Kumar Ch Venkata Surya, Subramanian Venkatesan
Inorganic and Physical Chemistry (Chemical Laboratory), CSIR-Central Leather Research Institute, Adyar, Chennai-600 020, India.
Phys Chem Chem Phys. 2017 Jun 14;19(23):15377-15387. doi: 10.1039/c7cp02220d.
Nitrogen fixation is a challenging reaction under ambient conditions. So far, a few metal-based catalysts have been reported; however, noticeable disadvantages including high cost, gas poisoning, and them being hazardous to the environment are still to be resolved. We have carried out density functional theory based calculations with the ωB97X-D/6-31G* level of theory to investigate the activation of dinitrogen using boron nitride based metal-free catalysts for the first time as they are environmentally friendly and corrosion resistant. The boron antisite of a boron nitride nanotube is found to be an active site for nitrogen activation. The activated N is characterized by the increase in bond length and the red shift in the stretching frequency of the N[triple bond, length as m-dash]N bond. The subsequent reduction mechanisms of activated N into ammonia through six-proton and six-electron processes have also been elucidated. The selectivity of the nitrogen reduction reaction between distal and alternating associative pathways is also rationalized. The reaction energetics highlight the distal associative mechanism as a feasible pathway under ambient conditions. The catalytic performance of B is further unraveled with the help of variation in the charge density. This work provides a rational model for the metal-free catalytic conversion of N to ammonia via an eco-friendly pathway under ambient conditions.
在环境条件下，氮固定是一个具有挑战性的反应。到目前为止，已经报道了一些基于金属的催化剂；然而，包括成本高、气体中毒以及对环境有害等明显缺点仍有待解决。我们首次使用基于密度泛函理论的ωB97X-D/6-31G*理论水平进行计算，以研究使用氮化硼基无金属催化剂活化二氮，因为它们环保且耐腐蚀。发现氮化硼纳米管的硼反位是氮活化的活性位点。活化的N的特征是键长增加和N≡N键拉伸频率的红移。还阐明了活化的N通过六质子和六电子过程还原为氨的后续机制。也对远端和交替缔合途径之间氮还原反应的选择性进行了合理化解释。反应能量学突出了远端缔合机制是环境条件下的可行途径。借助电荷密度的变化进一步揭示了B的催化性能。这项工作为在环境条件下通过生态友好途径将N无金属催化转化为氨提供了一个合理的模型。
