XPS analysis of dispersed catalysts prepared via w/o microemulsion

Rh/AI2O3 catalysts prepared by water in oil w/o microemulsion were studied by X-ray photoelectron spectroscopy. The effect of water content (Rw) on rhodium particle size formed in microemulsion was investigated. Interest is focused on core level binding energy shifting for Rh 3d5/2 peak and its relationship with rhodium particle size. The Rh 3d5/2 peak was found to undergo changes in terms of shifting in binding energy, and the amount of such changes depends on the size of rhodium particle. TEM (transmission electron spectroscopy) studied showed that rhodium particle size on Rh/AI2O3 catalysts increase as water content in microemulsion increases (Average diameter for catalysts with Rw = 4, 5.7 and 11.5 are 4 nm, 8 nm and form aggregate like). These results were correlated with XPS results where Rh 3d5/2 binding energy increases for catalysts with lower water content or smaller particle size (binding energy for catalysts with Rw = 4, 5.7 and 11.5 are 311.3 eV, 311.0 eV and 310.0 eV). The rhodium catalysts with smaller particle size were found to exhibit a higher catalytic activity for the methane oxidation in rich oxygen than those catalysts with bigger particle size. For catalysts with smaller particle size, surface to volume ratio of rhodium metal increases which will increase the active sites of Rh/AI2O3 catalysts and led to higher catalytic activity performance. (Author)