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首页> 外文期刊>Green chemistry >The effect of catalyst preparation method on the performance of supported Au-Pd catalysts for the direct synthesis of hydrogen peroxide
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The effect of catalyst preparation method on the performance of supported Au-Pd catalysts for the direct synthesis of hydrogen peroxide

机译：催化剂制备方法对直接合成过氧化氢的负载型Au-Pd催化剂性能的影响

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The direct synthesis of hydrogen peroxide from H2 and O2 offers the possibility of a new green production method for this important commodity chemical. Active catalysts for this reaction are typically prepared using an impregnation method and it is important to identify improvements in the preparation methodology that can result in more active catalysts that retain their stability. The effect of the precise procedure by which the metals are impregnated onto TiO2 and C supports during the preparation of supported Au-Pd catalysts has been investigated and it is shown that the two supports exhibit significant differences. The concentration of the solution of the mixed aqueous solution of HAuCl4 and PdCl2 immediately prior to the initial drying step has a profound effect on the structure and activity of the TiO2-supported catalysts. TiO2-supported catalysts prepared using impregnation with the minimal amount of added water whilst ensuring that the catalyst is not formed into a paste (i.e. still contains ca. 1.5-2 ml of H2O) prior to drying at 110 °C exhibit very high activity (ca. 120 mol H2O2 kg_(cat)~(-1) h~(-1)) which is equivalent to the corresponding carbon-supported catalyst. The presence of more water (ca. 2-28 ml) in the catalyst impregnation step prior to drying leads to a significant change in the particle size distribution and a bimodal distribution is observed for the TiO2-supported catalysts. These catalysts also show a change in the nature of the Au and Pd nanoparticles. Unfortunately, TiO2-supported catalysts prepared in this manner are not stable on re-use. However, catalysts prepared using a similar method, but with the removal of ca. 75% of the initial H2O ensuring that a paste is formed prior to drying, are found to be fully re-usable. In contrast, for carbon-supported catalysts dilution of the Au and Pd compounds during the initial impregnation step, coupled with subsequent removal of water to form paste with varying water content, did not affect the activity and these catalysts could be re-used without loss of catalyst performance. The effect of the catalyst structure on activity and re-usability is discussed.
机译：由H2和O2直接合成过氧化氢为这种重要的商品化学品提供了一种新的绿色生产方法的可能性。通常使用浸渍方法制备用于该反应的活性催化剂，并且重要的是确定制备方法的改进，这些改进可以导致保留其稳定性的更多活性催化剂。研究了在制备负载型Au-Pd催化剂过程中将金属浸渍到TiO2和C载体上的精确程序的效果，结果表明两种载体表现出显着的差异。刚好在初始干燥步骤之前，HAuCl4和PdCl2混合水溶液的溶液浓度对TiO2负载的催化剂的结构和活性产生了深远的影响。在110°C下干燥之前，使用少量的水浸渍浸渍制备的TiO2负载的催化剂，同时确保催化剂不会形成糊状物（即仍包含约1.5-2 ml的H2O），该催化剂具有很高的活性（约120 mol H2O2 kg_（cat）〜（-1）h〜（-1）），相当于相应的碳载催化剂。干燥前在催化剂浸渍步骤中存在更多的水（约2-28 ml）会导致粒径分布发生明显变化，并观察到TiO2负载的催化剂的双峰分布。这些催化剂还显示出Au和Pd纳米颗粒性质的变化。不幸的是，以这种方式制备的TiO 2负载的催化剂在重新使用时不稳定。然而，使用相似的方法制备的催化剂，但是除去了约20％的Ca。发现可以确保可重复使用的初始H2O的75％（确保在干燥前形成糊状物）。相反，对于碳载催化剂，在初始浸渍步骤中对Au和Pd化合物进行稀释，以及随后除去水以形成具有不同含水量的糊状物，都不会影响活性，因此这些催化剂可以重复使用而不会损失催化剂性能。讨论了催化剂结构对活性和可重复使用性的影响。

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