Funakawa Akiyasu, Yamanaka Ichiro, Otsuka Kiyoshi
Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8552, Japan.
J Phys Chem B. 2005 May 12;109(18):9140-7. doi: 10.1021/jp0448752.
Electrochemical oxidative carbonylation of methanol was studied over Au supported carbon anode in CO. The major carbonylation products were dimethyl oxalate (DMO) and dimethyl carbonate (DMC). The minor oxidation products were dimethoxy methane (DMM) and methyl formate (MF) from methanol and CO(2). Influences of various reaction conditions were studied on carbonylation activities and selectivities. The selectivities to DMO and DMC can be controlled by the electrochemical potential. Electrocatalysis of Au/carbon anode was studied by cyclic voltammetry (CV), stoichiometric reactions among Au(3+), methanol, and CO, and UV-vis spectra. The Au/carbon anode was characterized by XRD, SEM, and BE images before and after the carbonylation. These experimental facts strongly suggest that transition of oxidation states of Au affects changing of the carbonylation selectivities to DMO and DMC. Au(0) is the active species for the selective DMO formation by direct electrochemical carbonylation at low potentials (<+1.2 V (Ag/AgCl)). On the other hand, Au(3+) is the active spices for the selective DMC formation by indirect electrochemical carbonylation through Au(3+)/Au(+) redox at high potentials (>+1.3 V).
在一氧化碳氛围中，研究了甲醇在负载金的碳阳极上的电化学氧化羰基化反应。主要的羰基化产物是草酸二甲酯（DMO）和碳酸二甲酯（DMC）。次要的氧化产物是甲醇和二氧化碳生成的二甲氧基甲烷（DMM）和甲酸甲酯（MF）。研究了各种反应条件对羰基化活性和选择性的影响。对DMO和DMC的选择性可通过电化学电位来控制。通过循环伏安法（CV）、金（III）、甲醇和一氧化碳之间的化学计量反应以及紫外可见光谱研究了金/碳阳极的电催化作用。在羰基化反应前后，通过X射线衍射（XRD）、扫描电子显微镜（SEM）和背散射电子（BE）图像对金/碳阳极进行了表征。这些实验事实有力地表明，金氧化态的转变影响了对DMO和DMC羰基化选择性的变化。金（0）是在低电位（< +1.2 V（Ag/AgCl））下通过直接电化学羰基化选择性生成DMO的活性物种。另一方面，金（III）是在高电位（> +1.3 V）下通过金（III）/金（I）氧化还原间接电化学羰基化选择性生成DMC的活性物种。
