Photocatalysis and Environmental Protection

Photooxidations by O2 over Ti02 can also be carried out in the gas phase however, the presence of water still appears to be necessary to assist in the removal of intermediates or products from the solid surface. 

Commercial Ti02 (e.g., Degussa P25), which is usually mainly the 

1 Japanese chemists succeeded in obtaining good yields of methane by reaction of H2 with a mixture of carbon monoxide and carbon dioxide, at temperatures as low as 270 °C, by use of a special mixed catalyst containing nickel as the most important metallic constituent. Why is nickel used In the same vein, why is platinum or platinum-rhodium alloy (but not nickel) used in catalytic converters for automobile exhausts (See also Section 17.4.) 

2 Two important ways in which heterogeneously catalyzed reactions differ from homogeneous counterparts are the definition of the rate constant k and the form of its dependence on temperature T. The heterogeneous rate equation relates the rate of decline of the concentration (or partial pressure) c of a reactant to the fraction / of the catalytic surface area that it covers when adsorbed. Thus, for a first-order reaction, 

3 Show that a substance that is an effective catalyst for a particular reaction will also catalyze the reverse reaction (cf. Section 2.5 and Exercise 2.2). 

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