BDAF-PMDA型聚酰亚胺炭膜的制备及其气体分离性能的研究

以2,2-双[4-(4-氨基苯氧基苯基)]六氟丙烷(BDAF)为二胺单体,均苯四酸二酐(PMDA)为二酐单体,采用两步法制备了BDAF-PMDA型聚酰亚胺,进一步高温热解制备炭膜.采用红外、热重、X射线衍射分析其结构变化,并测试炭膜对纯组分及混合气体的渗透性能和分离选择性.结果表明,BDAF-PMDA型炭膜具有较高的气体渗透性,在CO2/H2体系中可优先渗透CO2.提高炭化温度,炭膜孔径减小,气体的渗透性能降低,选择性提高,并使得BDAF-PMDA型炭膜的分离机理由表面扩散为主逐渐变为表面扩散和分子筛分共同控制.

机械球磨法制备NiMo催化剂及其在菲加氢中的应用

采用机械球磨法制备NiMo催化剂,通过XRD、XPS等表征其结构,探究Ni/(Ni+Mo)比对催化剂组成和结构及菲加氢性能的影响。结果表明,该法制备的催化剂活性组分Ni和Mo的分散性好,为孔径集中分布于2−10 nm的介孔催化剂。随Ni/(Ni+Mo)比增加,催化剂的比表面积和Mo^(IV)含量呈现出先增加后降低趋势,均于0.33处达到最高。适量Ni促进Mo硫化形成NiMoS活性相,过量的Ni会形成Ni_(x)S_(y),覆盖活性位点,降低加氢活性。恒定Ni/(Ni+Mo)比为0.33,催化剂的比表面积随Ni、Mo含量增加明显降低,而MoIV含量增加。增加硫化剂硫代硫酸铵(ATS)的用量,可同时提高催化剂的比表面积和Mo^(IV)的含量。Ni/(Ni+Mo)比对菲转化率的影响表现出与催化剂中Mo^(IV)含量相一致的变化趋势,当Ni/(Ni+Mo)比为0.33时,菲转化率达最高值74.7%。在该比例下,Ni、Mo含量及S/Mo比分别增至4.8%、16%和4.5时,菲的转化率达96.5%,八氢菲和全氢菲的总选择性和产率分别为83.9%和80.9%,且菲主要从侧环进行深度加氢形成全氢菲。

掺氮纳米炭球担载高分散钯纳米催化剂的制备及其苯甲醇氧化性能(英文)

负载型贵金属纳米催化剂中的金属纳米粒子易发生团聚或流失,因此提高金属活性组分的分散性和稳定性很重要。我们报道了一种制备高分散钯纳米催化剂的方法,通过浸泡法将氯钯酸前驱体负载到苯并噁嗪聚合物上,再经过惰性气氛一步热解得到纳米炭球担载钯催化剂.催化剂性能通过温和条件下苯甲醇氧化反应进行评价.经过500℃热处理制备的催化剂,从TEM图可以看出Pd纳米粒子均匀分散在载体上,尺寸大小约为3 nm,这是由于载体和钯活性组分的配位作用有利于提高钯纳米粒子的分散性和稳定性.通过调控金属负载量及负载时间,尽可能地实现活性组分分布在载体外表面,制备的催化剂上最高TOF为690 h-1.此催化剂同时具有较好的循环稳定性,失活后的催化剂经过200℃焙烧即可实现再生.

Promotion effects of nickel-doped Al2O3-nanosheet-supported Au catalysts for CO oxidation

Supported gold catalysts show high activity toward CO oxidation, and the nature of the support significantly affects the catalytic activity. Herein, serial Ni doping of thin porous Al2 O3 nanosheets was performed via a precipitation-hydrothermal method by varying the amount of Ni during the precipitation step. The prepared nanosheets were subsequently used as supports for the deposition of Au nanoparticles(NPs). The obtained Au/Nix Al catalysts were studied in the context of CO oxidation to determine the effect of Ni doping on the supports. Enhanced catalytic performances were obtained for the Au/Nix Al catalysts compared with those of the Au supported on bare Al2 O3. The Ni content and pretreatment atmosphere were both shown to influence the catalytic activity. Pretreatment under a reducing atmosphere was beneficial for improving catalytic activity. The highest activity was observed for the catalysts with a Ni/Al molar ratio of 0.05, achieving complete CO conversion at 20 °C with a gold loading of 1 wt%. The in-situ FTIR results showed that the introduction of Ni strengthened CO adsorption on the Au NPs. The H2-TPR and O2-TPD results indicated that the introduction of Ni produced new oxygen vacancies and allowed the oxygen molecules to be adsorbed and activated more easily. The improved catalytic performance after doping Ni was attributed to the smaller size of the Au NPs and more active oxygen species.

Green and efficient epoxidation of methyl oleate over hierarchical TS-1

The epoxidation of methyl oleate(MO)was conducted in the presence of aqueous H2O2 as the oxidant and hierarchical TS-1(HTS-1)as the catalyst;the catalyst was synthesized using polyquaternium-6 as the mesopore template.The effects of various parameters,i.e.,H2O2/C=C molar ratio,oxidant concentration,amount of the catalyst,reaction temperature,and time,were systematically studied.Furthermore,response surface methodology(RSM)was used to optimize the conditions to maximize the yield of epoxy MO and to evaluate the significance and interplay of the factors affecting the epoxy MO production.The H2O2/C=C molar ratio and catalyst amount were the determining factors for MO epoxidation,wherein the maximum yield of epoxy MO reached 94.9%over HTS-1 under the optimal conditions.

Ordered macroporous boron phosphate crystals as metal-free catalysts for the oxidative dehydrogenation of propane

Ordered macroporous materials with rapid mass transport and enhanced active site accessibility are essential for achieving improved catalytic activity.In this study,boron phosphate crystals with a three-dimensionally interconnected ordered macroporous structure and a robust framework were fabricated and used as stable and selective catalysts in the oxidative dehydrogenation(ODH)of propane.Due to the improved mass diffusion and higher number of exposed active sites in the ordered macroporous structure,the catalyst exhibited a remarkable olefin productivity of^16 golefin gcat^-1 h^-1,which is up to 2–100 times higher than that of ODH catalysts reported to date.The selectivity for olefins was 91.5%(propene:82.5%,ethene:9.0%)at 515℃,with a propane conversion of 14.3%.At the same time,the selectivity for the unwanted deep-oxidized CO2 product remained less than 1.0%.The tri-coordinated surface boron species were identified as the active catalytic sites for the ODH of propane.This study provides a route for preparing a new type of metal-free catalyst with stable structure against oxidation and remarkable catalytic activity,which may represent a potential candidate to promote the industrialization of the ODH process.

A viewpoint on catalytic origin of boron nitride in oxidative dehydrogenation of light alkanes

Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics,but encounters difficulties in selectivity control for alkenes because of over-oxidation reactions that produce a substantial amount of undesired carbon oxides.Recent progress has revealed that boron nitride is a highly promising catalyst in the oxidative dehydrogenation of light alkanes because of its superior selectivity for and high productivity of light alkenes,negligible formation of CO2,and remarkable catalyst stability.From this viewpoint,recent works on boron nitride in the oxidative dehydrogenations of ethane,propane,butane,and ethylbenzene are reviewed,and the emphasis of this viewpoint is placed on discussing the catalytic origin of boron nitride in oxidative dehydrogenation reactions.After analyzing recent progress in the use of boron nitride for oxidative dehydrogenation reactions and finding much new evidence,we conclude that pure boron nitride is catalytically inert,and an activation period is required under the reaction conditions;this process is accompanied by an oxygen functionalization at the edge of boron nitride;the B-O species themselves have no catalytic activity in C-H cleavage,and the B-OH groups,with the assistance of molecular oxygen,play the key role in triggering the oxidative dehydrogenation of propane;the dissociative adsorption of molecular oxygen is involved in the reaction process;and a straightforward strategy for preparing an active boron nitride catalyst with hydroxyl groups at the edges can efficiently enhance the catalytic efficacy.A new redox reaction cycle based on the B-OH sites is also proposed.Furthermore,as this is a novel catalytic system,there is an urgent need to develop new methods to optimize the catalytic performances,clarify the catalytic function of boron species in the alkane ODH reactions,and disclose the reaction mechanism under realistic reaction conditions.

Highly selective catalysts for the hydrogenation of alkynols:A review

The semi-hydrogenation of alkynols to enols is a crucial process in the production of pharmaceuticals,agrochemicals,fragrances,and flavors that involves a complex set of parallel and consecutive isomerization and hydrogenation reactions and proceeds via several key intermediates.In view of the industrial importance of large-scale enol production through alkynol hydrogenation,various noble and non-noble metal(e.g.,Ni and Pd)-based catalysts promoting this transformation have been developed.This paper reviews the design of highly selective catalysts for the semi-hydrogenation of alkynols,focusing on the role of additives,second metals,catalyst supports,and reaction conditions and combining catalytic reaction kinetics with theoretical calculations to establish the reaction mechanism and the decisive factors for boosting selectivity.Finally,a strategy for designing highly efficient and selective catalysts based on the characteristics of aqueous-phase alkynol hydrogenation is proposed.

Highly dispersed boron-nitride/CuO_(x)-supported Au nanoparticles for catalytic CO oxidation at low temperatures

Supported-Au catalysts show excellent activity in CO oxidation,where the nature of the support has a significant impact on catalytic activity.In this work,a hexagonal boron nitride(BN)support with a high surface area and adequately exposed edges was obtained by the ball-milling technique.Thereafter,impregnation of the BN support with Cu(NO3)2 followed by calcination under air at 400℃ yielded a CuO-modified support.After Au loading,the obtained Au-CuO_(x)/BN catalyst exhibited high CO oxidation activity at low temperatures with a 50%CO conversion temperature(T50%)of 25℃ and a complete CO conversion temperature(T100%)of 80℃,well within the operational temperature range of proton exchange membrane fuel cells.However,the CO oxidation activity of Au/BN,prepared without CuO_(x) for comparison,was found to be relatively low.Our study reveals that BN alone disperses both Cu and Au nanoparticles well.However,Au nanoparticles on the surface of BN in the absence of CuO species tend to aggregate upon CO oxidation reactions.Conversely,Au nanoparticles supported on the surface of CuO-modified BN remain small with an average size of~2.0 nm before and after CO oxidation.Moreover,electron transfer between Au and Cu species possibly favors the stabilization of highly dispersed Au nanoparticles on the BN surface and also enhances CO adsorption.Thus,our results demonstrate that thermally stable and conductive CuO-modified BN is an excellent support for the preparation of highly dispersed and stable Au catalysts.

Effects of Ni particle size on amination of monoethanolamine over Ni-Re/SiO_2 catalysts

Ni-Re/SiO2 catalysts with controllable Ni particle sizes(4.5–18.0 nm)were synthesized to investigate the effects of the particle size on the amination of monoethanolamine(MEA).The catalysts were characterized by various techniques and evaluated for the amination reaction in a trickle bed reactor at 170℃,8.0 MPa,and 0.5 h^-1 liquid hourly space velocity of MEA(LHSVMEA)in NH3/H2 atmosphere.The Ni-Re/SiO2 catalyst with the lowest Ni particle size(4.5 nm)exhibited the highest yield(66.4%)of the desired amines(ethylenediamine(EDA)and piperazine(PIP)).The results of the analysis show that the turnover frequency of MEA increased slightly(from 193 to 253 h^-1)as the Ni particle sizes of the Ni-Re/SiO2 catalysts increased from 4.5 to 18.0 nm.Moreover,the product distribution could be adjusted by varying the Ni particle size.The ratio of primary to secondary amines increased from 1.0 to 2.0 upon increasing the Ni particle size from 4.5 to 18.0 nm.Further analyses reveal that the Ni particle size influenced the electronic properties of surface Ni,which in turn affected the adsorption of MEA and the reaction pathway of MEA amination.Compared to those of small Ni particles,large particles possessed a higher proportion of high-coordinated terrace Ni sites and a higher surface electron density,which favored the amination of MEA and NH3 to form EDA.

Synthesis of Ni^2+cation modified TS-1 molecular sieve nanosheets as effective photocatalysts for alcohol oxidation and pollutant degradation

lmprovement of the charge separation of titanosilicate molecular sieves is critical to their use asphotocatalysts for oxidative organic transformations.In this work,MFI TS-1 molecular sievenanosheets(TS-1 NS)were synthesized by a low-temperature hydrothermal method using a tai-lored diquaternary ammonium surfactant as the structure-directing agent.Introducing Ni^2+cationsat the ion-exchange sites of the TS-1 NS framework significantly enhanced its photoactivity in aero-bic alcohol oxidation.The optimized Ni cation-functionalized TS-1 NS(Ni/TS-1 NS)provide impres-sive photoactivity,with a benzyl alcohol(BA)conversion of 78.9%and benzyl aldehyde(BAD)se-lectivity of 98.8%using O as the only oxidant under full light irradiation;this BAD yield is approx-imately six times greater than that obtained for bulk TS-1,and is maintained for five runs.The ex-cellent photoactivity of Ni/TS-1 NS is attributed to the significantly enlarged surface area of thetwo-dimensional morphology TS-1 NS,extra mesopores,and greatly improved charge separation.Compared with bulk TS-1,Ni/TS-1 NS has a much shorter charge transfer distance.Theas-introduced Ni species could capture the photoelectrons to further improve the charge separa-tion.This work opens the way to a class of highly selective,robust,and low-cost titanosilicate mo-lecular sieve-based photocatalysts with industrial potential for selective oxidative transformationsand pollutant degradation.

Pyrrolic N or pyridinic N: The active center of N-doped carbon for CO_(2) reduction

Pyridinic N is widely regarded as the active center while pyrrolic N has low‐activity in metal‐free N‐doped carbon for electrocatalytic CO_(2) reduction reaction(CO_(2)RR)to CO,but this viewpoint remains open to question.In this study,through density functional theoretical calculations,we first illustrate that the intrinsic activity of pyrrolic N is high enough for effectively catalyzing CO_(2)RR,however,due to the interplay with the neighboring pyridinic N sites,the activity of pyrrolic N is dramatically suppressed.Then,experimentally,metal‐free N‐doped carbon spheres(NCS)electrocatalysts without significant pyridinic N content are prepared for CO_(2)RR.The pyrrolic N in NCS shows a direct‐positive correlation with the performance for CO_(2)RR,representing the active center with high activity.The optimum NCS could produce syngas with a wide range of CO/H_(2) ratio(0.09 to 12)in CO_(2)RR depending on the applied potential,meanwhile,the best selectivity of 71%for CO can be obtained.Intentionally adding a small amount of pyridinic N to the optimum NCS dramatically decreases the activity for CO_(2)RR,further verifying the suppressed activity of pyrrolic N sites by the neighboring pyridinic N sites.This work reveals the interaction between a variety of N species in N‐doped carbon,and the potential of pyrrolic N as the new type of active site for electrocatalysts,which can improve our understanding of the electrocatalysis mechanism and be helpful for the rational design of high‐efficient electrocatalysts.

Quaternary-ammonium-immobilized polystyrenes as efficient and reusable heterogeneous catalysts for synthesis of cyclic carbonate:Effects of linking chains and pendent hydroxyl group

Spherical polystyrene‐supported ammonium salts containing different linking chains between the support and ammonium groups were prepared as efficient and easily reusable heterogeneous catalysts for the cycloadditions of CO2and epoxides.The effects of the length of the linking chains and a hydroxyl group pendent on the linking chain on the catalytic performance of ionic liquid immobilized catalysts and their mechanisms were studied through experiments and density functional theory calculations.It was found that,compared with a short linking chain,a long chain can make the halogen anion more negative and provide a larger contact area of the catalysts with the reactants,thus enhancing the reaction kinetics.The hydroxyl group can stretch the C-O bonds of the epoxides,promoting the reaction thermodynamics.As a result,for the cycloaddition of propylene oxide,the yield of propylene carbonate is much higher for the catalyst with a long linking chain(yield:91.4%)compared with the yield for that with a short chain(yield:70.9%),and is further increased in the presence of pendent hydroxyl groups(yield:98.5%).The catalyst also shows a high catalytic activity even at mild temperature and good reusability(yield:≥96%for10cycles),and the selectivity is always above99%.

Rational design of bismuth-based catalysts for electrochemical CO_(2) reduction

Sustainable conversion of carbon dioxide(CO_(2))to high value-added chemicals and fuels is a promising solution to solve the problem of excessive CO_(2) emissions and alleviate the shortage of fossil fuels,maintaining the balance of the carbon cycle in nature.The development of catalytic system is of great significance to improve the efficiency and selectivity for electrochemical CO_(2) conversion.In particular,bismuth(Bi)based catalysts are the most promising candidates,while confronting challenges.This review aims to elucidate the fundamental issues of efficient and stable Bi-based catalysts,constructing a bridge between the category,synthesis approach and electrochemical performance.In this review,the categories of Bi-based catalysts are firstly introduced,such as metals,alloys,single atoms,compounds and composites.Followed by the statement of the reliable and versatile synthetic approaches,the representative optimization strategies,such as morphology manipulation,defect engineering,component and heterostructure regulation,have been highlighted in the discussion,paving in-depth insight upon the design principles,reaction activity,selectivity and stability.Afterward,in situ characterization techniques will be discussed to illustrate the mechanisms of electrochemical CO_(2) conversion.In the end,the challenges and perspectives are also provided,promoting a systematic understanding in terms of the bottleneck and opportunities in the field of electrochemical CO_(2) conversion.

纳米羟基磷灰石负载镍甲烷干重整催化剂的载体形貌效应

本研究通过对羟基磷灰石(HAP)的形貌调控,得到表面Ca、O、P分布不同的纳米棒状、片状和线状的HAP载体,负载1.25%的活性组分镍后,得到Ni/HAP-R、Ni/HAP-S和Ni/HAP-W催化剂进行甲烷干重整性能研究。其中,Ni/HAP-R催化剂表现出最优的活性和抗积炭性能。利用XRD、氮吸附-脱附、FT-IR、XPS及CO_(2)-TPD,对催化剂晶相结构、电子性质及表面酸碱性进行表征,证实棒状HAP具有最高的比表面积,有利于Ni的分散锚定,因此,活性最佳。且棒状HAP表面富Ca–O–P碱性位点,能够有效活化CO_(2),促进积炭消除。TPSR实验进一步证实Ni/HAP-R催化剂上甲烷的深度裂解生成积炭的过程受到抑制,且在CO_(2)存在时能够迅速转化为CO和H_(2),因此,具有良好的抗积炭性能。该研究为高稳定负载型催化剂的设计合成提供了新的思路。

Selective photocatalytic reduction of CO2 to CO mediated by a[FeFe]-hydrogenase model with a 1,2-phenylene S-to-S bridge

Photocatalytic reduction of CO2 to CO is a promising approach for storing solar energy in chemicals and mitigating the greenhouse effect of CO2.Our recent studies revealed that[(μ-bdt)Fe2(CO)6](1,bdt=benzene-1,2-dithiolato),a[FeFe]-hydrogenase model with a rigid and conjugate S-to-S bridge,was catalytically active for the selective photochemical reduction of CO2 to CO,while its analogous complex[(μ-edt)Fe2(CO)6](2,edt=ethane-1,2-dithiolato)was inactive.In this study,it was found that the turnover number of 1 for CO evolution reached 710 for the 1/[Ru(bpy)3]2+/BIH(BIH=1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]-imidazole)system under optimal conditions over 4.5 h of visible-light irradiation,with a turnover frequency of 7.12 min−1 in the first hour,a high selectivity of 97%for CO,and an internal quantum yield of 2.8%.Interestingly,the catalytic selectivity of 1 can be adjusted and even completely switched in a facile manner between the photochemical reductions of CO2 to CO and of protons to H2 simply by adding different amounts of triethanolamine to the catalytic system.The electron transfer in the photocatalytic system was studied by steady-state fluorescence and transient absorption spectroscopy,and a plausible mechanism for the photocatalytic reaction was proposed.

Reaction kinetics and phase behavior in the chemoselective hydrogenation of 3‐nitrostyrene over Co‐N‐C single‐atom catalyst in compressed CO_(2)

Single‐atom catalysts(SACs)have demonstrated excellent performances in chemoselective hydrogenation reactions.However,the employment of precious metals and/or organic solvents compromises their sustainability.Herein,we for the first time report the chemoselective hydrogenation of 3‐nitrostyrene over noble‐metal‐free Co‐N‐C SAC in green solvent—compressed CO2.An interesting inverted V‐curve relation is observed between the catalytic activity and CO2 pressure,where the conversion of 3‐nitrostyrene reaches the maximum of 100%at 5.0 MPa CO2(total pressure of 8.1 MPa).Meanwhile,the selectivities to 3‐vinylaniline at all pressures remain high(>99%).Phase behavior studies reveal that,in sharp contrast with the single phase which is formed at total pressure above 10.8 MPa,bi‐phase composed of CO2/H_(2)gas‐rich phase and CO2‐expanded substrate liquid phase forms at total pressure of 8.1 MPa,which dramatically changes the reaction kinetics of the catalytic system.The reaction order with respect to H_(2)pressure decreases from~0.5 to zero at total pressure of 8.1 MPa,suggesting the dissolved CO2 in 3‐nitrostyrene greatly promotes the dissolution of H_(2)in the substrate,which is responsible for the high catalytic activity at the peak of the inverted V‐curve.

离子液体非共价诱导制备碳纳米管/石墨烯集流体用于钠金属负极

钠金属电池因丰富的钠资源储备在大规模储能中具有广泛的应用前景.然而钠金属电池存在钠金属活性高、形成的固体电解质界面膜(SEI膜)不稳定、金属钠体积膨胀大等问题,限制了其应用.本工作利用离子液体与sp^(2)碳间的非共价作用,诱导碳纳米管和还原氧化石墨烯进行自组装,制备得到了碳纳米管支撑的石墨烯高导电三维多孔碳(3D-GC)集流体.制备得到的3D-GC具有三维多孔结构,可以为金属钠提供较大的储存空间.另外,复合材料具有较高的导电性,得到了较低的金属钠的沉积过电位(5.6 mV).3D-GC@Na负极具有良好的电化学性能,在电流密度为1 mA·cm^(−2),沉积容量为1 mAh·cm^(−2)时,在240次充放电循环过程中始终保持了较高的库伦效率(CE),平均CE为99.6%.与Na_(3)V_(2)(PO_(4))_(2)F_(3)组装全电池也表现出优异的电化学性能.