氟催化废弃硅基还原剂与CO_2还原转化反应（英文）

CO_2是最重要的可再生碳源之一.为了将CO_2转化为有用的有机化合物,我们研究了二种模型硅基"废"材料—乙硅烷和硅粉的反应活性.在这些反应中,氟盐的催化活性最高,在常压、在质子源水和硅基还原剂的存在下,CO_2可转化为甲酸.原位NMR和动力学分析表明,含氢硅烷和五配位的硅物种分别是反应中间物和活性物种.     

有机硅反应活性中间体的研究Ⅶ: 二(α-呋喃基)硅烯与烯烃加成反应的立体化学

硅烯是有机硅化学中一类基本的反应活性中间体.在研究硅烯与烯烃加成反应的立体化学过程中,我们曾研究了二苯基硅烯、苯基环丙基硅烯与烯加成反应的立体化学.近年来,Gaspar和Boudjouk分别报道了含大体积取代基的硅烯,如二金刚烷基硅烯、二叔丁基硅烯与烯烃的加成反应.我们从取代基的电子效应考虑曾研究了2-苯基-2-(a-噻吩基)六甲基三硅烷的光解,发现反应是自由基机理.氧和硫同属第Ⅵ主族,与噻吩相对应的含呋喃环三硅烷的光解又如何呢?因此,我们又设计并合成了二(α-呋喃基)硅烯的前体,2,2-二(α-呋喃基)六甲基三硅烷(1),并研究了这种硅烯与烯烃加成的立体化学.当1在光照下与trans-2-丁烯或cis-2-丁烯反应,所得硅杂环丙烷衍生物用甲醇开环时,得到了相同的2-丁基-二(α-呋喃基)甲氧基硅烷(3).     

醇(酚)羟基的硅烷化保护与去保护研究进展

醇(酚)羟基的硅烷化保护是一类重要的有机合成手段,目的在于使羟基稳定化,消除或减轻其引起的副反应。保护基中硅原子连接的基团空间位阻越小,该保护基的反应活性越大,生成的相应硅醚的稳定性则越差,在弱酸或弱碱的条件下即可脱除;硅原子连接的基团越大,该保护基的反应活性则越小,硅醚化反应越难发生,需要借助催化剂才能进行。本文尽可能全面地论述了有机硅烷保护基的类型,如三甲基硅烷、三乙基硅烷、叔丁基二甲基硅烷、三异丙基硅烷、苯基取代硅烷和桥型硅烷等,并讨论了其在不同环境下的活性及稳定性。     

有机硅反应活性中间体的研究I:光化学方法产生含呋喃环硅烯

2-(α-呋喃基)-2-苯基六甲基三硅烷在光照下可产生新型的有机硅活性中间体-α-呋喃基苯基硅烯.它与2,3-二甲基-1,3-丁二烯反应后,得到了相应的加成与插入反应产物;与环己烯反应后,再用甲醇分解所得硅杂环丙烷中间物得到了α-呋喃基环己基苯基甲氧基硅烷.     

不同形态ZrO2负载Co催化剂上CO+H2吸附与反应行为研究

利用FTIR,TPSR和微量反应技术考察了CO和CO/H2在无定形、四方相和单斜相3种形态氧化锆为载体的钴基催化剂上的吸附和反应行为.结果表明,CO在以不同形态氧化锆为载体的催化剂上的吸附形式和转化行为具有较大差异.在单斜氧化锆为载体的催化剂上生成桥式和多桥式吸附的CO,并容易进一步加氢生成烃类物种,具有较高的反应活性和C5+烃的选择性.而以四方氧化锆为载体的催化剂上桥式吸附的CO较稳定,加氢反应活性较低.     

有机硅反应活性中间体的研究 Ⅰ.光化学方法产生含呋喃环硅烯

2-(α-呋喃基)-2-苯基六甲基三硅烷在光照下可产生新型的有机硅活性中间体——α-呋喃基苯基硅烯.它与2,3-二甲基-1,3-丁二烯反应后,得到了相应的加成与插入反应产物;与环己烯反应后,再用甲醇分解所得硅杂环丙烷中间物得到了α-呋喃基环己基苯基甲氧基硅烷.     

Pd-Cu-Clx/Al2O3催化剂对CO氧化的稳定性

CO催化氧化广泛应用于空气净化、机动车尾气治理和CO气体传感器中.在CO氧化催化剂设计与制备过程中,催化剂与使用环境密切相关.例如工业和机动车尾气净化需要在高温(200–600°C)下进行,而对于半密闭空间(隧道或者地下停车场)空气净化需要在室温和高相对湿度下进行.频繁冷启动导致半密闭空间CO浓度累积而超过排放控制标准,因此制备室温、高相对湿度下CO氧化催化剂是面临的重要问题之一.负载型Wacker催化剂对于CO低温催化氧化的研究一直受到广泛关注.环境中少量水的存在会促进负载型Wacker催化剂对CO的低温氧化性能,但随着水沉积量的增加,活性位点将被覆盖,并且Pd和Cu活性组分之间的紧密结构被破坏,从而导致催化剂的失活,即催化剂的稳定性变差.因此,为了提高催化剂在高相对湿度下的稳定性,利用二乙氧基二甲基硅烷对Al2O3载体进行硅烷化处理,以增加载体的疏水性,考察载体疏水改性对CO低温氧化过程中催化剂稳定性的影响.催化剂的稳定性测试结果表明,在0°C,100%相对湿度条件下,未改性催化剂在约20 h内CO转化率由81%下降到50%;载体硅烷化后制备的催化剂在反应进行150 h后,CO转化率仍保持在78%,即反应活性未见降低.由此表明催化剂载体经有机硅烷改性后,可显著增强催化剂在低温、高相对湿度下的稳定性.N2吸附/脱附和水吸附实验结果表明,载体硅烷化改性并未对催化剂的比表面积产生影响,但显著降低了催化剂上水沉积速度和沉积量,未改性催化剂的初始吸水速度是改性后催化剂的4倍,但改性后催化剂的饱和吸水率仅占未改性催化剂的1/3.X射线衍射结果表明,载体预处理后活性物种Cu2(OH)3Cl晶粒尺寸有所增加.氢气程序升温还原、X射线光电子能谱结果表明,载体硅烷化预处理改善了催化剂中Cu和Pd物种的化学分布及接触状态,增加了与Pd物种紧密接触的Cu物种的量,从而促进了Cu物种的还原.与此同时,载体硅烷化显著降低了催化剂表面Cl离子的浓度,从而影响到对CO吸附.为了进一步研究水与催化剂稳定性之间的关系,采用原位红外漫反射(In situ DRIFT)对催化剂进行表征.负载型Wacker催化剂对CO氧化反应机理为:Pd是CO氧化反应的活性中心,通过Pd和Cu物种之间的氧化还原循环来实现CO氧化,且Pd+比Pd2+具有更高的CO氧化性能.反应气氛中水的存在,有利于CO在Pd+上氧化、以及金属态Pd被Cu2+物种再氧化的过程,同时水也显著促进了催化剂表面碳酸盐的生成以及抑制了活性物种Pd+生成.与表面碳酸盐累积相比,水对于活性物种Pd+生成的抑制作用是导致催化剂活性降低的主要原因.     

Pd-Cu-Cl_x/Al_2O_3催化剂对CO氧化的稳定性（英文）

CO催化氧化广泛应用于空气净化、机动车尾气治理和CO气体传感器中.在CO氧化催化剂设计与制备过程中,催化剂与使用环境密切相关.例如工业和机动车尾气净化需要在高温(200–600°C)下进行,而对于半密闭空间(隧道或者地下停车场)空气净化需要在室温和高相对湿度下进行.频繁冷启动导致半密闭空间CO浓度累积而超过排放控制标准,因此制备室温、高相对湿度下CO氧化催化剂是面临的重要问题之一.负载型Wacker催化剂对于CO低温催化氧化的研究一直受到广泛关注.环境中少量水的存在会促进负载型Wacker催化剂对CO的低温氧化性能,但随着水沉积量的增加,活性位点将被覆盖,并且Pd和Cu活性组分之间的紧密结构被破坏,从而导致催化剂的失活,即催化剂的稳定性变差.因此,为了提高催化剂在高相对湿度下的稳定性,利用二乙氧基二甲基硅烷对Al_2O_3载体进行硅烷化处理,以增加载体的疏水性,考察载体疏水改性对CO低温氧化过程中催化剂稳定性的影响.催化剂的稳定性测试结果表明,在0°C,100%相对湿度条件下,未改性催化剂在约20 h内CO转化率由81%下降到50%;载体硅烷化后制备的催化剂在反应进行150 h后,CO转化率仍保持在78%,即反应活性未见降低.由此表明催化剂载体经有机硅烷改性后,可显著增强催化剂在低温、高相对湿度下的稳定性.N_2吸附/脱附和水吸附实验结果表明,载体硅烷化改性并未对催化剂的比表面积产生影响,但显著降低了催化剂上水沉积速度和沉积量,未改性催化剂的初始吸水速度是改性后催化剂的4倍,但改性后催化剂的饱和吸水率仅占未改性催化剂的1/3.X射线衍射结果表明,载体预处理后活性物种Cu2(OH)3Cl晶粒尺寸有所增加.氢气程序升温还原、X射线光电子能谱结果表明,载体硅烷化预处理改善了催化剂中Cu和Pd物种的化学分布及接触状态,增加了与Pd物种紧密接触的Cu物种的量,从而促进了Cu物种的还原.与此同时,载体硅烷化显著降低了催化剂表面Cl离子的浓度,从而影响到对CO吸附.为了进一步研究水与催化剂稳定性之间的关系,采用原位红外漫反射(In situ DRIFT)对催化剂进行表征.负载型Wacker催化剂对CO氧化反应机理为:Pd是CO氧化反应的活性中心,通过Pd和Cu物种之间的氧化还原循环来实现CO氧化,且Pd+比Pd~(2+)具有更高的CO氧化性能.反应气氛中水的存在,有利于CO在Pd~+上氧化、以及金属态Pd被Cu~(2+)物种再氧化的过程,同时水也显著促进了催化剂表面碳酸盐的生成以及抑制了活性物种Pd~+生成.与表面碳酸盐累积相比,水对于活性物种Pd~+生成的抑制作用是导致催化剂活性降低的主要原因.     

硅烷化学改性环氧涂层的耐蚀性能

利用"活性"与"非活性"硅烷化学改性环氧涂层以提高其耐蚀性."活性"硅烷指含有可以与环氧树脂的环氧端基发生开环反应官能团的硅烷,通常为氨基硅烷;"非活性"硅烷指不与环氧端基发生反应,但在有机锡催化剂存在下可与环氧树脂骨架上的羟基发生缩合反应的硅烷.红外光谱显示,两类硅烷均可成功接枝在环氧树脂上.电化学阻抗谱(EIS)和加速腐蚀试验(Machu试验)测试表明,经硅烷化学改性后的环氧涂层均能提高其耐蚀性能.     

(CO)5MnSiR3与R 3SiH的光化学硅烷基交换反应研究

五羰基锰硅烷基配合物(CO)₅MnSiR₃ (3) [SiR₃＝SiMe₂Ph (3b), SiMePh₂ (3c), SiPh₃ (3d), SiHPh₂ (3e), SiEt₃ (3f)和SiMe₂Et (3h)]与不同氢硅烷R ₃SiH在5 ℃光解1 h, 这两个物种间的硅烷基交换达到平衡. 适中的产物与反应物自由能变化间隔使得这些反应实质上可逆. 光催化经由不饱和物种(CO)₄MnSiR₃ (1)和过渡中间体(CO)₄MnH(SiR₃)(SiR ₃) (4)进行. 物种3作为通过光活化前催化剂的可行性得到确认. 受电子效应和位阻效应的影响, 含有体积较大且推电子基团(如乙基)的硅烷基更容易被含有体积较小且吸纳电子基团(如负氢)的硅烷基从五羰基锰硅烷基配合物中置换出来.     

Effect of CO_2 on the structural variation of Na_2WO_4/Mn/SiO_2 catalyst for oxidative coupling of methane to ethylene

In this work,the influence of CO2 on the structural variation and catalytic performance of Na2WO4/Mn/Si O2 for oxidative coupling of methane to ethylene was investigated. The catalyst was prepared by impregnation method and characterized by XRD,Raman and XPS techniques. Appropriate amount of CO2 in the reactant gases enhanced the formation of surface tetrahedral Na2WO4 species and promoted the migration of O in MOx,Na,W from the catalyst bulk to surface,which were favorable for oxidative coupling of methane. When the molar ratio of CH4/O2/CO2 was 3/1/2,enriched surface tetrahedral Na2WO4 species and high surface concentration of O in MOx,Na,W were detected,and then high CH4 conversion of 33.1% and high C2H4 selectivity of 56.2% were obtained. With further increase of CO2 in the reagent gases,the content of active surface tetrahedral Na2WO4 species and surface concentration of O in MOx,Na,W decreased,while that of inactive species(Mn WO4 and Mn2O3) increased dramatically,leading to low CH4 conversion and low C2H4 selectivity. It could be speculated that Na2WO4 crystal was transformed into Mn WO4 crystal with excessive CO2 added under the reaction conditions. Pretreatment of Na2WO4/Mn/Si O2 catalyst by moderate amount of CO2 before OCM also promoted the formation of Na2WO4 species.     

以类水滑石为前驱体的Cu/ZnO/Al2O3催化剂用于COx加氢合成甲醇：CO在反应混合物中的作用

近年来,催化CO₂加氢合成甲醇被视为有望解决温室效应和燃料枯竭的有效途径。目前,铜基催化剂因具有较高的反应活性被广泛应用于工业生产。然而,竞争逆水煤气变换反应产生的CO导致甲醇选择性较低,同时副产物水引起Cu发生不可逆烧结,进而降低甲醇产率。众所周知,CO能够调整分子的表面竞争吸附和活性位的氧化还原行为,本工作拟向原料气中掺入具有还原性的CO以抑制逆水煤气变换反应和防止表面氧化中毒。另一方面,通常认为铜基催化的CO₂加氢制甲醇是结构敏感性反应,不同的前驱体能够显著影响催化剂结构和形貌,进而影响催化活性。因此,我们首先通过共沉淀法和蒸氨法制备了含有类水滑石前驱体(CHT-CZA)和复合物前驱体(CNP-CZA)结构的Cu/ZnO/Al₂O₃催化剂。随后,为探究CO掺杂后反应机理,在250 ℃,5 MPa的反应条件下,含有不同比例CO的原料气中(CO₂:CO:H₂:N₂ = x:(24.5 - x):72.5:3)评价两种催化剂对甲醇合成的性能。评价结果显示两种催化剂反应性能趋势相同,随着CO含量增加,CO₂转化率和STY_H2O不断降低,STY_MeOH逐渐增加。X射线光谱(XPS)显示随CO含量增加,催化剂表面还原性Cu比例增加。评价和表征结果说明CO引入抑制了逆水煤气变换反应的发生,通过还原被H₂O氧化的活性Cu表面,促使更多的活性Cu位点暴露参与甲醇合成。另一方面,透射电镜(TEM)显示掺杂的CO会过度还原而引起颗粒团聚,导致催化剂逐渐失活。相比之下,含有水滑石前驱体的催化剂在任何气氛下均表现出更加优越的反应性能和长周期稳定性。这可归因于类水滑石前驱体独特的片层结构通过结构限域作用有效避免了因CO过度还原而导致的金属颗粒团聚,从而减少活性位点损失。     

Design Strategies of Si/C Composite Anode for Lithium-Ion Batteries

Silicon-based materials that have higher theoretical specific capacity than other conventional anodes, such as carbon materials, Li₂TiO₃ materials and Sn-based materials, become a hot topic in research of lithium-ion battery (LIB). However, the low conductivity and large volume expansion of silicon-based materials hinders the commercialization of silicon-based materials. Until recent years, these issues are alleviated by the combination of carbon-based materials. In this review, the preparation of Si/C materials by different synthetic methods in the past decade is reviewed along with their respective advantages and disadvantages. In addition, Si/C materials formed by silicon and different carbon-based materials is summarized, where the influences of carbons on the electrochemical performance of silicon are emphasized. Lastly, future research direction in the material design and optimization of Si/C materials is proposed to fill the current gap in the development of efficient Si/C anode for LIBs.     

Modeling the active sites in metalloenzymes. 3. Density functional calculations on models for [Fe]-hydrogenase: structures and vibrational frequencies of the observed redox forms and the reaction mechanism at the Diiron Active Center.

Optimized structures for the redox species of the diiron active site in [Fe]-hydrogenase as observed by FTIR and for species in the catalytic cycle for the reversible H(2) oxidation have been determined by density-functional calculations on the active site model, [(L)(CO)(CN)Fe(mu-PDT)(mu-CO)Fe(CO)(CN)(L')](q)(L = H(2)O, CO, H(2), H(-); PDT = SCH(2)CH(2)CH(2)S, L' = CH(3)S(-), CH(3)SH; q = 0, 1-, 2-, 3-). Analytical DFT frequencies on model complexes (mu-PDT)Fe(2)(CO)(6) and [(mu-PDT)Fe(2)(CO)(4)(CN)(2)](2)(-) are used to calibrate the calculated CN(-) and CO frequencies against the measured FTIR bands in these model compounds. By comparing the predicted CN(-) and CO frequencies from DFT frequency calculations on the active site model with the observed bands of D. vulgaris [Fe]-hydrogenase under various conditions, the oxidation states and structures for the diiron active site are proposed. The fully oxidized, EPR-silent form is an Fe(II)-Fe(II) species. Coordination of H(2)O to the empty site in the enzyme's diiron active center results in an oxidized inactive form (H(2)O)Fe(II)-Fe(II). The calculations show that reduction of this inactive form releases the H(2)O to provide an open coordination site for H(2). The partially oxidized active state, which has an S = (1)/(2) EPR signal, is an Fe(I)-Fe(II) species. Fe(I)-Fe(I) species with and without bridging CO account for the fully reduced, EPR-silent state. For this fully reduced state, the species without the bridging CO is slightly more stable than the structure with the bridging CO. The correlation coefficient between the predicted CN(-) and CO frequencies for the proposed model species and the measured CN(-) and CO frequencies in the enzyme is 0.964. The proposed species are also consistent with the EPR, ENDOR, and M?ssbauer spectroscopies for the enzyme states. Our results preclude the presence of Fe(III)-Fe(II) or Fe(III)-Fe(III) states among those observed by FTIR. A proposed reaction mechanism (catalytic cycle) based on the DFT calculations shows that heterolytic cleavage of H(2) can occur from (eta(2)-H(2))Fe(II)-Fe(II) via a proton transfer to "spectator" ligands. Proton transfer to a CN(-) ligand is thermodynamically favored but kinetically unfavorable over proton transfer to the bridging S of the PDT. Proton migration from a metal hydride to a base (S, CN, or basic protein site) results in a two-electron reduction at the metals and explains in part the active site's dimetal requirement and ligand framework which supports low-oxidation-state metals. The calculations also suggest that species with a protonated Fe-Fe bond could be involved if the protein could accommodate such species.     

Infrared spectroscopy of Si(CO)n+ complexes: evidence for asymmetric coordination

Si(CO)(n)(+) and Si(CO)(n)(+)Ar complexes are produced via laser vaporization with a pulsed nozzle source and cooled in a supersonic beam. The ions are mass selected in a reflectron time-of-flight mass spectrometer and studied with infrared laser photodissociation spectroscopy near the free molecular CO vibration (2143 cm(-1)). Si(CO)(n)(+) complexes larger than n = 2 fragment by the loss of CO, whereas Si(CO)(n)(+)Ar complexes fragment by the loss of argon. All clusters have resonances near the free molecular CO stretch that provide distinctive patterns from which information on their structure and bonding can be obtained. The number of infrared-active bands, their frequency positions, and relative intensities indicate that larger species consist of an asymmetrically coordinated Si(CO)(2)(+) core with additional CO ligands attached via van der Waals interactions. Density functional theory computations are carried out in support of the experimental spectra.     

铜系催化剂低压合成甲醇的原位红外光谱研究

本文运用本组设计和制作的高压原位红外池, 在反应条件下对铜催化剂的表面吸附态进行了原位检测。测到了表面吸附态和等的特征吸收峰。证实了CO和H_2在同一类活性中心上的竞争吸附, 并对其竞争吸附的能力作了考察。据此提出了该体系的吸附机理。在反应条件下, 检测到可判断为和M—O—CH_2OH等表面反应中间物的红外吸收峰。根据在不同温度和原料气组成下表面态的变化规律, 提出了合成反应是通过多途径进行以及CO_2对实现多途径起了重要作用的机理假设。     

利用XPS 氩离子刻蚀表征锂离子电池Si/C负极材料中含硅的活性物质

以石墨、沥青和纳米硅粉为原料制备了锂离子电池Si/C负极材料,使用SEM/ BSE 、Raman、XRD、XPS及XPS氩离子刻蚀等方法对其硅活性物质进行了具体分析。结果表明,XRD和Raman仅判断出负极材料中含有活性物质单质Si;常规XPS结果发现近一半的Si已被氧化为惰性物质SiO2;而使用XPS氩离子刻蚀方法发现负极材料中Si存在5种化学态,包括活性物质单质Si、Si2O、SiO、Si2O3,及惰性物质SiO2;定量结果表明,复合材料的硅活性物质高于96.56%,且主要结构是低价态硅氧化物,而非单质Si。XPS氩离子刻蚀的分析方法为锂离子电池负极材料中硅活性物质的研究提供了新思路。     

Planar tetracoordinated silicon in silicon carbonyl complexes: a DFT approach

Recently, some works have focused attention on the reactivity of the silicon atom with closed-shell molecules. With CO, silicon may form a few relatively stable compounds, i.e., Si(CO), Si(CO)(2), and Si[C(2)O(2)], while the existence of polycarbonyl (n > 2) silicon complexes has been rejected by current literature. In this paper, the reaction of silicon with carbonyl has been reinvestigated by density functional calculations. It has been found that the tetracoordinated planar Si(CO)(4) complex is thermodynamically stable. In Si(CO), silicon carbonyl, and Si(CO)(2), silicon dicarbonyl, the CO moieties are datively bonded to Si, and Si[C(2)O(2)], c-silicodiketone, is similar to the compounds formed by silicon and ethylene; Si(CO)(4), silicon tetracarbonyl, may be viewed as a resonance between the extreme configurations (CO)(2)Si + 2CO and 2CO + Si(CO)(2). A detailed orbital analysis has shown that the Si bonding with four CO is consistent with the use of sp(2)d-hybridized orbitals on silicon, giving rise to a planar structure about Si.     

SiOx encapsulated FeSi2–Si eutectic nanoparticles as durable anode of lithium-ion batteries

Low-cost and high-efficiency production of silicon-based material is the key to improve the energy density of lithium-ion batteries. Herein, we propose a novel structure of FeSi₂–Si eutectic nanoparticles protected by the SiO_x shell. FeSi₂, as a buffer phase can improve the electrochemical stability of the electrode. A SiO_x shell is formed on the surface of the nanoparticles through the passivation process. SiO_x encapsulated FeSi₂–Si eutectic nanoparticles exhibit excellent capacity of 674.9 mAh/g after 500 charge/discharge cycles. The capacity retention rate is above 90% after the stabilization process. This work provides a new nanomaterial design for high performance silicon-based anode materials of lithium-ion batteries.     

Harnessing Greenhouse Gases Absorption by Doped Fullerenes with Externally Oriented Electric Field

In this work, a theoretical investigation of the effects caused by the doping of C₂₀ with silicon (Si) atom as well as the adsorption of CO, CO₂ and N₂ gases to C₂₀ and C₁₉Si fullerenes was carried out. In concordance with previous studies, it was found that the choice of the doping site can control the structural, electronic, and energetic characteristics of the C₁₉Si system. The ability of C₂₀ and C₁₉Si to adsorb CO, CO₂ and N₂ gas molecules was evaluated. In order to modulate the process of adsorption of these chemical species to C₁₉Si, an externally oriented electric field was included in the theoretical calculations. It was observed that C₁₉Si is highly selective with respect to CO adsorption. Upon the increase of the electric field intensity the adsorption energy was magnified correspondingly and that the interaction between CO and C₁₉Si changes in nature from a physical adsorption to a partial covalent character interaction.