木质素模型化合物的裂解工艺及机理的研究进展

化石资源的有限性、不可再生性及其利用所造成的环境污染,使木质生物质资源生产高附加值化学品和燃料受到广泛关注。因木质素是结构复杂的高分子聚合物,其综合有效利用受到极大限制,通常被作为燃料直接燃烧,同时给木质素解聚研究带来了巨大的困难。因此,围绕木质素模型化合物裂解工艺及机理的研究发展迅速。为梳理木质素模型化合物的裂解研究的现状和预测未来发展方向,本文综述了其裂解工艺和机理的研究进展。着重介绍木质素单体、二聚体和多聚体不同裂解工艺的特点、优势、应用前景以及相关的机理,最后预测了木质素模型化合物裂解研究未来的发展方向。     

非贵金属催化剂Ni/AC选择性氢解木质素C-O键

用浸渍法制备了具有高活性的非贵金属催化剂Ni/AC,采用X射线粉末衍射(XRD)、高分辨扫描透射电镜(STEM)对催化剂进行了表征,并研究了催化剂、温度、时间、氢气压力等因素对苯基苯醚选择性裂解C-O键的影响。结果表明Ni/AC在木质素α-O-4模型化合物的氢解反应中表现出较高的活性和选择性,获得了较高收率的甲苯和苯酚(>65.5%)。除此之外该催化剂在真实木质素的氢解反应中也展示出较好的活性。     

木质素及其模型化合物的加氢脱氧反应研究进展

随着化石能源的不断枯竭,以及所产生的环境问题-温室效应及其高硫含量引起的酸雨,迫使人类寻找新型替代能源.在众多可再生能源中,生物质因其碳中性,易获取,作为唯一可转化为液体燃料的可再生资源,正日益受到重视.全球每年生物质产出高达1.7×1011t,其中,含75%的碳水化合物如纤维素、甲壳素和淀粉,20%木质素,其他占     

苯中硫在Ni/ZnO催化剂上加氢吸附脱除的研究

比较了浸渍法与共沉淀法制备的Ni/ZnO催化剂对芳烃原料的深度脱硫活性和选择性,并采用H₂-TPR、XRD和BET等手段对催化剂进行了表征。结果表明,NiO与载体ZnO之间的相互作用程度对催化剂的性能有很大影响。与ZnO相互作用较弱的游离态NiO还原后生成的Ni⁰,导致苯加氢生成环己烷;与ZnO相互作用较强的NiO还原后生成的Ni⁰具有脱硫能力但不是苯加氢活性中心。共沉淀法制备的催化剂由于NiO与载体相互作用较强,游离态NiO较少,且比表面积相对较大,因而具有较高的活性和选择性。同时发现,还原温度对催化剂的性能具有很大影响,在400℃还原时开始出现Ni_xZn_y合金,且随着还原温度的升高,晶粒长大,比表面积降低,导致催化剂活性降低。Sn助剂的加入能增加NiO与载体的相互作用,抑制游离态的NiO生成,从而减少苯的损失。     

复合氧化物负载的Ni基催化剂上愈创木酚加氢脱氧性能

分别以Al₂O₃-SiO₂,Al₂O₃-TiO₂,TiO₂-SiO₂和TiO₂-ZrO₂双金属氧化物为载体研究Ni基催化剂的愈创木酚加氢脱氧性能. 重点考察了催化剂载体、溶剂种类、反应温度和压力对愈创木酚转化率及产物选择性的影响,并对催化剂的抗积碳性能、重复利用性能和愈创木酚加氢脱氧反应机理进行了探讨. 通过BET（Brunauer-Emmett-Teller）比表面积、X射线衍射（XRD）、NH₃程序升温脱附（NH₃-TPD）和H₂程序升温还原（H₂-TPR）等表征手段对催化剂的比表面积、物相结构、表面酸性、可还原性能进行了表征. 结果表明,Ni/TiO₂-ZrO₂催化性能相对较优. 在300 ℃、初始氢压4 MPa、以十氢萘为溶剂的最佳反应条件下,愈创木酚的转化率为100%,环己烷选择性高达86.4%. 该催化剂还具有抗积碳性能,反应后的催化剂上仅检测到3.2%（质量分数）的积碳量.     

木质素在不同Ru/Nb基催化剂上解聚和脱氧加氢制芳烃化合物

木质素高效转化为芳烃是木质素利用的一个非常重要的过程,一般通过解聚和脱氧加氢反应来实现.我们曾发现NbOx物种在木质素及其模型化合物的C–O键活化和断裂的过程中发挥了至关重要的作用.本文分别选择两种商业的铌基材料(HY-340和NbPO-CBMM)和实验室自制的具有层状结构的氧化铌材料(Nb_2O_5-Layer)为载体,制备了负载型Ru催化剂,将其用于木质素及其模型化合物的催化转化.同时,为了尽量避免Ru与铌基载体相互作用的影响,制备了较为均匀的Ru纳米胶粒并吸附于铌基载体上,得到Ru@铌基催化剂,并用于木质素模型化合物—对甲酚的催化转化反应中.研究表明,木质素在所有的Ru/铌基催化剂上都可以得到比较高的C7–C9碳氢化合物的收率.其中,在Ru/Nb_2O_5-Layer催化剂上C_7–C_9碳氢化合物的摩尔收率为99.1%,选择性为88.0%.采用X射线衍射、N_2吸附-脱附、热重分析、吡啶吸附红外光谱(Py-FTIR)、X射线光电子能谱(XPS)以及CO化学吸附等技术表征了Ru/铌基催化剂的性能与铌基材料的性质、金属Ru颗粒大小及其表面电子状态之间的关系.Py-FTIR结果表明, Nb_2O_5-Layer材料上几乎没有Br?nsted酸,但含有最多的Lewis酸,而NbPO-CBMM上的Lewis酸量最低.结合催化性能数据发现,单体产物收率与铌基载体的Lewis量成正相关关系,其中以Ru/Nb_2O_5-Layer催化剂上最高.CO化学吸附和XPS结果表明,不同的铌基载体负载的金属Ru的分散度和电子状态都有差异.在Ru/Nb_2O_5-Layer上Ru的分散度最好,颗粒尺寸最小,木质素转化得到的芳烃选择性最好;在Ru/HY-340和Ru/NbPO-CBMM上,虽然Ru的分散度相近,但其表面电子状态不同, Ru/HY-340上的金属态Ru带有更多的正电荷δ+,其得到芳烃的选择性高于Ru/Nb PO-CBMM.由此可见, Ru的颗粒尺寸和表面电子状态会影响芳烃选择性.对甲酚催化转化反应结果表明, Ru颗粒大小相同时,铌基载体性质会影响对甲酚转化率;而同一铌基载体上, Ru颗粒大小则影响芳烃选择性,较小的Ru颗粒有利于芳烃的生成.     

Ti掺杂SBA-15负载Ni基催化剂用于木质素衍生物定向加氢脱氧转化

本研究通过在SBA-15分子筛骨架内掺杂Ti物种并负载Ni纳米颗粒合成了“金属-酸”双功能催化剂(Ni/Ti-SBA-15)。Ti的掺杂不仅提高了催化剂酸性位点的数量,还促进了Ni纳米颗粒在载体上的高度分散。在绿色、温和条件下实现了香兰素到2-甲氧基-4-甲基苯酚(MMP)高效转化,目标产物选择性高达96.46%。此外,Ni/Ti-SBA-15催化剂价格低廉,制备工艺简单,这项工作为制备廉价高效催化剂提供了新的思路,有利于实现生物质衍生物的绿色、低成本升级转化。     

镧对苯选择加氢钌基非晶合金催化剂性能的影响

采用稀土镧作助剂，制备了Ru-La-B／ZrO2非晶合金催化剂，具有较好的活性、选择性和热稳定性。利用活性选择测定、HRTEM，SAED，XPS，高温XRD等研究了镧对苯选择加氢制环己烯非晶合金RuB／ZrO2催化剂性能的影响。研究表明，在稀土元素镧作为助剂加入催化剂后，在不降低选择性的情况下，可以明显提高Ru-B／ZrO2催化剂的活性。高温XRD说明从室温到673KRu没有单独成相，773K以上Ru晶化。HRTEM观察到RuB和La形成非晶使金均匀地分散在ZrO2上，粒径3-6nm，La的分散作用使Ru-La-B／ZrO2催化剂具有良好的热稳定性，选区电子衍射证实了Ru-La-B的非晶态结构；XPS表明La在催化剂中以La2O3形式存在。     

Ni基催化剂上CH4裂解制备纳米碳管的研究

本文研究了负载型Ni催化剂上, 以CH4为原料制备纳米碳管的方法。考察了载体、温度、CH4浓度及在反应气中添加O2或CO2等因素对纳米碳管的生长的影响。实验发现, 采用稀释的CH4在较低的温度下反应或在反应气中添加O2或CO2均有利于纳米碳管的生长。     

Rh基催化剂上CO加氢制C2含氧化合物的红外光谱研究

 用红外光谱法考察了Rh-Mn-Li-Ti/SiO2催化剂在CO加氢反应过程中表面吸附物种随压力、温度和H2/CO比的改变而变化的规律. 结果表明,高压有利于提高催化剂表面吸附的CO浓度和活性,高温有利于CO解离; 而高温、高压条件不但促进了CO吸附,而且提高并平衡了CO的解离和插入之间的相对活性,促进了C2含氧化合物的生成. H2/CO比的增大有利于CO在催化剂表面的吸附,从而促进了CO插入,尤其是CO的解离和加氢活性,但是过高的H2/CO比将导致过高的CO解离和加氢活性,引起CO插入活性的削弱而最终导致C2含氧化合物生成活性的下降. 同时,考察了助剂(Mn, Li和Ti)对Rh基催化剂表面吸附物种的影响. 结果表明,助剂的加入可提高C2含氧化合物的生成活性.     

Hydrolysis kinetics of benzyl phenyl ether in high temperature liquid water

The application of high temperature liquid water(HTLW) to decomposition of lignin as efficient and green solution for phenolic compounds recovery was studied.Benzyl phenyl ether(BPE),the lignin model compound,was treated at temperatures ranging from 220 to 250℃.BPE undergo hydrolysis in HTLW,and main products were phenol and benzyl alcohol with the minimum selectivities of 75.7%and 82.8%,respectively.Lower temperature led to higher selectivity in 220-250℃temperature range.The kinetics on BPE hydrolysis was studied and the activation energy was determined as 150.3±12.5 kJ/mol with the first-order kinetic equations.Based on products distribution,the reaction mechanism for decomposition of benzyl phenyl ether was proposed.The investigated process provides insights into the design of a commercial method for utilization of lignin.     

Selective cleavage of the linear ether bond in benzyl glycidyl ether and triphenylmethyl glycidyl ether by potassium alkalide as two-electron-transfer reagent

The linear ether bond was exclusively cleaved in benzyl glycidyl ether and triphenylmethyl glycidyl ether under the influence of K⁻, K⁺(15-crown-5)₂ (1), whereas the strongly strained three-membered oxacyclic ring remained undisturbed. Potassium glycidoxide and benzylpotassium were found as the primary reaction products of benzyl glycidyl ether with 1. Subsequently, benzylpotassium reacted with benzyl glycidyl ether giving the next potassium glycidoxide molecule and bibenzyl. Benzyl phenyl ether was used as a model compound to explain the mechanism of bibenzyl formation. The reaction of triphenylmethyl glycidyl ether with 1 resulted in potassium glycidoxide and stable triphenylmethylpotassium. After treating with a quenching agent a new glycidyl ether or glycidyl ester was obtained from potassium glycidoxide. These results were found when the reaction occurred at the excess of glycidyl ether. In another case, i.e. at the excess of 1 further reactions took place with the participation of potassium anions and various new compounds were observed in the reaction mixture after benzylation or methylation. Thus, the method of substrates delivery influences the course of studied processes in a decisive way.     

制备方法对煤焦油模型化合物裂解催化剂Ni/Al_2O_3结构及性能的影响

采用等体积浸渍法、浸渍沉淀法和机械化学法(市售载体和自制载体)制备了Cat-1、Cat-2、Cat-3和Cat-4四种催化剂,通过BET、H_2-TPR、XRD、XPS和NH_3-TPD等表征催化剂的结构特征,考察了各催化剂对煤焦油模型化合物甲苯和芘(3%,质量分数)裂解反应性能的影响。结果表明,四种催化剂均为介孔材料,且Cat-4的介孔有序度更高,比表面积最大,达235 m~2/g。Cat-4催化剂中,NiAl_2O_4尖晶石的还原峰面积最高,占总面积的85.2%,还原后Ni的分散度最大,粒径最小,约为10.0 nm,意味着活性位点多。实验表明,除Cat-1外,其他催化剂对芘的裂解活性基本相当,其中,Cat-4作用下的析碳量最低,为10.84%,经Cat-1、Cat-2和Cat-3裂解后,体系中的析碳量分别较Cat-4增加了35.0%、74.7%和45.7%。可见,机械化学法制备的催化剂不仅具有最高的比表面积利于活性组分分散,而且NiAl_2O_4尖晶石含量最高,可抑制裂解过程中积炭的生成,因而最适宜于甲苯+芘裂解体系。     

取代基对木质素三聚体模型化合物醚键均裂反应影响的密度泛函理论研究

利用密度泛函理论M062X/6-31++G(d,p)方法,对27种具有不同取代基(甲基、羟甲基和甲氧基)的木质素三聚体模型化合物的Cα-O和Cβ-O键均裂解离能进行了理论计算,探究了不同位置取代基对醚键解离能的影响规律。结果表明,当R2或R3位氢原子仅有一个被甲氧基取代时,Cβ-O键解离能变化很小;当R2、R3位氢原子均被甲氧基取代时,Cβ-O键解离能明显降低;且R4、R5位甲氧基能强化R2、R3位甲氧基对Cβ-O键解离能的降低程度,而不受R1位取代基的影响。当R4、R5位氢原子相继被甲氧基取代时,Cα-O键解离能逐渐降低,且R2、R3位甲氧基也能强化R4、R5位甲氧基对Cα-O键解离能的降低程度。当R1位氢原子相继被甲基、羟甲基取代时,Cα-O键解离能逐渐升高,然而R2、R3位甲氧基会弱化R1位甲基、羟甲基对Cα-O键解离能的升高程度;R1位甲基不会影响Cβ-O键解离能,羟甲基却能明显提高Cβ-O键解离能。     

Pyrolysis of arylglycol-β-propylphenyl ether lignin model in the presence of borosilicate glass fibers. : I. Pyrolysis reactions of β-ether compounds

Two β-aryl ether type model compounds, guaiacylglycol- and veratrylglycol-β-propylphenyl ethers, were copyrolyzed with borosilicate glass fibers. The results provided a better understanding of the effect of copyrolysis with the fibers on the yields of lignin-derived products from lignocellulosics.

The observed products indicated the following reactions occurring in the models; (1) cleavage of the C-aromatic ring bond, (2) cleavage of the β-ether bond, (3) cleavage of the C-Cβ bond, (4) ,β-dehydration, and (5) demethylation, and others. Of these reactions, reactions (1), (2) and (4) were the main pyrolysis reactions and fully explained the increase in the total yield of lignin-derived pyrolysis products from Japanese red pine (Pinus densiflora Sieb. et Zucc.) in the presence of borosilicate glass fibers. Reaction (1) was a particularly characteristic reaction in copyrolysis with the fibers. Important reactions relating to the increase in the total yield of lignin-derived pyrolysis products were reproduced on the models used.     

双功能催化剂Ru2P在N-杂环加氢和无受体脱氢反应中的几何效应和电子效应

饱和及不饱和N-杂环化合物是非常重要的药物中间体.由于它们在催化剂表面的吸附/脱附能力不同,设计具有合适电子结构和几何结构的催化剂用于饱和与不饱和N-杂环化合物的可逆转化具有很大挑战性.目前,负载型纳米金属催化剂通常被用于饱和N-杂环化合物的加氢反应或者不饱和杂环化合物的脱氢反应.然而反应过程中N-杂环化合物与纳米金属的强配位作用,不仅影响其他反应底物与活性位点的接触,而且导致催化剂的循环稳定性较差.在之前的研究中,钌(Ru)催化剂被用于喹啉化合物的选择加氢反应,但反应条件苛刻,循环稳定性差,不能实现杂环化合物的可逆转化.本文在Ru纳米颗粒的晶格中引入杂原子,诱导催化剂表现出不同的几何结构和电子性质,从而调节反应势垒和底物在催化剂表面的脱附能力以优化反应性能.本文以活性炭(AC)为载体,制备了Ru₂P,RuO₂,RuS₂和Ru四种负载型催化剂,以喹啉和四氢喹啉为模型反应物,考察其催化性能.研究发现,Ru₂P/AC可在温和条件下同时实现喹啉的加氢反应和四氢喹啉的无受体脱氢反应,且催化剂经过8次循环使用后,其转化率仍高达95%,选择性达到99%,远优于Ru/AC.密度泛函理论计算结果表明,Ru₂P中的P原子使得两个相邻的Ru-Ru原子的间距从2.61?增加到2.9?.同时P对催化剂几何结构的变化使反应底物在催化剂表面的吸附行为发生改变,即喹啉和四氢喹啉分子都更容易在Ru₂P的表面发生脱附,从而有利于反应进行.通过差分电荷分析,P原子掺杂会将Ru从零价状态调整为缺电子状态.随着P原子掺杂到Ru金属中,反应物表面的电荷大幅度下降,提高了加氢反应和脱氢反应中产物的扩散能力.进一步计算反应路径结果表明,Ru₂P实现了N-杂环化合物可逆加氢/脱氢过程中反应与扩散之间的平衡,从而在加氢和脱氢反应中均表现出优异的催化性能.通过浸渍、热解制备的Ru₂P/AC对一系列N-杂环化合物的加氢和脱氢反应均表现出优异的催化性能.这主要归因于P原子的掺入稀释了Ru-Ru团簇,引起的几何效应和电子效应的协同作用实现了N-杂环化合物加氢/脱氢过程反应与扩散的平衡,从而提高了可逆反应的催化性能.本文通过原子掺杂调控催化活性的本征结构,从而优化出具有平衡反应和产物扩散的优异催化剂.该合成策略具有直接通用的特点,易于拓展到其它复杂的反应体系当中.     

Conformational study of a guaiacyl beta-O-4 lignin model compound by NMR. Examination of intramolecular hydrogen bonding interactions and conformational flexibility in solution

Intramolecular H-bonding interactions were investigated in solution for the threo and erythro diastereomeric forms of a guaiacyl beta-O-4 lignin model compound by using the NMR data obtained from hydroxyl protons. Temperature coefficients of the chemical shifts (ddelta/dT) and coupling constants (3J(HCOH)) were measured in aprotic and protic solutions: DMSO-d6, acetone-d6 and acetone-d6-water. The NMR parameters do not support the existence of strong and persistent intramolecular H-bonds that could participate in the stabilization of the guaiacyl beta-O-4 structure in solution, but instead indicate that intermolecular H-bonds to solvent predominate. 1D NOE experiments nevertheless revealed the presence of a direct chemical exchange between the hydroxyl protons, suggesting the possible existence of weak and transient intramolecular H-bonding interactions. The conformational flexibility of the threo structure was also investigated in acetone solution from the measurement of long-range 1H, 1H and 1H, 13C coupling constants and from NOESY experiments. The NMR data are not consistent with any single conformation, indicating that different conformers co-exist in solution. The experimental results support the conformational flexibility predicted by molecular dynamics simulations performed in a previous study. Finally, both experimental and theoretical approaches indicate that weak intramolecular H-bonds can exist transiently in solution, breaking and reforming as the beta-O-4 molecule undergoes conformational interconversion, but cannot be invoked as possible means of conferring rigidity to the beta-O-4 structure.     

Do the molecules which form discotic liquid crystals have disc-like structures? The conformation of a simple model compound, 1,2-dihydroxydiacetylbenzene, determined from the NMR spectra of samples dissolved in liquid crystalline solvents

Many discotic mesogens are molecules with a central aromatic ring with adjacent alkylcarboxylate substituents. The simplest such molecule, 1,2-dihydroxydiacetylbenzene, which is not mesogenic, is studied by NMR spectroscopy as a solute in a nematic solvent. The spectra are analysed to give sets of residual dipolar couplings, D_ij , which are then used to test models for the conformation adopted by the acetate side groups. The conformations and geometry of an isolated molecule are calculated by the ab initio MP2/6-311G method and also by the DFT approach using the B3LYP functional with the 6-311++G** basis set. The quantum chemical calculations find that the minimum energy conformer has the acetate groups rotated in opposite directions out of the ring plane, and this kind of structure is also consistent with the NMR data.     

Phase separation in semicrystalline blends of poly(phenylene sulfide) and poly(ethylene terephthalate). I. Preparation of poly(phenylene sulfide)-graft-poly(ethylene terephthalate) copolymers by ester interchange and characterization utilizing the model compound 2,4-bis(phenylthio benzoic acid)

Blends of carboxyl functionalized poly(phenylene sulfide) (PPS) and poly(ethylene terephthalate) (PET) were shown to undergo an ester interchange reaction during melt blending. Pendent carboxyl functionality randomly incorporated along the PPS chain reacts with the ester moiety of PET to form a graft copolymer. A model compound, 2,4-bis(phenylthio benzoic acid), has been synthesized to assist in defining the level of carboxyl functionality on the PPS chain. Evidence of the grafting reaction has been gathered from infrared spectroscopy, solubility measurements, and electron microscopy. When added to blends of PPS and PET homopolymers, the graft copolymer significantly reduces the average domain size of the dispersed phase across the entire composition range. This study describes the role that graft copolymers formed by ester interchange reactions can play in compatibilizing this immiscible blend system, with particular focus on the conditions leading to increased grafting efficiency. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3473–3485, 1999