The sticking probability for H2 in presence of CO on some transition metals at a hydrogen pressure of 1Â bar

The sticking probability for H2 on Ni, Co, Cu, Rh, Ru, Pd, Ir and Pt metal films supported on graphite has been investigated in a gas mixture consisting of 10 ppm carbon monoxide in hydrogen at a total pressure of 1 bar in the temperature range 40-200 °C. Carbon monoxide inhibits the sticking probability significantly for all the metals, even at 200 °C. In the presence of 10 ppm CO, the sticking probability increases in the order Ir, Pt, Ni, Co, Pd, Rh, Ru, whereas for Cu, it is below the detection limit of the measurement, even in pure H2. The sticking probability for H2 in presence of CO relative to its value in pure hydrogen is largest for Pd and smallest for Pt and Ir. The high sensitivity to CO seen for Ir and Pt is explained by the fact that the difference in desorption energy for H and CO is largest for those metals.