Adsorption additive effect

In their electrochemical surface properties, a number of metals (lead, tin, cadmium, and others) resemble mercury, whereas other metals of the platinum group resemble platinum itself. Within each of these groups, trends in the behavior observed coincide qualitatively, sometimes even semiquantitatively. Some of the differences between mercury and other. y- or p-metals are due to their solid state. Among the platinum group metals, palladium is exceptional, since strong bulk absorption of hydrogen is observed here in addition to surface adsorption, an effect that makes it difficult to study the surface itself. 

The admixture of lead to platinum has a similar effect (Fig. 5). At the same time, the aromatizing activity increases up to about 1 1 Pt Pt atomic ratio 24). With even more lead it scatters aroimd somewhat lower values 66). Electron donation from lead to platinum has been proved by infrared spectroscopy, so one may wonder whether lead is present as metal in the catalyst (75). The additive effect can also be interpreted by its creating hydrogen-deficient surface sites favorable for aromatization. When more lead is present than platinum (i.e., where no more continuous platinum surface is probable), the inverse correlation between hydrogen adsorptivity and activity ceases to exist. 

An interesting additional effect of UV irradiation on some semiconductor surfaces is the increase in the extent and rate of adsorption of gases. As an example, in the absence of UV irradiation, SO2 adsorbs on the a-Fe203 surface with a very low sticking coefficient. However, formation of electron-hole pairs by UV irradiation results in the creation of Fe2+ defect sites, enhancing... 

Tsuruya and co-workers (83,84) recently reported that addition of alkaline earth metals (e.g., Ca, Sr, and Ba) to an Ag/SiOi catalyst by a coimpregnation method enhanced the catalytic activity of the partial oxidation of benzyl alcohols into benzaldehydes, with production of only small amounts of byproducts (carbon dioxide, toluene, and benzene). The formation of carbonaceous material was thought to be inhibited by the alkaline earth metals, which also helps to disperse the metallic silver and facilitate oxygen adsorption. This effect causes the formation of an oxygenated silver surface that is generally believed to be responsible for the partial oxidation of benzyl alcohol. 

For gas transport in small pores (say, less than the 10 nm range) the sizes of which are no longer much larger than those of the gas molecules, the contribution of viscous flow can be neglected and other considerations need to be factored in the model. First, the gas molecules are considered to be hard sphere with a finite size and the gas diffusion process is assumed to proceed in the membrane pores by random walk. The membrane pores are assumed to consist of smooth-wall circular capillaries. In addition to gas molecules colliding with the membrane pore walls, adsorption on the pore wall and the associated surface flow or diffusion are considered. Adsorption also effectively reduces the pore size for diffusion. 

The third class involves electroactive adsorbed species, yet it also encompasses the case in which, although originally inactive, the species is activated or modified in the adsorption process to give rise to the formation of electroactive adsorbed molecules. Obviously, all these effects discussed for the two previous classes are observed for this class, but additional effects are observed for the adsorbed species itself. Indeed, adsorption modifies (1) the concentration of the species at the electrode surface vis-a-vis that predicted from its bulk concentration, and (2) the energetics of the electron transfer reaction. The latter point arises because of additional thermodynamic contributions to be considered in the Rq/Ro or Po/P equilibria in Scheme 5 and also from changes in the reorganization energies. The former point leads to a variety of behaviors, since it is obviously a function of the kinetics of adsorption-desorption phenomena. A third additional effect of electroactive adsorbed species arises from their possible ability to act as electron transfer med-... 

FeClj was then added to the slurries to evaluate the effect of HFO precipitation on As(V) adsorption. Additional synthetic ground water was added to each slurry to make the final volume 500 mL. In one experiment, 10 mg/L Fe(III) was added. The slurries were then equilibrated for 3 days to allow complete precipitation of HFO. NaOH was then added to slowly increase pH. Slurries were equilibrated for 1 day following each addition of 0.1 N NaOH, followed by 0.4 itm filtering of 20 mL aliquots for As(V) and P(V) analysis. Additional FeCl3 was then added to increase the Fe(III) concentration to 100 mg/L and the experiment was repeated as above. Arsenate adsorption for the 100 mg/L Fe(III) concentration was measured for initial As(V) concentrations of 145 and 1000 lig/L. The iron additions of 10 and 100 mg/L are equivalent to 0.1 and 1.0 mg/g of basalt. 

The laboratory and field results show that the aquifer basalt has limited capacity for adsorption of As(V), presumably by naturally occurring HFO. However, addition of HFO can significantly increase As(V) adsorption. The effectiveness of HFO addition to this aquifer depends on the HFO concentration and the pH because the concentration of adsorption sites on HFO increases with decreasing pH. Initially, pH adjustment will only be... 

The additive effect of noble metals to NiO-MgO solid solution on the activity and on the resistance to the carbon deposition in oxidative steam reforming of methane under pressurized condition (I.O MPa) was investigated. It was found that the addition of small amount of Rh or Pd was effective to enhance the activity and to suppress the carbon deposition. The Pd and Rh K-edge EXAFS analysis indicated that M-Ni alloy phase (M=Rh or Pd) was formed, and FTIR spectra of CO adsorption suggests that the alloy could be formed on the surfece of bimetallic particles. 

Experimental data for adsorption of Ag, Cd, and Zn in two reference systems, Fe(OH)3 and Si02, were reproduced using MICROQL and the constant capacitance adsorption model. Model results for the reference systems were used to simulate the effects of soluble silica on sorption in Fe(OH)3 + Si02 binary suspensions. Adsorptive additivity is not observed in such systems. However, the experimental results are consistent with a scenario involving partial Si02... 

---