Selective hydrogenolysis of glycerol to propylene glycol on Cu–ZnO catalysts

Hydrogenolysis of biomass-derived glycerol is an alternative route to sustainable production of propylene glycol. Cu–ZnO catalysts were prepared by coprecipitation with a range of Cu/Zn atomic ratio (0.6–2.0) and examined in glycerol hydrogenolysis to propylene glycol at 453–513 K and 4.2 MPa H₂. These catalysts possess acid and hydrogenation sites required for bifunctional glycerol reaction pathways, most likely involving glycerol dehydration to acetol and glycidol intermediates on acidic ZnO surfaces, and their subsequent hydrogenation on Cu surfaces. Glycerol hydrogenolysis conversions and selectivities depend on Cu and ZnO particle sizes. Smaller ZnO and Cu domains led to higher conversions and propylene glycol selectivities, respectively. A high propylene glycol selectivity (83.6%), with a 94.3% combined selectivity to propylene glycol and ethylene glycol (also a valuable product) was achieved at 22.5% glycerol conversion at 473 K on Cu–ZnO (Cu/Zn = 1.0) with relatively small Cu particles. Reaction temperature effects showed that optimal temperatures (e.g. 493 K) are required for high propylene glycol selectivities, probably as a result of optimized adsorption and transformation of the reaction intermediates on the catalyst surfaces. These preliminary results provide guidance for the synthesis of more efficient Cu–ZnO catalysts and for the optimization of reaction parameters for selective glycerol hydrogenolysis to produce propylene glycol.     

The influence of acidity of carbon nanofibre-supported palladium catalysts in the hydrogenolysis of hydroxymatairesinol

The lignan hydroxymatairesinol (HMR, extracted from Norway spruce knots) was hydrogenolysed to matairesinol (MAT) over palladium supported by carbon nanofibres (Pd/CNF) in 2-propanol at 70 °C under hydrogen flow. The influence of support acidity on the activity and the selectivity to MAT was studied. The acidity of the Pd/CNF catalyst was varied by heat-treatment at different temperatures in nitrogen flow. The catalysts were characterized by transmission electron microscopy (TEM), inductively coupled plasma emission mass-spectrometry (ICP-MS, metal content), H₂-chemisorption (dispersion, metal particle size), and titration using NaOH. A more acidic support material was more active and selective to the desired product MAT. The major byproduct was 7-iso-propoxymatairesinol resulting from a reaction of the solvent with HMR over the acid sites on the support. The hydrogenolysis of HMR to MAT requires both the presence of metal and acidity.     

甘油催化氢解制备丙二醇催化剂研究进展

简要概括了近些年生物柴油副产物甘油催化氢解制备丙二醇催化剂研究新进展,对甘油氢解分别采用贵金属催化体系和过渡金属催化体系的催化活性和选择性以及可能的机理进行了解释说明。采用贵金属Pt/WO3负载型催化剂、ReO x改性的Rh/SiO2、Ir/SiO2催化剂、贵金属催化体系中加入有机溶剂以及采用Cu-STA(硅钨酸)/SiO2的气相催化工艺等方式都能得到相对较多的1,3-丙二醇(收率最高为38%)。高分散的纳米铜基催化剂对甘油氢解有着较高的活性、选择性和稳定性,具有工业应用前景。纳米钴催化剂具有特定的形态和良好的催化效果颇受关注。     

甘油催化氢解制备丙二醇的研究现状

随着生物柴油产业的快速发展,作为生物柴油副产物的甘油逐渐过剩,合理有效地利用甘油能促进生物柴油产业的良性发展。丙二醇(1,2-丙二醇和1,3-丙二醇)是重要的化工中间体,具有较高的经济价值,利用可再生的甘油催化氢解制备丙二醇替代传统的石化路线符合绿色化学的要求,因而具有广阔的应用前景。简述了利用甘油催化氢解制备丙二醇的研究背景,详细分析了甘油催化氢解的机理(包括脱水-加氢机理、脱氢-加氢机理、直接氢解机理和螯合机理),从催化剂的角度综述了甘油催化氢解制备丙二醇的研究现状和取得的研究成果,并提出了未来甘油氢解的研究方向。     

The origin of particle size effects in supported metal catalysts: Propane hydrogenolysis on Ru/Al2O3 catalysts

The kinetics of the hydrogenolysis of propane on Ru/Al₂O₃ catalysts differing in particle size have been analysed according to a classical rate equation which supposes the reactive species to be a dehydrogenated form of the alkane. With small ruthenium particles there is a sharp maximum in rate as hydrogen pressure is increased; with large particles the peak is broader and at higher hydrogen pressures. Published results showing the latter to give higher turnover frequencies are only valid at high hydrogen: alkane ratios. Ethane selectivity (S₂) is almost independent of hydrogen pressure on small particles, but on large particles it increases markedly as the hydrogen pressure is raised. The results are interpreted by supposing hydrogen chemisorption to be strong on small ruthenium particles, and weaker on large ones; effects of temperature on selectivities are also explained in this way. The geometric basis of structure-sensitivity is thereby called into question.     

内标法在甘油氢解反应中的运用以及相对校正因子的求出

本文利用内标法对甘油氢解反应中各组分含量进行了系统测定,实验选用各组分的标准样品与内标物正丁醇混合并稀释,再将混合样品在气相色谱中进行分析。选择HP-INNWAX毛细管柱,FID检测器,程序升温法。结果表明,各组分标准曲线线性关系良好,r达到0.997以上,并且得到各组分的相对质量校正因子,从而计算出甘油的转化率,目标产物的选择性以及目标产物的产量。此次探究将内标法更加系统,准确,为内标法运用与推广起到指导作用。     

Design of new solid catalysts for the selective conversion of glycerol

Glycerol is now obtained as a co‐product of biodiesel from renewable raw materials with a dramatically increasing production. It follows that one of the most important breakthroughs is to find new catalytic processes for chemical valorizations. The present paper gives a short overview of selective esterification, transesterification or etherification of glycerol via the use of new heterogeneous catalysts. The selectivity control is mainly the result of the synthesis of mesoporous materials for which acidic or basic properties as well as the surface hydrophilic‐lipophilic balance were optimized.     

Recent advancements in catalytic conversion of glycerol into propylene glycol: A review

The renewability of bio-glycerol has made it an attractive platform for the production of diverse compounds. Selective hydrogenolysis of glycerol to propylene glycol (PG) is one of the most promising routes for glycerol valorization, since this compound is an important chemical intermediate in a number of applications. In this article, advancements in the catalytic conversion of glycerol into propylene glycol are reviewed, which include advances in process development, effects of preparation and activation methods on catalytic activity and stability, and the performance of various types of catalysts. The feasibility of using bio-hydrogen and the challenges of utilizing crude glycerol for glycerol hydrogenolysis are also discussed.     

水及还原温度对氧化铕促进的Cu—ZnO催化剂上甘油氢解性能的影响

采用共沉淀法制备了氧化铕（Eu2O3）促进的Cu—ZnO催化剂,通过X射线衍射（XRD）、N2O脉冲吸附等手段对所制备的催化剂物化性质进行表征,考察了它们在连续流动固定床反应器中甘油氢解反应的催化性能,讨论了反应液中水的质量分数及还原温度对Eu2O3促进的Cu—ZnO催化性能的影响．结果表明：引入Eu203不改变甘油氢解反应的产物分布,但能显著提高催化剂的稳定性;减少反应液中水含量及降低还原温度有利于提高催化剂的稳定性;稀土Eu2O3能够增强Cu—ZnO的抗水氧化能力,使催化剂表面Cu^0难被水氧化而不易失活。     

Role of chromia in copper catalysts for dehydrogenation of ethanol

During direct vapour phase dehydrogenation of ethanol, a copper-on-silica catalyst lost much of its activity in 100 h. Analysis with X-ray diffraction, scanning electron microscopy and X-ray photoemission showed that both sintering and carbon deposition accompanied the drop in activity. In catalysts in which chromia was also present copper was found to be in a more highly dispersed form which was more resistant to sintering. The chromia catalyst accumulated carbon comparably to those containing copper only.     

Characterization and catalytic properties of the CuO/SiO2 catalysts prepared by precipitation-gel method in the hydrogenolysis of glycerol to 1,2-propanediol: Effect of residual sodium

The effect of residual sodium on the CuO/SiO₂ catalysts prepared by precipitation-gel (PG) method has been investigated in correlation with the detailed characteristics of active component performance and catalytic performance in glycerol hydrogenolysis. Characterization of the catalysts showed that the residual sodium had a negative effect on the chemical–physical properties of the catalysts, such as the BET surface area, the dispersion of copper, and the reducibility of Cu²⁺ species as well as the adsorbility of reactant molecules. As a consequence, the conversion and selectivity of the catalysts in glycerol reactions generally decreased with increasing sodium content. The leaching of sodium from catalyst surface as a base could, however, on the one hand, weakly promote the activity of the catalyst, and on the other hand, could help retard the leaching of the active copper component and reduce the deactivation rate of the catalyst. The glycerol hydrogenolysis reaction is supposed to be a structure-sensitive reaction, in which copper particle sizes lower than a critical limit or those that did not fulfill a certain ensemble requirement were not active for glycerol reaction. Such details explained the lower TOFs of the catalysts with much smaller sizes. A certain amount of sodium is deduced to be needed for CuO/SiO₂ catalyst to exhibit both high catalytic activity and good stability. In addition, a reaction mechanism based on the effect of sodium on the activity and selectivity in glycerol hydrogenolysis has been proposed.     

The effect of free fatty acid on the reactivity of copper-based catalysts for the hydrogenolysis of fatty acid methyl esters

In the synthesis of fatty alcohols by hydrogenolysis of fatty acid methyl esters, small amounts of free fatty acids in the feed negatively affect the reactivity of copper-silica based catalysts. The effect of the acid was investigated in relation to the production of water, the nature of the inhibiting species, and the degree of reduction of the catalyst. Inhibition is reversible and not due to catalyst deactivation. Water is not the inhibiting species. Furthermore, formation of copper and zinc soaps was excluded. Lauric acid in the methyl ester feed reacts preferentially, but at a lower rate than the ester. Inhibition most likely stems from a preferential adsorption of the acid at the active sites of the catalyst. The consequences for practical applications are discussed.     

Role of ZnO in methanol synthesis on copper catalysts

The varied results obtained by different groups concerning synergy between ZnO and Cu metal in methanol synthesis catalysts are shown to be a result of different experimental test conditions. It is suggested that synergy, when it occurs, arises from H spillover from ZnO to Cu metal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ammoxidation of propane to acrylonitrile on V---Sb---O catalysts. Role of ammonia in the reaction pathways

Transient experiments in the vacuum on the ammoxidation of propane over VSb₅O_x- and VSb₅O_x(30 wt%)/Al₂O₃ catalysts were performed. Additionally, the interaction of ammonia with the catalysts was investigated by means of TPD and DRIFT spectroscopic studies. The reported results reveal that short lived NH_x.-species, most probably NH_3,ads or NH⁺₄, are active species in the formation of acrylonitrile from propane. These species are also involved in the formation of the non-selective side-product N₂, which is formed via the intermediates NO and N₂O.     

铂系丙烷脱氢催化剂助剂研究进展

铂基催化剂用于丙烷催化脱氢的主要缺点是稳定性差、选择性低,通过添加助剂可以大大改善该催化剂的脱氢性能.针对催化剂助剂,综述了铂基丙烷脱氢催化剂的研究现状,分别介绍了碱金属、碱土金属、稀土金属和过渡金属作为助剂对铂基催化剂的影响,探讨了所添加助剂的作用机制,并对铂基催化剂研究前景进行了展望.     

Role of active oxygen transients in selective catalytic reduction of N2O with CH4 over Fe-zeolite catalysts

Sharp NO and O₂ desorption peaks, which were caused by the decomposition of nitro and nitrate species over Fe species, were observed in the range of 520–673 K in temperature-programmed desorption (TPD) from Fe-MFI after H₂ treatment at 773 K or high-temperature (HT) treatment at 1073 K followed by N₂O treatment. The amounts of O₂ and NO desorption were dependent on the pretreatment pressure of N₂O in the H₂ and N₂O treatment. The adsorbed species could be regenerated by the H₂ and N₂O treatment after TPD, and might be considered to be active oxygen species in selective catalytic reduction (SCR) of N₂O with CH₄. However, the reaction rate of CH₄ activation by the adsorbed species formed after the H₂ and N₂O or the HT and N₂O treatment was not so high as that of the CH₄ + N₂O reaction over the catalyst after O₂ treatment. The simultaneous presence of CH₄ and N₂O is essential for the high activity of the reaction, which suggests that nascent oxygen species formed by N₂O dissociation can activate CH₄ in the SCR of N₂O with CH₄.     

Effect of manganese on Cu/SiO2 catalysts for the dehydrogenation of cyclohexanol to cyclohexanone

The effect of the addition of manganese to Cu/SiO₂ catalysts for cyclohexanol dehydrogenation reaction was investigated. At reaction temperature of 250 °C, the conversion and the selectivity to cyclohexanone were both increased with the addition of manganese to Cu/SiO₂ catalyst. However, as the reaction temperature was further increased, higher loading of manganese in Cu/SiO₂ catalyst led to a decrease in the conversion of cyclohexanol. Manganese in Cu/ SiO₂ catalyst decreased the reduction temperature of copper oxide, increased the dispersion of copper metal, and decreased the selectivity to cyclohexene. It was found that the dehydration of cyclohexanol to cyclohexene occurred on the intermediate acid sites of catalyst. At high Mn loading, catalyst surface was more enriched with manganese in used catalyst compared to that in freshly calcined or reduced catalyst, which may account for the sharp decrease of the conversion at high temperature of 390 °C. Upon reduction, copper manganate on silica was decomposed into fine particles of copper metal and manganese oxide (Mn₃O₄).     

An effective catalyst,Cu-B2O3/SiO2, for hydrogenolysis of methyl formate and one-step synthesis of methanol in slurry-phase with potassium methoxide

Some chromium-free copper-based catalysts are tested for the gas-phase hydrogenolysis of methyl formate, in which Cu-B₂O₃/SiO₂ catalyst is identified to be the most promising. The behaviors of Cu-B₂O₃/SiO₂ catalysts are also examined in the slurry-phase hydrogenolysis of methyl formate, along with a discussion of the promoting effect of B₂O₃. Also, Cu-B₂O₃/SiO₂ is used with potassium methoxide as a co-catalyst for the carbonylation of methanol to regenerate the potassium methoxide from potassium formate and potassium methyl carbonate. Moreover, the slurry-phase one-step synthesis of methanol is studied using KOCH₃/Cu-B₂O₃/SiO₂ mixed catalyst under relatively mild conditions.     

Effects of base metal promoters in VOC catalysts for chlorocarbons and n-Hexane Oxidation

The oxidation reactions of dichloromethane, dichloroethane and n-hexane were carried out over honey-comb type platinum basic VOC catalyst (BVC) containing vanadium, chromium, manganese, cobalt, copper or barium. In dichloromethane and dichloroethane catalytic oxidation up to 450 °C, chromium was found as the most active component. Although vanadium was also effective initially, it was deactivated after treatment in the furnace at 800 °C for 120 hours. Chromium, cobalt, vanadium and barium promoted catalysts showed higher activities than BVC in the reaction of n-hexane.     

An investigation of alumina-supported catalysts for the selective catalytic oxidation of ammonia in biomass gasification

Alumina-supported catalysts containing different transition metals (Ni, Cu, Cr, Mn, Fe and Co) were prepared and tested for their activity in the selective oxidation of ammonia reaction at high temperatures (between 700 and 900 °C) using a synthetic gasification gas mixture. The catalysts were also characterised for their acidic properties by infrared studies of pyridine and ammonia adsorption and reaction/desorption. The Ni/Al₂O₃ and Cr/Al₂O₃ catalyst displayed the highest selective catalytic oxidation (SCO) activity in that temperature range with excellent N₂ selectivities. FT-IR studies of adsorbed pyridine and NH₃ indicate that Lewis acid sites dominate and that NH₃ adsorption on these sites is likely to be the first step in the SCO reaction. FT-IR studies on less active catalysts, particularly on Cu/Al₂O₃ allowed the detection of oxidation intermediates, amide (NH₂), and possibly hydrazine and imido and nitroxyl species. The amide and hydrazine intermediate gives credence to a proposed SCO mechanism involving a hydrazine intermediate, while the proposed imide, =N–H, and/or nitroxyl, HNO species could be intermediates in incomplete oxidation of NH₃ to N₂O.