Transient <i>in Situ</i> Infrared Methods for Investigation of Adsorbates in Catalysis

Abstract

This paper reports the details of a high-pressure and -temperature in situ transmission infrared reactor cell and experimental approaches for investigation of the nature of adsorbates in CO hydrogenation and NO-CO reaction on Rh/SiO 2 catalyst. The infrared cell used in this study allows easy assembling and reliable operation up to 773 K and 6.0 MPa. The structure and coverage of adsorbates during reaction are determined by an infrared spectrometer, and the composition of gaseous effluent from the infrared cell is monitored by a mass spectrometer. The steady-state 13 CO step transient shows that gaseous CO rapidly exchanges with adsorbed CO, which is slowly converted to CH 4 during CO hydrogenation at 513 K and 0.1 MPa. The pulsing CO study reveals that linear CO is more reactive than bridged CO during methane and CO 2 formation, and bridged CO sites are blocked from CO disproportionation. Steady-state 13 CO pulse transients show that the CO 2 response leads the CO response, and Rh-NCO and Si-NCO are not involved in the formation of CO 2 from CO during NO-CO reaction. The advantages and limitations of the in situ infrared and transient approaches for catalysis research will be discussed.