A Study of Stability of Tungstophosphoric Acid, H 3 PW 12 O 40, Using Synchrotron XPS, XANES, Hexane Cracking, XRD and IR Spectroscopy Pasl A. Jalil*, M. Faiz**, N. Tabet**, N.M. Hamdan § , Z. Hussain § *Chemistry Department, KFUPM, Dhahran 31261, Saudi Arabia **Physics Department, KFUPM, Dhahran 31261, Saudi Arabia § ALS, Lawrence Berkeley Lab, Berkeley CA 94720, USA Abstract: Tungstophosphoric Acid (HPW) has been investigated using different spectroscopic and chemical techniques. Bulk sensitive techniques such as x-ray diffraction (XRD) and infrared (IR) spectroscopy indicate that the acid is stable at temperatures as high as 300 ºC or higher. However, our work suggests that HPW starts loosing stability at temperature as low as 200 ºC. For instance, P 2p peak was not detected in the XPS spectrum of HPW preheated at 100 ºC, but was clearly observed after preheating the acid at 200ºC and 400 ºC. This suggests the destruction of the molecules of the surface leading to the enrichment of surface with phosphorous. These results may explain why HPW deactivates very fast, e.g. 8 min at 200 ºC, in hexane cracking experiments. This could limit the use of HPW in surface reactions that even require moderate temperatures. Detailed infrared spectroscopic investigation of the HPW as a function of temperature showed a gradual increase in 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 molecule was decreased upon heating.