Porous Vycor surfaces

Moudrakovski et investigated the interaction of HP xenon with porous Vycor surfaces and measured the diffusion of xenon through the small 42 A pore structure of the Vycor. Their measurement of the diffusion constant, 2.2 X 10 m s compared well with similar experiments using adsorption measurements and conventional xenon experiments. 

We have also obtained measurements for the relaxation time of octafluorocyclo-butane (c-C4F8) gas in porous Vycor glass. Vycor (Corning Glass, -96.5 wt-% Si02) has a specific surface area of approximately 120 m2 g-1, and was cleaned using H202 and evacuated to 10-8 Torr before all measurements. The Vycor was placed in... 

Solid surfaces nature of the surface of colloidal silica, clays, zeolites, silica gels, porous Vycor glasses, alumina rigidity, polarity and modification of surfaces... 

The interaction of Ru3(CO)i2 with Si02 seems to proceed via a hydride surface carbonyl species. An ulterior decomposition under vacuum mainly gives Ru particles of 1.4nm and Ru(II) carbonyl species ]90]. Similarly, [HRu3(CO)io( t-OSi)]surface specics are generated by the reachon of Ru3(CO)i2 with a porous Vycor glass at 65 °C under air ]103]. Above 130 °C it was reported that the surface cluster breaks down with formation of ]Ru(CO) (OSi)2]surface species (n = 2 and/or 3). When the initial surface species was heated in air at T> 250°C, decomposition of the cluster and formation of RUO2 nanoparticles were observed. 

Irradiation of porous Vycor glass with UV light (< 330 nm) in the presence of oxygen (256) leads to photoadsorption and an EPR signal with g = 2.0310, 2.0109, and 2.0053 this is again consistent with an ionic O2 on the surface. 

Porous vycor glass Surface-bound, octahedrally coordinated Fe3+ species obtained in the photolysis of Fe(CO)5 physisorbed onto the glass Magnetically ordered materials were obtained which exhibited magnetic hyperfine fields of 370 and 425 kG 798... 

Studies of inorganic photochemistry in unusual environments has attracted considerable attention. Photochemical studies conducted in organized assemblies such as micelles, microemulsions and vesicles,217 on surfaces such as porous Vycor glass,218 in a lamellar solid,219 and in the gas phase have been reported.220... 

Shiotani et at. (65b) have reported the formation of several oxygen species on titanium-supported surfaces. Two of these are produced by UV irradiation of the titanium-porous Vycor glass system in the presence of N20 or 02 at 77 K and one is believed to be an O- ion. Their g tensors are not complete and there is no further data from 17 O-labeled 02 or N20 or on their reactivity to support the assignment to O" ions. 

The present author has investigated the photochemistry of alkyl ketones adsorbed on porous Vycor glass to examine how the reactivity of the excited states or of the radical species themselves varies when they are formed on the solid surfaces. In those studies, we have found that the photochemical reactivities of adsorbed alkyl ketones are markedly different from those in the gas phase, leading to some general characteristics of the photochemistry in the adsorbed layer (5-13). 

This chapter deals with the characteristics of the photolyses of alkyl ketones adsorbed on porous Vycor glass which arises from the electronic perturbation and the steric hindrance effects of the surfaces upon the primary and secondary photochemical processes. The effects of surface hydroxyl groups upon the primary and secondary photochemical processes are also discussed, since surface hydroxyl groups have been found to play a significant role in the photochemistry of the adsorbed... 

Differences are observed in the photochemistry of Fe(C0)s adsorbed on silica and on porous Vycor. Irradiation of Fe(C0)s on Vycor at 350, 310, or 254 nm in a Rayonet reactor ( 1 mW/cm ) or with a frequency-tripled Nd YAG laser ( 400 mJ/cm - pulse) at Fe(C0)s loading levels of <10 mol/g results in formation of a species assigned as the oxidative addition product of photochemically-produced Fe(C0)4 with surface silanol groups and with chemisorbed... 

The authors have tried the method to apply photoreaction of metal carbonyl on solid surface for preparation of catalysts, and have found that metal carbonyls, M(CO)g(M=Mo, W), adsorbed on porous Vycor glass are activated as catalysts by their irradiation with UV light in the presence of reactants (20). Fig.6 shows a time course of the propene reaction carried out on the Mo(CO)g-, W(CO)g- or Cr(CO)g-adsorbed porous Vycor glass(denoted by Mo(CO)g/PVG, etc., hereafter). No reaction occurs under darlc. Propene is converted to equal molar amounts of ethene and butene under the irradiation of Mo(CO)g/PVG and W(CO)g/PVG, but no activation of Cr(CO)g/PVG has been observed. This result indicates the photoinduction of the catalytic activity of Mo(CO)g/PVG and W(CO)g/PVG for the metathesis of propene. The reaction continues for about 30 min even after the stop of the... 

Mo(CO)g and W(CO)6 adsorbed on porous Vycor glass or NaY zeolite become active when irradiated with a mercury lamp (> 290 nm) at room temperature in the presence of propene (Wada 1988). They remain active after irradiation ceases, indicating that the catalytically active species is formed by photoreduction of the metal carbonyl on the surface. The activity of Mo(CO)6/Al203 is enhanced by irradiation. 

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