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传统催化剂催化甲醇氧化羰基化合成碳酸二甲酯(DMC)因氯离子的存在易导致腐蚀、失活,通过负载、添加助剂或配体的铜催化体系可改善上述问题。本文介绍了各改进催化体系,并综述了其反应机理。其中负载CuCl2或CuCl催化剂的活性中间体是Cu(OCH3)Cl或Cu2(OH)3Cl;亚铜与配体混合时,配体的种类、数量、结构等会影响甲氧基铜物种的形成;固体离子交换得到的Cu-分子筛催化剂实现了无氯化,然而活性较低;将Si、Al、Ti等氧化物作为载体时,对载体表面结构的改性改善了催化性能。大多数铜催化体系的控制步骤为CO对甲氧基铜物种的插入反应,然而对于甲氧基铜物种的产生以及CO对甲氧基铜物种插入后的产物仍存在分歧。指出进一步研究各催化体系的反应机理仍然是今后工作的重点。 相似文献
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采用稀H2SO4和(NH4)2S2O8溶液浸渍Fe(OH)3,高温焙烧制得SO42-/Fe2O3和S2O82-/Fe2O3固体酸,然后与CuCl混合高温处理制备CuⅠ/SO42-/Fe2O3和CuI/S2O82-/Fe2O3催化剂。该催化剂在CH3OH液相氧化羰基化合成碳酸二甲酯(DMC)反应中表现出良好的催化活性,明显高于传统CuCl催化剂。载体和催化剂的XRD、NH3-TPD和XPS等表征结果表明,制备的SO42-/Fe2O3和S2O28-/Fe2O3固体酸为超强酸,与CuCl混合高温处理中发生了固体离子交换,形成了负载CuⅠ的低氯催化剂。固体酸载体酸量越多,离子交换负载的CuⅠ离子的含量越高,催化活性越好。550℃焙烧制备S2O82-/Fe2O3固体酸有较多的酸量,与CuCl热处理获得的CuⅠ/S2O82-/Fe2O3催化剂具有较好的催化活性,CH3OH转化率达到16.58%,DMC选择性和时空收率分别为97.00%和2.83g.g-1.h-1,且Cu/Cl原子比达到1.69。 相似文献
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以乙酸镁为前体,采用等体积浸渍法制备不同负载量的MgO/ZSM-5催化剂,在气相连续流动固定床反应器上对甲苯与碳酸二甲酯(DMC)择形烷基化合成对二甲苯进行了研究。采用XRD、NH3-TPD、吡啶吸附红外和2,4-二甲基喹啉吸附红外等手段对催化剂进行了表征。结果表明:B酸中心是甲苯与DMC烷基化反应的活性中心;随着MgO负载量的增加,甲苯转化率下降,对二甲苯的选择性上升;当MgO负载量大于9%时,甲苯转化率和对二甲苯选择性基本保持不变。2,4-二甲基喹啉吸附红外表征结果表明,乙酸镁在改性过程中未进入ZSM-5孔道内,焙烧分解生成的MgO主要分布在分子筛的外表面,分子筛孔内酸位并未受到影响。随着MgO负载量的增加,催化剂外表面的B酸位数量下降,当负载量大于9%时,外表面的B酸位基本消失。 相似文献
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ZSM-5分子筛酸性和晶体大小对醛氨缩合合成吡啶碱的影响 总被引:1,自引:0,他引:1
针对Chichibabin醛氨缩合合成吡啶碱,用离子交换法制备具有相同酸性位类型,但Br?nsted(B)酸量不同的ZSM-5催化剂,并选择硅铝比接近但晶粒大小不同的H-ZSM-5分子筛,以及与ZSM-5具有相同MFI晶体结构的TS-1分子筛进行催化性能的比较。探讨了ZSM-5分子筛催化剂酸性、酸量和晶粒大小对反应活性、吡啶碱选择性和收率以及催化剂稳定性的影响。结果表明B酸位是进行醛氨缩合反应合成吡啶碱不可缺少的活性位,但酸强度较弱的末端硅羟基B酸位合成吡啶碱的活性较低;催化剂B酸含量越大,其进行醛氨缩合反应的初始活性和吡啶碱收率越高,催化剂失活越慢;小晶粒分子筛的初始活性、稳定性优于大晶粒分子筛,但合成吡啶碱的选择性和初始收率较低,这主要是因为与大晶粒分子筛相比,小晶粒分子筛具有更多的活性中心,特别是外表面活性中心,和相对较短的分子筛孔道。 相似文献
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针对甲醇羰基合成碳酸二甲酯(DMC)反应体系,在综合分析以氯化亚铜、氯化铜以及铜分子筛为催化剂的氧化羰基化反应机理的基础上,着重介绍了多相催化剂的种类、结构、活性中心以及制备工艺的研究进展,并对各类催化剂的催化性能进行了分析和评价。通过溶胶-凝胶技术和分子筛包覆的方法制备的钴系催化剂,其活性和稳定性得到了提高;钯铜系催化剂经过载体改性和加入适当的助剂,甲醇转化率增大并在一定程度上抑制了氯离子的流失;无氯铜系催化剂避免了对设备的腐蚀,但催化活性和DMC的选择性普遍较低。最后指出利用各种现代表征手段以及分析技术研究表面过程深刻了解甲醇羰基合成机理,才能在催化剂的设计和开发上取得创新和突破。 相似文献
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介孔分子筛B-SBA-15催化合成柠檬酸三丁酯 总被引:4,自引:4,他引:0
采用直接和间接合成法,将硼原子嵌入介孔分子筛SBA-15骨架中,用柠檬酸与正丁醇的酯化反应评价催化剂的催化性能。间接和直接合成法合成的催化剂活性对比结果表明,间接合成法制备催化剂的活性高于直接合成催化剂。重点考察了催化剂中硅硼比、催化剂用量、反应温度和酸醇比等因素对间接合成催化剂酯化反应性能的影响。筛选出B-SBA-15催化剂最佳硅硼摩尔比为30∶1,最佳反应条件:催化剂用量为原料质量的1.5%,反应温度为130 ℃,酸醇摩尔比1∶6。试验结果表明,介孔分子筛催化剂 B-SBA-15具有较高的稳定性,是合成柠檬酸三丁酯较为理想的分子筛催化剂。 相似文献
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从铜离子交换次数、交换后有无中间焙烧等几方面详细讨论了铜离子交换条件对所制备的催化剂分解NO的活性的影响。实验结果表明,经过条件优化制备的分子筛对NO有较高的分解率。 相似文献
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Polyoxyethylene esters of fatty acids: an alternative synthetic route for high selectivity of monoesters 总被引:1,自引:0,他引:1
Sharifah Bee Abd Hamid Fatimah Zahara Abdullah Syamala Ariyanchira Maria Mifsud Sara Iborra Avelino Corma 《Catalysis Today》2004,97(4):271-276
Esterification reaction of fatty acids with polyoxyethylenes has been studied in the presence of solid acid catalysts and the results are compared with those obtained with a classical homogeneous catalyst, p-toluene sulphonic acid. Solid acid catalysts showed very high selectivities for monoesters even under less favorable reaction conditions of 1:1 molar ratios of oleic acid to PEG. Excess amount of PEG is normally required to ensure high selectivity for monoesters in the presence of homogeneous catalysts. The yields for monoesters given by heterogeneous catalysts such as zeolites, HPA and nafion were comparable to that with p-toluene sulphonic acid after 24 h of reaction. Results suggest that solid acid catalysts are potential catalysts for selective synthesis of monoesters from oleic acids and PEG even under severe reaction conditions. A screening study of different solid acid catalysts showed ZSM-5, zeolite-β, and nafion to be better catalysts than zeolite USY and mordenite, the former giving higher selectivity and yield to monoesters. The results suggest that the most important parameters in optimization catalyst performance for monoesters production is the acid strength and less so on other properties such as shape selectivity and concentration of active sites. 相似文献
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A new process for the synthesis of diphenyl carbonate from dimethyl carbonate and phenol over heterogeneous catalysts 总被引:13,自引:0,他引:13
The two-step synthesis of diphenyl carbonate (DPC) from dimethyl carbonate (DMC) and phenol has been compared in liquid phase
and gas phase, both over heterogeneous catalysts. In the first step, equilibrium yields of methyl phenyl carbonate (MPC) in
the transesterification of DMC and phenol were very low at low temperatures in the liquid phase although reaction rates were
fast. This endothermic reaction was more favorable at high temperatures in the gas-phase reaction. Titanium oxide catalysts
supported on SiO2 or activated carbon were found to be effective in a continuous gas flow reactor. In case of the second step, the disproportionation
of MPC, selective formation of DPC was not feasible in the gas-phase reaction due to extensive side reactions. However, there
was no by-product in the liquid-phase reaction over the TiO2/SiO2 catalyst. Therefore, our proposed two-step synthesis process consists of the gas-phase transesterification of DMC and phenol
followed by the liquid-phase disproportionation of MPC to DPC, both over the TiO2/SiO2 catalyst.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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A. V. Abramova 《Catalysis in Industry》2009,1(4):267-277
Using an integrated physicochemical approach to the study of zeolites and catalysts, scientific foundations for the targeted
synthesis of catalysts based on ZSM-5 type zeolites for selective production of lower olefins from methanol and dimethyl ether
have been developed. The selective synthesis of the C2= and C3= olefins takes place on medium-strength acid sites. The domination of strong acid sites increases the extent of the secondary
oligomerization, aromatization, and cracking reactions and intensifies the deactivation of the catalyst. The effects of reaction
conditions (feed partial pressure and temperature) on the outcomes of the process have been investigated. High-efficiency
Zn-containing catalysts based on modified pentasils and promoted with magnesium and phosphorus have been developed for C2=–C4= olefin synthesis. These catalysts compare well with the industrial catalyst used in the Lurgi process. 相似文献
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固体碱催化苯乙酮和碳酸二甲酯合成苯甲酸甲酯 总被引:1,自引:0,他引:1
以固体酸碱为催化剂,研究了碳酸二甲酯与苯乙酮合成苯甲酸甲酯的反应,考察了反应温度、反应时间、催化剂用量和原料摩尔配比等因素对反应结果的影响。实验结果表明,固体酸催化剂不利于苯甲酸甲酯的生成,而具有中强碱位的MgO对反应有较好的催化活性。当以MgO为催化剂,在反应温度为260℃,反应时间5 h,催化剂用量为反应物总质量的1.5%,n(苯乙酮)∶n(DMC)=1∶4的条件下,苯乙酮的转化率和苯甲酸甲酯的选择性分别达72.0%和59.8%。另外,反应的副产物主要为乙酸甲酯、少量苯乙酮缩合的产物、甲基化及醚化产物等。 相似文献
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