Effect of the oxidation state of gold on the complete oxidation of isobutane on Au/CeO2 catalysts

Catalysts of highly dispersed gold supported on ceria were prepared by deposition precipitation method. Au is dispersed as Au⁰, Au⁺ and Au³⁺ species on ceria. The content of Au⁺ and Au³⁺ was highest on catalyst prepared on uncalcined ceria, which possess least ordered surface. It is inferred that oxygen vacancy on disordered ceria surface is essential for the preparation of highly dispersed gold catalysts and in stabilizing monolayer surface Au⁺ clusters while cationic vacancies are sites for substitutional Au³⁺. Au/CeO₂ catalysts showed low-temperature isobutane oxidation activity with maximum conversion at 150–180°C. Ex-situ XPS results demonstrated that the low temperature isobutane oxidation activity was closely related to the content of Au⁺ which we interpreted as surface gold oxide formed under reaction conditions. Isobutane oxidation activity associated with ceria at temperature above 300°C was enhanced by substitutional Au³⁺.     

喷雾干燥法制备碳载铂钴镍合金催化剂及其甲醇催化氧化性能研究

本文以氯铂酸、氯化镍和硝酸钴为原料,XC-72炭黑为载体,通过雾化干燥法结合煅烧还原制备碳载铂基（PtCo Ni）分散性好的多元合金纳米粒子催化剂。重点研究表面经过改性的炭黑对合金纳米粒子形成和分散的影响规律,研究碳载PtCoNi（原子比为1:1:1）合金纳米粒子的甲醇催化氧化活性、抗CO中毒能力和耐久性,以及不同原子比对催化氧化甲醇活性和抗CO中毒能力的影响规律。研究结果表明,采用表面改性后的炭黑作为载体,制备的碳载铂基（PtCoNi）催化剂为合金纳米粒子,且纳米粒子在炭黑表面分散均匀,粒径分布在1-4nm,平均粒径为2.3nm;与商用的Pt/C催化剂相比,PtCoNi/C（原子比为1:1:1）催化剂具有更高的甲醇催化氧化活性、耐久性和抗CO中毒性;不同原子比铂基多元催化剂在催化氧化甲醇活性上的顺序为：PtCoNi/C>Pt3CoNi/C>Pt5CoNi/C,抗CO中毒性顺序为：PtCoNi/C>Pt3CoNi/C>Pt5CoNi/C。     

CO Catalytic Oxidation of Pt-Loaded Perovskite BaTiO_3 Near Ferroelectric-Phase Transition Temperature

Perovskite BaTiO_3(BTO) nanocrystals with a size of 150–200 nm have successfully been synthesized via a facile hydrothermal method by employing titanate nanowires as synthetic precursor. Tetragonality and spontaneous ferroelectric polarization of BTO nanocrystals have been determined by X-ray diffraction and transmission electron microscopy investigations. BTO nanocrystals loaded with Pt nanoparticles in a size of 2–5 nm have been explored as a catalyst towards CO oxidation to CO_2. It is interesting to find that CO catalytic conversion rate over Pt-BTO nanocrystals gradually decreased and further increased near 100 °C when the catalytic temperature keeps increasing, whereas the conversion behavior in oxides is expected to be enhanced upon the catalytic temperature grows. Using differential scanning calorimetry and first-principle calculations, the observed catalytic behavior has been discussed on the basis of the ferroelectric polarization effect and the ferroelectric–paraelectric transition of BTO nanocrystals with a Curie temperature of ~110 °C. Below Curie temperature, CO catalytic oxidation could be significantly tailored by ferroelectric polarization of BTO nanocrystals via a promoted dissociation of O_2 molecules. The findings suggest that a ferroelectric polarization in perovskite oxides could be an alternative way to modify the CO catalytic oxidation.     

Catalysis by Gold Nanoparticles

Gold catalysts have superior activity in CO and other oxidations at low temperatures. Both a small (~ 5nm) particle size and the presence of a partly reducible oxide (ceria or a transition metal oxide) have a beneficial effect on the catalyst performance. The present paper reviews our recent studies focused on understanding the specific role of the Au particle size and that of the oxide (MO). Our personal viewpoint on gold catalysis is outlined. The effects of Au particle size and of the oxidic additive are distinguished by using several alumina-supported gold catalysts having different gold particle sizes and various oxidic additives. The most active catalyst in CO oxidation is the multicomponent catalyst Au/MgO/MnOx/Al2O3 with MgO being a stabilizer for the Au particle size and MnOx being the cocatalyst. This catalyst also exhibits good performance in selective oxidation of CO in a hydrogen atmosphere, a reaction relevant for the development of polymer electrolyte fuel cell technology.     

Reducibility of ceria–lanthana mixed oxides under temperature programmed hydrogen and inert gas flow conditions

The present paper deals with the preparation and characterization of La/Ce mixed oxides, with La molar contents of 20, 36 and 57%. We carry out the study of the structural, textural and redox properties of the mixed oxides, comparing our results with those for pure ceria. For this aim we use temperature programmed reduction (TPR), temperature programmed desorption (TPD), nitrogen physisorption at 77 K, X-ray diffraction and high resolution electron microscopy. The mixed oxides are more easy to reduce in a flow of hydrogen than ceria. Moreover, in an inert gas flow they release oxygen in higher amounts and at lower temperatures than pure CeO₂. The textural stability of the mixed oxides is also improved by incorporation of lanthana. All these properties make the ceria–lanthana mixed oxides interesting alternative candidates to substitute ceria in three-way catalyst formulations.     

NiAl(Si)+CeO_2型高温涂层氧化行为的研究

采用复合技术制备了含弥散CeO_2的NiAl(Si)型高温涂层,并同几种铝化物涂层的氧化行为进行了对比研究,重点考察了CeO_2及Si在改善涂层抗氧化性能方面各自的作用及其相互关系。涂层组织及成分分析表明,少量Si固溶于β-NiAl相中,大部分Si以第二相的形式主要弥散分布于涂层的内侧,且合金渗Al-Si涂层中的Si含量明显高于同类复合NiAl(Sj)+CeO_2涂层。氧化实验表明,Si及CeO_2可有效地降低涂层1100℃的氧化速率。Si对涂层抗循环氧化性能的改善作用不显著,而CeO_2则具有益作用,特     

BaO对单Pd催化剂净化甲醇燃料车尾气性能的影响

利用FIB/SEM切片、XRD、TEM和EDX、EELS等先进分析技术对微球模板法所制备的Au/Ag泡沫材料的微观结构、形貌、成分及成分分布等进行了细致的研究.结果表明:由微球状Au/Ag球壳堆积而成的泡沫材料中微球直径约8 μm,微球壁厚200～1200 nm; Au/Ag泡沫材料的球壳可细分为3层,内层和外层为Au/Ag合金的微粒,中间主要是非晶碳层,夹杂有少量的Au/Ag微粒;Au/Ag泡沫材料的骨架由单个空心球壳组成,球壳之间通过接触点的金属镀层连接在一起;球壳上有小孔状结构,是在热分解法去除聚苯乙烯微球模板对形成的;球壳壁厚分布不均匀,少数球壳有塌陷、变形、破裂等现象.这些详细的分析有助于改进工艺,提高Au/Ag泡沫材料的制备质量.     

PtPb/ C 催化剂的制备及其对甲酸电氧化的催化性能

目的通过Pb元素的添加来提高Pt/C催化剂电催化氧化甲酸的性能。方法通过乙二醇协助硼氢化钠还原法,以氯铂酸为Pt源和硝酸铅为Pb源制备不同原子比的PtxPb/C催化剂。采用X射线衍射光谱法(XRD)和透射电子显微镜技术(TEM)表征样品的晶体结构和颗粒形貌;采用循环伏安法表征样品催化氧化甲酸的性能。结果利用乙二醇协助硼氢化钠还原法成功制得了Pt和Pb原子比不同的PtxPb/C催化剂,XRD和TEM测试结果表明这些样品均为Pt的面心立方结构,且颗粒大小均一、分散均匀,其平均粒径为4 nm左右。循环伏安测试结果表明PtxPb/C催化剂催化氧化甲酸的性能优于商业Pt/C催化剂的催化性能,且受Pt和Pb原子比的影响,当原子比为5∶1时,其对氧化甲酸的催化性能最好,峰电位对应的Pt的比质量活性达到2000 m A/(mg Pt),远远高于商业Pt/C,同时计时电流曲线表明其具备良好的稳定性。结论 Pb原子的加入影响了Pt原子的电子结构,与Pb对Pt的协同作用共同促进了CO等中间产物在Pt表面的快速氧化,降低了催化氧化甲酸的初始电位,促使甲酸在低电位直接氧化为CO2和H2O,提高了其催化氧化甲酸的峰电流,有效减轻了Pt中毒,提高了其催化活性。     

Studies on the electrocatalytic properties of PtRu/C-TiO2 toward the oxidation of methanol

PtRu/C-TiO₂ catalysts were prepared by hydrolysis of Ti(OBu)₄ on commercial PtRu/C. The catalyst was characterized by XRD, TEM, and XPS. The electrochemical performance of catalysts was testified by cyclic voltammetry (CV) and chronoamperometry (CA) in 0.5 M C₂H₅OH + 0.5 M H₂SO₄ solution. The results showed that the added TiO₂ can improve the electrocatalytic properties of the catalyst toward methanol oxidation. The mechanism for the effects of TiO₂ on catalytic activity of PtRu/C to methanol oxidation is also discussed.     

pH值对CeO2/SiO2纳米复合磨粒分散性的影响

以胶体SiO₂溶液作硅源,采用均相沉淀工艺制备壳-核结构完整的CeO₂/SiO₂纳米复合磨粒。采用X射线衍射仪和透射电子显微镜对复合磨粒样品进行物相组成分析和微观形貌观察;通过粒径分布、Zeta电位分析,研究水相分散系中pH值对CeO₂/SiO₂复合磨粒分散性的影响。结果表明:所制备的CeO₂/SiO₂复合磨粒为壳-核包覆结构完整的纳米微球,粒径约110 nm,内核为无定形SiO₂,壳层为立方萤石型CeO₂;CeO₂/SiO₂复合磨粒的等电位点pH值约为5,其值由SiO₂等电位点向CeO₂等电位点明显偏移。CeO₂/SiO₂复合磨粒在酸性水相介质中分散性差,容易出现严重的团聚现象;而在碱性环境下,CeO₂/SiO₂复合磨粒分散性良好。      

Catalytic properties of metallic fibers fabricated by tempering of melt on a rotating heat-receiver

Metallic fibers fabricated by the method of directly suspended melt-droplet extraction are promising for application in catalysis as carriers of catalytically active compounds and as catalytic systems themselves due to their physicochemical properties, structure, surface defects, and low hydrodynamic resistance of porous permeable materials formed from them. The catalytic activity of fibers based on copper, nickel, iron, aluminum, and titanium, also containing noble, transition, refractory, and rare-earth metals, in the reaction of CO oxidation has been estimated. Among the studied samples, fibers based on copper, copper–nickel alloy, and Nichrome with addition of noble metals have been found promising to perform further studies for their application as catalysts of oxidation–reduction reactions.     

稀土在直接甲醇燃料电池铂基催化剂中的应用及研究进展

直接甲醇燃料电池(DMFC)以其高效、低污染的特点而备受关注。铂基电催化剂被认为是DMFC阳极的有效催化剂。但由于在甲醇氧化过程中铂的活性中心容易被产生的中间产物如CO等吸附和堵塞,导致催化活性降低,稳定性差,严重制约了直接甲醇燃料电池推广应用。稀土元素由于其4f轨道独特的电子结构和相应的镧系收缩效应,在铂基电催化剂中可有效提高铂催化剂的活性和耐久性。本文简要总结近年来稀土氧化物作为铂基电催化剂的助催化剂、碳材料掺杂改性剂和载体在甲醇氧化反应中的催化活性和抗CO中毒能力应用研究,以及铂-稀土金属(Pt-RE)纳米合金催化剂对DMFC长期运行稳定性的影响;并对稀土元素在铂基电催化剂中的应用发展提出了展望。     

光/电催化剂的表面调控在苯甲醇绿色氧化中的应用

综述了近年来国内外关于高效光/电催化剂在水分解制氢耦合苯甲醇绿色氧化中的相关研究进展,重点阐述了构筑不同形貌、表面缺陷工程和掺杂改性的催化剂对促进苯甲醇氧化的作用机制,并对催化剂的合成方法、光/电化学性能、反应机制进行了详细概括。在光催化领域,介绍了抑制催化剂表面光生电子和空穴的复合、调控活化活性位点等方法。在电催化领域,介绍了催化剂活性位的筛选、导电性和本征活性提升的有效策略以及将电催化与膜分离相结合的一体化技术,并构建了双功能催化剂,实现高效、低能耗产生H2的同时,能选择性地将BA氧化。最后提出了该领域未来需要面对的挑战和机遇,从不同的角度和方面综合分析,为进一步提升水分解制氢耦合绿色合成高附加值有机化学品的光/电催化剂提供理论指导。     

Recent advance in single-atom catalysis

Single-atom catalysts(SACS) have obtained a great deal of attention in many catalytic fields due to the high atom utilization efficiency and high catalytic activity.Recently,great achievements on S ACs have been made for thermocatalysis,electrocatalysis,and photocatalysis which play an important role in obtaining value-added products.However,it remains a great challenge to fabricate S ACs with high metal loading and investigate their reaction mechanisms.Therefore,it is necessary to highlight the recent development of S ACs in these fields to guide future research.In this review,we overviewed the thermocatalysis applications of SACs in CO oxidation,preferential oxidation of CO,water-gas shift reaction,methane conversion,methanol steam reforming,aqueous-phase reforming of methanol,hydrogenation of alkynes and dienes,hydrogenation of CO,and hydrogenation of substituted nitroarenes.Moreover,the oxygen reduction reaction(ORR),hydrogen evolution reaction(HER),oxygen evolution reaction(OER),CO_2 reduction reaction(CO_2 RR),and N_2 reduction reaction(N_2 RR) for photocatalytic and electrocatalytic fields were also overviewed.Lastly,the opportunities and challenges of SACs were pointed out.     

New gold and silver-gold catalysts in the shape of sponges and sieves

Gold with a nanoporous sponge-like morphology, generated by leaching of AuAg alloys is presented as a new unsupported material system for catalytic applications. The role of residual silver for catalytic activity towards CO oxidation in the temperature range from −20 to 50°C has been investigated by comparison with Au and Au/Ag zeolite catalysts. As revealed by a systematic variation of the silver content in the zeolite catalysts, bimetallic systems exhibit a significantly higher activity than pure gold, probably due to activation/dissociation of molecular oxygen by silver. By STEM tomography we can unambiguously prove that at least some of the particles form inside the zeolite lattice.     

Enhanced Thermochemical H_2 Production on Ca-Doped Lanthanum Manganite Perovskites Through Optimizing the Dopant Level and Re-oxidation Temperature

Perovskite material is one of the promising classes of redox catalysts for hydrogen production through two-step thermochemical H20 splitting. Herein, an analogue of La_(1-x)Ca_xMnO_3 perovskite was systematically investigated as a catalyst for thermochemical H2 evolution. The Ca doping level(x = 0.2, 0.4, 0.6, 0.8) and re-oxidation temperature were comprehensively optimized for the improvement of catalytic performance. According to our experimental results, La_(0.6)-Ca_(0.4)MnO_3 perovskite displayed the highest yield of H2 at the re-oxidation temperature of 900℃ and the obtained H2 production was-10 times higher than that of the benchmark ceria catalyst under the same experimental condition. More importantly, La_(0.6)Ca_(0.4)MnO_3 perovskite catalyst exhibited impressive cyclic stability in repetitive O_2 and H_2 test.     

Electrocatalytic oxidation of methanol on carbon-nanotubes/graphite electrode modified with platinum and molybdenum oxide nanoparticles

Electrochemical codeposition and electrocatalytic properties of platinum and molybdenum oxide nanoparticles(Pt-MoOx) on carbon-nanotubes/graphite electrode for methanol oxidation were investigated.The micrograph and elemental composition of the resulting Pt-MoOx/CNTs/graphite electrode were characterized by scanning electron microscopy(SEM)and energy dispersive X-ray spectroscopy(EDS).The results show that the Pt-MoOx particles with the average size of about 50 nm are highly dispersed on the CNTs surface.The Pt-MoOx/CNTs/graphite electrode delivers excellent electrocatalytic properties for methanol oxidation.The highest mass activity(Am)reaches 264.8 A/g at the loading mass of 159.3μg/cm2.This may be attributed to the small particle size and high dispersion of Pt-MoOx catalysts deposited on the CNTs surface.The kinetic analysis from electrochemical impedance spectroscopy(EIS)reveals that the existed MoOx phase can improve the chemisorptive and catalytic properties for methanol oxidation.     

Hydrodesulfurization cobalt-based catalysts modified by gold

Cobalt catalysts supported on amorphous SiO2 and ordered mesoporous silica (MCM-41) were prepared by incipient wetness impregnation. Gold was added by consecutive impregnation or by co-impregnation. The materials were characterised by XPS, XRD and TPR techniques and evaluated in the hydrodesulfurization (HDS) of thiophene in order to investigate the effect of the noble metal on the structure and on the catalytic behaviour of the supported cobalt. Co/MCM-41 exhibited higher HDS activity and higher stability than the Co/SiO2. Moreover, in contrast to silica case, the gold impregnated MCM-41, produced an enhancement of the cobalt catalytic activity, and this is likely to be related to an increased cobalt reducibility. Both the support and the addition of gold improve the cobalt dispersion.     

On the use of the micromarker technique for studying the growth mechanism of thin oxide films

The high temperature behavior of microscopic markers, deposited on to pure and ceria-coated nickel, was tested. The markers, having a form of 20-nm-thick palladium bumps with a fractional surface coverage of 0.05 and 30-nm thick gold bumps with a surface coverage of 0.25, apparently interfered with the oxide growth, increasing the oxidation rate on their surface at 973 K over one order of magnitude. As detected by a combination of Auger electron spectroscopy and Rutherford backscattering spectrometry, for ceria modified nickel, the markers’ depth-position coincided with the ceria particles dispersed in the vicinity of the oxide–gas interface. For pure nickel oxide films, the markers were easily incorporated into the growing oxide during very early stages of oxidation and were difficult to detect at the oxide–metal interface. It is proposed that the catalytic behavior of the markers was caused by their fragmentation into a large number of islands, leading to the refinement of the oxide grains, which in turn accelerated the substrate oxidation rate. Some precautions necessary in conducting the marker experiments are defined.     

Ultra-stable metal nano-catalyst synthesis strategy:a perspective

Supported metal nanoparticles(NPs) as an important heterogeneous catalyst have been widely applied in various industrial processes.During the catalytic reaction,size of the particles plays an important role in determining their catalytic performance.Generally,the small particles exhibit superior catalytic activity in comparison with the larger particles because of an increase in lowcoordinated metal atoms on the particle surface that work as active sites,such as edges and corner atoms.However,these small NPs are typically unstable and tend to migrate and coalescence to reduce their surface free energy during the real catalytic processes,particularly in high-temperature reactions.Therefore,a means to fabricate stable small metal NP catalysts with excellent sinter-resistant performance is necessary for maintaining their high catalytic activity.In this study,we have summarized recent advances in stabilizing metal NPs from two aspects including thermodynamic and kinetic strategies.The former mainly involve preparing uniform NPs(with an identical size and homogeneous distribution) in order to restrain Ostwald ripening to achieve stability,while the latter primarily involves fixing metal NPs in some special confinement materials(e.g.,zeolites,mesoporous silica and mesoporous carbons),encapsulating NPs using an oxide-coating film(e.g.,forming core-shell structures),or constructing strong metal-support interactions to improve stability.At the end of this review,we highlight our recent work on the preparation of high-stability metal catalysts via a unique interfacial plasma electrolytic oxidation technology,that is,metal NPs are well embedded in a porous MgO layer that has both high thermal stability and excellent catalytic activity.