Chemisorption

About: Chemisorption is a research topic. Over the lifetime, 16298 publications have been published within this topic receiving 554989 citations.

The Reactions of Oxygen at Dark and Irradiated Zinc Oxide Surface

Abstract: Studies of the kinetics of adsorption of oxygen on zinc oxide over the temperature range from 25 to 390 $^\circ$C have provided evidence for two distinct types of chemisorption, one prevalent below 200 and the other above 300 $^\circ$C. This pattern of activity has been confirmed by measurements of desorption rates over the same temperature range. The mode of preparation and pretreatment of the oxido oxort a strong influence on the adsorption behaviour, and these differences are accentuated when the processes of adsorption and desorption are studied in the presence of irradiation in the ultra-violet and visible. Photodesorption of oxygen is confirmed to be the normal behaviour for zine oxide, but photo-adsorption has been observed under conditions of high excess zinc concentration. The photo-effects are especially marked below 300 $^\circ$C. The adsorption studies have been followed up by experiments on the rate of the intermolecular oxygen reaction $^{18}$O$\_2$+$^{16}$O$\_2 \leftrightharpoons$ 2$^{18}$O$^{16}$O, and on the influence of irradiation on this catalysis. It is evident that irradiation stimulates both adsorption and desorption, but the balance between them depends on the previous history of the specimen. The experiments with heavy oxygen have also included a brief study of oxygen exchange with zinc oxide at 400 to 500 $^\circ$C. The results as a whole are discussed in terms of the model of zinc oxide as an n-type semiconductor with interstitial zinc, and oxygen chemisorbed as O$^-$ and O$^{2^-}$, respectively, are held to be mainly responsible for the phenomena observed. The relationship with conductivity studies is emphasized and the depletive chemisorption of oxygen, forming a boundary layer, is discussed in some detail. The depletion of electrons is not exhaustive for normal specimens of zinc oxide, and the treatment of this case leads to an expression consistent with the observed kinetics. Several possible mechanisms for photo-adsorption are put forward, and the association with high donor concentrations is discussed. Interstitial zinc diffusing under the influence of the electric field of chemisorbed oxygen is considered to play an important role in specimens heated above 300 $^\circ$C.

Corrosion Inhibition in HCl Using Methyl Pyridines

Abstract: The inhibiting effect of pyridine and seven of its methyl derivatives on the corrosion of iron in O2‐free, at 35°C was determined. Corrosion rates were measured by colorimetric analysis for iron with mercaptoacetic acid. The relative inhibitor efficiency and cathodic potential shift increased with increasing inhibitor concentration and, for a given concentration, with increasing electron density at the nitrogen atom. Both increased slightly with decreasing concentration, but a temperature increase of 10°C had no effect on either. The proposition that chemisorption is involved in corrosion inhibition is supported by these experiments. As a supplementary item the great importance of careful purification of the organic compounds used in such researches as this is documented.

Surface diffusion of hydrogen and CO on Rh(111): Laser‐induced thermal desorption studies

Abstract: Surface diffusion of hydrogen, deuterium, and CO on Rh(111) has been investigated by laser‐induced thermal desorption (LITD) and compared with previous results for these species on Pt(111) and on other metals. As the coverage θ of deuterium increases from 0.02 to 0.33, the preexponential factor D0 remains constant at 8×10−2 cm2/s, but the diffusion activation energy Ediff rises from 3.7 to 4.3 kcal/mol. Ediff for hydrogen is 0.6 kcal/mol lower than for deuterium, consistent with the difference in zero‐point energy. For CO, Ediff =7 kcal/mol at all coverages, but D0 rises from 10−3 to 10−2 cm2/s between θ=0.01 and 0.40. Values of Ediff for these adsorbates vary by several orders of magnitude for surfaces on which heats of adsorption are essentially identical. These differences appear to correlate with differences in heats of adsorption in different binding states which form saddle point configurations in surface diffusion. Ediff is found to be nearly identical to the reaction activation energies for the CO...