Catalytic performance of a Ti added Pd/SiO2 catalyst for acetylene hydrogenation

A series of Pd/SiO₂ and Pd–Ti/SiO₂ catalysts were prepared by the incipient wetness impregnation method. The catalytic performance for selective hydrogenation of acetylene to ethylene was measured under “high concentration acetylene”, “high space velocity” and “no dilution gas” conditions. The crystal structure and particle size of the catalysts were characterized by the X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), nitrogen physisorption using the BET method and transmission electron microscope (TEM). The results showed that the titanium oxide in Pd–Ti/SiO₂ catalyst was amorphous and the addition of Ti reduced the particle size of Pd significantly. Comparing to the Pd/SiO₂ catalyst, the ethylene yield increased from 64.1% to 88.3% under Pd–Ti/SiO₂ catalytic system.     

工艺条件对钯系催化剂乙炔选择性加氢性能的影响

为了研究工艺条件对钯系催化剂选择性加氢性能的影响,制备Pd/Al_2O_3、Pd-Ag/Al_2O_3和Pd-Ag/Al_2O_3-KOH催化剂,并在微型催化剂评价装置上进行乙炔选择性加氢反应,考察了工艺条件(压力、空速)对催化剂性能的影响。结果表明,随着压力的升高,催化剂活性提高,乙烯选择性会下降;随着空速的提高,催化剂乙炔转化率先升高后降低,MAPD转化率迅速下降,乙烯选择性提高。     

负载型纳米金催化剂在乙炔选择性加氢反应中的研究进展

介绍了乙炔选择性加氢制乙烯催化剂的研究和开发进展。针对负载型纳米金催化剂的发展趋势及其对乙炔加氢反应产物中乙烯的独特选择性,重点对比单金属纳米金催化剂及合金型催化剂的催化性能差异,发现合金型纳米金催化剂具有较高的乙炔转化率和稳定性。影响催化性能的主要因素有纳米粒子的大小及活性组分之间的相互协同作用。分析积炭的形成以及导致催化剂失活的原理。展望低温条件下具有高转化率与高稳定性的合金型纳米金催化剂的应用前景。     

钯基乙炔选择性加氢催化剂研究进展

催化选择加氢去除乙烯中微量乙炔是石化工业重要的反应过程,工业钯基催化剂选择性低、催化剂使用寿命较短。本文综述了近年来国内外乙炔选择性加氢钯基催化剂的研究进展。主要探讨了过渡金属、金属氧化物与非金属配体助剂能调变钯粒子空间结构,隔离分散钯粒子并与钯粒子产生电子效应;阐明了钯粒子尺寸与织构形貌的调控能改变钯的晶面结构,影响钯对乙烯的吸脱附和对氢气的活化与解离性能;评述了单一氧化物、复合金属氧化物、碳材料等载体为催化剂提供合适的表面酸碱性并加强了与活性中心之间的相互作用,稳定钯粒子抑制其发生迁移与团聚。提高乙烯选择性与催化剂稳定性是该研究的重点与难点,负载型钯基催化剂的发展方向是构建高分散钯粒子,并在反应过程中保持稳定。     

表面润湿性可控的碳纳米管负载钯催化剂及其在1,8-二硝基萘选择性加氢中的催化性能

首先通过原子转移自由基聚合技术（atom transfer radical polymerization，ATRP）在碳纳米管（CNT）表面接枝聚N-异丙基丙烯酰胺（PNIPAM），成功制备出表面润湿性可控的复合载体（CNT-PNIPAM），并以其为载体制备Pd催化剂（Pd/CNT-PNIPAM）。采用红外光谱仪（FTIR）、热重仪（TGA）、有机元素分析仪（OEA）、差示量热仪（DSC）、X射线衍射仪（XRD）、透射电镜（TEM）和N₂吸附等手段对材料进行表征。制备的催化剂用于1,8-二硝基萘（1,8-DNN）选择性加氢反应，并研究表面化学对催化性能的影响。结果表明，CNT-PNIPAM的最低临界溶液温度（LCST）为37℃左右。利用温敏效应，CNT-PNIPAM在25℃（＜LCST）下负载Pd纳米颗粒，粒径为3.6nm±0.8nm。载体在低温下的亲水表面提高了Pd纳米颗粒在其上的分散。Pd/CNT-PNIPAM在120℃ （＞LCST）下表面润湿性发生转换。PNIPAM接枝引起催化剂表面化学性质的变化，进而使其对底物的吸附性能发生改变。Pd/CNT-PNIPAM上Pd颗粒的高度分散及其对1,8-DNN优良的吸附性能不仅使催化活性得以提高（反应速率常数k=2.1h^-1），而且对1,8-DAN的选择性也更高（完全反应时1,8-DAN选择性达98%）。     

Catalysis of semihydrogenation of acetylene to ethylene: current trends,challenges, and outlook

Ethylene is an important feedstock for various industrial processes, particularly in the polymer industry. Unfortunately, during naphtha cracking to produce ethylene, there are instances of acetylene presence in the product stream, which poisons the Ziegler–Natta polymerization catalysts. Thus, appropriate process modification, optimization, and in particular, catalyst design are essential to ensure the production of highly pure ethylene that is suitable as a feedstock in polymerization reactions. Accordingly, carefully selected process parameters and the application of various catalyst systems have been optimized for this purpose. This review provides a holistic view of the recent reports on the selective hydrogenation of acetylene. Previously published reviews were limited to Pd catalysts. However, effective new metal and non-metal catalysts have been explored for selective acetylene hydrogenation. Updates on this recent progress and more comprehensive computational studies that are now available for the reaction are described herein. In addition to the favored Pd catalysts, other catalyst systems including mono, bimetallic, trimetallic, and ionic catalysts are presented. The specific role(s) that each process parameter plays to achieve high acetylene conversion and ethylene selectivity is discussed. Attempts have been made to elucidate the possible catalyst deactivation mechanisms involved in the reaction. Extensive reports suggest that acetylene adsorption occurs through an active single-site mechanism rather than via dual active sites. An increase in the reaction temperature affords high acetylene conversion and ethylene selectivity to obtain reactant streams free of ethylene. Conflicting findings to this trend have reported the presence of ethylene in the feed stream. This review will serve as a useful resource of condensed information for researchers in the field of acetylene-selective hydrogenation.     

微乳法制备Pd-Cu双金属催化剂

选择Cu为助剂,采用微乳法分别优选具有较好稳定性的Cu和Pd微乳液体系,并将Cu和Pd依次负载于Al_2O_3载体上,经干燥、活化和还原制备了Pd-Cu/Al_2O_3催化剂。采用原位IR、CO化学吸附和HRTEM等对催化剂进行表征,结果表明,与常规溶液负载法制备的Pd-Ag/Al_2O_3催化剂相比,采用微乳法降低了催化剂表面酸性,提高了活性组分Pd分散度,Pd粒径分布更为均匀。在750 mL加氢反应器中,采用C_2后加氢原料对催化剂性能进行评价,结果表明,与常规溶液负载法相比,微乳法制备的催化剂在反应温度低4℃条件下,乙炔转化率相当,选择性高9.9个百分点,绿油生成量较低。微乳法制备Pd-Cu双金属催化剂具有良好的工业应用前景。     

Phenol hydrogenation to cyclohexanone over palladium nanoparticles loaded on charming activated carbon adjusted by facile heat treatment

Selective phenol hydrogenation is a green approach to produce cyclohexanone. It still remains a big challenge to prepare efficient supports of the catalysts for the phenol hydrogenation via a simple and cost-effective approach. Herein, a facile approach was developed, i.e., direct calcination of activated carbon (AC) under argon at high temperature, to improve its structure and surface properties. The modified AC materials were supported with Pd nanoparticles (NPs) to fabricate the Pd/C catalysts. The as-prepared Pd/C600 catalyst exhibits superior catalytic performance in the phenol hydrogenation, and its turnover frequency (TOF) value is 199.2 h⁻¹, 1.31 times to that of Pd/C-raw. The Pd/C600 catalyst presents both better hydrophobicity and more structural defects, contributing to the improved dispersibility in the reaction solution (phenol-cyclohexane), the better Pd dispersion and the smaller Pd size, which result in the enhancement of the catalytic performance. Furthermore, the as-prepared Pd/C600 catalyst shows a good recyclability.     

Tailoring electronic properties and kinetics behaviors of Pd/N-CNTs catalysts for selective hydrogenation of acetylene

Pd catalyzed selective hydrogenation of acetylene shows remarkable electronic effects. In this work, a strategy is proposed to tailor the electronic properties of Pd nanoparticles by nitrogen doping of carbon nanotubes (CNT) support toward the improved reaction kinetics. While excluding the Pd size effects, the intrinsic promotional effects of the nitrogen doping are demonstrated, which are mainly due to the increased Pd electron density resultant from the presence of more graphitic nitrogen species based on X-ray photoelectron spectroscopy measurements and density functional theory (DFT) calculations. Kinetics analysis and C₂H₂/C₂H₄-temperature-programmed desorption (TPD) measurements reveal that the electron-rich Pd catalyst with the moderately weakened adsorption strength can give rise to the decreased activation energy and thus the simultaneously enhanced activity, selectivity, and stability. The aspects demonstrated here could guide the rational design and optimization of Pd catalysts for the selective hydrogenation of acetylene.     

Acetylene Hydrogenation on Au-Based Catalysts

Hydrogenation of acetylene has been investigated on Au/TiO₂, Pd/TiO₂ and Au-Pd/TiO₂ catalysts at high acetylene conversion levels. The Au/TiO₂ catalyst (avg. particle size: 4.6 nm) synthesized by the temperature-programmed reduction-oxidation of an Au-phosphine complex on TiO₂ showed a remarkably high selectivity to ethylene formation even at 100% acetylene conversion. Au/TiO₂ prepared by the conventional incipient wet impregnation method (avg. particle size: 30 nm), on the other hand, showed negligible activity for acetylene hydrogenation. Although the Au catalysts showed a high selectivity for ethylene, the acetylene conversion activity and catalyst stability were inferior to the Pd-based catalysts. Au-Pd catalysts prepared by the redox method showed high acetylene conversions as well as high selectivity for ethylene. Interestingly Au-Pd catalysts prepared by depositing Pd via the incipient wetness method on Au/TiO₂ showed very poor selectivity (comparable to mono-metallic Pd catalysts) for ethylene. High-resolution transmission electron microscopy (TEM) studies coupled with energy dispersive X-ray spectroscopy (EDS) showed that while the redox method produced bimetallic Au-Pd catalysts, the latter method produced individual Pd and Au particles on the support.     

Size-controlled Pd nanoparticles supported on α-Al2O3 as heterogeneous catalyst for selective hydrogenation of acetylene

Size-controlled Pd nanoparticles （PdNPs） were synthesized in aqueous solution, using sodium car-boxymethyl cellulose as the stabilizer. Size-controlled PdNPs were supported onα-Al2O3 by the incipient wetness impregnation method. The PdNPs onα-Al2O3 support were in a narrow particle size distribution in the range of 1-6 nm. A series of PdNPs/α-Al2O3 catalysts were used for the selective hydrogenation of acetylene in ethylene-rich stream. The results show that PdNPs/α-Al2O3 catalyst with 0.03%（by mass） Pd loading is a very effective and sta-ble catalyst. With promoter Ag added, ethylene selectivity is increased from 41.0%to 63.8%at 100 ＆#176;C. Comparing with conventional Pd-Ag/α-Al2O3 catalyst, PdNPs-Ag/α-Al2O3 catalyst has better catalytic performance in acety-lene hydrogenation and shows good prospects for industrial application.     

氮化碳负载钯催化剂催化苯酚加氢制环己酮

为了开发苯酚加氢制环己酮高效催化剂,将脲在550 ℃高温聚合,制备了片层状氮化碳催化剂载体g-CN;负载钯纳米粒子后,得到Pd/g-CN催化剂。采用红外光谱、X射线粉末衍射、透射电镜和X射线光电子能谱对催化剂进行表征。将Pd/g-CN催化剂用于催化苯酚水相加氢,考察了不同载体和反应温度对催化性能的影响,并对催化剂重复使用性能进行研究。结果表明,载体g-CN含有大量的含N基团,能有效稳定金属纳米粒子,从而获得粒径较小、分散较好的Pd纳米粒子;同时,g-CN具有较强碱性,有利于苯酚的吸附,可提高苯酚的反应速率和环己酮选择性。采用负载Pd质量分数2%的Pd/g-CN催化剂,在反应温度80 ℃、反应压力0.1 MPa、n(Pd)∶n(苯酚)=0.02、苯酚1 mmol、水3 mL和反应时间3 h条件下,苯酚可完全转化,环己酮选择性高达99%。Pd/g-CN催化剂制备工艺简单,原料价廉,催化性能优异。     

以KMnO4改性炭黑为载体的Pd-Ni催化剂的制备和性能

以不同浓度的KMnO4溶液预处理的炭黑为载体，通过沉淀共还原法合成了3种Pd1Ni1/ACx (x=3,5,7)催化剂，并将3种催化剂与商业Pd/C催化剂进行了性能对比。用XPS、ICP、XRD和TEM对催化剂了进行表征。结果表明：Pd1Ni1/AC5的Pd负载量（质量分数，下同）最大（3.66%），Pd晶粒的平均粒径最小（4.71 nm），且均匀地分布在KMnO4氧化处理后的碳载体上，活性位点较多；XRD显示，3种Pd1Ni1/ACx催化剂中的Ni均以无定形存在。在电化学性能测试中，3种催化剂均表现出比商业Pd/C更好的电化学稳定性和存活率；其中，Pd1Ni1/AC5电化学活性表面积达62.21 m2/gPd，且乙醇催化活性为1797.85 A/gPd。     

Hydrogenation activity and selectivity behavior of supported palladium nanoparticles

Enhancement in activity and selectivity of catalytic hydrogenation using supported nanosize palladium catalyst has been investigated. Pd/C catalyst prepared in the presence of polyvinyl pyrrolidone (PVP) as a stabilizer gave Pd particle size in a narrow range of 3–5 nm. While, evaluating for hydrogenation of 2-butyne-1,4-diol, the rate enhancement was found to be 10 times higher as compared to the conventional (bulk) Pd catalysts. A proper choice of stabilizer (PVP) giving small particle size as well as highly dispersed nature of nano particles were the major factors for such a dramatic enhancement of activity.     

Selective hydrogenation of acetylene on Pd/SiO2 catalysts promoted with Ti, Nb and Ce oxides

Transition-metal oxides added to Pd/SiO₂ improve significantly the activity and the ethylene selectivity of the catalyst in acetylene hydrogenation, which is caused by the interaction between the oxides and the Pd surface similar to the case of the oxide-supported catalysts. It has been confirmed through experiments that metal oxides spread on and modify both geometrically and electronically the Pd surface after the catalyst is reduced at 500°C. Such a behavior of metal oxides in the catalyst is correlated well with their promotional effect on the catalyst performance. That is, the oxides on the Pd surface retard the sintering of the dispersed Pd particles, suppress the adsorption of ethylene in the multiply-bound mode, and facilitate the desorption of ethylene produced by acetylene hydrogenation. Among the three metal oxides examined in this study, Ti oxide is found to have the most promotional effect.     

合成气经二甲醚羰基化及乙酸甲酯加氢制无水乙醇的研究进展

合成气经二甲醚羰基化及乙酸甲酯加氢路线制无水乙醇技术因具有诸多优点而备受市场关注。本文综述了该工艺的核心反应机理和最近研究进展。主要探讨了丝光沸石8元环与12元环对羰基化反应的作用。阐明了如何通过调变丝光沸石8元环与12元环的活性位来提高羰基化催化剂的活性与稳定性。评述了铜纳米粒子的粒径、分散度以及Cu⁺与Cu⁰的分布等特点对铜基催化剂加氢催化活性的影响。提高乙醇选择性与催化剂稳定性是该研究的重点与难点。指出羰基化催化剂的优化重点是调变丝光沸石的孔道结构,加氢催化剂的发展方向是构建高分散度的铜纳米粒子,并在反应过程中保持稳定。     

载体对不饱和醛/酮中C=O选择性加氢催化剂性能的影响

研究载体活性炭对沉淀法制备的Pd/C催化剂催化活性的影响,在不饱和醛/酮加氢反应中通过考察载体粒度和试剂改性等条件对催化剂催化活性以及C=O选择性的影响。结果表明,将粒度(100~200)目的活性炭在80℃的10%HNO_3溶液中浸泡120 min,洗涤干燥后得到活性炭载体制备的Pd/C催化剂具有较高的活性和C=O选择性,不饱和醛转化率达95.2%,不饱和醇选择性达96.3%。     

Pd/HZSM-5催化剂催化加氢丙酮合成甲基异丁基酮

以HZSM-5为载体,采用浸渍法制备系列Pd/HZSM-5催化剂,在高压连续流动固定床反应器中考察Pd/HZSM-5催化剂催化加氢丙酮一步法合成甲基异丁基酮性能,并对工艺条件进行优化。结果表明,当HZSM-5载体上Pd负载质量分数为0.5%时,在反应温度140 ℃、氢压1 MPa、空速0.48 h^-1和氢酮物质的量比为1条件下,Pd/HZSM-5催化剂催化活性较高,丙酮转化率为45.91%,甲基异丁基酮选择性为94.33%。采用XRD、H₂-TPD、SEM、EDS和TGA等对催化剂进行表征,结果表明,负载质量分数0.5%的Pd在HZSM-5分子筛表面分散均匀,且0.5%Pd/HZSM-5催化剂具有较高氢吸附能力,失活的主要原因为催化剂表面积炭,采用流化床反应器取代传统的固定床反应器可以很好的解决催化剂积炭问题。     

乙炔选择性加氢：催化剂结构敏感性分析及调控

Pd催化乙炔选择性加氢是石脑油蒸汽裂解和煤基电石乙炔路径制备聚合级乙烯的关键。传统的Pd基催化剂使用成本较高且选择性和稳定性较差。本文综述了近年来乙炔选择性加氢催化剂结构敏感性及其调控方面的相关研究进展，重点介绍了包括活性金属粒径、纳米颗粒形貌和电子结构等对乙炔选择性加氢反应性能的重要作用，进而阐明了催化剂结构调控的目标与方向。进一步归纳总结了针对该反应特性的催化剂结构定向调控的研究进展，主要包括合金和金属间化合物催化剂、单原子及其合金催化剂的设计。通过合理地调控催化剂结构，优化关键物种的吸脱附和反应动力学行为，能够显著提高乙炔加氢催化剂的选择性及稳定性。在未来的研究中，如何针对该反应特性，构筑高效、稳定和低成本的催化剂将会是该体系催化剂研究的重点与难点。     

低负载Pd/Al2O3催化剂的制备及其对CO室温催化性能研究

采用等体积浸渍法和还原法结合制备了Pd/Al_2O_3催化剂,通过N_2吸附-脱附、SEM、TEM、X射线衍射、X射线光电子能谱和CO原位漫反射傅里叶变换红外光谱等表征手段对制备的样品微观结构进行了系统分析,考察了不同Pd负载量和测试条件下CO催化氧化性能。实验结果表明,水合肼还原法实现了Pd在Al_2O_3载体上的均匀分散,Pd颗粒的直径在9 nm左右,且为Pd单质;负载后的催化剂呈现明显的中孔结构特征,有利于气体分子的扩散。在0.2%～0.5%的低负载质量分数下,CO的催化性能随着Pd负载量的增加而增加,随着CO进口浓度和空速的升高而逐渐降低,在进口浓度为0.05%,空速为4 017 h~(-1)时,不同负载量的催化剂均能使CO完全催化;温度对催化剂的催化效果影响显著,从常温到50℃催化剂的性能变化显著;湿度增加对催化有一定的促进作用。Pd负载质量分数0.5%的催化剂稳定性测试表明,催化剂能够在100 h内保持92%以上的稳定转化率。