Micro-Raman Spectroscopic System for in situ Evaluation of Tube Wall Type Catalyst

Abstract

A Raman micro-spectrophotometer was applied to perform in situ characterization of silica supported platinum catalyst. A custom-designed catalytic microcatalytic reactor cell for Raman observation was fabricated and dehydrogenation of cyclohexane was carried out as a model reaction. Surface of silicon microchannel was oxidized to make SiO₂ support layer and platinum catalyst was supported on the surface. The in situ catalytic microreactor cell with inlet/outlet ports was prepared using Pyrex glass cover that served as the viewing window.  The reaction temperature inside the cell was controlled by plate heater set on the Raman microscope stage. The spectra were collected under the reaction conditions and outlet gas was analyzed by GC.

Without platinum catalyst component, no reaction of either reactant or products   were observed at 393 K. When Pt catalyst was supported on the SiO₂ reactor wall, GC analysis showed that dehydrogenation reaction has carried out at 393 K and Raman spectra of 1,450 cm^-1 which was identified as π-allylic intermediates were observed. At the same time, peaks at 1,600 and 1,350 cm^-1 were observed. These could be identified as graphitic carbon and amorphous carbon, respectively. These carbon materials on the surface might be resulted in the subsequent reaction and caused the deactivation of the catalyst. All the Raman peaks were easily removed by N₂ gas purging at 393 K.