van Rooij G J, van den Bekerom D C M, den Harder N, Minea T, Berden G, Bongers W A, Engeln R, Graswinckel M F, Zoethout E, van de Sanden M C M
Dutch Institute for Fundamental Energy Research, P.O. box 6336, 5600 HH Eindhoven, The Netherlands.
Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands.
Faraday Discuss. 2015;183:233-48. doi: 10.1039/c5fd00045a.
The strong non-equilibrium conditions provided by the plasma phase offer the opportunity to beat traditional thermal process energy efficiencies via preferential excitation of molecular vibrations. Simple molecular physics considerations are presented to explain potential dissociation pathways in plasma and their effect on energy efficiency. A common microwave reactor approach is evaluated experimentally with Rayleigh scattering and Fourier transform infrared spectroscopy to assess gas temperatures (exceeding 10(4) K) and conversion degrees (up to 30%), respectively. The results are interpreted on a basis of estimates of the plasma dynamics obtained with electron energy distribution functions calculated with a Boltzmann solver. It indicates that the intrinsic electron energies are higher than is favorable for preferential vibrational excitation due to dissociative excitation, which causes thermodynamic equilibrium chemistry to dominate. The highest observed energy efficiencies of 45% indicate that non-equilibrium dynamics had been at play. A novel approach involving additives of low ionization potential to tailor the electron energies to the vibrational excitation regime is proposed.
等离子体相所提供的强烈非平衡条件，为通过优先激发分子振动来超越传统热过程的能源效率提供了机会。本文提出了简单的分子物理学考量，以解释等离子体中的潜在解离途径及其对能源效率的影响。通过瑞利散射和傅里叶变换红外光谱对一种常见的微波反应器方法进行了实验评估，分别用以评估气体温度（超过10⁴ K）和转化程度（高达30%）。基于用玻尔兹曼求解器计算的电子能量分布函数所获得的等离子体动力学估计值，对结果进行了解释。结果表明，由于解离激发，本征电子能量高于优先振动激发所适宜的能量，这导致热力学平衡化学占主导地位。所观察到的最高能源效率为45%，这表明非平衡动力学发挥了作用。本文提出了一种新方法，即加入低电离势添加剂，以使电子能量适应振动激发区域。
