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The alkylation of ethylbenzene with t-butyl alcohol was studied over Al-MCM-41 (Si/Al = 50 and 90) and Al, Mg-MCM-41 (Si/(Al+Mg) = 50) in the vapour phase from 200 to 400°C. The products were p- t-butylethylbenzene ( p-t-BEB), p-t- butylvinylbenzene ( p- t-BVB) and m- t-butylethylbenzene ( m- t-BEB). Ethylbenzene conversion decreased with increase in temperature and increase in the ethylbenzene content of the feed. The reaction between the freely diffusing ethylbenzene in the channel and the t-butyl cations remaining as charge compensating ions yielded p-t- BEB. p- t-BVB, an unexpected product in this investigation, was produced by dehydrogenation of p- t-BEB over alumina particles present in the channels of the molecular sieves. Adsorption of ethylbenzene on Brønsted acid sites and its subsequent reaction with very closely adsorbed t-butyl cations proved to be necessary to obtain m- t-BEB. Though m- t-BEB was obtained, the corresponding m- t-butylvinylbenzene was not observed in this study. Study of time durations indicated rapid and slow catalyst deactivation at lower and higher streams respectively. [ABSTRACT FROM AUTHOR]

The photocatalytic degradation of a textile dye, reactive red 2 in presence of sunlight using TiO2 and ZnO as photocatalysts is reported. The experimental studies have indicated complete decolourisation of the dye in a short period and degradation within 8 hr of irradiation. ZnO was found to be more effective in the removal of colour than TiO2, but the degradation efficiency was found to be more with TiO2. ZnO decomposes on prolonged irradiationwhile TiO2 is not photocorrosive. The percent degradationof the dye is high for both the catalysts at an optimum concentration of the catalysts. The first order rate constant is found to increase with decreasing dye concentration. [ABSTRACT FROM AUTHOR]

Abstract: Photocatalytic activity of TiO2 and zeolites supported TiO2 were investigated using propoxur as a model pollutant. Hβ, HY and H-ZSM-5 zeolites were examined as supports for TiO2. Hβ was chosen as the TiO2 support based on the adsorption capacity of propoxur on these zeolites (Hβ>HY=H-ZSM-5). TiO2/Hβ photocatalysts with different wt.% were prepared and characterized by XRD, FT-IR and BET surface area. The progress of photocatalytic degradation of aqueous propoxur solution using TiO2 (Degussa P-25) and TiO2 supported on Hβ zeolite was monitored using TOC analyzer, HPLC and UV–vis spectrophotometer. The degradation of propoxur was systematically studied by varying the experimental parameters in order to achieve maximum degradation efficiency. The initial rate of degradation with TiO2/Hβ was higher than with bare TiO2. TOC results revealed that TiO2 requires 600min for complete mineralization of propoxur whereas TiO2/Hβ requires only 480min. TiO2/Hβ showed enhanced photodegradation due to its high adsorption capacity on which the pollutant molecules are pooled closely and hence degraded effectively. [Copyright &y& Elsevier]

Abstract: Magnesium and barium doped TiO2 nanoparticles were synthesised by sol-gel technique. The materials were characterised by XRD, BET, UV-Vis, FT-IR, SEM and TEM techniques. The pure TiO2 nanoparticles gave both anatase and rutile phases together, but the presence of either Mg2+ or Ba2+ metal ion in TiO2 gave only anatase phase. The framework substitution of Mg2+ in TiO2 was established by XRD and FT-IR techniques. However, Ba2+ was retained only on the surface of TiO2 as BaCO3 and the absence of framework substitution of Ba2+ in TiO2 was evident from XRD and FT-IR analysis. The band gap values of Mg2+ and Ba2+ doped nano TiO2 were higher than the parent nano TiO2. The photocatalytic activity in the degradation of bisphenol-A was found to be higher for metal doped nano TiO2 than both pure nano TiO2 and commercial TiO2 (Degussa P-25). [Copyright &y& Elsevier]

Abstract: Zr4+ doped nano titania was prepared by sol–gel method using titanium(IV) isopropoxide and zirconium nitrate as precursors. The materials were characterized by XRD, BET, UV–vis, FT-IR, SEM-EDX and TEM techniques. The nanoparticles of pure TiO2 contained both anatase and rutile phases together but Zr4+ doped TiO2 gave anatase phase only. The framework substitution of Zr4+ in TiO2 was established by XRD, SEM-EDX and FT-IR techniques. The band gap value of Zr4+ doped TiO2 was higher than the parent nano TiO2. TEM observations confirmed the nanocrystalline nature of Zr4+ doped TiO2. The presence of dopants therefore could suppress the growth of TiO2 grains, increase the surface area, decrease the anatase–rutile phase transformation and accelerate the surface hydroxylation. These properties resulted higher photocatalytic activity for Zr4+ doped nano TiO2 than undoped nano TiO2. The presence of anatase type structure in TiO2 with high crystallinity and high phase stability, even after annealing at 800°C substantially indicated that the dopants might inhibit densification and crystallite growth by providing dissimilar boundaries. The photocatalytic activity in the degradation of 4-chlorophenol was found to be higher for Zr4+ doped TiO2 than both nano TiO2 and commercial TiO2 (Degussa P25). The experimental parameters such as initial concentration of 4-chlorophenol, catalyst loading, pH and light intensity were optimized for maximum degradation efficiency. [Copyright &y& Elsevier]