Catalytic conversion of lignocellulosic biomass to fine chemicals and fuels

Lignocellulosic biomass is the most abundant and bio-renewable resource with great potential for sustainable production of chemicals and fuels. This critical review provides insights into the state-of the-art accomplishments in the chemocatalytic technologies to generate fuels and value-added chemicals from lignocellulosic biomass, with an emphasis on its major component, cellulose. Catalytic hydrolysis, solvolysis, liquefaction, pyrolysis, gasification, hydrogenolysis and hydrogenation are the major processes presently studied. Regarding catalytic hydrolysis, the acid catalysts cover inorganic or organic acids and various solid acids such as sulfonated carbon, zeolites, heteropolyacids and oxides. Liquefaction and fast pyrolysis of cellulose are primarily conducted over catalysts with proper acidity/basicity. Gasification is typically conducted over supported noble metal catalysts. Reaction conditions, solvents and catalysts are the prime factors that affect the yield and composition of the target products. Most of processes yield a complex mixture, leading to problematic upgrading and separation. An emerging technique is to integrate hydrolysis, liquefaction or pyrolysis with hydrogenation over multifunctional solid catalysts to convert lignocellulosic biomass to value-added fine chemicals and bio-hydrocarbon fuels. And the promising catalysts might be supported transition metal catalysts and zeolite-related materials. There still exist technological barriers that need to be overcome (229 references).     

Phosphomolybdic heteropolycompounds as oxidation catalysts. Effect of transition metals as counter-ions

Phosphomolybdic compounds were first described as active catalysts in heterogeneous catalytic reactions some twenty-five years ago. Research on these catalysts underwent a huge acceleration when an industrial application in the oxidation of methacrolein to methacrylic acid was reported. They were later developed with success as catalysts for the oxidative dehydrogenation of isobutyric acid into methacrylic acid for which they surpass in many aspects the FePO catalysts. More recently phosphomolybdic catalysts were shown to be very efficient for the oxidation of light alkanes. The structure of these ionic solids with discrete cations and anions can be defined at the molecular level of the heteropolyanion 〚PMo₁₂O₄₀〛^3–, this feature makes them attractive for fundamental studies on catalytic reaction mechanism or catalytic site visualization. In the latter case they represent a unique model of a mixed oxide cluster that can be advantageously used to design new catalysts. Starting from the acid H₃〚PMo₁₂O₄₀〛 two substitution types leading to important modifications of the catalytic properties are possible: (i) the substitution of protons with counter-cations, (ii) the substitution of molybdenum in the anions. This review addresses the effect of transition metals substituting protons on both catalytic and physicochemical properties. It will focus on the influence of iron, copper and vanadyl directly introduced as counter-cations and that of vanadium initially substituting molybdenum in the anion but which moves out due to a partial rebuilding of the anions under catalytic reaction conditions. These transition metals have important and complex effects and have been widely studied. In both cases alkaline metals substituting protons have been also studied.     

Lacunar Keggin Heteropolyacid Salts: Soluble,Solid and Solid-Supported Catalysts

Polyoxometalates are an important class of environmentally friendly catalysts. The Keggin heteropolyacids containing tungsten or molybdenum addenda atoms have received great attention because they have attractive acid and redox properties, which may be easily tunable through changes in their composition and structure. The replacement of their protons by large radium cations makes insoluble the Keggin heteropolyacids and increases their surface area. On the other hand, the removal of tungsten or molybdenum atoms from the Keggin heteropolyanion generates vacancies, which can activate different organic substrates. Therefore, solid lacunar heteropolyacid salts are potentially active catalysts and selective in a plethora of reactions. These catalysts are used either in homo- or heterogeneous conditions. In this review, we wish would highlight recent advances achieved in the chemistry of lacunar Keggin heteropolyacids. We describe their use as solid, soluble or solid-supported catalysts in reactions of oxidation of alcohols and olefins, oxidative desulfurization and acid-catalyzed reactions such as acetalization, esterification, and transesterification.     

固载超强酸催化剂制备及催化合成乙酸正丁酯的研究

研究了把稀土硫酸盐,分别固载于人工沸石、活性炭和强酸型阳离子树脂作为酯化催化剂,从中选出了较好的酯化催化剂－强酸型阳离子树脂固载稀土催化剂,此催化剂用于合成乙酸正丁酯,产率达到97.24%,并对催化剂的催化性能进行了讨论。     

铜基非贵金属异相催化剂在环境修复中的应用（英文）

近年来,全球经济和工业高速发展带来的环境问题,不仅严重影响着经济社会的可持续发展,更极大地危害着人类健康.石油化工、医药生产和交通运输等过程产生的气、液、固相污染物可直接或间接造成臭氧层空洞、光化学烟雾及水体污染等重大环境问题.气相污染物中,CO和可挥发性有机物(VOCs)不仅具有生物毒性,更是形成光化学烟雾等大气污染的主要前驱体.NO_x和SO2会造成酸雨的形成,极大地破坏生态系统.工业废水中难分解的有机污染物可对环境造成持续性破坏.而不完全燃烧产生的碳烟颗粒物不仅影响气候和大气环境,同时可导致心血管疾病高发,危害人体健康.源头控制是环境污染治理的关键,而催化净化是当前污染物源头控制最有效的技术之一.因此,设计和开发稳定、高效的环境修复催化剂是科学家们面临的一个关键问题.传统贵金属(Pt,Rh,Pd)催化剂虽然催化活性高,但是存在价格昂贵且易中毒等不足.而过渡金属及其氧化物因具有高活性、价格低廉和高储量等特点有望成为贵金属的替代催化剂.铜是具有3d轨道的过渡金属,有活泼的物理化学性质,是工业中大量应用的有色金属.铜基氧化物因高氧化还原电势和低环境危害被广泛应用于热催化、电催化和光催化.基于文献报道,铜基催化剂主要分为三类:铜氧化物(CuO_x),负载型铜氧化物(CuO_x/support)和固溶体铜氧化物(CuO_x-X).本篇综述首先探讨了铜氧化物的价态、晶体结构、形貌、暴露晶面以及载体与催化剂活性之间的内在联系,阐明铜基催化剂结构与性能的构效关系及高效催化剂的设计原则;继而全面总结了近年来不同类型的铜基材料在催化净化环境污染物中的应用,主要介绍了以下5类反应:CO的催化氧化,NO_x的选择性催化还原(SCR),VOCs的完全燃烧,废水中有机污染物降解,以及碳烟颗粒物催化燃烧.我们深入阐述铜氧化物的催化活性位点和催化机制;分析负载型铜基催化剂的比表面积、分散度、协同作用和界面作用对催化剂的活性和稳定性的影响;阐明固溶体催化剂的独特原子组成设计与性能关系,为高效催化剂设计提供思路.此外,本综述对铜基催化剂在环境催化中的研究现状以及尚未解决的问题进行了剖析与展望.通过铜氧化物表面调控,复合催化剂的界面调控,具有更高稳定性和抗中毒性的高效催化剂有望开发成功,而团簇及单原子铜催化剂也有望在此领域有所突破.     

Development of Bifunctional Catalysts for the Conversions of Cellulose or Cellobiose into Polyols and Organic Acids in Water

The efficient utilization of renewable lignocellulosic biomass has attracted much attention in recent years. One of the most desirable routes for the transformation of cellulose, the main component of lignocellulosic biomass, is to convert cellulose under mild conditions selectively into a value-added chemical or into a platform compound, which can be easily converted to versatile chemicals or fuels in the subsequent step. The activation of cellulose, typically starting by the cleavage of its glycosidic bonds, under mild conditions and the selective formation of a particular molecule are critical challenges. Bifunctional catalysts coupling the acid sites for the activation of the glycosidic bonds via hydrolysis and the metal nanoparticles for the hydrogenation or oxidation of glucose intermediate have shown promising performances for the conversion of cellulose or cellobiose into hexitols or gluconic acid in water under mild conditions. This short review has summarized some recent studies on the development of such bifunctional catalysts or catalytic systems. The following two kinds of bifunctional catalysts or catalytic systems have mainly been discussed: (1) a liquid acid in combination with a supported metal catalyst, (2) solid acid-supported metal nanoparticles. Emphases have been laid on the conversions of cellulose or cellobiose into sorbitol and gluconic acid catalyzed respectively by ruthenium and gold nanoparticles loaded on carbon nanotubes bearing acid sites.     

Elucidation of structure and location of V(IV) ions in heteropolyacid catalysts H4PVMo11O40 as studied by hyperfine sublevel correlation spectroscopy and pulsed electron nuclear double resonance at W- and X-band frequencies.

Electron spin resonance, pulsed electron nuclear double resonance (ENDOR) spectroscopy at W- and X-band frequencies, and hyperfine sublevel correlation (HYSCORE) spectroscopy have been employed to determine the location of the V(IV) ions in H4PVMo11O40 heteropolyacid catalysts. In these materials the heteropolyanions have the well-known structure of the Keggin molecule. Interactions of the unpaired electrons of the paramagnetic vanadyl ions (VO(2+)) with all relevant nuclei 1H, 31P, and 51V) could be resolved. The complete analysis of the hyperfine coupling tensor for the phosphorus nucleus in the fourth coordination sphere of the V(IV) ion allowed for the first time a detailed structural analysis of the paramagnetic ions in heteropolyacids in hydrated and dehydrated catalysts. The 31P and 1H ENDOR results show that V(IV) ions are incorporated as vanadyl pentaaqua complexes [VO(H2O)5](2+) in the void space between the heteropolyanions in the hydrated heteropolyacid. For the dehydrated H4PVMo11O40 materials the distance between the V(IV) ion and the central phosphorus atom of the Keggin molecule could be determined with high accuracy on the basis of orientation-selective 31P ENDOR experiments and HYSCORE spectroscopy. The results give a first direct experimental evidence that the paramagnetic vanadium species are not incorporated at molybdenum sites into the Keggin structure of H4PVMo11O40 and also do not act as bridges between two Keggin units after calcination of the catalyst. The vanadyl species are found to be directly attached to the Keggin molecules. The VO(2+) ions are coordinated to four or three outer oxygen atoms from one PVMo11 heteropolyanion in a trigonal-pyramidal or slightly distorted square-pyramidal coordination geometry, respectively.     

Synergic Effect of Active Sites in Zinc‐Modified ZSM‐5 Zeolites as Revealed by High‐Field Solid‐State NMR Spectroscopy

Understanding the nature of active sites in metal‐supported catalysts is of great importance towards establishing their structure–property relationships. The outstanding catalytic performance of metal‐supported catalysts is frequently ascribed to the synergic effect of different active sites, which is however not well spectroscopically characterized. Herein, we report the direct detection of surface Zn species and ¹H–⁶⁷Zn internuclear interaction between Zn²⁺ ions and Brønsted acid sites on Zn‐modified ZSM‐5 zeolites by high‐field solid‐state NMR spectroscopy. The observed promotion of C?H bond activation of methane is rationalized by the enhanced Brønsted acidity generated by synergic effects arising from the spatial proximity/interaction between Zn²⁺ ions and Brønsted acidic protons. The concentration of synergic active sites is determined by ¹H–⁶⁷Zn double‐resonance solid‐state NMR spectroscopy.     

芳香胺氰乙基化催化反应的研究进展

从催化剂的应用角度,总结了酸、路易斯酸、固体酸性氧化物、强酸性阳离子交换树脂、无机碱、有机碱以及由酸/路易斯酸、路易斯酸/路易斯酸、路易斯酸/路易斯碱等催化体系在催化芳香胺的氰乙基化反应中的应用进展,阐述了芳香胺的氰乙基化反应的酸催化和碱催化机理,并对芳香胺的氰乙基化反应的今后发展方向进行了展望。     

密度泛函理论计算研究金属-N4大环化合物在酸性介质中的稳定性

质子交换膜燃料电池(PEMFCs)是一种能够有效地将化学能转换成电能的装置,其具有较高的效率及功率密度,还兼具环境友好的优点,因而在电动车和分布式电站等领域有广泛应用前景.然而,昂贵的价格及较差的耐久性阻碍了 PEMFCs的广泛应用.阴极氧还原反应(ORR)缓慢的动力学是限制 PEMFCs性能的主要因素.目前, Pt及其合金仍然是最有效的 ORR催化剂.有限的 Pt供应量是 PEMFC商业化的主要障碍之一.因此,具有较高 ORR活性的非贵金属催化剂越来越多的引起了人们的关注.在众多非贵金属 ORR催化剂中, Fe, Co等金属与氮共掺杂的碳材料最有望取代 Pt.一般认为,这类材料中起催化作用的活性中心是与金属酞菁(MPc)和卟啉(MP)等大环分子类似的金属-N4配位结构.无论是 MPc和 MP,还是掺杂碳材料催化剂,在酸性介质中的耐久性都不够好.具体原因至今仍没有定论.一些研究者认为中心金属离子与酸性介质中的质子交换引起的去金属中心是原因之一.我们通过密度泛函理论计算和热力学分析研究酸性介质(pH=1)中金属大环分子中金属离子和溶液中质子的交换反应,探讨去金属中心是否是造成金属大环类分子催化剂和金属与氮共掺杂碳基催化剂在酸性介质中不稳定的原因.
　　我们建立了研究金属大环化合物中心金属离子与溶液中质子的交换反应的热力学分析方法.在此基础上借助密度泛函理论计算获得各种金属酞菁和卟啉在强酸性介质中的金属离子平衡浓度,以确定相应金属大环分子的稳定性.研究结果表明,在酸性介质中铬、锰、锌类酞菁和卟啉分子很容易被质子化而形成相应的非金属酞菁和卟啉,原因可能是这三类金属的二价阳离子的3d轨道均为半充满或者全充满状态,使得它们与氮的配位能力下降;而铁、钴、镍、铜类酞菁和卟啉在酸性介质中金属化离子的平衡浓度几乎为零,表明它们基本上不发生金属离子与质子的交换反应,且稳定性趋势为 CoPc > NiPc > FePc > CuPc和 CoP > NiP > CuP > FeP,同时,相应的金属酞菁比金属卟啉更稳定.这表明具有氧还原活性的铁、钴类大环分子催化剂及铁、钴与氮共掺杂的碳材料在酸性溶液中的活性衰减并不是由于金属离子与质子的交换引起的.
　　我们还考察了取代基对大环分子中金属离子与质子交换反应的影响,结果发现,给电子取代基(甲基,氨基,叔丁基)会极大地增强酞菁铁和酞菁钴在酸性介质中的稳定性.对于酞菁铁而言,具有中等强度吸电子效应的四氯、四氟和十六氯取代后,其在酸性中稳定性有一定程度的增强,而具有强烈吸电子效应的四硝基及十六氟取代后,稳定性则降低.对于酞菁钴而言,上面提到的所有吸电子取代基都会使得其在酸性介质中变得更加不稳定,并且其不稳定程度随着取代基吸电子能力的增强而上升.     

Importance of Size and Distribution of Ni Nanoparticles for the Hydrodeoxygenation of Microalgae Oil

Improved synthetic approaches for preparing small‐sized Ni nanoparticles (d=3 nm) supported on HBEA zeolite have been explored and compared with the traditional impregnation method. The formation of surface nickel silicate/aluminate involved in the two precipitation processes are inferred to lead to the stronger interaction between the metal and the support. The lower Brønsted acid concentrations of these two Ni/HBEA catalysts compared with the parent zeolite caused by the partial exchange of Brønsted acid sites by Ni²⁺ cations do not influence the hydrodeoxygenation rates, but alter the product selectivity. Higher initial rates and higher stability have been achieved with these optimized catalysts for the hydrodeoxygenation of stearic acid and microalgae oil. Small metal particles facilitate high initial catalytic activity in the fresh sample and size uniformity ensures high catalyst stability.     

State of the copper-containing component and the catalytic properties of Cu/ZSM-5 in selective NO reduction with propane

Supported Cu/ZSM-5 catalysts have been synthesized by ion exchange and impregnation using aqueous ammonia solutions of copper nitrate containing orbital-ordered copper ions. The state of the copper-containing component in the pore space of the catalysts and copper sorption in the catalysts have been investigated by a complex of physicochemical methods. The catalytic properties of Cu/ZSM-5 in the selective catalytic reduction of NO with propane are reported. The catalytic properties depend on the copper precursor structure and deposition method, which determine the size of the copper oxide clusters on the outer surface of zeolite crystals.     

A study of the surface region of the Mo-V-Te-O catalysts for propane oxidation to acrylic acid

The bulk mixed Mo-V-Te oxides possess high activity and selectivity in propane oxidation to acrylic acid and represent well-defined model catalysts for studies of the surface molecular structure-activity/selectivity relationships in this selective oxidation reaction. The elemental compositions, metal oxidation states, and catalytic functions of V, Mo, and Te in the surface region of the model Mo-V-Te-O system were examined employing low energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS). This study indicated that the surfaces of these catalysts are terminated with a monolayer, which possesses a different elemental composition from that of the bulk. The rates of propane consumption and formation of propylene and acrylic acid depended on the topmost surface V concentration, whereas no dependence of these reaction rates on either the surface Mo or Te concentrations was observed. These findings suggested that the bulk Mo-V-Te-O structure may function as a support for the unique active and selective surface monolayer in propane oxidation to acrylic acid. The results of this study have important practical consequences for the development of improved selective oxidation catalysts by introducing surface metal oxide components to form new surface active V-O-M sites for propane oxidation to acrylic acid.     

甲醇选择氧化金属氧化物催化剂的结构与其催化性能的关系

甲醇是一个重要的平台分子, 实现其高效转化为能源和化学品的关键是揭示相关反应过程中催化剂的结构与催化性能之间的关系和反应机理. 围绕这个关键问题, 以甲醇选择氧化为探针反应, 本文总结了负载氧化钼、负载氧化钒和杂多酸等典型催化剂体系以及近年来发展的氧化铼、氧化钌等新催化剂体系在认识催化活性中心结构和反应机理, 进而调控它们的氧化中心和酸中心等方面所取得的进展. 这些认识将有助于设计制备性能优异的新催化剂和实现甲醇到目标氧化产物的定向转化.     

PROPERTIES OF POLYMER SUPPORTED Ni-Cu BIMETALLIC CATALYSTS PREPARED BY SOLVATED METAL ATOM IMPREGNATION

D-72 resin supported nickel-copper catalysts prepared by solvated metal atom impreg-nation (SMAI) were studied by magnetic measurements and X-ray photoelectron spectro-scopy (XPS). The Ni particles on the catalysts are very highly dispersed and displaysuperparamagnetic behaviour. Ni-Cu alloy clusters were found to be formed. The sur-face compositions are different from the bulk concentrations. In contrast with the surfaceenrichment in copper generally observed on conventional Ni-Cu catalysts, the surfaces ofthese catalysts are enriched in nickel. The nickel is in both zero and valent states, whilecopper is mainly in metallic state. Catalytic data show that the formation of Ni-Cu alloyclusters has a profound effect on the catalytic activities of the catalysts in the hydrogena-tion of furfural. The activity of the Ni:Cu ratio of one bimetallic catalysts is much higherthan that of the Ni or Cu monometallic catalyst.     

Copper-catalyzed allylic amination of olefins with nitrosoarenes

The transition metal catalyzed allylic amination of olefins are studied. A screening of catalysts known for the intermediacy of PhNO in the amination of alkene with phenylhydroxylamine reveals that the hydrated copper salt in conjugation with copper powder as reductant has the best catalytic properties using nitrosobenzene as nitrogen-fragment donor. The catalytic system has been studied for a variety of alkenes. Unsymmetrical alkenes react with high regioselectivity with N-functionalization at the less substituted vinylic carbon.     

Reductive amination of cyclohexanol/cyclohexanone to cyclohexylamine using SBA-15 supported copper catalysts

Amination of cyclohexanol was investigated in vapour phase over copper catalysts supported on mesoporous SBA-15. The different products identified during reductive amination of cyclohexanol reaction were cyclohexanone, cyclohexylamine, along with small amounts of N-Cyclohexylidinecyclohexylamine and dicyclohexylamine. Among several catalysts tested for the reductive amination, 5% Cu supported on SBA-15 exhibited better catalytic performance than other catalysts with 36% selectivity towards cylclohexylamine at 80% cyclohexanol conversion. The optimum reaction conditions employed to achieve the best catalyst performance were at 250 °C, 0.1 MPa of H₂/NH₃, TOS-10h. The active Cu sites, acidity of the catalyst, and effect of reaction parameters play a pivotal role in the reductive amination reaction. The prepared catalysts were characterized by XRD, BET, SEM, H₂-TPR and NH₃-TPD. The dispersion of Cu, particle size, and metal surface area (m²/g) calculated from pulse N₂O decomposition method. TPR findings reveal the presence of substantially dispersed copper oxide species at lower loadings which is easily reducible than the bulk copper oxide species found at higher Cu loadings. The acidity measurements by NH₃-TPD analysis suggest that the maximum acidic strength was obtained at 5 wt% copper on porous SBA-15, and decreased with Cu loadings. The catalytic properties are well in agreement with the findings of catalysts characterization.     

Support Modification of Supported Nickel Catalysts for Hydrogen Production by Auto-thermal Reforming of Ethanol

Recent progress on support modification of supported nickel catalysts for hydrogen production by auto-thermal reforming of ethanol was reported in this review. Nickel catalysts supported on various materials, including metal oxides and metal oxide-stabilized mesoporous zirconias, were prepared by an incipient wetness impregnation method for use in hydrogen production by auto-thermal reforming of ethanol. Various experimental measurements such as NH₃-TPD (temperature-programmed desorption) and TPR (temperature-programmed reduction) were carried out to elucidate the different catalytic performance of supported nickel catalysts. It was revealed that acid property of supporting materials served as one of the important factors determining the catalytic performance. Hydrogen yield over nickel catalysts supported on metal oxides showed a volcano-shaped curve with respect to acidity of the supports. Among the catalysts tested, Ni/ZrO₂ catalyst with an intermediate acidity exhibited a superior catalytic performance. It was also observed that reducibility of nickel catalysts supported on metal oxide-stabilized mesoporous zirconias played a key role in determining the catalytic performance in the auto-thermal reforming of ethanol for hydrogen production. Hydrogen yield over nickel catalysts supported on metal oxide-stabilized zirconias increased with increasing reducibility of the catalysts (with decreasing TPR peak temperature of the catalysts).     

Vanadyl salen complexes covalently anchored to an imidazolium ion as catalysts for the cyanosilylation of aldehydes in ionic liquids

Two vanadyl salen complexes having peripheral styryl substituents have been reacted with 1-methyl-3-(3-mercaptopropyl)-imidazolium chloride using azoisobutyronitrile as radical initiator. The resulting compounds contain at the same time a vanadyl salen complex and one imidazolium cation. In agreement with the expectations in view of their structure, these compounds were insoluble in conventional organic solvents, but completely miscible in imidazolium ionic liquids. These vanadyl salen complexes bonded to an imidazolium cation are highly active and reusable catalysts for the cyanosilylation of aldehydes. Moderate enantiomeric excesses were obtained using the chiral version of this complex.