Micro-Raman spectroscopy of Pd-B/SiO2 amorphous alloy catalyst

Multi-channel confocal micro-Raman spectroscopy was used to characterize silica-supported PdCl2 powder (PdCl2/SiO2) and Pd–B amorphous alloy catalyst (Pd–B/SiO2) which is formed by reducing PdCl2/SiO2 with KBH4. The results show that PdCl2/SiO2 gives mainly a complicated broad ν(PdCl) bands in the 150–650 cm−1 region arising from surface palladium complex species such as [PdCl4]2− and/or its various hydrolysis products. The Raman spectrum of Pd–B/SiO2 amorphous alloy shows broad bands in the 300–500 cm−1 and ca 800 cm−1 regions. They may be assigned to Pd–B vibration overlapping that of the amorphous SiO2 support compared with the Raman spectra of unsupported Pd–B amorphous alloy and SiO2 support calcined at 873 K. Pd–B/SiO2 would be gradually converted to metallic Pd and elemental boron containing a certain amount of positive boron ions upon heating in N2 from 673 to 873 K. The effects of laser power and irradiation time on Pd–B and Pd–B/SiO2 show that Pd–B/SiO2 has better thermal stability than the unsupported material. Copyright © 2000 John Wiley & Sons, Ltd.