Applied Catalysis A: General, 84 (1992) 123-139 Elsevier Science Publishers B.V., Amsterdam 123 APCAT 2253 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Effect of WO, loading on the surface acidity of WO,/Al,O, composite oxides R. Zhang’, J. Jagiello’, J.F. Hu3, Z.-Q. Huang4 and J.A. Schwarz Department of Chemical Engineering and Materials Science, Syracuse University, Syracuse, NY 13244 (USA) A. Datye Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87131 (USA) (Received 5 December 1991, revised manuscript received 8 January 1992) Abstract High-resolution transmission electron microscopy, X-ray energy dispersive spectroscopy, colorimet- ric titration and inverse gas chromatography (IGC ) were used to study the changes in acidity of a series of W03/A1203 composite oxides with increasing loading of tungsten. The addition of WOa increases the Lewis and Brensted acidity of the series of composites. We find that, for the highly dispersed solid acid, WO,/Al,O,, the modified Benesi titration provides an estimate of the number of acid sites and that Lewis and Brenstedpartitioning cannot be conclusively assessed. The inverse gas chromatography tech- nique offers certain advantages in that it can be performed at elevated temperatures (close to reaction temperatures), in a gaseous environment, and on colored samples. The electron donating properties of the probes used in IGC have enabled us to speculate on the source of Brensted acidity introduced into this system by the presence of the second-phase oxide. Charge delocalization into the support due to terminal oxygen atoms is proposed to be the source of this increased Brensted acidity and is analogous to that occurring when halides are added to alumina. Keywords: acidity, acid sites, alumina, inverse gas chromatography, tungsten oxides, tungsten trioxide/ alumina, INTRODUCTION Binary oxides formed by the impregnation of a supporting primary oxide by a metal oxide precursor form a new class of catalytic materials referred to as Correspondence to: Professor J.A. Schwarz, Department of Chemical Engineering and Materials Science, Syracuse University, Syracuse, NY 13244, USA. Tel. (+l-315)4434575, Fax. (+l- 315)4432559. ‘On leave from Scientific Committee of Lanzhou, China. ‘On leave from Institute of Energochemistry of Coal and Physicochemistry of Sorbents, Univer- sity of Mining and Metallurgy, 30-059 Krakbw, Poland. 30n leave from Fudan University, Shanghai, China. %n leave from Shanghai Second Polytechnic University, China. 0926-860X/92/$05.00 0 1992 Elsevier Science Publishers B.V. All rights reserved.