In-situ Fourier transform infrared studies of reaction mechanisms in heterogeneous catalysis

Abstract

An I.R. cell which can be used, in heterogeneous catalysis, as a continuous flow reactor up to 3 MPa and 575K is described. It is coupled to an on-line gas chromatograph for product analysis. It simultaneously allows recording the I.R. spectra of adsorbed species during the reaction, a pressed wafer being the catalyst. Using a FT-JR spectrometer, spectra can be recorded every 5 seconds. The system has been used to study different reactions such as i) n-hexane isomerization on H-mordenite and Pt-H-mordenite catalysts; ii) CO hydrogenation over Rh/CeO2 catalysts; iii) methanol synthesis on Cu-ZnAl2O4 catalysts with variable CO + CO2 + H2 feeds. Special attention has been paid to determine if the species which are observed are intermediates in the studied processes. In such a case, their detection provides very useful access to the reaction mechanisms. Moreover, the system allows us to follow the state of catalysts, under working conditions, for instance the degree of the zeolite deactivation or the reduction state of copper in the case of methanol catalysis.