Enantioselective hydrogenation of N-acetyl dehydrophenylalanine methyl ester using cinchonine-modified Pd/TiO2 catalysts

The enantioselective hydrogenation of N-acetyl dehydrophenylalanine methyl ester (NADPME) to N-acetyl phenylalanine methyl ester is investigated using cinchonine-modified Pd/TiO₂ catalysts. The catalysts were prepared using deposition–reduction and wet impregnation methods and were evaluated for reaction using methanol as solvent with various cinchonine/NADPME molar ratios. Enantioselectivity was sensitive to this ratio and comparison with Pd/γ-Al₂O₃ showed that the Pd/TiO₂ gave marginally higher enantioselectivity when tested under comparable conditions. The effect of Pd loading and dispersion was investigated and the maximum enantiomeric excess observed was dependent on the dispersion; the role of the Pd particle size is discussed in the context of cinchonine adsorption. The reactions were carried out in solvents (methanol and dimethyl formamide) and mixed solvents (methanol–water and dimethyl formamide–water); the enantiomeric excess was significantly enhanced using dimethyl formamide. The addition of water does not have a significant effect for the Pd/TiO₂ catalysts. In this paper we report the highest enantiomeric excess for the hydrogenation of a prochiral ester using an immobilised catalyst.     

精C_5饱和加氢Pd/Al_2O_3催化剂的制备

研究负载在Al2O3载体上的Pd催化剂对精C5饱和加氢反应的性能。以工厂精C5为原料,考察载体焙烧温度、Pd负载量和催化剂制备工艺对催化剂性能的影响。结果表明,载体最佳焙烧温度为700℃,Pd最佳负载质量分数为0.3%,Pd最佳负载时间为4 h,催化剂最佳焙烧温度为500℃,催化剂最佳焙烧时间为4 h,以此条件制备的催化剂进行C5饱和加氢评价,加氢效率不低于94%。     

Pd/Al2O3液相选择加氢催化剂抗硫性能研究

研究了助剂对Pd/Al2O3催化剂裂化汽油液相选择加氢活性及其抗硫性能的影响。着重探讨了Co助剂的作用规律。结果表明，助剂对Pd/Al2O3催化剂的加氢活性有不同影响，其中加入Ag、Cu和Co助剂时，可以提高催化剂加氢活性，而Co助剂的提高最为明显，通过对催化剂进行XPS和反应后催化剂硫含量的分析，表明Co助剂改善Pd/Al2O3催化剂液相加氢活性的作用有两方面，一是与Pd金属产生电子相互作用，改变其电子状态，减弱对硫化物的吸附；二是Co具有吸硫作用，使部分硫化物吸附在助剂Co上，从而减少了在活性中心Pd上的吸附，导致Pd－Co/Al2O3催化剂具有良好的液相选择加氢活性。     

Pd／Al2O3催化剂上裂解C5馏分选择性加氢反应研究

研究了负载在Al2O3载体上的贵金属钯（Pd）基催化剂在裂解C5馏分中选择性加氢反应中的性能。结果表明,Pd／Al2O3催化剂上可进行选择性加氢的反应条件区域为压力0．5～1．0MPa、体积空速2—4h^-1、氢油体积比100：1～300：1和反应温度为55—65℃,在此反应条件下,炔烃能被完全加氢去除,同时二烯烃发生部分转化,转化产物主要为单烯烃,其中二烯烃转化的产物主要是热力学相对稳定的单烯烃;在选定的反应条件中,随温度升高、压力增加、氢油比增加,炔烃、二烯烃转化率提高;而随液时空速增加,二烯烃转化率有所下降;在各反应条件中,温度和压力对催化剂加氢性能影响较为显著;制备的Pd／Al2O3催化剂对于炔烃和二烯烃具有好的选择性加氢能力,可能原因一方面是由于反应条件选择较缓和,另一方面是原料中硫的存在。     

Unexpected inversion of enantioselectivity during the hydrogenation of ethyl pyruvate using hydroquinine and hydroquinidine modified Pt/Al2O3

In the enantioselective hydrogenation of ethyl pyruvate using hydroquinidine 4-chlorobenzoate modified Pt/γ-Al₂O₃ catalyst, the sense of the enantioselectivity is a function of the modifier concentration. At low concentration (S)-ethyl lactate is preferred and at higher concentration (R)-ethyl lactate is formed; the opposite trend is observed with hydroquinine 4-chlorobenzoate. This is the first example where enantio-inversion is induced solely as a function of the chiral modifier concentration.     

Fabrication of hydrophobic Pd/Al2O3-phosphoric acid via P-O-Al bond for liquid hydrogenation reaction

Alumina (Al₂O₃) is widely used in the chemical industry as the catalyst and support due to its high specific surface area, abundant pore size distribution and chemical stability. However, the occurrence of hydration in water environment, result in outstanding decrease in specific surface area and collapse of pore structure. In this work, dodecyl phosphoric acid (PA) is used to modify the surface of Al₂O₃ to obtain a series of hydrophobic material (Al₂O₃-PA). Based on XPS and NMR analysis, PA is chemically bonded on Al₂O₃ to form P-O-Al bond. Furthermore, BET and WCA results display that Al₂O₃-1PA exhibits excellent the hydrophobicity and hydrothermal stability while maintains the pore structure. Take it as the substrate to support the Pd nanoparticles, the as-prepared Pd/Al₂O₃-PA shows the superior catalytic performance in the hydrogenation of phenol and anthraquinone relative to Pd/Al₂O₃, indicating the accessibility of Pd sites after PA modification. Especially, the significantly enhanced stability is also obtained in four cycles for aqueous phenol hydrogenation. This can be ascribed that the PA modification inhibits the aggregation of Pd nanoparticles and the products adhesion in the reaction process. The extension of PA coatings to monolithic catalysts could expand their current capabilities in industrial applications and warrants ongoing investigation.     

Ca助剂对钯负载催化剂在苯酚液相原位加氢反应中的影响

利用等体积浸渍法制备了一系列不同助剂的Pd／Al2O3催化剂,并利用固定床管式反应器考察了以上催化剂在“苯酚＋甲醇＋水”耦合反应体系中的性能。结果表明Ca的促进作用较明显,进一步考察了Ca助剂的含量对催化剂活性的影响,并通过BET和CO吸附表征探讨了Ca助剂对催化剂结构以及Pd分散度的影响。     

Pd/Al2O3催化剂用于连续重整汽油全馏分加氢的失活分析

研究了负载在氧化铝载体上的贵金属Pd基催化剂在重整生成油选择性加氢脱烯烃反应中的性能。结果表明,在连续重整生成油全馏分的选择性加氢实验中，采用现有工业常用的工艺条件，单使用Pd作活性组分的Pd/Al₂O₃催化剂不能满足产品质量要求。探讨了切割馏分油加氢反应中催化剂失活原因，并对失活前后的催化剂采用XRD、SEM和FTIR等手段进行分析表征。结果表明，造成催化剂失活原因是催化剂表面油品中重组分等热敏类物质强吸附或聚合作用的结果。改进后的双金属Pd基催化剂UDO-01可用于重整生成油全馏分的选择性加氢脱烯烃反应，加氢后产品的溴价小于200 mg Br·(100 g-油)^-1,芳烃损失小于0.5%，且表现出好的稳定性。     

Regeneration of S-poisoned Pd/Al2O3 and Pd/CeO2/Al2O3 catalysts for the combustion of methane

This work investigates the regeneration of S-poisoned Pd/Al₂O₃ and Pd/CeO₂/Al₂O₃ catalysts under different CH₄ containing atmospheres. Under lean combustion conditions in the presence of excess O₂, partial regeneration took place for both systems only above 750 °C after decomposition of stable sulphate species adsorbed on the support. Under alternate lean combustion/CH₄-reducing pulse regeneration is markedly anticipated down to 550–600 °C. Experiments evidenced an effective role of ceria in preventing PdO from sulphation and in promoting regeneration via sulphates decomposition under reducing conditions.     

不同Pd/Ag配比Pd-Ag/Al2O3催化乙炔加氢微观反应动力学分析

乙炔加氢是乙烯工业中的重要精制反应。以α-Al₂O₃作为载体,采用分步等量浸渍法制备了不同Pd/Ag配比的加氢催化剂,使用N₂物理吸附、XRD、ICP、XPS、TEM和CO化学吸附等手段表征催化剂的结构和组成,根据正交实验设计方案进行动力学实验,建立了微观反应动力学模型,并根据动力学模拟结果和动力学参数值的变化分析了Ag助剂含量对乙炔加氢反应动力学的影响。研究结果表明,以Pd-Ag催化剂上碳二加氢的DFT计算结果为基础参数来源,经过吸脱附步骤活化能的优化,微观反应动力学模型可以很好地模拟不同Pd/Ag配比催化剂上的乙炔加氢反应动力学结果;在所研究范围内,各催化剂上加氢反应的表面最丰物种皆为C₂H₄^*,速率控制步骤为乙烯基加氢,不会随着Ag含量的不同发生变化;但是Ag含量的增加显著降低了氢气脱附活化能,提高了乙烯的选择性,这可能与Ag含量的提高增加了催化剂表面Ag和Pd之间的电子转移现象有关。     

Ru/Al_2O_3催化剂上邻苯二甲酸二丁酯加氢合成1,2-环己烷二甲酸二丁酯

以浸渍法制备Ru/Al2O3催化剂,研究在高压反应釜中Ru/Al2O3上催化加氢邻苯二甲酸二丁酯(DBP)合成1,2-环己烷二甲酸二丁酯(CDADE)。采用X射线衍射(XRD)、H2程序升温还原(H2-TPR)、扫描电镜(SEM)、X射线能谱仪(EDS)和透射电子显微镜(TEM)对催化剂进行表征。结果表明,Ru负载量为3.0%(质量分数),200℃氢气气氛中还原的Ru/Al2O3催化剂,在催化DBP合成CDADE的反应中具有较高的催化活性。在反应温度80℃、反应压力2.0~2.5 MPa和搅拌转速800 r/min下,DBP转化率和CDADE选择性分别达到99.972%和99.904%,催化剂重复使用9次后仍有较高活性,但继续使用,由于活性组分Ru部分流失、团聚和催化剂表面积炭,催化剂活性有所下降。     

不同粒径Pd/Al2O3催化乙炔加氢反应微观动力学分析

采用等量浸渍法制备了α-Al₂O₃负载的系列Pd催化剂,运用BET、XRD、ICP-AES、CO化学吸附、TEM等手段对催化剂进行了表征;根据部分析因实验设计方案进行动力学实验,采用微观反应动力学方法模拟和分析了所获稳定期本征动力学实验结果。结果发现,制备所得催化剂Pd颗粒的平均粒径分别为1.6、3.4、5.5 nm,CO化学吸附所测定达到活性稳定期后的催化剂表面Pd原子数与Hardeveld模型计算的Pd（111）表面原子数一致;模拟结果表明该微观动力学模型可以很好地模拟不同粒径催化剂上的动力学结果,在所研究范围内表面最丰物种为C₂H₄^*和C₂H₃^*,通过微观与宏观动力学的特征判断3种催化剂上乙炔加氢的速率控制步骤为乙烯基加氢生成乙烯。     

Pd/Al2O3催化剂的制备及其在对氨基苯酚合成中的应用

用等体积浸渍法制备了Pd/Al2O3催化剂。采用ICP、XRD、HRTEM和XPS等对催化剂的组成和形貌进行表征。结果表明，Pd粒子均匀分布在Al₂O₃的表面，粒径约为5 nm。在对硝基苯酚催化加氢制备对氨基苯酚的反应中，对催化剂的催化性能进行了考察。Pd/Al₂O₃催化剂的催化活性随着Pd负载量的增大而增大；其与市售的骨架镍、纳米镍以及2%Pd/C相比，显现了优异的催化活性；Pd/Al₂O₃具有高的催化选择性；Pd/Al2O3的催化活性稳定性明显优于骨架镍；随着使用次数的增加，Pd/Al₂O₃的催化活性有所降低，这可能是因为Pd粒子的团聚。     

ZnO诱导的Pd/Al2O3@ZIF-8核壳催化剂制备及其催化性能

利用同源氧化锌有利于ZIF-8结构的成核生长原理,采用粒径为1~2 mm 的负载型Pd/Al₂O₃微球作为核、ZIF-8膜作为外壳,ZnO诱导生长制备了Pd/Al₂O₃@ZIF-8核壳催化剂,用XRD、EDX、SEM、ICP等分析手段对其结构进行了表征,并采用不同大小分子烯烃加氢反应对其壳层连续完整性进行了性能测试。结果表明,Pd/Al₂O₃微球表面预先引入的ZnO纳米粒子层对外层连续ZIF-8膜壳层的形成,起到了很好的成核生长点和连接点的作用,诱导合成了连续完整的ZIF-8膜包覆的Pd/Al₂O₃@ZIF-8核壳结构材料,ZIF-8膜层的厚度可通过ZIF-8合成的次数进行调变。该Pd/Al₂O₃@ZIF-8核壳催化剂对不同分子大小的烯烃加氢反应表现出明显的筛分选择性,并对外加苯并噻唑作为毒物分子的反应体系具有良好的抗中毒性能和防催化活性金属Pd组分流失的功能。     

Hydrogenation of Nitrobenzene over a Pd/Al2O3 Catalyst – Mechanism and Effect of the Main Operating Conditions

The catalytic hydrogenation of nitrobenzene (NB) was studied in a three‐phase basket reactor with a commercial Pd/Al₂O₃ sample as catalyst. The kinetic experiments allowed a better understanding of the mechanism behind the formation of aniline (ANL) and by‐products, a topic not yet well comprehended. The effect of some operating conditions was studied and the existence of more by‐products than mentioned in the literature was stated; specifically, benzene formation was verified. Both the reaction kinetics and selectivity were found to be strongly dependent on the temperature, while the effect of total pressure is not that pronounced. Moreover, the high selectivity of the catalyst used in the present work was proved, and as such the deep hydrogenation of ANL to form by‐products only occurs in considerable extension when the NB concentration in the reaction mixture becomes negligible.     

Pd/Al2O3催化剂上低浓度CO氧化的研究

采用共沉淀法和浸渍法制备了2%Pd-Al2O3催化剂,在固定反应器中评价不同制备方法(共沉淀和浸渍)、助剂(1%K和1%Mg)、预处理方法(快速氧化和缓慢还原)、空速(726h-1、1638h-1和5274h-1)情况下2%Pd-Al2O3催化剂对CO氧化的催化活性。结果表明,共沉淀法制备的2%Pd50%Zr-Al2O3催化剂有较高的反应活性,该催化剂经缓慢还原预处理活化,在温度为70℃时就可以使低浓度的CO完全氧化。     

硫化物对裂解汽油一段加氢用Pd/Al_2O_3催化剂性能的影响

采用固定床反应器考察了多种硫化物(二硫化碳、二甲基二硫与噻吩)对裂解汽油一段加氢用Pd/Al2O3催化剂加氢性能的影响。在相同的工艺条件下,硫化物的毒性顺序为:二硫化碳二甲基二硫噻吩。CS2对催化剂加氢性能的影响最为明显,原料油中CS2质量分数达到6μg/g后,催化剂就迅速发生中毒,产品双烯值增高。催化剂失活的原因是CS2主要以物理吸附的方式占据催化加氢活性中心,导致催化剂对共轭烯烃与氢气失去吸附活性。     

Pd/Al2O3催化剂上CH4选择性还原NO的研究

考察了Pd/Al₂O₃、In/Al₂O₃和Co/Al₂O₃对甲烷选择性还原NO的催化活性。结果表明，采用浸渍法制备的Pd/Al₂O₃、In/Al₂O₃和Co/Al₂O₃三种催化剂，在有氧气氛下，用CH₄作还原剂催化还原NO时，Pd/Al₂O₃催化剂的活性最佳，热稳定性好，在550 ℃，用CH₄选择还原NO，Pd/Al₂O₃催化剂表现出较强的催化能力，NO的转化率达到100%。在高空速实验中，该催化剂亦表现出较高的活性，其活性顺序为Pd/Al₂O₃>In/Al₂O₃>Co/Al₂O₃。实验研究了助催化剂、氧含量以及空速对Pd/Al₂O₃催化剂活性的影响。     

NO + H2 reaction on Pd/Al2O3 under lean conditions: kinetic study

This paper deals with the kinetics of the NO + H₂ + O₂ reactions on Pd/γ-Al₂O₃. Steady state rate measurements have been discussed in the light of previous mechanism proposals involving a dissociation step of molecular NO adsorbed species on Pd. In the absence of oxygen, the dissociation of NO_ads species is assisted by chemisorbed H atoms. However, different kinetic features have been observed in the presence of oxygen. Practically, the light-off curve of NO shifts towards higher temperature in the presence of O₂. In addition the H₂ + O₂ reaction extensively occurs in the temperature range of this study. Such tendencies have been explained by changes in the adsorptive properties of noble metals and also in the nature of elementary steps for the dissociation of NO. In the presence of a large extent of O₂, hydrogen coverage would sharply drop and would not further assist the dissociation of NO as in the absence of O₂.     

Decomposition and oxidation of CH3 13CH2OH on A12O3, Pd/Al2O3, and PdO/Al2O3 catalysts

Temperature-programmed desorption (TPD) and oxidation (TPO) were used to investigate the decomposition and oxidation of ethanol on Al₂O₃, Pd/Al₂O₃, and PdO/Al₂O₃. Ethyl--¹³C alcohol (CH₃ ¹³CH₂OH) was adsorbed on the catalysts so that reaction pathways of the two carbons could be distinguished. Alumina was mainly a dehydration catalyst, but dehydrogenation was also observed and some carbon remained on the surface. In the presence of O₂, A1₂O₃ oxidized the decomposition products and the-carbon was oxidized faster. Ethanol, which was adsorbed on A1₂O₃, decomposed much faster on Pd/A1₂O₃ by diffusing to Pd and undergoing CO elimination to form CH₄,¹³CO, H₂, and surface carbon. On PdO/A1₂O₃, the decomposition was slower than on Pd/A1₂O₃ until lattice oxygen was extracted above 450 K; the decomposition products were oxidized by lattice oxygen. In the presence of gas phase O₂, Pd/Al₂O₃ was an active oxidation catalyst at low temperature, but lattice oxygen had to be extracted from PdO/A1₂O₃ before it had significant oxidation activity.