 755. (12) Aboukaı ¨s, A.; Bennani, A.; Aı ¨ssi, C. F.; Wrobel, G.; Guelton, M.; Ve ´drine, J. C. J. Chem. Soc., Faraday Trans. 1992, 88(4), 615. (13) Aboukaı ¨s, A.; Bennani, A.; Aı ¨ssi, C. F.; Wrobel, G.; Guelton, M. J. Chem. Soc., Faraday Trans. 1992, 88 (9), 1321. 3862 Chem. Mater. 2001, 13, 3862-3870 10.1021/cm000043e CCC: $20.00 © 2001 American Chemical Society Published on Web 09/20/2001