Comparison with photocatalytic oxidation

Comparison with Direct Photolysis Process. The Ti02-mediated photocatalytic oxidation reaction involves a complex free-radical reaction mechanism in which OH radicals are responsible for the oxidation of 4-chlorophenol. The initial reaction step produces 4-chlorocatechol as the main product. In contrast, the direct photolysis of 4-chlorophenol produces a different set of reaction products. Figure 8 shows that the direct photolysis of... 

Nb- and Ti-containing silica-based mesoporous molecular sieves were used as catalysts for photocatalytic oxidation of methane. It is found that methanol was formed at 323 K and water pre-adsorbed samples exhibited higher catalytic activity than their pure metal oxides. By comparison with Nb-MCM-41, Ti-MCM-41 gave better methane conversion and methanol yield although traces of formaldehyde were observed over Nb-MCM-41 catalyst. Interestingly, OH radical was detected by the in-situ ESR spectroscopy using DMPO as trapper. 

Turchi, C.S., Wolfrum, E., Miller, R.A., 1994, Gas-Phase Photocatalytic Oxidation Cost Comparison with Other Air Pollution Control Technologies, NREL/TP-471-7014. Golden, CO National Renewable Energy Laboratory. Watt, A. S., Magrini, K. A., Carlson-Boyd, L. C., Wolfrum, E. J., Larson, S. A., Roth, C., and Glatzmaier, G. C., A Pilot-Scale Demonstration of an Irmovative Treatment for Vapor Emissions , J. of Air and Waste Management, November, 1999. 

A membrane-induced structure—reactivity trend, which may be exploited to achieve selective processes, was observed in polymeric catalytic membranes prepared by embedding decatungstate within porous membranes made of PVDF or dense polydimethyl-siloxane (PDMS) membranes. These photocatalytic systems are characterized by different and tunable properties depending on the nature of the polymeric microenvironment (Bonchio et al., 2003). The polymeric catalytic membranes prepared were used for the batch-selective photooxidation of water-soluble alcohols. Membrane-induced discrimination of the substrate results from the oxidations of a series of alcohols with different polarity, through comparison with the homogeneous reactions (Fig. 27.7). 

Let us now turn to a comparison of theory with experiment. Comparing (95), (84), and (68), we find that the dependence of the photocatalytic effect K on the position of the Fermi level at the surface s and in the bulk cv of an unexcited sample for the oxidation of water is the same as for the oxidation of CO or for the hydrogen-deuterium exchange reaction. For this reason, such factors as the introduction of impurities into a specimen, the adsorption of gases on the surface of the specimen, and the preliminary treatment of the specimen will exert the same influence on the photocatalytic effect in all the three reactions indicated above. The dependence of K on the intensity I of the exciting light must also be the same in all the three cases. 

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