n-heptane reforming over Pt supported on beta zeolite exchanged with Cs and Li cations

Raman spectra of SO_x adsorbed on γ-alumina and Pt/γ-alumina model catalysts have been obtained with a 244 nm Raman spectrometer. Strong peaks in the 980–1380 cm^-1 region characteristic of adsorbed sulfates are clearly portrayed in the spectra, which contrast with fluorescence-dominated scans obtained using visible excitation. Broad bands are also observed in the 3500–3700 cm^-1 O–H stretch region on the γ-alumina, which belong to weakly-bound physisorbed water and more strongly-bound surface hydroxyls. These features are monitored as the samples are heated up to 600°C in the presence of nitrogen. The sulfate peaks vary in position depending on whether or not the γ-alumina is loaded with platinum, hydrated, or dehydrated. Platinum appears to inhibit the physisorption of water and the formation of hydroxyls on the γ-alumina surface, as evidenced by the absence of O–H stretch vibrations on the Pt-loaded sample. Our spectral data demonstrate that UV Raman spectroscopy is a useful technique for analytical studies of adsorbed SO_x on γ-alumina, and holds promise for future in situ investigations of other adsorbed species on catalytic substrates of automotive interest. This revised version was published online in July 2006 with corrections to the Cover Date.