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Sirijaraensre J.,Kasetsart University | Limtrakul J.,Kasetsart University | Limtrakul J.,Vidyasirimedhi Institute of Science and Technology
Physical Chemistry Chemical Physics | Year: 2015

Decorating graphene with nano-clusters offers potential for a wide range of industrial applications. For catalysis, embedding precisely controlled mono- and bimetallic nanoclusters into graphene can greatly increase their catalytic activities, especially for oxidation reactions. The catalytic performance of a gold nanocluster can be modified dramatically by changing its electronic properties. The results of this work demonstrate by means of DFT calculations that by strategic doping and promotion from the support material the catalytic activity improvement of a gold-based catalyst for the partial oxidation reaction of methane can be drastically enhanced. The transition metal-mediated catalysis is significantly affected by the two spin-state reactivities over them. The investigated catalytic processes consist of N2O decomposition and methane hydroxylation over three subnanoclusters (Au5, Au4Pd, and Au4Pt) deposited on a single vacancy graphene support. It was found that graphene acts not only as a support but also supports the catalysis through charge transfer between the subnanocluster and graphene. Graphene-supported Au4Pd exhibits enhanced catalytic activity for both steps of methane-to-methanol conversion, whereas the supported Au5 is good for N2O decomposition but ineffective for methane hydroxylation, mainly due to the involvement of a very stable intermediate (methyl-hydroxo-grafted nanocluster). The activation energies for N2O decomposition, C-H bond activation and methanol formation over the supported Au4Pd cluster are 13.8, 15.7, and 24.9 kcal mol-1, respectively. Without the graphene support, the catalytic trend is reversed and Au4Pd becomes an inert cluster for these reactions. © 2015 the Owner Societies.

Goto T.,Waseda University | Ogawa M.,Vidyasirimedhi Institute of Science and Technology
RSC Advances | Year: 2016

Synthetic saponite containing a photosensitizing metal complex was complexed with colloidal anatase and used for the visible light photocatalytic reaction of aqueous benzene to phenol. The addition of phenol to the initial aqueous benzene solution was effective in improving the reaction yield and the product selectivity. © The Royal Society of Chemistry 2016.

Roschat W.,Suranaree University of Technology | Siritanon T.,Suranaree University of Technology | Yoosuk B.,National Metal and Materials Technology Center | Promarak V.,Vidyasirimedhi Institute of Science and Technology
Energy Conversion and Management | Year: 2016

In the present work, rice husk-derived sodium silicate was prepared and employed as a solid catalyst for simple conversion of oils to biodiesel via the transesterification reaction. The catalyst was characterized by TG-DTA, XRD, XRF, FT-IR, SEM, BET and Hammett indicator method. Under the optimal reaction conditions of catalyst loading amount of 2.5 wt.%, methanol/oil molar ratio of 12:1, the prepared catalysts gave 97% FAME yield in 30 min at 65 °C, and 94% FAME yield in 150 min at room temperature. The transesterification was proved to be pseudo-first order reaction with the activation energy (Ea) and the frequency factor (A) of 48.30 kJ/mol and 2.775 × 106 min-1 respectively. Purification with a cation-exchange resin efficiently removed all soluble ions providing high-quality biodiesel product that meets all the ASTM and EN standard specifications. Rice husk-derived sodium silicate showed high potential to be used as a low-cost, easy to prepare and high performance solid catalyst for biodiesel synthesis. © 2016 Elsevier Ltd. All rights reserved.

Okabe Y.,Waseda University | Ogawa M.,Vidyasirimedhi Institute of Science and Technology
RSC Advances | Year: 2015

By UV irradiation to a toluene solution of a spiropyran-containing suspended mesoporous silica particles, the photochemically formed photomerocyanine was adsorbed into the mesoporous silica to give a red-colored product, which is very stable for a long time at room temperature. The red color faded on visible light irradiation, indicating that photomerocyanine desorbed from the mesoporous silica to give a toluene solution of spiropyran. Bistability was achieved in the presence of two different chemical environments for the photochromic molecules: toluene, which stabilizes organophilic spiropyran, and mesoporous silica, which stabilizes hydrophilic photomerocyanine. © The Royal Society of Chemistry.

Maihom T.,Kasetsart University | Probst M.,University of Innsbruck | Limtrakul J.,Vidyasirimedhi Institute of Science and Technology
ChemPhysChem | Year: 2015

Tungsten-methylidene formation from ethene on either the WIV, WV, or WVI active sites of a W/ZSM-5 zeolite is investigated by using the M06-L functional. The reaction is assumed to proceed in two steps; the first step is the [2+2] cycloaddition between ethene and the WO active site to form an oxametallacycle intermediate. The intermediate is then decomposed to produce the W-methylidene active site from the metathesis reaction. The overall activation barrier of the reaction on WVI (27.3kcalmol-1) is considerably lower than the ones for WIV and WV (69.4 and 37.1kcalmol-1, respectively). Moreover, the reaction involving the WVI site also stabilizes intermediates and products to a larger extent than the ones on the WIV and WV sites. As a result, we have demonstrated that the reaction of the W-methylidene metathesis active site is both kinetically and thermodynamically favored to occur on the WVI active site of the zeolite. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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