Estimation of the number of co molecules adsorbed in various modes on different crystal planes of alumina supported polycrystalline palladium

Abstract

The chemisorbed CO species formed on different crystal faces of polycrystalline palladium is not uniformly held on the metal surface. Parallel infrared and chemisorption measurements have demonstrated that the two-fold coordinated CO molecules on the Pd(111) plane are the most strongly adsorbed species. Under room-temperature evacuation of a sample with monolayer coverage about 20% of the double-bonded CO molecules on Pd(100) are desorbed. As to be expected, the weakest adsorbed CO species is the linear one on both the Pd(111) and Pd(100) faces. Using the variation in the CO bond strength some specially conducted experiments have made possible to find out a correlation between the integrated band intensities and the number of CO molecules adsorbed in various modes on the exposed crystal planes of the metal. Ratios between the integrated absorption coefficients of the IR bands from CO adsorbed in various modes were estimated. Empirical equations expressing a correlation between the number of CO molecules adsorbed on a definite face in a particular mode and the integrated intensities of the respective IR bands are proposed. Speculations concerning the crystal structure of the palladium particles are also presented.