Institute for Computational Molecular Science, Temple University, 1900 N. 12th Street, Philadelphia, Pennsylvania 19122, USA.
J Phys Chem B. 2011 Dec 8;115(48):14136-40. doi: 10.1021/jp204007w. Epub 2011 Jul 20.
The reversible decomposition of formic acid (HCOOH ⇌ CO(2) + H(2)) has been attracting attention for its potential utility in hydrogen storage and production. It is therefore of interest to explore the influence of solvents on the decomposition reaction. To this end, Born-Oppenheimer (BO) molecular dynamics (MD) calculations have been performed to explore the mechanism involved in hydrogen (H(2)) evolution from formic acid decomposition in an ionic liquid solvent. Specifically, for a solvent consisting of 1,3-dimethylimidazolium cations and formate anions, evolution of hydrogen (H(2)) and carbon dioxide (CO(2)) was observed within a few picoseconds when BO-MD trajectories were carried out at an elevated temperature of 3000 K. The observed dehydrogenation involved a reaction between a formic acid solute and a nearby solvent formate anion. The observed mechanism contrasts with the unimolecular mechanism proposed in the gas phase. Specifically, in the ionic liquid, the reaction is initiated from a C-H bond dissociation of a formate anion to produce a short-lived hydride anion, which subsequently captures the acidic proton of a nearby formic acid molecule. The present BO-MD computations suggest that the high reducing ability of formic acid in the ionic liquid is due in part to its acid-dissociated form: the formate anion, which is encouraged to dissociate into a hydride anion and CO(2) by the strong electrostatic field of the ionic liquid solvent.
甲酸（HCOOH ⇌ CO(2) + H(2)）的可逆分解因其在储氢和制氢方面的潜在应用而受到关注。因此，探索溶剂对分解反应的影响是很有意义的。为此，进行了 Born-Oppenheimer（BO）分子动力学（MD）计算，以探索甲酸在离子液体溶剂中分解时涉及的氢（H(2)）释放机制。具体来说，对于由 1,3-二甲基咪唑阳离子和甲酸盐阴离子组成的溶剂，当在 3000 K 的高温下进行 BO-MD 轨迹时，在几皮秒内观察到氢（H(2)）和二氧化碳（CO(2)）的脱氢。观察到的脱氢涉及甲酸溶质与附近溶剂甲酸盐阴离子之间的反应。观察到的机制与气相中提出的单分子机制形成对比。具体而言，在离子液体中，反应是从甲酸盐阴离子的 C-H 键解离开始的，产生短寿命的氢化物阴离子，随后该氢化物阴离子捕获附近甲酸分子的酸性质子。本 BO-MD 计算表明，甲酸在离子液体中的高还原能力部分归因于其酸解离形式：甲酸盐阴离子，它受到离子液体溶剂的强静电场的鼓励而解离成氢化物阴离子和 CO(2)。
