Hydride Formation Diminishes CO Reduction Rate on Palladium.

The catalytic hydrogenation of CO includes the dissociation of hydrogen and further reaction with CO and intermediates. We investigate how the amount of hydrogen in the bulk of the catalyst affects the hydrogenation reaction taking place at the surface. For this, we developed an experimental setup described herein, based on a magnetic suspension balance and an infrared spectrometer, and measured pressure-composition isotherms of the Pd-H system under conditions relevant for CO reduction. The addition of CO has no influence on the measured hydrogen absorption isotherms. The pressure dependence of the CO formation rate changes suddenly upon formation of the β-PdH phase. This effect is attributed to a smaller surface coverage of hydrogen due to repulsive electronic interactions affecting both bulk and surface hydrogen.