Effect of rhodium modification on structures of sulfided Rh-Mo-K/Al2O3 catalysts studied by XAFS

Abstract

Local structures of the molybdenum sulfide species in the sultided Rh-Mo-K/Al2O3 catalysts with various rhodium loadings have been investigated by XAFS. From the fitting results, the Mo-Mo coordination number for the sample free of rhodium (ca. 3.7) is similar to that for the crystalline MoS2, indicating that the supported sulfided molybdenum species mainly present as large patches of MoS2-like slabs. For the rhodium-modified samples, however, the amplitudes of the MoS and Mo-Mo coordination shells are sharply reduced, revealing a high dispersion of the MoS2-like species in the catalysts. The scheme of the microstructures of the sulfided molybdenum species stabilized on the alumina support is discussed based upon the analysis of the EXAFS data.