Smart tailoring of molecular catalysts:Mounting approach to oxygen reduction reaction

Efficient electrocatalytic rupture of energy-rich molecules(H_(2)and O_(2))is a green approach for gener-ating clean energy for modern societies.In this context,porphyry-type molecular electrocatalysts act intelligently toward oxygen reduction reaction(ORR),a fundamental process in fuel cells,due to their redox-rich chemistry,which involves core metal ions and macrocyclic ligands.The concerned scientific community has tried many times to correlate the ORR intermediates with their formation kinetics and simplify the associated multi H+/e-stages during the ORR process,constructing several volcano plots be-tween catalytic Tafel data,turnover frequencies,and overpotentials for many electrocatalysts.Despite the fact that many review articles on molecular electrocatalysts for ORR have been published,understanding the strategic implications and molecular catalyst intelligence towards homogenous ORR has been poorly explored.This review examined the relationships between volcano plots of current vs.thermodynamic parameters and the Sabatier principle in order to explain the intelligence of molecular electrocatalysts and approaches for their creation,as well as the difficulties and potential prospects of molecular electro-catalysts.These facts distinguish this review from previously published articles and will pique the scien-tific community’s interest in avoiding trial-and-error procedures for catalyst creation while also allowing for more exact evaluations of the molecular catalyst’s performance.

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.

Ligand centered electrocatalytic efficient CO_(2) reduction reaction at low overpotential on single-atom Ni regulated molecular catalyst

Electrochemical CO_(2) reduction reaction(CO_(2)RR)into value-added chemicals/fuels is crucial for realizing the sustainable carbon cycle while mitigating the energy crisis.However,it is impeded by the relatively high overpotential and low energy efficiency due to the lack of efficient electrocatalysts.Herein,we develop an isolated single-atom Ni catalyst regulated strategy to activate and stabilize the iron phthalocyanine molecule(Ni SA@FePc)toward a highly efficient CO_(2)RR process at low overpotential.The well-defined and homogenous catalytic centers with unique structures confer Ni SA@FePc with a significantly enhanced CO_(2)RR performance compared to single-atom Ni catalyst and FePc molecule and afford the atomic understanding on active sites and catalytic mechanism.As expected,Ni SA@FePc exhibits a high selectivity of more significant Faraday efficiency(≥95%)over a wide potential range,a high current density of~252 mA·cm^(−2) at low overpotential(390 mV),and excellent long-term stability for CO_(2)RR to CO.X-ray absorption spectroscopy measurement and theoretical calculation indicate the formation of NiN_(4)-O_(2)-FePc heterogeneous structure for Ni SA@FePc.And CO_(2)RR prefers to occur at the raised N centers of NiN4-O_(2)-FePc heterogeneous structure for Ni SA@FePc,which enables facilitated adsorption of*COOH and desorption of CO,and thus accelerated overall reaction kinetics.

A hybrid artificial photosynthesis system with molecular catalysts covalently linked onto TiO2 as electron relay for efficient photocatalytic hydrogen evolution

Efficient charge carrier transfer from light harvesters to catalysts greatly determines the photocatalytic activity in an artificial photosynthesis(AP) system for solar hydrogen evolution.In this study,an AP system composed of xanthene dye as light harvester and cobaloxime molecular complex as catalyst,with TiO2 as electron relay,was designed for photocatalytic hydrogen evolution under visible light(λ>420 nm).It was demonstrated that with cobaloxime molecule covalently linked onto the TiO2 electron relay,the resulting hybrid AP system exhibited much increased photocatalytic activity as compared to that without TiO2.The greatly increased photocatalytic activity should be due to the efficient electron transfer from xanthene dye as light harvester and cobaloxime molecular complex as catalyst,shuttled by the TiO2 electron relay,for the following water reduction reaction.The present study demonstrates a facile and feasible strategy to guide the design of high performance AP systems through the electron relay shuttled and promoted cha rge transfer process.

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.

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...

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.

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.

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 ...

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。

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-22分子筛合成及其正十二烷烃临氢异构化性能:模板剂和动态晶化的影响

以二乙胺(DEA)或1,6-己二胺(DAH)为模板剂,分别在静态或动态条件下合成具有不同形貌和聚集状态的ZSM-22分子筛,采用XRD、SEM、EDS、TEM、NH3-TPD及N2吸附/脱附表征手段对其进行表征分析。并负载Pt在Al2O3上和ZSM-22机械混合制备双功能催化剂,考察其正十二烷的临氢异构化反应性能。结果表明,模板剂和动态晶化会改变ZSM-22分子筛的形貌及聚集状态,并且会影响其酸性、比表面积和临氢异构活性。其中,以二乙胺为模板剂,静态晶化72h合成的ZSM-22具有最优的催化性能,在310℃反应温度下,正十二烷异构化转化率为66%时,异构十二烷的选择性达到90%。但是,模板剂及动态晶化条件对单支链异构体的产物分布影响较小,异构体产物以支链靠近端位的2-甲基十一烷为主,且随着反应温度升高,2-甲基异构体选择性明显降低。

A perspective on the electrocatalytic conversion of carbon dioxide to methanol with metallomacrocyclic catalysts

Electrocatalytic carb on dioxide reducti on(CO_(2)R)presents a promising route to establish zero-e mission carb on cycle and store in termittent ren ewable energy into chemical fuels for steady energy supply.Methanol is an ideal energy carrier as alternative fuels and one of the most important commodity chemicals.Nevertheless,methanol is currently mainly produced from fossil-based syngas,the production of which yields tremendous carb on emission globally.Direct CO_(2)R towards metha nol poses great potential to shift the paradigm of methanol production.In this perspective,we focus our discussions on producing methanol from electrochemical CO_(2)R,using metallomacrocyclic molecules as the model catalysts.We discuss the motivation of having methanol as the sole CO_(2)R product,the documented application of metallomacrocyclic catalysts for CO_(2)R,and recent advance in catalyzing CO_(2) to methanol with cobalt phthalocyanine-based catalysts.We attempt to understand the key factors in determining the activity,selectivity,and stability of electrocatalytic CO_(2)-to-methanol conversion,and to draw mechanistic insights from existing observations.Finally,we identify the challenges hindering methanol electrosynthesis directly from CO_(2) and some intriguing directions worthy of further investigation and exploration.

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。

基于不同原料的碳分子筛制备技术及其应用研究进展

碳分子筛(CMS)具有孔隙结构发达、孔径分布均匀、热稳定性高等优点,可用于吸附、催化等领域。本文从CMS制备技术及其应用入手,介绍了煤、有机高分子聚合物和生物质作为CMS制备原料的性能差异,比较了活化法、沉积法、热缩聚法和模板法等方法制备CMS的优缺点,其中,炭化法、活化法及热缩聚法操作简单,但炭化法对原料要求高,活化法使用KOH等活化剂易产生有毒废水,热缩聚法则能耗较高;苯沉积法和模板法都可调节孔径结构,但苯沉积受沉积温度、流速等因数影响,而模板法与活化法一样,易产生有毒废水。重点阐述KOH活化法和苯类气相沉积法制备CMS的原理,以及可以利用减少CMS晶粒尺寸、引入空心或多级孔结构、保留微孔提供的催化活性中心等CMS改性方式来提高CMS性能。总结了CMS在吸附分离、催化等领域的应用现状,对CMS的发展方向进行了展望。

封装型Ni基催化剂制备及其原位提质煤热解焦油的性能

为实现煤热解焦油原位轻质化,分别用原位封装法和浸渍法制备Ni基催化剂,并考察这两种催化剂对热解焦油原位催化提质的影响。与不加催化剂相比,Ni含量2%Ni/HZSM-5可使焦油中轻质组分产率由5.8%提至6.9%,而相同Ni含量的Ni@HZSM-5可使轻质焦油产率提至7.6%。进一步分析Ni/HZSM-5和Ni@HZSM-5催化剂对焦油各馏分产率的影响,结果表明,2种催化剂均使焦油中重质组分明显降低,沥青质产率分别由5.4%降至1.3%和2.0%,但相较Ni/HZSM-5,Ni@HZSM-5使焦油中轻油和酚油产率分别上升38.5%和25.5%,萘油产率也有所上升,说明封装法制备的Ni基催化剂可使焦油中轻质组分最大程度保留。因为在Ni/HZSM-5中焦油裂解和热解气中富氢组分活化均发生在Ni表面,在促进富氢气体活化的同时也造成焦油过度裂解。而Ni@HZSM-5中Ni主要分布于分子筛孔道内,其良好择形催化性可使富氢气体分子进入HZSM-5分子筛内部与Ni接触产生·H和·CH x等富氢自由基,而焦油中大分子无法进入HZSM-5孔道,其裂解仅发生在分子筛外表面酸性位点上,避免了金属Ni参与焦油裂解,从而定向调控焦油裂解碎片和富氢自由基数量,达到体系内氢碳平衡,有效避免焦油碎片过度裂解,提高轻质焦油产率。

Deactivation mechanisms and anti-deactivation strategies of molecular sieve catalysts for NO_(x)reduction

Molecular sieve catalysts,owing to their unique chemical properties,are widely used as catalysts among various catalytic reactions.Abundant Br?nsted acid sites in molecular sieve catalysts usually enable active components to disperse well on the catalyst surface,and help to adsorb a large number of gas molecules to achieve maximum catalytic performance.Therefore,a variety of molecular sieve catalysts have been developed and used in the selective catalytic reduction of NO_(x)by NH_(3)(NH_(3)-SCR).For example,Cu molecular sieve catalysts such as Cu-SSZ-13 and Cu-SAPO-34 with wide temperature windows and stable structure are considered and applied as commercial catalysts for NO_(x)removal in diesel vehicles for a long time.Although molecular sieve catalysts possess many advantages,they still cannot avoid the serious deactivation caused by various factors in practical applications.In this review,reasons leading to the deactivation of molecular sieve catalysts for NO_(x)reduction in actual working conditions were concluded.The deactivation mechanisms of molecular sieve catalysts for NO_(x)reduction were analyzed and the corresponding anti-deactivation strategies were summarized.Finally,challenges and prospects of molecular sieve catalysts for NO_(x)reduction were also proposed.

过渡金属多相催化分子氧选择性氧化邻二醇的研究进展

邻二醇选择性氧化断键生成醛、酮和羧酸是重要和基本的有机反应,氧化剂通常采用化学计量的高碘酸盐或四乙酸铅,无论从经济还是环保的角度考虑,这些传统方法都有违绿色化工的发展理念。理论上以分子氧为氧化剂选择性氧化邻二醇断键的副产物只有水,而且分子氧廉价易得,因而具有环境友好和经济可行的双重优势。经过多年探索,人们已开发了多个基于不同过渡金属为活性组分的多相催化剂或催化体系用于分子氧选择性氧化邻二醇断键反应,为未来广泛应用奠定了基础。该文按贵金属和非贵金属分类综述此类催化剂及相关反应工艺的研究进展,并指出该领域的发展方向。

NaY分子筛复合材料及其催化裂化催化剂性能

以高岭土和水玻璃为原料,采用水热法原位晶化合成了NaY分子筛复合材料,通过离子交换法改性并制备出催化裂化催化剂,利用X射线荧光仪、N2吸附-脱附仪、扫描电子显微镜等仪器对试样进行结构表征,在固定流化床微型反应器装置上进行催化剂裂化反应性能评价。结果表明:该NaY分子筛复合材料的外比表面积为93.70 m^(2)/g,介孔孔容为0.19 cm^(3)/g,颗粒直径约在300~500 nm;改性后复合材料的介孔主要分布在2~20 nm,且为双孔分布,分布峰分别为3.8,5.6 nm;与常规NaY型分子筛催化剂相比,采用该NaY型分子筛复合材料所制备的催化剂其反应转化率、液化气和总液体收率依次提高6.18,5.16,1.61个百分点,重油收率下降3.34个百分点,生焦因子下降0.80。