过渡金属基材料的可控制备及其电催化醇类氧化研究

氢能作为一种来源丰富、绿色、应用广泛的二次能源,可实现化学能与电能的相互转换,是实现多领域深度清洁脱碳的重要路径,将成为能源转型发展中不可或缺的载体。电解水制氢技术因反应高效、简单易控、无污染等特点而成为研究热点。然而,阳极析氧反应(OER)所需过电位高,反应动力学迟缓,严重制约了电解水制氢的整体效率,因此,使用更易氧化的有机小分子作为阳极添加剂辅助水分解制氢,如电催化醇氧化,不仅可以显著降低水分解制氢的过电势,还能合成绿色高附加值产品。基于此,结合本课题组的研究工作,综述了近年来国内外关于醇类氧化辅助水分解制氢的研究进展,重点探讨了过渡金属催化醇类氧化的反应机理及反应性能、产物选择性和构效关系,并对醇类氧化辅助水分解制氢催化剂所面临的挑战和发展进行展望,旨在为高效的醇类电化学氧化辅助水分解制氢催化剂的合理设计提供指导思想。

金属有机骨架封装的硅钼钒多酸催化苯乙醇选择氧化

以三种SiMoV_n@rht-MOF-1(n=1,2,3)多酸基金属有机骨架为催化剂,催化苯乙醇氧化。通过对反应试剂和反应条件优化,配合物3在催化苯乙醇氧化的过程中显示出优异的催化性能,对苯乙酮的选择性高达99%。进一步对底物拓展发现,该配合物对多种不同类型的醇底物均具有高的催化选择氧化性能。为了验证自由基反应的机理,通过2,2,6,6-四甲基哌啶-氮-氧化物(2,2,6,6-tetramethylpiperidine-1-oxyl,TEMPO)对反应自由基进行了捕获,证明了自由基的存在。进一步通过电子顺磁共振(Electron paramagnetic resonance,EPR)光谱捕获到了t-BuO·自由基,验证了SiMoV@rht-MOF-1催化醇氧化自由基机理。

醇类选择性催化氧化的研究进展

醇类选择性氧化制备相应羰基(醛或酮)化合物是有机合成中的重要反应。综述醇类选择性催化氧化的研究现状,主要有液均相氧化、液多相氧化和水/有机两相催化氧化,对所用催化剂发展状况和反应机理分别进行阐述。均相催化氧化催化剂难于从反应体系分离,造成成本过高,而且污染环境。大部分多相催化剂来自均相催化剂的负载,活性中心分布不均匀,结构不明确,存在活性组分易从载体上脱落和流失的现象,导致催化剂活性下降。以水作溶剂,不仅清洁无污染,且产物和催化剂容易分离,催化剂可以循环使用,从经济和环保角度值得大力推广,但该体系价格昂贵,反应条件不够温和,还需进一步改进。因此,多相催化氧化和水/有机两相催化氧化相对于均相催化剂有更广阔的发展和应用空间,是今后的研究方向。

光照及需氧条件下Al_2O_3-AlBr_x催化醇的选择性氧化反应

以脱脂棉为模板制备了多孔管状结构的Al2O3材料,用不同浓度的氢溴酸对多孔管状结构的Al2O3材料进行化学剪裁,制备了活性量可控,比表面积可调,不同形貌的负载型催化剂Al2O3-AlBr x。采用电场发射扫描电镜(SEM)和X射线衍射仪(XRD)对催化剂进行了表征。结果表明,该催化剂较好地复制了棉纤维的宏观和微观结构,呈现出明显的生物形貌特征。在光照条件下以空气为氧化剂的醇的选择性氧化反应中,发现催化剂Al2O3-AlBr x-3可以高选择性地将醇氧化为相应的醛、酮或酸,并对反应机理进行了探讨。该催化剂循环使用3次仍保持较高的催化活性。

醇的催化氧化的研究进展

概述了醇的催化氧化的研究进展,从金属催化剂、非金属催化剂对其进行了综述,并对今后醇氧化体系进行了展望。

用于催化剂载体的羟基磷灰石的合成研究

本文以氯化钙和磷酸氢二钠为原料,在40℃的温度下合成了具有六方晶系的羟基磷灰石。此法合成的羟基磷灰石可用作由分子氧氧化一些醇类进行有机合成的催化剂载体。

Effect of pore size in mesoporous MnO_2 prepared by KIT-6 aged at different temperatures on ethanol catalytic oxidation

KIT‐6 mesoporous silica aged at 40,100,and 150°C were used as hard templates to prepare different mesoporous MnO2 catalysts,marked as Mn‐40,Mn‐100,and Mn‐150,respectively.The catalytic activities of these catalysts and the effect of pore sizes on ethanol catalytic oxidation were investigated.Mn‐40,Mn‐100,and Mn‐150 have triple,double,and single pore systems,respectively.On decreasing the aging temperature of KIT‐6,the pore sizes of KIT‐6 decrease and that of mesoporous MnO2 catalysts increase.The pore sizes and catalytic activities increase in the order:Mn‐40>Mn‐100>Mn‐150.Mn‐40 catalyst has a higher TOF(0.11 s–1 at 120°C)and the best catalytic activity for ethanol oxidation because of a bigger pore size with three pore systems with maximum distribution at 1.9,3.4,and 6.6 nm,decrease in symmetry and degree of order,more surface lattice oxygen species,oxygen vacancies resulting from more Mn3+ions,and better low‐temperature reducibility.

Promoting effects of Fe_2O_3 to Pt electrocatalysts toward methanol oxidation reaction in alkaline electrolyte

Fe_2O_3 nanorods and hexagonal nanoplates were synthesized and used as the promoters for Pt electrocatalysts toward the methanol oxidation reaction（MOR） in an alkaline electrolyte.The catalysts were characterized by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy,cyclic voltammetry and chronoamperometry.The results show that the presence of Fe_2O_3 in the electrocatalysts can promote the kinetic processes of MOR on Pt,and this promoting effect is related to the morphology of the Fe_2O_3 promoter.The catalyst with Fe_2O_3 nanorods as the promoter（Pt-Fe_2O_3/C-R） exhibits much higher catalytic activity and stability than that with Fe_2O_3 nanoplates as the promoter（Pt-Fe_2O_3/C-P）.The mass activity and specific activity of Pt in a Pt-Fe_2O_3/C-R catalyst are 5.32 A/mgpt and 162.7 A/m^2_（Pt）,respectively,which are approximately 1.67 and 2.04 times those of the Pt-Fe_2O_3/C-P catalyst,and 4.19 and 6.16 times those of a commercial PtRu/C catalyst,respectively.Synergistic effects between Fe_2O_3 and Pt and the high content of Pt oxides in the catalysts are responsible for the improvement.These findings contribute not only to our understanding of the MOR mechanism but also to the development of advanced electrocatalysts with high catalytic properties for direct methanol fuel cells.

The effect of ethanol on the performance of CrO_x/SiO_2 catalysts during propane dehydrogenation

The effects of ethanol vapor pretreatment on the performance of CrOx/SiO2 catalysts during the dehydrogenation of propane to propylene were studied with and without the presence of CO2.The catalyst pretreated with ethanol vapor exhibited better catalytic activity than the pristine CrOx/SiO2,generating 41.4% propane conversion and 84.8% propylene selectivity.The various catalyst samples prepared were characterized by X-ray diffraction,transmission electron microscopy,temperature-programmed reduction,X-ray photoelectron spectroscopy and reflectance UV-Vis spectroscopy.The data show that coordinative Cr^3＋ species represent the active sites during the dehydrogenation of propane and that these species serve as precursors for the generation of Cr^3＋.Cr^3＋ is reduced during the reaction,leading to a decrease in catalytic activity.Following ethanol vapor pretreatment,the reduced CrOx in the catalyst is readily re-oxidized to Cr^6＋ by CO2.The pretreated catalyst thus exhibits high activity during the propane dehydrogenation reaction by maintaining the active Cr^3＋ states.

Carbon dioxide-expanded ethanol-assisted synthesis of carbon-based metal composites and their catalytic and electrochemical performance in lithium-ion batteries

Highly dispersed metals,metal oxides and their composites on substrates have received considerable interest in catalysis and lithium-ion batteries,because of their superior properties compared with their single-component counterparts.In this review,we introduce the properties of supercritical carbon dioxide（scCO2） expanded ethanol,such as low viscosity,near-zero surface tension and high diffusivity.We discuss the deposition procedure and formation mechanism of carbon-based composites in scCO2-expanded ethanol.This method has been used to fabricate several carbon-based composites,such as metal and metal oxide composites deposited on zero-dimensional colloidal carbon,one-dimensional carbon nanotubes,two-dimensional graphene,and three-dimensional hierarchical porous carbon.These materials and their performance as anodic materials for lithium-ion batteries will also be reviewed.

High-performance Pt catalysts supported on hierarchical nitrogen-doped carbon nanocages for methanol electrooxidation

Hierarchical nitrogen-doped carbon nanocages （hNCNC） with large specific surface areas were used as a catalyst support to immobilize Pt nanoparticles by a microwave-assisted polyol method. The Pt/hNCNC catalyst with 20 wt% loading has a homogeneous dispersion of Pt nanoparticles with the average size of 3.3 nm, which is smaller than 4.3 and 4.9 nm for the control catalysts with the same loading supported on hierarchical carbon nanocages （hCNC） and commercial Vulcan XC-72, respec- tively. Accordingly, Pt/hNCNC has a larger electrochemical surface area than Pt/hCNC and Pt/XC-72. The Pt/hNCNC catalyst exhibited excellent electrocatalytic activity and stability for methanol oxidation, which was better than the control catalysts. This was attributed to the en- hanced interaction between Pt and hNCNC due to nitrogen participation in the anchoring function. By making use of the unique advantages of the hNCNC support, a heavy Pt loading up to 60 wt% was prepared without serious agglomeration, which gave a high peak-current density per unit mass of catalyst of 95.6 mA/mg for achieving a high power density. These results showed the potential of the Pt/hNCNC catalyst for methanol oxidation and of the new hNCNC support for wide applications.

Selective hydrogenolysis of glycerol to 1,3-propanediol over Pt-W based catalysts

The selective hydrogenolysis of glycerol to 1,3-propanediol(1,3-PDO)is an attractive reaction due to the high demand for valorization of huge excess amounts of glycerol supply as well as the important application of 1,3-PDO in polyester industry.Nevertheless,the formation of 1,3-PDO is thermodynamically less favorable than 1,2-PDO,which necessitates the development of efficient catalysts to manipulate the reaction kinetics towards the 1,3-PDO formation.Among others,Pt-W based catalysts have shown promising activities and selectivities of 1,3-PDO although the reaction mechanism is not well addressed at the molecular level.In this short review,we have compared the performances of different Pt-W based catalysts and discussed the key factors influencing the activity and selectivity.Three possible reaction mechanisms have been discussed in terms of the synergy between Pt and WO_x and the origin of acid sites.Finally,the long-term stability of the Pt-W catalysts has been discussed.We hope this review will provide useful information for the development of more efficient catalysts for this important reaction.

Synthesis of Ni^2+cation modified TS-1 molecular sieve nanosheets as effective photocatalysts for alcohol oxidation and pollutant degradation

lmprovement of the charge separation of titanosilicate molecular sieves is critical to their use asphotocatalysts for oxidative organic transformations.In this work,MFI TS-1 molecular sievenanosheets(TS-1 NS)were synthesized by a low-temperature hydrothermal method using a tai-lored diquaternary ammonium surfactant as the structure-directing agent.Introducing Ni^2+cationsat the ion-exchange sites of the TS-1 NS framework significantly enhanced its photoactivity in aero-bic alcohol oxidation.The optimized Ni cation-functionalized TS-1 NS(Ni/TS-1 NS)provide impres-sive photoactivity,with a benzyl alcohol(BA)conversion of 78.9%and benzyl aldehyde(BAD)se-lectivity of 98.8%using O as the only oxidant under full light irradiation;this BAD yield is approx-imately six times greater than that obtained for bulk TS-1,and is maintained for five runs.The ex-cellent photoactivity of Ni/TS-1 NS is attributed to the significantly enlarged surface area of thetwo-dimensional morphology TS-1 NS,extra mesopores,and greatly improved charge separation.Compared with bulk TS-1,Ni/TS-1 NS has a much shorter charge transfer distance.Theas-introduced Ni species could capture the photoelectrons to further improve the charge separa-tion.This work opens the way to a class of highly selective,robust,and low-cost titanosilicate mo-lecular sieve-based photocatalysts with industrial potential for selective oxidative transformationsand pollutant degradation.

A palladium single-atom catalyst toward efficient activation of molecular oxygen for cinnamyl alcohol oxidation

Selective aerobic oxidation of alcohols under mild conditions is of great importance yet challenging,with the activation of molecular oxygen(O2)as a crucial capability of the catalysts.Herein,we demonstrate that an Al2O3-supported Pd single-atom catalyst leads to higher activity and selectivity compared to Pd nanoparticles for the oxidation of cinnamyl alcohol.The Al2O3 support used in this study is rich in coordinately unsaturated Al3+sites,which are apt for binding to Pd atoms through oxygen bridges and present a distinct metal-support interaction(MSI).The suitable MSI then leads to a unique electronic characteristic of the Pd single atoms,which can be confirmed via X-ray photoelectron spectroscopy,normalized X-ray absorption near-edge structure,and diffuse reflectance Fourier transform infrared spectroscopy.Moreover,this unique electronic state is proposed to be responsible for its high catalytic activity.With the help of in-situ UV-vis spectra and electron spin resonance spectra,a specific alcohol oxidation route with O2 activation mechanism is then identified.Active oxygen species behaving chemically like singlet-O2 are generated from the interaction of O2 with Pd1/Al2O3,and then oxidize the partially dehydrogenated intermediates produced by the adsorbed allylic alcohols and Pd atoms to the desired alkenyl aldehyde.This work provides a promising path for the design and development of high-activity catalysts for aerobic oxidation reactions.

Highly dispersed Cd cluster supported on TiO_(2) as an efficient catalyst for CO_(2) hydrogenation to methanol

The conversion of CO_(2) to methanol with high activity and high selectivity remains challenging owing to the kinetic and thermodynamic limitations associated with the low chemical reactivity exhibited by CO_(2).Herein,we report a novel Cd/TiO_(2) catalyst exhibiting a methanol selectivity of 81%,a CO_(2) conversion of 15.8%,and a CH_(4) selectivity below 0.7%.A combination of experimental and computational studies revealed that the unique electronic properties exhibited by the Cd clusters supported by the TiO_(2) matrix were responsible for the high selectivity of CO_(2) hydrogenation to methanol via the HCOO*pathway at the interfacial catalytic sites.

Ordered mesoporous carbon supported bifunctional PtM(M=Ru,Fe,Mo)electrocatalysts for a fuel cell anode

The deposition onto an ordered mesoporous carbon（OMC）support of well dispersed PtM（M = Ru,Fe,Mo）alloy nanoparticles（NPs）were synthesized by a direct replication method using SBA-15 as the hard template,furfuryl alcohol and trimethylbeneze as the primary carbon sources,and metal acetylacetonate as the alloying metal precursor and secondary carbon source.The physicochemical properties of the PtM-OMC catalysts were characterized by N2 adsorption-desorption,X-ray diffraction,transmission electron microscopy,X-ray absorption near edge structure,and extended X-ray absorption fine structure.The alloy PtM NPs have an average size of 2-3 nm and were well dispersed in the pore channels of the OMC support.The second metal（M）in the PtM NPs was mostly in the reduced state,and formed a typical core（Pt）-shell（M）structure.Cyclic voltammetry measurements showed that these PtM-OMC electrodes had excellent electrocatalytic activities and tolerance to CO poisoning during the methanol oxidation reaction,which surpassed those of typical activated carbon-supported PtRu catalysts.In particular,the PtFe-OMC catalyst,which exhibited the best performance,can be a practical anodic electrocatalyst in direct methanol fuel cells due to its superior stability,excellent CO tolerance,and low production cost.

Tuning the electronic structure of platinum nanocrystals towards high efficient ethanol oxidation

Direct ethanol fuel cell is a promising low temperature fuel cell,but its development is hindered by sluggish kinetics of anode catalysts for ethanol oxidation.Here a high efficient platinum/tin oxide/Graphene nanocomposite is synthesized through a facile and environmentally benign method.The structure and morphology are carefully characterized by X-ray diffraction and Transmission electron microscopy,showing a clear platinum/tin oxide heterostructure uniformly dispersed on graphene support.This catalyst demonstrates the highest activity among the reported catalysts and much higher durability towards ethanol oxidation compared to conventional platinum nanocatalysts.The ultrahigh activity originates from promoted removal of poisoning carbon monoxide immediate species on platinum due to a strong electronic donating effect from both tin oxide and graphene,which is fully supported by carbon monoxide stripping and X-ray photoelectron spectroscopy analysis.Our platinum/tin oxide/Graphene appears to be a promising candidate for ethanol oxidation electrocatalysts.

Glycerol hydrogenolysis to n‐propanol over Zr‐Al composite oxide‐supported Pt catalysts

Zr‐Al mixed oxide supported Pt catalysts with different Zr/Al mole ratios（2.5%Pt/ZrxAl（1–x）Oy） were synthesized by an impregnation method and used for the selective hydrogenolysis of glycerol to n‐propanol in an autoclave reactor. The catalysts were fully characterized by X‐ray powder diffrac‐tion, Brunauer‐Emmett‐Teller surface area analysis, CO chemisorption, H2 temperature‐ pro‐grammed reduction, pyridine‐infrared spectroscopy, and NH3‐temperature‐programmed desorp‐tion. The results revealed that the Zr/Al ratio on the support significantly affected the size of the platinum particles and the properties of the acid sites on the catalysts. The catalytic performance was well correlated with the acidic properties of the catalyst; specifically, more acid sites contrib‐uted to the conversion and strong acid sites with a specific intensity contributed to the deep dehy‐dration of glycerol to form n‐propanol. Among the tested catalysts, 2.5 wt% Pt/Zr（0.7）Al（0.3）Oy exhibited excellent selectivity for n‐propanol with 81.2% glycerol conversion at 240 °C and 6.0 MPa H2 pres‐sure when 10% aqueous glycerol solution was used as the substrate. In addition, the effect of vari‐ous reaction parameters, such as H2 content, reaction temperature, reaction time, and number of experimental cycles were studied to determine the optimized reaction conditions and to evaluate the stability of the catalyst.

Catalytic Performance of Graphite Oxide Supported Au Nanoparticles in Aerobic Oxidation of Benzyl Alcohol： Support Effect

Various Au/GO catalysts were prepared by depositing Au nanoparticles on thermally- and chemically-treated graphite oxide （GO） supports using a sol-immobilization method. The surface chemistry and structure of GO supports were characterized by a series of analytical techniques including X-ray photoelectron spectroscopy, temperature-programmed desorption and Raman spectroscopy. The results show that thermal and chemical treatments have large influence on the presence of surface oxygenated groups and the crystalline structure of GO supports. A strong support effect was observed on the catalytic activity of Au/GO catalysts in the liquid phase aerobic oxidation of benzyl alcohol. Compared to the amount and the type of surface oxygen functional groups, the ordered structure of GO supports may play a more important role in determining the catalytic performance of Au/GO catalysts.

Facile synthesis of 3D nanoporous Pd/Co_2O_3 composites with enhanced catalytic performance for methanol oxidation

To simultaneously reduce noble metal Pd usage and enhance electrocatalytic performance for methanol oxidation,Pd/Co2O3 composites with ultrafine three-dimensional(3D)nanoporous structures were designed and synthesized by simple one-step dealloying of a melt-spun Al-Pd-Co alloy with an alkaline solution.Their electrocatalytic activity in alkaline media was determined by a Versa-STAT MC workstation.The results indicate that the typical sizes of the ligaments and pores of the composites were approximately 8-9 nm.The Co2O3 was uniformly distributed on the Pd ligament surface.Among the as-prepared samples,the nanoporous Pd/Co2O3 composite generated from dealloying of the Al84.5Pd15Co0.5 alloy had the best electrocatalytic activity,and its activity was enhanced by approximately 230%compared with the nanoporous Pd from dealloying of Al85Pd15.The improvement of the electrocatalytic performance was mainly attributed to the electronic modification effect between Pd and Co as well as the bifunctional mechanism between Pd and Co2O3.