625 nm低能量光子作用下WO3-x光催化烯烃异构化

烯烃异构化广泛用于合成药物、高强度材料和精细化学品.近年来,光催化烯烃异构化的发展解决了传统烯烃异构化的设备腐蚀、活性和选择性较差等问题.如Pd@TiO2和Pd配合物均可用于烯烃的光催化异构化,但仅对烯丙基苄基衍生物有效.K(o)nig等利用可见光、Co(acac)2和合适的配体实现了烯烃位置可控的异构化,但该反应仅限于末端烯烃.因此,需要开发一种简单高效的光催化烯烃异构化方法,一方面可以通过光催化烯烃异构化将末端烯烃或内烯烃转化为一个或多个位置异构化产物,将石油衍生物中存在的烯烃混合物转化为有价值的单一烯烃产品,另一方面能够大幅提高光催化烯烃异构化的效率.本文研究发现,在625 nm光照射下,氧缺陷WO3-x表现出较好的催化1-癸烯异构化活性.该催化剂不仅可以将各种链状和环状末端烯烃转化为相应的内烯烃异构体,而且能够将内烯烃混合物转化为单一末端烯烃产品.通过控制烯烃碳链的长度可以得到热力学和动力学异构化产物,当烯烃的碳数小于13时,主要得到动力学产物.在无光照时没有检测到产物,说明只有在光照下反应才能进行.WO3-x的氧缺陷使WO3-x的漫反射紫外可见(DR UV-vis)光谱在大于450 nm时出现了局域表面等离子体共振(LSPR)强吸收.不同波长光照下1-癸烯异构化反应转化率的变化趋势与WO3-x的DR UV-vis光谱一致,而且在625 nm红光照射下,1-癸烯的转化率最高达到99.4％,进一步说明反应是由光驱动的.625nm的光可以将WO3-x价带上的电子激发到缺陷能级,且该电子可以进一步被转移到WO3-x吸附的烯烃上(激发电子转移路径).为进一步研究氧缺陷对光催化烯烃异构化活性的影响,在300℃焙烧不同时间得到氧缺陷含量不等的WO3-x样品.X射线衍射谱、DR UV-vis光谱、X射线光电子能谱和电子顺磁共振光谱结果表明,随着焙烧时间的增加,催化剂中氧缺陷含量逐渐减少,其光催化1-癸烯异构化活性逐渐降低,证明催化剂中氧缺陷的存在可以提高其光催化性能.利用原位漫反射傅里叶变换红外光谱研究了氧缺陷对烯烃表面吸附和中间体形成的影响.结果 表明,WO3-x表面氧缺陷产生的不饱和W5+位点会与烯烃配位从而原位形成表面π配合物和π-烯丙基钨中间体.通过在反应体系中添加4-叔丁基邻苯二酚证明了反应是通过自由基机理进行的.综上所述,WO3-x与625 nm红光结合,实现了烯烃的光催化异构化.通过调节烯烃的碳链长度,可得到热力学和动力学产物,且该催化体系可以将石油衍生物中的内烯烃混合物转化为单一末端烯烃产品.WO3-x的氧缺陷既可以提高其光捕获能力,又可以用作光催化烯烃异构化的吸附和活化位点.本文提供了一种利用低能量光子进行烯烃高效选择性异构化的简便方法,该方法是传统烯烃异构化方法的补充.     

调变MTO反应中双循环机理的比重:ZSM-5分子筛上不同接触时间的作用（英文）

低碳烯烃(乙烯、丙烯和丁烯)是重要的有机化工原料,是现代石油化工的基础,主要通过石脑油裂解和烷烃脱氢制备.现阶段我国原油对外依存度已超过60%,"多煤、缺油、少气"的能源现状决定了以煤或天然气为原料经甲醇制取石化产品成为一种重要的替代途径.甲醇制取低碳烯烃(MTO)过程成为连接煤化工和石油化工的桥梁.ZSM-5分子筛以其高效的甲醇转化能力、优异的低碳烯烃选择性和出色的抗积碳性能成为非常理想的MTO反应催化剂.研究发现ZSM-5分子筛催化MTO反应过程中,乙烯的生成规律与其它C_3–C_7链状烯烃不一致,认为乙烯主要来源于芳烃缩环/扩环循环,而C_3–C_7链状烯烃主要来源于烯烃甲基化/裂解循环,两种循环同时存在.本文于300°C在ZSM-5分子筛上进行MTO反应,通过考察不同空速(WHSV)条件下的MTO反应性能和分析催化剂内留存物种的生成和所起的作用,研究甲醇转化机理.气相流出物种和催化剂内留存物种的分析表明,ZSM-5分子筛催化MTO反应时遵循双循环机理——以多甲基苯和多甲基环戊二烯为主要活性物种的芳烃循环机理和以链状烯烃为主要活性物种的烯烃循环机理.在双循环机理中,芳烃循环和烯烃循环并不是简单叠加,而是相互影响,芳烃循环产生的烯烃可以作为烯烃循环的活性物种促进烯烃循环,烯烃循环中较高级的烯烃经过环化、氢转移作用,能够转化成富氢的烷烃和贫氢的芳烃、环戊二烯物种,贫氢的芳烃和环戊二烯物种又可以作为芳烃循环的主要物种促进芳烃循环的进行.氢转移反应是联系烯烃循环和芳烃循环的重要过程,与反应过程中原料甲醇与催化剂床层的接触时间有关,~(12)C/~(13)C甲醇切换实验揭示了双循环机理与氢转移反应的相关性,通过调变原料甲醇与催化剂床层的接触时间,可以调变氢转移反应的剧烈程度,进而对催化剂上芳烃循环和烯烃循环的甲醇转化能力产生不同的影响.当空速较低时,进料甲醇与催化剂床层的接触时间较长,有利于产物烯烃的氢转移反应,加速了分子筛催化剂上芳烃物种和环戊二烯物种的生成和累积,促进了芳烃循环,主要由芳烃循环生成的乙烯和多甲基苯的气相选择性提高;反之,当空速较高时,进料甲醇与催化剂床层的接触时间减少,产物烯烃的氢转移反应受到抑制,氢转移反应的产物——芳烃和环戊二烯物种的生成数量和累积速率降低,芳烃循环活性不高,使得烯烃循环成为甲醇转化的主要途径,C_3–C_7烯烃显示出更高的活性,在气相流出物种中的选择性也更高.总之,原料甲醇与催化剂床层的接触时间能够显著影响催化剂内留存物种的生成和累积,进而改变两种循环的比重.这些发现对于实现ZSM-5分子筛催化MTO反应过程中的产物烯烃和芳烃的选择性调控具有重要意义.     

625 nm低能量光子作用下WO_(3–x)光催化烯烃异构化（英文）

烯烃异构化广泛用于合成药物、高强度材料和精细化学品.近年来,光催化烯烃异构化的发展解决了传统烯烃异构化的设备腐蚀、活性和选择性较差等问题.如Pd@Ti O_2和Pd配合物均可用于烯烃的光催化异构化,但仅对烯丙基苄基衍生物有效.K?nig等利用可见光、Co(acac)_2和合适的配体实现了烯烃位置可控的异构化,但该反应仅限于末端烯烃.因此,需要开发一种简单高效的光催化烯烃异构化方法,一方面可以通过光催化烯烃异构化将末端烯烃或内烯烃转化为一个或多个位置异构化产物,将石油衍生物中存在的烯烃混合物转化为有价值的单一烯烃产品,另一方面能够大幅提高光催化烯烃异构化的效率.本文研究发现,在625 nm光照射下,氧缺陷WO_(3–x)表现出较好的催化1-癸烯异构化活性.该催化剂不仅可以将各种链状和环状末端烯烃转化为相应的内烯烃异构体,而且能够将内烯烃混合物转化为单一末端烯烃产品.通过控制烯烃碳链的长度可以得到热力学和动力学异构化产物,当烯烃的碳数小于13时,主要得到动力学产物.在无光照时没有检测到产物,说明只有在光照下反应才能进行.WO_(3–x)的氧缺陷使WO_(3–x)的漫反射紫外可见(DR UV-vis)光谱在大于450 nm时出现了局域表面等离子体共振(LSPR)强吸收.不同波长光照下1-癸烯异构化反应转化率的变化趋势与WO_(3–x)的DR UV-vis光谱一致,而且在625 nm红光照射下,1-癸烯的转化率最高达到99.4%,进一步说明反应是由光驱动的.625 nm的光可以将WO_(3–x)价带上的电子激发到缺陷能级,且该电子可以进一步被转移到WO_(3–x)吸附的烯烃上(激发电子转移路径).为进一步研究氧缺陷对光催化烯烃异构化活性的影响,在300oC焙烧不同时间得到氧缺陷含量不等的WO_(3–x)样品.X射线衍射谱、DR UV-vis光谱、X射线光电子能谱和电子顺磁共振光谱结果表明,随着焙烧时间的增加,催化剂中氧缺陷含量逐渐减少,其光催化1-癸烯异构化活性逐渐降低,证明催化剂中氧缺陷的存在可以提高其光催化性能.利用原位漫反射傅里叶变换红外光谱研究了氧缺陷对烯烃表面吸附和中间体形成的影响.结果表明,WO_(3–x)表面氧缺陷产生的不饱和W~(5+)位点会与烯烃配位从而原位形成表面π配合物和π-烯丙基钨中间体.通过在反应体系中添加4-叔丁基邻苯二酚证明了反应是通过自由基机理进行的.综上所述,WO_(3–x)与625 nm红光结合,实现了烯烃的光催化异构化.通过调节烯烃的碳链长度,可得到热力学和动力学产物,且该催化体系可以将石油衍生物中的内烯烃混合物转化为单一末端烯烃产品.WO_(3–x)的氧缺陷既可以提高其光捕获能力,又可以用作光催化烯烃异构化的吸附和活化位点.本文提供了一种利用低能量光子进行烯烃高效选择性异构化的简便方法,该方法是传统烯烃异构化方法的补充.     

调变 MTO反应中双循环机理的比重：ZSM-5分子筛上不同接触时间的作用

低碳烯烃(乙烯、丙烯和丁烯)是重要的有机化工原料,是现代石油化工的基础,主要通过石脑油裂解和烷烃脱氢制备。现阶段我国原油对外依存度已超过60%,“多煤、缺油、少气”的能源现状决定了以煤或天然气为原料经甲醇制取石化产品成为一种重要的替代途径。甲醇制取低碳烯烃(MTO)过程成为连接煤化工和石油化工的桥梁。 ZSM-5分子筛以其高效的甲醇转化能力、优异的低碳烯烃选择性和出色的抗积碳性能成为非常理想的 MTO反应催化剂。研究发现 ZSM-5分子筛催化 MTO反应过程中,乙烯的生成规律与其它 C3–C7链状烯烃不一致,认为乙烯主要来源于芳烃缩环/扩环循环,而 C3–C7链状烯烃主要来源于烯烃甲基化/裂解循环,两种循环同时存在。本文于300°C在 ZSM-5分子筛上进行 MTO反应,通过考察不同空速(WHSV)条件下的 MTO反应性能和分析催化剂内留存物种的生成和所起的作用,研究甲醇转化机理。气相流出物种和催化剂内留存物种的分析表明, ZSM-5分子筛催化 MTO反应时遵循双循环机理——以多甲基苯和多甲基环戊二烯为主要活性物种的芳烃循环机理和以链状烯烃为主要活性物种的烯烃循环机理。在双循环机理中,芳烃循环和烯烃循环并不是简单叠加,而是相互影响,芳烃循环产生的烯烃可以作为烯烃循环的活性物种促进烯烃循环,烯烃循环中较高级的烯烃经过环化、氢转移作用,能够转化成富氢的烷烃和贫氢的芳烃、环戊二烯物种,贫氢的芳烃和环戊二烯物种又可以作为芳烃循环的主要物种促进芳烃循环的进行。氢转移反应是联系烯烃循环和芳烃循环的重要过程,与反应过程中原料甲醇与催化剂床层的接触时间有关,12C/13C甲醇切换实验揭示了双循环机理与氢转移反应的相关性,通过调变原料甲醇与催化剂床层的接触时间,可以调变氢转移反应的剧烈程度,进而对催化剂上芳烃循环和烯烃循环的甲醇转化能力产生不同的影响。当空速较低时,进料甲醇与催化剂床层的接触时间较长,有利于产物烯烃的氢转移反应,加速了分子筛催化剂上芳烃物种和环戊二烯物种的生成和累积,促进了芳烃循环,主要由芳烃循环生成的乙烯和多甲基苯的气相选择性提高;反之,当空速较高时,进料甲醇与催化剂床层的接触时间减少,产物烯烃的氢转移反应受到抑制,氢转移反应的产物——芳烃和环戊二烯物种的生成数量和累积速率降低,芳烃循环活性不高,使得烯烃循环成为甲醇转化的主要途径, C3–C7烯烃显示出更高的活性,在气相流出物种中的选择性也更高。总之,原料甲醇与催化剂床层的接触时间能够显著影响催化剂内留存物种的生成和累积,进而改变两种循环的比重。这些发现对于实现 ZSM-5分子筛催化 MTO反应过程中的产物烯烃和芳烃的选择性调控具有重要意义。     

由1,1,2,3-四氯丙烯合成一些氟氯化合物

以1,1,2,3-四氯丙烯(1)为原料,合成了多种具有工业价值的氟氯化合物。首先,以叔胺-2HF为氟化试剂,亲核取代1得到3-氟-1,1,2-三氯丙烯(2);随后在AlCl3催化下异构2得到3-氟-2,3,3-三氯丙烯(3),在FeCl3或KCl催化下异构3得到1-氟-1,2,3-三氯丙烯(4);最后在铬基氟化催化剂催化下,气相氟化2高转化地得到2-氯-3,3,3-三氟丙烯(5),在SbCl5催化下,液相氟化3一步得到2-氯-1,1,1,2-四氟丙烷(6)。本文所合成的化合物5和6均是合成新一代环保型制冷剂HFO-1234yf的重要中间体。     

Effect of Phenyl CI Substituent Position on the Catalytic Performance for Olefin Epoxidation of Tetraphenylmetalloporphyrins

以苯乙烯、环己烯和反式二苯乙烯为烯烃底物,以双氧水、叔丁基过氧化氢和异丙苯过氧化氢为氧化剂,以苯环上对位和邻位氯取代的四苯基金属卟啉为仿生催化剂,对烯烃的催化环氧化反应进行了对比研究.讨论了不同氯取代位的四苯基金属卟啉对烯烃环氧化性能的影响.实验结果表明,在没有助催化剂存在下,邻位氯代的四（2,6-二氯苯基）铁（锰）卟啉对烯烃的环氧化具有优异的催化性能,烯烃底物的转化率和环氧选择性都比对位氯代的四苯基铁（锰）卟啉高,且反应条件温和.其中FeⅢ（TDCPP）Cl的催化性能最好,环氧化选择性最高,催化氧化苯乙烯时,环氧苯乙烷的选择性达到了90.4%.相同金属离子不同配体的金属卟啉传递氧原子的能力为TDCPP〉T（p-Cl）PP〉TPP.氧化剂的结构对环氧化物的选择性有较大影响.过氧键连有吸电子基团的异丙苯过氧化氢对环氧化物的选择性最高.根据实验结果,对金属卟啉催化环氧化机理进行了分析.     

由1,1,2,3-四氯丙烯合成氟氯化合物

以1,1,2,3-四氯丙烯(1)为原料,合成了多种具有工业价值的氟氯化合物。首先,以叔胺-2HF为氟化试剂,亲核取代1得到3-氟-1,1,2-三氯丙烯(2);随后在AlCl3催化下异构2得到3-氟-2,3,3-三氯丙烯(3),在FeCl3或KCl催化下异构3得到1-氟-1,2,3-三氯丙烯(4);最后在铬基氟化催化剂催化下,气相氟化2高转化地得到2-氯-3,3,3-三氟丙烯(5),在SbCl5催化下,液相氟化3一步得到2-氯-1,1,1,2-四氟丙烷(6)。本文所合成的化合物5和6均是合成新一代环保型制冷剂HFO-1234yf的重要中间体。     

苯环上氯取代位对四苯基金属卟啉催化烯烃环氧化性能的影响

以苯乙烯、环己烯和反式二苯乙烯为烯烃底物,以双氧水、叔丁基过氧化氢和异丙苯过氧化氢为氧化剂,以苯环上对位和邻位氯取代的四苯基金属卟啉为仿生催化剂,对烯烃的催化环氧化反应进行了对比研究.讨论了不同氯取代位的四苯基金属卟啉对烯烃环氧化性能的影响.实验结果表明,在没有助催化剂存在下,邻位氯代的四(2,6-二氯苯基)铁(锰)卟啉对烯烃的环氧化具有优异的催化性能,烯烃底物的转化率和环氧选择性都比对位氯代的四苯基铁(锰)卟啉高,且反应条件温和.其中FeⅢ(TDCPP)Cl的催化性能最好,环氧化选择性最高,催化氧化苯乙烯时,环氧苯乙烷的选择性达到了90.4%.相同金属离子不同配体的金属卟啉传递氧原子的能力为TDCPP>T(p-Cl)PP>TPP.氧化剂的结构对环氧化物的选择性有较大影响.过氧键连有吸电子基团的异丙苯过氧化氢对环氧化物的选择性最高.根据实验结果,对金属卟啉催化环氧化机理进行了分析.     

不同结构SAPO-34催化剂上1-己烯催化裂解制丙烯

制备了100%SAPO-34,30%SAPO-34和介孔-SAPO-34三种不同类型的SAPO-34分子筛催化剂,并采用氮吸附、扫描电镜、X射线衍射和红外光谱等方法对催化剂进行了表征.三种催化剂的微孔结构、比表面积和总酸最近似,但具有不同的催化剂组成和次级结构.以1-己烯裂解为模型反应考察了三种催化剂的催化活性.对于30%SAPO-34催化剂,由于添加了粘结剂.其外表面酸性和扩散性能下降,导致催化活性降低:100%SAPO-34催化剂则具有较好的催化性能:介孔 SAPO-34催化剂次级结构的存在使其失活较慢,从而提高了原料的转化率.详细讨论了1-己烯催化裂解制丙烯的活性和选择性曲线,以进一步说明催化剂组成和结构的影响.     

氯化亚铜催化3-氯-1-丁烯异构为1-氯-2-丁烯研究

采用一价铜盐为催化剂、二甲基甲酰胺为溶剂,在均相体系中催化3-氯-1-丁烯异构化生成1-氯-2-丁烯.考察了溶剂、反应温度、催化剂种类和加入量对反应的影响,研究发现反应温度和催化剂的加入量对异构化反应有较大影响.在最优条件3-氯-1-丁烯1 mL,二甲基甲酰胺9 mL,CuCl 0.10 g,60℃反应5 h,产物和原料的浓度比为3.88 mmol L-1.采用在线红外光谱对反应过程进行监测,检测到有红外吸收峰在反应过程中先增加后减少的变化过程,提出了可能的反应机理.     

Isomerization of n-Hexane over Chlorinated Pt/γ-Al2O3 Catalysts

Chlorided 0.57 wt. % Pt/γ-Al₂O₃ is a moderately active and highly selective catalyst for the isomerization of n-hexane at 300 °C when an excess of H₂ is present. Chlorine, which is continuously lost from the catalyst, may be replaced by adding a small amount of chloroform to the reactant stream. The catalyst exhibits activity and high isomerization selectivity even at 150 °C. Under the conditions of these lower temperature experiments, the equilibrium concentration of C₆ alkenes would be only 8 × 10^?7 Torr. This suggests that the classical mechanism, which involves the formation of n-hexene on the Pt, is not applicable. Rather, it is proposed that isomerization of the alkane occurs at acid sites on the catalyst, and the role of Pt is to catalyze the hydrogenation of any alkenes that might be formed as a result of cracking reactions. At temperatures ≤ 300 °C Brönsted acid sites are present in the catalyst, and presumably are responsible for the isomerization and cracking activity, but at higher temperatures Lewis acid sites play a dominant role.     

Preparation and characterization of supports with a synthesized layer of catalytic filamentous carbon: III. Synthesis of carbon nanofibers on nickel supported onto aluminum oxide

The synthesis of catalytic filamentous carbon (CFC) on catalysts prepared by supporting Ni²⁺ compounds onto the surface of various alumina modifications (macroporous α-Al₂O₃ and mesoporous ?-Al₂O₃ and δ-Al₂O₃) using two procedures (impregnation and homogeneous precipitation) was studied. The texture characteristics (specific surface area and pore structure) of the parent supports and adsorbents with a CFC layer were compared. The effect of the supporting procedure on the surface morphology of Ni/Al₂O₃ catalysts and the synthesized CFC layer was studied by scanning electron microscopy. It was found that the carbon yield on a macroporous catalyst prepared by homogeneous precipitation was higher than that on a catalyst prepared by impregnation by a factor of ～2. The CFC layer exhibited a mesoporous structure because of a chaotic interlacing of carbon nanofibers, and the synthesis of CFC on macroporous supports resulted in the formation of a bidisperse pore structure of the adsorbent. Active and stable heterogeneous biocatalysts were prepared by the adsorptive immobilization of enzymatically active substances (glucoamylase and nongrowing baker’s yeast cells) on CFC.     

Low temperature isomerization of n-hexane on catalyst systems Al2O3/ZrO2/SO4/Pt

As a result of investigating low temperature isomerization of n-hexane at 130, 140, 150, 160°C in a flow reactor with a fixed bed of catalyst of the Al₂O₃/ZrO₂/SO₄/Pt type a ratio of components in the catalyst system was selected and process conditions were defined, which allow to obtain highly branched high-octane isomers with a yield of up to 40% relative to a transformed raw material. A kinetic model of the process was proposed and kinetic parameters were calculated.     

Nature of active sites in hybrid metal-zeolite catalysts for the Fischer-Tropsch synthesis

The temperature-programmed reduction, powder X-ray diffraction, and oxygen titration were applied to study reducibility, phase composition, and structure of the active surface of the hybrid metal-zeolite catalysts Mβ@Co/Al₂O₃ (M = Pd, Co, and Fe). The results of physicochemical studies were compared with the data on activity and selectivity of the catalysts in the synthesis of liquid hydrocarbons from the synthesis gas. The nature of transition metal and the method of its introduction into the catalyst influence the composition of synthetic liquid hydrocarbons. A comparison of the Feβ@Co/Al₂O₃ catalyst prepared by the ion-exchange method that exhibits the highest activity in the synthesis of liquid hydrocarbons with a similar catalyst Fe/(Hβ@Co/Al₂O₃) prepared by the impregnation method indicated a distinct advantage of the ion exchange procedure. A mechanism of isomerization and cracking of primary linear alkanes on the M _n ^δ+ clusters in the Mβ@Co/Al₂O₃ systems was proposed. The mechanism explains the main features governing the group and fractional composition of the obtained synthetic hydrocarbons.     

Synthesis and modification of multi-walled carbon nano-tubes (MWCNTs) for water treatment applications

Synthesis of MWCNTs by chemical vapor deposition (CVD) of acetylene is investigated at different temperatures. Fe-Co/CaCO₃ catalyst/support prepared by wet impregnation method is used. CaCO₃ was found to be a good support as a high selective material for deposition of CNTs with high purity. The effect of temperature on catalyst/support phases and crystal size was identified by using XRD. The crystallite size was decreased with increase temperature. The effect of growing time and temperature on carbon yield was studied and the deposited MWCNTs increased with temperature. The structure and purity of synthesized CNTs at different temperatures was examined by TEM and the effect of temperature on the surface area of the synthesized MWCNTs was investigated, the surface area decreased as the temperature increased. The prepared CNTs were purified using chemical oxidation method and the effect of acid treatment on CNTs surface was examined by TEM and SEM. The function groups produced at CNTs surface were investigated by using FTIR spectroscopy also the effect of CNTs preparation temperature on FTIR spectra was studied. The functionalized CNTs were used for adsorption of some heavy metals and for removal of some organic dyes from water.     

Ag-polymer composite microspheres with patterned surface structures

Novel silver-poly(acrylamide-co-methacrylic acid) [Ag-P(AM-co-MAA)] composite microspheres, in tens of micrometer size range, with patterned surface and core/shell structures were prepared by chemical reduction of Ag₂CrO₄-P(AM-co-MAA) composite microspheres in ethanol. Characterization with various techniques revealed that the chemical composition of the “shell” is dominated by Ag, but the “core” is dominated by the template, P(AM-co-MAA). It was also demonstrated that the surface morphology of the Ag-polymer composite microspheres is similar to that of their precursors and can be controlled to a certain extent by varying the composition of template copolymer, approaches, and amount of Ag₂CrO₄ deposited. This morphology transfer technique is also applicable for other silver salts-polymer composite microspheres. The same silver-polymer composite microspheres with very different morphology have also been prepared by utilizing this technique, but the different precursor microspheres, Ag₃PO₄-P(AM-co-MAA), were used. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Formation of a supported cobalt catalyst for the synthesis of carbon nanofibers on aluminum oxide

Comparative studies of the effect of the physicochemical characteristics of a support (aluminum oxide) on the formation of a supported Co catalyst and its activity in the pyrolysis of alkanes (propane-butane) were performed. The effect of the crystalline modification of alumina on the yield of catalytic filamentous carbon (CFC) ((g CFC)/(g Co)) was studied. The surface morphologies of Co-containing catalysts and synthesized carbon deposits were studied by scanning electron microscopy. It was found that carbon deposits with a well-defined nanofiber structure were synthesized by the pyrolysis of a propane-butane mixture in the presence of hydrogen at 600°C on supported Co catalysts prepared by homogeneous precipitation on macroporous corundum (α-Al₂O₃). The yield of CFC was no higher than 4 (g CFC)/(g Co). On the Co catalyst prepared by homogeneous precipitation on mesoporous Al₂O₃, the intense carbonization of the initial support; the formation of cobalt aluminates; and, as a consequence, the deactivation of Co⁰ as a catalyst of FC synthesis occurred. The dependence of the yield of CFC on the preheating temperature (from 200 to 800°C) of Co catalysts before pyrolysis was studied. It was found that, as the preheating temperature of supported Co/Al₂O₃ catalysts was increased, the amount of synthesized carbon, including CFC, decreased because of Co⁰ deactivation due to the interaction with the support and coke formation.     

n-Hexane Isomerization by Pt/WO3-ZrO2 Using Hydrothermally Synthesized Hydrous Zirconia as Support

A series of hydrous zirconia samples were prepared by the hydrothermal method, and the Pt/WO₃-ZrO₂ catalyst was prepared by impregnation. The effects of hydrothermal temperature of Zr(OH)₄ on the isomerization activity of the catalyst was investigated. The crystalline structure, acidity, and reduction properties of the catalyst were characterized by X-ray diffraction, NH₃ temperature-programmed desorption, and H₂ temperature-programmed reduction, respectively. The results indicated that the crystalline structure of hydrous zirconia and the catalyst varied with the hydrothermal temperature, and the increase of hydrothermal temperature reduced the fraction of tetragonal zirconia. Strong acid sites on the catalyst and the isomerization activity increased with the crystallization of Zr(OH)₄. It was proposed that the higher isomerization activity may be related to the existence of large numbers of strong acid sites.     

Activation of electrode surfaces: semiquantitative characterization of electrode surfaces modified with heteropolyanions

Several Techniques have been used successively or in combination to approach a better understanding of surfaces modified by silicotungstic heteropolyanion. Due to the strikingly high activity of these electrodes for the hydrogen evolution reaction, in particular, there exists a need to identify the chemical composition of the catalyst, to evaluate the amount of catalyst on the surface, and to study the electrochemical behaviour of the “catalyst” itself. Plasma emission spectrometry shows semi-quantitatively that the catalyst resembles the starting material closely, although it is not possible at present to give the exact chemical formula. Electron microprobe analysis (EMA) confirms the presence of tungsten, and especially silicon, on the surface, even though the concentration of this last element is very low. The absence of platinum in the starting HPA, as well as on the electrode surface, is also clearly demonstrated by EMA, which is of prime importance in showing that the “HPA catalyst” is active by itself. Combined coulometry and UV-visible spectroscopy have been used to evaluate the amount of HPA consumed during electrolysis. Cyclic voltammetry shows a surface redox couple corresponding to the catalyst, and well separated from the first redox couple of SiW₁₂O^4-₄ in 0.5 M H₂SO₄ solution. A better understanding of the activation-deactivation processes of the catalytic electrode surface ensues.     

Carbon dioxide reforming of methane on a cobalt catalyst subjected to plasma–chemical treatment

The effect plasma–chemical treatments of 5 wt % Со/SiO₂ catalyst have on its activity in the carbonic acid conversion of methane in the interval of 700 to 900°C is studied. A plasma glow discharge in oxygen and argon was used along with high-frequency plasma in hydrogen for preliminary treatment of the catalyst. A multiple increase in СН₄ and СО₂ conversion and a 30–50 K drop in the temperature of the onset of the reaction are observed after plasma–chemical treatments. The strongest increase in activity is measured after the catalyst is treated with oxygen plasma. X-ray photoelectron spectroscopy is used to determine the change in the composition of the catalyst’s surface after it is treated with plasma, indicating that active forms of carbon atoms can be included in new active centers.