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Structural characterization of Ti centres in Ti-silicalite and reaction mechanisms in cyclohexanone ammoximation 总被引:3,自引:0,他引:3
A. Zecchina S. Bordiga C. Lamberti G. Ricchiardi C. Lamberti G. Ricchiardi D. Scarano G. Petrini G. Leofanti M. Mantegazza 《Catalysis Today》1996,32(1-4):97-106
The main results obtained by means of many physical methods (IR, Raman, UV-Vis and XAFS spectroscopies) concerning the structure of the Ti centre in titanium silicalite and the reaction intermediates in the ammoximation of cyclohexanone are concisely reviewed.
The Ti is in tetrahedral coordination in vacuo and expands its coordination sphere upon interaction with adsorbates. In the presence of H2O and H2O/H2O2 solutions one of the SiOTi bridges is hydrolyzed with formation of (SiO)3L2TiOH (LH2O) and (SiO)3L2TiOOH species, respectively. When NH3 is dosed on (SiO)3L2TiOOH structures (SiO)3L2TiOO−NH4+ species are formed. These species are thought to play an important role in the ammoximation reaction. The geometries of the peroxidic species (open or bridged) are discussed also on the basis of ab initio calculations. 相似文献
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基于陶瓷膜反应器开发出无有机溶剂的环己酮氨肟化新工艺,探讨TS-1催化剂失活机制。采用XRD及Rietveld全谱拟合、FT-IR、N2吸附-脱附、TGA/DSC、GC-MS等手段对TS-1分子筛的骨架结构、晶胞参数、比表面积和有机物种类进行了表征分析。结果表明,无有机溶剂的环己酮氨肟化反应过程中,存在硅流失的现象,但TS-1骨架完整,晶胞参数未明显变化;环己酮、环己酮肟及反应副产物等吸附在TS-1催化剂的表面及孔道内,使比表面积下降52.6%、孔体积减少了41.6%,是造成TS-1失活的主要原因,空气氛围中于600℃煅烧3 h,可以恢复催化剂的活性。 相似文献
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A heterostructured titanium silicalite-1 catalytic composite for cyclohexanone ammoximation 总被引:1,自引:0,他引:1
Alex Chi-Kin Yip Frank Leung-Yuk Lam Xijun Hu 《Microporous and mesoporous materials》2009,120(3):368-374
Submicron-sized titanium silicalite-1 is difficult to recover in industrial process because of their fineness and rapid decrease in catalytic activity due to particle agglomeration. To solve these problems, we present a heterostructured titanium silicalite-1 (TS-1) catalytic composite using bentonite clay as the catalyst support. The catalytic composite is synthesized by hydrothermal treatment which directly crystallizes TS-1 on the bentonite clay surface. The synthesized composite has been characterized using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The TS-1 crystals have been found on and between the layers of the bentonite with strong attachment. Characterizations suggest that crystallization temperature of 175 °C is the optimum hydrothermal temperature to produce TS-1 on the bentonite support with characteristics necessary to promote selective catalytic reactions. It is found that prolonged crystallization duration does not necessarily increase the crystallinity of TS-1 on the bentonite surface. The heterostructured composite is able to maintain high conversion of cyclohexanone (97%) and oxime selectivity (83%) after three reaction cycles which is contrary to the unsupported TS-1 that shows apparent decrease in activity (>10%), especially in the selectivity to oxime. The synthesized composite also has significant improvement in separation efficiency with respect to the unsupported catalytic system. Therefore, we conclude that the heterostructured TS-1 composite is a promising catalytic material for cyclohexanone ammoximation and potentially for other TS-1 related processes where catalyst recovery and reuse are required. 相似文献
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研制了一种应用于环己酮自缩合反应的新型固体催化剂CC-1。与传统的浓硫酸催化剂相比,CC-1催化剂具有更优异的选择性,操作更简便。通过对不同用量的带水剂包括环己烷、正庚烷以及甲苯的使用效果进行考察,发现以用量为50 mL的正庚烷作带水剂的效果最理想,环己酮的转化率和二聚物的选择性分别达到87.5%和97.9%。对CC-1催化环己酮缩合反应的进程研究表明,该反应具有典型的连串反应特点。对CC-1催化剂的再生性能考察表明,该催化剂具有优良的再生性能,至少可以再生8次,维持催化剂活性在转化率85%和选择性96%左右。 相似文献
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The ammoximation in gas phase of cyclohexanone is a reaction with an oxidation step performed on an insulator oxide such as amorphous silica. Conventional mechanisms for such a kind of reaction are not useful. This paper reviews the efforts carried out to understand the catalytic behavior of the silica and highlights the particular catalytic features of the tars, the carbonaceous products formed during the ammoximation, in the oxidation step of the reaction. The catalytic behavior and the role of the acid sites, of the tars and of the activated forms of molecular oxygen were investigated on several commercial amorphous silicas and on pure and doped silicas prepared by sol-gel method. The silica catalyst shows a bifunctional behavior: acid sites are necessary for the formation of imine, the intermediate of the reaction, and oxidizing sites for the formation of oxime. For the first step the presence of silanols of the right acidity results is essential. For the oxidative step the carbonaceous products formed during the reaction seem to play an essential role. It has been suggested that the tars are formed by a polymerization reaction which occurs at the silica surface and involves, in the initiation stage, activated oxygen species generated by the silica surface. The reaction progression with time involves increasing amounts of the carbonaceous products, with a corresponding decline in access to the active sites by pore blockage and, as a consequence, with a corresponding decline in the catalytic activity. 相似文献
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以30%H2O2为氧源,NaHSO4.H2O、KHSO4为酸性配体,磷钨酸为催化剂催化氧化环己酮合成了己二酸。考察了催化剂用量、H2O2用量、酸性配体用量、反应时间以及催化剂重复使用性等因素对己二酸收率的影响。结果表明,磷钨酸在反应体系中有良好的催化活性,并且具有操作方便,条件温和等优点。适宜反应条件为n(环己酮)∶n(磷钨酸)=1∶0.002(摩尔比),硫酸氢钠0.1 g,30%H2O245 mL,回流反应6 h,己二酸收率66.7%;以KHSO4为酸性配体时,己二酸的收率可达71.2%。 相似文献
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以氢氧化铝、正磷酸和钛酸四异丙酯为原料,N-甲基二环己基胺为模板剂,采用水热晶化法合成一系列具有不同Ti含量的TAPO-5分子筛,通过XRD、N_2物理吸附-脱附、DR UV-Vis和XRF分别对分子筛结构、织构性质、Ti的存在状态以及Ti含量等进行表征。结果表明,TAPO-5分子筛为微孔-介孔材料,其中,Ti以骨架、非骨架和锐钛矿相3种形式存在;随着Ti含量增加,3种形式的Ti含量均增加,伴随着TAPO-5分子筛的结晶度、比表面积和孔容降低。环己酮氨肟化结果表明,随着Ti含量增加,环己酮转化率和环己酮肟选择性逐渐提高,当Ti质量分数为14.8%时,环己酮转化率和环己酮肟选择性分别为92.5%和95.4%,优于目前过渡金属掺杂磷酸铝分子筛催化环己酮氨肟化的最佳结果。 相似文献
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催化氧化法合成环己酮技术研究进展 总被引:1,自引:0,他引:1
介绍了以环己烷为原料催化氧化合成环己酮的主要方法,分析了环己烷氧化采用的主要催化剂。环己烷硼酸催化氧化法和钴盐催化氧化法存在环己烷转化率低及结渣现象;分子筛催化氧化法、金属氧化物以及金属络合物仿生催化氧化法可提高环己烷转化率及醇酮选择性;金属络合物仿生催化氧化法具有良好的开发应用前景。 相似文献
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综述了从不同原料出发通过氧化法制备环己酮的最新研究进展以及未来的发展方向。重点介绍了目前国内外生产环己酮的主要方法——环己烷催化氧化法,提出探索一种高效、高选择性的环己烷绿色氧化技术是今后的发展方向。 相似文献
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环己酮氨肟化工艺是制取化工原料的重要工艺,但该反应具有放热失控风险。为了确定氨肟化反应的最危险场景,筛选了环己酮氨肟化工艺可能存在的6个危险场景,并对每一危险场景设定了实验方案。采用泄放设计装置Ⅱ(VSP2)绝热量热仪对每一场景对应的方案进行了量热实验,实验发现:环己酮氨肟化反应为快速强放热反应,能够使反应体系的温度瞬间提高至200℃左右。反应结束后,继续升高温度,无二次反应失控。双氧水质量分数过高是环己酮氨肟化工艺最危险场景。针对氨肟化反应的泄放设计,必须以此场景作为设计依据。建议对双氧水进料线进行重点监控,以防止反应失控发生。 相似文献
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Zhigang Xu Xiongfei Jin Tao Zhou Qian Zou Longcheng Liu zhongbo Wang Hanbing Sheng Huasheng Xie 《中国化学工程学报》2022,47(7):11-17
The liquid phase direct ammoximation of 5-isooctyl salicylaldehyde with ammonia and hydrogen peroxide was studied using titanium silicalite-1 (TS-1) catalyst. The effect of reaction parameters on the yield of the product was studied, which include reaction temperature, reaction time, molar ratio of ammonia to aldehyde as well as hydrogen peroxide to aldehyde. The influence of the amount of catalyst on the reaction results was also investigated. The maximum 5-isooctyl salicylaldoxime yield of 98.76% was achieved under the following optimal reaction conditions:the molar ratio of 5-isooctylaldehyde to hydrogen peroxide and ammonia of 1:1.4:1.6, the reaction temperature of 70℃, the amount of TS-1 of 17.5 g·mol-1 (5-isooctyl salicylaldehyde), and the feeding time of 2 h. This method has the mild reaction conditions and avoids the shortcomings of traditional methods. Moreover, useless inorganic salts by-products are avoided, and there is no environmental pollution. 相似文献
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采用气相色谱法测定了环己酮氨肟化反应尾气中氨气含量,探讨了气相色谱操作条件,并与奥氏气体化学吸收法进行了比较。结果表明:采用Porapark Q,Porapark N混合色谱柱,柱温80℃,汽化温度120℃,检测温度150℃,检测器为热导检测器,桥流100 mA,载气为H2,流量为25 mL/min,以外标法定量,能够准确测定环己酮氨肟化反应尾气中的氨气;该方法的回收率为97.6%~100.5%,相对标准偏差为0.46%~0.92%;该方法较奥氏气体化学吸收法误差小、准确度高。 相似文献
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采用无机法,以水玻璃为硅源,硫酸铝为铝源,钨酸为钨源,在酸性条件下合成了具有ZSM-5结构的微孔分子筛(WZSM-5),经过离子交换合成了WHZSM-5分子筛。通过X射线衍射、红外吸收光谱等手段对催化剂进行了表征。结果表明:所制得的分子筛具有ZSM-5的特征结构,钨原子进入了ZSM-5骨架;以质量分数30%双氧水为氧化剂,环己酮与双氧水体积比为1:5时,催化剂用量为5 g/L,反应温度100℃,反应时间为6 h,催化氧化效果最好,环己酮转化率达93%;催化剂连续使用5次,反应活性基本不变。 相似文献
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Selective conversion of cyclohexane to cyclohexanol and cyclohexanone using a gold catalyst under mild conditions 总被引:1,自引:0,他引:1
Yi-Jun Xu Philip Landon Dan Enache Albert F. Carley M. W. Roberts Graham J. Hutchings 《Catalysis Letters》2005,101(3-4):175-179
The oxidation of cyclohexane to cyclohexanol and cyclohexanone are investigated using supported gold catalysts using mild conditions of temperature and pressure. These catalysts are found to show some limited activity at 70 °C. However, the gold catalysts do not exhibit significantly different behaviour from supported Pt or Pd catalysts, and the selectivity observed is solely a function of conversion which in turn is a function of reaction time. It is clear that at very low conversions very high selectivities can be observed, but high selectivity under these mild reaction conditions cannot be maintained at higher conversions. 相似文献