Titanium dioxide catalyst

The reaction uses a fixed-bed vanadium pentoxide-titanium dioxide catalyst which gives good selectivity for phthalic anhydride, providing temperature is controlled within relatively narrow limits. The reaction is carried out in the vapor phase with reactor temperatures typically in the range 380 to 400°C. 

Photolytic. An aqueous solution containing p-chloronitrobenzene and a titanium dioxide (catalyst) suspension was irradiated with UV light ilk >290 nm). 2-Chloro-5-nitrophenol was the only compound identified as a minor degradation product. Continued irradiation caused additional degradation yielding carbon dioxide, water, hydrochloric and nitric acids (Hustert et al., 1987). 

Jacoby et al. (1994) studied the photocatalytic reaction of gaseous trichloroethylene in air in contact with UV-irradiated titanium dioxide catalyst. The UV radiation was kept less than the maximum wavelength so that the catalyst could be excited by photons, i.e., X <356 nm. Two reaction pathways were proposed. The first pathway includes the formation of the intermediate dichloroacetyl chloride. This compound has a very short residence time and is quickly converted to the following compounds phosgene, carbon dioxide, carbon monoxide, carbon dioxide, and hydrogen chloride. The second pathway involves the formation of the final products without the formation of the intermediate. 

Mendez-Roman and Cardona-Martinez [55] examined titanium dioxide catalysts with FTIR spectroscopy during the photocatalytic oxidation of toluene. Reaction intermediates, believed to be benzaldehyde and benzoic acid, were reported to accumulate on catalyst samples. This accumulation of intermediates was found to be reduced in the presence of gas-phase water. Mendez-Roman and Cardona-Martinez concluded that toluene appeared to be converted to benzaldehyde, which was then oxidized further to form benzoic acid. They suggested that the accumulation of benzoic acid led to the observed apparent catalyst deactivation. Other researchers, however, have argued that benzoic acid is unlikely to be the compound responsible for apparent deactivation in the photocatalytic oxidation of aromatics. For example, Larson and Falconer [43] concluded, based on higher CO2 evolution rates for benzoic acid relative to toluene during photooxidation, that benzoic acid was not sufficiently recalcitrant to be responsible for the deactivation seen with aromatic contaminants. 

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... 

This case shows the degradation of 4-chlorophenol (4-CP) employing UVA radiation and Aldrich titanium dioxide catalyst (S = 9.6cm g , nominal diameter of the elementary particle 200 nm) in a slurry reactor at pH 2.5, which was found to provide the most efficient reaction condition (Satuf et al., 2007a, b, 2008). 

Wilson, E. Titanium Dioxide Catalysts Break Down Pollutants, Chem. Eng. News, Jan. 15, 1996, 23-24. 

Aromatic hydrocarbons can be oxidatively cleaved either on a side chain or in the ring (Eq. 6) [60]. Even saturated hydrocarbons can be induced to become oxygenated or to participate in isotope exchange on irradiated platinum/ titanium dioxide catalysts [151, 155, 156]. Competitive trapping of the photogenerated conduction band electron by adsorbed protons is thought to be responsible for the reduced contribution of oxygen at lower pH. 

Decomposition of alkyl halides also occurs in solution under the influence of silver. Thus it is possible to bring about photochemical C-halogen bond fission in chloroform on irradiation in aqueous solutions with titanium dioxide catalysts. The efficiency of the process is enhanced by up to 25% when the catalyst is loaded with silver18. 

S. Kasaoka, E. Sasaoka, and H. Nanba, "Deactivation Mechanism of Vanadium Pentoxide-Titanium Dioxide Catalyst by Deposited Alkali Salts and Regeneration Method of Deactivated Catalyst in Reduction of Nitric Oxide with Ammonia", Nippon Kagaku Kaishi. Japan, 1984,3, 486-494. 

Catalyst preparation The titanium dioxide catalysts were prepared by suspending 40 g of TiOa (99% Merck) in a solution of the appropriate amount of sulfuric acid in 100 ml of super-dry methanol, during 4 hrs, with slow agitation. After this period of time the solvent was completely evaporated under vacuum. The resultant powder was then dried in air at 70 C during 22 hrs. Finally, the material was crushed down to a granulation of less than 1mm, activated in air at convenient temperatures and times as described below, and stored under vacuum. 

S. Sato, J. M. White, Photoassisted water-gas shift reaction over platinized titanium dioxide catalysts, J. Am. Chem. Soc. 102 (1980) 7206-7210. 

G. (2010) Photocatalytic oxidation of cyclohexane by titanium dioxide catalyst deactivation and regeneration. J. Catal., 272, 198-201. 

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