高(111)晶面暴露的Pd纳米颗粒的制备与表征及其加氢性能（英文）

通过液相氢气还原法,在不同温度下制备出了不同(111)晶面占比的Pd单晶纳米颗粒,用活性炭吸附制备成Pd/C纳米催化剂。通过透射电子显微镜(TEM)、傅里叶变换(FFT)、X射线衍射(XRD)表征证实了低温下制备的Pd纳米颗粒具有较高的(111)晶面占比。氢氧脉冲滴定(H_2-O_2)和H_2-程序升温脱附(H_2-TPD)结果显示,上述催化剂表面吸附氢气量与其Pd(111)晶面占比呈线性关系。此外,该系列Pd/C催化剂具有相似的粒径4.3 nm以及较窄的尺寸分布,相近的孔隙参数和Pd负载量,从而可对比(111)晶面比例差异对其加氢性能的影响。3个探针反应(苯乙烯、环己烯和对硝基甲苯的加氢反应)的实验结果表明,相比于低(111)晶面暴露比例的Pd/C催化剂,含有高(111)晶面暴露比例的Pd/C催化剂显示出更高的加氢活性,且Pd(111)晶面比例与氢气消耗速率呈一定的线性关系,这归因于H_2优先吸附于Pd(111)晶面促进了活性氢原子的形成。基于以上分析,高(111)晶面暴露的Pd基催化剂有利于加氢性能的提高。     

Ni/SiO2-Al2O3催化乙酰丙酸加氢制γ-戊内酯

采用溶胶-凝胶法制备了一系列不同Al₂O₃含量的SiO₂-Al₂O₃复合氧化物,以该系列复合氧化物为载体,采用等体积浸渍法制备了Ni负载量15%（重量百分比）的催化剂,用于催化乙酰丙酸加氢制γ-戊内酯.采用N₂物理吸附、X射线衍射（XRD）、H₂程序升温还原（H₂-TPR）、H₂程序升温脱附（H₂-TPD）、NH₃程序升温脱附（NH₃-TPD）和吡啶吸附红外（Py-IR）等手段对催化剂进行了表征.结果表明,不同载体催化剂的活性组分分散度及表面酸性质存在明显差异,显著影响了催化剂吸附、活化H₂与C=O键的能力,进而影响了催化剂的乙酰丙酸加氢活性.其中,Ni/SiO₂-Al₂O₃催化剂上的L酸中心能够促进C=O键的吸附、活化,与金属Ni上的H₂吸附活性位协同作用,大大提高了乙酰丙酸加氢活性.因此,具有最多L酸中心和丰富H₂吸附活性位的Ni/SiO₂-8Al₂O₃催化剂表现出最高的乙酰丙酸加氢活性,在180℃、4 MPa氢气压力下,乙酰丙酸转化率达到90.5%,目标产物γ-戊内酯选择性为100%.     

原子层沉积构筑Pd/TiO2限域催化剂及其在1,4-丁炔二醇加氢的应用

利用ALD制备了TiO₂限域的Pd催化剂, 研究了限域空间内Pd纳米颗粒与TiO₂的界面作用对1,4-丁炔二醇(BYD)加氢性能的影响. 相比于管外负载型催化剂, 限域催化剂在催化1,4-丁炔二醇选择性加氢反应中体现出非常高的催化活性和1,4-丁烯二醇的选择性. HR-TEM、 EDX-Mapping、 XRD、 XPS和H₂-TPR表征说明, 限域体系中Pd-TiO₂的界面相互作用强于传统TiO₂表面负载型Pd催化剂, 这种强界面作用不仅能够提高BYD的加氢活性, 也可抑制半加氢产物1,4-丁烯二醇的异构化和深度加氢, 提高1,4-丁烯二醇的选择性, 而且限域结构也可阻止管内壁Pd纳米颗粒的脱落, 提高催化剂的稳定性.     

双功能Pd/ZrHP催化剂的制备及其在苯酚选择性加氢反应中的应用

苯酚加氢制备环己酮是合成纤维（尼龙）生产过程中的重要环节。采用微波法快速合成了具有层状结构的固体酸（磷酸氢锆,ZrHP）和ZrHP负载的Pd催化剂,利用X射线衍射（XRD）、扫描电子显微镜（SEM）、高倍透射电子显微镜（HRTEM）、氮气吸附-脱附、X射线光电子能谱（XPS）和程序升温脱附（TPD）技术对催化剂的结构、形貌和表面特性进行了详细的表征,并将其应用于苯酚选择性加氢制环己酮的反应中。研究发现：在温和条件（100℃,1.0 MPa H₂）下,Pd/ZrHP比传统的氧化物（Al₂O₃、SiO₂、MgO）、分子筛（H-Beta）、活性炭（XC-72）负载的Pd催化剂具有更高的活性和稳定性,催化剂表面Pd原子的比活性最高可达612.2 h^-1,并且经过5次循环使用后催化剂无明显失活。结合表征结果推断,金属中心Pd与ZrHP表面的酸性位点之间的协同作用可能是影响苯酚加氢产物停留在环己酮阶段的关键因素。     

柱状Co3O4催化剂的乏风催化燃烧性能

通过两步法成功合成了由纳米粒子组装成的柱状Co₃O₄。第一步是通过简单的冷凝回流法合成柱状CoC₂O₄·2H₂O。第二步将所制备的柱状CoC₂O₄·2H₂O在350℃下煅烧2 h,使其分解形成Co₃O₄而不破坏原始形貌。通过粉末X射线衍射（PXRD）,X射线光电子能谱（XPS）,氮气吸附－脱附,扫描电镜（SEM）,高分辨率透射电子显微镜（HRTEM）和H₂程序升温还原（H₂-TPR）表征柱状Co₃O₄的物化性质。结果表明,柱状Co₃O₄对乏风甲烷燃烧的催化活性远远高于商业Co₃O₄。柱状Co₃O₄优异的催化性能可能归因于其表面较高的Co³⁺含量,较高的表面吸附氧和大量暴露的{111}晶面族。     

助剂对Ni/SiO2催化剂微观结构及二硝基甲苯催化加氢性能的影响

采用等体积浸渍法制备了负载型Ni/SiO₂催化剂,研究了Ce、Zr、La、Co和Fe助剂对催化剂微观结构及其催化二硝基甲苯（DNT,C₆H₃CH₃（NO₂）₂）加氢制备甲苯二胺（TDA,C₆H₃CH₃（NH₂）₂）性能的影响。通过XRD,BET,H₂-TPD、H₂-TPR和XPS技术对催化剂进行了表征。结果表明,助剂的引入促进了Ni物种在载体表面的分散,减小了Ni晶粒的尺寸,使得NiO晶粒更易还原。添加La、Fe和Zr助剂增加了有效的Ni活性中心数,有利于催化活性的提高,其中,添加La助剂制备的催化剂催化性能最优,DNT转化率和TDA选择性分别为98.1%和99.1%。但Co和Ce助剂的加入降低了化学氢吸附量,使得有效的Ni活性中心数降低,降低了催化剂的催化活性。     

Pd/C气体扩散电极电化学降解4-氯酚的比较研究

分别采用氢气还原法和甲醛还原法制备了Pd/C催化剂, 利用XRD、TEM及XPS对催化剂进行了表征, 并由催化剂制备成Pd/C气体扩散阴极, 采用先通氢气后通空气的方式在隔膜电解体系中对4-氯酚进行降解, 比较了不同电极体系下4-氯酚的去除效果. 结果表明, 制备的Pd/C气体扩散阴极既对4-氯酚具有还原脱氯作用(通入H₂时), 又能够促进O₂还原生成H₂O₂(通入O₂时), 它们对4-氯酚的去除效果要好于不掺杂Pd的气体扩散阴极. 使用氢气还原法制备出的Pd/C催化剂中Pd表面的活性点比甲醛还原法制备出的要多, 电极稳定性好, 反应60 min后 4-氯酚转化率和脱氯率接近100%, 120 min后阴极室COD去除率为87.4%.     

AgPd双金属纳米空心球的合成及其催化性能

以Ag纳米颗粒为牺牲模板,H₂PdCl₄为前驱体,抗坏血酸为还原剂,聚乙烯吡咯烷酮为表面活性剂,在70℃下采用电偶置换法结合还原法制备出AgPd双金属纳米空心球。采用紫外可见光谱、粉末X射线衍射、透射电镜结合能量色散等手段对由不同体积的0.01 mol·L^-1 H₂PdCl₄溶液制备的产物进行结构表征。结果表明,随着H₂PdCl₄溶液体积的增加,产物的空心化程度逐渐升高,晶粒的尺寸逐渐增大。当H₂PdCl₄溶液体积为120 μL时,合成的AgPd双金属纳米空心球组成和结构较为均匀,其粒径约为25 nm,壳层厚度2~3 nm。双金属中,由于Ag和Pd电负性的差异,电子从Ag转移到了Pd,使Pd表面出现电子富集区,显著提高了其催化效率。将所合成的AgPd双金属以及纯金属Ag和Pd作为催化剂,分别用于硼氢化钠催化还原4-硝基苯酚的反应,发现AgPd双金属的催化性能远高于纯金属Ag和Pd,其中AgPd-120纳米空心球(H₂PdCl₄溶液体积120 μL)作催化剂时的反应速率常数最高,是同等尺寸纯Ag纳米球的24.0倍,纯Pd纳米立方体的14.7倍。     

AgPd双金属纳米空心球的合成及其催化性能

以Ag纳米颗粒为牺牲模板,H₂PdCl₄为前驱体,抗坏血酸为还原剂,聚乙烯吡咯烷酮为表面活性剂,在70 ℃下采用电偶置换法结合还原法制备出AgPd双金属纳米空心球。采用紫外可见光谱、粉末X射线衍射、透射电镜结合能量色散等手段对由不同体积的0.01 mol·L^-1 H₂PdCl₄溶液制备的产物进行结构表征。结果表明,随着H₂PdCl₄溶液体积的增加,产物的空心化程度逐渐升高,晶粒的尺寸逐渐增大。当 H₂PdCl₄溶液体积为 120 μL时,合成的 AgPd双金属纳米空心球组成和结构较为均匀,其粒径约为 25 nm,壳层厚度 2~3 nm。双金属中,由于 Ag 和 Pd 电负性的差异,电子从 Ag 转移到了 Pd,使 Pd 表面出现电子富集区,显著提高了其催化效率。将所合成的AgPd双金属以及纯金属Ag和Pd作为催化剂,分别用于硼氢化钠催化还原4-硝基苯酚的反应,发现AgPd双金属的催化性能远高于纯金属Ag和Pd,其中AgPd-120纳米空心球(H₂PdCl₄溶液体积120 μL)作催化剂时的反应速率常数最高,是同等尺寸纯Ag纳米球的24.0倍,纯Pd纳米立方体的14.7倍。     

Y-Mn-O负载的Ni基催化剂用于乙酸自热重整产氢

为了有效地从生物质衍生的乙酸中获得高氢气产率,通过水热法合成了一系列的NiMnY催化剂并用于乙酸自热重整（ATR）过程中,并采用X射线衍射（XRD）、N₂吸附-脱附测试、H₂程序升温还原（H₂-TPR）探究催化剂中的内在联系。在Ni_0.39Mn_0.61YO_3.11±δ催化剂中,经焙烧后形成了类钙钛矿型（Ni,Mn）YO₃物相;经氢气还原后,转化为含有MnO、Y₂O₃和高分散Ni纳米粒子的热稳定的Ni-Mn-Y-O物种。Ni_0.39Mn_0.61YO_3.11±δ具有高效稳定的产氢催化性能,乙酸转化率高达100%,氢气产率达到2.68 mol_H2·mol_HAc^-1。     

Silica supported nanopalladium prepared by hydrazine reduction

Palladium catalysts (1–10 wt.% Pd) supported on silica were prepared by hydrazine reduction of palladium chloride at room temperature. They were characterized by XRD, TEM, EDX, H₂-adsorption, and H₂-TPD and tested in the gas phase hydrogenation of benzene in the temperature range 75–250 °C. A conventional catalyst (1 wt.% Pd) obtained by calcination then hydrogen reduction of the same metal precursor was studied for comparison. Metal particles with a size range 6.8–28.4 nm were obtained. Dispersion, hydrogen storage and activity in benzene hydrogenation increased with decreasing particle size. In comparison, the classical catalyst was found much more dispersed (mean particle size of 1.6 nm) and more active (specific rate 1.6–3.7 times higher) than the homolog hydrazine catalyst. However, unexpectedly, turnover frequency (TOF) calculations indicated a greater reactivity of the metal surface atoms for the hydrazine catalyst. It also stored more hydrogen. These contrasting results are discussed in relation with the metal particle morphology.     

Liquid-phase hydrogenation of alkenes and aromatic compounds with Pd-loaded oxidized diamond catalyst

Hydrogenation reactions of alkenes (cyclohexene, ethyl acrylate, styrene and 1,5-cyclooctadiene) and aromatic compounds (o-, m- and p-xylene) were carried out in order to examine the activity of palladium-loaded surface-oxidized diamond (Pd/O-Dia) catalyst in liquid-phase hydrogenation. The catalytic performance was compared to commercial palladium-loaded activated carbon (Pd/C) catalyst. The catalyst activities were evaluated by conversions of reactants and H₂ uptake rates in the early stage of the reaction. In all the hydrogenation reactions of alkenes and aromatic compounds, the activity of Pd/O-Dia was almost the same as or slightly higher than that of Pd/C. Dispersion of Pd metal was measured by a CO-pulsed adsorption technique and TEM observations of the catalysts. Pd dispersions were on the same order of magnitude according to the CO-pulsed adsorption technique, although the Pd/C catalyst had a higher surface area (718 m²/g) than that of Pd/O-Dia (23 m²/g). The Pd particle sizes on O-Dia measured by TEM observation were slightly smaller than those on the activated carbon. Such highly dispersed Pd particles on O-Dia would contribute to higher activity for the hydrogenation reaction of alkenes and aromatic compounds.     

Harmonious Heterointerfaces Formed on 2D-Pt Nanodendrites by Facet-Respective Stepwise Metal Deposition for Enhanced Hydrogen Evolution Reaction

The performance of nanocrystal (NC) catalysts could be maximized by introducing rationally designed heterointerfaces formed by the facet- and spatio-specific modification with other materials of desired size and thickness. However, such heterointerfaces are limited in scope and synthetically challenging. Herein, we applied a wet chemistry method to tunably deposit Pd and Ni on the available surfaces of porous 2D−Pt nanodendrites (NDs). Using 2D silica nanoreactors to house the 2D-PtND, an 0.5-nm-thick epitaxial Pd or Ni layer ( e - Pd or e -Ni ) was exclusively formed on the flat {110} surface of 2D−Pt, while a non-epitaxial Pd or Ni layer ( n - Pd or n -Ni ) was typically deposited at the {111/100} edge in absence of nanoreactor. Notably, these differently located Pd/Pt and Ni/Pt heterointerfaces experienced distinct electronic effect to influence unequally in electrocatalytic synergy for hydrogen evolution reaction (HER). For instance, an enhanced H₂ generation on the Pt{110} facet with 2D-2D interfaced e -Pd deposition and faster water dissociation on the edge-located n -Ni overpowered their facet-located counterparts in respective HER catalysis. Therefore, a feasible assembling of the valuable heterointerfaces in the optimal 2D n -Ni/e-Pd/Pt catalyst overcame the sluggish alkaline HER kinetics, with a catalytic activity 7.9 times higher than that of commercial Pt/C.     

H+−H− Pairs in Partially Oxidized MAX Phases for Bifunctional Catalytic Conversion of Furfurals into Linear Ketones

Currently, less favorable C=O hydrogenation and weak concerted acid catalysis cause unsatisfactory catalytic performance in the upgrading of biomass-derived furfurals (i.e., furfural, 5-methyl furfural, and 5-hydroxymethyl furfural) to ketones (i.e., cyclopentanone, 2,5-hexanedione, and 1-hydroxyl-2,5-hexanedione). A series of partially oxidized MAX phase (i.e., Ti₃AlC₂, Ti₂AlC, Ti₃SiC₂) supporting Pd catalysts were fabricated, which showed high catalytic activity; Pd/Ti₃AlC₂ in particular displayed high performance for conversion of furfurals into targeted ketones. Detailed studies of the catalytic mechanism confirm that in situ hydrogen spillover generates Frustrated Lewis H⁺−H⁻ pairs, which not only act as the hydrogenation sites for selective C=O hydrogenation but also provide acid sites for ring opening. The close intimate hydrogenation and acid sites promote bifunctional catalytic reactions, substantially reducing the reported minimum reaction temperature of various furfurals by at least 30–60 °C.     

Preparation of Pd/C catalysts via deposition of palladium hydroxide onto Sibunit carbon and their application to partial hydrogenation of rapeseed oil

Pd/Sibunit catalysts were prepared by deposition of palladium hydroxide onto the support surface in an alkaline medium. It was found that the palladium distribution throughout the catalyst grain, and the dispersion of Pd particles depend on (i) the order of the addition of H₂PdCl₄ and Na₂CO₃ to carbon suspension, (ii) Na₂CO₃ to H₂PdCl₄ ratio, and (iii) aging time of the mixture H₂PdCl₄ + Na₂CO₃ before its addition to the carbon. The catalysts were tested in the hydrogenation of cyclohexene and rapeseed oil under static conditions. The yield of trans-isomers as products of partial hydrogenation of rapeseed oil was found to decrease with decreasing the Pd particle size in the catalysts, as well as with increasing the Pd concentration on the periphery of the support grains.     

密度泛函理论计算研究表面应力对钯催化乙炔选择性加氢活性与选择性的影响（英文）

在石油催化裂解过程中,除了生成乙烯、丙烯及丁烯等烯烃,还会产生部分炔烃.目前工业上通常采用炔烃选择性加氢转化为对应的单烯烃,以除去其中炔烃.由于产品烯烃中的炔烃等杂质含量需极低,这就对用于加氢催化剂的活性和选择性提出了很高的要求,即催化剂需要选择性吸附炔烃并加氢,而不损失其中的烯烃.经过前期大量的基础研究工作,目前工业中炔烃选择性加氢应用最广泛的催化剂是负载型钯基催化剂.然而,单独的钯金属选择性并不理想,因而对其选择性以及活性进行调控成为了当前关注的研究课题.本文采用密度泛函理论计算结合微观反应动力学模拟手段,研究了钯金属表面应力存在条件下的活性与选择性,以及形成次表层物种的可能性和形成后的活性与选择性.研究发现,改变钯金属的晶格参数与表面应力,反应物、表面反应中间体和产物的吸附能都会产生相应的变化,且吸附能与晶格参数的变化存在线性关系,晶格参数越大,吸附越强.利用表面反应过渡态能量与初始态能量之间的线性关系,相应的乙炔加氢生成乙烯的反应速率可以通过微观反应动力学模拟得到.结果显示,不同晶格参数的钯催化剂催化乙炔加氢生成乙烯的反应活性位于相应火山型曲线的强吸附侧,即减弱乙炔和氢的吸附强度可提高乙烯的生成速率.在此基础上,本文研究了不同表面应力的钯催化剂在次表面吸附不同覆盖度碳原子和氢原子的情况,发现晶格参数越大越有利于碳原子和氢原子在次表面的吸附.同时,研究发现在次表面碳掺杂的条件下,不同表面应力条件下的钯催化剂的活性均有所增强.此外,由于乙烯在所有研究的钯催化剂表面脱附比进一步加氢容易,因而乙烯都可以选择性生成.     

Preparation and catalytic properties of NR-stabilized palladium colloids

Palladium colloids revealing narrow particle size distributions can be obtained by chemical reduction using tetra–alkylammonium hydrotriorganoborates. Combining the stabilizing agent [NR] with the reducing agent [BEt₃H^?] provides a high concentration of the protecting group at the reduction centre. Alternatively, NR₄X (X = halogen) may be coupled to the metal salt prior to the reduction step: addition of N(octyl)₄Br to Pd(ac)₂ in THF, for example, evokes an active interaction between the stabilizing agent and the metal salt. Reduction of NR-stabilized palladium salts with simple reducing agents such as hydrogen at room temperature yields stable palladium organosols which may be isolated in the form of redispersible powders. The anion of the palladium salt is crucial for the success of the colloid synthesis. Electron microscopy shows that the mean particle size ranges between 1.8 and 4.0 nm. An X–ray–photoelectron spectrscopic examination demonstrated the presence of zerovalent palladium. These palladium colloids may serve as both homogeneous and heterogeneous hydrogenation catalysts. Adsorption of the colloids onto industrially important supports can be achieved without agglomeration of palladium particles. The standard activity of a charcoal catalyst containing 5% of colloidal palladium determined through the cinnamic acid standard test was found to exceed considerably the activity of the conventional technical catalysts. In addition, the lifespan of the catalyst containing a palladium colloid, isolated from the reduction of [N(octyl)₄]₂PdCl₂Br₂ with hydrogen, is superior to conventionally prepared palladium/charcoal (Pd/C) catalysts. For example, the activity of a conventional Pd/C catalyst is completely suppressed after 38×10³ catalytic cycles per Pd atom, whereas the colloidal Pd/C catalyst shows activity even after 96times;10³ catalytic cycles.     

Selective hydrogenation of phenylacetylene on Pd/Al2O3: Effect of the addition of Pt and particle size

Phenylacetylene hydrogenation on Pd, Pt and Pd–Pt/Al₂O₃ catalysts has been studied. In all catalysts activity was found not to depend on particle size. However, selectivity to styrene was found to depend on Pd/Al₂O₃ catalysts. Carbon deposition in both metal and support explains such a behavior. Nevertheless, in small Pd particles a longer residence time of styrene may control the selectivity.     

Influence of the thermal treatment conditions and composition of bimetallic catalysts Fe—Pd/SiO2 on the catalytic properties in phenylacetylene hydrogenation

The supported bimetallic Fe—Pd/SiO₂ catalysts with the different Fe (0.025—8 mass.%) and Pd (0.05—3.2 mass.%) loadings were synthesized by the incipient wetness impregnation of support. The samples were heat-treated under different conditions (calcination in air at 240—350 °C or reduction in an H₂ flow at 400 °C). The X-ray phase analysis revealed the formation of Pd⁰, α-Fe₂O₃ and Fe₃O₄ phases after calcination of the samples at 240—260 °C. The reduction of the calcined Fe—Pd samples in an H₂ flow at 400 °C enables the formation of Fe⁰ nanoparticles of size 17—20 nm. The synthesized catalytic systems were studied in the selective hydrogenation of phenylacetylene at room temperature and atmospheric pressure in a solvent (ethanol, propanol). The catalytic properties of the Fe—Pd catalysts depend on the nature of solvent, catalyst composition, and thermal treatment conditions. The application of the Fe—Pd bimetallic catalysts with a low Pd loading of 0.05—0.1 mass.% made it possible to reach the high activity and selectivity to styrene (91%) at the complete conversion of phenylacetylene.     

Pd/Cu(111)双金属表面催化糠醛脱碳及加氢的反应机理

采用密度泛函理论(DFT)研究糠醛在最稳定Pd/Cu(111)双金属表面上的吸附构型和糠醛脱碳及加氢的反应机理。结果表明,当糠醛初始吸附于O_3-Pd-top、O_7-Cu-hcp位时,吸附构型最稳定,其吸附能为73.4 kJ/mol。糠醛在Pd/Cu(111)双金属表面上更易发生脱碳反应。对于糠醛脱碳反应,所需活化能较低,各个基元反应均为放热反应,糠醛更易先失去支链上的H形成(C_4H_3O)CO,然后中间体脱碳加氢得到呋喃,其中,C_4H_3O加氢生成呋喃所需活化能(72.6 kJ/mol)最高,是反应的控速步骤。对于加氢反应,糠醛与首个氢原子的反应需要最大的活化能(290.4 kJ/mol),是反应的限速步骤。