Role of pH in the stabilization of two types of silver clusters

Conditions for stabilization of silver clusters peaking at 320 nm are fond. Role of pH in stabilization of two types of silver clusters peaking at 320 and 290 nm is discussed.     

Stability of silver clusters in mordenites with different SiO2/Al2O3 molar ratio

The stability and decay of silver clusters characterized by absorption bands 320 and 285 nm incorporated in mordenites with different SiO₂/Al₂O₃ molar ratios were studied under ambient conditions. Significantly different rates of disappearance of these two bands were the basis for assigning them to different silver species. Oxidation converts the clusters peaking at 320 and 285 nm into other silver clusters characterized by absorption bands at 310 and 240 nm, respectively. The oxidation of silver clusters peaking at 285 nm is significantly faster than that at 320 nm. The stability of both original clusters decreases with acid site strength that, in its turn, depends on Si0₂/Al₂O₃ molar ratio. The minimum lifetime of clusters peaking at 320 and 285 nm equal to ca. 40 and 20 days, respectively, was observed for mordenite characterized by the strongest acid sites. For mordenites possessing weaker acid sites, the lifetime of these clusters is found to be more than 50 months. The oxidation of silver clusters is reversible, and re-reduced silver clusters were revealed to possess the same electron structure as original ones.     

Copper clusters and small particles stabilized within nanoporous materials

Copper was incorporated into mordenites with variable SiO₂/Al₂O₃ molar ratio, porous silica xerogels, natural pumice, and -alumina. The UV/Visible spectroscopy of the copper species produced as the result of hydrogen reduction and catalytic runs is presented. Different spectral features were detected assignable to nanoparticles, few-atomic clusters, oxide forms and Cu(II) compounds. The significant effect of support upon the redox-behavior of copper is discussed on the basis of experimental data.     

Optical response of Cu clusters in zeolite template

Optical properties of Cu clusters embedded in mordenite are studied experimentally and theoretically. In this work we discuss spectral features of the system at various reduction steps and compare then with the results of spectra obtained within a theoretical model. The model employed consists of Cu clusters embedded in a homogeneous matrix. A second model employed introduced further variation considering a three component system where air or water can be present. The macroscopic dielectric response of the system is obtained within the Maxwell Garnett approximation. In this approach the complex non-local in homogeneous dielectric response of the zeolite+copper system is replaced by an effective homogeneous dielectric function. Metallic clusters can occupy specific available cavities in the zeolite framework. The presence of clusters that are smaller than the cavities in which they reside can lead to an air-Cu or water-Cu interface which allows shifts in surface plasmon resonance energies. As observed experimentally the energy of the main resonance is seen to be insensitive to the filling fraction ratios and highly susceptible to the embedding matrix properties. Reflectance spectra have been obtained which can be explained within this model.     

Effect of the exposure time at recording an X-ray photoelectron spectrum on the charge state and environment of copper in mordenites

The effect of the exposure time at recording an X-ray photoelectron spectrum on the valence state and environment of copper in mordenite-type zeolite has been studied. It has been found that X-ray irradiation under the conditions of the experiment results in the redistribution of copper ions between the existing forms determined by differences in their coordination but without change in their valence state.     

Features of Component Interaction in Concentrated Solutions of Multicomponent Systems

Classical complex formation processes in the multicomponent systems Cd(NO₃)₂-MCl-H₂O (M = Li, Cs) occur at preeutectic concentrations of salts. At posteutectic concentrations of salts the formation of cadmium chloride complexes is of structurally enforced nature and depends on the type of the cybotactic group dominating in the solution. The example of the system Cd(NO₃)₂-LiCl-H₂O was used to show that the law of mass action does not apply to systems in which structurally enforced processes occur. Differences in the solubility of MCl (M = Li, Cs, Na) in concentrated solutions of cadmium nitrate are proposed to explain in terms of differences in interactions of cybotactic groups formed by cadmium nitrate and the corresponding chloride.     

LOCAL STRUCTURE OF PROTONATED MORDENITES WITH SiO2/Al2O3 ≈ 15 PROBED BY MULTINUCLEAR NMR

Journal of Structural Chemistry - Two samples of protonated mordenite with close nominal molar ratios (MRs) SiO2/Al2O3 equal to 15.0 and 15.2 are studied by various physicochemical methods. Both...