The surface of supported tungstophosphoric acid H3PW12O40 (HPW) on all-silica MCM-41 has been investigated using high-resolution X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). The results show the interaction between HPW and MCM-41 upon impregnation. Nuclear magnetic resonance (NMR) spectroscopy results also seem to confirm the above conclusion. Heating the supported acid increased the structural damage of HPW and MCM-41. Our results also suggest the formation of tungsten oxides on the surface upon heat treatment at 400 degreesC. A detailed analysis of the infrared (IR) spectra showed a gradual increase in the absorbance of the W-O-W corner shared vibration relative to the absorbance of the other bands. This indicates that the symmetry, and hence the stability of the bulk molecules were also decreased upon heating. (C) 2003 Elsevier B.V. All rights reserved.