T.K. Varadarajan

Photocatalytic reduction of nitrite and nitrate ions to ammonia on M/TiO2 catalysts

Abstract Noble metal loaded TiO 2 catalysts have been employed as catalysts for the photocatalytic reduction of nitrite and nitrate ions to ammonia. The yield of ammonia was found to depend on the nature, amount of metal and the method of metallization. An optimum metal content is beneficial for the activity. Beyond the optimum content the activity decreases.

Photocatalytic reduction of dinitrogen to ammonia over noble-metal-loaded TiO2

Abstract The photocatalytic reduction of dinitrogen to ammonia is influenced by the nature and amount of metal loading on TiO2. The optimum metal content varies depending on the nature of the metal. A correlation between the ammonia yield and the intermediary Mue5f8H bond strength is established (low bond strength gives rise to low ammonia yield).

Selective oxidation and dehydrogenation of benzyl alcohol on ABB′O3 (A=Ba, B=Pb, Ce, Ti and B′=Bi, Cu, Sb)-type perovskite oxides-temperature programmed reduction studies

Selective oxidation and dehydrogenation of benzyl alcohol have been carried out on ABB′O3 (A=Ba, B=Pb, Ce, Ti and B′=Bi, Cu, Sb)-type perovskite oxides in the absence and in the presence of oxygen. Partial reduction of the catalyst is observed when the reaction is carried out in the absence of oxygen or at low partial pressures of oxygen. Reduced catalysts were characterised by XRD. Temperature-programmed reduction studies were carried out to determine the reducibility of the catalyst. Catalytic activity is found to depend on the reducibility of the catalysts. Copper-containing perovskites are highly reducible and BaTiO3 and BaCeO3 are the least reducible. Catalytic activity and reducibility are correlated with the metal–oxygen bonding as well as free energy of reduction of B site cations. A mechanism is proposed, which explains the ratio of benzaldehyde to toluene based on the reducibility.

Catalytic oxidation of toluene with molecular oxygen over Cr-substituted mesoporous materials

AbstractThesynthesesofthermallystablechromium-incorporatinghexagonalmesoporousaluminophosphateandcubicCr-MCM-48have been reported. Characterization of the catalysts was made using low angle XRD, N 2 adsorption, UV-VISDRS, thermalanalysis, ICP-AES and ESR. Mesoporous Cr-AlPO 4 and Cr-MCM-48 catalysts have been found to be active for the vapourphase oxidation of toluene with molecular oxygen. Mesoporous Cr-AlPO 4 is found to exhibit both acidic and redox propertiesand hence oxidation as well as dealkylation reactions are taking place in a concerted manner, whereas, the cubic silicateanalogue acts as a pure redox catalyst.© 2002 Elsevier Science B.V. All rights reserved. Keywords: Chromium; Aluminophosphates; Mesoporous materials; Partial oxidation 1. IntroductionAluminophosphate materials, recently developed ascrystalline microporous materials are of potential useincatalysis[1].Flanigenetal.[2]reportedtheincorpo-ration of various elements into the framework sites ofaluminophospahtes and the resulting systems are ac-tiveforvariouscatalytictransformations.However,thepore dimensions of these materials are not sufficient toaccommodate a broad spectrum of organic moleculesin their cavities. With the first discovery of M41S bythe Mobil researchers, a series of mesoporous ma-terials with pore dimensions greater than 20A havebeen synthesised using structure-directing templates

Photocatalytic reduction of nitrite on CdS

CdS catalysts, prepared using difference precursors, were characterized and tested for the photocatalytic reduction of nitrite to ammonia using sodium sulphate and sodium sulphite as sacrificial agents. The catalyst prepared from cadmium nitrate and sodium sulphide and treated at 623 K showed maximum activity. The activity was enhanced by loading with noble metals, such as Ru, Pd or Ir, or by the use of hole transferring agents, such as RuO2. The photoefficiency for the photocatalytic reduction of nitrite to ammonia was found to be 2.6%.

Photocatalytic reduction of nitrite and nitrate ions over TiO2 semiconductors

Photocatalysis has recently gained attention in the field of pollutant degradation [1-4]. Among the various semiconductors employed, anatase phase of TiO2 appears to be a promising photocatalyst [5, 6]. TiO; has become a benchmark semiconductor, showing the best compromise between catalytic performance and stability at any pH value of aqueous dispersion. It has been reported that for the same photoreaction, the preparation of TiO2 and its thermal treatment significantly affect the activity of the semiconductors. Indeed, preparation parameters influence the photoactivity since the physico-chemical features are determined by the catalysts origin and preparation. The sol-gel method provides a convenient method for the preparation of several inorganic oxides with tailored physical and chemical properties. We report here the synthesis and photocatalytic performance of TiO2 prepared by a sol-gel method and compare its activity with a commercial sample of T iQ (J. T. Baker, USA). TiO2 gels were prepared by the acid catalysed solgel method. The sol was prepared by mixing Ti(IV) isopropoxide with anhydrous 2-propanol, H20 and HNO3 at ambient temperature with stirring. A series of gels with varying ratio of alcohol, water content and different molar ratio between titanium (IV) isopropoxide and acid was prepared, The gels were dried at 383 K for 12h. Crystallization to anatase was achieved in air by heating at 823 K for 24 h. Titanium hydroxide was precipitated by reacting an aqueous solution of TiC14 with an aqueous ammonia solution (25 wt%). This was done by adding the latter drop-wise to the metal solution at room temperature, with vigorous stirring owing to the exothermicity of the reaction. After standing for 24 h at room temperature, the solid was filtered and repeatedly washed with double distilled water until free of chloride ions. The resulting solid was dried at 393 K for 24h and then fired in air at 823 K for 24 h. X-ray diffractograms were obtained for the powdered samples using a Philips diffractometer (Philips Generator, Holland; Model PW 1130) provided with an online recorder and dot-matrix printer (Tele type, USA). The diffraction patterns were recorded at room temperature using Ni-filtered CuKa radiation (/1, = 0.154 18 nm) for all samples. A

Characterization of Sn-5at.%Sb mixed oxide catalyst studied by x-ray photoelectron spectroscopy and Auger electron spectroscopy

Abstract X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses of an Sn-5at.%Sb mixed oxide catalyst showed that activation leads to an increase in concentration of antimony on its surface. This surface segregation is induced by the presence of oxygen in the gas phase. The active catalyst probably contains both antimony(V) and antimony(III) in addition to antimony(V) in solid solution with SnO 2 .

ALKYLATION OF TOLUENE WITH METHANOL ON MICROPOROUS MXH3-XPW12O40 M = K+, CS+, NH4+ AND TL+

Alkylation of toluene was carried out on microporous salts of phosphotungstic acid. Among the systems studied, M2.5H0.5PW12O40 showed maximum catalytic activity.p-Xylene selectivity was evaluated as a function of x. A linear correlation was observed betweenpara-selectivity and number of strong acid sites with strength of H0≤−5.6.

Studies of the structural stability of Sn-Sb mixed oxide in the decomposition of isopropyl alcohol

Abstract Typical Sn-80at.%Sb mixed oxide undergoes structural reduction during the decomposition of isopropyl alcohol in the absence of gas phase oxygen, and the active phase may contain metallic tin and Sb2O3. However, in the presence of oxygen the catalyst retains its structural stability and acetone is the major product together with small amounts of CO2 and propylene. Product inhibition studies with acetone reveal that oxidation of the acetone to CO2 occurs in preference to oxidation of isopropyl alcohol. The effect of the partial pressure of isopropyl alcohol and the partial pressure of oxygen on the decomposition of isopropyl alcohol was investigated. The presence of a large excess of oxygen favours CO2 formation, whereas smaller amounts of oxygen favour acetone formation. A possible mechanism for the reaction in the presence of gas phase oxygen is proposed.

Alkylation of toluene with methanol on heteropoly compounds: p-xylene selectivity

Abstract Alkylation of toluene with methanol was carried out on potassium, ammonium, cesium and thallium salts of phosphotungstic acid (M x H 3x PW 12 O 40 ; M=K + ,NH4 + ,Cs + and Tl + , x is varied from 0 to 3). The major products obtained are xylenes, tri - and tetra-methylbenzenes. The selectivity of p-xylene was found to be higher than the equilibrium values. The salts with composition M 2.5 H 0.5 PW 12 O 40 showed maximum activity and para selectivity. p-Xylene selectivity was evaluated as a function of x. It is seen that para selectivity correlates linearly with the number of strong acid sites with a strength of H o ≤5.6.