The Adsorption of Water and Carbon Monoxide by Zinc Oxide

Kinetics of Chemisorption of Gases on Solids.

“…the ratio of the values («1/0:2) > 1, where the subscripts 1 and 2 refer here to the « value for the segments appearing first and last, respectively. Such behavior is similar to that found by Decrue and Susz (64) in part for the same system, but even more so for the system hydrogen-tungsten(IV) sulfide (64) and also for water-zinc oxide (196).…”

“…of water vapor, a = 15 and a = 6.5. Low and Taylor (196) found similar effects with the same system and reported that the rates and extents of adsorption of water by zinc oxide were greatly decreased by preadsorbed hydrogen. (191)).…”

“…Although equilibrium seems to be verified by experiments whereby the end-point of an adsorption is approached from high and from low pressures (35,98,163), sufficient facts on pressure effects, desorption, and kinetics exist to permit criticism of the general acceptance and applicability of a terminal equi- librium of the type invoked for physical adsorption. Desorption of chemisorbed gas is known frequently to require a drastic change of conditions from those of adsorption (24, 161, 312); sometimes the gas is not recoverable in the form in which it was adsorbed (107,196,281) and the presence of a gas phase aids desorption (150,180,330). Also, the generally applicable Elovich equation has the form of an expression representing the course of a reaction going to completion with negligible reverse reaction.…”

Photocatalytic Water Oxidation on ZnO: A Review

“…There are two types of sites available for H 2 O physisorption on the surface of ZnO, i.e., heterogeneous and homotattic character [25]. The physisorption sites on ZnO possess energies less than 21 kJ/mol H 2 O, and chemisorption sites with energies of 84-96 kJ/mol, whereas the enthalpy of H 2 O chemisorption on ZnO is −150 ± 10 kJ/mol [26]. The hydroxylated metal oxide surface increases the likelihood to catalyze the dissociation of H 2 O, but also affects the material's proton transfer reactivity [27].…”