Desorption and catalytic properties of palladium, supported on Al2O3-La2O3, prepared by the sol-gel method

Desorption and catalytic properties of 0.3 wt% Pd catalysts supported on alumina-lanthana, prepared by the sol-gel method, were studied. A large excess of consumed hydrogen was observed during TPR experiments on these catalysts due to the partial reduction of lanthana. The enhanced hydrogen adsorption (H/Pd varies from 8 to 15) detected by TPD for these catalysts is supposed to be a consequence of spillover. Spillover of hydrogen is favored by a high dispersion of palladium on the support surface and the presence of lanthana reduced species. Palladium on alumina-lanthana catalysts show a higher catalytic activity than palladium on alumina catalysts because reduced species of lanthana stabilize palladium particles. Similarity of ammonia selectivity at high temperatures allows one to suggest that reduced lanthana is involved in the reaction on pure alumina-lanthana support and palladium on alumina-lanthana catalysts at these temperatures. A synergetic effect between small palladium particles and reduced species of lanthana is suggested to be responsible for observed behavior of the lanthana-promoted palladium catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Co-Bi-B三元复合材料的制备及其在NaBH4水解制氢中的应用

通过液相共还原法制备了一种新型Co-Bi-B三元复合催化剂材料,并采用X射线衍射仪（XRD）、扫描电子显微镜（SEM）、X射线光电子能谱分析（XPS）等表征手段对材料的结构、形貌和元素分布进行了分析。系统考察了Co-Bi-B不同掺杂摩尔比和不同温度对催化NaBH₄水解制氢速率的影响。结果表明：掺杂Bi得到的三元合金催化剂呈晶体结构,且能够显著减小催化剂的粒径、减轻团聚现象。当化学还原温度为0℃、掺杂摩尔比Bi∶Co=1∶9时,Co-Bi-B三元催化剂展示了最佳的催化性能,并通过阿伦尼乌斯（Arrhenius）方程计算得到该催化剂的活化能为38.97kJ/mol。     

流化床型络合液再生工艺研究

随着工业化进程的加快,如何减少氮氧化物的排放受到了人们的强烈关注。目前,由于络合吸收法对一氧化氮(NO)具有良好的吸收性能,被视为未来脱硝技术的重要发展方向,但络合液的再生仍然是一个难题。本文针对络合脱硝中Fe(II)EDTA-NO络合液再生困难且无法连续运行问题进行了探究。以氮掺杂多孔碳为载体,钯纳米微团为活性组分制备出颗粒状Pd/NPCs催化剂,通过X射线衍射、透射电子显微镜、X射线光电子能谱对Pd/NPCs进行表征。结果表明,钯纳米微团成功负载到载体上,其平均粒径为2.36 nm,Pd⁰含量为68%(质量分数),对还原Fe(II)EDTA-NO有着良好的催化活性。进一步探究了溶液pH、反应温度、氧含量及液气比等因素对催化剂催化还原Fe(II)EDTA-NO的影响,搭建了一套可持续运转的流化床试验装置,其评价试验结果表明在气流量为200 L/h,NO含量为0.07%(体积分数)条件下,可以维持脱硝率80%以上3 h。     

Characterization and oxidation states of Cu and Pd in Pd–CuO/ZnO/ZrO2 catalysts for hydrogen production by methanol partial oxidation

Copper and zinc oxide based catalysts prepared by coprecipitation were promoted with palladium and ZrO₂, and their activity and selectivity for methanol oxidative reforming was measured and characterized by N₂O decomposition, X-ray absorption spectroscopy, BET, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature programmed reduction. Addition of ZrO₂ increased copper dispersion and surface area, with little effect on activity, while palladium promotion significantly enhanced activity with little change of the catalytic structure. A catalyst promoted with both ZrO₂ and palladium yielded hydrogen below 150 °C. EXAFS results under reaction conditions showed that the oxidation state of copper was influenced by palladium in the catalyst bulk. A palladium promoted catalyst contained 90% Cu⁰, while the copper in an unpromoted catalyst was 100% Cu¹⁺ at the same temperature. Palladium preferentially forms an unstable alloy with copper instead of zinc during reduction, which persists during reaction regardless of copper oxidation state. A 100-h time on stream activity measurement showed growth in copper crystallites and change in copper oxidation state resulting in decreasing activity and selectivity. A kinetic model of the reaction pathway showed that palladium and ZrO₂ promoters lower the activation energy of methanol combustion and steam reforming reactions.     

太阳能光解水制氢的核心催化剂及多场耦合研究进展

太阳能光解水制氢可从根本上解决能源需求及碳排放造成的环境污染问题,是各国关注的热点之一。利用太阳能全光谱光催化制氢是目前研究的主要方式,但存在催化效率较低,难以实际应用的问题。造成光催化剂催化效率低的主要因素在于比表面积小、光吸收能力弱、禁带宽度较宽、载流子迁移能力弱。对光催化机理和催化剂的优化策略进行了总结,通过敏化材料掺杂、元素掺杂、异质结构建、助催化剂负载、高导电性石墨烯掺杂等策略来有效提高光催化剂对可见光的吸收、降低光生载流子的复合、增加活性位点、加速表面反应。此外,对光电、光热及光热电催化等近年发展起来的多场耦合催化制氢做了系统的介绍,对太阳能制氢催化剂理论和实践的未来发展做出了展望。     

Dependence of Synergetic Effect of Palladium–Manganese-Hexaaluminate Combustion Catalyst on Nature of Palladium Precursor

A synergetic effect in the methane oxidation activity of palladium and manganese hexaaluminate was studied over Pd-modified manganese-hexaaluminate catalysts, prepared by incipient wetness impregnation and calcined at 1,200?°C. The magnitude of the synergetic effect is found to be depends on the palladium precursor: it is higher for palladium nitrate and palladium acetate than for tetrachloropalladic acid. The Pd/MnLaAl₁₁O₁₉ catalysts were characterized by X-ray diffraction, X-ray microanalysis, transmission electron microscope and temperature-programmed reduction with hydrogen. These data were compared with the properties of Pd/Al₂O₃ catalysts. At variation of Pd-precursors, a minor trend to the decrease of the Pd particle size was observed at transition from the ex-chloride Pd/MnLaAl₁₁O₁₉ catalyst with uniform Pd-distribution profile to the ex-nitrate and ex-acetate catalysts with egg-shell Pd-distribution. Slightly smaller size of metal palladium particles in the ex-nitrate and ex-acetate catalysts leads to the formation of larger amount of PdO dispersed on their surface during oxygen-pretreatment in H₂-TPR experiments (Pd/PdO atomic ratio was 1/4) and under methane-oxidation mixture in comparison with ex-chloride catalysts (Pd/PdO?=?4/1). The palladium addition to manganese-hexaaluminate changes strongly its redox properties, as result Mn³⁺ reduction to Mn²⁺ take place about 100?°C below that of pure hexaalunimate. The latter indicate probably on the higher oxygen mobility in Pd-modified manganese-hexaaluminate. A higher PdO/Pd ratio formed in the ex-nitrate and ex-acetate Pd-modified manganese-hexaaluminate catalysts together with the high oxygen mobility provide the synergetic effect in methane oxidation activity at light-off temperature region. The high catalytic activity of manganese-hexaaluminate ensures methane combustion efficiency of the Pd-modified manganese-hexaaluminate catalysts at temperature above 700?°C.     

Catalytic Pd–Ag nanoparticles immobilized on fiber glass by surface self-propagating thermal synthesis

Pd–Ag nanoparticles with different Pd/Ag ratio were deposited onto fiber glass by using the technique of surface self-propagating thermal synthesis (SSTS) and characterized by X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (ААS), and EXAFS spectroscopy. The samples reduced in hydrogen exhibited the formation of Pd–Ag alloy whose tentative structure and composition were suggested. Thermally scheduled reduction of Pd–Ag catalysts in hydrogen made the Ag atoms partially oxidized. Reported are the catalytic properties of synthesized Pd–Ag samples in selective hydrogenation of acetylene.     

硫化处理对负载钯催化剂甲烷低温催化燃烧性能的影响

采用浸渍法制备氧化硅负载钯催化剂,考察硫化气氛和硫化时间对催化剂性能的影响,并采用XRD对催化剂进行表征。结果表明,硫化后形成的Pd4S物种可以提高催化剂抗硫中毒性能,同时催化剂表面的SPd4S/SPd对催化活性有重要影响,改变硫化气氛和硫化时间可以调节Pd4S物种的形成和SPd4S/SPd。     

Structural change of palladium particles supported on cerium oxide in catalytic methanol synthesis

Ultrafine palladium particles supported on cerium oxide by the coprecipitation method effectively catalyzes the methanol synthesis from carbon monoxide and hydrogen, while the catalytic activity increases in the initial stage. The Pd K-edge EXAFS (extended X-ray absorption fine structure) of the catalyst shows that a small part of palladium is still oxidized after the pretreatment with hydrogen at 573 K for 1 h. During the reaction the palladium particles in the catalyst are further oxidized due to the formation of Pd–O–Ce bonding which may stabilize the cationic palladium species being active to the reaction.     

钯负载锰氧化物基双金属复合氧化物催化氧化羰基化合成碳酸二苯酯

采用共沉淀法分别制备锰掺杂钨、钒、铋3种双金属复合氧化物载体,以氯化钯为活性组分制备负载型催化剂,并用于苯酚氧化羰基化合成碳酸二苯酯（DPC）。通过气相色谱（GC）、X射线衍射（XRD）、氢气程序升温还原（H₂-TPR）、X射线光电子能谱（XPS）等表征手段,对催化剂结构和性能进行表征。结果表明:钨-锰载体随掺杂比例和焙烧温度升高,逐步形成四氧化三锰晶粒,同时钨渗入锰氧化物晶格中,在掺杂比（物质的量比）为1:1、焙烧温度为600 ℃条件下制备的催化剂性能最佳,DPC收率为5.20%;钒-锰载体在焙烧温度为400 ℃、掺杂比为1:5条件下形成二氧化锰晶相,催化剂性能明显提高,DPC收率为10.46%,而较高的焙烧温度会破坏晶型的完整;铋-锰载体在掺杂比为1:5、焙烧温度为400 ℃条件下制备的催化剂催化效果最好,DPC单程收率可达到13.13%。     

Support effect on complete oxidation of volatile organic compounds over Ru catalysts

Catalytic combustion of ethyl acetate, acetaldehyde, and toluene was investigated on various supported Ru catalysts prepared by the impregnation method, and the effect of reduction treatment on the activity was examined. Among the as-calcined catalysts tested, Ru/CeO₂ showed the highest activity for all tests regardless of the pre-treatment in hydrogen atmosphere. The catalytic activity of Ru/SnO₂ was significantly degraded by the reduction treatment, whereas the activity of Ru/ZrO₂ and Ru/γ-Al₂O₃ was enhanced. To reveal these phenomena, the as-calcined and reduced catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transmission electron microscopy (TEM), and BET surface area. The dispersion of ruthenium on the supports was evaluated by chemisorption methods of carbon monoxide. The catalytic activity was strongly related to ruthenium species easily oxidizable and reducible at low temperatures. Such ruthenium species were loaded on CeO₂ in a highly dispersed state, resulting in the highest activity.     

氮掺杂对TiO_2催化剂吸附性能及光催化性能的影响

以低浓度碱溶剂热法制备钛酸纳米纤维,利用二次水热法掺杂氮元素制得N-Ti O2催化剂;采用X射线衍射和扫描电子显微镜对制备的催化剂进行表征。以亚甲基蓝溶液模拟有机废水,考察氮掺杂量对催化剂吸附性能和光催化性能的影响,揭示吸附性和光催化性能的内在联系。结果表明,掺杂氮元素未改变Ti O2的晶型,但能改变Ti O2晶体尺寸,对其形貌有一定影响,同时显著提高N-Ti O2催化剂的吸附性能和催化活性。氮掺杂量越高,晶粒尺寸越小,比表面积越大,吸附和光催化性能越好。在n(N)∶n(Ti)=1∶1时,Ti O2光催化活性和吸附性能最佳。     

钯/铁铬铝烧结毡整体催化剂表征及 对甲苯催化性能研究

采用新型的化学镀技术在铁铬铝（FeCrAl）烧结毡上直接负载贵金属钯（Pd）,制备了不同钯负载量的无过渡涂层的钯基整体式燃烧催化剂。首先对该类催化剂进行扫描电镜（SEM）、能谱（EDS）和X射线衍射（XRD）表征分析,结果表明：采用化学镀技术,钯组分能够很好地在铁铬铝烧结毡基体表面富集,催化剂的活性中心主要以金属钯晶相形式存在;而且在钯负载量为0.3%（质量分数）时,钯组分以0.3~0.5 μm的规整球状颗粒恰好在基体表面均匀分散并覆盖完全。同时该类催化剂在甲苯催化净化反应中表现出很好的低温催化性能,可使甲苯在190 ℃起燃后,在220 ℃就迅速达到100%完全转化,而且催化剂也显示出良好的催化稳定性。     

Investigation of palladium interaction with cerium oxide and its state in catalysts for low-temperature CO oxidation

Palladium catalysts supported on nanosized CeO₂ supports were synthesized by different methods. The catalysts showed high low-temperature activity (LTA) in CO oxidation. The synthesized palladium–ceria catalysts for low-temperature CO oxidation were investigated by a complex of physicochemical methods, and their catalytic performance was determined in the light-off regime. It was shown using high-resolution transmission electron microscopy (HRTEM) and EDX microanalysis that the catalysts with high LTA are characterized by exceptionally high dispersity of palladium on the surface of the supports. Two different states of palladium were observed by XPS. They correspond to the surface interaction phases (SIPs) as Pd_xCeO_2−δ and small metal clusters (<10 Å). According to diffraction images obtained by HRTEM, the latter have flattened shape due to epitaxial binding between (1 1 1) facets of palladium and CeO₂. Two types of CO adsorption sites (Pd²⁺ and Pd⁰) were distinguished by FTIR. They can be attributed to SIP (Pd²⁺) and palladium in flat metal clusters (Pd^δ+ and Pd⁰). The drop of LTA in CO oxidation is related to the loss of the palladium chemical interaction with the surface of the support and palladium sintering to form PdO nanoparticles. The formation of PdO particles is stimulated by crystallization of CeO₂ particle surface due to the calcination of support at temperatures above 600 °C. The XPS, HRTEM and FTIR data give reliable evidence that PdO particles are not responsible for LTA in CO oxidation.In this work, the structure of the active sites consisting of two phases: atomically dispersed palladium within the SIP and palladium metal nanoclusters is proposed. The catalyst pretreatment in hydrogen was found to improve significantly its catalytic (LTA) properties. The effect of the hydrogen pretreatment was supposed to be related to the formation of hydroxyl groups and their effect on the electronic and geometrical state of the surface active sites and their possible direct participation in CO oxidation.     

碱土金属醇类低共熔溶剂强化钒磷氧催化剂的制备及催化性能研究

钒磷氧(VPO)催化剂是目前实现正丁烷选择性氧化的唯一工业催化剂。利用金属助剂掺杂以及有机助剂强化是提高VPO催化剂性能的有效手段。本工作通过加入氯化镁醇类金属低共熔溶剂,实现了有机-金属助剂同时对VPO催化剂性能的调控。利用扫描电子显微镜(SEM)、BET全自动比表面与孔隙度分析仪(BET)、X射线衍射仪(XRD)和X射线光电子能谱仪(XPS)等表征手段,深入探讨了合成过程中加入不同氢键供体乙二醇(EG)、1-4丁二醇(BDO)和甘油(GL)的低共熔溶剂对VPO催化剂微观形貌、比表面积、物相、表面性质和晶相转变温度的影响,同时利用固定床反应器对VPO催化剂催化正丁烷氧化制备顺酐的性能进行了评价。结果表明,氯化镁乙二醇低共熔溶剂调控制备的VPO催化剂具有分散性良好、比表面积大、活性面(020)的数量多、表面P原子富集和表面V平均价态低等特点,在丁烷氧化选择性制顺酐反应中表现出了良好的催化性能,为VPO催化剂的制备提供了新思路。     

Fischer-Tropsch synthesis: characterization and catalytic properties of rhenium promoted cobalt alumina catalysts☆

The unpromoted and promoted Fischer-Tropsch synthesis (FTS) catalysts were characterized using techniques such as X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray absorption spectroscopy (XAS), Brunauer-Emmett-Teller surface area (BET SA), hydrogen chemisorption and catalytic activity using a continuously stirred tank reactor (CSTR). The addition of small amounts of rhenium to a 15% Co/Al₂O₃ catalyst decreased the reduction temperature of cobalt oxide but the percent dispersion and cluster size, based on the amount of reduced cobalt, did not change significantly. Samples of the catalyst were withdrawn at increasing time-on-stream from the reactor along with the wax and cooled to become embedded in the solid wax for XAS investigation. Extended X-ray absorption fine structure (EXAFS) data indicate significant cluster growth with time-on-stream suggesting a sintering process as a major source of the deactivation. Addition of rhenium increased the synthesis gas conversion, based on catalyst weight, but turnover frequencies calculated using sites from hydrogen adsorption and initial activity were similar. A wide range of synthesis gas conversion has been obtained by varying the space velocities over the catalysts.     

Heterogeneous hydrogenation of nitrobenzenes over recyclable Pd(0) nanoparticle catalysts stabilized by polyphenol-grafted collagen fibers

A novel heterogeneous palladium (Pd) nanoparticle catalyst stabilized by collagen fibers (CF) was synthesized. Epigallocatechin-3-gallate (EGCG), a typical natural polyphenol, was grafted onto the CF surface to improve the stabilization and immobilization of Pd(0) nanoparticles. The main physical and chemical properties of the catalyst were characterized by means of Scanning Electron Microscopy, Fourier Transform-Infrared Spectroscopy, X-ray Photoelectron Spectroscopy, X-ray Diffraction and Transmission Electron Microscopy. This catalyst is in an ordered fibrous state with high flexibility. The Pd(0) nanoparticles with diameters of 3–4 nm are homogeneously dispersed onto the outer surfaces of CF, and they are stabilized by the coordinative interactions between the surface Pd atoms of nanoparticle and the surrounding oxygen and nitrogen atoms of the EGCG-grafted CF. These stabilized Pd(0) nanoparticles were found to be active and selective catalysts for nitrobenzene and its derivatives, directly hydrogenating to the correspondingly reductive anilines under mild conditions. Both Pd particle size and activity of the catalyst showed a marked dependence on the grafting degree of EGCG on CF. These catalysts can be easily recovered, reused multiple times, and stored for two months in air while maintaining high catalytic efficiencies. All these facts suggest that the EGCG-grafted CF can be used as an effective stabilizer for the preparation of Pd(0) nanoparticle catalysts.     

A study of the palladium size effect on the direct synthesis of hydrogen peroxide from hydrogen and oxygen using highly uniform palladium nanoparticles supported on carbon

Highly monodisperse carbon-supported palladium nanoparticles with controllable size (3 nm, 6.5 nm, 9.5 nm) were prepared using a simple colloidal method, and the size dependence of the catalytic performance for the direct synthesis of hydrogen peroxide from hydrogen and oxygen was studied. Smaller-sized supported palladium nanoparticles showed both higher conversion of hydrogen and selectivity for hydrogen peroxide, compared to larger-sized supported particles. Among the catalysts tested, 3-nm Pd nanoparticles supported on carbon showed the highest yield for hydrogen peroxide because of the small size and high crystallinity.     

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。     

Study of Methane Decomposition on Fe/MgO-Based Catalyst Modified by Ni,Co, and Mn Additives

Catalytic decomposition of methane (CDM) generates clean hydrogen and carbon nanomaterials. In this study, methane decomposition to hydrogen and carbon was investigated over Ni-, Co-, or Mn-doped Fe/MgO catalysts. The doping effect of different metals, varying from 3 to 10?wt%, was investigated. The catalytic performance of the obtained materials (noted 15%Fe+x%metal/MgO) revealed that the doping effect of Ni, Co, and Mn significantly improved the activity of Fe/MgO. Among the Ni-doped catalyst series, the 15%Fe+3%Ni/MgO catalyst performed better than the rest of the Ni catalysts. The 6%Co-containing catalyst remained the best in terms of activity in the Co-doped catalyst series and the 15%Fe+6%Mn/MgO solid showed better methane conversion for the Mn-doped series. Overall, 3%Ni-containing catalyst displayed the best catalytic performance among all Ni-, Co-, and Mn-doped catalysts. XRD, N₂ sorption, and H₂ temperature-programmed reduction (TPR), Laser–Raman spectroscopy, thermogravimetric analysis (TGA) under air, and temperature-programmed oxidation (TPO) were used for catalyst characterization. The results revealed that all the doped catalysts exhibited better metallic active site distribution than 15%Fe/MgO and proved that metal doping played a crucial role in catalytic performance.