Synthesis and characterization of niobium-promoted cobalt/iron catalysts supported on carbon nanotubes for the hydrogenation of carbon monoxide

Bimetallic Co /Fe catalysts supported on carbon nanotubes( CNTs) were prepared,and niobium( Nb) was added as promoter to the 70 Co ∶30Fe /CNT catalyst. The physicochemical properties of the catalysts were characterized,and the catalytic performances were analyzed at the same operation conditions( H_2 ∶CO( volume ratio) = 2 ∶1,p = 1 MPa,and t = 260 ℃) in a tubular fixed-bed microreactor system. The addition of Nb to the bimetallic catalyst decreases the average size of the oxide nanoparticles and improves the reducibility of the bimetallic catalyst. Evaluation of the catalyst performance in a Fischer-Tropsch reaction shows that the catalyst results in high selectivity to methane,and the selectivity to C_(5+) increased slightly in the bimetallic catalyst unlike that in the monometallic catalysts. The addition of 1% Nb to the bimetallic catalyst increases CO conversion and selectivity to C_(5+). Meanwhile,a decrease in methane selectivity is observed.     

Synergic effect of palladium-based bimetallic catalysts for the hydrogenation of nitroaromatics

Bimetallic catalysts, PdCl₂-MX_n and PdCl₂(PhCN)₂-Mx_n (MX_n=FeCl₃, Fe(acac)₃, Co(OAc)₂, CoCl₂, Co(acac)₂, NiCl₂, Ni(OAc)₂, RuCl₃, Cu(OAc)₂, CuCl₂), exhibit remarkable synergic effect which can obviously increase the activity of the monometallic Pd catalyst for the hydrogenation of nitroaromatics, whereas MX_n alone is not catalytically active under the same reaction conditions.     

Catalytic behavior of supported Pd catalysts in the selective hydrogenation of campholenic aldehyde to naturanol

Selective catalytic reduction of campholenic aldehyde to naturanol was investigated over Sn-and Fe-doped SiO₂, and Fe₂O₃-supported Pd catalysts. On Pd/SiO₂ and Pd-Sn/SiO₂ only saturated campholenic aldehyde is formed. Addition of Fe increases the C=O hydrogenation rate producing the corresponding unsaturated alcohol with a good selectivity. Also Fe₂O₃-supported catalysts were found to be more selective towards carbonyl hydrogenation. Addition of tin to Pd/Fe₂O₃ contributes to a further selectivity enhancement towards naturanol.     

NiFe双金属催化剂用于月桂酸甲酯加氢的研究

负载型Ni Fe/γ-Al₂O₃双金属催化剂的物理化学性质明显受还原温度的影响,进而影响月桂酸甲酯的加氢活性和产物选择性。金属Ni活性中心主要促进脱羰/脱羧(DOC)反应,Fe的加入能促进月桂酸甲酯发生加氢脱氧反应,促进C₁₂烷烃化合物生成。H₂-TPR、XRD、H₂-TPD和BET结果表明,高的还原温度有利于金属或合金活性中心形成,NiFe双金属催化剂的加氢活性取决于金属Ni、Fe和NiFe合金的含量;NiFe双金属催化剂吸附与活化H₂分子的能力明显受还原温度的影响。在研究的温度范围内,Ni活性中心具有优异的加氢和裂解性能,Fe物种的引入能有效抑制裂解性能。双金属催化剂的加氢活性顺序:NF420>NF360>NF450>NF300,在420℃下经H₂还原制得的NF420催化剂具有最佳的月桂酸甲酯加氢性能,在反应温度为380℃时,月桂酸甲酯加氢转化率和烷烃化合物选择性分别高达93.3%和90.0%。     

Preparation and catalytic performance of monolayer-dispersed Pd/Ni bimetallic catalysts for hydrogenation

Pd/Ni bimetallic catalysts were prepared by replacement reactions, characterized by X-ray diffraction, CO chemisorption and H₂ temperature-programmed desorption, and evaluated for hydrogenation of cyclohexene, styrene and acetone. The results show that Pd atoms are monolayer-dispersed on the Ni surface in these Pd/Ni catalysts. Consequently, Pd/Ni catalysts are much more active than Pd/Ni and Pd/c-Al₂O₃ with the same Pd loading prepared by the conventional impregnation method. __________ Translated from Chinese Journal of Catalysis, 2007, 28(8): 676–680 [译自: 催化学报]     

CO oxidation over ceria supported Au22 nanoclusters: Shape effect of the support

CO oxidation over ceria-supported Au₂₂ nanoclusters shows strong dependence on the support shape: the lattice oxygen in CeO₂ rods is more reactive than in the cubes and thus make rods a superior support for Au nanoclusters in catalyzing low temperature CO oxidation.     

Kinetics of toluene hydrogenation over platinum-titania catalysts in conditions of strong metal-support interaction

Toluene hydrogenation was investigated over different platinum-titania catalysts. It was found that the form of kinetic equation of the reaction does not depend on the modifications of titania (rutile, anatase) but the catalyst activity is different. The catalyst reduction at temperature higher than 300^oC leads to strong metal-support interaction (SMSI) which is manifested in a decrease of the reaction rate.     

Au-Ir催化剂用于生物质衍生物加氢

采用沉积-沉淀法制备了TiO2负载的Au-Ir和Au-Ru催化剂,用于乙酰丙酸加氢制γ-戊内酯反应,并与相应的单金属催化剂性能进行了比较。有趣的是, Ir/TiO2中添加Au抑制了催化剂活性,而添加Ru则表现出正效应的协同作用。这两个催化剂均在H2中还原,使得M0–Au0间相互作用增强。结合以前的密度泛函理论计算和催化反应结果,我们认为, Au-Ir/TiO2催化剂活性低于Ir/TiO2催化剂是由于Au影响了Ir原子的氧化还原过程。     

Influence of ceria preparation method on the performance of CuO/CeO2 catalysts

Ceria were prepared by various processes. The prepared samples and commercial ceria were used as supports to prepare the CuO/CeO₂ catalysts via an impregnation method. The samples were characterized by using TEM, XRD, H₂-TPR, and their catalytic activities in low-temperature CO oxidation were also investigated.     

负载型铈基催化剂在NH3-SCR反应中的载体效应

近年来,氨-选择催化还原(NH3-SCR)技术被公认为是控制燃煤烟气和柴油车尾气氮氧化物(NOx)排放的最有效手段之一.V2O5-WO3/TiO2和V2O5-MoO3/TiO2催化剂在300–400°C范围内表现出优异的脱硝性能和抗H2O和SO2中毒性能,因而被广泛用于NH3-SCR过程.然而,钒基催化剂存在一些缺点,如氧化SO2到SO3的活性较高、高温下将部分NH3非选择性地氧化成N2O、V2O5具有生物毒性等.因此,非钒基脱硝催化剂的研制引起人们越来越多的关注.二氧化铈(CeO2)因具有氧化还原性能优异、储/释氧能力强和Ce3+/Ce4+转换容易等优点而广泛用于NH3-SCR反应.然而,单纯CeO2的脱硝性能并不理想.研究表明,将CeO2制备成铈基复合金属氧化物催化剂和负载型铈基催化剂可显著提高其在NH3-SCR反应中的催化性能.尤其是负载型铈基催化剂由于催化性能优异、比表面积大、热稳定性高及活性组分用量少而成为研究热点.众所周知,对于负载型金属氧化物催化剂,载体并不只是惰性材料,它会显著影响表面负载组分的物理化学性质和催化性能.因此,关于载体与组分间相互作用的研究常见诸报道.但是,对于负载型铈基催化剂,具有不同晶相结构的载体对其理化性质和NH3-SCR催化性能的影响规律尚不明晰.此外,SiO2,γ-Al2O3,ZrO2和TiO2是工业上常用的四种催化剂载体,它们具有不同的晶相结构和应用场合,究竟哪一个最适合作为负载型铈基催化剂的载体用于NH3-SCR反应尚无定论.因此,为了阐明负载型铈基催化剂在NH3-SCR反应中的载体效应,筛选出最佳的催化剂载体,我们首先采用溶胶-凝胶法和沉淀法合成了SiO2,γ-Al2O3,ZrO2和TiO2四个载体,再通过浸渍法制备了一系列负载型铈基催化剂(CeO2/SiO2,CeO2/γ-Al2O3,CeO2/ZrO2和CeO2/TiO2)用于NH3-SCR反应.并借助于X射线衍射(XRD)、拉曼光谱(Raman)、比表面积测定(BET)、X射线光电子能谱(XPS)、氢气-程序升温还原(H2-TPR)以及氨气-程序升温脱附(NH3-TPD)等表征手段对上述载体和催化剂进行了较为全面的分析.研究结果表明,这些负载型铈基催化剂的理化性质和脱硝性能强烈地依赖于催化剂载体.首先,CeO2/γ-Al2O3催化剂的表面Ce3+含量明显大于CeO2/SiO2,CeO2/ZrO2和CeO2/TiO2催化剂,有利于氧空位的产生以促进NO分子的解离,进而导致优异的NH3-SCR反应性能.其次,CeO2/γ-Al2O3催化剂具有最佳的还原性能,有利于NO氧化为NO2,进而通过"快速NH3-SCR"途径提升其催化性能.再者,CeO2/γ-Al2O3催化剂表面酸性位最多,能够促进反应物NH3分子的吸附与活化,从而提高脱硝性能.最后,CeO2/γ-Al2O3催化剂在H2O和SO2存在的条件下同样表现出最佳的催化性能,表明其有望用于实际燃煤烟气脱硝.     

Effect of particle size in the hydrogenation of crotonaldehyde on supported Pt and Pt-Sn catalysts

The present work reports the effect of metal particle size on the selectivity to crotyl alcohol (S_UOL) in the liquid phase hydrogenation of crotonaldehyde over SiO₂ and a-Al₂O₃-supported Pt and Pt-Sn catalysts. It was demonstrated that, for the monometallic catalysts, a higher particle size led to a higher S_UOL, while for the bimetallic catalysts, this effect was not so important.     

Infrared spectroscopic study on the reaction mechanism of CO hydrogenation over Pd/CeO2

In situ infrared spectroscopy was applied to elucidate the reaction mechanism of CO hydrogenation over Pd/CeO₂. Instead of direct dissociation of CO, a new reaction pathway is proposed for methane formation, involving geminal dicarbonyl intermediates and (HCO)₂(a) intermediates, which may be located on the surface of Pd covered with thin layers of reduced ceria (SMST effect). Transformation of methane formation sites into methanol formation ones by the oxidation with water vapor formed during the CO-H₂ reaction is proposed, which may be located on the Pd (111) planes adjacent to ceria support.     

Pd/Amberlyst-45催化剂催化水相中苯酚选择性加氢制环己酮(英文)

环己酮是重要的有机化工原料和工业溶剂,是制造尼龙、己内酰胺和己二酸的主要中间体,环己酮的绿色生产工艺受到人们关注.目前全世界环己酮年产量接近900万吨,但环己酮生产仍主要以环己烷为原料,采用富氧空气氧化为环己基过氧化氢,再在铬酸叔丁酯催化剂作用下分解为环己醇和环己酮的混合物,然后经一系列蒸馏精制后得到环己酮、工艺复杂、能耗高,而且设备腐蚀、环境污染及安全问题严重.因此,大量工作正致力于新工艺和新催化剂研究,其中光催化氧化、分子筛催化氧化和金属氧化物催化氧化等都有相关报道,同时还有学者开发了其它环己酮制备新方法,如环己烯水合法、苯加氢法、环己醇氧化法和苯酚加氢法等.苯酚直接选择性加氢合成环己酮研究具有重要意义.苯酚加氢通常有两种工艺,气相加氢和液相加氢,由于液相加氢具有无需将反应物汽化、能耗较低和催化剂反应活性高等优势而受到广泛关注.但是目前大量文献报道的苯酚加氢过程仍需要高温条件且较易产生环己醇和环己烷等副产物,大部分催化反应需在有机溶剂中进行,因此如何提高环己酮选择性,减小环境影响成为近年来的热门课题.在过去数年中,人们筛选了大量催化剂,其中Pd催化剂具有较高活性和目的产物选择性,因为其对羰基表现出较低的催化活性.研究还发现,催化剂载体对苯酚加氢产物分布有重要影响,酸性载体或酸性助剂的加入均能提高苯酚转化率和环己酮选择性,可能的原因是催化剂表面可与苯酚羟基形成O-H…π强相互作用,使苯酚分子更容易吸附在载体表面,而一旦苯酚经催化加氢生成环己酮,由于失去羟基与载体表面相互作用,环己酮更容易从载体表面脱附,从而避免过度加氢生成环己醇,同时酸性位点可以增强Pd的电子密度,提高催化加氢活性.另外,通过添加助剂也可有效改善催化剂性能.然而,到目前为止,通过单一的一种催化剂仍然很难同时实现苯酚的高转化率和环己酮的高选择性.因此,开发新催化剂和简便的生产工艺对环己酮高效高质量生产具有重要意义.本文使用一种多孔、不易溶解的酸性离子交换树脂Amberlyst-45(A-45)为载体,采用简单的浸渍工艺制备了一系列不同Pd负载量的Pd/A-45催化剂,详细考察了催化剂在水相中对苯酚选择性加氢制环己酮的催化活性和选择性,包括反应温度、催化剂用量、反应时间和Pd负载量等对反应活性的影响及催化剂重复使用情况,并且与传统的SiO_2,ZnO,MgO,Al_2O_3和活性炭负载的Pd催化剂进行对比.研究发现,Pd/A-45催化剂在温和反应条件(40-100℃,0.2-1 MPa)下具有极高的催化活性和选择性,在适宜的反应条件下苯酚转化率达到100%,环己酮选择性高于89%.进一步分析由不同活性金属负载量制备的不同粒径Pd/A-45催化剂的活性规律发现,苯酚加氢生成环己酮是一个结构敏感型反应,其中Pd颗粒尺寸为12-14 nm时更有利于环己酮生成.     

Selective hydrogenation of nitrate to nitrite in water over Cu-Pd bimetallic clusters supported on active carbon

Hydrogenation of nitrate (200 ppm) in water with H₂ over Cu-Pd clusters supported on active carbon (AC) was investigated at 333 K using a gas–liquid co-current flow system. Two types of Cu-Pd bimetallic clusters, stabilized with either poly(vinylpyrrolidone) (PVP) or sodium citrate (SC), revealed that the catalysts possessed similar activity (per unit weight of Pd) and high selectivity toward nitrite when pH was 10.5 at the outlet of the reactor. The high selectivity toward nitrite on PVP-stabilized cluster/AC was minimally influenced by the atomic ratio of Cu/Pd (=0.5–4.0); activity was maximal at a ratio of 1:1. Increasing pH to 12.4 by addition of NaOH enhanced the selectivity toward nitrite to 93% over SC-stabilized Cu_0.63-Pd cluster/AC, but caused a decrease in the reaction rate. Over Cu_0.63-Pd cluster/AC, hydrogenation of nitrite as an intermediate occurred much more slowly than that of nitrate at pH 10.5, suggesting that high selectivity toward nitrite is attained by OH⁻ inhibiting adsorption of nitrite. XRD and STEM gave the size of the Cu_0.63-Pd cluster on AC as 4 nm; the structure of the cluster remained almost unchanged during the reaction. The activity and selectivity of the Cu_0.63-Pd cluster/AC was superior to those of the Cu_0.63-Pd cluster on oxides such as TiO₂, Al₂O₃, and ZrO₂. In addition, the Cu_0.63-Pd cluster/AC was more active and selective than conventionally prepared Cu_0.63-Pd/AC, indicating that the Cu-Pd cluster is an excellent precursor for selective catalysts in the hydrogenation of nitrate to nitrite.     

1-辛烯在Co/CNTs催化剂上的氢甲酰化研究： 钌的促进作用

采用等体积浸渍法制备了碳纳米管负载的钴及钴-钌双金属催化剂，并以1-辛烯的氢甲酰化反应为探针，研究了所制催化剂的催化性能；用TEM、XRD、TPR、TG技术对催化剂的形貌、物相结构、还原行为和热稳定性进行了研究。结果表明，金属钌能够促进金属钴在碳纳米管上的均匀担载，并有助于金属钴的还原，降低了催化剂的还原温度。1-辛烯的氢甲酰化反应结果表明，少量钌的加入，可明显提高反应的转化率和C9-醛的选择性；在双金属催化剂中，金属催化剂的粒径更小，分布更均匀，钌的加入对钴金属催化剂有促进作用。     

Interaction of cobalt with ceria thin films and its influence on supported Au nanoparticles

The interaction of Co with ceria thin films and its influence on the sintering behavior of Au were investigated by scanning tunneling microscopy(STM), synchrotron radiation photoemission spectroscopy(SRPES) and X-ray photoelectron spectroscopy(XPS). The strong interaction between Co and CeO_2(111) leads to oxidation of Co to Co~(2+) at 300 K, accompanied by partial reduction of ceria surface at low Co coverages. Subsequent Co deposition results in an increasing fraction of metallic Co. Annealing to high temperatures induces Co~(2+)ions diffuse into the CeO_2 film, while the small metallic Co islands agglomerate into larger ones. The bimetallic Co–Au particles were prepared by deposition of Au on the existing Co particles on ceria surfaces. The sintering behavior of Co–Au bimetallic surfaces is found to be highly determined by the stoichiometry of ceria supports. The addition of Co to the Au/CeO_2 surface suppresses the sintering of Au particles at high temperatures in comparison with that of pure Au particles. However, Au particles are less stable on the Co/CeO_(1.82) layer than on CeO_(1.82) surface.     

二氧化铈催化剂的氧化还原和酸碱性质的原位光谱表征

二氧化铈作为催化剂、催化剂载体和助剂被广泛应用于各类氧化还原的催化反应中,是多相催化领域中至关重要的金属氧化物.氧化铈因具有丰富的缺陷结构、较强的氧化还原能力以及异常的酸碱功能等独特性质,在催化领域中非常重要.在分子层面上理解氧化铈的储氧能力、氧化还原效应和酸碱性质对建立催化构效关系尤为重要,是有效合理地改善和设计铈基催化材料的关键.在诸多的表征手段中,光谱在氧化铈结构和表面性质的研究中显示出无可争议的优势,可以提供原子和分子层面的化学信息.本文总结了各种光谱方法(包括光学、X射线、中子、电子和核磁谱学)对氧化铈表面性质表征的研究进展.分析了直接光谱表征及其与探针分子耦合两种方法在氧化铈表征中的应用;归纳了预处理条件、氧化铈纳米粒子的形貌和尺寸对其表面位点的性质、强度和密度的影响.最后展望了如何利用反应条件下的原位光谱来更好地理解和揭示铈基材料的催化作用机制的可能性.     

Ni基双金属催化剂加氢脱氧性能的研究

考察了Ni-M/γ-Al2O3（M＝Co、Cu、Fe、La）双金属催化剂对醇、酸、酮有机含氧化合物（丁醇、丁酸、丁酮）的加氢脱氧性能,并对其中间产物进行了考察。通过TPR、XRD表征手段对Ni基催化剂的还原性能、表面分散度等特性进行了研究。结果表明,Ni基催化剂中第二活性组分相对不同有机含氧化合物表现出不同的加氢活性和选择性。对于丁酸,在Ni基催化剂中加入Fe表现出较好的活性;对于丁醇,加入La有较好的加氢脱氧性能;而对于丁酮,加入Cu更有利于提高催化剂的脱除性能。醇和酯是有机酸在Ni/γ-Al2O3催化剂上加氢转化的中间产物。     

Catalytic behavior of Al2O3-TiO2 supported Pd-Ru bimetallic catalyst for the partial hydrogenation of palm oil

Summary Al₂O₃-TiO₂ supported Pd-Ru bimetallic catalysts were prepared and characterized by X-ray photoelectron spectroscopy and X-ray diffraction (XRD) techniques. The catalytic system was evaluated in the partial hydrogenation of palm oil. Based on these results, it was deduced that core-shell model particles, with Ru cores, would be most likely formed in the bimetallic catalysts. As a result, the dispersing effect of ruthenium on palladium and the charge transfer from ruthenium to palladium may be closely related to the excellent catalytic performance. Besides, the highly dispersed TiO₂ on γ-alumina support seems to be crucial for inhibiting the formation of trans fatty acid.     

Cu对Ni-Cu/SiO2催化1,4-丁炔二醇加氢性能的影响

采用超临界干燥法和等体积浸渍法制备了不同Ni/Cu比例的Ni-Cu/SiO₂双金属催化剂,利用ICP、BET、XRD、H₂-TPR、H₂-TPD、NH₃-TPD等手段对催化剂进行了结构表征,考察了不同Ni/Cu比例对催化剂结构以及1,4-丁炔二醇加氢性能的影响.结果表明,少量Cu的引入不仅能够提高Ni活性物种的分散性,而且Ni-Cu双金属间的相互作用改善了NiO物种的还原性能及氢活化能力,有利于氢和1,4-丁炔二醇在活性位点的快速转化.在反应温度50℃,氢压1 MPa,反应时间3 h的加氢评价条件下,Ni/Cu比为3：1时,15Ni5Cu/SiO₂催化材料不仅可以实现BYD的完全转化,而且能够有效降低难分离副产物2-羟基四氢呋喃的含量,具有最优的加氢活性和对1,4-丁烯二醇及1,4-丁二醇的选择性.