Molecular engineering binuclear copper catalysts for selective CO_(2) reduction to C_(2) products

Molecular copper catalysts serve as exemplary models for correlating the structure-reaction-mechanism relationship in the electrochemical CO_(2) reduction(eCO_(2)R),owing to their adaptable environments surrounding the copper metal centres.This investigation,employing density functional theory calculations,focuses on a novel family of binuclear Cu molecular catalysts.The modulation of their coordination configuration through the introduction of organic groups aims to assess their efficacy in converting CO_(2) to C_(2)products.Our findings highlight the crucial role of chemical valence state in shaping the characteristics of binuclear Cu catalysts,consequently influencing the eCO_(2)R behaviour,Notably,the Cu(Ⅱ)Cu(Ⅱ)macrocycle catalyst exhibits enhanced suppression of the hydrogen evolution reaction(HER),facilitating proton trans fer and the eCO_(2)R process.Fu rthermore,we explo re the impact of diverse electro n-withdrawing and electron-donating groups coordinated to the macrocycle(R=-F,-H,and-OCH_3)on the electron distribution in the molecular catalysts.Strategic placement of-OCH_3 groups in the macrocycles leads to a favourable oxidation state of the Cu centres and subsequent C-C coupling to form C_(2) products.This research provides fundamental insights into the design and optimization of binuclear Cu molecular catalysts for the electrochemical conversion of CO_(2) to value-added C_(2) products.

Surface Molecular Encapsulation with Cyclodextrin in Promoting the Activity and Stability of Fe Single-Atom Catalyst for Oxygen Reduction Reaction

Fe single-atom catalysts(Fe-SACs)have been extensively studied as a highly efficient electrocatalyst toward the oxygen reduction reaction(ORR).Nonetheless,they suffer from stability issue induced by dissolution of Fe metal center and the OH^(−)blocking.Herein,a surface molecular engineering strategy is developed by usingβ-cyclodextrins(CDs)as a localized molecular encapsulation.The CD-modified Fe-SAC(Fe-SNC-β-CD)shows obviously improved activity toward the ORR with 0.90 V,4.10 and 4.09 mA cm^(-2)for E_(1/2),J_(0)and Jk0.9,respectively.Meanwhile,the Fe-SNC-β-CD shows the excellent long-term stability against aggressive stress and the poisoning.It is confirmed through electrochemical investigation that modification ofβ-CD can,on one hand,regulate the atomic Fe coordination chemistry through the interaction between the CD and FeN_(x) moiety,while on the other mitigate the strong adsorption of OH^(−)and function as protective barrier against the poisoning molecules leading to enhanced ORR activity and stability for the Fe-SACs.The molecular encapsulation strategy demonstrates the uniqueness of post-pyrolysis surface molecular engineering for the design of single-atom catalyst.

Metal-N_(4) model single‐atom catalyst with electroneutral quadri‐pyridine macrocyclic ligand for CO_(2) electroreduction

Metal–N–C single‐atom catalysts,mostly prepared from pyrolysis of metalorganic precursors,are widely used in heterogeneous electrocatalysis.Since metal sites with diverse local structures coexist in this type of material and it is challenging to characterize the local structure,a reliable structure–property relationship is difficult to establish.Conjugated macrocyclic complexes adsorbed on carbon support are well‐defined models to mimic the singleatom catalysts.Metal–N_(4) site with four electroneutral pyridine‐type ligands embedded in a graphene layer is the most commonly proposed structure of the active site of single‐atom catalysts,but its molecular counterpart has not been reported.In this work,we synthesized the conjugated macrocyclic complexes with a metal center(Co,Fe,or Ni)coordinated with four electroneutral pyridinic ligands as model catalysts for CO_(2) electroreduction.For comparison,the complexes with anionic quadri‐pyridine macrocyclic ligand were also prepared.The Co complex with the electroneutral ligand expressed a turnover frequency of CO formation more than an order of magnitude higher than that of the Co complex with the anionic ligand.Constrained ab initio molecular dynamics simulations based on the well‐defined structures of the model catalysts indicate that the Co complex with the electroneutral ligand possesses a stronger ability to mediate electron transfer from carbon to CO_(2).

Catalytic Transformation of Bio-oil to Olefins with Molecular Sieve Catalysts

Catalytic conversion of bio-oil into light olefins was performed by a series of molecular sieve catalysts, including HZSM-5, MCM-41, SAPO-34 and Y-zeolite. Based on the light olefins yield and its carbon selectivity, the production of light olefins decreased in the following order： HZSM-5〉SAPO-34〉MCM-41〉Y-zeolite. The highest olefins yield from bio-oil using HZSM- 5 catalyst reached 0.22 kg/kgbio-oil with carbon selectivity of 50.7% and a nearly complete bio-oil conversion. The reaction conditions and catalyst characterization were investigated in detail to reveal the relationship between the catalyst structure and the production of olefins. The comparison between the pyrolysis and catalytic pyrolysis of bio-oil was also performed.

SUPPORTED ZIEGLER-NATTA CATALYSTS FOR ETHYLENE SLURRY POLYMERIZATION AND CONTROL OF MOLECULAR WEIGHT DISTRIBUTION OF POLYETHYLENE

The effect of chemical composition of highly active supported Ziegler-Natta catalysts with controlled morphology on the MWD of PE has been studied.It was shown the variation of transition metal compound in the MgCl_2-supported catalyst affect of MWD of PE produced in broad range:Vanadium-magnesium catalyst(VMC)produce PE with broad and bimodal MWD(M_w/M_n=14-21).MWD of PE,produced over titanium-magnesium catalyst(TMC)is narrow or medium depending on Ti content in the catalyst(M_w/M_n=3.1-4.8).The oxidation ...

Gas-phase epoxidation of propylene by molecular oxygen over Ag-Cu-Cl/BaCO_3 catalyst:Effects of Cu and Cl loadings

Ag‐Cu‐Cl/BaCO3 catalysts with different Cl and Cu loadings, prepared by the reduction deposition impregnation method, were investigated for gas‐phase epoxidation of propylene by molecular oxygen and characterized by X‐ray diffraction, X‐ray photoelectron spectroscopy and O2 temperatureprogrammed desorption. Ag‐Cu‐Cl/BaCO3 catalyst with 0.036 wt% Cu and 0.060 wt% Cl exhibitedthe highest catalytic performance for gas‐phase epoxidation of propylene by molecular oxygen. Apropylene oxide selectivity of 83.7% and propylene conversion of 1.2% were achieved under thereaction conditions of 20% C3H6‐10% O2‐70% N2, 200 °C, 0.1 MPa and 3000 h?1. Increasing the Clloading allowed Ag to ensemble easier, whereas changing the Cu loading showed little effect on Agcrystallite size. The appropriate Cl loading of Ag‐Cu‐Cl/BaCO3 catalyst can reduce the dissociationadsorption of oxygen to atomic oxygen species leading to the combustion of propylene to CO2, whichbenefits epoxidation of propylene by molecular oxygen. Excessive Cl loading of Ag‐Cu‐Cl/BaCO3catalyst decreases propylene conversion and propylene oxide selectivity remarkably because of Clpoisoning. The appropriate Cu loading of Ag‐Cu‐Cl/BaCO3 catalyst is efficient for the epoxidation ofpropylene by molecular oxygen, and an excess Cu loading decreases propylene oxide selectivitybecause the aggregation of Cu species increases the exposed surfaces of Ag nanoparticles, whichwas shown by slight increases in atomic oxygen species adsorbed. The appropriate loadings of Cu and Cl of Ag‐Cu‐Cl/BaCO3 catalyst are important to strike the balance between molecular oxygen and atomic oxygen species to create a favorable epoxidation of propylene by molecular oxygen.

Interfacial engineering of heterogeneous molecular electrocatalysts using ionic liquids towards efficient hydrogen peroxide production

Efficient and selective oxygen reduction reaction(ORR)electrocatalysts are critical to realizing decentralized H_(2)O_(2)production and utilization.Here we demonstrate a facile interfacial engineering strategy using a hydrophobic ionic liquid(IL,i.e.,[BMIM][NTF2])to boost the performance of a nitrogen coordinated single atom cobalt catalyst(i.e.),cobalt phthalocyanine(CoPc)supported on carbon nanotubes(CNTs).We find a strong correlation between the ORR performance of CoPc/CNT and the thickness of its IL coatings.Detailed characterization revealed that a higher O_(2)solubility(2.12×10^(−3)mol/L)in the IL compared to aqueous electrolytes provides a local O2 enriched surface layer near active catalytic sites,enhancing the ORR thermodynamics.Further,the hydrophobic IL can efficiently repel the as‐synthesized H_(2)O_(2)molecules from the catalyst surface,preventing their fast decomposition to H_(2)O,resulting in improved H_(2)O_(2)selectivity.Compared to CoPc/CNT without IL coatings,the catalyst with an optimal~8 nm IL coating can deliver a nearly 4 times higher mass specific kinetic current density and 12.5%higher H2O2 selectivity up to 92%.In a two‐electrode electrolyzer test,the optimal catalyst exhibits an enhanced productivity of 3.71 molH2O2 gcat^(–1)h^(–1),and robust stability.This IL‐based interfacial engineering strategy may also be extended to many other electrochemical reactions by carefully tailoring the thickness and hydrophobicity of IL coatings.

Highly Branched Polyethylene with Low Molecular Weight Prepared through Ethylene Polymerization on Nickel-Based Catalyst

Nickel-based catalyst [N,N]NiBr2, in which [N,N] stands for N-(2,6-diisopropylphenyl)pyridine-2-carboxaldimine, shows high activity for ethylene polymerization in the presence of organoaluminum compounds under high ethylene pressure to yield polyethylene characteristic of low molecular weight and highly branched chains. Toluene as the solvent is more in favor of catalyst activity, higher molecular weight and branched chains in polyethylene structure as compared to hexane solvent.

Preparation of Ultra-High Molecular Weight Polypropylene Using Ziegler-Natta Catalyst via Combining Internal Electron Donor and Cocatalyst Loading

Due to the development of the new energy industry,polypropylene with ultra-high molecular weight plays a crucial role for battery isolation membrane.This work investigated the effect of internal electron donor of Ziegler-Natta catalyst system on the molecular weight of the obtained polypropylene.The scanning electron microscope(SEM)and Canon camera were used to characterize the surface morphologies of catalyst particles and polymer particles,respectively.Compared with the polypropylene particles featuring a spherical shape,these study results confirmed that the morphology duplication theory from the catalyst particle to the morphology of polymer particle was exhibited.The gel permeation chromatography(GPC)results revealed that the obtained polypropylene has a much higher average molecular weight than those prepared by conventional method.The Fourier transform infrared spectrometry(FT-IR)and X-ray photoelectron spectroscopy(XPS)revealed that the carbonyl oxygen atom on ester group was preferentially bound to Mg and Ti,as compared to the ether oxygen atom.The XPS results showed that the ratio of Ti^(3+)/Ti^(4+)could be changed by internal electron donors.When Ti3+content was nearly 99%in the Ziegler-Natta catalyst system,isotactic polypropylene with an ultra-high molecular weight of up to 1.42×10^(6)g/mol was obtained by Cat.3.This result implied that internal electron donor ID3 could reduce theβ-hydride elimination reaction to further increase the molecular weight of the obtained polymer.

Catalytic Oxidative Conversion from Naphthol to 2-Hydroxy-1, 4-naphthoquinone over Iron Porphyrin Catalysts by Molecular Oxygen in an Alkaline 2-Propanol Solution

In an alkaline 2-propanol solution with 5,10,15,20-tetra(4-methoxyl phenyl) porphyrin iron chloride(TOMPPFeCl) as a catalyst and oxygen as a cheap green oxidant, 2-naphthol was conversed to 2-hydroxy-\{1,4-naphthoquinone(HNQ)\} with a yield of 62.17% and a selectivity of 100%, and the conversion number of TMOPPFeCl catalyst was 8.32/min. The catalytic oxidation products were characterized by means of UV-Vis, IR, GC-MS, ~ 1H NMR and melting point determination. In this catalytic oxidation, the catalytic activity of TMOPPFeCl was researched in detail and the reacting conditions were optimized. A possible reaction mechanism is summarized based on in situ EPR determination.

Researches on the In Situ Copolymerization of Ethylene with Catalysts Immobilized onto the Molecular Sieves

In this paper,the bi-functional catalyst system composed of molecular sieve（MCM-41） immobilized oligomerization catalyst（C25H17Cl2N3·FeCl2） and copolymerization catalyst（Et（Ind）2ZrCl2） was employed in the in situ copolymerization of ethylene aiming to prepare the Linear low density polyethylene（LLDPE）.In this paper,we mainly argued the regular pattern of the in situ copolymerization of ethylene in limited nano-space and compared it with that happening in free space.The impact of variance of the reaction temperature,Fe/Zr value and the A1/（Fe＋Zr） value on the activity of the in situ copolymerization of ethylene has also been introduced.Furthermore,the degree of branching,thermal properties and crystalline changes of the obtained polymerization products prepared from different reactivity were investigated.

THE INFLUENCE OF SUBSTITUENT ELECTRONIC EFFECT ON ETHYLENE OLIGOMERIZATION ACTIVITIES OF BIS(IMINO)PYRIDYL Fe(Ⅱ) CATALYSTS:A COMBINED MOLECULAR MECHANICS AND CHARGE EQUILIBRATION METHOD

Bis(imino)pyridyl Fe(Ⅱ) complexes are important catalysts in ethylene oligomerization for preparingα-olefins. The metal net charge-activity relationship of bis(imino)pyridyl Fe(Ⅱ) complexes was investigated by molecular mechanics (MM) and net charge equilibration(QEq) method with modified Dreiding force field.It was found that metal net charge was in reverse ratio to ethylene oligomerization activity.Electron-donor substituents with less steric hindrance to the central metal were favorable to Fe complex act...

Coupling metal oxide nanoparticle catalysts for water oxidation to molecular light absorbers

Water oxidation, as a mandatory reaction of solar fuels conversion systems, requires the use of light absorbers with electronic properties that are well matched with those of the multi-electron catalyst in order to achieve high efficiency. Molecular light absorbers offer flexibility in fine tuning of orbital energetics,and metal oxide nanoparticles have emerged as robust oxygen evolving catalysts. Hence, these material choices offer a promising approach for the development of photocatalytic systems for water oxidation.However, efficient charge transfer coupling of molecular light absorbers and metal oxide nanoparticle catalysts has proven a challenge. Recent new approaches toward the efficient coupling of these components based on synthetic design improvements combined with direct spectroscopic observation and kinetic evaluation of charge transfer processes are discussed.

Antipoisoning catalysts for the selective oxygen reduction reaction at the interface between metal nanoparticles and the electrolyte

One of the primary challenges in relation to phosphoric acid fuel cells is catalyst poisoning by phosphate anions that occurs at the interface between metal nanoparticles and the electrolyte.The strong adsorption of phosphate anions on the catalyst surface limits the active sites for the oxygen reduction reaction(ORR),significantly deteriorating fuel cell performance.Here,antipoisoning catalysts consisting of Pt-based nanoparticles encapsulated in an ultrathin carbon shell that can be used as a molecular sieve layer are rationally designed.The pore structure of the carbon shells is systematically regulated at the atomic level by high-temperature gas treatment,allowing O_(2) molecules to selectively react on the active sites of the metal nanoparticles through the molecular sieves.Besides,the carbon shell,as a protective layer,effectively prevents metal dissolution from the catalyst during a long-term operation.Consequently,the defect-controlled carbon shell leads to outstanding ORR activity and durability of the hybrid catalyst even in phosphoric acid electrolytes.

Endeavors on the development of efficient and sustainable supported metal catalysts for chemical synthesis on solid-liquid interfaces

Supported metal catalysts,particularly for precious metals,have gained increasing attention in green synthetic chemistry.They can make metal-catalyzed organic synthesis more sustainable and economical due to easy separation of product with less metal residue,as well as reusability of the high-cost catalysts.Although great effort has been spent,the precise catalytic mechanism of supported metal-catalyzed reactions has not been clearly elucidated and the development of efficient and stable recyclable catalysts remains challenging.This highlight reveals a“molecular fence”metal stabilization strategy and discloses the metal evolution in Pd-catalyzed C-C bond formation reactions using Nheterocyclic carbene(NHC)-functionalized hypercrosslinked polymer support,wherein the polymeric skeleton isolates or confines the metal species involved in the catalytic reactions,and NHC captures free low-valent metal species in solution and stabilizes them on the support via strong metal-support coordination interaction.This strategy creates a novel route for the development of supported metal catalysts with high stability and provides insights into the reaction mechanism of heterogeneous catalysis.

有机硅烷对介孔Y型分子筛理化特性及费托性能影响研究

为了合成对汽油段、柴油段产物有高选择性的催化剂载体,以多种有机硅烷为模板剂原位合成了高结晶度介孔Y型分子筛,考察了硅烷剂浓度以及有机硅烷剂中的取代基对Y型分子筛性能的影响,并以合成的介孔分子筛为载体通过浸渍法负载钴制备了催化剂,考察了催化剂的费托反应性能;采用X射线衍射、比表面积测试、扫描电子显微镜等测试手段分析了介孔分子筛及催化剂的物性特征,分别使用气相色谱质谱联用仪、气相色谱对反应产物进行了定性和定量分析。结果表明:有机硅烷剂中的硅与硅凝胶中的硅摩尔比为1∶30时达到饱和,继续提高硅烷剂浓度将导致分子筛结晶度下降,且大量的微孔损失,粒径明显减小。通过改变有机硅烷剂的取代基链长,分子筛的平均介孔尺寸可在4.9~9.0 nm进行调控。极性有机硅烷剂更有利于合成高结晶度与大比表面积的介孔分子筛,其中最大比表面积达到683.7 m^(2)/g,且相较于相同链长的非极性有机硅烷剂合成的分子筛其微孔孔容增加了约30%,而介孔孔容几乎相同。在以合成气为原料气的费托合成实验中,极性有机硅烷剂合成的分子筛催化剂对柴油段C_(10-20)产物具有较高选择性,最高达31.1%;非极性有机硅烷剂合成的分子筛催化剂对汽油段C_(5-12)产物具有较高选择性,最高达39.7%。

ZSM-5/USY/Beta分子筛催化剂对四氢萘加氢裂化制备BTEX的性能研究

分别采用ZSM-5、USY、Beta 3种分子筛通过等体积浸渍法制备了NiMo/ZSM-5、NiMo/USY、NiMo/Beta 3种催化剂,分别标记为cat-1、cat-2、cat-3。利用XRD、NH3-TPD、SEM对催化剂进行表征分析,在固定床反应器上以四氢萘作为模型化合物,研究其加氢裂化制备BTEX的催化性能,考察了四氢萘加氢裂化的工艺条件,并探讨了加氢裂化机理。结果表明,Beta分子筛制备的催化剂cat-3金属组分颗粒大小均匀,呈现出高度分散的状态,并且酸量适中。在反应温度为400℃、氢油比为600、反应压力为4MPa、2h-1空速的最佳反应条件下,与cat-1、cat-2相比,cat-3具有最佳的四氢萘转化率和BTEX选择性,分别高达95%和70%左右。

甲醇制烯烃技术研究进展

甲醇制烯烃(MTO)转化是C1化学中最重要的反应之一,它为非石油生产基础石化产品提供了一条途径.自20世纪70年代以来,甲醇转化为烯烃的工艺得到了发展并实现了商业化.许多研究机构和公司在MTO反应的机理研究方面付出了巨大努力,并在MTO工艺研发中采用择形催化剂,如ZSM-5和SAPO-34实现了甲醇高效转化为轻质烯烃、乙烯和丙烯的高选择性.我们对MTO技术的发展进行了简要的综述,并讨论了MTO反应早期初始C―C键形成的反应机制、间接反应机理、沸石和沸石催化剂上甲醇转化的复杂反应以及MTO反应的失活.

加氢裂化复合分子筛催化剂研究进展

分子筛催化剂是加氢裂化的核心,传统分子筛催化剂只具有单一性质,无法兼具酸性强、水热稳定性及催化活性高等优点,因此复合分子筛催化剂的使用受到业界广泛关注。分别对微孔、介孔组成的复合分子筛进行介绍,通过将多种具有不同孔道结构和特性的分子筛进行复合,制备出在加氢裂化反应中性能优异的复合分子筛催化剂,并对加氢裂化催化剂的发展趋势进行展望。

CTAB辅助晶种法制备ZSM-5催化MTP反应

在晶种法合成过程中添加不同比例的十六烷基三甲基溴化铵(CTAB)作为晶体生长抑制剂制备了一系列纳米ZSM-5团聚体分子筛样品。采用XRD、SEM、ICP、氩气物理吸附、NH_(3)-TPD等分析手段表征了催化剂的孔结构和酸性等,并阐述了CTAB对ZSM-5分子筛物化性质的影响:适量CTAB的添加在促进ZSM-5分子筛晶化的同时可抑制晶体的进一步生长,使初级纳米晶粒产生团聚,增加了比表面积,促进了微孔孔道的构筑,增加了酸性位点。采用固定床反应器评价了样品在高空速下的甲醇制丙烯(MTP)催化性能。结果显示,样品Z5-2(合成初始物料中CTAB/SiO_(2)摩尔比为0.02)具有适宜的孔结构和酸量,表现出较好的催化性能,丙烯选择性为47.6%。