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Surfactant controlled magnesium oxide synthesis for base catalysis

机译：表面活性剂控制氧化镁合成对碱催化

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Magnesium oxide catalysts were used to investigate the influence of novel preparative techniques for surface site control on activity. Firstly, magnesium hydroxide was prepared under hydrothermal conditions with sodium dodecyl sulphate and either sodium hydroxide or a quaternary ammonium ion as morphological and surface controlling agents. Particles with a hexagonal, plate-like morphology were produced with varying dimensions relative to the concentrations of surfactant to ammonium ion. These materials were dehydrated at 420 degrees C for 2 hours and then characterised by nitrogen adsorption, X-ray diffraction, electron microscopy and the surface hydroxyl density was measured via H-1 MAS NMR. Analysis of electron microscopy images of the resulting MgO materials indicted that the morphology of the precursor hydroxide was retained. The MgO materials were then used as catalysts for Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate. The activity of the MgO samples was found to correspond to the surface hydroxyl density; higher activities (ca. 18 mol(prod) kg(-1) h(-1)) were observed for catalysts with a surface hydroxyl density of > 1.3 mmol g(-1). Knoevenagel condensation relies greatly on distribution of neighbouring -Mg2+ and -O2- sites, the catalysts with a higher density of potentially low coordination -O2- sites resulted in higher product yields. The hydroxyl density was found to be independent of surface area, such that the combination of precipitating agent and surfactant can effectively control crystal growth to tailor the basic active surface of MgO.
机译：镁氧化物催化剂用于调查新型制备技术的影响表面网站控制活动。氢氧化镁制备水热条件与钠十二烷基硫酸和氢氧化钠或季铵离子形态和表面控制代理。六角,平板状形态相对于不同维度铵离子浓度的表面活性剂。这些材料在420摄氏度脱水2小时,然后以氮吸附、x射线衍射、电子显微镜和表面羟基密度通过h - MAS NMR测定。结果分别以材料的显微图像起诉的形态学的前兆氢氧化是保留。然后用作诺文葛耳催化剂苯甲醛的缩合和乙以。发现与表面羟基相对应密度;公斤(1)h(1))为催化剂与观察表面羟基的密度> 1.3更易与g(1)。诺文葛耳凝结极大地依赖分布的邻国-Mg2 +和- 02 -网站,催化剂具有更高的密度潜在的低协调- 02——网站了在更高的产品产量。被发现独立的表面积,这样吗沉淀剂的组合表面活性剂能有效控制晶体生长调整基本采用的积极面。

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