Photocatalytic reaction scheme

Baretto RD, KA Gray, K Anders (1995) Photocatalytic degradation of methyl-ferf-butyl ether in TiOj slurries a proposed reaction scheme Water Res 29 1243-1248. 

Abstract. The photocatalytic oxidation cycle (POC) is that process in chalking in which the pigment participates. This paper has shown the chemical reaction scheme for the course of this process as well as the experimental results confirming this scheme. 

Reaction scheme of photocatalytic decomposition of acetic acid under deaerated condition is analyzed based on the flow-rate dependence of the radical fomiation30) combined with the reported mechanism. In this scheme, CH3 radicals are formed via two reaction pathways. One is indirect oxidation via OH radicals which are formed by the oxidation of water with photoinduced holes (h+) at the valence band. Another is direct oxidation of adsorbed molecules by the hole. On the other hand, 011200011 radicals are not formed by direct oxidation but only by indirect oxidation via 0H radicals. The reaction scheme is proposed as illustrated in Fig. 5.7. 

Based on photosynthesis and the energy cycie on the earth, an artificial photosynthetic system was proposed (Fig. 19.2) tc create fuels from solar energy and water by utilizing photocatalytic reactions.95 This scheme takes minimum requirements to achieve photochemical energy conversion. 

The photocatalytic reaction proceeds via a similar mechanism with complex 12 (Scheme 6). However, the elimination reaction of the SCN ligand from the OER species of 12 is slower than that of the Cl ligand from la. Thus, the photocatalytic reaction proceeds with OER species accumulated to some extent in the solution. Therefore, it is believed that the high photocatal5rtic activity of 12 arises as a result of the rapid electron transfer from the OER species to the CO2 adduct (64). 

Fig. 9. (a) Model interpreting a rate-determining step in a four-step series reaction. Step 3 with largest activation energy determines the overall rate, (b) Simplified scheme of photocatalytic reaction with a photocatalyst pc. It is clear that this process is not a series reaction since a deactivation step is included. 

Scheme I shows one of the possible reaction pathways involving OH radicals as the main reaction species in the Ti02-mediated photocatalytic oxidation of 4-chlorophenol. Only nonradical species were detected in this reaction scheme.

Laboratory studies have provided evidence that photochemical and photocatalytic (Section 6.8) steps might play an important role in the formation of amino acids or various heterocyclic compounds from very simple molecules. For example, UVC irradiation of acetonitrile ammonia water mixture produces hexamethylenetetramine, a potential precursor of amino acids, via two-step photoinitiated fragmentation of acetamide (formed by acetonitrile hydrolysis) to give carbon oxide, which undergoes further photochemical and dark reactions (Scheme 6.184).1183... 

One reaction scheme that accounts for the pH dependence of the turnover number is shown in Fig. 13. In this scheme, the Pt2(pop)4Cl2 is photoconverted to Pt2(pop)4 , which is the photocatalytic species. 

Fig. 13. Possible reaction scheme for the photocatalytic oxidation of 1-phenylethanol...

Recently Tsumura et al. [7] have shown that the photocatalytic decomposition of NO to N2 and CO2 can proceed in the presence of CO on a related Mo-MCM-41 system. The same reaction scheme as that proposed by us in [6] was adopted for the photocatalytic process on Mo-MCM-41. 

A kinetic description of the full reaction scheme including all seven reactions is more difficult, because the system of corresponding differential equations cannot be analytically solved. However, as a first approximation, we can restrict ourselves by considering only reactions (1) to (6) which describe N2O and CO2 formation by CO + 2 NO CO2 + N2O reaction. In this case, corresponding kinetic description is applicable either to the foil photocatalytic process or to the first part of it (until the N2O maximum), depending on the composition of initial CO-NO mixtures. 

Scheme 18.3 Reaction scheme of the photocatalytic decomposition of NO on the Ag" /ZSM-5 catalyst at 298 K.

An extension of tlie Turchi and Ollis (1990) kinetic scheme for photocatalytic reactions involving hydroxyl radical attack. In this work the precise evaluation of the photon-solid catalyst interaction and the proper knowledge of theLVRPA [c (x, C p)] were incorporated into the kinetic expression. The final result can be applied to any photocatalytic reactor regardless of its irradiation level. 

Scheme 7 Photocatalytic reaction mechanism using the 28 + 26 mixed system [45]...

Taking photosynthesis as a model for photochemieal solar energy conversion, an artifieial photosynthetie system has been proposed for the creation of fuels from solar energy and water by utilizing photocatalytic reactions (Fig. 13-3) [9], This scheme considers the minimum requirements for achieving photochemical energy conversion. 

Photochemists divide photocatalytic reactions into two categories, those that are catalytic in photons and those that are not. Selected examples that demonstrate fundamental principles and synthetic utility will be discussed here. A typical role of the photon in a reaction that is catalytic in photons is to generate a vacant coordination site. An example is the Fe(CO)s-catalyzed isomerization of olefins, shown in Scheme 13, where photodissociation of an Fe-CO bond generates Fe(CO)4. ... 

Photochemical methods are useful both for the preparation and the reaction of alkyl halides. In the former case, a convenient procedure obtains alcohol activation through a visible-light-mediated photocatalytic reaction. The procedure, based on the redox chemistry of Ru (bipy) complexes, was demonstrated to convert alcohols into the corresponding bromides and iodides in good yields and with exceptional functional group tolerance (see Scheme 26). ... 

Organic Reactions and Synthesis, Scheme 1 Mechanism for photocatalytic reaction of organic substrates RH... 

During the past two decades a number of authors have contributed to define what is meant by photocatalysis. Thus, independent on our earlier contributions[4] - [8], Wrighton[9], Moggi[10] and Salomon[ll] have proposed several detailed mechanistic schemes to specify photocatalytic reactions. Some of these pathways have been illustrated by Kutal[12] in summarizing of a number of experimental results preferably with respect to definitions given by Salomon[ll]. Recently, Pelizzetti and Serpone [16] have edited an excellent collection of reviews illustrating the state of art in photocatalysis with fundamental definitive contributions of Kisch [17] and Chanon [18]. 

The simplified scheme (figure 2, equations (1) - (7)) presents the various kinds of interactions which are presently labelled as photocatalytic reactions. 

---