Graduate Institute of Environmental Engineering, National Taiwan University , Taipei, 106, Taiwan.
Environ Sci Technol. 2015 Feb 17;49(4):2405-17. doi: 10.1021/es505301x. Epub 2015 Feb 4.
As gradual increases in atmospheric CO2 and depletion of fossil fuels have raised considerable public concern in recent decades, utilizing the unlimited solar energy to convert CO2 to fuels (e.g., formic acid and methanol) apparently could simultaneously resolve these issues for sustainable development. However, due to the complicated characteristics of CO2 reduction, the mechanism has yet to be disclosed. To clarify the postulated pathway as mentioned in the literature, the technique of electron paramagnetic resonance (ESR) was implemented herein to confirm the mechanism and related pathways of CO2 reduction under visible light using graphene-TiO2 as catalyst. The findings indicated that CO(-•) radicals, as the main intermediates, were first detected herein to react with several hydrogen ions and electrons for the formation of CH3OH. For example, the generation of CO(-•) radicals is possibly the vital rate-controlling step for conversion of CO2 to methanol as hypothesized elsewhere. The kinetics behind the proposed mechanism was also determined in this study. The mechanism and kinetics could provide the in-depth understanding to the pathway of CO2 reduction and disclose system optimization of maximal conversion for further application.
近几十年来，大气中 CO2 的逐渐增加和化石燃料的枯竭引起了公众的极大关注，利用取之不尽的太阳能将 CO2 转化为燃料（例如甲酸和甲醇）显然可以同时解决这些可持续发展问题。然而，由于 CO2 还原的复杂特性，其机制尚未被揭示。为了阐明文献中提到的假定途径，本文采用电子顺磁共振（ESR）技术，利用石墨烯-TiO2 作为催化剂，在可见光下证实了 CO2 还原的机制和相关途径。研究结果表明，首先在此检测到 CO(-•)自由基作为主要中间体，与几个氢离子和电子反应生成 CH3OH。例如，CO(-•)自由基的生成可能是 CO2 转化为甲醇的关键控制步骤，这与其他地方的假设一致。本研究还确定了所提出机制的动力学。该机制和动力学可以深入了解 CO2 还原的途径，并揭示最大转化率的系统优化，以进一步应用。
