高比表面纳米MgO的制备及其影响因素研究

在溶液中采用不同的原料制备了三种前体MgC2O4•2H2O, 经高温焙烧得到高比表面MgO. 用XRD、BET、TEM和TG-DTA等表征手段对前体及产物MgO进行了表征. 结果表明, 以醋酸镁和草酸为原料制备前体草酸镁并在焙烧过程中消除水汽的影响是得到高比表面MgO的关键. 最优条件下制备的样品经520 ℃焙烧后比表面积高达534 m2•g−1, 晶粒尺寸仅为4～5 nm的MgO粒子堆积成一定程度上长程有序的介孔结构, 并具有十分优良的抗高温烧结性能. 650 ℃和800 ℃焙烧2 h后, 其比表面积仍分别高达229 m2•g−1和134 m2•g−1.     

溶剂热合成具有海绵状结构的介孔SnO2

采用溶剂热方法, 以SnCl4·5H2O/尿素/乙醇三元体系合成了具有特定结构的前驱体, 该前驱体经焙烧后得到了具有海绵状结构的介孔SnO2. 利用X射线粉末衍射(XRD)、傅立叶红外吸收光谱(FT-IR)、透射电镜(TEM)、热分析(TG-DTA)和氮气等温吸附鄄脱附等方法对产物的结构、形貌和热稳定性进行表征. 结果表明, 300 ℃焙烧处理后的样品由粒径约为5 nm的纳米粒子堆积而形成海绵状结构, 其中孔的尺寸范围在2-8 nm, 样品比表面积达到了134 m2·g-1.     

高热稳定性Cu-Mn-O催化燃烧催化剂的制备

采用共沉淀法制备Cu-Mn-O前驱体, 以水洗和醇洗的方式去除杂质, 在空气气氛下干燥焙烧获得催化剂. 用BET、 XRD、 SEM对此催化剂的比表面积、晶相结构以及颗粒形貌进行了表征, 并以甲苯催化燃烧为探针反应考察了催化剂的性能. 结果表明, 在500 ℃焙烧, Cu-Mn-O催化剂的比表面积可以达到67.9 m2/g, 颗粒尺寸在100 nm左右并高度分散. 与水洗样品相比, 醇洗样品的活性相CuMn2O4热稳定性得到较大提高, 经700 ℃焙烧的Cu-Mn-O上甲苯完全燃烧温度降低了60 ℃;800 ℃焙烧后, 甲苯完全燃烧温度降低了约50 ℃.     

γ-Fe_2O_3纳米纤维的丙酮敏感特性

采用静电纺丝法制备了PVP/FeC6H5O7复合纳米纤维,并将复合纤维在500℃高温烧结3 h,X射线衍射分析(XRD)表明,烧结后的产物为正尖晶石结构的γ-Fe2O3晶体.扫描电子显微镜(SEM)观测结果表明,制得了直径均匀、连续的复合纳米纤维,其平均直径约为1000 nm;烧结后的γ-Fe2O3纳米纤维保持了其连续性,但纤维发生了收缩,直径较烧结前小,平均约为600 nm.比表面积分析表明,γ-Fe2O3纳米纤维比表面积为57.18 m2/g.气敏性能测试结果表明,230℃为γ-Fe2O3纳米纤维检测丙酮气体的最佳工作温度.在此温度下,γ-Fe2O3纳米纤维对丙酮气体表现出高响应度[S=6.9,c(Acetone)=7.88×104mg/m3]和线性度(7.88×102~1.58×105mg/m3浓度范围内).同时,γ-Fe2O3纳米纤维气体传感器件还表现出良好的长期稳定性.     

大比表面积γ-Al2O3的制备及辅助剂蔗糖的用量对γ-Al2O3 织构的影响

 在由硝酸铝经氨水沉淀制备氧化铝的过程中,用蔗糖作为辅助剂制得了具有大比表面积的γ-Al2O3,并考察了蔗糖加入量对γ-Al2O3织构的影响. 将硝酸铝和蔗糖共溶于水,滴加氨水至Al3+全部沉淀(pH=5.2),所得沉淀连同母液一起在80 ℃水浴中搅拌得到溶胶,将溶胶于110 ℃失水后即得凝胶. 凝胶进一步失水后发生燃烧得到含碳的前体,再经600 ℃焙烧即得到γ-Al2O3(比表面积可达350 m2/g左右). 利用差热-热重分析、元素分析、氮吸附-脱附等温线、X射线粉末衍射和透射电子显微镜对前体及 γ-Al2O3 样品进行了表征. 结果表明,γ-Al2O3不但具有大的比表面积,而且孔径较小,分布较为集中. 通过改变蔗糖的用量,还可在一定程度上对γ-Al2O3的比表面积和孔结构等进行调控.     

高热稳定性、 高比表面积低铈型铈锆钇储氧材料的制备及其性能研究

采用氨水 碳酸铵混合沉淀剂制备了低铈型铈锆钇三组分储氧材料. 采用X射线衍射、 BET、 氧脉冲吸附和H2程序升温还原(H2-TPR)等技术对材料的晶体结构、 比表面积、 孔结构、 储氧性能和还原性能进行了研究. 结果表明， 该材料经873 K焙烧4 h后比表面积达到116.8 m2/g, 孔容达到0.30 cm3/g, 经1 273 K老化10 h后, 比表面积和孔容仍然保持在68.1 m2/g和 0.22 cm3/g. 由XRD结果可知, 材料的物相组成为四方相的Zr0.84 Ce0.16 O2, 在热处理过程中物相结构稳定. 氧脉冲吸附和程序升温还原的结果表明, 材料储氧性能保持较好.     

新方法合成LiFePO4/C

以Fe(NO3)3·9H2O、LiNO3、NH4H2PO4和蔗糖为原料,在超临界CO2流体中反应合成,进而经二次焙烧制得LiFePO4/C。 结果表明,在超临界CO2流体中经50 ℃反应24 h,在350和600 ℃焙烧后制得粒径分布在0.5~1.0 μm的纯LiFePO4/C,该材料作为锂离子电池正极的放电比容量达156.6 mA·h/g,经50次循环后容量几乎没有衰减。     

新型介孔SO4^2-/TiO2固体酸的制备及其催化酯化性能

以无定形高比表面积水合钛酸(H2Ti2O5·xH2O)为载体,采用等体积浸渍法制备了新型晶须状介孔SO42-/TiO2固体酸催化剂,利用X射线衍射、N2吸附-脱附、扫描电镜、红外光谱、热重和氨程序升温脱附等技术考察了催化剂的结构特征和表面酸性及其对乙酸与正丁醇液相酯化反应的催化活性.结果表明,SO42-/TiO2同体酸催化剂不仅具有纳米级晶粒、晶须状形貌、高比表面积和介孔结构,还保持了完善的锐钛矿晶型、较强的酸性和较高的热稳定性;当焙烧温度高于500℃时,催化剂表面结合的SO42-逐渐流失,酸中心数逐渐减少.在m(催化剂)=0.2 g、n(正丁醇)/n(乙酸)=1.5和反应时间3 h条件下,500℃焙烧的催化剂活性最高,正丁醇转化率达94%,乙酸正丁酯选择性为100%,且催化性能和分离沉降性能均优于SO42-/P25催化剂.     

纳米复合锆基固体超强酸的制备及其催化酯化反应

采用改性技术和浸渍—沉淀法制备出纳米固体超强酸催化剂S2O82-/ZrO2-Al2O3。通过正交试验获得催化剂制备的最佳条件,即ω(Al2O3)为2.0%,-15℃陈化24h,浸渍液(NH4)2S2O8浓度为0.8mol/L,焙烧温度为650℃,焙烧时间为3h。用XRD、TEM、BET、TG-DTG和化学分析等手段分析了S2O82-/ZrO2-Al2O3的晶化过程、比表面积、含硫量和热稳定性,分析结果表明这四个方面对催化剂的酸性有较大影响。500~650℃焙烧温度下制备的催化剂属纳米材料(<41nm),有较大比表面积和较好的热稳定性。以优化的催化剂S2O82-/ZrO2-Al2O3用于催化合成丁酸异丁酯的最佳条件为:n(异丁醇):n(丁酸)=1.8:1.0,催化剂用量为1.0g(以0.3mol丁酸为准),脱水剂环己烷用量为10mL,反应时间为3.0h,催化剂重复使用8次后酯化率仍在90%以上,该催化剂具有催化活性高、不污染环境、可重复使用等特点。     

Ba、Mn对Al2O3热稳定性和甲烷催化燃烧活性的影响

采用溶胶-凝胶法制备BaO•6Al2O3系列催化剂.考察了Ba、Mn的引入对Al2O3的热稳定性及甲烷催化燃烧性能的影响.结果表明, Ba在高温下与Al2O3首先生成BaAl2O4，然后进一步与Al2O3反应生成具有β-Al2O3结构的BaAl12O19六铝酸盐，抑制了Al2O3进一步的烧结，提高了催化剂的热稳定性. Mn的引入也能够促进六铝酸盐的生成并提高催化剂的甲烷燃烧活性.采用超临界干燥法可抑制干燥过程中因毛细收缩引起的比表面积降低.所制备的BaMnAl11O19催化剂经1200 ℃焙烧4 h后，比表面积为35.1 m2•g－1，在空速40000 h－1条件下，10％甲烷转化温度(T10％)为500 ℃，催化活性明显高于常规干燥法制备的相应催化剂.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.