Characterization and reactivity of γ-Al_2O_3 supported Pd–Ni bimetallic nanocatalysts for selective hydrogenation of cyclopentadiene

Several g-Al2O3 supported Pd–Ni bimetallic nanocatalysts(Pd–Ni(x:y)/Al2O3; where x and y represent the mass ratio of Pd and Ni, respectively) were prepared by the impregnation method and used for selective hydrogenation of cyclopentadiene to cyclopentene. The Pd–Ni/Al2O3 samples were confirmed to generate Pd–Ni bimetallic nanoparticles by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). The catalytic activity was assessed in view of the effects of different mass ratios of Pd and Ni, temperature, pressure, etc. Among all the samples, the Pd–Ni(1:1)/Al2O3(PN-1:1) catalyst showed extremely high catalytic ability. The conversion of cyclopentadiene and selectivity for cyclopentene can be simultaneously more than 90%.     

铌改性的Pd/Al2O3催化剂催化苯燃烧反应简

采用浸渍法制备了Nb改性的Pd/Al2O3催化剂,考察了该催化剂催化苯燃烧反应性能,并研究了催化剂的稳定性. 结果表明,Nb的添加明显提高了Pd/Al2O3催化剂性能,在195 ℃时苯转化率达到90%,苯的完全燃烧温度降低了40 ℃. 采用X射线衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、H2 程序升温还原(H2-TPR)、NH3程序升温脱附(NH3-TPD)和氮气吸附等手段对催化剂进行了表征,结果表明,Nb的加入不仅提高了Pd物种的分散度,同时改变了部分Pd的价态,形成适宜反应的PdO-Pd物种,并促进了催化剂表面氧浓度的增加,使氧物种氧化能力增强,从而提高了催化性能. 1%Pd-5%Nb/Al2O3催化剂的催化活性高于2.0%Pd/Al2O3催化剂.     

添加钒对Pd/Al2O3-TiO2 催化剂上醇醛催化氧化性能及表面特性的影响

采用浸渍法分别制备了Pd/Al₂O₃-TiO₂、V/Al₂O₃-TiO₂和不同钒含量的V-Pd/Al₂O₃-TiO₂催化剂,并对乙醇、乙醛的完全催化氧化性能进行了测试。结果表明,添加适量的钒组分(1%~3%)能够有效地提高催化剂的深度氧化活性。采用XRD、NH₃-TPD、N₂吸附等技术分析研究催化剂的表面特性与催化活性之间的关系,发现Pd/Al₂O₃-TiO₂催化剂添加适量钒组分后,调变了催化剂的表面酸性、比表面积和孔容,使得V组分和Pd组分与载体之间产生较强的相互作用,双金属组分的协同效应提高了催化剂对乙醇、乙醛的深度氧化活性。     

Carbonization of alumina-based catalysts in propionitrile ammonolysis

Summary The asymmetric hydrogenation of ethyl 2-acetoxyacrylate (EtA) by cinchonidine modified Pd/Al2O3 and Pt/Al2O3 catalyst is described (ee up to 60 %). This is the first example of asymmetric hydrogenation of an enol esters in heterogenized conditions.     

Ni的引入对Pd/Al2O3催化甲烷燃烧性能的影响

采用浸渍法制备了Ni掺杂的Pd/Al2O3催化剂,考察了其低浓度甲烷催化燃烧活性和水热稳定性.结果表明,随着Ni的引入及其含量的增加,Pd/Al2O3催化剂性能明显提高,Ni含量至20%时,在0.4%CH4,4%H2O和空气平衡的原料气组成,80000h-1空速和600oC条件下反应150h后,CH4转化率仍能保持在97.5%以上.X射线衍射、H2程序升温还原、NH3程序升温脱附和透射电镜等结果表明,NiAl2O4晶相的形成改善了载体酸性和活性组分的分散度,从而提高了催化剂性能.     

Oxidative Esterification of Methacrolein to Methyl Methacrylate over Supported Palladium Catalyst

Methyl methacrylate (MMA) is an important monomer, widely used for producing acrylic plastics, polymer dispersions for paints and coatings. Traditional acetone cyanhydrin (ACH) method involves toxic hydrogen cyanide and a large quantity of ammonium bisulf…     

铈和镧改性γ-Al2O3担载Pd催化剂的结构效应

分别以镧-铈、铈-镧顺序浸渍和镧铈共浸渍的方式在γ-Al2O3载体上引入助剂La2O3和CeO2，然后担载Pd制备了一系列催化剂.以甲醇分解为探针反应，采用XRD、EXAFS和XPS对催化剂的体相和表面结构进行表征，用BET法测定比表面积，并进行了吸附态CO的FTIR研究.结果表明,La2O3容易进入CeO2的晶格中，促进了CeO2在γ-Al2O3上的分散.但不同的La2O3、CeO2加入方式对活性组分Pd在改性载体上的分散度、优势暴露面及其与CeO2之间的相互作用产生不同的影响.关联甲醇分解性能测试结果说明,Pd在载体上的高度分散以及Pd和CeO2之间通过界面产生的强相互作用是催化剂具有高活性的关键.     

Two-faced reactivity of alkenes: cis- versus trans-aminopalladation in aerobic Pd-catalyzed intramolecular aza-Wacker reactions

A number of different PdII catalyst systems have been reported recently for the Wacker-type aerobic oxidative cyclization of alkenes bearing tethered nitrogen nucleophiles. This study examines the stereochemistry of the aminopalladation step with five different catalyst systems: Pd(OAc)2/DMSO (A), PdX2/pyridine [X = OAc (B), O2CCF3 (C)], Pd(IMes)(O2CCF3)2(OH2) (D), and Pd(O2CCF3)2/(-)-sparteine (E). Use of a stereospecifically deuterated cyclopentene substrate reveals that four of the five catalyst systems (A, B, C, and E) promote exclusive cis-aminopalladation of the alkene, whereas both cis- and trans-aminopalladation occur with the N-heterocyclic-carbene (NHC) catalyst system. If stoichiometric Br?nsted base (NaOAc, Na2CO3) is added to the latter reaction conditions, however, only cis-aminopalladation is observed. The identity of the nitrogen nucleophile also affects the aminopalladation pathway, with results ranging from exclusively cis- to exclusively trans-aminopalladation. These results have important implications for ongoing efforts to develop enantioselective methods for Pd-catalyzed oxidative amination of alkenes.     

Pb促进的Pd/γ-Al2O3催化剂上H2O2氧化甘油反应

制备了Pd含量为1 wt%、不同Pb/Pd摩尔比的γ-Al2O3负载Pd-Pb双金属催化剂,并用于常压、45°C和pH =11条件下H2O2氧化甘油反应中.催化剂的形貌和分散度采用扫描电镜-X射线电子散射谱和透射电镜进行了表征;双金属催化剂中合金相用X射线光电子能谱进行了验证.单金属Pd催化剂上反应结束后甘油转化率为19%,但随着Pb的加入甘油转化率增大到约100%.所制四个不同Pb/Pd原子比的双金属催化剂PdPb0.25, PdPb0.50, PdPb1.00和PdPb1.60均可氧化甘油至二羟基丙酮(DIHA),反应结束后DIHA选择性分别可达59%,58%,34%和25%.     

Theoretical and experimental study on formation and adsorption of enolic species on Ag-Pd/Al2O3 catalyst

The formation and adsorption of enolic species on a palladium promoted Ag/Al2O3 catalyst (denoted Ag-Pd/Al2O3) during the selective catalytic reduction (SCR) of NOx by C3H6 has been studied by means of DRIFTS and density functional calculations. The structure of the enolic species adsorbed on Ag-Pd/Al2O3 catalyst has been established based on the in situ DRIFTS spectra and simulated results. The reaction mechanism from C3H6 to enolic species on Ag-Pd/Al2O3 catalyst was proposed and the hypothesis about the Pd promotion was discussed.