Enhanced catalytic performance for direct synthesis of dimethyl ether from syngas over a La_2O_3 modified Cu-ZrO_2/γ-Al_2O_3 hybrid catalyst

A series of hybrid catalysts were made by physically mixing Cu-ZrO2 and γ-A12O3, for former it was modified with different loadings of La2O3 prepared by co-precipitation method. The catalysts were characterized by BET, XRD, N2O-adsorption, EXAFS, H2-TPR, NH3-TPD techniques and evaluated in the synthesis of dimethyl ether from syngas. The results show that La2O3 promoted catalysts displayed a significantly better catalytic performance compared with Cu-ZrO2#y-A12O3 catalyst in CO conversion and DME selectivity, and the optimum catalytic activity was obtained when the content of La2O3 was 12 wt%. The characterizations reveal that high copper dispersion, facile reducibility of copper particles and appropriate amount of acidic sites are responsible for the superior catalytic performance.

Reduced formation of peroxide and radical species stabilises iron-based hybrid catalysts in polymer electrolyte membrane fuel cells

The incorporation of Pt into an iron-nitrogen-carbon(Fe NC)catalyst for the oxygen reduction reaction(ORR)was recently shown to enhance catalyst stability without Pt directly contributing to the ORR activity.However,the mechanistic origin of this stabilisation remained obscure.It is established herein with rotating ring disc experiments that the side product,H_(2)O_(2),which is known to damage FeNC catalysts,is suppressed by the presence of Pt.The formation of reactive oxygen species is additionally inhibited,independent of intrinsic H_(2)O_(2) formation,as determined by electron paramagnetic resonance.Transmission electron microscopy identifies an oxidised Fe-rich layer covering the Pt particles,thus explaining the inactivity of the latter towards the ORR.These insights develop understanding of Fe NC degradation mechanisms during ORR catalysis,and crucially establish the required properties of a precious metal free protective catalyst to improve Fe NC stability in acidic media.

Methanol and DME Co-production from CO2 hydrogenation over hybrid catalysts

Catalytic hydrogenation of CO2 into methanol and dimethyl ether was carried out over hybrid catalysts consisting of methanol-synthesis catalyst and zeolite. The methanol-synthesis catalyst, Cu/ZnO/Al2O3, was prepared by a co-precipitation method. Then it was physically mixed with HZSM-5 zeolite at weight ratios of 2：1, 1：1 and 1：2. The CO2 hydrogenation reaction was conducted in a fixed-bed microreactor at 250℃ and 40 bar in pre-mixed H2/CO2 feed with H2：CO2 molar ratios of 3：1 and 7：1. Products detected include methanol, dimethyl ether, carbon monoxide and water. Conversion of CO2 and yield of oxygenated products were influenced by the weight ratio of Cu/ZnO/Al2O3：HZSM-5 in the hybrid system and also the feed ratio. The Cu/ZnO/Al2O3： HZSM-5 hybrid at 1：1 resulted in methanol yield of 22.0% and was found to be an efficient hybrid catalyst for the CO2 hydrogenation reaction.

Fischer-Tropsch Synthesis of the Promoted Co/ZSM-5 Hybrid Catalysts for the Production of Gasoline Range Hydrocarbons

Fischer-Tropsch synthesis (FTS) reaction for the direct production of gasoline range hydrocarbons (C5-C9) from syngas was investigated on Ru, Pt, and La promoted Co/ZSM-5 (Si/Al = 25) catalysts. The hybrid catalysts were characterized by BET surface area, XRD, H2-TPR, NH3-TPD and XPS analyses. These physico-chemical properties were correlated with activity and selectivity of the catalysts. The promoted Co/ZSM-5 hybrid catalysts were found to be superior to the unpromoted Co/ZSM-5 catalyst in terms of better C5-C9 selectivity. Pt-Co/ZSM-5 exhibited the highest catalytic activity because of the small cobalt particle size.

Conversion of syngas into lower olefins over a hybrid catalyst system

Lower olefins,produced from syngas through Fischer-Tropsch synthesis,has been gaining worldwide attention as a non-petroleum route.However,the process demonstrates limited selectivity for target products.Herein,a hybrid catalyst system utilizing Fe-based catalyst and SAPO-34 was shown to enhance the selectivity toward lower olefins.A comprehensive study was conducted to examine the impact of various operating conditions on catalytic performance,such as space velocity,pressure,and temperature,as well as catalyst combinations,including loading pattern,and mass ratio of metal and zeolite.The findings indicated that the addition of SAPO-34 was beneficial for enhancing catalytic activity.Furthermore,compared with AlPO-34 zeolite,the strong-acid site on SAPO-34 was identified to crack the long-chain hydrocarbons,thus contributing to the lower olefin formation.Nevertheless,an excess of strong-acid sites was found to detrimentally impact the selectivity of lower olefins,attributed to the increased aromatization and polymerization of lower olefins.The detailed analysis of a hybrid catalyst in Fischer-Tropsch synthesis provides a practical strategy for improving lower olefins selectivity,and has broader implications for the application of hybrid catalyst in diverse catalytic systems.

MoS2-rGO hybrid architecture as durable support for cathode catalyst in proton exchange membrane fuel cells

Carbon black is utilized as a conventional electrocatalyst support material for proton exchange membrane fuel cells. However, this support is prone to corrosion under oxidative and harsh environments, thus limiting the durability of the fuel cells. Meanwhile, carbon corrosion would also weaken the linkage between Pt and the support material, which causes Pt agglomeration, and consequently, deterioration of the cell performance. To overcome the drawbacks of a Pt/C electrocatalyst, a hybrid support material comprising molybdenum disulfide and reduced graphene oxide is proposed and synthesized in this study to exploit the graphitic nature of graphene and the availability of the exposed edges of MoS2. TEM results show the uniform dispersion of Pt nanoparticles over the MoS2-rGO surface. Electrochemical measurements indicate higher ECSA retention and better ORR activity after 10000 potential cycles for Pt/MoS2-rGO as compared to Pt/C, demonstrating the improved durability for this hybrid support material.

A dicationic ionic liquid-modified phosphotungstate hybrid catalyst for the heterogeneous oxidation of alcohols with H_2O_2

An ionic hybrid catalyst 1,1＇-（butane- 1,4-diyl）-bis（3-methylimidazolium） phosphotungstate （abbreviated [Dmimh.sPW） has been prepared by anion-exchange of the divalent ionic liquid （1L） 1,1 ＇-（butane-1,4-diyl）-bis（3-methylimidazolium） di（bromide） with the Keggin phosphotungstic acid H3PW12O40, and characterized by IR, 1H NMR, 13C NMR, ESI-MS, TG, SEM, XRD, BET surface area measurements, elemental analysis, and melting point. The hybrid material was evaluated as a catalyst for the oxidation of alcohols with aqueous hydrogen peroxide under various conditions. The catalytic performance of [Dmim]t.sPW was also compared with related catalysts bearing other cations or anions. The new hybrid [Dmim]1.5PW proved to be an effi- cient liquid-solid heterogeneous catalyst for H2O2-based oxidation of alcohols, with the advantages of high conversion and se- lectivity, easy recovery, and quite good reusability.

Preparation and Microstructural Characterization of Activated Carbon-Metal Oxide Hybrid Catalysts:New Insights into Reaction Paths

In catalysis processes, activated carbon （AC） and metal oxides （MOs） are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and MO nanoparticles in a single hybrid material usually entails both chemical and microstructural changes, which may largely influence the potential catalytic suitability and performance of the resulting product. Here, the prepa- ration of a wide series of AC-MO hybrid catalysts is studied. Three series of such catalysts are prepared by support first of MO （Al2O3, Fe2O3, SnO2, TiO2, WO3, and ZnO） precursors on a granular AC by wet impregnation and oven-drying at 120 ℃, and by subsequent heat treatment at 200 or 850℃ in inert atmosphere. Both the chemical composition and microstructure are mainly investigated by powder X-ray diffraction. Yield and ash content are often strongly dependent on the MO precursor and heat treatment temperature, in particular for the Sn catalysts. With the temperature rise, trends are towards the transformation of metal hydroxides into metal oxides, crystallinity improvement, and occurrence of drastic composition changes, ultimately leading to the formation of metals in elemental state and even metal carbides. Reaction paths during the preparation are explored for various hybrid catalysts and new insights into them are provided.

Phthalocyanine-derived catalysts decorated by metallic nanoclusters for enhanced CO_(2)electroreduction

Electrochemical CO_(2)reduction(CO_(2)RR)over molecular catalysts is a paramount approach for CO_(2)conversion to CO.Herein,we report a novel phthalocyanine-derived catalyst synthesized by a two-step method with a much improved electroconductivity.Furthermore,the catalyst contains both Ni-N4sites and highly dispersed metallic Ni nanoclusters,leading to an increased CO_(2)RR currents by two folds.Isotope labelling study and in situ spectroscopic analysis demonstrate that the existence of metallic Ni nanoclusters is the key factor for the activity enhancement and can shift the CO_(2)RR mechanism from being electron transfer(ET)-limited(forming*COO^(-))to concerted proton-electron transfer(CPET)-limited(forming CO).

Diffusion process in enzyme-metal hybrid catalysts

Enzyme-metal hybrid catalysts bridge the gap between enzymatic and heterogeneous catalysis,which is significant for expanding biocatalysis to a broader scope.Previous studies have demonstrated that the enzyme-metal hybrid catalysts exhibited considerably higher catalytic efficiency in cascade reactions,compared with that of the combination of separated enzyme and metal catalysts.However,the precise mechanism of this phenomenon remains unclear.Here,we investigated the diffusion process in enzyme-metal hybrid catalysts using Pd/lipase-Pluronic conjugates and the combination of immobilized lipase(Novozyme 435)and Pd/C as models.With reference to experimental data in previous studies,the Weisz-Prater parameter and efficiency factor of internal diffusion were calculated to evaluate the internal diffusion limitations in these catalysts.Thereafter,a kinetic model was developed and fitted to describe the proximity effect in hybrid catalysts.Results indicated that the enhanced catalytic efficiency of hybrid catalysts may arise from the decreased internal diffusion limitation,size effect of Pd clusters and proximity of the enzyme and metal active sites,which provides a theoretical foundation for the rational design of enzyme-metal hybrid catalysts.

Pyridine-H_5PMo_(10)V_2O_(40) hybrid catalysts for liquid-phase hydroxylation of benzene to phenol with molecular oxygen

Pyridine(Py)-modified Keggin-type vanadium-substituted heteropoly acids(PynPMo10V2O40,n=1 to 5) were prepared by a precipitation method as organic/inorganic hybrid catalysts for direct hydroxylation of benzene to phenol in a pressured batch reactor and their structures were detected by FT-IR.Among various catalysts,Py3PMo10V2O40 exhibits the highest catalytic activity(yield of phenol,11.5%),without observing the formation of catechol,hydroquinone and benzoquinone in the reaction with 80 vol% aqueous acetic acid,molecular oxygen and ascorbic acid used as the solvent,oxidant and reducing reagent,respectively.Influences of reaction temperature,reaction time,oxygen pressure,amount of ascorbic acid and catalyst on yield of phenol were investigated to obtain the optimal reaction conditions for phenol formation.Pyridine can greatly promote the catalytic activity of the Py-free catalyst(H5PMo10V2O40),mostly because the organic π electrons in the hybrid catalyst may extend their conjugation to the inorganic framework of heteropoly acid and dramatically modify the redox properties,at the same time,pyridine adsorbed on heteropoly acids can promote the effect of "pseudo-liquid phase",thus accounting for the enhancement of phenol yield.

Hybrid enzyme catalysts synthesized by a de novo approach for expanding biocatalysis

The two major challenges in industrial enzymatic catalysis are the limited number of chemical reaction types that are catalyzed by enzymes and the instability of enzymes under harsh conditions in industrial catalysis.Expanding enzyme catalysis to a larger substrate scope and greater variety of chemical reactions and tuning the microenvironment surrounding enzyme molecules to achieve high enzyme performance are urgently needed.In this account,we focus on our efforts using the de novo approach to synthesis hybrid enzyme catalysts that can address these two challenges and the structure-function relationship is discussed to reveal the principles of designing hybrid enzyme catalysts.We hope that this account will promote further efforts toward fundamental research and wide applications of designed enzyme hybrid catalysts for expanding biocatalysis.

Heterostructured Electrocatalysts for Hydrogen Evolution Reaction Under Alkaline Conditions

The hydrogen evolution reaction(HER) is a half-cell reaction in water electrolysis for producing hydrogen gas. In industrial water electrolysis, the HER is often conducted in alkaline media to achieve higher stability of the electrode materials. However, the kinetics of the HER in alkaline medium is slow relative to that in acid because of the low concentration of protons in the former.Under the latter conditions, the entire HER process will require additional effort to obtain protons by water dissociation near or on the catalyst surface. Heterostructured catalysts, with fascinating synergistic effects derived from their heterogeneous interfaces, can provide multiple functional sites for the overall reaction process. At present, the activity of the most active known heterostructured catalysts surpasses(platinum-based heterostructures) or approaches (noble-metal-free heterostructures) that of the commercial Pt/C catalyst under alkaline conditions, demonstrating an infusive potential to break through the bottlenecks. This review summarizes the most representative and recent heterostructured HER catalysts for alkaline medium. The basics and principles of the HER under alkaline conditions are first introduced, followed by a discussion of the latest advances in heterostructured catalysts with/without noblemetal-based heterostructures. Special focus is placed on approaches for enhancing the reaction rate by accelerating the Volmer step. This review aims to provide an overview of the current developments in alkaline HER catalysts, as well as the design principles for the future development of heterostructured nano-or micro-sized electrocatalysts.

Comparison of dry reforming of methane in low temperature hybrid plasma-catalytic corona with thermal catalytic reactor over Ni/γ-Al_2O_3

In the current study, the hybrid effect of a corona discharge and γ-alumina supported Ni catalysts in CO2 reforming of methane is investigated. The study includes both purely catalytic operation in the temperature range of 923-1023 K, and hybrid catalytic-plasma operation of DC corona discharge reactor at room temperature and ambient pressure. The effect of feed flow rate, discharge power and Ni/γ-Al2O3 catalysts are studied. When CH4/CO2 ratio in the feed is 1/2, the syngas of low Ha/CO ratio at about 0.56 is obtained, which is a potential feedstock for synthesis of liquid hydrocarbons. Although Ni catalyst is only active above 573 K, presence of Ni catalysts in the cold corona plasma reactor （T≤523 K） shows promising increase in the conversions of methane and carbon dioxide. When Ni catalysts are used in the plasma reaction, H2/CO ratios in the products are slightly modified, selectivity to CO increases whereas fewer by-products such as hydrocarbons and oxygenates are formed.

双层单原子催化剂用于促进高活性和选择性电催化硝酸盐还原制氨

高效、高选择性的单原子催化剂(SACs)在电催化硝酸盐还原制氨过程中具有重要作用。然而,由于中间体、金属活性中心和配位环境之间复杂的竞争性电子相互作用,仍然面临挑战。本研究采用密度泛函理论(DFT)计算,对27种SACs以及双层SACs(BSACs)进行了系统研究,通过轴向d-d轨道杂化提高了从SACs到BSACs的电催化硝酸盐还原反应(NO_(3)RR)的活性和选择性。考虑到可能的O端、N端、NO端和NO二聚体途径,计算结果显示,在单层SACs中,Ti-Pc和V-Pc分别具有优异的极限电位(U_(L)),分别为-0.24和-0.48V。形成能、溶解势以及从头算分子动力学结果表明,在反应条件下,这些催化剂非常稳定。在这些单层TM-Pc中,它们的d带能级和占据数受到d_(xz)/d^(yz)和p_(z)轨道杂化的影响。其轴向d_(z^(2))轨道的可用性通过形成d_(z^(2))-d_(z^(2))相互作用来进一步调整d带和反应性。在此基础上,以Ti-Pc和V-Pc为底物,通过形成轴向d-d轨道杂化来构建BSACs,为调节NO_(3)RR催化性能提供了一种独特的新途径。重要的是,我们发现d带中心(εd)、d_(xz)+d_(yz)轨道的占据数和U_(L)之间存在二维火山关系,用于描述它们的NO_(3)RR催化性能。最佳的BSACs应该同时具备适当的ε_(d)和d_(xz)+d_(yz)占用数。Ti-Mo和Ti-Ta被确定为出色的NO_(3)RR催化剂,其U_(L)均降低至-0.13 V。而d_(z^(2))-d_(z^(2))轨道之间的杂化则增强了双层金属之间的电荷转移和结构稳定性。缺乏相邻的金属位点将导致生成NO_(2)、NO和N_(2)的能垒较高,从而抑制副产物生成。最终,本研究揭示了在SACs和BSACs上对硝酸盐还原进行合理优化的方法,可为改进电催化剂的设计提供指导。

Conversion of CO_(2)to added value products via rWGS using Fe-promoted catalysts:Carbide,metallic Fe or a mixture?

Fe-based catalysts are efficient systems for CO_(2)conversion via reverse water-gas shift(rWGS)reaction.Nevertheless,the nature of the active phase,namely metallic iron,iron oxide or iron carbide remains a subject of debate which our paper is meant to close.Fe0 is a much better catalyst for the rWGS than Fe_(3)C.The activity of Fe0 can be promoted by the addition of Cs and Cu whose presence hinders iron carburisation while favouring both higher conversion and enhanced selectivity.When the samples are aged in the rWGS reaction mixture during stability test a new phase appear:Fe_(5)C_(2),resulting in a more active but less selective catalysts than Fe0 for the rWGS reaction.Hence our results indicate that we could potentially achieve an optimal activity/selective balance upon finely tuning the proportion Fe/Fe_(5)C_(2).Beyond the fundamental information concerning active phase we have observed the presence of advanced Fischer-Tropsch-like products at ambient pressure opening new opportunities for the design of hybrid rWGS/Fischer-Tropsch systems.

贵金属载量对油电混合动力汽车尾气污染物排放特性的影响研究

以某2.0T油电混合动力汽车的尾气排放特征和减排效果为研究重点,设计了同一系列不同Pd、Rh含量的三效催化剂,并对该系列催化剂老化前后的起燃性能、空燃比窗口特性以及WLTC循环的整车排放性能进行了测试。原始排放测试结果表明,该车型排气温度在300~560℃,相对于燃油车,排气温度低,空燃比偏大,混合气整体偏稀燃;冷起动阶段,THC和NOx排放控制较难。引入该系列催化剂后,该车型的排放测试结果表明,催化剂的起燃性能与催化剂贵金属总含量呈线性关系;贵金属含量增加,能使污染物快速达到完全转化。新鲜催化剂的整车排放测试结果表明,THC和NOx的整车排放受贵金属总含量的影响比CO大。由催化剂老化后的整车排放测试结果可以看出,催化剂中,Pd含量对THC的整车排放影响较大,而Rh含量对NOx的整车排放影响较大;CO的整车排放受贵金属总含量的影响较小,当贵金属总含量超过2.21 g时,CO的整车排放基本相同。研究结果能够为油电混合动力汽车三效催化剂的研发和贵金属减量研究提供参考。

Building highly active hybrid double-atom sites in C_(2)N for enhanced electrocatalytic hydrogen peroxide synthesis

Two-electron(2 e^(-))oxygen reduction reaction(ORR)shows great promise for on-site electrochemical synthesis of hydrogen peroxide(H_(2)O_(2)).However,it is still a great challenge to design efficient electrocatalysts for H_(2)O_(2)synthesis.To address this issue,the logical design of the active site by controlling the geometric and electronic structures is urgently desired.Therefore,using density functional theory(DFT)computations,two kinds of hybrid double-atom supported on C_(2)N nanosheet(RuCu@C_(2)N and PdCu@C_(2)N)are screened out and their H_(2)O_(2)performances are predicted.PdCu@C_(2)N exhibits higher activity for H_(2)O_(2)synthesis with a lower overpotential of 0.12 V than RuCu@C_(2)N(0.59 V),Ru_(3)Cu(110)facet(0.60 V),and PdCu(110)facet(0.54 V).In aqueous phase,the adsorbed O_(2)is further stabilized with bulk H_(2)0 and the thermodynamic rate-determining step of 2 e^(-) ORR change.The activation barrier on PdCu@C_(2)N is 0.43 eV lower than the one on RuCu@C_(2)N with 0.68 eV.PdCu@C_(2)N is near the top of 2 e^(-) ORR volcano plot,and exhibits high selectivity of H_(2)O_(2.)This work provides guidelines for designing highly effective hybrid double-atom electrocatalysts(HDACs)for H_(2)O_(2)synthesis.

酶-金属单原子复合催化剂在一锅法生物-化学反应的应用

酶催化与金属单原子催化结合,理论上可开发众多新的绿色化学合成反应,是催化科学的一个重要研究前沿方向.酶-金属单原子复合催化剂兼具酶和金属单原子催化剂的高效、高立体选择性等优点.目前已成功构建的单原子分散金属催化剂的载体一般为刚性的无机载体,利用柔性蛋白分子作为载体制备单原子分散金属催化剂的技术瓶颈问题在于蛋白分子具有柔性、构象易变的特点,并且氨基酸残基与金属原子之间的相互作用力较弱,蛋白分子表面的氨基酸残基难以与金属单原子稳定结合.针对这样一个关键技术瓶颈问题,我们建立了酶-金属单原子复合催化剂的光化学合成方法.本文研究酶-金属单原子复合催化剂在生物-化学一锅级联反应合成联苯类手性醇中的催化性能.联苯类手性醇是手性药物的重要中间体,通常通过多步化学法或生物-化学级联法制备.相比于多步化学法,利用生物-化学级联反应制备联苯类手性化合物具有反应条件温和、选择性高、环境友好等优点.采用光化学法合成脂肪酶-钯单原子复合催化剂(Pd_(1)/CALB-Pluronic),通过球差矫正扫描透射电镜和扩展X射线吸收精细结构表征复合催化剂的形貌.首先研究了Pd_(1)/CALB-Pluronic复合催化剂中单原子分散Pd催化的C-C偶联反应催化效率,然后考察了它在生物-化学一锅级联反应中的催化性能;发现该催化剂在C-C偶联反应中具有比常用的Pd均相催化剂和Pd非均相催化剂更好的活性.在碘苯和苯乙炔的Sonogashira反应中,Pd_(1)/CALB-Pluronic的TOF值大于均相催化剂Pd(PPh3)4,是多相商业催化剂Pd/C的3.5倍.Pd_(1)/CALB-Pluronic重复使用10次后,活性仍保留97%,具有很好的稳定性.通过DFT计算分析催化反应路径,提出了Pd_(1)/CALB-Pluronic复合催化剂的2价Pd单原子在Sonogashira反应中可能存在Pd^(Ⅱ)/Pd^(Ⅳ)催化机理.本文开发了(R)-1-(4-联苯)乙醇的生物-化学一锅级联反应合成新路线:Pd_(1)/CALB-Pluronic复合催化剂在30℃的水溶液中催化(±)-1-(4-溴苯基)乙酸乙酯和苯硼酸反应生成(R)-1-(4-联苯)乙醇.在该过程中,CALB催化的立体选择性水解反应和Pd单原子催化的C-C偶联反应同时进行.其中,CALB催化(±)-1-(4-溴苯基)乙酸乙酯中的R型异构体水解为(R)-1-(4-溴苯基)乙醇,Pd单原子催化(R)-1-(4-溴苯基)乙醇与苯硼酸进行Suzuki反应生成(R)-1-(4-联苯)乙醇.Pd_(1)/CALB-Pluronic复合催化剂在30 oC下催化生物-化学一锅级联反应合成(R)-1-(4-联苯)乙醇,其催化效率是商业催化剂Pd/C和CALB-Pluronic催化剂组合的31.3倍.

用于SO_(2)去极化电解制氢的铂基催化剂

综述了铂基SO_(2)去极化电解(SDE)阳极催化剂的研究进展。SDE阳极反应条件苛刻,铂基催化剂因具备良好的导电性、抗腐蚀性,并能够有效抵抗H_(2)S等硫物质的毒化,成为SDE阳极催化剂的首选。通过引入Al、Cr、Ni等非贵金属元素,可有效提高铂基催化剂性能并减少Pt的用量。在载体方面,综述和讨论了活性炭、石墨、炭黑、石墨烯以及SiC/TiC等对铂基催化剂性能的影响,此外分析了催化剂制备工艺对催化剂结构参数和性能的影响。尽管已经取得了很多研究成果,但当前对铂基SDE阳极催化剂的长期稳定性、多金属催化剂各金属元素间的相互作用等方面的研究尚较少,进一步优化催化剂设计、加强载体筛选及其改性,开发新的制备工艺,提高Pt利用率及催化剂的活性和稳定性,是未来相关研究的关键所在。