Chemisorption of diatomic molecules (H 2, N 2, CO) on transition d-metals

Abstract

The interaction energies of diatomic molecules, H 2, N 2, and CO with transition d-metal surfaces are empirically calculated using a bond energy bond order (BEBO) approach developed in earlier papers. The two problems, i.e., (i) does a molecule chemisorb on a given surface and (ii) whether the adsorbed species is in a molecular form or dissociative form, are examined from the potential energy curves obtained. The metals are then classified approximately into four groups, A, B, C, and D. The A group metals, which consist mainly of IV B, V B, and VI B group metals in the periodic table of the elements, strongly chemisorb all the above gases including O 2 and NO molecules in a dissociative form at room temperature. The group D metals consisting of noble d-metals, on the other hand, chemisorb NO and CO in a molecular form and do not decompose CO and N 2 molecules. The group B (Fe, Re) and C (Co, Ni, Tc) metals which are known as main elements of catalysts for the reactions of Fischer-Tropsch and ammonia syntheses have intermediate adsorption properties between the A and D group metals. These qualitative and quantitative results of heats of dissociative and nondissociative adsorption are summarized in tables and compared with the experiments.