X-ray absorption spectroscopic study on the states of gallium and platinum in Pt/Ga/H-beta zeolites

X-ray absorption (XANES and EXAFS) at the Ga K-edge and the Pt Ledge was used to monitor the variation of chemical states of gallium and platinum under in situ redox treatments in Pt/Ga/H-beta zeolites prepared by incipient wetness impregnation. It was found that the Ga species exist mainly as isolated GaO4, units after calcination. Upon reduction, the gallium(III) cations are removed from the lattice to form gallium hydride oligomers or attach to metallic platinum particles on the support. The gallium hydride oligomer is considered to be two Ga atoms separated by a distance of 2.99 Angstrom with bridging H atoms. Both Ga K-edge and Pt L-edge EXAFS analyses indicate the formation of GaPt bimetallic species with an interatomic distance of 2.51-2.54 Angstrom. These can prevent the sintering of Pt aggregates to large particles and affect the role of Pt in Pt/Ga/zeolites in aromatization of light paraffins. (C) 2000 Elsevier Science B.V. All rights reserved.