Nickel single atom overcoordinated active sites to accelerate the electrochemical reaction kinetics for Li-S cathode

Lithium-sulfur(Li-S)batteries with high theoretical energy density are promising advanced energy storage devices.However,shuttling of dissolute lithium polysulfide(LiPSs)and sluggish conversion kinetics impede their applications.Herein,single nickel(Ni)atoms on two-dimensional(2D)nitrogen(N)-doped carbon with Ni-N_(4)-O overcoordinated structure(SANi-N_(4)-O/NC)are prepared and firstly used as a sulfur host of Li-S batteries.Due to the efficient polysulfides traps and highly LiPSs conversion effect of SANi-N_(4)-O/NC,the electrochemical performance of Li-S batteries obviously improved.The batteries can well operate even under high sulfur loading(5.8 mg cm^(-2))and lean electrolyte(6.1μL mg^(-1))condition.Meanwhile,density functional theory(DFT)calculations demonstrate that Ni single atom’s active sites decrease the energy barriers of conversion reactions from Li_(2)S_(8)to Li2S due to the strong interaction between SANi-N_(4)-O/NC and LiPSs.Thus,the kinetic conversion of LiPSs was accelerated and the shuttle effect is suppressed on SANi-N_(4)-O/NC host.This study provides a new design strategy for a 2D structure with single-atom overcoordinated active sites to facilitate the fast kinetic conversion of LiPSs for Li-S cathode.

Three-Dimensional Welded Mn_(1) Site Catalysts with nearly 100% Singlet Oxygen Fabrication for Contaminant Elimination

Reactive oxygen species(ROS)have a significant part in the elimination of recalcitrant organic pollutants and commonly coexist in one advanced oxidation system.It is difficult for us to make clear the effect of the co-instantaneous generation of radicals and nonradicals,which would cover and obscure the transformation pathway.Herein,a coordinate welding process is presented for fabricating accessible Mn1 site catalysts(Mn SSCs)in order to clarify the nonradical(singlet oxygen/^(1)O_(2))generated pathway and transformation in oxidative removal of contaminants.The Mn SSCs achieve nearly 100%^(1)O_(2) fabrication by activating peroxymonosulfate,which displays an excellent sulfamethoxazole elimination performance,super anti-anion interference,and extraordinary stability.As revealed by density functional theory calculations,the Mn SSCs with a special welded three-dimensional nanostructure could significantly boost the activation process by oxidizing the peroxymonosulfate at the interlayer of Mn SSCs and reducing dissolved oxygen on the surface of Mn SSCs.This design of Mn SSCs with a three-dimensional welded nanostructure might offer a potential approach for employing single site catalysts for environmental remediation.

Graphene-anchored sodium single atoms:A highly active and stable catalyst for transesterification reaction

Solid strong base catalysts have received considerable attention in various organic reactions due to their facile separation,neglectable corrosion,and environmental friendliness.Although great progress has been made in the preparation of solid strong base catalysts,it is still challenging to avoid basic sites aggregation on support and active sites loss in reaction system.Here,we report a tandem redox strategy to prepare Na single atoms on graphene,producing a new kind of solid strong base catalyst(Na1/G).The base precursor NaNO_(3)was first reduced to Na2O by graphene(400℃)and successively to single atoms Na anchored on the graphene vacancies(800℃).Owing to the atomically dispersed of basicity,the resultant catalyst presents high activity toward the transesterification of methanol and ethylene carbonate to synthesize dimethyl carbonate(turnover frequency(TOF)value:125.7 h^(−1)),which is much better than the conventional counterpart Na2O/G and various reported solid strong bases(TOF:1.0-90.1 h^(−1)).Furthermore,thanks to the basicity anchored on graphene,the Na1/G catalyst shows excellent durability during cycling.This work may provide a new direction for the development of solid strong base catalysts.

Atomically dispersed Fe sites on hierarchically porous carbon nanoplates for oxygen reduction reaction

Developing cost-effective,robust and stable non-precious metal catalysts for oxygen reduction reaction(ORR) is of paramount importance for electrochemical energy conversion devices such as fuel cells and metal-air batteries.Although Fe-N-C single atom catalysts(SACs) have been hailed as the most promising candidate due to the optimal binding strength of ORR intermediates on the Fe-N_(4) sites,they suffer from serious mass transport limitations as microporous templates/substrates,i.e.,zeolitic imidazolate frameworks(ZIFs),are usually employed to host the active sites.Motivated by this challenge,we herein develop a hydrogen-bonded organic framework(HOF)-assisted pyrolysis strategy to construct hierarchical micro/mesoporous carbon nanoplates for the deposition of atomically dispersed Fe-N_(4) sites.Such a design is accomplished by employing HOF nanoplates assembled from 2-aminoterephthalic acid(NH_(2)-BDC) and p-phenylenediamine(PDA) as both soft templates and C,N precursors.Benefitting from the structural merits inherited from HOF templates,the optimized catalyst(denoted as Fe-N-C SAC-950) displays outstanding ORR activity with a high half-wave potential of 0.895 V(vs.reversible hydrogen electrode(RHE)) and a small overpotential of 356 mV at 10 mA cm^(-2) for the oxygen evolution reaction(OER).More excitingly,its application potential is further verified by delivering superb rechargeability and cycling stability with a nearly unfading charge-discharge gap of 0.72 V after 160 h.Molecular dynamics(MD) simulations reveal that micro/mesoporous structure is conducive to the rapid mass transfer of O_(2),thus enhancing the ORR performance.In situ Raman results further indicate that the conversion of O_(2) to~*O_(2)-the rate-determining step(RDS) for Fe-N-C SAC-950.This work will provide a versatile strategy to construct single atom catalysts with desirable catalytic properties.

Hydrogen etching induced hierarchical meso/micro-pore structure with increased active density to boost ORR performance of Fe-N-C catalyst

Rational regulation on pore structure and active site density plays critical roles in enhancing the performance of Fe-N-C catalysts. As the microporous structure of the carbon substrate is generally regarded as the active site hosts, its hostility to electron/mass transfer could lead to the incomplete fulfillment of the catalytic activity. Besides, the formation of inactive metallic Fe particles during the conventional catalyst synthesis could also decrease the active site density and complicate the identification of real active site. Herein, we developed a facial hydrogen etching methodology to yield single site Fe-N-C catalysts featured with micro/mesoporous hierarchical structure. The hydrogen concentration in pyrolysis process was designated to effectively regulate the pore structure and active site density of the resulted catalysts.The optimized sample achieves excellent ORR catalytic performance with an ultralow H2O2 yield(1%)and superb stability over 10,000 cycles. Our finding provides new thoughts for the rational design of hierarchically porous carbon-based materials and highly promising non-precious metal ORR catalysts.

Covalent Organic Frameworks Based Single-site Electrocatalysts for Oxygen Reduction Reaction

Single site catalysts(SSCs)are a new type of heterogeneous catalysts formed by isolated metal atoms supported on kinds of substrates.SSCs have shown great potential for energy conversion and storage in recent years,especially for oxygen reduction reactions(ORR).Typically,SSCs are confined on the substrate by strong chemical interactions,such as coordination bonds.Therefore,the surface chemical environment and porous properties of the supports are crucial to the performance of SSCs.In recent years,COFs have become excellent candidates for preparing SSCs as they can precisely assemble monomers into highly ordered crystalline porous materials with a fine structure and definite components.In this review,we not only summarize the characteristics and advantages of COFs based SSCs,but also highlight the applications of COFs constructed from different single active sites for ORR in recent years.Finally,challenges in practical application,feasible strategies and perspectives are proposed for the of COFs based SSCs.

缺陷氮掺杂碳耦合Co-N5单原子位点用于高效锌-空气电池

锌-空气电池(ZAB)因其能量密度高、环境友好、成本低以及安全性高而备受关注.然而,空气电极上的氧还原反应(ORR)动力学缓慢,严重限制了ZAB的输出功率.尽管铂基催化剂展现出优异的ORR催化活性,但高昂的成本制约其大规模商业化应用.因此,迫切需要开发高效、低成本的ORR电催化剂.研究表明,具有原子分散Co-N4活性位点的Co-N-C单原子催化剂是理想的ORR非贵金属催化剂,但其仍然存在与反应关键中间体结合能较高的难题.目前的研究主要通过调控单原子配位环境与增大活性位点密度来提高Co-N-C催化剂的活性,但如何精确控制中心金属电子结构以及避免高温下金属原子的团聚仍面临巨大挑战.除了单原子活性位点外,催化剂载体的键合结构、电荷分布状态亦会影响载体本身和单原子位点的催化活性.然而,现有的研究主要聚焦于单原子位点或无金属催化剂单方面活性的提升,关于它们之间的相互作用对于催化性能影响的研究相对很少.为了进一步提高Co单原子催化剂的催化活性,本文通过简单的模板法与NH3二次处理策略制备了氮掺杂缺陷碳负载的Co-N_(5)位点单原子催化剂.电感耦合等离子体发射光谱结果表明,单原子Co的金属负载量高达2.57 wt%.此外,相比于未经过NH3二次处理的Co-Nx/HC样品,Co-N_(5)/DHC样品在电子顺磁共振谱中g=2.003处呈现出更明显的共振信号,在C 1s高分辨谱中具有更低的C-C(sp2杂化)/C-N(sp3杂化)比例以及明显增加的吡啶氮信号,证实了Co-N_(5)/DHC显著提升的氮掺杂碳缺陷浓度并具有丰富的边界/缺陷位点.同时,X射线吸收谱与球差矫正透射电子显微镜结果表明所制备的样品为原子分散的Co-N_(5)结构,从而证明成功制备了缺陷氮掺杂碳耦合Co-N_(5)位点单原子催化剂.电化学测试结果表明,缺陷氮掺杂碳耦合Co-N_(5)位点后表现较好的ORR性能,半波电位达到0.877 V,明显高于Co-Nx/HC对比样品和商业化Pt/C催化剂.Koutecky-Levich曲线和旋转盘环电极测试结果表明,Co-N_(5)/DHC催化剂的高效4e-反应路径.且在10000次的加速老化测试中,Co-N_(5)/DHC半波电位仅降低了7 m V,稳定性优于Pt/C.以Co-N_(5)/DHC为阴极催化剂组装的ZAB开路电压为1.45 V,峰值输出功率密度能够达到160.7 m W cm^(-2),并能提供766.2 m A h gZn-1的比容量,展现出较高的应用前景.密度泛函理论计算表明,Co-N_(5)位点与缺陷氮掺杂碳的相互作用诱导Co中心位点电子的重新分布,降低了ORR反应能垒.综上,本文为设计与合成高性能的Co单原子催化剂,用于先进的可再生能源转换系统提供了一种新思路.

Cobalt single atom site catalysts with ultrahigh metal loading for enhanced aerobic oxidation of ethylbenzene

The oxidation of hydrocarbons to produce high value-added compounds(ketones or alcohols)using oxygen in air as the only oxidant is an efficient synthetic strategy from both environmental and economic views.Herein,we successfully synthesized cobalt single atom site catalysts(Co SACs)with high metal loading of 23.58 wt.%supported on carbon nitride(CN),which showed excellent catalytic properties for oxidation of ethylbenzene in air.Moreover,Co SACs show a much higher turn-over frequency(19.6 h^(−1))than other reported non-noble catalysts under the same condition.Comparatively,the as-obtained nanosized or homogenous Co catalysts are inert to this reaction.Co SACs also exhibit high selectivity(97%)and stability(unchanged after five runs)in this reaction.DFT calculations reveal that Co SACs show a low energy barrier in the first elementary step and a high resistance to water,which result in the robust catalytic performance for this reaction.

Amino-metalloporphyrin polymers derived Fe single atom catalysts for highly efficient oxygen reduction reaction

Recently,nitrogen-doped porous carbon supported single atom catalysts(SACs)have become one of the most promising alternatives to precious metal catalysts in oxygen reduction reaction(ORR)due to their outstanding performance,especially those derived from porphyrin-based materials.However,most of them involve other metal residuals,which would cause the tedious pre-and/or post-treatment,even mislead the mechanistic investigations and active-site identification.Herein,we report a precursor-dilution strategy to synthesize Fe SACs through the Schiff-based reaction via co-polycondensation of amino-metalloporphyrin,followed by pyrolysis at high temperature.Systematic characterization results provide the compelling evidence of the dominant presence of atomically dispersed Fe-Nxspecies.Our catalyst shows superior ORR performance with positive half-wave potential(E1/2=0.85 V vs.RHE)in alkaline condition and moderate activity(E1/2=0.68 V vs.RHE)under the acidic condition,excellent methanol tolerance and good long-term stability.All the results indicate Fe SACs would be a promising candidate for replacing the precious Pt in metal-air batteries and fuel cells.

Graphitic carbon nitride based single-atom photocatalysts

Single-atom photocatalysts,due to their high catalysis activity,selectivity and stability,become a hotspot in the field of photocatalysis.Graphitic carbon nitride(g-C3N4)is known as both a good support for single atoms and a star photocatalyst.Developing g-C3N4-based single-atom photocatalysts exhibits great potential in improving the photocatalytic performance.In this review,we summarize the recent progress in g-C3N4-based single-atom photocatalysts,mainly including preparation strategies,characterizations,and their photocatalytic applications.The significant roles of single atoms and catalysis mechanism in g-C3N4-based single-atom photocatalysts are analyzed.At last,the challenges and perspectives for exploring high-efficient g-C3N4-based single-atom photocatalysts are presented.

Tuning the reaction path of CO_(2) electroreduction reaction on indium single-atom catalyst:Insights into the active sites

Modulating the local coordination structure of metal single-atom catalysts(SACs)is extensively employed to tune the catalytic activity,but rarely involved in regulating the reaction pathway which fundamentally determines the product selectivity.Herein,we report that the product selectivity of electrochemical CO_(2)reduction(CO_(2)RR)on the single-atom indium-NxC4-x(1≤x≤4)catalysts could be tuned from formate to CO by varying the carbon and nitrogen occupations in the first coordination sphere.Surprisingly,the optimal In SAC showed great promise for CO production with the maximum Faradic efficiency of 97%,greatly different from the reported In-based catalysts where the formate is the dominant product.Combined experimental verifications and theoretical simulations reveal that the selectivity switch from formate to CO on In SACs originates from active sites shift from indium center to the indium-adjacent carbon atom,where the indium site favors formate formation and the indium-adjacent carbon site prefers the CO pathway.The present work suggests the active sites in metal SACs may shift from the widely accepted metal center to surrounding carbon atoms,thereby offering a new implication to revisit the active sites for metal SACs.

初生态低缠结超高分子量聚乙烯催化剂研究进展

超高分子量聚乙烯(UHMWPE)具有高耐磨性、高强度和刚度、轻质、耐腐蚀、低摩擦系数、生物相容性等特点,作为一种优异的工程塑料广泛应用于高端新材料等各领域,而调控高分子链的缠结程度对于更好地应用UHMWPE至关重要。从均相催化和非均相催化两方面综述了制备初生态低缠结UHMWPE的催化剂技术的研究进展,其中,单中心催化体系和修饰型Ziegler-Natta催化剂在制备初生态低缠结UHMWPE的工业应用中前景广阔。

合金纳米颗粒原子级分散制备的双位点催化剂中单点Ag1对Pd1在炔烃双烷氧羰基化反应中的促进作用

炔烃烷氧羰基化反应是一种原子经济反应,可以生成α,β-不饱和羧酸、二羧羧酸酯及其衍生物.其中,乙炔的双烷氧羰基化产物(丁烯二酸二酯)可通过两段加氢制备1,4-丁二醇,该反应路径对于生产生物可降解材料聚丁二酸丁二醇酯(PBS)具有重要意义.然而,目前广泛应用的均相Pd基催化体系存在催化剂分离困难、金属流失以及需要添加有机膦配体或各种磺酸助剂等问题,这不仅增加了制备成本,还可能引入不必要的杂质.此外,尽管纳米催化剂在催化领域有着广泛的应用,但大多数纳米催化剂在炔烃双烷氧基羰基化反应中仍表现出反应活性低和稳定性差的问题,这限制了其在工业生产中的应用.相比之下,多相单金属点催化剂因其100%的原子利用率和较好的催化活性而备受关注.然而,由于多相单金属点催化剂具有相对简单的结构和配位环境,其应用仍受到一定的限制.为了克服这一难题,合成具有不同金属的双位点催化剂成为了一个研究热点.双位点催化剂有望进一步释放单金属位点催化剂的潜力,提高反应活性和稳定性.然而,尽管双位点催化剂具有巨大的应用前景,但目前仍面临着制备方法的挑战.如何设计并实用可行地制备出具有高效催化性能的双位点催化剂,是当前科研领域亟待解决的问题.本文提出一种由CO/CH3I混合物诱导分散Pd-Ag合金纳米颗粒的处理方法,用于制备Pd1-Ag1/AC双位点催化剂.利用X射线衍射、X射线光电子能谱和高角环形暗场扫描透射电子显微镜等方法对分散过程进行表征.结果表明,在分散过程中,CO和CH3I与金属发生协同作用,通过配位生成一种独特的双核络合物(PdI2(CO)-I2-AgI)结构.这种络合物结构逐一从合金纳米颗粒上剥落,直至完成原子级的分散.乙炔双烷氧羰基化反应结果表明,与单金属Pd1/AC相比,在相同反应条件下,双位点Pd1-Ag1/AC催化剂上的乙炔转化率提高了2倍.同时,在保持丁烯二酸二酯选择性为98%的情况下,该催化剂循环使用10次后催化剂性能未见明显变化.炔烃底物拓展结果表明,Pd1-Ag1/AC的协同作用不仅可以提高催化活性,而且在高位阻存在的情况下可以提高产物的立体选择性,这表明双位点协同促进作用对炔烃双羰基化反应具有良好的普适性.微分吸附量热表征结果证明了通过碘配体桥连的Pd1和Ag1单金属点之间的协同效应可以增强催化剂对乙炔的吸附能力.此外,结合拓展边X射线精细结构等实验结果,对催化剂的结构变化和反应机理进行了进一步的探究.第一性原理计算得到的反应能垒和过渡态结果表明,乙炔吸附是反应的速率决定步骤.与Pd1/AC相比,Pd1-Ag1/AC催化剂在反应决速步上表现出了更低的活化能,这从热力学和动力学两个层面解释了其具有更好催化性能的原因.Bader电荷分析和投影态密度计算的结果表明,由于Ag1位点的引入,使Pd1-Ag1/AC催化剂的电荷转移能力和吸附能力均得到增强.相较于Pd1/AC,Pd1-Ag1/AC具有更低的形成能,表明Ag1位点不仅可以提升催化活性,也可以增强双位点结构的稳定性.因此,在催化反应中,Ag1位点的存在起到了重要的促进作用,使得Pd1-Ag1/AC催化剂表现出更优异的性能.综上,本文制备的双位点Pd1-Ag1/AC催化剂在乙炔双烷氧羰基化反应中表现出较好的催化活性和稳定性,证明了双位点协同效应的重要性,为高效催化剂的设计和应用提供了新的思路.

非茂单活性中心-BCG复合催化剂用于制备双峰高密度聚乙烯

用负载化的非茂单活性中心催化剂和工业上聚乙烯气相法BCG催化剂复合,在单釜中进行了双峰高密度聚乙烯(双峰HDPE)的合成实验。通过考察氢气分压、聚合温度、聚合时间、乙烯压力、共聚单体等对乙烯聚合性能的影响,研究了双峰HDPE的相对分子质量及其分布、熔体流动指数和密度的变化规律,获得了双峰HDPE制备的有效调控方法。实验结果表明,此复合催化体系可在单反应器中制备出高相对分子质量部分高支化度和低相对分子质量部分低支化度的理想双峰HDPE。

Al_(2)O_(3)负载Pt基催化剂表面动态变化的谱学研究

明确多相催化剂表面在反应过程的动态变化对催化剂的优化、设计有重要意义.我们通过控制Pt的不同负载量制备了一系列Al_(2)O_(3)负载的Pt/Al_(2)O_(3)催化剂,利用X-射线衍射、X-光电子能谱、球差扫描电镜、CO-探针的红外光谱、低能离子散射谱、程序升温氧化和拉曼光谱等研究Pt/Al_(2)O_(3)的表面结构和反应过程中的变化,以丙烷直接脱氢(PDH)反应为探针,考察反应过程存在“诱导”期的表面动态变化,特别是表面积碳、表面形貌、活性位点等的演化.进而与其催化反应性能关联,发现Pt纳米粒子(NP)和团簇上丙烷易深度脱氢或断裂C-C键生成CH_(4)的同时形成积碳、随后失去活性;而孤立的Pt单原子位点(SAC)上不易生成积碳、是丙烯生成的关键活性位.

单活性中心茂金属催化剂催化乙烯与1-己烯共聚合

采用自制的单活性中心茂金属催化剂为主催化剂,甲基铝氧烷为助催化剂进行乙烯与1-己烯的共聚合。考察了溶剂、助催化剂用量、反应温度、反应压力、共聚单体浓度等对催化剂活性和共聚物性能的影响。结果表明:单活性中心茂金属催化剂催化乙烯与1-己烯共聚合的适宜溶剂为正庚烷,适宜的工艺条件为n(Al)∶n(Zr)=700~1 000,反应温度100~120℃,反应压力1.20~2.00 MPa,1-己烯浓度1.00~1.84 mol/L。

Peroxidase-like single Fe atoms anchored on Ti_(3)C_(2)T_(x)MXene as surface enhanced Raman scattering substrate for the simultaneous discrimination of multiple antioxidants

Single-atom nanozymes(SAzymes)are emerging as promising alternatives to mimic natural enzyme,which is due to high atomic utilization efficiency,well-defined geometric,and unique electronic structure.Herein,Fe single atoms supported on Ti_(3)C_(2)T_(x)(Fe-SA/Ti_(3)C_(2)T_(x))with intrinsic peroxidase activity is developed,further constructing a sensitive Raman sensor array for sensing of five antioxidants.Fe-SA/Ti_(3)C_(2)T_(x)shows excellent peroxidase-like performance in catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine(TMB)with colorimetric reactions.X-ray adsorption fine structure(XAFS)reveals that the electron transport between the Ti_(3)C_(2)T_(x)and Fe atoms occurs along Fe-O-Ti ligands,meanwhile the density functional theory(DFT)calculations confirm the spontaneous dissociation of H_(2)O_(2)and the formation of OH radicals.Furthermore,the peroxidase-like Fe-SA/Ti_(3)C_(2)T_(x)was used as surface enhanced Raman scattering(SERS)substrate of oxidized TMB(TMB+)and achieved satisfied signal amplification performance.Using the blocking effects of free radical reactions,one-off identification of 5 antioxidants,including ascorbic acid(AA),uric acid(UA),glutathione(GSH),melatonin(Mel),and tea polyphenols(TPP),could be realized with this high identifiable catalytic property.This principle could realize 100%distinguish accuracy combined with linear discriminant analysis(LDA)and heat map data analysis.A wide detection concentration ranges from 10^(-8)to 10^(-3)M for five antioxidants was also achieved.

基于酸促进的单原子活性位点Ir-La-S/AC催化剂在甲醇羰基化中的应用（英文）

甲醇羰基化是世界上重要的均相催化反应之一.无论是Rh或者Ir体系,虽然碘甲烷的引入会带来腐蚀问题,但是绝大多数的甲醇羰基化反应过程都需要碘甲烷作为助催化剂才能有较好的活性.多年来人们在不断研究非均相羰基化过程(即均相多相化),以避免均相中间歇生产和产物分离的缺点.其中Ir体系的非均相羰基化报道很少,值得关注的是Eastman公司将Ir-La/AC体系成功地应用于非均相的甲醇羰基化过程.基于此,本文试图引入硫元素以提高Ir-La/AC催化剂的羰基化活性,即将含有La和Ir前驱体的硫酸溶液通过共浸渍法制备了高活性的Ir-La-S/AC催化剂,评价了该系列催化剂的性能,并进行了深入的表征.Ir-La-S/AC催化剂的TOF最高可达2760 h^(-1),远远高于Ir-La/AC催化剂1000 h^(-1).HAADF-STEM的结果表明,Ir-La-S/AC催化剂中Ir物种绝大多数处于单分散状态,而Ir-La/AC催化剂中的Ir物种为平均粒径为1.5 nm的纳米颗粒状态,说明Ir-La-S/AC催化剂中Ir的使用效率要远远高于Ir-La/AC.其次,NH3-TPD的结果显示在制备过程中硫酸的加入使催化剂的酸性位点大幅度增多,而酸性位可以加速Ir体系机理中CO插入这一决速步骤.目前普遍认为,Ir^+物种为甲醇羰基化的活性中心,故通过TPR和原位XPS测试证实了Ir-La-S/AC催化剂比Ir-La/AC中的Ir物种在通过CO/H_2=10:1混合气活化后更容易还原到Ir^+,而且这又说明在Ir-La-S/AC催化剂中更易发生Ir^(3+)物种还原消除为Ir^+物种且同时产生酰基碘(AcI)这一重要循环步骤.所以Ir-La-S/AC催化剂具有更多的酸促进位点,更高的Ir分散度和更多的Ir^+活性物种.此外,Ir-La-S/AC催化剂的羰基化活性在66 h之后才趋于稳定(1660 h^(–1)),通过XRF测试发现该过程中有少量的硫流失,而大部分剩余的硫比较稳定的存在于催化剂表面,且通过ICP-MS结果显示Ir和La没有明显的流失,因此66 h之前活性下降主要是由于部分S的流失,而不是金属物种Ir和La流失造成的.总之,我们成功地制备了一种硫促进的双功能Ir-La-S/AC催化剂,这种方法不仅减轻了由液体酸带来的环境污染和设备腐蚀,同时避免了液相铱体系催化剂的循环使用问题.

C_2对称茂金属配合物催化丙烯均聚及丙烯与高级α-烯烃共聚

研究了C2对称的[Me2Si(2-Me-4-Ph-Ind)2]Zr Cl2双茂锆催化剂在不同条件下对丙烯均聚及丙烯与高级α-烯烃共聚反应的催化特性。研究结果表明:配合物的催化活性随着铝锆比、温度、压力的增加而提高;聚合物数均相对分子质量随着温度的提高而降低,在25℃、1 MPa丙烯压力下,可以获得数均相对分子质量高达40万的等规聚丙烯。该催化体系具有良好的共聚活性,共单体的侧链长度并不影响聚合活性。通过改变共单体的投料比,可控制共聚物中共单体的含量。

Single copper sites dispersed on hierarchically porous carbon for improving oxygen reduction reaction towards zinc-air battery

The demand for high-performance non-precious-metal electrocatalysts to replace the noble metal-based catalysts for oxygen reduction reaction(ORR)is intensively increasing.Herein,single-atomic copper sites supported on N-doped three-dimensional hierarchically porous carbon catalyst(Cu_(1)/NC)was prepared by coordination pyrolysis strategy.Remarkably,the Cu_(1)/NC-900 catalyst not only exhibits excellent ORR performance with a half-wave potential of 0.894 V(vs.RHE)in alkaline media,outperforming those of commercial Pt/C(0.851 V)and Cu nanoparticles anchored on N-doped porous carbon(CuNPs/NC-900),but also demonstrates high stability and methanol tolerance.Moreover,the Cu_(1)/NC-900 based Zn-air battery exhibits higher power density,rechargeability and cyclic stability than the one based on Pt/C.Both experimental and theoretical investigations demonstrated that the excellent performance of the as-obtained Cu_(1)/NC-900 could be attributed to the synergistic effect between copper coordinated by three N atoms active sites and the neighbouring carbon defect,resulting in elevated Cu d-band centers of Cu atoms and facilitating intermediate desorption for ORR process.This study may lead towards the development of highly efficient non-noble metal catalysts for applications in electrochemical energy conversion.