Interaction of gaseous hydrogen chloride and water with oxide surfaces: I. Alumina

Abstract

The influence of temperature, pressure, and outgas conditions on the adsorption of hydrogen chloride and water vapor on both α- and γ-alumina has been studied. Characterization of the adsorbents was performed using X-ray powder diffraction, scanning electron microscopy (SEM), low-temperature nitrogen adsorption—desorption measurements, BET nitrogen surface area measurements, and electron spectroscopy for chemical analysis (ESCA). Water vapor adsorption isotherms at 30, 40, and 50°C were measured on α- and γ-alumina after outgassing at 80, 200, and 400°C. Both outgas temperature and adsorption temperature influenced the adsorption of water vapor on the aluminas. The water vapor adsorption was completely reversible, α-Alumina adsorbed more water per unit area than γ-alumina. Isosteric heats of adsorption for water vapor on the aluminas were determined over a limited range of surface coverage. Hydrogen chloride adsorption isotherms at 30, 40, and 50°C were measured on the two aluminas after outgassing at 80, 200, and 400°C. Again, α-alumina adsorbed more hydrogen chloride per unit area than γ-alumina. The adsorption was only partially reversible, indicative of a chemisorption process. ESCA spectra of both aluminas were obtained after exposure to hydrogen chloride. The pH of slurries and the heats of immersion of the aluminas, outgassed from 80 to 400°C, were determined in both water and hydrochloric acid solutions of varying concentrations to complement the vapor phase measurements.