纳米Fe2O3-K2O催化剂的制备及其催化乙苯脱氢性能

采用浸渍-热分解法制备了纳米Fe2O3-K2O催化剂,并在常压和520～580℃的条件下,考察了其对乙苯催化脱氢反应的催化性能.结果发现,纳米Fe2O3-K2O催化剂表现出很好的活性和稳定性.在550℃,N2/H2O/乙苯摩尔比为30.7/10/1和WHSV=0.43h-1的条件下,纳米Fe2O3-K2O催化乙苯脱氢的转化率为71.9%,苯乙烯选择性为91.1%.透射电子显微镜和X射线衍射测试结果表明,氧化铁的粒径为10～14nm.催化剂的尖晶石结构和高比表面积是其表现出高催化性能的主要原因.     

助剂α-Sb2O4对杂多化合物催化剂选择氧化异丁烷的影响

采用组合法制备了具有Keggin结构的杂多化合物催化剂，采用FTIR、UV-VIS-DR、H2-TPR、BET、TG-DTA和SEM对合成的催化剂的结构和性质进行了研究．探讨了催化剂中助剂α-Sb2O4含量对异丁烷选择性催化氧化的影响．并考察了反应温度对催化剂的催化性能影响．实验表明，助剂含量为8．3％，在C4H10／O2／N2／H2O=1／2．6／6／1，GHSV为910h^-1，温度为380℃的条件下，甲基丙烯酸的收率可达10．4％，选择性为44．3％．     

Re/Ga2O3/WO3/ZrO2催化剂对正己烷异构化反应的催化性能

通过浸渍法制备了系列Re/Ga2O3/WO3/ZrO|2(ReGWZ)催化剂,采用X射线衍射、氢气程序升温还原和氨气程序升温脱附等方法对催化剂进行了表征,考察了该催化剂催化正己烷异构化反应性能.结果表明,Re的引入改变了催化剂的氧化还原性能和酸中心分布,且使催化剂由单一的酸中心催化变成由酸中心与金属中心共同催化,因而正己烷异构化率和2,2-二甲基丁烷选择性显著增加.在195℃,1.0MPa,LHSV=1.0h-1和n(H2)/n(C6)=2.0的反应条件下,1.0Re/1.0GWZ催化剂上正己烷转化率、异己烷选择性和2,2-二甲基丁烷选择性分别达到84.8%,97.7%和20%,裂解产物(C5-)选择性为2.1%.150h的稳定性实验表明该催化剂性能稳定.     

V2O5/ACF催化剂低温下选择性催化还原NO的机理

将V2O5担载在活性炭纤维(ACF)上制得V2O5/ACF催化剂,并采用暂态响应实验和NH3吸附氧化实验等考察了影响V2O5/ACF催化剂上选择性催化还原(SCR)反应的关键因素.结果表明,NH3在催化剂表面的吸附是必要的,而且该吸附是一个快速过程;气相O2的存在有利于形成催化剂中所需的活性氧化态物种.NH3吸附.脱附与原位质谱相结合的实验表明,V2O5/ACF催化剂具有吸附NH3和将NH3氧化为N2H2的能力,N2H2为NH3氧化的一种中间体.     

H_3[PMo_(12)O_(40)]·nH_2O/SiO_2催化剂的制备及其催化性能

采用浸渍法制备了一系列H3[PMo12O40]·nH2O/SiO2催化剂(Catω),其结构和性能经XRD,N2-BET和NH3-TPD表征。以甘油脱水制备烯丙醇为探针反应,考察了Catω的催化性能。结果表明:H3[PMo12O40]·nH2O负载量为1.0%(ω=1%)的催化剂(Cat1)具有最佳的催化性能,甘油转化率,烯丙醇选择性和时空收率分别为100%,35.9%,3.2 mmol·g-1·h-1;催化剂的催化性能与H3[PMo12O40]·nH2O负载量有很好的相关性。     

Ru/ZrO2·xH2O催化剂催化肉桂醛选择性加氢制肉桂醇

采用共沉淀法制备了7.5%Ru/ZrO2·xH2O催化剂,运用N2物理吸附-脱附法、X射线衍射、X射线光电子能谱和高分辨透射电子显微镜等技术对催化剂进行了表征,并用于催化肉桂醛选择加氢制肉桂醇反应中,考察了温度、H2压力和溶剂对肉桂醛转化率和肉桂醇选择性的影响.结果表明,肉桂醛转化率随着温度或H2压力的升高而升高,而肉桂醇选择性则随之下降.该催化剂在极性溶剂中比在非极性溶剂中表现出更高的活性和肉桂醇选择性.尤其在极性溶剂三乙胺(Et3N)中反应活性最高,且具有较高的肉桂醇选择性.在Et3N中加入水可进一步提高反应活性和选择性.以V(Et3N)/V(H2O)=4的混合物为溶剂,在4MPa和70℃的优化条件下,反应6h,肉桂醛转化率为97.9%,肉桂醇选择性达85.2%.     

铬掺杂对V2O5/TiO2催化氧化3-甲基吡啶合成烟酸性能的影响

为进一步提高V2O5/TiO2催化剂对气相一步催化合成烟酸反应的活性和选择性.通过浸渍法制备一系列掺杂过渡金属铬的V2O5/TiO2催化剂,并对催化剂进行了BET、XRD、H2-TPR、NH3-TPD表征.结果表明,掺杂Cr后催化剂产生了新晶相CrVO4,减小了V2O5晶粒尺寸,并提高了催化剂的酸性,可较大地提高催化剂...     

Sb对Pd基催化剂用于常压直接合成H2O2的促进效应

H2O2作为一种高效绿色氧化剂, 广泛应用于造纸、纺织、水处理等工业领域. 目前蒽醌法是工业上生产 H2O2的主要方法, 相比之下, 利用 H2和 O2直接合成 H2O2, 能耗低, 污染小, 适合与下游工艺技术进行耦合. 而缺乏高性能催化剂是制约直接法合成 H2O2工业化的主要原因. 本文通过浸渍法制备了一系列负载型 Pd-Sb/TiO2双金属催化剂, 并用于常压下H2O2直接催化合成反应. 利用透射电子显微镜 (TEM), X 射线光电子能谱 (XPS), H2/O2程序升温脱附 (H2/O2-TPD), X 射线衍射 (XRD), 原位 CO 吸附的傅里叶变换漫反射红外光谱 (CO-DRIFTS) 等手段对催化剂的电子和几何结构进行解析, 深入研究了助剂 Sb 对该体系的促进作用.结果显示, 与单金属 Pd 催化剂相比, 适量金属 Sb 的加入有效提高了催化性能, 抑制了副反应的发生. 当 Pd/Sb 摩尔比为 50/1(Pd50Sb) 时, H2O2的选择性高达 73%; 但是当 Pd/Sb 为 2 时, 催化剂对生成 H2O2几乎没有活性. TEM 和 XRD 证明, Sb 的加入显著促进了 Pd 颗粒在载体 TiO2上的分散. XPS 和 H2-TPD 实验, 发现, Sb 改变了催化剂表面 Pd2+/Pd0的比例, 抑制了金属 Pd 的氧化; 同时, Sb 主要以氧化态存在, 在催化剂表面形成 Sb2O3氧化层, 覆盖表面的 Pd 活性位, 从而抑制了反应中 H2在催化剂表面的活化以及 H2O2加氢副反应的发生. O2-TPD 结果表明, 随着 Sb 的加入, O2的脱附峰明显减弱, 表明 Pd-Sb/TiO2不利于 O2的解离吸附. 此外, 原位 CO-DRIFTS 实验结果表明, Sb 均匀分布在 Pd-Sb 催化剂表面, 致使有利于生成 H2O 的连续 Pd 活性位明显减少, 而有利于合成 H2O2的单个 Pd 原子活性位明显增加.总的来说, Sb 对 Pd 表面起到了显著的修饰作用, 提高了催化剂表面 O2的非解离活化, 从而促进了 H2O2的高选择性合成. 但是过量 Sb 的加入会抑制催化剂对 H2的活化作用, 致使催化剂活性下降, 因此优选 Pd/Sb 的比例对于提高催化剂性能具有重要作用.     

双功能催化剂催化CO2加氢制低碳烯烃反应中In2O3的尺寸效应

CO2催化加氢转化成高附加值化学品如低碳烯烃(C2=–C4=)等是减少碳排放的有效途径之一.采用金属氧化物/分子筛双功能催化剂可以实现CO2加氢直接高选择性合成C2+碳氢化合物.通常认为,金属氧化物组分可以活化CO2转化为甲醇等含氧中间体,该中间体在分子筛孔道内进一步转化为各种烃.氧化铟(In2O3)/SAPO-34双功能催化剂由于具有出色的催化CO2加氢制低碳烯烃反应性能而备受关注,然而,仍需进一步提升催化剂的催化性能以推动该反应的工业应用.目前,氧化物的结构与双功能催化剂性能之间的关系还不明确,这不利于其催化性能的改善.现有关于金属氧化物纳米粒子的尺寸(特别是小于23 nm)效应及其对双功能催化CO2加氢反应的活性和产物分布的影响的报道较少,对此深入理解将有利于设计更高性能的催化剂.本文采用沉淀法,通过控制焙烧温度得到了一系列尺寸为7～28 nm的立方相In2O3,通过多种表征手段探究了In2O3的尺寸对其结构与表面化学性质的影响.结果表明,随着In2O3晶粒尺寸的减小,其氧空位数目、CO2、H2与NH3吸附量以及Lewis较强酸性位比例均逐渐增加.在350oC,3 Mpa,9000 mL·gcat–1·h–1和H2/CO2比为3的反应条件下,研究了In2O3/SAPO-34双功能催化剂中In2O3粒径对其催化CO2加氢制低碳烯烃反应性能的影响.结果表明,随着双功能催化剂中In2O3尺寸的增大,低碳烯烃(尤其是丙烯)选择性、收率及烯烃与烷烃比例均先升高后降低,在尺寸为19 nm的In2O3上达到最大值,分别为76.9％、12.3 mmol goxide–1 h–1和4.8.较小尺寸的In2O3虽然具有较大的比表面积和更多的氧空位,并为CO2和H2的活化提供了更多的活性位,但小于19 nm的颗粒更容易烧结;In2O3的尺寸还会影响其与SAPO-34的协同效应,进而影响双功能催化剂的催化活性.此外,相对于其它尺寸的In2O3,19 nm的In2O3更有利于甲醇中间体的生成.因而19 nm In2O3耦合SAPO-34的双功能催化剂性能最好,其催化CO2转化率最高,为14.1％.综上,适中尺寸的In2O3能够促进In2O3/SAPO-34上CO2加氢制低碳烯烃反应.这些结果为通过平衡结构稳定性和催化性能来设计更有效的催化CO2转化的复合催化剂提供了理论指导.     

CO2氧化异丁烷制异丁烯用Pd/V2O5-SiO2催化剂

 利用表面化学反应改性法制备了不同V2O5负载量的V2O5-SiO2表面复合物载体,进而采用等体积浸渍法制备了负载型Pd催化剂. 用N2吸附、 X射线衍射、透射电镜、 X射线光电子能谱、程序升温脱附、化学吸附-红外光谱和微反技术对系列Pd/V2O5-SiO2催化剂的比表面积、晶相结构、价态、异丁烷的化学吸附性能和CO2部分氧化异丁烷制异丁烯的催化性能进行了研究. 结果表明, Pd/V2O5-SiO2催化剂中的钒以V5+形式存在, V5+在催化剂表面形成活性位V=O, 其中 V=O 晶格氧与 i-C4H10分子的-CH3 和-CH 中的H产生化学吸附作用; 催化剂中金属Pd与V4+协同作用使CO2在催化剂上产生了卧式吸附态; 晶格氧参加了催化氧化反应,催化剂中 V5+←→V4+ 的变化构成了催化反应的氧化还原过程. 在525 ℃, CO2/i-C4H10体积比为1和空速为 1200 h-1的条件下,以Pd/25%V2O5-SiO2为催化剂时异丁烷转化率为22.8%, 异丁烯选择性为89.1%.     

Selective hydrogen peroxide oxidation of sulfides to sulfoxides or sulfones with MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions

Selective oxidation of sulfides to sulfoxides and sulfones with hydrogen peroxide under organic solvent-free conditions was demonstrated by the MWW-type titanosilicate zeolite catalyst. Sulfides were oxidized smoothly to give sulfoxides with good selectivities at ambient temperature using 1.0–1.2 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst. Especially, the Ti-MWW with an interlayer-expanded structure (Ti-IEZ-MWW) catalyst showed high activity with good chemoselectivity for the oxidation of various sulfides. The catalyst is recyclable for at least five cycles, and the only byproduct is water. Sulfides were directly oxidized to give sulfones in high yields by 2.5 equiv of hydrogen peroxide with the MWW-type titanosilicate zeolite catalyst under organic solvent-free conditions.     

Selective oxidation of sulfide catalyzed by peroxotungstate immobilized on ionic liquid-modified silica with aqueous hydrogen peroxide

Two kinds of catalysts of peroxotungstates immobilized on ionic liquid-modified silica have been synthesized and characterized. By comparing with other heterogeneous catalysts, the most characteristic of these heterogeneous catalysts is the catalyst formed from the combination of catalytic active center peroxotungstate with an ionic liquid. Thereinto, ionic liquid-modified supported catalysts provide the hydrophobic environment for organic reactions. We presume that the heterogeneous catalyst would display excellent catalytic ability depending on the additive effect of an ionic liquid and peroxotungstate. Their catalytic properties in oxidation of sulfides to sulfoxides and sulfones were investigated with 30% aqueous hydrogen peroxide at room temperature. These recoverable catalysts both exhibit high catalytic activities in the oxidation reaction of sulfoxides and provide excellent chemselectivities towards sulfur groups with unsaturated double bonds when the aqueous hydrogen peroxide was greatly in excess. The yields of methyl phenyl sulfoxide were still satisfied when the catalyst was reused for a sixth time.     

Oxidation of sulfoxides by hydrogen peroxide,catalyzed by methyltrioxorhenium(VII)

Dialkyl and diaryl sulfoxides are oxidized to sulfones by hydrogen peroxide using methyltrioxorhenium as the catalyst. The reaction rate is negligible without a catalyst. The kinetics study was performed in CH3CN-H2O (4:1 v/v) at 298 K with [H+] at 0.1 M, conditions which make the equilibration between MTO and its peroxo complexes more rapid than the oxygen-transfer step. The values for the rate constant for the oxygen-transfer step lie in the range 0.1-3 L mol-1 s-1. The rate constants were significantly smaller than for the oxidation of sulfides to sulfoxides. A study of ring-substituted diaryl sulfoxides yielded kinetics results that are consistent with nucleophilic attack of the sulfur atom on the peroxide oxygen group since rho = -0.65. The results cited refer to the reactions of the diperoxo from the catalyst, MeRe(O)(eta 2-O2)2H2O. The monoperoxo complex showed no measurable reactivity toward sulfoxides, in contrast with the situation for nearly every other substrate. That unusual finding suggests a hydrogen-bonded interaction between the substrate and the diperoxorhenium compound which cannot exist with the monoperoxo compound.     

Oxidation of olefins and sulfides with different oxidants catalyzed by meso-tetra(n-propyl)porphyrinatomanganese(III) acetate: comparison with meso-tetra(phenyl)porphyrinatomanganese(III) acetate

In this study, the catalytic activity of meso-tetra(n-propyl)porphyrinatomanganese(III) acetate, MnT(n-pr)(OAc) in oxidation of olefins and sulfides with tetra-n-butylammonium Oxone (TBAO), tetra-n-butylammonium periodate (TBAP), aqueous hydrogen peroxide, sodium periodate and Oxone in the presence of imidazole (ImH) has been studied. The comparison of catalytic performance of MnT(n-pr)P(OAc) and MnTPP(OAc) in oxidation of olefins with TBAP shows that while the latter is four times more efficient than the former, the extent of oxidative degradation of the former is ca. 3.5 times greater than the latter. The use of excess amount of styrene resulted in only a ca. 10 % increase in the catalyst stability, suggesting a mainly intramolecular mechanism for the catalyst degradation. On the other hand, in the case of TBAO, the oxidative degradation of the former is four times greater than the latter, but the catalytic performance of the latter for the oxidation of cyclohexene was only ca. 2 times larger than the former. This observation shows that the decreased catalytic performance of MnT(n-pr)P(OAc) relative to MnTPP(OAc) is essentially due to the high degree of degradation of the former. Due to the high degree of catalyst degradation, oxidation of olefins with periodate and Oxone in the presence of the two manganese porphyrins in aqueous solution (or with hydrogen peroxide in dichloromethane) gave little or no product. Oxidation of sulfides with TBAO and TBAP in the presence of MnT(n-pr)P(OAc) showed a conversion of ca. 15 % for the catalytic oxidation of sulfides to sulfones.     

Selective oxidation of sulfides to sulfoxides using 30% hydrogen peroxide catalyzed with a recoverable silica-based tungstate interphase catalyst

Various types of aromatic and aliphatic sulfides are selectively oxidized to sulfoxides and sulfones in good to excellent yields using 30% H2O2 in the presence of catalytic amounts of a novel recoverable silica-based tungstate interphase catalyst at room temperature. The catalyst can be recovered and reused for at least eight reaction cycles under the described reaction conditions without considerable loss of reactivity. [reaction: see text]     

Cu(II)–Schiff base complex‐functionalized magnetic Fe3O4 nanoparticles: a heterogeneous catalyst for various oxidation reactions

Cu(II)–Schiff base complex‐functionalized magnetic Fe₃O₄ nanoparticles were prepared and characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy techniques. This compound acts as a highly active and selective catalyst for the oxidation of sulfides and thiols. These reactions can be carried out in ethanol or solvent‐free conditions in the presence of hydrogen peroxide with complete selectivity and very high conversion under mild reaction conditions. The designed catalytic system prevents effectively the over‐oxidation of sulfides to sulfones. Separation and recycling can also be easily done using a simple magnetic separation process. Copyright © 2015 John Wiley & Sons, Ltd.     

Dendrimeric organochalcogen catalysts for the activation of hydrogen peroxide: improved catalytic activity through statistical effects and cooperativity in successive generations

Dendrimeric polyphenylsulfides, -selenides, and -tellurides are prepared in high yield using propyloxy spacers to connect the phenylchalcogeno groups to the dendrimeric core. The selenides and tellurides catalyze the oxidation of bromide with hydrogen peroxide to give positive bromine species that can be captured by cyclohexene in two-phase systems. The corresponding sulfides show no catalytic activity. The increase in the rate of catalysis followed statistical effects for 1, 6, and 12 phenyltelluro groups. However, the increase in the rate of catalysis exceeds statistical contributions for the first few generations with 1, 3, 6, and 12 phenylseleno groups and suggested cooperativity among phenylseleno groups. The increase in catalytic rate was lost upon replacing all but one phenylseleno group with phenoxy groups. On the basis of H2O2 consumed, the dendrimer with 12 phenylseleno groups has a turnover number of >60 000 mol of H2O2 consumed per mole of catalyst.     

Tetrabutylammonium phosphomolybdate on fluorapatite: an efficient solid catalyst for solvent-free selective oxidation of sulfides

A new synthetic method of sulfoxides and sulfones using solvent-free oxidations of sulfides with urea–hydrogen peroxide complex (urea–H₂O₂) and tetrabutylammonium phosphomolybdate catalyst on fluorapatite ((Bu₄N)₃[PMo₁₂O₄₀]/FAp). In the solid-phase system the oxidations of aromatic and alkyl sulfides proceeded at 4–25 °C and the corresponding sulfoxides or sulfones were selectively obtained in good yields by controlling the amount of urea–H₂O₂.     

原子级分散Fe-N-C温和条件下选择性氧化催化特性

采用非溶液法制备了原子级分散的Fe-N-C催化剂, 并用于硫醚和二级醇的选择性氧化. 研究结果表明, 这种原子级分散的Fe-N-C催化剂可在温和条件下选择性地将硫醚转化为亚砜, 而不会产生过度氧化的砜. 该工艺具有反应条件温和、 反应速度快、 收率高等优点; 该催化剂对二级醇氧化制酮反应具有较高的催化活性, 产率较高. 作为一种非均相催化剂, Fe-N-C催化剂循环使用5次后活性未见显著下降; 在实验结果和参考文献的基础上还提出了一种可能的自由基反应机理.     

Oxidation of Sulfides with Hydrogen Peroxide to Sulfoxides and Sulfones

Oxidation of sulfides with hydrogen peroxide to sulfoxides and then sulfones was studied. The conditions optimal for the formation of sulfoxides and sulfones were found.