共查询到18条相似文献,搜索用时 62 毫秒
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Because fossil fuels are continuously depleted, valorization of biomass into valuable liquid products and chemicals is of great significance yet it remains challenging. Among many biomass-derived products, lactic acid is one of the most important renewable monomers for preparing the degradable polymer polylactic acid. The use of raw biomass to produce lactic acid through catalytic conversion is an attractive approach. In this work, the catalytic reaction performance and mechanism of different Lewis acids (Y3+, Sc3+, and Al3+) for the production of lactic acid from cellulose were investigated in detail by isotopic nuclear magnetic resonance (NMR) and mass spectrometry. The production of lactic acid from cellulose includes tandem and competing reactions. The order of catalytic activity for the one-pot conversion of cellulose into lactic acid is as follows: Y3+ > Al3+ > Sc3+. The main tandem reactions involve the hydrolysis of cellulose into glucose, the isomerization of glucose into fructose (the order of catalytic activity, the same below: Y3+ > Al3+, Y3+ > Sc3+), the cleavage of fructose via a retro-aldol reaction to glyceraldehyde (GLY) and 1, 3-dihydroxyacetone (DHA) (Sc3+ > Y3+ > Al3+), and the conversion of DHA or GLY to the final product lactic acid (Al3+ > Y3+ > Sc3+). It was found that the process of glucose isomerization to fructose was the key step to the final selectivity of the tandem reaction of cellulose conversion to lactic acid, and it was clarified that the production of lactic acid from DHA underwent a keto-enol (K-E) tautomerization process rather than a classical 1, 2-shift process. First, DHA was transformed into GLY via the isomerization process, then the adjacent hydroxyl group of GLY was removed in the form of water to produce an α, β-unsaturated species. After that, the α, β-unsaturated species underwent K-E tautomerization to generate unsaturated aldehyde-ketone intermediates. Meanwhile, a molecule of water was added to aldehyde-ketone intermediates to obtain a diol product, the hydrogen atom at the methine position was transferred and the lactic acid was finally obtained through the K-E tautomerization process. The in-depth understanding of the reaction mechanism presented in this work will help to design more selective catalysts for cellulose conversion into value-added oxygen-containing small molecule chemicals.
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微波辅助的金属氯化物Lewis酸催化纤维素水解 总被引:3,自引:2,他引:3
研究了微波辐射下四种金属氯化物Lewis酸的催化纤维素酸水解反应性能,发现CuCl2的催化性能最好。反应温度、反应时间、微波功率、催化剂用量和酸种类对纤维素水解转化率、葡萄糖和5-羟甲基糠醛(5-HMF)的选择性均有明显影响。与传统热反应相比,微波辐射明显加快纤维素酸水解速率,提高葡萄糖的选择性。0.5g纤维素和15g水,在微波功率800W,温度到达225℃时立即停止反应的条件下,当CuCl2用量为0.05mmol时,纤维素转化率和葡萄糖选择性达72.6%和62.3%;当CuCl2用量为0.15mmol时,5-HMF的选择性最高为13.2%;当CuCl2用量为0.30mmol时,纤维素的转化率高达90.6%,但葡萄糖选择性只有6.7%。 相似文献
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本研究基于原位水热合成和气相浸渍的方法分别合成了含有Br?nsted/Lewis酸的Beta分子筛和只含有Lewis酸的AlCl3@Si-Beta样品,并通过原位漫反射红外技术对比研究了Br?nsted酸和Lewis酸催化直链和侧链戊烯同分异构体转化作用机理的差异。结果表明,同时含有Br?nsted/Lewis酸的Beta分子筛中,Br?nsted酸起主要的活化作用,催化戊烯进行异构和叠合反应时均遵循经典的碳正离子机理;而AlCl3@Si-Beta中的Lewis酸不含氢质子或羟基,催化α-戊烯进行双键迁移和2-戊烯的顺反异构反应时遵循AB-AD机理,以类烯丙基物种作为中间体,无法催化戊烯进行骨架异构和叠合反应。 相似文献
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一种新的高分子Lewis酸催化剂的制备及其催化活性的研究 总被引:14,自引:0,他引:14
本文研究了高分子催化剂CPVC-FeCl_3在酯化、酯交换、缩醛或缩酮的合成及呐 重排反应中的应用。本催化剂具有操作简便、无腐蚀性,催化剂易从反应混合物中分离、并能重复使用等优点。 相似文献
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不同Na/P比磷酸钠盐催化剂对乳酸转化反应的影响 总被引:2,自引:0,他引:2
将NaH2PO4与不同比例的Na2CO3或H3PO4混合,通过浸渍法负载在硅胶上,经过焙烧,制备了Na/P比不同的磷酸钠盐催化剂.利用所制备的催化剂考察了乳酸生成丙烯酸的脱水反应.运用XRD、Raman以及31PNMR等手段对所制备的催化剂结构进行了表征,并使用NH3-TPD对磷酸钠盐催化剂的酸强度和酸性位密度进行了测量.结合催化剂的结构表征结果,对磷酸钠盐的表面酸性进行了探讨.基于磷酸钠催化剂的结构和酸性,讨论了它们的催化性能. 相似文献
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Yan Yan Li Tian‐Ya He Rui‐Rong Dai Yong‐Liang Huang Xiao‐Ping Zhou Tianfeng Chen Dan Li 《化学:亚洲杂志》2019,14(20):3682-3687
A family of gyroidal metal–organic frameworks (STUs) composited with transition metal ions and bi‐imidazolate ligands (BIm) were prepared and applied as both Lewis base and acid catalysts. Benefiting from the intrinsic basicity of the ligands and the Lewis acidic sites of the open metal centres, the STUs materials show excellent catalytic activities as Lewis base for the Knoevenagel condensation reaction between various aldehydes and malononitrile, and as Lewis acid for cyanosilylation reactions. Among these STUs, STU‐4 (Ni(BIm)) shows the best catalytic efficiency (conversions >99 %) in both Knoevenagel condensation and cyanosilylation reactions under mild conditions, providing thus an advanced material for both Lewis base and Lewis acid catalysis. 相似文献
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Dr. Jeanne‐Marie Begouin Prof. Dr. Meike Niggemann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(25):8030-8041
Recently, Lewis acidic calcium salts bearing weakly coordinating anions such as Ca(NTf2)2, Ca(OTf)2, CaF2 and Ca[OCH(CF3)2]2 have been discovered as catalysts for the transformation of alcohols, olefins and carbonyl compounds. High stability towards air and moisture, selectivity and high reactivity under mild reaction conditions render these catalysts a sustainable and mild alternative to transition metals, rare‐earth metals or strong Brønsted acids. 相似文献
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Dr. Haruno Murayama Dr. Qi-An Huang Dr. Eiji Yamamoto Prof. Dr. Makoto Tokunaga Dr. Tamao Ishida Dr. Mitsutaka Okumura Dr. Tetsuo Honma Dr. Tadahiro Fujitani Dr. Atsuko Isogai 《Chemical record (New York, N.Y.)》2023,23(11):e202300148
Heterogeneous noble metal catalysts exhibit various functions. Although their redox functions have been extensively studied, we focused on their soft Lewis acid functions. Supported Au, Pt, and Pd catalysts electrophilically attack the π-electrons of soft bases such as alkynes, alkenes, and aromatic compounds to perform addition and substitution reactions. Hydroamination, intramolecular cyclization of alkynyl carboxylic acids, isomerization of allylic esters, vinyl exchange reactions, Wacker oxidation, and oxidative homocoupling of aromatics are introduced based on a discussion of the active species and reaction mechanisms. Furthermore, the adsorption of sulfur compounds, which are soft bases, onto the supported AuNPs is discussed. The adsorption and removal of 1,3-dimethyltrisulfane (DMTS), which is the compound responsible for the stale odor of “hine-ka” in alcoholic beverages, particularly Japanese sake, is described. 相似文献
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磁性碳基磺酸化固体酸催化剂的制备及其催化水解纤维素 总被引:6,自引:0,他引:6
以纤维素和硝酸铁为原料,发烟硫酸为磺酸化试剂,采用热解法合成了磁性碳基磺酸化固体酸催化剂(Fe/C-SO3H).利用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、傅里叶变换红外(FT-IR)光谱仪和振动样品磁强计(VSM)等手段对催化剂进行了表征,评价了催化剂在纤维素水解反应中的催化活性.结果表明,Fe是以γ-Fe2O3的形式存在于碳本体中,催化剂呈现超顺磁性.对于纤维素的水解反应,在优化条件下,纤维素的转化率可达40.6%.此外,催化剂可稳定分散于反应体系中,并在外加磁场作用下可快速与反应体系分离.但催化剂重复使用时催化活性有所下降,其失活原因经初步认定是由于表面部分磺酸基团在反应过程中脱落. 相似文献
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Kodchakon Kun-asa Prof. Prasert Reubroycharoen Dr. Kiyoyuki Yamazaki Dr. Naoki Mimura Dr. Osamu Sato Dr. Aritomo Yamaguchi 《ChemistryOpen》2021,10(3):308-315
Although chitin, an N-acetyl-D-glucosamine polysaccharide, can be converted to valuable products by means of homogeneous catalysis, most of the chitin generated by food processing is treated as industrial waste. Thus, a method for converting this abundant source of biomass to useful chemicals, such as lactic acid, would be beneficial. In this study, we determined the catalytic activities of various metal oxides for chitin conversion at 533 K and found that MgO showed the highest activity for lactic acid production. X-ray diffraction analysis and thermogravimetry-differential thermal analysis showed that the MgO was transformed to Mg(OH)2 during chitin conversion. The highest yield of lactic acid (10.8 %) was obtained when the reaction was carried out for 6 h with 0.5 g of the MgO catalyst. The catalyst could be recovered as a solid residue after the reaction and reused twice with no decrease in the lactic acid yield. 相似文献