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    Platinum group metals substituted MCM-41 molecular sieves: Synthesis, characterization and application as novel catalysts for the reduction of NO by CO
    (01-01-2009)
    Ravat, Vilas
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    Mantri, Dinesh B.
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    Mesoporous MCM-41 molecular sieves with Si/M (molar) ratios of 100 containing platinum group metals (Pd, Pt, Rh, Ir) were synthesized by the hydrothermal method. These catalysts were systematically characterized by various analytical and spectroscopic techniques, viz., XRD, TEM, DRUV-vis, N2 sorption. XRD analysis confirmed that the presence of platinum metals did not influence the parent structure and phase purity of the MCM-41 catalysts. DRUV-vis spectral studies of MCM-41 indicate the presence of platinum metal ions. The catalytic activities of these catalysts were evaluated for the reduction of NO by CO as a function of temperature. The study revealed that the catalytic activity is, in the order (Rh>Ir>Pd>Pt). Our experimental results are in good agreement with theoretical previous analysis based on the NO* dissociation activation energy. © 2009 Elsevier B.V. All rights reserved.
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    Supported 12-tungstophosphoricacid: An efficient and selective solid acid catalyst for tert-butylation of phenol and cresols
    (01-04-2008)
    Bhatt, Nikunj
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    Sharma, Pankaj
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    Patel, Anjali
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    12-Tungstophosphoricacid (30%) supported onto zirconia was synthesized by impregnation. The synthesized catalyst was characterized by solid state NMR and XPS in order to study the nature of active species on support surface. The acidity of the catalyst was measured by temperature programmed desorption (TPD) of NH3. Liquid phase alkylation of phenol and cresols with tert-butyl alcohol was carried out using fresh as well as calcined catalyst under mild conditions. The catalysts show high activity in terms of conversion and selectivity for the desired product under mild conditions. The process could be economically viable as the un-reacted phenol could be separated by simple distillation and reused for further reaction. Studies also reveal that the regenerated catalyst could be used for achieving high yield transformation. © 2008 Elsevier B.V. All rights reserved.
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    An in situ FT-IR study of photo-oxidation of alcohols over uranyl-anchored MCM-41: Possible reaction pathways
    (01-04-2007)
    Vidya, K.
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    Kamble, V. S.
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    Gupta, N. M.
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    Photosensitive uranyl ions anchored onto MCM-41 mesoporous molecular sieves serve as remarkable photocatalysts in the degradation of alcohols, under ambient conditions of light, temperature, and air. The rates of conversion of alcohols to carbon dioxide was found to decrease in the order methanol > ethanol > 2-propanol > 1-propanol, with the difference in reactivity attributed to the stability of the carbon-centered radicals formed during photo-oxidation. Kinetics revealed that the photo-oxidation of alcohols followed a first-order reaction. A detailed in situ FT-IR analysis was used to identify the transient species formed during the photo-oxidation of ethanol and 2-propanol over uranyl-anchored photocatalyst. Acetic acid, ethyl acetate, and acetaldehyde were the intermediates obtained over UO2+2/MCM-41 during photo-oxidation of ethanol, whereas acetate species, methyl acetate, and acetone were detected during photo-oxidation of 2-propanol. Based on the intermediate species formed, their growth with respect to irradiation time, and their intensities, appropriate reaction mechanisms were proposed to corroborate our observations. © 2007 Elsevier Inc. All rights reserved.
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    Synthesis, characterization and catalytic properties of microporous cobalt aluminosilicate (CoLTL) molecular sieves
    (01-01-2008) ;
    Rajasekar, S.
    Thermally stable divalent cobalt substituted microporous aluminosilicate (CoLTL) molecular sieves were synthesized and characterized. These studies revealed isomorphous substitution of divalent cobalt in tetrahedral framework of LTL structure. In addition, the typical blue color of CoLTL confirms the tetrahedral environment of divalent cobalt in the framework, and as a result the catalyst showed excellent activity for the oxidation of cyclohexane under mild reaction conditions. Furthermore, unlike the many other cobalt-based microporous (heterogeneous) catalysts reported so far, CoLTL does not show any dislodgement or segregation of cobalt upon calcination or any other post-synthesis treatments. In this study, the performance of CoLTL was also compared with cobalt-containing aluminophosphate and silicate molecular sieves having AFI and MF1 structures, respectively. © 2008 al-Farabi Kazakh National University.
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    Uranyl-anchored MCM-41 as a highly efficient photocatalyst in the oxidative destruction of short chain linear alkanes: An in situ FTIR study
    (09-10-2008)
    Krishna, Vidya
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    Kamble, Valmik S.
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    Gupta, Narendra M.
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    Uranyl ions anchored in the mesopores of MCM-41 molecular sieve were found to be a highly efficient heterogeneous photocatalyst in the complete degradation of short chain linear alkanes such as methane, ethane, propane, and butane, carried out under ambient conditions of light irradiation. In addition to the formation of carbon dioxide and water, a negligible amount of methane was detected during the photooxidation of ethane, propane, and butane. Further, small amounts of ethane were also obtained during photooxidation of butane, suggesting quenching of *UO22+ by a C - C bond cleavage, in addition to a hydrogen atom abstraction. An in situ Fourier transform IR spectroscopy analysis was employed in order to monitor the photooxidation of methane and ethane over UO22+/MCM-41, where formic acid, formaldehyde, and formate species were the transient species identified from methane, and acetic acid, acetaldehyde, and acetate species were the intermediates obtained from ethane. Appropriate reaction pathways were proposed based on the formation of these species (C - H cleavage) and also from the negligible quantitites of methane and ethane obtained during photooxidation of higher alkanes (C - C cleavage). © 2008 American Chemical Society.
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    A highly selective, heterogeneous route to enones from allylic and benzylic compounds over mesoporous CrMCM-41 molecular sieves
    (25-07-2007)
    Mohapatra, S. K.
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    A unique combination of oxidant, solvent, and catalyst is proposed for the allylic and benzylic oxidation of alkenes to enones with 100% selectivity and good conversion. The proposed catalyst, CrMCM-41, in combination with H2O2 is found to be highly active and selective for this purpose. The catalyst is also found to be very useful for selective oxidation of toluene and aniline. It is also proved that the catalyst can be reused several times while maintaining its structural integrity and activity. © 2007 Elsevier Inc. All rights reserved.
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    Hydrogenation of nitrobenzene over palladium-supported catalysts-Effect of support
    (01-02-2009)
    Sangeetha, P.
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    Shanthi, K.
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    Rao, K. S.Rama
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    Viswanathan, B.
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    Vapor phase hydrogenation of nitrobenzene is reported on 1 wt.% Pd supported on hydrotalcite, MgO and γ-Al2O3 catalysts. The catalysts were prepared in the laboratory using a wet impregnation method and were characterized by XRD, BET surface area, TPR, TEM, XPS and CO chemisorption studies. The conversion of nitrobenzene was studied in the temperature region of 498-573 K and compared on all the catalysts. An impressive catalytic performance of nitrobenzene conversion was observed on hydrotalcite supported Pd catalyst. CO chemisorption and TEM results prove that palladium disperses better on hydrotalcite supports when compared with other conventional supports such as MgO and γ-Al2O3, which is responsible for the high conversion of nitrobenzene. © 2008 Elsevier B.V. All rights reserved.
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    Computational chemistry for industrial innovation
    (01-01-2006) ;
    Tsuboi, Hideyuki
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    Koyama, Michihisa
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    Endou, Akira
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    Takaba, Hiromitsu
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    Kubo, Momoji
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    Del Carpio, Carlos A.
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    Miyamoto, Akira
    Computational chemistry has been successfully applied to the investigations of various physico-chemical properties of materials in order to have a clear understanding at the electronic, atomic, and molecular levels. However, it has ineffectively contributed to the practical design of new materials and the pragmatic demand from the different industries, viz., electronics, automobile, battery and fuel cells, etc., is still unanswered mainly due to the limitations of suitable computational methodology and theory. On the other hand, the current progress of the computer hardware together with the development of novel software, it is now possible to have investigations of realistic complex systems. Thus, by integrating our newly developed computational methodologies with advancement of computational techniques, we realized holistic simulations of industrially important materials and processes. We have applied our integrated computational chemistry programs to very many practically important areas of materials research. This approach will eventually lead to the industrial innovations by inspiring and promoting the design and development of new materials. In this review, we address some of the recent improvements and their applications of computational chemistry methodologies for the design and development of a variety of materials including catalysts, polymers, composite materials, and electrode materials for fuel cells as well as electrical, magnetic, optical and dielectric materials.
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    Fresh and calcined supported 12-tungstosilicicacid: Synthesis, characterization and application to some acid catalyzed reactions
    (17-09-2007)
    Bhatt, Nikunj
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    Patel, Anjali
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    Sidhpuria, Kalpesh
    A series of catalyst containing 20-70% of 12-tungstosilicicacid (TSA) supported onto neutral alumina (A) has been synthesized, characterized and evaluated for esterification of 1° and 2° alcohols. The best catalyst, TSA3/A (30% loading of 12-tungstosilicicacid onto neutral alumina) has been compared with TSA3/Z (30% loading of 12-tungstosilicicacid onto hydrous zirconia) in order to see the effect of nature of support. The catalytic activity of TSA3/A and TSA3/Z has also been explored for tert-butylation of phenol by varying different parameters. Both the catalysts were calcined in the temperature range of 300-500 °C and characterized by FT-IR, DRS and XRD to see the structural change in the calcined materials. Their catalytic activity was also evaluated for the esterification as well as tert-butylation of phenol under optimized conditions. An attempt has also been made to regenerate and to reuse the present catalysts, especially for tert-butylation of phenol. © 2007 Elsevier B.V. All rights reserved.
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    Probing the Fe(III) sites in mesoporous FeMCM-41
    (15-03-2009)
    Badamali, Sushanta K.
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    Spectroscopic techniques such as 29Si MAS-NMR, Mössbauer, magnetic susceptibility, EPR and microwave variation EPR studies were used in order to study the location, coordination, oxidation state and stability of trivalent in FeMCM-41. 29Si MAS-NMR studies revealed that paramagnetic Fe(III) is present in the direct vicinity of [SiO4] tetrahedral and therefore results in broadening of spectral lines. Absence of side spinning bands are attributed to the uniform dispersion of FexOy within the matrix. Observed isomer shift value of <0.3 mm/s and the appearance of sexset pattern in Mössbauer spectrum is attributed to the tetrahedral coordination of Fe(III) and superparamagnetic FexOy nanoparticles, respectively. The co-existence of paramagnetic and superparamagnetic Fe(III) is also inferred from magnetic susceptibility studies. Analysis of EPR spectrum indicated that Fe(III) is present in two different tetrahedral sites along with octahedral coordination [S.K. Badamali, A. Sakthivel, P. Selvam, Catal. Lett. 65 (2000) 153]. Room temperature microwave power variation electron paramagnetic resonance (EPR) (0.5-10 mW) studies are in good agreement with above interpretations. During template removal, Fe(III) is preferably dislodged from the distorted framework sites irrespective of calcination temperature. The population of unsymmetrical Fe(III) species is inferred to be relatively less as compared to the symmetrical sites, in the calcined form. © 2008 Elsevier B.V. All rights reserved.