共溶剂对超临界CO2注入技术制备聚丙烯/SiO2纳米复合材料的影响

采用超临界CO2注入技术制备聚合物-无机纳米粒子复合材料, 以乙醇作为共溶剂, 在超临界CO2中将正硅酸乙酯(TEOS)注入到聚丙烯(PP)中, 重点研究共溶剂乙醇对TEOS在PP中注入率的影响. 实验结果表明注入率随着共溶剂加入先增加后减小. 同时研究了在共溶剂的存在下其他实验条件对注入率的影响. 并采用卢瑟福背散射能谱法(RBS)分析了聚丙烯/SiO2纳米复合材料的注入元素深度分布, 发现Si元素在PP中的浓度分布不均匀, 随着深度的增加而减小.     

Preparation of silane-coated TiO2 nanoparticles in supercritical CO2

Nanometric inorganic pigments are widely used as fillers for hybrid composite materials. However, these nanometric powders are hydrophilic in nature and their surface must be functionalized before use. In this work, titanium dioxide (TiO₂) nanoparticles were coated using silane coupling agents with alkyl functionality. A supercritical carbon dioxide (scCO₂) method was used for surface silanization. Five alkylalkoxysilanes with different alkyl chain length and structure were studied: methyltrimethoxy, isobutyltriethoxy, octyltriethoxy, octyldimethylmethoxy and octadecyltrimethoxysilane. The microstructure and thermal stability of deposited monolayers were characterized using thermogravimetric analysis, ATR–IR spectroscopy, transmission electron microscopy, wettability characterization and low-temperature N₂ adsorption/desorption analysis. The use of scCO₂ as a solvent provided an effective approach to functionalize individual inorganic nanoparticles due to the enhanced diffusivity of the solution molecules in the aggregates interparticle voids. The trifunctional silanes employed here yielded surfaces with better thermal stabilities and greater hydrophobicities than the used monofunctional silane.     

Enzymatic kinetic resolution of organochalcogenides in supercritical CO2

1-(Phenylthio)-, 1-(phenylseleno)- and 1-(phenyltelluro)-propan-2-ol were efficiently resolved by CAL-B in sc-CO₂.     

Metal(salen)-catalyzed oxidation of limonene in supercritical CO2

Summary The Mn(Salen)Cl and Ni(Salen)-catalyzed oxidation of limonene has been carried out. The catalytic cycle involved PhIO via a rebound mechanism. In all cases the use of organic solvents resulted in reasonable selectivities of oxidized products. The use of supercritical carbon dioxide (SCCO₂) led at least to comparable results in terms of conversions, but showed different selectivities. In ordinary solvents epoxidation appears to predominate over allylic oxidation. This tendency, in SCCO₂, appears only after 4 h of reaction. Shorter reaction times (2 h) appear to lead to opposite selectivity. These results showed the advantages of using SCCO₂ as solvent in these reactions. SCCO₂ is much more compatible with green technology than are organic solvents.     

超临界二氧化碳偶合超声预处理强化玉米秸秆酶水解(英)

提出了一个木质纤维素生物质预处理的全绿色加工过程.以玉米秸秆和玉米芯为原料,以超临界CO₂和超声偶合法对木质纤维素进行预处理.超临界CO₂预处理条件为:压力15-25 MPa,温度120₁70℃,含水量50%,反应时间0.5₄ h.超声场功率600W,温度80℃,作用时间2-8 h.用纤维素酶水解反应获得的还原糖总量来评价预处理效果.结果表明,单纯超临界CO₂和超临界CO₂偶合超声预处理都能够提高生物质水解反应还原糖产量.对于玉米芯,超临界CO₂预处理（170℃,20 MPa,3 0min）后,还原糖产率为62%（未预处理的为12%）.对于玉米秸秆（170℃,20 MPa,2.5 h）,还原糖产率为46.4%.对于玉米芯,超临界CO₂偶合超声预处理（600 W,80℃下超声处理6 h,然后用170℃,20 MPa超临界CO₂预处理30 min）后,还原糖产率为87%.对于玉米秸秆,超临界CO₂偶合超声预处理（600 W,80℃下超声处理8 h,然后用170℃,20 MPa超临界CO₂预处理1 h）后,还原糖产率为25.5%.与未处理生物质相比,X射线衍射结果表明玉米秸秆和玉米芯在超临界CO₂和超声预处理后其结晶度没有明显变化.扫描电镜分析则发现木质纤维素的表面积显著增加.     

CO2在纳米SiO2/TiO2悬浮体系中的光催化还原

用水热法合成了氧化硅改性的具有高比表面积、高催化活性的锐钛型二氧化钛, 并在其悬浮体系中将CO₂光催化还原合成甲醇. 采用XRD, TEM, 物理吸附, UV-Vis吸收光谱和FTIR等表征手段对催化剂结构特征进行了研究. 结果表明: 添加氧化硅后, 氧化硅和二氧化钛之间形成Si—O—Ti键, 抑制了TiO₂晶粒生长, 提高了锐钛型TiO₂的比表面积, 且随着含硅量的增加, SiO₂/TiO₂的UV吸收逐步蓝移, 禁带宽度增加. 还原反应结果表明: SiO₂/TiO₂具有光催化还原活性, 且随着含硅量的增加先增加后减小, 当SiO₂质量分数为3.5%时, SiO₂/TiO₂复合催化剂反应活性最强, 5 h内甲醇产量可达到21.0 mg/L, 并有少量甲醛生成.     

超临界二氧化碳中PdCl2-CuCl2体系催化末端炔烃氧化偶联反应

研究了在超临界二氧化碳中实现PdCl₂-CuCl₂体系催化末端炔烃的氧化偶联反应, 研究结果表明: 催化剂、超临界二氧化碳及其共溶剂对反应结果有着重要的影响, 炔烃的取代基会影响末端炔烃在氧化偶联反应中的反应活性.     

Efficient synthesis of 2-oxazolidinones and quinazoline-2,4(1H,3H)-diones from CO2 catalyzed by tetrabutylammonium fluoride

By employing tetrabutylammonium fluoride (TBAF) as a catalyst, the various carboxylative cyclizations of the propargylic amines having internal alkynes with CO₂ proceeded to afford the corresponding 2-oxazolidinones. In this case, it was also found that the generated 2-oxazolidinones were tautomerized into the corresponding 2-oxazolones due to the basicity of TBAF. In addition, we performed the synthesis of quinazoline-2,4(1H,3H)-dione from 2-aminobenzonitrile and CO₂ by using TBAF as a catalyst.     

高温下锆酸锂吸收二氧化碳的研究

Li₂ZrO₃ to be used as a CO₂ absorbent at 450℃ to 710℃ is synthesized. The results indicate that the loading capacity of Li₂ZrO₃ for CO₂ is slightly improved than that reported previously. The absorption capacity attain to about 25(±0.6)%(wt)at 500℃ kept 3h in an atmosphere containing 20% CO₂ (balanced by air). Moreover， the temperature of synthesis is lower than the temperature reported in the literature， and also the time of synthesis is shorter.     

Facile synthesis of indoles by K2CO3 catalyzed cyclization reaction of 2-ethynylanilines in water

The cyclization reaction of 2-ethynyl-N-sulfonylanilides proceeded efficiently in water with the presence of a catalytic amount of K₂CO₃ under transition metal-free condition to give indoles in high yields. The recovery and reusability of the present catalytic system were investigated.     

Solubility of trans-Co2(CO)6 [3,5-bis(CF3)C6H3P(i-C3H7)2] in dense carbon dioxide

The title compound (1) was prepared by the reaction of 3,5-bis(CF₃)C₆H₃P(i-C₃H₇)₂ (L1) and Co₂(CO)₈. Its solubility in supercritical carbon dioxide was measured at varying temperatures and pressures using a modified analytical extraction device. Solubility data were determined in the temperature and pressure ranges between 40 and 70 °C and between 100 and 300 bar, respectively. The solubility of 1 is lower compared to (p-CF₃C₆H₄)₃P, but much higher than for transition metal complexes bearing phosphines without fluorinated substituents.     

高温下硅酸锂吸收CO2的研究

以SiO₂和Li₂CO₃为反应原料，采用高温固相法于不同温度下合成了一系列可在高温500~750 ℃之间直接吸收CO₂的硅酸锂(Li₄SiO₄)材料。采用扫描电子显微镜(SEM)、X射线粉末衍射仪(XRD)分别观察和评价了合成材料的表面形貌与结构特征，用热重分析仪(TG)研究了硅酸锂材料吸收CO₂的性能。实验结果表明，在750 ℃下煅烧6 h即可合成出吸收CO₂性能良好的硅酸锂材料，在CO₂气氛下，于700 ℃保持约15 min即可达到吸收平衡，其吸收量约达43%(wt)左右。与文献报道相比，材料的合成条件有所改善，材料吸收CO₂的容量也有较大提高。     

CO2吸附活化的研究进展

本文分析讨论了CO₂ 在金属催化剂和金属氧化物催化剂上吸附活化的机理及活化吸附态的反应性能, 提出了CO₂ 作为一种温和氧化剂在化工生产中加以综合利用的有效途径。     

过渡金属催化不饱和烃与二氧化碳的羧化反应研究与进展

CO₂是一种无毒、廉价易得、储量丰富的可再生资源,通过化学方法将其转化为具有高附加值的化学品已成为实现可持续发展的战略性课题。其中,以CO₂作为羧化试剂合成羧酸及其衍生物的研究已成为CO₂催化活化领域的研究热点。本文按照不同过渡金属催化的不饱和烃与CO₂的羧化反应,分类归纳了近些年来的羧化反应研究进展。     

纳米Li_2ZrO_3吸收剂原位移除CO_2强化水煤气变换反应制氢

采用浸渍法制备了在水煤气变换(WGS)反应中具有高催化活性的Ni/γ-Al2O3催化剂,使用柠檬酸法合成出高效CO2吸收剂Li2ZrO3纳米材料.在固定床微反应器上对WGS和吸附强化水煤气变换(SE-WGS)反应制氢过程进行了比较研究.前者只使用20%Ni/γ-Al2O3催化剂,而后者将20%Ni/γ-Al2O3催化剂与纳米Li2ZrO3吸收剂混合装填.结果表明,纳米Li2ZrO3具有比已报道的CO2吸收剂更快的吸收速率及优异的吸脱附循环稳定性,可应用于吸附强化过程,通过原位吸收WGS反应产生的CO2,使得反应超越化学平衡限制,直接制得高纯度H2.在823K,0.1MPa和H2O/CO=4的条件下,在SE-WGS过程一步制得纯度高于98%的H,验证了吸附强化反应进程制高纯氢的可行性.     

Supercritical CO2 improved phosphine imide reaction on peracetylated β-cyclodextrin

Supercritical CO₂ (sCO₂) was successfully used as solvent and reagent in the ‘one-pot’ phosphine imide reaction. In sCO₂ smooth conditions and with or without assistance of triphenylphosphine-bounded polymer, the reaction efficiently leads to the desired urea β-Cd compounds in a short time, bringing an interesting alternative for solving problems of OVC and hazardous reagent substitution in the synthesis of ureido-Cds and, by extension, of urea derivatives.     

ZIF-8基复合材料高效、稳定电催化还原CO2

电催化CO₂还原反应(eCO₂RR)受到催化剂本征活性以及传质的限制,导致材料的催化活性低、反应起始电位高等问题。我们以类沸石锌盐咪唑骨架(ZIF-8)材料为研究对象,探究了不同粒径ZIF-8材料的eCO₂RR性能。优选粒径为50 nm的ZIF-8材料,进一步引入碳纳米管(CNT)作为其导电基底材料,通过原位生长,构建了复合材料ZIF-8-50@CNT的多级孔结构和疏水界面。eCO₂RR实验结果表明,CNT的引入提高了催化剂的导电性,优化后的复合材料有效地降低了反应的起始电位。在-1.1 V(相对可逆氢电极(RHE))电位下,CO部分电流密度为15.6 mA·cm^-2,ZIF-8-50@CNT催化剂的比表面活性提升了3.5倍(相比ZIF-8-50),塔菲尔斜率降低到136 mV·dec^-1。并且产物CO的选择性和稳定性得到了提高,在宽电势窗口-0.9～-1.2 V(vs RHE)内,CO的法拉第效率(FE)保持在80%以上。在10 h稳定性测试中,催化剂活...     

ZIF-8基复合材料高效、稳定电催化还原CO2

电催化CO₂还原反应(eCO₂RR)受到催化剂本征活性以及传质的限制,导致材料的催化活性低、反应起始电位高等问题。我们以类沸石锌盐咪唑骨架(ZIF-8)材料为研究对象,探究了不同粒径ZIF-8材料的eCO₂RR性能。优选粒径为50 nm的ZIF-8材料,进一步引入碳纳米管(CNT)作为其导电基底材料,通过原位生长,构建了复合材料ZIF-8-50@CNT的多级孔结构和疏水界面。eCO₂RR实验结果表明,CNT的引入提高了催化剂的导电性,优化后的复合材料有效地降低了反应的起始电位。在-1.1 V (相对可逆氢电极(RHE))电位下,CO部分电流密度为15.6 mA·cm^-2,ZIF-8-50@CNT催化剂的比表面活性提升了3.5倍(相比ZIF-8-50),塔菲尔斜率降低到136 mV·dec^-1。并且产物CO的选择性和稳定性得到了提高,在宽电势窗口-0.9~-1.2 V (vs RHE)内,CO的法拉第效率(FE)保持在80%以上。在10 h稳定性测试中,催化剂活性保持稳定,整体增强了复合材料eCO₂RR的性能。     

超临界CO2中苯乙烯RAFT分散聚合

以末端带有三硫代碳酸酯的聚二甲基硅氧烷(PDMS-TTC)为大分子链转移剂,在超临界CO2中通过苯乙烯的可逆加成-断裂链转移(RAFT)聚合制备了聚二甲基硅氧烷-b-聚苯乙烯(PDMS-b-PS)嵌段共聚物,对聚合反应动力学以及产物的组成、分子量和形貌等进行了表征.由于PDMS链段可溶于超临界CO2而PS链段不溶,因此在超临界CO2中制备PDMS-b-PS嵌段共聚物的过程是以嵌段共聚物自身作为分散稳定剂的RAFT分散聚合,产物为粒径较均一的球形颗粒.     

超临界 CO2 辅助制备 TiO2 外负载火山岩复合体及其光催化降解亚甲基蓝性能

 以钛酸丁酯为前驱体, 封堵的火山岩为载体, 通过超临界 CO₂ 辅助制备了 TiO₂ 外负载火山岩复合体, 并将其用于光催化降解亚甲基蓝反应, 考察了溶液 pH 值及催化剂浓度对反应性能的影响. 结果表明, TiO₂ 外负载火山岩复合体的光催化性能优于纯 TiO₂ 和 TiO₂ 体负载火山岩复合体. 这是由于外负载复合体对亚甲基蓝的高吸附性、小晶粒尺寸的 TiO₂ 颗粒以及吸附和光催化降解间的协同效应. 亚甲基蓝浓度为 1.5 mg/L, 溶液 pH 为 8, 催化剂浓度为 6.8 mg/L 时, 外负载 TiO₂ 火山岩复合体上亚甲基蓝降解速率最高, 且使用后的催化剂仍具有高的光催化活性.