Lim Seulgi, Kwon Seungdon, Kim Nagyeong, Na Kyungsu
Department of Chemistry, Chonnam National University, Gwangju 61186, Korea.
Nanomaterials (Basel). 2021 Jun 10;11(6):1536. doi: 10.3390/nano11061536.
Au nanoparticles bound to crystalline CeO nanograins that were dispersed on the nanoplate-like Mg(OH), denoted as Au/CeO-Mg(OH), were developed as the highly active and selective multifunctional heterogeneous catalyst for direct oxidative esterification of aldehydes with alcohols to produce alkyl esters under base-free aerobic conditions using oxygen or air as the green oxidants. Au/CeO-Mg(OH) converted 93.3% of methacrylaldehyde (MACR) to methyl methacrylate (MMA, monomer of poly(methyl methacrylate)) with 98.2% selectivity within 1 h, and was repeatedly used over eight recycle runs without regeneration. The catalyst was extensively applied to other aldehydes and alcohols to produce desirable alkyl esters. Comprehensive characterization analyses revealed that the strong metal-support interaction (SMSI) among the three catalytic components (Au, CeO, and Mg(OH)), and the proximity and strong contact between Au/CeO and the Mg(OH) surface were prominent factors that accelerated the reaction toward a desirable oxidative esterification pathway. During the reaction, MACR was adsorbed on the surface of CeO-Mg(OH), upon which methanol was simultaneously activated for esterifying the adsorbed MACR. Hemiacetal-form intermediate species were subsequently produced and oxidized to MMA on the surface of the electron-rich Au nanoparticles bound to partially reduced CeO with electron-donating properties. The present study provides new insights into the design of SMSI-induced supported-metal-nanoparticles for the development of novel, multifunctional, and heterogeneous catalysts.
负载于分散在纳米片状氢氧化镁上的结晶氧化铈纳米颗粒上的金纳米颗粒（记为Au/CeO-Mg(OH)），被开发为一种高活性、高选择性的多功能非均相催化剂，用于在无碱有氧条件下，以氧气或空气作为绿色氧化剂，使醛与醇直接氧化酯化生成烷基酯。Au/CeO-Mg(OH)在1小时内可将93.3%的甲基丙烯醛（MACR）转化为甲基丙烯酸甲酯（MMA，聚甲基丙烯酸甲酯的单体），选择性为98.2%，并且无需再生即可重复使用八次循环。该催化剂被广泛应用于其他醛和醇以制备所需的烷基酯。综合表征分析表明，三种催化组分（Au、CeO和Mg(OH)）之间的强金属-载体相互作用（SMSI），以及Au/CeO与Mg(OH)表面之间的紧密接触是加速反应朝着理想的氧化酯化途径进行的突出因素。在反应过程中，MACR吸附在CeO-Mg(OH)表面，在此表面上甲醇同时被活化以酯化吸附的MACR。随后生成半缩醛形式的中间物种，并在与具有供电子性质的部分还原的CeO结合的富电子金纳米颗粒表面被氧化为MMA。本研究为设计用于开发新型、多功能和非均相催化剂的SMSI诱导负载金属纳米颗粒提供了新的见解。
