- Fluoride-free and low concentration template synthesis of hierarchical Sn-Beta zeolites: Efficient catalysts for conversion of glucose to alkyl lactate
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Hierarchical Sn-Beta zeolite was prepared through a hydrothermal postsynthesis method, which employed no fluoride and only a small amount of tetraethyl ammonium hydroxide (TEAOH). The dual roles of TEAOH as a base and as a structure directing agent were discussed in detail, which were significantly affected by its concentration. At a TEAOH concentration of 0.2-0.4 mol L-1, hierarchical Sn-Beta zeolites with the most probable mesopore diameter of 7.8 nm were achieved. Other physicochemical properties of the hierarchical Sn-Beta including the content and state of Sn and the acidity were also characterized. The hierarchical Sn-Beta zeolite gave a higher yield of methyl lactate (58%) than the microporous Sn-Beta zeolite synthesized in fluoride medium (47%) due to the promoting effect of the hierarchical porosity on the conversion of glucose in methanol, which is an important and challenging process of a biorefinery. The hierarchical Sn-Beta zeolite is stable and can be recycled and reused five times without significant loss of activity and selectivity.
- Yang, Xiaomei,Bian, Jingjing,Huang, Jianhao,Xin, Weiwen,Lu, Tianliang,Chen, Chen,Su, Yunlai,Zhou, Lipeng,Wang, Feng,Xu, Jie
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- Conversion of sugars to methyl lactate with exfoliated layered stannosilicate UZAR-S4
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Biomass has been shown as an alternative to fossil fuels for obtaining chemicals. In this work, the transformation of sugars into methyl lactate (ML) at 160 °C was carried out using the layered stannosilicate UZAR-S3 (University of Zaragoza-solid number 3) and the delaminated material UZAR-S4 (University of Zaragoza-solid number 4) obtained from its exfoliation. The exfoliation of UZAR-S3 to UZAR-S4 increased the accessibility of the compounds to the catalytic sites and the medium-strength acidity. Thus, the yield to ML for sucrose transformation increased from 8% for UZAR-S3 to 49.9 % for UZAR-S4. In the reusability tests, the UZAR-S4 catalyst was characterized before and after reaction by several techniques such as X-ray diffraction, thermogravimetry analysis, scanning electronic microscopy, energy dispersive X-ray spectroscopy and nitrogen adsorption. A deactivation of the catalyst was observed, which was related to carbonaceous deposits that decreased the specific surface area and the pore volume of the catalyst.
- Murillo, Beatriz,de la Iglesia, óscar,Rubio, César,Coronas, Joaquín,Téllez, Carlos
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- Zeolite-catalysed conversion of C3 sugars to alkyl lactates
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The direct conversion of C3 sugars (or trioses) to alkyl lactates was achieved using zeolite catalysts. This reaction represents a key step towards the efficient conversion of bio-glycerol or formaldehyde to added-value chemicals such as lactate derivatives. The highest yields and selectivities towards the desired lactate product were obtained with Ultrastable zeolite Y materials having a low Si/Al ratio and a high content of extra-framework aluminium. Correlating the types and amounts of acid sites present in the different zeolites reveals that two acid functions are required to achieve excellent catalysis. Bronsted acid sites catalyse the conversion of trioses to the reaction intermediate pyruvic aldehyde, while Lewis acid sites further assist in the intramolecular rearrangement of the aldehyde into the desired lactate ester product. The presence of strong zeolitic Bronsted acid sites should be avoided as much as possible, since they convert the intermediate pyruvic aldehyde into alkyl acetals instead of lactate esters. A tentative mechanism for the acid catalysis is proposed based on reference reactions and isotopically labelled experiments. Reusability of the USY catalyst is demonstrated for the title reaction.
- Pescarmona, Paolo P.,Janssen, Kris P. F.,Delaet, Chloe,Stroobants, Christophe,Houthoofd, Kristof,Philippaerts, An,De Jonghe, Chantal,Paul, Johan S.,Jacobs, Pierre A.,Sels, Bert F.
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experimental part
p. 1083 - 1089
(2010/08/20)
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- Tin-catalyzed conversion of trioses to alkyl lactates in alcohol solution
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Tin chlorides, SnCl2 and SnCl4·5H2O are excellent catalysts for the reactions of trioses, dihydroxyacetone and glyceraldehyde with alcohols (MeOH, EtOH and nBuOH) to give alkyl lactates, whose reaction mechanism involves the intermediary formation of pyruvic aldehyde followed by its esterification, which is distinctively promoted by tin halides. The Royal Society of Chemistry 2005.
- Hayashi, Yukiko,Sasaki, Yoshiyuki
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p. 2716 - 2718
(2007/10/03)
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- Reactions of alcohols with α-alkoxyacroleins at room temperature
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The first stage of the reactions of alcohols with α-alkoxyacroleins in an acidic medium at 20°C under kinetically controlled conditions is the Markovnikoff addition at the C=C bond to form 2,2-dialkoxypropanals (methylglyoxal ketals). Under conditions of thermodynamic control, subsequent acetalization of the aldehyde group occurs to form 1,1,2,2-tetraalkoxypropanes. When the duration of the reaction is further increased in the absence of a water acceptor, the ketal group undergoes hydrolysis and methylglyoxal acetals are formed. A method was developed for the preparation of methylglyoxal ketals.
- Keiko,Chuvashev,Stepanova,Voronkov
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p. 2422 - 2425
(2007/10/03)
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