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首页> 外文期刊>ACS catalysis >Liquid Phase Direct Synthesis of H2O2: Activity and Selectivity of Pd-Dispersed Phase on Acidic Niobia-Silica Supports
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Liquid Phase Direct Synthesis of H2O2: Activity and Selectivity of Pd-Dispersed Phase on Acidic Niobia-Silica Supports

机译：H 2 O 2的液相直接合成：Pd分散相对酸性铌瘤 - 二氧化硅载体的活性和选择性

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摘要

In this work, acidic niobia-silica (NbS, 4-14 wt % Nb) materials used as supports of dispersed Pd particles (1.0-2.0 wt % Pd) have been prepared from different Nb-precursors (niobium ethoxide, NBE, and ammonium niobium oxalate, ANBO) and techniques (coprecipitation and deposition), characterized, and tested in the direct synthesis of H2O2 in water and methanol solvents. In particular, on a typical NbS sample, the evolution of morphology (by N-2-adsorption desorption), crystalline-phase (by XRD), electronic structure (by UV-vis-DRS), and surface acidity with time/temperature of treatment (350-800 C for 4-100 h) has been investigated. Surface acidity was measured by titrations with 2-phenylethylamine adsorption in various liquids: cyclohexane, for the intrinsic acidity, and water, methanol, and water methanol mixtures for the effective acidities. Direct H2O2 synthesis reaction was performed in semibatch slurry reactor with continuous feeding of the gaseous mixture (H-2, O-2, and N-2), under pressure (5 X 10(3) kPa or 10(4) kPa) at 5 degrees C in methanol or in water. In both solvents, reaction rates only little decreased with time on stream (ca. 5% of rate decrease after 4 h of reaction from initial rate of ca. 0.5 g(H2O2)center dot(kg(solution).min)(-1), according with the slight Pd sintering observed by TEM images. Catalysts prepared by deposition of NBE on silica gave better performances than those prepared from ANBO. In general, selectivity to H2O2 in water and in methanol was observed to be similar; the unexpected good selectivity in water was due to the higher effective acid strengths of the catalytic surfaces in water than in methanol, as experimentally proven.
机译：在这项工作中，用作分散的Pd颗粒的载体（1.0-2.0wt％pd）的酸性铌菊原（Nbs，4-14wt％Nb）材料由不同的Nb-前体（乙醇铌，NE和铵草酸铌，anbo）和技术（共沉淀和沉积），其特征在于水和甲醇溶剂的直接合成H 2 O 2。特别地，在典型的NBS样品上，形态（通过N-2吸附解吸）的演化，结晶相（通过XRD），电子结构（通过UV-Vis-DRS），以及具有时间/温度的表面酸度已经研究了治疗（350-800℃，4-100小时）。通过用各种液体中的2-苯基乙胺吸附滴定来测量表面酸度：环己烷，用于本征酸度，水，甲醇和水甲醇混合物的有效酸性。在半靶浆料反应器中进行直接H 2 O 2合成反应，在压力（5×10（3）KPA或10（4）KPA）下连续进给气态混合物（H-2，O-2和N-2）甲醇或水中的5℃。在溶剂中，反应速率随着物流的时间几乎没有减少（约1.0.5g（H2O2）中心点（kg（溶液）.min）（ - 1 [），根据TEM图像观察的轻微PD烧结。通过沉积NBE在二氧化硅上制备的催化剂比由anbo制备的那些更好的性能。通常，观察到在水和甲醇中的选择性与H 2 O 2相似;意外的好水中的选择性是由于水中催化表面的较高的酸强度，而不是在甲醇中，如实验证明。

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