Role of preparation parameters of Cu–Zn mixed oxide catalyst in solvent free glycerol carbonylation with urea

Solvent-free carbonylation of glycerol with urea to glycerol carbonate (GC) was achieved over heterogeneous Cu–Zn mixed oxide catalyst. Cu–Zn catalysts with different ratios of Cu:Zn were prepared using co-precipitation (CP) and oxalate gel (OG) methods. As compared to CuO–ZnO(2:1) catalyst prepared by oxalate gel (OG) method, much higher conversion of glycerol and highest selectivity towards glycerol carbonate (GC) was achieved with CuO–ZnO_CP(2:1) catalyst. Physicochemical properties of prepared catalysts were investigated by using XRD, FT-IR, BET, TPD of CO₂ and NH₃ and TEM techniques. The effect of stoichiometric ratio of Cu/Zn, calcination temperature of CuO–ZnO catalysts and effect of reaction parameters such as molar ratio of substrates, time and temperature on glycerol conversion to GC were critically studied. Cu/Zn of 2:1 ratio, glycerol–urea 1:1 molar ratio, 145 ​°C reaction temperatures were found to be optimized reaction conditions to achieve highest glycerol conversion of 86% and complete selectivity towards GC. The continuous expel of NH₃ from reaction the mixture avoided formation of ammonia complex with CuO–ZnO catalyst. As a result of this, CuO–ZnO catalyst could be recycled up to three times without losing its initial activity.     

活性炭担载的铂催化剂在碱性条件下选择性氧化甘油制备乳酸

生物柴油是一种环境友好的燃料,随着其生产及应用的快速增长,其生产过程中重要的副产物甘油将会大量过剩.因此,将甘油转化为高附加值的化学品对于提高生物柴油整体竞争力具有重大意义.乳酸是重要的化工原料,可用于制备生物兼容和可降解的聚乳酸塑料,广泛应用于食品和医药等领域.近年来,由甘油制乳酸的研究受到格外关注,相对于水热反应和氢解反应等,催化选择氧化反应因温和的反应条件而更具竞争力.
　　目前,甘油催化选择氧化制乳酸一般需加入较高比例的NaOH,而碱的类型对反应性能的影响鲜有报道.另外,催化剂常采用TiO2和CeO2等氧化物载体,而炭载体具有比表面积较大、在酸碱溶液中稳定及贵金属易于回收等优点,在催化领域有着广泛应用.因此,本文研究了活性炭(AC)担载的Pt催化剂在甘油催化选择氧化制乳酸反应中的催化性能.
　　首先研究了Pt/AC催化剂和碱在甘油催化选择氧化制乳酸过程中的催化作用.实验发现, Pt/AC和碱协同作用才能得到乳酸. Pt/AC催化剂在甘油脱氢生成中间产物(甘油醛和二羟基丙酮)的过程中起主导作用,碱的存在能够促进甘油羟基脱氢;中间产物实验证实,中间产物生成乳酸过程中碱起主导作用,它促进甘油醛和二羟基丙酮脱水反应和坎尼扎罗重排反应获得乳酸.进一步研究发现,中间产物二羟基丙酮比甘油醛更有利于乳酸生成,而Pt/AC催化剂有利于中间产物氧化为甘油酸.
　　进一步研究了不同类型的碱对反应性能的影响.结果表明,碱金属氢氧化物(LiOH, NaOH, KOH)比碱土金属氢氧化物(Ba(OH)2)更有利于提高甘油转化率和乳酸选择性.在加入碱金属氢氧化物条件下,甘油转化率与其离子半径呈正相关,而乳酸选择性则呈相反趋势.在LiOH存在下,乳酸选择性明显高于NaOH和KOH条件.当LiOH：甘油摩尔比为1.5时,甘油转化率和乳酸选择性均最高.在较低的LiOH与甘油摩尔比时,随着反应的消耗,溶液中的OH–减少,其促进甘油脱氢的作用变弱,并且不利于中间产物进行坎尼扎罗反应,故反应活性和乳酸选择性较差;而当LiOH比例过高时,会导致溶解氧浓度迅速降低,从而使甘油转化率和乳酸选择性下降,同时副产物甘油酸的选择性有所提高.这可能是因为较高比例的碱会促进中间产物甘油醛生成,该中间产物在Pt/AC催化作用下发生进一步氧化反应生成甘油酸.
　　研究了反应时间对催化性能的影响.结果表明,反应6 h后,甘油已经完全转化,乳酸选择性最高,达到69.3%;进一步延长反应时间,乳酸选择性有所下降,而副产物乙酸选择性略有增加,这可能是部分乳酸分解所致. Pt/AC催化剂经5次循环使用后仍保持了较高的甘油转化率和乳酸选择性.     

不同载体负载Cu催化剂上甘油氢解制1,2-丙二醇催化性能的研究

采用等体积浸渍法合成了一系列不同载体负载的Cu基催化剂,并研究了其在甘油氢解反应中的催化性能。借助X射线衍射(XRD)、程序升温还原(H₂-TPR)和氨气程序升温脱附(NH₃-TPD)等手段对催化剂进行了表征,同时考察了反应温度、反应压力、反应时间和催化剂重复使用次数对其催化性能的影响。结果表明,载体对催化剂反应性能影响较大,且甘油氢解反应需要适当的酸性;当在催化剂8Cu/γ-Al₂O₃用量为反应原料质量的2.5%、反应温度513 K、反应压力6 MPa、反应时间6 h、反应原料为质量分数为10%的甘油水溶液的条件下,其催化效果最优,甘油转化率最高为88.4%,1,2-丙二醇的选择性可达到86.2%,且催化剂显示了良好的稳定性。     

Zr-Al 复合氧化物负载 Pt 催化甘油氢解制正丙醇

近年来, 甘油氢解的研究主要集中在生成 1,2-丙二醇和1,3-丙二醇二元醇. 与二元醇相比, 正丙醇也是一种昂贵的化学品, 用过量的甘油直接氢解合成高选择性的正丙醇将是一个非常好的生产途径. 因为铂金属具有较强的断 C-O 键的能力, 所以甘油氢解制正丙醇的催化剂主要采用铂作为活性组分. 本文以铂为活性组分, 采用浸渍法将其负载到不同 Zr/Al比的 Zr-Al 复合氧化物上制得 2.5%Pt/ZrxAl1-xOy催化剂, 并将其应用到甘油氢解反应中, 探讨了 Zr/Al 比对甘油氢解制正丙醇反应性能的影响.表征结果发现, 锆铝混合氧化物经过 400 ℃ 焙烧后为无定形态的复合金属氧化物, 载体中无单相氧化锆或氧化铝存在. 随着锆含量增加, 催化剂酸性位点向强酸方向移动. 不同 Zr/Al 比的锆铝混合氧化物负载铂催化剂的评价结果发现, 甘油转化率随催化剂中铝含量增加而增大; 锆铝比大于 5:5 时, 丙醇 (正丙醇+异丙醇) 的选择性很高, 普遍大于 87%; 锆铝比至 7:3 时, 正丙醇选择性最高. 通过 X 射线衍射、CO 化学吸附、H2程序升温还原、吡啶吸附、氨气程序升温脱附等方法对催化剂进行了表征, 发现随着锆铝混合氧化物中锆含量的增加, 催化剂的酸性位点向强酸方向移动, 调变 Zr/Al 比促进了铂颗粒的分散, 实现了催化剂表面酸量和强酸位点的定向调控. 当锆铝比增加至 7:3 时, 催化剂的强酸位点占总酸含量的91.2%. 对比催化剂酸性分析和反应结果可知, 催化剂表面的总酸含量高有助于甘油转化; 强酸位点有助于甘油深度脱水生成丙醇; 正丙醇的选择性则可能与 NH3脱附温度在 580 ℃ 处的强酸位和较大的 Pt 颗粒有关. 当 Zr/Al 比为 7:3 时, 催化剂表面强酸位点占 91.2%, 而强酸位点的增加有助于甘油的深度脱水形成正丙醇. 因此, 以 10% 甘油水溶液为原料, 在240 ℃和6.0 MPa 初始氢气压力条件下反应 8 h, 甘油转化率和正丙醇的选择性分别达到 81.2% 和 86.3%. 催化剂经过 5 次循环使用后, 甘油转化率和丙醇 (正丙醇+异丙醇) 选择性几乎不变, 但正丙醇的选择性略有降低. 使用 5 次后的催化剂表面的总酸量变化不大, 但酸分布变化较大, 即强酸比例下降. 可见, 催化剂活性变化小是由于其表面酸量变化不大, 而正丙醇选择性下降与强酸位点比例下降有关.     

介孔氧化钨担载Pt催化剂上甘油氢解制备1,3-丙二醇

采用蒸发诱导自组装法制备了介孔氧化钨(m-WO3),担载Pt后应用于催化甘油氢解制1,3-丙二醇.结果表明,与商业氧化钨(c-WO3)相比,m-WO3具有高比表面积和易还原的优点,从而使得Pt纳米粒子高度分散于其上.在180oC和5.5MPaH2下反应12h,Pt/m-WO3催化剂上甘油转化率和1,3-丙二醇的选择性分别为18.0%和39.2%,明显高于Pt/c-WO3催化剂.     

磁性纳米颗粒负载钯催化剂对Heck反应的催化活性

采用水热法合成了碳包埋磁性纳米复合颗粒C/(Au@Fe),并以之为载体制备了纳米钯催化剂,利用透射电镜、X射线光电子能谱和振动样品磁强计等手段对催化剂进行了表征,评价了催化剂对Heck反应的催化活性.结果表明,催化剂的平均粒径约为300nm,表面覆盖着一层粒径为12nm的钯颗粒,整个催化剂呈现超顺磁性.对于碘代苯与丙烯酸之间的Heck反应,在乙酸钠或三乙胺碱性条件下反应4h,碘代苯转化率可达95%以上.催化剂重复使用10次时仍可保持很高的催化活性(碘代苯转化率88%).对于其他不同反应底物之间的Heck反应,催化剂同样显示有较高的催化活性.催化剂可稳定分散于反应体系中,并可在外磁场作用下快速与反应体系分离.     

One-step synthesis of solid sulfonic acid catalyst and its application in the acetalization of glycerol: crystal structure of cis-5-hydroxy-2-phenyl-1,3-dioxane trimer

A one-pot method was employed to immobilize sulfonic acid onto silica obtained from rice husk ash using 3-(mercaptopropyl)trimethoxysilane to form a solid catalyst denoted as RHASO₃H. BET measurements of the catalyst showed the surface area to be 340 m² g^?1 with the average pore volume of 0.24 mL g^?1 and the pore diameter of 2.9 nm. Acidity test of cation exchange capacity and pyridine adsorption studies revealed the presence of Br?nsted acid sites on the catalyst surface. The catalyst was used in the acetalization reaction of glycerol with benzaldehyde. Under optimized conditions, the reaction showed the maximum conversion of 78 % after 8 h with 67 % selectivity towards the five membered ring isomer. Variation in the glycerol concentration had a significant effect on the reactants conversion. A single crystal X-ray study of one of the products proved the existence of a unique trimer formed by hydrogen bonding by the six-membered cis-isomer. The catalyst was several times recycled without any loss of its catalytic activity.     

Room temperature synthesis of glycerol carbonate catalyzed by N-heterocyclic carbenes

N-Heterocyclic carbenes were used as efficient organocatalysts for the synthesis of glycerol carbonate from glycerol and dimethyl carbonate. The reaction takes place in a liquid mixture of reactants without solvent at room temperature. It provides glycerol carbonate in high yield using 2.6–4 mol % of catalyst in a reaction period of 20–30 min.     

Synthesis of glycerol carbonate with high surface area ZrO2–KOH catalyst

High surface area ZrO₂–KOH sample was prepared and used the catalyst for the synthesis of glycerol carbonate (GC) from dimethyl carbonate (DMC) and glycerol. The structure properties of ZrO₂–KOH were characterized by XRD, BET, CO₂-TPD, XPS, and ICP-OES. It was found that the strong basicity of ZrO₂–KOH might be attributed to the oxygen vacancies as well as the big surface area. Experiments were developed to evaluate the effects of catalysis loading, proportion of reactants, temperature and reaction time on the conversion of glycerol to GC. The consequences showed that ZrO₂–KOH was a highly efficient basic catalyst for synthesis of GC from glycerol. The catalytic performance of ZrO₂–KOH is much better than that of ZrO₂–KOH–CP, ZrO₂–NH₄OH, and some reported heterogeneous catalysts. And the higher performance of ZrO₂–KOH was ascribed to the strong basicity. 99.43% conversion was obtained in a particular situation of catalyst/glycerol weight ratio of 3 wt%, DMC/glycerol molar ratio of 3:1, reaction temperature of 80 °C, and reaction time of 2 h. The plausible reaction mechanism for the transesterification on the strong basic active sites was discussed.

     

Hydrogenolysis of glycerol to propanediols over supported Ag–Cu catalysts

Hydrogenolysis of glycerol to 1,2-propanediol and 1,3-propanediol has significant scientific importance and commercial interest due to the huge surplus of glycerol and the various application of propanediols. A series of supported Ag–Cu catalysts synthesized by impregnation method were studied for hydrogenolysis of glycerol to propanediols. The catalysts were characterized by H₂-TPR, NH₃-TPD, XRD, BET, N₂O chemisorption, TG, ICP and SEM. It was observed that the loading of 5% Ag–Cu-based catalysts facilitated the reduction, surface acidity and dispersion of the Cu particles, which improved the conversion of glycerol and promoted the generation of propanediols. It was also found that when loading Ag and Cu simultaneously on Al₂O₃, the catalyst had a better performance for the reaction because of the higher acidity, dispersion and surface area of the Cu species on the catalyst surface. In addition, effects of metal concentrations, metal impregnation sequence, reaction temperature, reaction pressure, reaction time, solvent and pH value of the solution on glycerol hydrogenolysis together with the recyclability of catalyst were investigated in detail. The optimal 5Ag–15Cu/Al₂O₃ achieved 66.4% glycerol conversion with 68.2% 1,2-propanediol and 3.1% 1,3-propanediol selectivity at 200 °C under 3.5 MPa in ethanol for 8 h.     

Glycerol as a promoting medium for cross-coupling reactions of diaryl diselenides with vinyl bromides

We described herein the use of glycerol as a novel solvent in the cross-coupling reaction of diaryl diselenides with vinyl bromides catalyzed by CuI. This cross-coupling reaction was performed with diaryl diselenides and (Z)- or (E)-vinyl bromides bearing electron-withdrawing and electron-donating groups, affording the corresponding vinyl selenides in good to excellent yields. The mixture glycerol/catalyst can be directly reused for further cross-coupling reactions.     

A review on catalytic role of heterogeneous acidic catalysts during glycerol acetylation to yield acetins

Glycerol is a colorless, odorless, and non-toxic compound and has application in food, paint, and pharmaceutical industries. At an industrial scale, glycerol (GL) commonly forms as a by-product of soap and biodiesel producing industries. To utilize the excess GL of biodiesel industry, former has been employed as a building block to manufacture value added products such as acetins by fine chemical manufacturers. Acetins, including monoacertin (MA), diacetin (DA) and triacetin (TA), has diverse application such as in cosmetics, fuel additives, pharmaceuticals, leather, and food processing. Specifically, TA is employed as an additive to improve the anti-knocking property of gasoline and viscosity and cold flow properties of biofuel. The acetins are frequently produced at an industrial scale via a homogeneous Brønsted acid catalysed process employing acetic acid or acetic anhydride as an acetylating agent. Homogeneous acid catalysts are corrosive, non-reusable, difficult to separate from the reaction mixture, and sensitive to water, which is formed as a by-product during the glycerol acetylation. To address the issues, Brønsted or Lewis acidic group have been immobilized over various matrices (e.g., mixed metal oxides, mesoporous silica, ion exchange resins, carbon, zeolites, and magnetic nanoparticles) to prepare the heterogeneous acidic catalysts for the glycerol acetylation. Both the sites assisted the carbocation mediated esterification of glycerol with acetic acid or acetic anhydride. The ease of catalyst separation from the reaction mixture and reusability are the major advantages of their usage. However, lower conversion levels with low product selectivity, catalysts deactivation, and partial dissolution in the reaction mixture are the concerns related to the catalysts. To address these issues, novel catalyst preparation techniques to incorporate the variety of active sites over the matrix surface have been employed in the literature, which will be highlighted in detail in the present review article.     

多相固体催化剂用于甘油氧化制乳酸研究进展

随着新的全球气候协议下的中国双碳行动计划的实施, 开发和利用可再生生物质资源显得极为重要. 甘油作为生物柴油在生产过程中的主要副产物, 将其催化转化成各种高附加值衍生物受到广泛关注, 其中甘油选择性氧化为乳酸具有巨大的应用前景. 近年来, 采用固体催化剂催化氧化甘油制乳酸成为国内外学者研究的热点. 我们综述了固体催化剂用于甘油催化转化制备乳酸的研究现状, 对甘油催化转化为乳酸的反应途径做了分析, 并讨论了影响催化剂活性的因素, 对当前所存在的问题提出建议, 也对未来相关催化剂制备发展进行了展望.     

磺化Salen金属配合物插层水滑石选择性催化氧化甘油制备二羟基丙酮的研究

制备了一系列含不同金属离子的磺化Salen金属配合物插层水滑石催化剂用于甘油催化氧化制备二羟基丙酮(DHA)。利用X射线粉末衍射(XRD)、傅里叶变换红外光谱(FT-IR)及电感耦合等离子发射光谱(ICP)分析手段对催化剂进行了表征。结果表明,磺化Salen配体插入镁铝水滑石(LDH)层板间,金属离子与磺化Salen配体配合,制备出磺化Salen金属配合物插层的水滑石非均相催化剂。反应结果表明,含Cr³⁺及含Cu²⁺催化剂有利于H₂O₂活化,催化活性较高,含Cu²⁺催化剂利于甘油脱氢,DHA选择性较高。含Cu²⁺催化剂用于甘油催化氧化反应时,在pH值为7、60 ℃条件下反应4 h,甘油转化率为40.3%,DHA选择性达到52.9%。     

Enzymatic Biodiesel Synthesis in Semi-Pilot Continuous Process in Near-Critical Carbon Dioxide

A semi-pilot continuous process (SPCP) for enzymatic biodiesel synthesis utilizing near-critical carbon dioxide (NcCO₂) as the reaction medium was developed with the aim of reducing the reaction time and alleviating the catalyst inhibition by methanol. Biodiesel synthesis was evaluated in both lab-scale and semi-pilot scale reactors (batch and continuous reactors). In a SPCP, the highest conversion (～99.9 %) in four and a half hours was observed when three-step substrate (methanol) addition (molar ratio [oil/methanol]?=?1:1.3) was used and the reaction mixture containing enzyme (Lipozyme TL IM, 20 wt.% of oil) was continuously mixed (agitation speed?=?300 rpm) at 30 °C and 100 bar in a CO₂ environment. The biodiesel produced from canola oil conformed to the fuel standard (EU) even without additional downstream processing, other than glycerol separation and drying.     

N-arylation of indoles with aryl halides using copper/glycerol as a mild and highly efficient recyclable catalytic system

A simple, efficient, and inexpensive copper catalyzed protocol has been developed for cross-coupling of indoles with aryl halides by using glycerol as a green recyclable solvent and DMSO as an additive. The reaction was carried out at low catalyst loading furnishing various N-aryl indoles in good to excellent yield. This copper/glycerol mixture was recycled up to four runs without any loss in its catalytic activity.     

An efficient catalytic system for the synthesis of glycerol carbonate by oxidative carbonylation of glycerol

Glycerol carbonate was synthesized by the oxidative carbonylation of glycerol catalyzed by the commercial Pd/C with the aid of NaI.High conversion of glycerol(82.2%),selectivity to glycerol carbonate(>99%),and TOF(900 h–1)were obtained under the conditions of 5 MPa(pCO:pO2=2:1),140 oC,2 h.The highly active palladium species were generated in situ by dissolution from the carbon support and stabilized by re-deposition onto the support surface after the reaction was finished.Palladium dissolution and re-deposition were crucial and inherent parts of the catalytic cycle,which involved heterogeneous reactions.This Pd/C catalyst could be recycled and efficiently reused for four times with a gradual decrease in activity.Moreover,the influences of various parameters,e.g.,types of catalysts,solvents,additives,reaction temperature,pressure,and time on the conversion of glycerol were investigated.A reaction mechanism was proposed for oxidative carbonylation of glycerol to glycerol carbonate.     

Investigation of reaction routes for direct conversion of glycerol over zirconia?Ciron oxide catalyst

Conversion of glycerol to useful chemicals was examined using a zirconia?Ciron oxide catalyst. An aqueous glycerol solution was used as feedstock, and the catalytic reaction was carried out in a fixed-bed flow reactor at 623?K under atmospheric pressure. Useful chemicals, for example propylene, allyl alcohol, carboxylic acids, and ketones, were obtained from the aqueous glycerol solution. The reaction was found to involve a series of consecutive reactions, with allyl alcohol and carboxylic acids as reaction intermediates which were converted to propylene and ketones, respectively. Moreover, the catalyst had high and stable activity in the reaction of a 50 wt% glycerol solution.     

Kinetics of Hydrogenolysis of Glycerol into 1,2-Propylene Glycol on a Copper Catalyst

Kinetics and Catalysis - The kinetics of hydrogenolysis of glycerol to 1,2-propylene glycol on a catalyst containing 60 wt % copper on Al2O3 was studied. A reaction scheme for the conversion of...     

A Novel Non-phosgene Process for the Synthesis of Methyl N-Phenyl Carbamate from Methanol and Phenylurea： Effect of Solvent and Catalyst

A novel environmentally benign process for the synthesis of methyl N-phenyl carbamate (MPC) from methanol and phenylurea was studied. Effect of solvent and catalyst on the reaction behavior was investigated. The IR spectra of methanol and phenylurea dissolved in different solvents were also recorded. Compared with use of methanol as both a reactant and a solvent, phenylurea conversion and selectivity to MPC increased by using toluene, benzene or anisole as a solvent, while phenylurea conversion decreased slightly by using n-octane as a solvent. The phenylurea conversion declined nearly 50% when dimethyl sulfoxide (DMSO) was used as a reaction media, and MPC selectivity decreased as well. The catalytic reaction tests showed that a basic catalyst enhanced the selectivity to MPC while an acidic catalyst promoted the formation of methyl carbamate and aniline. Moderate degree of basicity showed the best catalytic performance in the cases studied.