Infrared Study of the Dynamics of Adsorbed Species During Co Hydrogenation

The dynamics of adsorbed species on Rh/SiO 2 catalyst during CO hydrogenation to form methane was studied using in situ infrared (IR) spectroscopy combined with steady-state isotopic transient and pulsing CO methods. In situ IR spectra and transient responses reveal that gaseous CO rapidly exchanges with adsorbed CO and hydrogenation of CH x intermediate is the rate-determining step under steady-state conditions. Compartment modeling and site distribution analysis of the transient responses show that CH x is hydrogenated to CH 4 with a bimodal distribution of the rate constant. When CO is pulsed into H 2 flow, CO dissociation is the rate-determining step and linear CO depletes faster than bridged CO. The rate-determining step for methanation is a delicate balance of intermediate concentrations, surface intrinsic properties, and reaction conditions. Mechanistic and kinetic studies of catalytic reactions have to be performed under practical reactor conditions.