尿素在ZnO(1010)表面的吸附

运用VASP(Vienna ab-initio simulation package),采用基于密度泛函理论(DFT)的第一原理计算,研究了尿素在ZnO(101軈0)表面的吸附行为.计算结果表明:尿素分子在ZnO(101軈0)表面主要发生分子吸附,稳定的吸附产物通过尿素分子中的氮原子或氧原子与表面锌原子之间的键合作用而形成,吸附能分别为-1.48和-1.41eV;表面吸附的尿素分子也可以发生解离,生成表面吸附的异氰酸根、氨气和一个表面羟基,吸附能为-1.66eV.     

改性羟基磷灰石催化尿素醇解合成碳酸丙烯酯

<正>碳酸丙烯酯(PC)是性能优良的有机溶剂和有机合成原料。PC的合成方法包括环氧丙烷环加成法、光气法和尿素醇解法,其中以尿素和1,2-丙二醇为原料的尿素醇解法,因环境友好、反应条件温和、操作安全,还能有效避免环氧丙烷环加成法对石油的依赖和光气法的剧毒,被认为是PC合成的绿色工艺。     

高分散纳米银催化剂一锅高效催化生物质基甘油和苯胺合成3-甲基吲哚

将ZnO改性的高分散纳米银催化剂(Ag/SiO₂-ZnO)成功地用于生物质基甘油与苯胺一锅高效合成3-甲基吲哚的反应中。 通过X射线衍射(XRD)、透射电子显微镜(TEM)、氢气程序升温还原(H₂-TPR)、氨气和二氧化碳程序升温脱附(NH₃-TPD或CO₂-TPD)、热重(TG)分析和电感耦合等离子体(ICP)发射光谱技术手段研究了银基催化剂的结构和性能。 结果表明,向Ag/SiO₂-ZnO催化剂加入ZnO助剂能增强银与载体之间的相互作用,使银粒子可以牢固地锚定在SiO₂-ZnO载体上,不仅提高了银的分散度,而且有效抑制了反应过程中银纳米粒子的聚集或烧结。 此外,ZnO还能显著增加银基催化剂的酸性位点及碱性位点,这对甘油氢解生成1,2-丙二醇非常有利,明显促进了3-甲基吲哚的合成。 反应16 h,3-甲基吲哚收率高达64%,催化剂重复使用4次,收率仅降低4%。 另外,提出了甘油和苯胺在Ag/SiO₂-ZnO催化剂上合成3-甲基吲哚的机理,其中1,2-丙二醇是制备3-甲基吲哚的中间体。     

磁性纳米粒子催化尿素与1,2丙二醇制备碳酸丙烯酯

制备了不同类型的磁性纳米粒子催化尿素与1,2-丙二醇反应合成碳酸丙烯酯,其中的NiFe2O4催化活性最高.反应通过对实验的结果进行分析,可以得到反应的优化条件是:反应温度为170℃,n(PG)∶n(urea)∶n(catalysts)=4∶1∶0.015,反应时间为5h,在此反应条件下,PC的最高收率达到了93.4%.反应为多相催化体系,可方便实现催化剂与产物的分离.     

无碱条件下Au/ZnO选择性催化氧化1,3-丙二醇合成3-羟基丙酸甲酯

采用溶胶-沉积法合成了高选择性的Au/ZnO催化剂,用于1,3-丙二醇选择性氧化酯化为3-羟基丙酸甲酯的反应.研究了保护剂PVA用量、金溶胶合成温度、金负载量及催化剂循环利用对反应的影响,且优化了反应温度和反应压力,并对催化剂进行了XRD和TEM表征.结果表明,PVA∶Au(m/m)=1∶4、金溶胶合成温度25℃、金负载量1%的Au/ZnO对目标反应的催化活性最好,在100℃和Po2=2MPa的条件下1,3-丙二醇的转化率达82.8%,产物3-羟基丙酸甲酯的选择性达95.4%.Au纳米粒子的粒径影响催化性能,在Au平均粒径为2.8~6.1nm的范围内,产物选择性随Au纳米粒子的粒径的减小而增大,平均粒径在2.8~4.8nm的范围内时,催化剂具有较好的产物选择性(大于90%);Au/ZnO催化剂循环利用4次后催化性能(转化率和选择性)无明显下降;并推测了无碱条件下Au/ZnO选择性催化氧化1,3-丙二醇合成3-羟基丙酸甲酯的反应机制.     

二价钐配合物和异氰酸苯酯的反应[(CH3C5H4)2(THF)Sm]2[μ-η4-(PhN)OCCO(NPh)]*2THF的合成、晶体结构及其催化性能

报道了二价配合物(CH3C5H4)2Sm(THF)和SmI2(THF)x与异氰酸苯酯的反应. (CH3C5H4)2Sm(THF)和异氰酸苯酯反应生成配合物[(CH3C5H4)2(THF)Sm]2[μ-η4-(PhN)OCCO(NPh)]*2THF(1), 而SmI2(THF)x则被异氰酸苯酯氧化为[SmI2(THF)5][SmI4(THF)2]. (CH3C5H4)2Sm(THF)和配合物1都能催化异氰酸苯酯的齐聚反应.(CH3C5H4)2Sm(THF)和异氰酸苯酯作用生成配合物1的反应可以认为是 (CH3C5H4)2Sm(THF)催化异氰酸苯酯齐聚的引发反应, 而配合物1是该齐聚反应的活性中间体. X射线衍射分析表明, 配合物1是一个由草酰胺双负离子桥联的双金属化合物.     

酸性介质中1,2-丙二醇在铂电极上吸附和氧化过程的原位FTIR反射光谱研究

应用电化学循环伏安和原位FTIR反射光谱研究1,2-丙二醇在Pt电极上吸附和氧化过程。结果指出1,2-丙二醇的电氧化可按双途径进行。其一经1,2-丙二醇在Pt上解离吸附产物氧化至CO_2。但在较低电位下这些解离吸附产物(红外检测为CO_(ad)、[﹥C=CH_2]_(ad)等)累积吸附于电极上, 毒化Pt表面抑制其它反应。当电位大于0.3 V后它们一经生成即氧化脱附, 从而使1,2-丙二醇得以在未毒化Pt表面经反应中间体氧化至CO_2。在实验条件下,原位FTIR反射光谱检测到的反应中间体可能有HOC-CHOHCH_3(或CH_2OHCOCH_3)和HOOC-COCH_3(或HOOC-CHOHCH_3)等物种。     

酸性介质中1,2-丙二醇在铂电极上吸附和氧化过程的原位FTIR反射光谱研究

应用电化学循环伏安和原位FTIR反射光谱研究1,2-丙二醇在Pt电极上吸附和氧化过程。结果指出1,2-丙二醇的电氧化可按双途径进行。其一经1,2-丙二醇在Pt上解离吸附产物氧化至CO_2。但在较低电位下这些解离吸附产物(红外检测为CO_(ad)、?C=CH_2]_(ad)等)累积吸附于电极上,毒化Pt表面抑制其它反应。当电位大于0.3V后它们一经生成即氧化脱附,从而使1,2-丙二醇得以在未毒化Pt表面经反应中间体氧化至CO_2。在实验条件下,原位FTIR反射光谱检测到的反应中间体可能有HOC-CHOHCH_3(或CH_2OHCOCH_3)和HOOC-COCH_3(或HOOC-CHOHCH_3)等物种。     

CuZnAl/碳纤维复合材料催化合成气制备低碳醇

采用共沉淀法制备CuZnAl类水滑石,将其担载于活化碳纤维(ACFs)表面,通过焙烧还原合成功能化复合催化剂(CuZnAl/ACFs)。借助XRD、FT-IR及N2吸附-脱附等方法对该复合物进行表征,并将其应用于合成气制备低碳醇的反应中,进行活性评价。结果表明,复合催化剂中活性组分在碳纤维表面均匀分散,碳纤维表面催化剂的颗粒尺寸减小,比表面积增大。ACFs的导电性加速醇合成过程中的电子传递,促进反应进行,因而CO转化率的提高(最高可达47%)。同时,ACFs提高催化剂表面ZnO的分散度,从而促进Cu与ZnO形成金属氧化物界面。这有利于低碳醇的生成,因而使C2以上醇的选择性高达39%。     

Ni2P/SiO2 和Ni/SiO2 催化剂甘油氢解反应性能比较:催化剂活性及产物选择性影响因素的探讨（英文）

采用浸渍法及程序升温还原法制备了Ni2P/SiO2和Ni/SiO2催化剂,利用N2吸附-脱附、X射线衍射、X射线荧光、CO化学吸附、氢气程序升温脱附及氨气程序升温脱附等手段对催化剂进行了表征并用于甘油氢解反应.结果表明,Ni2P/SiO2和Ni/SiO2具有相近的表面Ni密度,但前者表面酸中心和表面氢物种(包括吸附氢和溢流氢)密度明显更高,且在甘油氢解反应中的活性也更高,这与其酸性中心与金属中心之间的协同作用有关.Ni2P/SiO2催化剂上主要产物为1,2-丙二醇及1-丙醇,而Ni/SiO2催化剂上主要产物为1,2-丙二醇、乙二醇和乙醇.提高反应温度和H2压力不能促进Ni2P/SiO2上乙醇和乙二醇的生成,但促进了1,2-丙二醇进一步氢解转化为1-丙醇.由此可见,Ni2P/SiO2具有较强的C-O键断裂活性及较弱的C-C键断裂活性,这可能分别与其较多酸性中心和电子及几何结构性质密切相关.     

Catalytic performance of metal oxides for the synthesis of propylene carbonate from urea and 1,2-propanediol

The influences of acid–base properties of metal oxides on the catalytic performance for synthesis of propylene carbonate from urea and 1,2-propanediol was investigated, and the reaction was stepwise. The amphoteric ZnO showed the best activity, and the yield of propylene carbonate reached 98.9%. The urea decomposition over oxides was characterized by using FTIR. ZnO, CaO, MgO and La₂O₃ were favorable to promote urea decomposition to form the isocyanate species, and the formation of isocyanate species was the key to urea alcoholysis. The catalytic activity of urea decomposition was consistency to the catalytic performance for synthesis of propylene carbonate. Based on these, the probable reaction mechanism was proposed.     

Synthesis of propylene carbonate from urea and 1,2-propylene glycol over ZnO/NaY catalyst

Propylene carbonate (PC) was produced from 1,2-propylene glycol (1,2-PG) and urea in a continuous-flow fixed bed reactor over heterogeneous ZnO catalyst supported on NaY. Among different ZnO loadings of ZnO/NaY catalysts, 5 wt% ZnO loadings of ZnO/NaY showed the highest activity. Characterization and reaction results indicated that the catalysts with a balanced strength of acid and base sites performed well for the synthesis of propylene carbonate from urea and 1,2-PG.     

Synthesis of propylene carbonate from urea and 1,2-propanediol

The production of propylene carbonate(PC)from urea and 1,2-propanediol(PG)was investigated in a batch process.The catalytic performances of zinc chloride and magnesium chloride were investigated for this reaction system.The influences of various operation conditions on the PC yield were explored.In this work,MgCl_2 and ZnCl_2 showed the excellent catalytic activity toward PC synthesis,and the yields of propylene carbonate reached 96.5%and 92.4%,respectively.The optimum reaction conditions were as follows...     

Synthesis of dimethyl carbonate and propylene glycol from transesterification of propylene carbonate and methanol using quaternary ammonium salt catalysts

Summary The synthesis of dimethyl carbonate (DMC) was investigated through the transesterification of propylene carbonate (PC) with methanol using quaternary ammonium salt catalysts. The reaction was carried out in an autoclave at 120-140 oC under carbon dioxide pressure of 250-400 psig. The main by-product was propylene glycol. The quaternary salts of larger alkyl group and more nucleophilic counter anion exhibited higher catalytic activity. Kinetic studies were also performed to better understand the reaction mechanism. Quaternary ammonium chlorides immobilized on polystyrene supports were also tested for their possible uses as heterogeneous catalysts.     

离子交换树脂催化合成碳酸亚丙酯

碘型离子交换树脂在某些偶极非质子性溶剂的作用下，能有效地催化二氧化碳与环氧丙烷合成碳酸亚丙酯，并能重复使用至少10次而仍能保持较高的催化活性。     

Restoration of protein foam stability through electrostatic propylene glycol alginate-mediated protein–protein interactions

The action of propylene glycol alginate in the enhancement of foam stability of a destabilised Tween 20/bovine serum albumin mixed system was evaluated. A significant increase in the foam stability was observed in the presence of low concentrations of propylene glycol alginate. A pseudo-plateau level of foam stability was obtained in the presence of approximately 0.8 μg/ml propylene glycol alginate in the solution used to form the foam. Foam stability enhancement due to bulk viscosity changes and surface effects were elucidated. The increase in foam stability was investigated by reference to the properties of thin liquid films and the macroscopic interface of test solutions. Propylene glycol alginate was found to slow the rate of thin film drainage, increase the equilibrium thickness of the films, slow the lateral diffusion of a fluorescent probe molecule located in the adsorbed layer and increase the elasticity of the interface. Data are consistent with propylene glycol alginate-induced crosslinking of protein in the adsorbed layer. This polysaccharide presents a means for controlling protein foam stability.     

Tunable synthesis of propylene glycol ether from methanol and propylene oxide under ambient pressure

A series of basic and acidic ionic liquids, 1-butyl-3-methylimidazolium hydroxide (BMIMOH), 1-acetyl-3-methylimidazolium chloride (AcMIMCl) and AcMIMCl-FeCl₃, or analogues of AcMIMCl, namely 1-potassium acetate-3-methylimidazolium chloride (KAcMIMCl), 1-potassium (sodium, ammonium) acetate-3-methylimidazolium hydroxides (KAcMIMOH, NaAcMIMOH and NH₄AcMIMOH), were prepared and used as catalysts for catalytic synthesis of propylene glycol ether via reaction of propylene oxide (PO) with methanol under mild reaction conditions. KAcMIMOH exhibited outstanding catalytic performance with 94.2% of conversion of PO and 99.1% of selectivity to 1-methoxy-2-propanol (MP-2) at 60°C and ambient pressure for 4 h. However, AcMIMCl-FeCl₃ showed a good catalysis performance with high selectivity to 2-methoxy-1-propanol (MP-1). The tunable synthesis of MP-2 or MP-1 catalyzed by basic compound KAcMIMOH or acidic ionic liquid AcMIMCl-FeCl₃ was realized.     

Morphology and Stress Whitening of Heterophasic Poly(propylene) Copolymer/High Density Polyethylene Blends

Summary: Effect of high density polyethylene (HDPE) addition on the morphology of heterophasic poly(propylene) copolymer (HPC) was investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Stress whitening developed upon dart impact was evaluated using Gardner-type impact tester. In the TEM study of HPC/HDPE blends, a core-shell morphology was observed of HDPE encapsulated by ethylene-propylene rubber (EPR). At low HDPE weight fractions (95/5 and 90/10 HPC/HDPE), the size of dispersed phase increased compared to pure HPC. However, further increase in HDPE leads to a decrease in domain size. The impact strength reached a maximum at 90/10 HPC/HDPE blend, and then decreased with further increase in HDPE content. The stress whitening of HPC was decreased with addition of HDPE. This decrease is attributed to the difference in the shrinkage between HPC and HPC/HDPE blends. The pressure-volume-temperature relationship supports that an additional volume contraction of HDPE can reduce the stress whitening of HPC.     

Synthesis and degradation profile of cast films of PPG-DMPA-IPDI aqueous polyurethane dispersions based on selective catalysts

Waterborne polyurethane (WBU) dispersions synthesized from poly(propylene glycol) (PPG), dimethylolpropionic acid (DMPA), and isophorone diisocyanate (IPDI) with catalysts of different selectivity were prepared via by the conventional prepolymer isocyanate process. Two types of chain extenders were used, ethylene glycol (EG) and propylene glycol (PG), producing polyurethanes. The dispersions were neutralized by the addition of triethylamine. The thermal stability of the materials, obtained as cast films prepared from aqueous dispersions was evaluated by thermogravimetry (TG). It was observed that initial degradation temperatures were above 140 °C, with two-step degradation profiles. The use of a more selective catalyst in the formulations led to materials with higher thermal stability. DTG curves exhibited stages not perceptible in the curves of weight loss, which were mainly influenced by the differences in the formulations. Thermal decomposition of the obtained polyurethanes was followed by TG coupled with FTIR spectroscopy.     

OCCURRENCE OF PHOTOREVERSIBLE ABSORPTION CHANGES IN DISSOCIATED ALLOPHYCOCYANIN AND PHYCOCYANIN

Abstract— Photochromic response of allophycocyanin (APC) and phycocyanin (PC) was studied. Phycobiliproteins were isolated from the blue-green alga Tolypothrix tennis and supplementary from Anabaena cylindrica. The response was found in both APC and PC when they were dissociated into monomer in the presence of propylene glycol at high concentration. APC in propylene glycol solution showed two photoresponses identical with those of "phycochromes" c and d , respectively. PC showed the photoresponse "phycochrome" a type. After re-association by removal of propylene glycol, photoresponse activities disappeared.
We concluded that (i) some of monomer APC's and PC's became photoreactive when APC and PC were dissociated into monomer thus that (ii) photoresponses of "phycochromes" a, c and d were not attributed to the special pigments independent of APC and PC, but were responsible to special molecules of monomer APC and PC. Spectral patterns of photoresponses were discussed in relation to dissociation-association of protein.