The stoichiometry and poisoning by sulfur of hydrogen, oxygen and carbon monoxide chemisorption on unsupported nickel

Abstract

Hydrogen chemisorption and BET measurements (argon and nitrogen) have been used to determine the stoichiometry of hydrogen adsorption on nickel powder. The hydrogen adsorption isotherms were measured at room temperature and at 200 °C. The experimental results indicate that the H/Ni s ratio on unsupported nickel is 1:1 at both temperatures. Nickel powder samples were also poisoned with H 2S at a level of 5 ppm for 6 hr. The samples poisoned with H 2S suffer no loss in overall surface area determined by BET measurements; however, hydrogen chemisorption is substantially reduced, although less at 200 °C than at 25 °C. Data for CO adsorption on a nickel powder at 25 °C show a CO/H value of 2.09 suggesting surface carbonyl formation. After evacuation at 25 °C, however, the ratio decreases to 1.16, showing that reversible adsorption-desorption occurs. At −83 °C, a value of CO/H of 0.54 is obtained both before and after evacuation indicating no reversible adsorption. The number of CO molecules irreversibly adsorbed per surface nickel atom is 0.54. Data for adsorption of oxygen at 25 °C show that three oxygen atoms adsorb for every nickel surface atom and that approximately one of three oxygen atoms can interact with but not be removed by titration with hydrogen at 25 °C.