Photocatalytic reactions on solid catalysts

In 1972, Fujishima and Honda 185-187) opened a new research field in heterogeneous photocatalysis with their discovery of the photocatalytic splitting of water on TiO2 electrodes. Thereafter, TiOj, in part because of its high stability and lack of 

Photocatalytic Conversion of Chlorine-Containing Organic Compounds 

170 mg of Ti02 in the presence of gaseous oxygen (60pmol). The UV irradiation time is indicated in 

The photocatalysis of TCE on the Ti02-coated optical microfibers in the presence of oxygen was further investigated by in situ C MAS NMR spectroscopy (191). The major products are phosgene and carbon dioxide, with small quantities of DCAA and trichloroacetaldehyde remaining on the catalyst at the end of the reaction. Solid-state NMR spectroscopy has also been applied successfully for the investigation of the photocatalytic degradation of dichloromethane (192,193). 

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Analysis of photocatalytic kinetics in various reactions over solid catalysts is based essentially on the classical Langmuir approach, assuming one relatively rapid reaction achieving adsorption equilibrium followed by a single, slow surface reaction step... 

That products of intermediate oxidation level can be detected in the photocatalytic reactions of hydrocarbons and fossil fuels is also consistent with a surface bound radical intermediate . Photocatalytic isotope exchange between cyclopentane and deuterium on bifunctional platinum/titanium dioxide catalysts indicates the importance of weakly adsorbed pentane at oxide sites. The platinum serves to attract free electrons, decreasing the efficiency of electron-hole recombination, and to regenerate the surface oxide after exchange. Much better control of the exchange is afforded with photoelectrochemical than thermal catalysis > ) As before, hydrocarbon oxidations can also be conducted at the gas-solid interface... 

Photocatalytic reactions are promoted by solid photocatalyst particles that usually constitute the discrete phase distributed within a continuous fluid phase in the reactor. Therefore, at least two phases, that is, liquid and solid, are present in the reactor. The solid phase could be dispersed (SPD) or stationary (SPS) within the reactor. SPD photoreactors may be operated with the catalyst particles and the fluid phase(s) agitated by mechanical or other means. Depending on the means of agitation, the photoreactor resembles that of slurry or fluidized bed reactors. In numerous investigations, an aqueous suspension of the catalyst particles in immersion or annular-type photo reactors has been used. However, the use of suspensions requires the... 

Many physical-chemical processes on surfaces of solids involve free atoms and radicals as intermediate particles. The latter diffuse along the adsorbent-catalyst surface and govern not only kinetics of catalytic, photocatalytic, or some heterogeneous radiative processes, but also creation of certain substances as a result of the reaction. 

This chapter presents a quantitative method to determine the photoadsorption capacity of a polycrystalline semiconductor oxide irradiated in liquid-solid system. The determination is performed imder reaction conditions so that it is really indicative of the photoadsorption capacity. The method uses the experimental results obtained in typical batch photoreactivity runs on this ground it has been applied to the following photocatalytic processes carried out in aqueous suspensions (i) oxidation of phenol in the presence of a commercial Ti02 catalyst (Degussa P25) and... 

This chapter reviews some of the main topics involved in the design and modeling of solar photocatalytic reactors, with particular emphasis on the authors research experience. Solar photons are source of energy that initiates photocatalytic degradation. Thus, proper consideration of radiative processes is key to address this subject. The determination of the directional and spectral characteristics of solar UV radiation, the interaction of the catalyst with radiation inside reaction spaces, the optical design of solar collectors, and the optical properties of the materials involved are all subjects where these concepts are necessary. Therefore, developments in this area should be solidly grounded on the fields of solar collector optics and radiative transfer, besides the more traditional chemical engineering aspects involved. This requires a multidisciplinary approach. 

The kinetics of photocatalytic degradation of the dye on the surface of the catalyst follows pseudo first-order kinetics. It is rationalized in terms of the Langmuir-Hinshelwood model, which is modified to accommodate reactions occurring at a solid-liquid interface, as shown by Eq. 1 [3] ... 

A final difference between photocatalytic CO2 reduction and hydrogen evolution from water is the large number of possible reaction products that can be formed in the process. The products that have been detected in photocatalytic CO2 conversion include oxalic acid or oxalate, formate, methanol, methane, ethane, CO, and even elemental C. The problem arises from the fact that some of the possible products are gaseous, while others are liquids or even solids. If solids are deposited on the photocatalyst surface performing the reaction in the gas phase at low temperatures, deactivation of the catalyst should occur by blocking of the surface by carbon and liquid products that poison the photocatalyst. The large diversity of products that can be formed in CO2 reduction and their difference in physical states... 

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