Influence of potassium on the adsorption of hydrogen on platinum(III)

Abstract

The influence of potassium adatoms on the adsorption and desorption kinetics of hydrogen on the Pt(111) single-crystal surface has been studied by temperature-programmed desorption (TPD). The authors report measurements of the dissociative sticking coefficient for H{sub 2} on Pt(111) over the entire range of coverages of H{sub (a)} and K{sub (a)} between zero and monolayer coverage. Small amounts of potassium strongly reduce the dissociative sticking coefficient for H{sub 2} on Pt(111) and eliminate the influence of a precursor in the adsorption kinetics. For example, when the K coverage, {circle_minus}{sub K}, is 0.043 (defined relative to the Pt(111) surface atom density) the initial sticking coefficient of H{sub 2} on Pt(111) at 150 K is reduced by a factor of 20. However, hydrogen adatoms on the K-modified surface are thermally stabilized compared to Pt(111). The peaks observed during H{sub 2} TPD occur at temperatures up to 150 K higher on the K-modified surface than for equivalent hydrogen coverages on K-free Pt(111). Comparisons with the Bi-modified surface demonstrate that the influence of K{sub a} exceeds local site blocking effects. The authors explain these observations in terms of a model in which K{sub a} modifies the electronic structure of the surface Pt atoms inmore » nearby sites. 51 refs., 11 figs.« less