SUIDIES ON SOME PROPERTIES AND CATALYSIS OF RARE EARTH HETEROPOLY ACIDS

INTRODUCTIONThough potassium salts of rare earth substituted silicotungsticacids were synthesized early in 1971 by R.D.Peacock etc.,sofar the reports about the application of the corresponding acidshave not been found.We prepared fourteen rare earth substitutedsilicotungstic acids and determined their thermal stability,IRabsorption Spectra and x-ray diffraction spectra.Furthermore,thecatalytic activities of the fourteen heteropoly acids in acid cata-lytic reaction were investigated.Our experimental results demonstrated rare earth substituted silico-tungstic acids have very high catalytic activity in the reaction of

Selective esterification of glycerol with acetic acid to diacetin using antimony pentoxide as reusable catalyst

Glycerol can be obtained as a by-product during biodiesel manufacture. It is important to convert glycerol to value-added products. Glycerol esterification with acetic acid is one of the most promising approaches for glycerol utilization. It is usually difficult to obtain diacetin with good activity and selectivity. In this work, glycerol esterification with acetic acid over different metal oxides, such as Bi2O3, Sb2O3, SnO2, TiO2, Nb2O5 and Sb2O5, was investigated. It was found that in the six investigated metal oxides, only Sb205 resulted in good activity and selectivity to diacetin. Under the optimized conditions, the glycerol conversion reached 96.8%, and the selectivity to diacetin reached 54.2%, while the selectivity to monoacetin and triacetin was 33.2% and 12.6%, respectively. The catalysts were characterized with FT-IR spectra of adsorbed pyridine, which indicated that in the six investigated metal oxides, only Sb2O5 possessed Bronsted acid sites strong enough to protonate adsorbed pyridine. The good catalytic activity and selectivity to diacetin might be mainly attributable to the Bronsted acid sites of Sb2O5. Reusability tests showed that with 5b205 as catalyst, after six reaction cycles, no significant change in the glycerol conversion and the selectivity to diacetin was observed.

Trimethyl-1,4-Benzoquinone Synthesis via 2,3,6-Trimethylphenol Catalytic Oxidation by Oxygen in the Presence of Non-Keggin-Type Mo-V-Phosphoric Heteropoly Acid Solutions

In the present study, the modified （non-Keggin-type） aqueous solutions of Mo-V-phosphoric heteropoly acids HaPzMoyVx,Oh （HPA-x＇） were applied as homogeneous catalysts for the two-stage oxidation of TMP （2,3,6-trimethylphenol） by oxygen into TMQ （2,3,5-trimethyl-l,4-benzoquinone）, the latter being the key intermediate in the synthesis of vitamin E. The TMQ yield was analyzed regarding solvent type, reaction temperature, molar HPA-x ＇：TMP ratio, and the concentration of vanadium （V） in the HPA-x＇ solution. The TMQ yield was found to depend strongly on the catalyst redox potential and the rate of electron transfer. The results obtained enabled to establish the optimal reaction conditions as well as to suggest the reaction mechanism. In the target reaction, which proceeds in the two-phase system, the TMQ yield is higher than 99%. After phase separation, the catalyst is rapidly regenerated by oxygen and reused.

Studies on Production of Biodiesel by Esterification of Fatty Acids by a Lipase Preparation from Candida sp. 99-125

A self-made lipase preparation from Candida sp. 99-125 was used for the production of biodiesel through enzymatic esterification of fatty acids. The crude lipase powder and fermentation broth were immobilized on a cheap fiber cloth carrier. The conditions of lipase-catalyzed esterification between long-chain fatty acids and methanol in a solvent system were investigated in detail, including the temperature, pH value, substrate concentration, solvent, absorbent agent, enzyme dosage and purity, immobilization method, the mode of addition of substrate. The results show that reaction temperature, pH of lipase micro-environment, substrate concentration, enzyme dosage and purity affect the esterification strongly. Several new methods and enzymatic procedures for improving the enzymatic reaction involving the process cost are also discussed, such as fossil diesel fuel as reaction solvent, immobilization method, multi-step gradient addition of methanol. The esterification degree of 92.8% was obtained with oleic acid and methanol under the optimal reaction condition after 12.5 h reaction time. The half-life of the immobilized lipase preparation from crude free lipase powder for esterification was 15 days.

Polyoxometalates-based heterogeneous catalysts in acid catalysis

Acid catalysis,one of the most important industrial processes,suffers from the toxicity,corrosion and recyclability problems of conventional homogeneous acid catalysts.Thus,the development of green heterogeneous acid catalysts becomes the focus of fundamental research and industrial catalysis.As a class of discrete anionic metal-oxygen clusters with tunable structure at the molecular and atomic scales,polyoxometalates(POMs)benefit from their super strong Br?nsted acidity,high proton mobility,and thermal stability.POMs-based heterogeneous catalysts have been used as the potential green alternatives to conventional homogeneous acid catalysts.In this review,we summarize recent progress on the design strategies of the POMs-based heterogeneous catalysts and their catalytic properties in acid-catalyzed reactions,where they are combined with functionalized cations,modified through covalent interactions,supported onto the non-precious metal support,and introduced into the framework of porous polymers.The design,functional strategies and catalytic performance of these POMs-based heterogeneous catalysts in specific acid-catalyzed reactions are emphasized.

Catalytic performances of heteropoly compounds supported on dealuminated ultra-stable Y zeolite for liquid-phase esterification

A series of catalysts of 12-Phosphotungstic acid(PW)and its cesium salts immobilizedon dealuminated ultra-stable Y zeolite(DUSY)were prepared.Their specific surface area and acidstrength were characterized,and their catalytic activity,selectivity and stability were evaluated in theliquid-phase esterification of acetic acid with n-butanol.It was found that the catalytic activity could beimproved remarkably by introducing PW onto dealuminated USY(from 49.5%to 86.4%).Howeverthis obvious promotion effect of PW could not be observed on USY supported PW catalyst,whichshowed rather low conversion of less than 25.0%.The supported cesium salt of PW on DUSY catalysgave a very high conversion of n-butanol of 94.6%and the 100%selectivity for n-butyl acetate.Thecatalytic stability test revealed that after 5 reaction cycles,the catalytic activity over PW/DUSY drastically dropped to 47.6%,by contrast,the PW cesium salt/DUSY still showed a high conversion o81.6%.The leaching test for catalysts in water showed that the decrease of activity was closely associated with the solubility of the active heteropoly components on supports into the polar solvent,whichindicates that the catalytic deactivation was mainly due to the lose of the heteropoly species in thereaction medium.The high catalytic stability of the supported cesium salts of PW is suggested to bederived from the water-tolerance of cesium salts of PW in the polar reaction system.

Selective esterification of non-conjugated carboxylic acids in the presence of conjugated or aromatic carboxylic acids over active carbon supported methanesulfonic acid

Non-conjugated carboxylic acids are selectively esterified in good yields in the presence of conjugated or aromatic carboxylic acids by stirring over active carbon supported methanesulfonic acid in di-chloromethane at room temperature.

Reaction Kinetics of Biodiesel Synthesis from Waste Oil Using a Carbon-based Solid Acid Catalyst

The kinetics of simultaneous transesterification and esterification with a carbon-based solid acid catalyst was studied.Two solid acid catalysts were prepared by the sulfonation of carbonized vegetable oil asphalt and petroleum asphalt.These catalysts were characterized on the basis of elemental analysis,acidity site concentration,the Brunauer-Emmett-Teller（BET）surface area and pore size.The kinetic parameters with the two catalysts were determined,and the reaction system can be described as a pseudo homogeneous catalyzed reaction.All the forward and reverse reactions follow second order kinetics.The calculated concentration values from the kinetic equations are in good agreement with experimental values.

Chemical functionalization of chitosan biopolymer and chitosan-magnetite nanocomposite with sulfonic acid for acid-catalyzed reactions

Chemical functionalization of chitosan biopolymer and chitosan-magnetite nanocomposite was performed with sulfonic acid functional groups to achieve new solid acid materials.The sulfonic acid functional groups were created through the ring opening nucleophilic reaction of amine groups of chitosan with 1,4-butane sultone.Fourier transform infrared spectroscopy(FT-IR)and X-ray photoelectron spectroscopies(XPS)verified the successful sulfonic acid functionalization of chitosan.The obtained sulfonic acid functionalized chitosan-magnetite nanocomposite showed superparamagnetic properties according to the vibrating sample magnetometry analysis and exhibited magnetic separation feature from dispersed mixtures.Nitrogen adsorption-desorption analysis indicated the increase in surface area after formation of chitosan-magnetite nanocomposite and functionalization with sulfonic acid.Both of the prepared solid acids exhibited high catalytic activities in the acid-catalyzed acetic acid esterification with n-butanol and benzaldehyde acetalization with ethylene glycol as model reactions.Furthermore,they can be reused several times without considerable loss of their activities.

Coke-tolerant SiW_(20)-Al/Zr_(10) catalyst for glycerol dehydration to acrolein

Glycerol dehydration to acrolein over a series of supported silicotungstic acid catalysts(SiWx‐Al/Zry)was investigated.Characterization results showed that the final catalyst had high thermal stability,a large pore diameter,strong Lewis acidic sites,and a large specific surface area.X‐ray photoelectron survey spectra clearly showed peaks attributable to W(W4f=35.8eV),Al2O3(Al2p=74.9eV),and ZrO2(Zr3d=182.8eV).The highest acrolein selectivity achieved was87.3%at97%glycerol conversion over the SiW20‐Al/Zr10catalyst.The prepared catalysts were highly active and selective for acrolein formation even after40h because of the presence of high concentrations of Lewis acidic sites,which significantly reduced the amount of coke on the catalyst surface.Response surface methodology optimization showed that87.7%acrolein selectivity at97.0%glycerol conversion could be obtained under the following optimal reaction conditions:0.5wt%catalyst,reaction temperature300°C,and feed glycerol concentration10wt%.Evaluation of a mass‐transfer‐limited regime showed the absence of internal and external diffusions over pellets of diameter dP<20μm.These results show that glycerol dehydration over a strong Lewis acid catalyst is a promising method for acrolein production.

活性炭固载杂多酸催化合成柠檬酸三丁酯

用自制的固载杂多酸催化柠檬酸与正丁醇反应合成柠檬酸三丁酯。探讨了催化剂用量、反应时间、反应温度、酸醇比等因素对反应结果的影响。在酸醇的摩尔比为１∶６．５、催化剂的用量为柠檬酸质量的１％、反应温度１４５℃、反应时间３ｈ的条件下，柠檬酸的酯化率可达９７．４％。

TiSiW_(12)O_(40)/TiO_2催化合成环己酮1,2-丙二醇缩酮

以固载杂多酸盐TiSiW1 2 O4 0 /TiO2 为多相催化剂 ,通过环己酮和 1 ,2 丙二醇反应合成了环己酮 1 ,2 丙二醇缩酮 ,探讨TiSiW1 2 O4 0 /TiO2 对缩酮反应的催化活性 ,较系统地研究了酮醇量比 ,催化剂用量 ,反应时间诸因素对产品收率的影响。实验表明 :TiSiW1 2 O4 0 /TiO2 是合成环己酮 1 ,2 丙二醇缩酮的良好催化剂 ,在n(酮 )∶n(醇 ) =1 0∶1 5 ,催化剂用量为反应物料总质量的 0 6 % ,环己烷为带水剂 ,反应时间 40min的优化条件下 ,环己酮 1 ,2 丙二醇缩酮的收率可达 92 2 %。

活性炭固载杂多酸催化合成柠檬酸三丁酯

用自制的固载杂多酸催化剂催化柠檬酸与正丁醇酯化反应合成柠檬酸三丁酯。探讨了催化剂固载量、反应时间、反应温度、酸醇比等因素对反应结果的影响。实验表明，此固载型催化剂不仅反应活性高、酯化率高、反应后处理简单。

Zr(SO_4)_2·4H_2O的层状结构、插层及催化性能

利用ＸＲＤ，ＴＰＤＥ，ＴＰＤ和ＴＧＤＴＡ等为主要研究手段，深入分析了Ｚｒ（ＳＯ４）２·４Ｈ２Ｏ的层状结构特征和插层性能，并以乙酸与乙二醇单醚的酯化反应为目标反应考察了其催化性能．研究结果表明：Ｚｒ（ＳＯ４）２·４Ｈ２Ｏ是一种具有中等强度酸性的层状化合物，位于层间的结晶水是产生Ｂ酸中心的来源；有机胺类分子具有较强的插层能力，胺的插入可将层板撑开并使层间距增大，从而进一步证实存在层间结晶水所产生的Ｂ酸中心；

难溶杂多酸盐催化合成对羟基苯甲酸酯的研究

以钨硅酸和三乙醇胺为原料首先合成了钨硅酸三乙醇胺盐 ,并首次用于对羟基苯甲酸酯的催化合成研究。实验考察了催化剂用量、醇酸的量比、反应时间对酯收率的影响。结果表明 ,该催化剂具有较高的催化活性 ,酯收率达到 91.6 % ,且不溶于醇 ,易于回收 ,可重复使用

杂多酸催化剂连续法合成乙酸乙酯

乙酸乙酯是重要的化工原料,它是油漆、人造制革等的溶剂,也是制药、染料、香料等基本有机合成的原料。工业上乙酸乙酯多采用硫酸法间歇生产,存在着设备腐蚀、环境污染、生产不连续、选择性差、最高收率只有70％左右等缺点。近年来有人用分子筛、固载杂多酸为催化剂进行气相合成,活性高,选择性好,但存在着催化剂易流失,原料需汽化到150℃,产品酸值和醇含量不易控制等缺点。

硅胶负载磷钨酸催化正丁醇和乙酸液相酯化反应

以硅胶为载体,用浸渍法制备了一系列不同负载量的磷钨酸催化剂,通过X射线衍射、低温N2物理吸附、程序升温氨脱附以及Hammett指示剂法表征了催化剂的物化性质,并考察了催化剂在乙酸与正丁醇液相酯化反应中的催化性能。结果表明,通过控制杂多酸负载量,可有效调整催化剂的表面性质、酸性及酯化反应性能;酯化反应结果与催化剂酸量、比表面积及磷钨酸在载体表面分散状况有直接关系。磷钨酸负载量为40%时,反应物的转化率及酯的产率均明显高于纯磷钨酸催化剂的结果。在反应温度为395K、催化剂在反应体系中的质量分数为3.5%、反应时间为120min的条件下,正丁醇转化率达89.8%,乙酸丁酯选择性为100%。

微波催化酯化合成丙酸苄酯

在硅胶担载ＰＴＳＡ催化下，利用微波技术，快速合成了丙酸苄酯，当反应量为２．５／２．５（ｍｍｏｌ／ｍｍｏｌ）、ＰＴＳＡ担载质量分数为６．０％、催化剂用量为０．５ｇ时，微波加热５．０ｍｉｎ，产率可达９５．０％。对微波催化酯化反应规律进行了探讨，发现醇酸比为１／１时效果较好。同传统酯化法比较，该法缩短了反应时间，缓解了腐蚀作用，减少了环境污染，降低了反应成本。

脂肪酶催化合成生物柴油的研究

生物柴油是用动植物油脂或长链脂肪酸与甲醇等低碳醇合成的脂肪酸甲酯 ,是一种替代能源。这里探讨了生物法制备生物柴油的过程 ,采用脂肪酶酯化和酯交换两条工艺路线进行催化合成。深入研究制备过程中 ,不同脂肪酶、酶的用量和纯度、有机溶剂、低碳醇的抑制作用、吸水剂的作用、反应时间和进程、底物的特异性和底物摩尔比等参数对酯化过程的影响。试验结果表明 ,采用最佳酯化反应参数和分批加入甲醇并用硅胶作脱水剂的工艺过程 ,酯化率可以达到 92 % ,经分离纯化后的产品GC分析的纯度可达 98%以上 ,固定化酶的使用半衰期可达到36 0h。同时对酯交换制备生物柴油过程中 ,甲醇的用量和甲醇的加入方式对脂肪酶催化过程的影响作了初步研究 ,优化后的酯交换率可达到 83%。

硫酸铁铵催化合成肉桂酸酯

利用十二水合硫酸铁铵为催化剂 ,使肉桂酸与醇类发生酯化反应合成了肉桂酸甲酯、肉桂酸乙酯、肉桂酸正丙酯、肉桂酸正丁酯、肉桂酸异丁酯、肉桂酸正戊酯和肉桂酸异戊酯 ,测定了各种酯的沸点 (或熔点 )、折光率、元素组成和