Ni/Al_2O_3 catalysts for CO methanation: Effect of Al_2O_3 supports calcined at different temperatures

The correlation between phase structures and surface acidity of Al2O3 supports calcined at different temperatures and the catalytic performance of Ni/Al2O3 catalysts in the production of synthetic natural gas(SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al2O3 catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al2O3 supports were adjusted by calcining the commercial γ-Al2O3 at different temperatures(600–1200 C). CO methanation reaction was carried out in the temperature range of 300–600 C at different weight hourly space velocities(WHSV = 30000 and 120000 mL·g-1h-1) and pressures(0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al2O3 supports due to the rapid decrease of the specific surface area and acidity of Al2O3 supports. Interestingly, Ni catalysts supported on Al2O3 calcined at 1200 C(Ni/Al2O3-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al2O3-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures(600, 800 and 1000 C). These findings would therefore be helpful to develop Ni/Al2O3 methanation catalyst for SNG production.

High-performance Si-Containing anode materials in lithium-ion batteries: A superstructure of Si@Co-NC composite works effectively

To mitigate the massive volume expansion of Si-based anode during the charge/discharge cycles,we synthesized a superstructure of Si@Co±NC composite via the carbonization of zeolite imidazolate frameworks incorporated with Si nanoparticles.The Si@Co±NC is comprised of Sinanoparticle core and N-doped/Co-incorporated carbon shell,and there is void space between the core and the shell.When using as anode material for LIBs,Si@Co±NC displayed a super performance with a charge/discharge capacity of 191.6/191.4 mA h g^(-1)and a coulombic efficiency of 100.1%at 1000 mA g^(-1)after 3000 cycles,and the capacity loss rate is 0.022%per cycle only.The excellent electrochemical property of Si@Co±NC is because its electronic conductivity is enhanced by doping the carbon shell with N atoms and by incorporating with Co particles,and the pathway of lithium ions transmission is shortened by the hollow structure and abundant mesopores in the carbon shell.Also,the volume expansion of Si nanoparticles is well accommodated in the void space and suppressed by the carbon host matrix.This work shows that,through designing a superstructure for the anode materials,we can synergistically reduce the work function and introduce the confinement effect,thus significantly enhancing the anode materials’electrochemical performance in LIBs.

Coking-resistant Ni-ZrO_2/Al_2O_3 catalyst for CO methanation

Highly coke-resisting ZrO2-decorated Ni/A1203 catalysts for CO methanation were prepared by a two-step process. The support was first loaded with NiO by impregnating method and then modified with ZrO2 by deposition-precipitation method （IM-DP）. Nitrogen adsorption- desorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetdc analysis, H2 temperature- programmed reduction and desorption, NH3 temperature-programmed desorption, and zeta potential analysis were employed to characterize the samples. The results revealed that, compared with the catalysts with the same composition prepared by co-impregnation （CI） and sequential impregnation （SI） methods, the Ni/A1203 catalyst prepared by IM-DP showed much enhanced catalytic performance for syngas methanation under the condition of atmospheric pressure and a high weight hourly space velocity of 120000 mL.g-1 .h-1. In a 80 h life time test under the condition of 300-600 ~C and 3.0 MPa, this catalyst showed high stability and resistance to coking, and the amount of deposited carbon was only 0.4 wt%. On the contrary, the deposited carbon over the catalyst without ZrO2 reached 1.5 wt% after a 60 h life time test. The improved catalytic performance was attributed to the selective deposition of ZrO2 nanoparticles on the surface of NiO rather than A1203, which could he well controlled via changing the electrostatic interaction in the DP procedure. This unique structure could enhance the dissociation of CO2 and generate surface oxygen intermediates, thus preventing carbon deposition on the Ni particles in syngas methanation.

NiO@Ni nanoparticles embedded in N-doped carbon for efficient photothermal CO_(2) methanation coupled with H_(2)O splitting

Photothermal carbon dioxide(CO_(2))methanation has attracted increasing interest in solar fuel synthesis,which employs the advantages of photocatalytic H_(2)O splitting as a hydrogen source and photothermal catalytic CO_(2) reduction.This work prepared three-dimensional(3D)honeycomb N-doped carbon(NC)loaded with core–shell NiO@Ni nanoparticles generated in situ at 500℃(NiO@Ni/NC-500).Under the photothermal catalysis(200℃,1.5 W/cm^(2)),the CH_(4) evolution rate of NiO@Ni/NC-500 reached 5.5 mmol/(g·h),which is much higher than that of the photocatalysis(0.8 mmol/(g·h))and the thermal catalysis(3.7 mmol/(g·h)).It is found that the generated localized surface plasmon resonance enhances the injection of hot electrons from Ni to NiO,while thermal heating accelerates the thermal motion of radicals,thus generating a strong photo-thermal synergistic effect on the reaction.The CO_(2) reduction to CH_(4) follows the*OCH pathway.This work demonstrates the synergistic effect of NiO@Ni and NC can enhance the catalytic performance of photothermal CO_(2) reduction reaction coupled with water splitting reaction.

A general bottom-up synthesis of CuO-based trimetallic oxide mesocrystal superstructures for efficient catalytic production of trichlorosilane

Mesocrystals, the non-classical crystals with highly ordered nanoparticle superstructures, have shown great potential in many applications because of their newly collective properties. However, there is still a lack of a facile and general synthesis strategy to organize and integrate distinct components into complex mesocrystals, and of reported application for them in industrial catalytic reactions. Herein we report a general bottom-up synthesis of CuO-based trimetallic oxide mesocrystals (denoted as CuO-M1Ox-M2Oy, where M1 and M2 = Zn, In, Fe, Ni, Mn, and Co) using a simple precipitation method followed by a hydrothermal treatment and a topotactic transformation via calcination. When these mesocrystals were used as the catalyst to produce trichlorosilane (TCS) via Si hydrochlorination reaction, they exhibited excellent catalytic performance with much increased Si conversion and TCS selectivity. In particular, the TCS yield was increased 19-fold than that of the catalyst-free process. The latter is the current industrial process. The efficiently catalytic property of these mesocrystals is attributed to the formation of well-defined nanoscale heterointerfaces that can effectively facilitate the charge transfer, and the generation of the compressive and tensile strain on CuO near the interfaces among different metal oxides. The synthetic approach developed here could be applicable to fabricate versatile complicated metal oxide mesocrystals as novel catalysts for various industrial chemical reactions.

Ordered mesoporous Cu-Ca-Zr:A superior catalyst for direct synthesis of methyl formate from syngas

It is still a big challenge to obtain both highly active and stable Cu-based catalysts for direct synthesis of methyl formate(MF)from syngas.To address the issue,we have designed and synthesized a series of ternary Cu-Ca-Zr catalysts,namely,the ordered mesoporous Cu-Ca-Zr catalyst prepared by one-pot evaporation-induced self-assembly(EISA)method,and the supported CuO/CaO-ZrO_(2)catalysts by impregnating with copper precursor or by immobilizing copper nanoparticles.In the latter two catalysts,the ordered mesoporous CaO-ZrO_(2)support was also prepared by the EISA method.The catalysts were characterized by techniques such as ICP,XRD,TEM,N2 isotherm adsorption-desorption,XPS and H2-TPR,and used for direct synthesis of MF.The results indicated that the catalyst prepared by onepot EISA method,in which the CuO species are highly dispersed in frame of CaO-ZrO_(2),exhibits much better activity and stability as compared with the other two catalysts with most of CuO located on the outer surface of the CaO-ZrO_(2)support,because the former has a higher specific surface area,enhanced synergistic effect and stronger interaction between the CaO-ZrO_(2)support and CuO active constituent.

Partially charged single-atom Ru supported on ZrO_(2) nanocrystals for highly efficient ethylene hydrosilylation with triethoxysilane

Homogeneous noble metal catalysts used in alkene hydrosilylation reactions to manufacture organosilicon compounds commercially often suffer from difficulties in catalyst recovering and recycling,undesired disproportionation reactions,and energyintensive purification of products.Herein,we report a heterogeneous 0.5Ruδ+/ZrO_(2) catalyst with partially charged single-atom Ru(0.5 wt.%Ru)supported on commercial ZrO_(2) nanocrystals synthesized by the simple impregnation method followed by H2 reduction.When used in the ethylene hydrosilylation with triethoxysilane to produce the desired ethyltriethoxysilane,0.5Ruδ+/ZrO_(2) showed excellent catalytic performance with the maximum Ru atom utilization and good recyclability,even superior to homogeneous catalyst(RuCl3·H2O).Structural characterizations and density functional theory calculations reveal the atomic dispersion of the active Ru species and their unique electronic properties distinct from the homogeneous catalyst.The reaction route over this catalyst is supposed to follow the typical Chalk-Harrod mechanism.This highly efficient and supported singleatom Ru catalyst has the potential to replace the current homogeneous catalyst for a greener hydrosilylation industry.

二氧化碳甲烷化催化剂及反应机理研究进展

在“双碳”目标的背景下,明确碳处理路径至关重要。利用可再生能源制得的氢,将二氧化碳(CO_(2))通过甲烷化反应制备合成天然气(SNG)被广泛认为是一种高效、有前景的碳捕集利用技术,有望实现碳循环利用。近年来,二氧化碳甲烷化催化剂及相关反应机理均取得了许多新进展。鉴于此,本工作对该反应进行了系统的综述。首先,介绍了CO_(2)甲烷化反应的热力学研究中不同反应条件的影响;随后从活性金属、载体、制备方法及辅助技术等四方面介绍了CO_(2)甲烷化催化剂的研究进展,其中活性组分包括非贵金属基(Ni,Fe,Co和Mo)和贵金属基(Ru,Rh,Pt和Pd),载体包括传统氧化物(Al2O3,SiO_(2),TiO_(2),ZrO_(2)和CeO_(2))和新型载体材料(金属有机框架和碳基材料),催化剂制备方法包括传统制备方法(浸渍法、共沉淀法、水热法、溶胶-凝胶法和固相合成法)和合成辅助技术(超声波、微波和等离子体等);总结了CO_(2)甲烷化反应遵循的两条机理路径(甲酸盐路径和CO路径),并指出CO_(2)甲烷化的具体反应途径与催化剂表面特性(如羟基丰富度和O_(2)-位点)和反应条件(如反应温度和压力)相关;最后提出了当前研究存在的挑战,并对研究前景作出展望。

Dual single-atom Ce-Ti/MnO_(2)catalyst enhances low-temperature NH_(3)-SCR performance with high H_(2)O and SO_(2)resistance

Mn-based catalysts have exhibited promising performance in low-temperature selective catalytic reduction of NOx with NH_(3)(NH_(3)-SCR).However,challenges such as H_(2)O-or SO_(2)-induced poisoning to these catalysts still remain.Herein,we report an efficient strategy to prepare the dual single-atom Ce-Ti/MnO_(2)catalyst via ball-milling and calcination processes to address these issues.Ce-Ti/MnO_(2)showed better catalytic performance with a higher NO conversion and enhanced H_(2)O-and SO_(2)-resistance at a lowtemperature window(100−150°C)than the MnO_(2),single-atom Ce/MnO_(2),and Ti/MnO_(2)catalysts.The in situ infrared Fourier transform spectroscopy analysis confirmed there is no competitive adsorption between NOx and H_(2)O over the Ce-Ti/MnO_(2)catalyst.The calculation results showed that the synergistic interaction of the neighboring Ce-Ti dual atoms as sacrificial sites weakens the ability of the active Mn sites for binding SO_(2)and H_(2)O but enhances their binding to NH_(3).The insight obtained in this work deepens the understanding of catalysis for NH_(3)-SCR.The synthesis strategy developed in this work is easily scaled up to commercialization and applicable to preparing other MnO_(2)-based single-atom catalysts.

Engineering oxygen vacancies and localized amorphous regions in CuO-ZnO separately boost catalytic reactivity and selectivity

Generating different types of defects in heterogeneous catalysts for synergetic promotion of the reactivity and selectivity in catalytic reactions is highly challenging due to the lack of effective theoretical guidance.Herein,we demonstrate a facile strategy to introduce two types of defects into the CuO-ZnO model catalyst,namely oxygen vacancies(OVs)induced by H2 partial reduction and localized amorphous regions(LARs)generated via the ball milling process.Using industrially important Rochow–Müller reaction as a representative,we found OVs predominantly improved the target product selectivity of dimethyldichlorosilane,while LARs significantly increased the conversion of reactant Si.The CuO-ZnO catalyst with optimized OVs and LARs contents achieved the best catalytic property.Theoretical calculation further revealed that LARs promote the generation of the Cu3Si active phase,and OVs impact the electronic structure of the Cu3Si active phase.This work provides a new understanding of the roles of different catalyst defects and a feasible way of engineering the catalyst structure for better catalytic performances.

Rambutan-like hierarchically heterostructured CeO2-CuO hollow microspheres： Facile hydrothermal synthesis and applications

Hierarchically heterostructured hollow spheres are of great interest for a wide range of applications owing to their unique structural features and properties. However, the fabrication of well-defined hollow spheres with highly specific morphology for mixed transition metal oxides on a large scale remains challenging. In this work, uniform rambutan-like heterostructured CeO2~CuO hollow microspheres with numerous copper-ceria interfacial sites and nanorods and nanoparticles as building blocks are prepared via a facile hydrothermal method followed by calcination. Importantly, this approach can be readily scaled up and is applicable to the synthesis of various CuO-based mixed metal oxide complex hollow spheres. The as-prepared CeO2-CuO hollow rambutans exhibit superior performance both as electrode materials for supercapacitors and as Cu-based catalysts for the Rochow reaction, mainly due to the small primary nanoparticle constituents, high surface area, and formation of numerous interior heterostructures.

One-dimensional Cu-based catalysts with layered Cu-Cu20-CuO walls for the Rochow reaction

A series of copper catalysts with a core-shell or tubular structure containing various contents of Cu, Cu2O, and CuO were prepared via controlled oxidation of Cu nanowires （NWs） and used in the synthesis of dimethyldichlorosilane （M2） via the Rochow reaction. The Cu NWs were prepared from copper （Ⅱ） nitrate using a solution-based reduction method. The samples were characterized by X-ray diffraction, thermogravimetric analysis, temperature-programmed reduction, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. It was found that the morphology and composition of the catalysts could be tailored by varying the oxidation temperature and time. During the gradual oxidation of Cu NWs, the oxidation reaction inflated on the outer surface and gradually developed into the bulk of the NWs, leading to the formation of catalysts with various structures and layered compositions, e.g., Cu NWs with surface Cu2O, ternary Cu-Cu2O-CuO core-shell NWs, binary Cu2O-CuO nanotubes （NTs）, and single CuO NTs. Among these catalysts, ternary Cu-Cu2O-CuO core-shell NWs exhibited superior M2 selectivity and Si conversion in the Rochow reaction. The enhanced catalytic performance was mainly attributed to improved mass and heat transfer resulting from the peculiar heterostructure and the synergistic effect among layered components. Our work indicated that the catalytic property of Cu-based nanoparticles can be improved by carefully controlling their structures and compositions.

Converting industrial waste contact masses into effective multicomponent copper-based catalysts for the Rochow process

In this work, we report a simple and inexpensive approach to synthesize effective multicomponent Cu-Cu2O-CuO catalysts for the Rochow process from industrial waste contact masses （WCMs）. WCMs from the organosilane industry were treated with acid followed by reduction with metallic iron powder. The obtained copper powder was then subjected to controlled oxidation in air at different temperatures, followed by ball milling. The orthogonal array approach was applied to optimize this process, and the stirring speed and pH were found to significantly affect the leaching ratio and copper yield, respectively. When used for the Rochow process, the optimized ternary Cu-Cu2O-CuO catalyst greatly enhanced the dimethyldichlorosilane selectivity and Si conversion compared with Cu-Cu2O-CuO catalysts prepared without ball milling, bare Cu catalysts, and Cu-Cu2O-CuO catalysts with different compositions. This could be attributed to their small particle size and the strong synergistic effect among the multiple components in the catalyst with the optimized composition.

Solid-state synthesis of Li[Li_(0.2)Mn_(0.56)Ni_(0.16)Co_(0.08)]O_2 cathode materials for lithium-ion batteries

Layered Li[Li0.2Mn.56Ni0.6Co0.08]O2 cathode materials were synthesized via a solid-state reaction for Liion batteries, in which lithium hydroxide monohydrate, manganese dioxide, nickel monoxide, and cobalt monoxide were employed as metal precursors. To uncover the relationship between the structure and electrochemical properties of the materials, synthesis conditions such as calcination temperature and time as well as quenching methods were investigated. For the synthesized Li[Li0.2Mn.56Ni0.6Co0.08]O2 materials, the metal components were found to be in the form of Mn4＋, Ni2＋, and Co3＋, and their molar ratio was in good agreement with stoichiometric ratio of 0.56：0.16：0.08. Among them, the one synthesized at 800 ℃ for 12 h and subsequently quenched in air showed the best electrochemical performances, which had an initial discharge specific capacity and coulombic efficiency of 265.6 mAh/g and 84.0%, respectively, and when cycled at 0.5, 1, and 2 C, the corresponding discharge specific capacities were 237.3, 212.6, and 178.6 mAh/g, respectively. After recovered to 0.1 C rate, the discharge specific capacity became 259.5 mAh/g and the capacity loss was only 2.3% of the initial value at 0.1 C. This work suggests that the solid-state synthesis route is easy for preparing high performance Li[Li0.2Mn0.56Ni0.16Co0.08]O2 cathode materials for Li-ion batteries.

In-situ growth of heterophase Ni nanocrystals on graphene for enhanced catalytic reduction of 4-nitrophenol

Generating heterophase structures in nanomaterials,e.g.,heterophase metal nanocrystals,is an effective way to tune their physicochemical properties because of their high-energy nature and unique electronic environment of the generated interfaces.However,the direct synthesis of heterophase metal nanocrystals remains a great challenge due to their unstable nature.Herein,we report the in situar direct synthesis of heterophase Ni nanocrystals on graphene.The heterostructure of face-centered cubic(fee)and hexagonal close-packed(hep)phase was generated via the epitaxial growth of hep Ni and the partial transformation of fee Ni and stabilized by the anchoring effect of graphene toward fee Ni nanocrystal and the preferential adsorption of surfactant polyethylenimine(PEI)toward epitaxial hep Ni.Comparing with the fee Ni nanocrystals grown on graphene,the heterophase(fcc/hcp)Ni nanocrystals in situ grown on graphene showed a greatly improved catalytic activity and reusability in 4-nitrophenol(4-NP)reduction to 4-aminophenol(4-AP).The measured apparent rate constant and the activity parameter were 2.958 min^(-1) and 102 min^(-1)·mg^(-1),respectively,higher than that of the best reported non-noble metal catalysts and most noble metal catalysts.The control experiments and density functional theory calculations reveal that the interface of the fee and hep phases enhances the adsorption of substrate 4-NP and thus facilitates the reaction kinetics.This work proves the novel idea for the rational design of heterophase metal nanocrystals by employing the synergistic effect of surfactant and support,and also the potential of creating the heterostructure for enhancing their catalytic reactivity.