SiO2负载Au-Pd双金属纳米颗粒催化甲醇选择性氧化合成甲酸甲酯（英文）

Selective oxidation of methanol to methyl formate over bimetallic Au-Pd nanoparticles supported on SiO2

甲醇选择氧化制备甲酸甲酯(MF)是延伸甲醇产业链、开发高附加值下游产品的有效途径之一,负载型Au及Pd催化剂在这一反应中表现出优异的低温催化性能。为探索实用、高效和易再生的甲醇选择氧化催化剂,同时揭示双金属颗粒中Au和Pd的协同效应及甲醇氧化反应机理,本研究制备了一系列二氧化硅负载的Au-Pd催化剂(Au-Pd/SiO2),详细研究了其对甲醇选择氧化制甲酸甲酯的催化性能。结果表明,Au和Pd总负载量为0.6%、且Au/Pd质量比为2时,所制备的Au2-Pd1/SiO2催化剂表现出优异的甲醇氧化催化性能;在130℃下,甲醇转化率达到57.0%,MF选择性为72.7%。多种表征结果显示,Au-Pd双金属纳米颗粒粒径为2-4nm,高度分散于SiO2载体表面,倾向于生成孪晶结构并暴露(111)晶面,这些因素是Au-Pd/SiO2具有优异催化性能的主要原因。通过DRIFTS表征研究,提出了一个可能的MF生成机理:即甲醇首先与处于Au-Pd纳米粒子界面的表面氧作用,生成化学吸附的甲氧基;随后,甲氧基经去质子作用生成吸附的甲醛物种,后者与相邻的甲氧基物种亲核反应,并经β-H消除后得到目标产物MF。

Selective oxidation of methanol to methyl formate (MF) is one of the most attractive processes to get valuable methanol-downstream products, where the supported Au and Pd catalysts were proved rather effective at low temperature. To search for highly active, regenerable and practical catalysts as well as to reveal the synergy of Au-Pd and reaction mechanism for the methanol oxidation, a series of silica supported Au-Pd nanoparticles (Au-Pd/SiO2) were prepared and their catalytic performance in the oxidation of methanol to MF with molecular oxygen was investigated in this work. The results indicate that the Au2-Pd 1/SiO2 catalyst with an Au+Pd loading of only 0.6% and a Au/Pd mass ratio of 2 exhibits excellent performance in the methanol oxidation with oxygen;the conversion of methanol over Au2-Pd 1/SiO2 reaches 57.0% at 130 ℃, with a selectivity of 72.7% to MF. Various characterization results illustrate that the Au-Pd bimetallic nanoparticles (2-4 nm) are highly dispersed on the silica surface, inclined to take a twinned structure and present the (111) planes, which may contribute to the high activity of Au-Pd/SiO 2 in the oxidation of methanol to MF. A possible reaction mechanism was proposed on the basis of DRIFTS results: methanol was first activated by surface oxygen on the interface of Au-Pd nanoparticles, forming the chemisorbed methoxy species;the methoxy species was then deprotonated to adsorbed formaldehyde species, which reacted with another methoxy species, producing MF by nucleophilic attack and subsequent β-H elimination.