Micro-Raman spectroscopy of Pd–B/SiO<INF>2</INF> amorphous alloy catalyst

Multi-channel confocal micro-Raman spectroscopy was used to characterize silica-supported PdCl<INF>2</INF> powder (PdCl<INF>2</INF>/SiO<INF>2</INF>) and Pd–B amorphous alloy catalyst (Pd–B/SiO<INF>2</INF>) which is formed by reducing PdCl<INF>2</INF>/SiO<INF>2</INF> with KBH<INF>4</INF>. The results show that PdCl<INF>2</INF>/SiO<INF>2</INF> gives mainly a complicated broad ν(PdCl) bands in the 150–650 cm⁻¹ region arising from surface palladium complex species such as [PdCl<INF>4</INF>]²⁻ and/or its various hydrolysis products. The Raman spectrum of Pd–B/SiO<INF>2</INF> 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 SiO<INF>2</INF> support compared with the Raman spectra of unsupported Pd–B amorphous alloy and SiO<INF>2</INF> support calcined at 873 K. Pd–B/SiO<INF>2</INF> would be gradually converted to metallic Pd and elemental boron containing a certain amount of positive boron ions upon heating in N<INF>2</INF> from 673 to 873 K. The effects of laser power and irradiation time on Pd–B and Pd–B/SiO<INF>2</INF> show that Pd–B/SiO<INF>2</INF> has better thermal stability than the unsupported material. Copyright © 2000 John Wiley & Sons, Ltd.