γ-Mo_2N催化剂上的乙炔选择加氢

采用固定床连续流动反应器对γ Mo2 N催化剂上的乙炔加氢反应进行了研究 .在 15 0℃的反应温度下 ,乙炔的转化率为 95 % ,乙烯的选择性达到 80 % ,乙烷和丁烯的选择性分别为 4%和 10 % .反应温度和空速的变化对反应产物的选择性没有明显的影响 .在同样的反应条件下 ,钯催化剂上乙炔加氢反应的主要产物是乙烷 ,产物组成随反应温度和空速的变化而变化 .对γ Mo2 N上的乙炔选择加氢生成乙烯的机制进行了解释 ,认为γ Mo2 N表面上滞留的强吸附的碳氢物种可能有利于乙炔高选择性地生成乙烯 .     

γ-Mo2N催化剂上的乙炔选择加氢

 采用固定床连续流动反应器对γ－Mo2N催化剂上的乙炔加氢反应进行了研究．在150℃的反应温度下,乙炔的转化率为95％,乙烯的选择性达到80％,乙烷和丁烯的选择性分别为4％和10％．反应温度和空速的变化对反应产物的选择性没有明显的影响．在同样的反应条件下,钯催化剂上乙炔加氢反应的主要产物是乙烷,产物组成随反应温度和空速的变化而变化．对γ－Mo2N上的乙炔选择加氢生成乙烯的机制进行了解释,认为γ－Mo2N表面上滞留的强吸附的碳氢物种可能有利于乙炔高选择性地生成乙烯．     

CO吸附原位红外光谱结合分子模拟计算研究FCC汽油加氢脱硫催化剂的选择性

以脱硫选择性不同的2组催化裂化汽油加氢脱硫催化剂为研究对象, 采用CO吸附原位红外光谱表征了2组催化剂的活性相特征, 并通过分子模拟计算方法比较了助剂Co加入前后噻吩和1-己烯在催化剂表面的电荷分布、吸附能及其加氢反应的活化能等, 探讨了助剂Co的加入对选择性加氢脱硫催化剂脱硫选择性的作用机理. 结果表明, 加氢脱硫催化剂CoMoS活性相的增加有利于提高催化剂的加氢脱硫/加氢降烯烃(HDS/HYD)选择性. 与1-己烯加氢位相比, Co的加入显著提高了噻吩分子加氢位的缺电子性, 噻吩在催化剂表面的吸附度增强, 显著降低噻吩加氢反应的能垒, 从而使噻吩加氢反应更易进行. 这也表明CoMoS为高HDS活性、高HDS/HYD选择性的活性相.     

活性炭负载钯催化剂对邻硝基甲苯波相加氢制邻甲苯胺的研究

本文研究了不同载体负载的钯催化剂对邻硝基甲苯催化加氢制邻甲苯胺的性能,考察了载体的性能、钯的分散度对催化加氢速率的影响,探讨了该反应的动力学特征.结果表明,Pd/C催化剂液相催化邻硝基甲苯加氢制邻甲苯胺活性高,选择性好,寿命长.该反应为双分子吸附的表面反应.属于非择形反应.     

K_2O和MnO助剂对Fe／Silicalite－2催化剂CO加氢制低碳烯烃性能的影响

在Ｓｉｌｉｃａｌｉｔｅ－２分子筛担载的铁催化剂中添加ＭｎＯ和Ｋ２Ｏ助剂，可显著提高其ＣＯ加氢制低碳烯烃的选择性及催化活性．ＭｎＯ助剂主要抑制乙烯和丙烯的加氢反应而提高烯／烷比值；Ｋ２Ｏ助剂则增加催化剂对ＣＯ的吸附能力，同时抑制乙烯在催化剂表面的二次反应（主要是乙烯的歧化反应），从而有利于提高低碳烯烃的选择性及催化剂活性．     

担体对Fe—MnO催化剂上乙烯二次反应的影响

以乙烯为探针分子，采用TPSR手段研究催化剂担体对乙烯二次反应的影响。结果表明，担体的性质差异导致不同类型的乙烯二次反应，从而将直接影响到烯烃选择性。结果催化剂CO加氢反应结果及催化剂表面CO／H2－TPSR、C2H4／H27脉冲反应表征，发现担体的碱性促使乙烯歧化生成甲烷和丙烯，而担体的酸性促使乙烯歧化的同时，存在强烈的丙烯加氢作用，从而促进乙烯歧化，导致烯烃选择性大幅度下降，因而酸性担体不利于烯烃生成。     

Pd/ZnO在乙炔选择加氢反应中的不同催化机制研究(英文)

化学选择性是评价催化剂性能最重要的参数之一,它直接决定了产物的经济价值及后续的分离成本.传统的负载型金属催化剂由于其金属粒径分布不均,且不同原子数组成的粒子通常具有特征产物选择性,从而限制化学选择性的提高;另一方面,对于金属多原子活性中心,反应物在催化剂表面可以存在多种吸附构型进而衍化为不同产物,产物可控性差.因此,获得金属尺寸均一,且具有原子分散的活性中心,即单原子催化剂,成为官能团多相催化转化高选择性的迫切需求.本课题组通过400 oC还原1%-Pd/ZnO得到PdZn金属间化合物,依据其规律排布的Pd-Zn-Pd单元获得Pd基单原子催化剂.该催化剂在乙烯化工中少量乙炔的加氢转化反应中获得令人欣喜的催化性能——兼具有乙炔的高转化率和乙烯的高选择性.结合微量吸附量热、理论计算等表征,Pd活性中心在PdZn金属间化合物中的特殊空间排布是其优异催化性能的根源,即乙炔以较强的σ键吸附在两个相邻的单Pd金属中心,易吸附活化加氢生成乙烯,而乙烯则吸附于单Pd金属中心,较弱的π键形式吸附有利于其脱附避免过渡加氢.基于前期研究,构筑具有均一单金属中心的负载型单原子催化剂是获得高选择性的另一有效方法,且较之于PdZn金属间化合物催化剂,该类单原子催化剂兼具有原子利用率最大化的优点.本文采用等体积浸渍法制备Pd/ZnO催化剂,通过降低Pd金属含量(1 wt%→0.1 wt%→0.01 wt%)并在较低的温度下(100 oC)还原(H2-TPR表明高温还原形成PdZn金属间化合物型合金)得到负载型单原子催化剂(Pd1/ZnO SAC).高分辨电镜结果表明,当Pd负载量由1%降至0.1%,金属纳米颗粒的粒径尺寸显著降低,而在0.01%-Pd/ZnO催化剂表面,Pd活性中心则以单原子状态分散于载体ZnO表面.X-射线吸收光谱及电子能谱表明,随着负载量的降低,Pd活性物种具有更高的正电性.该催化剂在乙炔选择性加氢反应中表现出更加优越的催化性能,具有与PdZn催化剂相当的高选择性,而更优的比活性.这归结于Pd1/ZnO单原子催化剂的Pdδ+单原子活性中心有助于其与乙炔的静电相互作用并吸附活化加氢生成乙烯,并促使乙烯以较弱的π键吸附,从而易于从催化剂表面脱附获得高选择性.     

IB金属对Ni/SiO2催化剂乙炔选择性加氢反应性能的影响

乙烯是合成聚乙烯的原料,其主要来源是石油裂解气,其中少量的乙炔杂质会严重毒化生产聚乙烯的催化剂,因此需要将其去除.对于乙炔选择加氢反应,传统工业上使用的是Pd基催化剂,尽管其乙炔转化率很高,但对乙烯的选择性很低.我们前期的研究发现,IB族金属(Au,Ag和Cu)与Pd形成的合金单原子催化剂可以有效地提高乙烯的选择性.作为与Pd同组的非贵金属,Ni催化剂在多种催化加氢反应中显示出优异活性,而在乙炔选择加氢反应中,Ni是否能够替代贵金属Pd尚无定论.本文系统地研究了IB金属对Ni/SiO2催化剂乙炔选择性加氢性能的影响.与Pd/SiO2催化剂不同,单金属Ni/SiO2催化剂在低温下不具有活性.将IB金属添加到Ni/SiO2催化剂中,可以显著提高其催化活性以及对乙烯的选择性.其中,AuNix/SiO2和CuNix/SiO2催化剂的催化活性随还原温度升高而提高,而AgNix/SiO2催化剂对预处理温度不敏感.通过调变IB/Ni原子比和还原温度优化了催化剂的催化性能,发现优化后的三种催化剂(CuNi0.125/SiO2、AgNi0.5/SiO2和AuNi0.5/SiO2)的活性和选择性随反应温度升高表现出相似的变化趋势.催化稳定性考察结果显示,CuNi0.125/SiO2催化剂表现出最高选择性和稳定性;尽管AuNi0.5/SiO2的初始活性最高,但是稳定性最低.采用XRD、TPR和微量吸附量热等表征手段对不同IB金属对Ni基催化剂性质的影响进行了系统考察.以Cu-Nix/SiO2催化剂为例,H2-TPR测试结果表明,Cu-Ni双金属纳米颗粒的形成使得还原温度低于相应的单金属催化剂,表明铜和镍之间存在明显的相互作用.此外,通过TPR获得的CuNix/SiO2催化剂上的氢气消耗量与理论耗氢量相吻合,表明在还原处理的过程中双金属催化剂中的CuO和NiO可以被完全还原.乙炔的微量吸附量热结果表明,在CuNi0.125/SiO2,AgNi0.5/SiO2,AuNi0.5/SiO2和Ni0.5/SiO2催化剂上的初始吸附热分别为187,196,304和103 kJ/mol,即它们的初始乙炔吸附强度顺序为AuNi0.5/SiO2>AgNi0.5/SiO2>CuNi0.125/SiO2>Ni0.5/SiO2.该结果与三者的初始催化活性顺序一致,表明IB金属的加入可以增强乙炔在催化剂表面的吸附,从而提高催化活性.     

聚苯乙烯二苯基膦-钯络合物的合成及其加氢催化活性

高分子金属络合物催化剂具有独特的优点,近十年来发展很快.有不少工作是关于含铑、钯、铂和钌等金属的高分子催化剂用于催化烯烃和炔烃等的加氢.据报道,由二氯化钯与线性聚苯乙烯二苯基膦或聚-γ-氨丙基硅氧烷反应制得的催化剂,对烯烃和炔烃的加氢反应具有很高的催化活性.该催化剂比Bailar制得的催化剂活性高.     

K2O和MnO助剂对Fe/Silicalite-2催化剂CO加氢制低碳烯烃性能的影响

在Ｓｉｌｉｃａｌｉｔｅ－２分子筛担载的铁催化剂中添加ＭｎＯ和Ｋ２Ｏ助剂，可显著提高其ＣＯ加氢制碳烯烃的选择性及催化活性，ＭｎＯ助剂主要抑制乙烯和丙烯的加氢反应而提高烯／烷比值，Ｋ２Ｏ助剂则增加催化剂对ＣＯ的吸附能力，同时抑制乙烯在催化剂表二次反应（主要是乙烯的歧化反应），从而有利于提高低碳烯烃的选择性及催化剂活性。     

Molecule Saturation Boosts Acetylene Semihydrogenation Activity and Selectivity on a Core-Shell Ruthenium@Palladium Catalyst

Increasing selectivity without the expense of activity is desired but challenging in heterogeneous catalysis. By revealing the molecule saturation and adsorption sensitivity on overlayer thickness, strain, and coordination of Pd-based catalysts from first-principles calculations, we designed a stable Pd monolayer (ML) catalyst on a Ru terrace to boost both activity and selectivity of acetylene semihydrogenation. The least saturated molecule is most sensitive to the change in catalyst electronic and geometric properties. By simultaneously compressing the Pd ML and exposing the high coordination sites, the adsorption of more saturated ethylene is considerably weakened to facilitate the desorption for high selectivity. The even stronger weakening to the least saturated acetylene drives its hydrogenation such that it is more exothermic, thereby boosting the activity. Tailoring the molecule saturation and its sensitivity to structure and composition provides a tool for rational design of efficient catalysts.     

A DFT+U study of acetylene selective hydrogenation on oxygen defective anatase (101) and rutile (110) TiO2 supported Pd4 cluster

The reaction mechanisms for selective acetylene hydrogenation on three different supports, Pd(4) cluster, oxygen defective anatase (101), and rutile (110) titania supported Pd(4), cluster are studied using the density functional theory calculations with a Hubbard U correction (DFT+U). The present calculations show that the defect anatase support binds Pd(4) cluster more strongly than that of rutile titania due to the existence of Ti(3+) in anatase titania. Consequently, the binding energies of adsorbed species such as acetylene and ethylene on Pd(4) cluster become weaker on anatase supported catalysts compared to the rutile supported Pd(4) cluster. Anatase catalyst has higher selectivity of acetylene hydrogenation than rutile catalyst. On the one hand, the activation energies of ethylene formation are similar on the two catalysts, while they vary a lot on ethyl formation. The rutile supported Pd catalyst with lower activation energy is preferable for further hydrogenation. On the other hand, the relatively weak adsorption energy of ethylene is gained on anatase surface, which means it is easier for ethylene desorption, hence getting higher selectivity. For further understanding, the energy decomposition method and micro-kinetic analysis are also introduced.     

负载型Pd/TiO2和Pd-Ag/TiO2催化剂的乙炔选择性加氢催化性能

利用程序升温还原(TPR)、X-射线衍射(XRD)、CO吸附-红外光谱(CO-IR)、电子顺磁共振(EPR)和微型催化反应评价等手段, 研究了负载Pd/γ-Al2O3, Pd/TiO2和Pd-Ag/TiO2催化剂的结构和乙炔选择性加氢催化性能. 结果表明, Pd/TiO2催化剂具有较Pd/γ-Al2O3催化剂更优良的乙炔选择性加氢催化性能, 这与Pd-TiO2之间的强相互作用密切相关. Pd-TiO2之间的强相互作用不仅使负载型钯金属催化剂具有较高的乙炔加氢催化选择性, 而且具有较高的乙炔加氢催化活性. Pd/TiO2催化剂中添加Ag 组分后, Pd金属可促进Ag+的还原并可能形成Pd-Ag合金, 催化剂的乙烯选择性虽有所增加, 但乙炔转化率和乙烯收率下降.     

Hydroxyl improving the activity,selectivity and stability of supported Ni single atoms for selective semi-hydrogenation

Atomically dispersed metal catalysts with high atomic utilization and selectivity have been widely studied for acetylene semi-hydrogenation in excess ethylene among others. Further improvements of activity and selectivity, in addition to stability and loading, remain elusive due to competitive adsorption and desorption between reactants and products, hydrogen activation, partial hydrogenation etc. on limited site available. Herein, comprehensive density functional theory calculations have been used to explore the new strategy by introducing an appropriate ligand to stabilize the active single atom, improving the activity and selectivity on oxide supports. We find that the hydroxyl group can stabilize Ni single atoms significantly by forming Ni₁(OH)₂ complexes on anatase TiO₂(101), whose unique electronic and geometric properties enable high performance in acetylene semi-hydrogenation. Specifically, Ni₁(OH)₂/TiO₂(101) shows favorable acetylene adsorption and promotes the heterolytic dissociation of H₂ achieving high catalytic activity, and it simultaneously weakens the ethylene bonding to facilitate subsequent desorption showing high ethylene selectivity. Hydroxyl stabilization of single metal atoms on oxide supports and promotion of the catalytic activity are sensitive to transition metal and the oxide supports. Compared to Co, Rh, Ir, Pd, Pt, Cu, Ag and Au, and anatase ZrO₂, IrO₂ and NbO₂ surfaces, the optimum interactions between Ni, O and Ti and resulted high activity, selectivity and stability make Ni₁(OH)₂/TiO₂(101) a promising catalyst in acetylene hydrogenation. Our work provides valuable guidelines for utilization of ligands in the rational design of stable and efficient atomically dispersed catalysts.

Hydroxyl group can stabilize significantly Ni single atom by forming Ni₁(OH)₂ complexes on anatase TiO₂(101), which displays high catalytic performance in acetylene semi-hydrogenation.     

Formation of C4 Oligomers in Hydrogenation of Acetylene over Pd/Al2O3 and Pd/TiO2 Catalysts

Selectivity of product formation has been tested in hydrogenation of acetylene over 0.3 wt.% Pd/-alumina and 0.5 wt.% Pd/TiO₂catalysts. Non-steady-state regime of catalyst operation was tested in pulse-flow experiments. Significant carbon poisoning appears to be a necessaryrequisite for selective formation of ethylene. The effect of hydrogen and acetylene partial pressure has been tested on the selectivity of C₄products. At 273–298 K the catalysts showed 26–35% selectivity for C₄ hydrocarbons and <2.5% for ethane production at conversionsof 30–40%. Deuterium distribution in ethylene and 1,3-butadiene and the deuterium content of the surface hydrogen pool have been compared and mechanismof diene formation has been discussed.     

Supported catalysts based on Pd–In nanoparticles for the liquid- phase hydrogenation of terminal and internal alkynes: 2. catalytic properties

Pd–In/Al₂O₃ and Pd–In/MgAl₂O₄ catalysts prepared from dinuclear Pd–In acetate complexes were studied in the hydrogenation of alkyne compounds with different structures. The Pd–In catalysts demonstrate high selectivity in the hydrogenation of internal alkynes comparable with that of the Lindlar catalyst. Similar activity/selectivity characteristics are reached at a significantly lower Pd content. For terminal alkynes, the favorable effect of Indium introduction is considerably less pronounced. An analysis of the In effect on the selectivity and the ratio between the rates of the first and second hydrogenation steps suggests that the reaction selectivity is determined to a large extent by a thermodynamic factor (adsorption–desorption equilibrium between the reactants and the reaction products).     

负载Pd基碳二选择加氢催化剂上乙炔加氢反应的原位红外光谱研究

以乙烯和乙炔为探针分子, 采用原位红外光谱技术研究了Pd-Ag/Al₂O₃和Pd/Al₂O₃催化剂上乙炔加氢反应, 通过乙炔吸附, 乙炔和氢的共吸附和交替吸附表征了催化剂表面吸附物种的变化. 结果表明, 在Pd-Ag/Al₂O₃催化体系中, 乙炔在Pd-Ag/Al₂O₃和Pd/Al₂O₃催化剂有着不同的吸附性能, 另外, 加氢反应会导致在催化剂表面形成由长分子链的烷烃组成的碳氢化合物层, 该吸附层与绿油有着相似的红外光谱特征, 最关键的是乙炔和氢的吸附顺序和碳氢化合物层的生成量之间存在着一定的关系, 这将直接影响催化剂的加氢性能.     

Properties of Pd–Ag/C catalysts in the reaction of selective hydrogenation of acetylene

Samples of Pd/C and Pd–Ag/C, where C represents carbon nanofibers (CNFs), are synthesized by methane decomposition on a Ni–Cu–Fe/Al₂O₃ catalyst. The properties of Pd/CNF are studied in the reaction of selective hydrogenation of acetylene into ethylene. It is found that the activity of the catalyst in hydrogenation reaction increases, while selectivity decreases considerably when the palladium content rises. The obtained dependences are caused by the features of palladium’s interaction with the carbon support. At a low Pd content (up to 0.04 wt %) in the catalyst, the metal is inserted into the interlayer space of graphite and the catalytic activity is zero. It is established by EXAFS that the main share of palladium in catalysts of 0.05–0.1 wt % Pd/CNF constitutes the metal in the atomically dispersed state. The coordination environment of palladium atoms consists of carbon atoms. An increase in the palladium content in a Pd/CNF catalyst up to 0.3 wt % leads to the formation of highly dispersed (0.8–1 nm) Pd particles. The Pd/CNF samples where palladium is mainly in the atomically dispersed state exhibit the highest selectivity in the acetylene hydrogenation reaction. The addition of silver to a 0.1 wt % Pd/CNF catalyst initially probably leads to the formation of Pd–Ag clusters and then to alloyed Pd–Ag particles. An increase in the silver content in the catalyst above 0.3% causes the enlargement of the alloyed particles and the palladium atoms are blocked by a silver layer, which considerably decreases the catalytic activity in the selective hydrogenation of acetylene.