INVESTIGATION OF V OXIDATION-STATES IN REDUCED V AL2O3 CATALYSTS BY XPS (VOL 160, PG 27, 1996)/

The distribution of vanadium oxidation states in a 5.9 wt% V/Al2O3 cat alyst reduced in Hz or CO was determined from XPS V 2p spectra. Princi pal component analysis (PCA) was used to statistically determine the n umber of components (oxidation states) that describe the V 2p(3/2) env elope of the reduced V/Al2O3 catalyst. The peak positions and FWHMs of the components were obtained from iterative target transformation fac tor analysis (ITTFA). The V 2p(3/2) envelope is composed of two compon ents (oxidation states), which are centered at 517.2 and 515.5 eV (FWH Ms of 2.6 and 2.3 eV, respectively) when H-2 is the reducing agent and at 517.3 and 515.8 eV (FWHMs 2.7-2.8 eV) when CO is the reducing agen t. The components were assigned to V5+ and V3+ based on the difference in the binding energies and the results of a volumetric study of cata lyst reduction in CO. The spectral information gained from PCA and ITT FA was used to curve fit the V 2p envelopes. The extent of reduction o f the V phase was estimated from the relative abundances of V5+ and V3 + determined by curve fitting and corrected for the presumably lower d ispersion of the V3+ species. The results indicated a decrease in the average oxidation state of V to 3.5 with increasing the reduction temp erature in H-2 up to 662 degrees C. Reduction in the presence of CO wa s measured volumetrically and showed a decrease in the average oxidati on state from 5 to 3.3 over the temperature range 155-510 degrees C. C urve fitting the spectra of the GO-reduced samples using the two spect ral components identified through factor analysis yielded an average o xidation state of ca. 3.6 upon reduction at 510 degrees C. (C) 1996 Ac ademic Press, Inc.