In Situ X-ray Absorption Study of the Genesis and Nature of the Reduced Gallium Species in Ga/HZSM5 Catalysts

In situ gallium K edge XAFS spectroscopy experiments were performed with GaZSM5 catalysts containing two different gallium loadings (2 and 4%) under hydrogen or propane in the 703-823K temperature range. It was found that, irrespective of the gallium loading and reducing gas, linear correlations were found between the coordination numbers of both the first (Ga-O scattering legs) and second (Ga-Ga scattering legs) gallium coordination spheres estimated from EXAFS and the degree of reduction estimated by XANES. The results showed that the reduction proceeds from Ga3+ binuclear species 4-fold coordinated to oxygen to an isolated Ga+ ion coordinated to a single oxygen atom.