The preparation of silica entrapped homogeneous hydrogenation catalysts by conventional and ionic liquid mediated sol-gel routes

[RhCl(PPh₃)₃] has been entrapped inside silica matrices by two methods: a conventional sol-gel synthesis in ethanol/water and a new route performed in an ionic liquid. The activity of these heterogenised catalysts has been tested for the hydrogenation of styrene. The catalyst prepared in an ionic liquid was found to be more active and have low Rh leaching.     

Silica-gel-confined ionic liquids: a new attempt for the development of supported nanoliquid catalysis

A new concept of designing and synthesizing highly dispersed ionic-liquid catalysts was developed through physical confinement or encapsulation of ionic liquids (with or without metal complex) in a silica-gel matrix through a sol-gel process. We studied ionic liquids such as EMImBF4, BuMImBF4, DMImBF4, CMImBF4, BuMImPF6, either with or without [Pd(PPh3)2Cl2] and [Rh(PPh3)3Cl], in a silica-gel matrix (E = ethyl, Bu = butyl M = methyl, D = decyl, C = cetyl and Im = imidazolium). The contents of ionic liquids and loadings of Pd or Rh were 8-53 wt % and 0.1 approximately 0.15 wt %, respectively. Analyses of FT-Raman spectra showed that abnormal Raman spectra of the confined ionic liquids were observed in comparison with the bulk and pure ionic liquids. EMImBF4 and BuMImBF4 ionic liquids could be completely washed out from the silica-gel matrix under vigorous reflux conditions, but ionic liquids with larger molecular size, for example, DMImBF4 or CMImBF4, could be confined into the silica-gel nanopores relatively firmly. These results suggested that the ionic liquids were physically confined or encapsulated into the silica gel. The N2 adsorption measurements indicated that the silica-gel skeleton was mesoporous with 50-110 A pore size after the BuMImBF4 ionic liquid was removed completely. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis showed that the silica-gel matrix was amorphous and non-uniformly mesoporous. Carbonylation of aniline and nitrobenzene for synthesis of diphenyl urea, carbonylation of aniline for synthesis of carbamates, and oxime transformation between cyclohexanone oxime and acetone were used as test reactions for these catalysts. Catalytic activities were remarkably enhanced with much lower amounts of ionic liquids needed with respect to bulk ionic-liquid catalysts or silica-supported ionic-liquid catalysts prepared with simple impregnation, in which the ionic liquid may be deposited as a thin layer on the support. Such unusual enhancement in catalytic activities may be attributed to the formation of nanoscale and high-concentration ionic liquids due to the confinement of the ionic liquid in silica gel; this results in unusual changes in the symmetry and coordination geometry of the ionic liquids.     

The use of imidazolium ionic liquids for the formation and stabilization of ir0 and rh0 nanoparticles: efficient catalysts for the hydrogenation of arenes

Stable transition-metal nanoparticles of the type [M(0)](n) are easily accessible through the reduction of Ir(I) or Rh(III) compounds dissolved in "dry" 1-n-butyl-3-methylimidazolium hexafluorophosphate ionic liquid by molecular hydrogen. The formation of these [M(0)](n) nanoparticles is straightforward; they are prepared in dry ionic liquid whereas the presence of the water causes the partial decomposition of ionic liquid with the formation of phosphates, HF and transition-metal fluorides. Transmission electron microscopy (TEM) observations and X-ray diffraction analysis (XRD) show the formation of [Ir(0)](n) and [Rh(0)](n) nanoparticles with 2.0-2.5 nm in diameter. The isolated [M(0)](n) nanoparticles can be redispersed in the ionic liquid, in acetone or used in solventless conditions for the liquid-liquid biphasic, homogeneous or heterogeneous hydrogenation of arenes under mild reaction conditions (75 degrees C and 4 atm). The recovered iridium nanoparticles can be reused several times without any significant loss in catalytic activity. Unprecedented total turnover numbers (TTO) of 3509 in 32 h, for arene hydrogenation by nanoparticles catalysts, have been achieved in the reduction of benzene by the [Ir(0)](n) in solventless conditions. Contrarily, the recovered Rh(0) nanoparticles show significant agglomeration into large particles with a loss of catalytic activity. The hydrogenation of arenes containing functional groups, such as anisole, by the [Ir(0)](n) nanoparticles occurs with concomitant hydrogenolysis of the C-O bond, suggesting that these nanoparticles behave as "heterogeneous catalysts" rather than "homogeneous catalysts".     

理性设计核-壳Rh@沸石催化材料用于二烯烃选择加氢反应

Selective hydrogenation of dienes and alkynes to monoenes is an important topic of research in the fields of pharmacology and organic synthesis. Catalyst design plays a key role in this process, where a general principle involves controlling the steric diene adsorption by modifying the surface of the metal nanoparticles. For example, upon introducing Bi species into Rh nanoparticles, the resulting RhBi/SiO₂ showed 90% selectivity to 2-hexene, with 95% conversion of 1, 4-hexadiene under ambient conditions, because of the suppressed adsorption of the internal C＝C bond. However, the catalyst activity decreased remarkably; that is, the activity of the unmodified Rh/SiO₂ was about 27 times higher than that of RhBi/SiO₂. Controlled steric adsorption of the diene molecules could also be achieved by the constructing porous channels around the metal nanoparticles. For example, metal-organic framework (ZIF-8) or mesoporous silica (MCM-41) encapsulated noble metals showed high selectivity for the hydrogenation of terminal C＝C bonds. However, these catalysts had poor durability under the thermal/hydrothermal reaction/regeneration conditions. In contrast, zeolites have superior durability under harsh reaction conditions, but they are rarely used in semi-hydrogenation reactions. We recently found that metal nanoparticles fixed within zeolite crystals (e.g., ZSM-5 and Beta) efficiently catalyze the selective hydrogenation of molecules bearing multiple reducible groups. Thus inspired, we developed a catalyst by fixing Rh nanoparticles within zeolite crystals via an inter-zeolite transformation method. The Rh@CHA catalyst was synthesized by introducing Rh species into the parent Y zeolite (Rh@Y) and transformation of the Y zeolite to chabazite (CHA zeolite) under hydrothermal conditions. X-ray diffraction patterns, N₂ sorption isotherms, scanning/transmission electron microscopy images, and model reactions (hydrogenation of probe molecules) confirmed the successful fixation of the Rh nanoparticles inside the CHA zeolite crystals. As expected, the Rh@CHA catalyst was highly selective for the hydrogenation of dienes. For example, Rh@CHA showed a 2-hexene selectivity of 86.7%, with 91.2% conversion of 1, 4-hexadiene. In contrast, the generally supported Rh nanoparticle catalyst (Rh/CHA) showed a low 2-hexene selectivity of 37.2% under identical reaction conditions. Considering that Rh@CHA and Rh/CHA comprise the same CHA zeolite crystals and have similar Rh nanoparticle sizes, the remarkably high selectivity of Rh@CHA is assigned to the steric adsorption of dienes on the Rh surface controlled by the micropores of the CHA zeolite. This work demonstrates that a zeolite-fixed metal core-shell structure is a powerful tool for developing efficient catalysts to be used in diene hydrogenation.     

The Co‐Entrapment of a Homogeneous Catalyst and an Ionic Liquid by a Sol–gel Method: Recyclable Ionogel Hydrogenation Catalysts

Molecular hydrogenation catalysts have been co‐entrapped with the ionic liquid [Bmim]NTf₂ inside a silica matrix by a sol–gel method. These catalytic ionogels have been compared to simple catalyst‐doped glasses, the parent homogeneous catalysts, commercial heterogeneous catalysts, and Rh‐doped mesoporous silica. The most active ionogel has been characterised by transmission electron microscopy, X‐ray photoelectron spectroscopy, and solid state NMR before and after catalysis. The ionogel catalysts were found to be remarkably active, recyclable and resistant to chemical change.     

A silica-supported, switchable, and recyclable hydroformylation-hydrogenation catalyst

A homogeneous hydroformylation catalyst, designed to produce selectively linear aldehydes, was covalently tethered to a polysilicate support. The immobilized transition-metal complex [Rh(A)CO]+(1+)), in which A is N-(3-trimethoxysilane-n-propyl)-4,5-bis(diphenylphosphino)phenoxazine, was prepared both via the sol-gel process and by covalent anchoring to silica. 1+ was characterized by means of (31)P and (29)Si MAS NMR, FT-IR, and X-ray photoelectron spectroscopy. Polysilicate immobilized Rh(A) performed as a selective hydroformylation catalyst showing an overall selectivity for the linear aldehyde of 94.6% (linear to branched aldehyde ratio of 65). In addition 1-nonanol, obtained via the hydrogenation of the corresponding aldehyde, was formed as an unexpected secondary product (3.6% at 20% conversion). Under standard hydroformylation conditions, 1+ and HRh(A)(CO)(2)(1) coexist on the support. This dual catalyst system performed as a hydroformylation/hydrogenation sequence catalyst (Z), giving selectively 1-nonanol from 1-octene; ultimately, 98% of 1-octene was converted to mainly 1-nonanal and 97% of the nonanal was hydrogenated to 1-nonanol. The addition of 1-propanol completely changes Z in a hydroformylation catalyst (X), which produces 1-nonanal with an overall selectivity of 93%, and completely suppresses the reduction reaction. If the atmosphere is changed from CO/H(2) to H(2) the catalyst system is switched to the hydrogenation mode (Y), which shows a clean and complete hydrogenation of 1-octene and 1-nonanal within 24 h. The immobilized catalyst can be recycled and the system can be switched reversibly between the three "catalyst modes" X, Y, and Z, completely retaining the catalyst performance in each mode.     

TiOx(x＜2)表面修饰Ni/TiO2-SiO2催化顺酐液相选择加氢合成γ-丁内酯

以TiO2-SiO2复合氧化物气凝胶为载体,制备了一系列Ni/TiO2-SiO2催化剂,并采用N2物理吸附-脱附、H2程序升温还原/脱附、X射线衍射及原位漫反射傅里叶变换红外光谱等技术对催化剂进行了表征,考察了载体中钛含量对催化剂结构、表面性质及其催化顺酐液相选择加氢合成γ-丁内酯反应性能的影响.结果表明,较小的Ni0...     

Aerobic oxidation of alcohols in carbon dioxide with silica-supported ionic liquids doped with perruthenate

The replacement of toxic Cr(VI) for O2 and of chlorinated solvents for supercritical carbon dioxide (or ionic liquids) in the oxidation of alcohols remains hindered by the low selectivity and activity of the current heterogeneous catalysts. Using an integrated approach that combines sol-gel entrapped perruthenate as aerobic catalyst, an encapsulated ionic liquid as solubility promoter, and scCO2 as the reaction solvent, we have developed a system capable of rapidly converting different alcohols into carbonyl compounds with complete selectivity, including substrates which are otherwise difficult to oxidise. The methodology is generally applicable and may easily be extended to other waste-free, catalytic syntheses of fine chemicals.     

Rh-Mn-Li/SiO2催化剂上CO加氢制C2含氧化合物:载体硅烷化程度的影响

以三甲基氯硅烷为硅烷化试剂,对硅胶进行不同程度硅烷化预处理,采用浸渍法制备了其负载的Rh-Mn-Li催化剂,用于CO加氢制C₂含氧化合物的反应,并运用红外光谱、N₂吸附-脱附法、C含量测定、透射电镜、H₂程序升温还原和程序升温表面反应等手段对载体和催化剂进行了表征。结果表明,制得的不同硅烷化程度硅胶织构性质变化不大,它们负载的催化剂上Rh平均粒径均在3nm左右,硅烷化对催化剂吸附CO的形态和Rh的还原性能的影响均很小,但随着载体硅烷化程度的提高,催化剂上Rh解离CO的能力增加,因而其活性逐渐增加,且不影响C₂含氧化合物的选择性。     

Properties of proton-conducting materials formed by the sol-gel method

Proton-conducting materials produced by the sol-gel method were studied by spectroscopic methods. Films and xerogels were formed from silica sols modified with orthophosphoric and sulfuric acids, as well as with a mixture of these acids, with subsequent drying at room temperature and 150°C. The ionic conductivity of the xerogels and IR transmission of the films were examined.     

铑-三苯基膦配合物功能化的聚合物@介孔氧化硅复合材料在1-辛烯氢甲酰化反应中的应用(英文)

通过在介孔氧化硅材料中原位聚合的方法制备了三苯基膦功能化的有机聚合物@介孔氧化硅复合材料PPh3polymer@FDU-12.采用X射线衍射、氮气吸附脱附、透射电镜和热重等手段对其结构和组成进行了表征.该复合材料与金属前驱体Rh(acac)(CO)2配位后得到的固体催化剂,在长链烯烃1-辛烯的氢甲酰化反应中,醛选择性可达92%–96%,并表现出高于聚合物的活性(99%转化率).这主要归因于介孔氧化硅材料的高比表面积和有序的孔结构更有利于反应物和催化活性中心的接触.研究发现,调变复合材料中聚合物的含量或使用不同孔道结构的氧化硅载体(SBA-15,MCM-41和FDU-12)都会影响固体催化剂的反应活性和选择性.该方法得到的多相催化剂具有较好的循环使用性能,在循环使用15次后仍能保持较好的反应活性,但醛选择性有所降低.     

Hydrogenation of non-activated alkenes catalysed by water-soluble ruthenium carbonyl clusters using a biphasic protocol

The use of the water soluble ruthenium clusters Ru₃(CO)_12−x(TPPTN)_x (x=1 1, 2 2 or 3 3) and H₄Ru₄(CO)₁₁(TPPTN) 4 (TPPTN=P{m-C₆H₄SO₃Na)₃) as catalyst precursors in the hydrogenation of non-activated alkenes under biphasic conditions is described. Each cluster displays activity under moderate conditions, ca. 60 atm. H₂ at 60°C, with catalytic turnovers up to ca. 500. The trinuclear clusters undergo transformation during reaction but can be reused repeatedly without loss of activity. Other methodologies such as ionic liquid–organic and the use of silica supports have been attempted with these clusters but they are less effective than the aqueous–organic regime.     

One-pot sequences of reactions with sol-gel entrapped opposing reagents: an enzyme and metal-complex catalysts

We extend our sol-gel methodology of one-pot sequences of reactions with opposing reagents to an enzyme/metal-complex pair. Sol-gel entrapped lipase and sol-gel entrapped RhCl[P(C(6)H(5))(3)](3) or Rh(2)Co(2)(CO)(12) were used for one-pot esterification and C-C double bond hydrogenation reactions, leading to saturated esters in good yields. When only the enzyme is entrapped, the homogeneous catalysts quench its activity and poison it. Thus, when 10-undecenoic acid and 1-pentanol were subjected in one pot to the entrapped lipase and to homogeneously dissolved RhCl[P(C(6)H(5))(3)](3) under hydrogen pressure, only 7% of the saturated 1-pentyl undecanoate was obtained. The yield jumped 6.5-fold when both the enzyme and the catalyst were immobilized separately in silica sol-gel matrixes. Similar one-pot esterifications and hydrogenations by sol-gel entrapped lipase and heterogenized rhodium complexes were carried out successfully with the saturated nonoic, undecanoic, and lauric acids together with several saturated and unsaturated alcohols. The use of (S)-(-)-2-methylbutanol afforded an optically pure ester. The heterogenized lipase is capable of inducing asymmetry during esterification with a prochiral alcohol. Both the entrapped lipase and the immobilized rhodium catalysts can be recovered simply by filtration and recycled in further runs without loss of catalytic activity.     

Hydrogenation of arenes over silica-supported catalysts that combine a grafted rhodium complex and palladium nanoparticles: evidence for substrate activation on Rh(single-site)-Pd(metal) moieties

The complex Rh(cod)(sulfos) (Rh(I); sulfos = (-)O(3)S(C(6)H(4))CH(2)C(CH(2)PPh(2))(3); cod = cycloocta-1,5-diene), either free or supported on silica, does not catalyze the hydrogenation of benzene in either homogeneous or heterogeneous phase. However, when silica contains supported Pd metal nanoparticles (Pd(0)/SiO(2)), a hybrid catalyst (Rh(I)-Pd(0)/SiO(2)) is formed that hydrogenates benzene 4 times faster than does Pd(0)/SiO(2) alone. EXAFS and DRIFT measurements of in situ and ex situ prepared samples, batch catalytic reactions under different conditions, deuterium labeling experiments, and model organometallic studies, taken together, have shown that the rhodium single sites and the palladium nanoparticles cooperate with each other in promoting the hydrogenation of benzene through the formation of a unique entity throughout the catalytic cycle. Besides decreasing the extent of cyclohexa-1,3-diene disproportionation at palladium, the combined action of the two metals activates the arene so as to allow the rhodium sites to enter the catalytic cycle and speed up the overall hydrogenation process by rapidly reducing benzene to cyclohexa-1,3-diene.     

Nanoscale Pt(0) particles prepared in imidazolium room temperature ionic liquids: synthesis from an organometallic precursor,characterization, and catalytic properties in hydrogenation reactions

The reaction of Pt(2)(dba)(3) (dba = bis-dibenzylidene acetone) dispersed in room temperature 1-n-butyl-3-methylimidazolium (BMI) hexafluorophosphate ionic liquid with molecular hydrogen (4 atm) at 75 degrees C leads to stable and isolable nanometric Pt(0) particles. The X-ray diffraction analysis (XRD) of the material indicated that it is constituted of Pt(0). Transmission electron microscopy (TEM) analysis of the particles dispersed in the ionic liquid shows the formation of [Pt(0)](n) nanoparticles of 2.0-2.5 nm in diameter. A detailed examination of the nanoparticles imbibed in the ionic liquid and their environment shows an interaction of the BMI.PF(6) ionic liquid with the Pt(0) nanoparticles. The isolated [Pt(0)](n) nanoparticles can be redispersed in the ionic liquid or in acetone or used in solventless conditions for liquid-liquid biphasic, homogeneous, or heterogeneous hydrogenation of alkenes and arenes under mild reaction conditions (75 degrees C and 4 atm). The recovered platinum nanoparticles can be reused as a solid or redispersed in the ionic liquid several times without any significant loss in catalytic activity.     

催化剂表面分形结构对催化反应的影响

用溶胶－凝胶方法制备了ＳｉＯ２并以其及另一种ＳｉＯ２气凝胶作载体,用浸渍法制备了两种铑基催化剂。以ｎ－Ｃ５～Ｃ８烷烃为探针分子,测得两种催化剂的表面分形维数Ｄ分别为３和２。在两种催化剂上,ＣＯ加氢和丙烷氢解反应的选择性没有显著差别,但在Ｄ＝２的催化剂上,ＣＯ加氢和丙烷氢解反应的速度显著高于Ｄ＝３的催化剂     

喹啉及其衍生物的多相不对称氢转移反应

喹啉及其衍生物的多相不对称氢转移是制备杂环手性化合物的理想策略.多相手性催化体系具有催化剂可循环利用及产物分离提纯容易等优势.然而,喹啉及其衍生物的多相手性高效催化体系鲜有报道.这主要是由于多相手性氢转移为水-油-固三相反应,在反应的过程中,传质问题极大影响固体催化剂的催化性能.因此,发展具有相转移功能的手性催化材料,是提高多相氢转移体系催化效率的有效途径.本文采用一锅法合成策略,通过离子液体(ILs)为连接基团实现了TsDPEN手性配体在SBA-15介孔孔道中的嫁接.与Rh盐配位后,获得手性固体催化剂SBA-ILBF4-TsDPEN-Rh.FI-IR光谱和13C NMR结果表明,手性催化活性中心成功负载在SBA-15中,随着手性活性中心负载量的增加,SBA-ILBF4-TsDPEN-Rh的比表面积、孔径和孔容逐渐降低.在喹啉衍生物不对称氢转移反应中,SBA-ILBF4-TsDPEN-Rh系列催化剂催化得到产物的ee值为91％,表明多相手性催化剂具有较高的手性选择性.多相手性催化剂的催化活性随着活性中心负载量的上升而呈现下降的趋势,这主要是由于活性中心负载量较低的多相催化剂具有更高的比表面积和孔容,更有利于催化过程中的传质.与均相手性催化剂相比,优化后的多相手性催化剂表现出更高的催化活性(TOF值分别为75和92 h-1).作为对比,本文还合成了采用烷基链为连接基团的SBA-TsDPEN25-Rh,并以其为基础进一步嫁接了ILs基团,得到SBA-TsDPEN20-ILBF4-Rh.在相同的反应条件下,SBA-ILBF4-TsDPEN50-Rh表现出更高的催化活性.上述结果证实了ILs基团在反应过程中起到相转移以及富集氢源甲酸盐的作用,极大促进了喹哪啶不对称氢转移多相催化体系的活性,并且ILs基团和手性活性中心在空间距离上的接近更有利于催化活性的提高.此外,本文还研究了反应体系pH值对固体催化剂上反应速率的影响,随着反应的进行,反应溶液的pH会呈现明显上升的趋势,导致反应速率减缓以及底物转化受限.通过在反应过程中加入适量甲酸或者选用浓度更高的缓冲溶液可以有效防止催化过程中反应速率的减慢.综上可见,负载手性催化剂中的连接基团对多相手性催化剂的催化性能有重要影响.通过改变手性配体的连接基团提高手性固体催化剂的催化活性和手性选择性的策略可以拓展到其他多相手性催化体系.     

Rh基催化剂上CO加氢制C2含氧化物的原位红外光谱研究

 用原位红外光谱考察了Rh-Mn-Li-Fe/SiO2和Rh/SiO2催化剂表面上CO的吸附态及CO加氢反应过程中吸附物种的变化. 结果表明,CO在Rh/SiO2催化剂上仅有线式吸附态存在,而CO在Rh-Mn-Li-Fe/SiO2催化剂上既有线式吸附态存在,又有孪生吸附态存在. 这说明Rh-Mn-Li-Fe/SiO2催化剂中Rh的分散度较高. 经CO加氢反应(3.0 MPa,593 K)后,在Rh-Mn-Li-Fe/SiO2催化剂上可观测到C2含氧化物前驱物种的吸收谱带,而在Rh/SiO2催化剂上未观测到相应的谱带; CO在这两种催化剂上主要以线式吸附态存在,孪生吸附态基本消失. 结合催化剂对CO加氢的催化性能,可以认为线式吸附的CO对生成C2含氧化物有贡献. Rh-Mn-Li-Fe/SiO2催化剂的高活性是由于助剂的存在削弱了其表面吸附CO的 C-O键,促进了CO的活化,从而有利于C2含氧化物前驱物的生成.     

吸附相反应技术制备双金属 Ag-Ni 催化剂用于硝基苯液相加氢

 浙江大学化学工程与生物工程学系, 浙江杭州 310027 摘要：采用吸附相技术在乙醇-水体系中分别制备了硅胶和高岭土负载的 Ag-Ni 双金属催化剂, 并用于硝基苯低温液相加氢制苯胺反应. 考察了催化剂中 Ni 含量和 Ni/Ag 比对催化剂形貌和活性的影响. 结果表明, 高岭土或硅胶负载的催化剂在 Ni/Ag = 5 (摩尔比) 时活性较高, 且都存在一个最佳 Ni 含量, 分别为 0.04% 和 0.03%. 在相同条件下, 以高岭土负载的 Ag-Ni 催化剂的活性和苯胺收率更高.     

KIT-5负载离子液体催化甲缩醛和三聚甲醛合成聚甲醛二甲醚

采用包埋法将离子液体封装在分子筛KIT-5孔笼内,制备了四种负载型离子液体催化剂,用于甲缩醛和三聚甲醛合成聚甲醛二甲醚(PODE_n),研究了不同条件对三聚甲醛转化率和目标产物PODE_(3-5)选择性的影响。结果表明,催化合成PODEn的最佳反应条件为:反应时间2 h、100℃、甲缩醛与三聚甲醛物质的量比1.5、催化剂含量3%,在此条件下,四种催化剂均表现出了很好的催化效果。与离子液体催化剂相比,负载型催化剂的催化活性基本保持不变,而且性能稳定,可多次使用,具有一定的实用价值。