The Hydrogen–Oxygen Reaction on Lanthanide Oxides. I. Hydrogen and Oxygen Adsorption on Some Lanthanide Oxides

Abstract

Hydrogen and oxygen adsorption have been measured on neodymium oxide and dysprosium oxide from 77 to 771 °K up to equilibrium pressures of approximately 6 Torr. In addition, hydrogen adsorption measurements have been made on samarium oxide and gadolinium oxide from 77 °K to approximately 100 °K. The adsorption is effectively instantaneous in all cases except for oxygen adsorption on neodymium oxide at 491 and 541 °K. Adsorption appears to be dissociative for all cases studied except for hydrogen adsorption on neodymium oxide at all temperatures and for hydrogen adsorption on dysprosium oxide at high temperatures. For neodymium oxide and dysprosium oxide three types of adsorption are observed in different temperature ranges. At low temperatures, the adsorption is probably physical; at intermediate temperatures, it is either physical, or chemical on isolated double sites; and at high temperatures it is chemical. In general, the Freundlich isotherm gives the highest correlation between calculated and experimental data. The isosteric heat of adsorption and the equilibrium uptake of hydrogen increase as the ionic radius of the metal ion decreases.