Hydrogen Evolution from Formic Acid in an Ionic Liquid Solvent: A Mechanistic Study by ab Initio Molecular Dynamics
详细信息 查看全文
- 作者：B. L. Bhargava ; Yoshiro Yasaka ; Michael L. Klein
- 刊名：Journal of Physical Chemistry B
- 出版年：2011
- 出版时间：December 8, 2011
- 年：2011
- 卷：115
- 期：48
- 页码：14136-14140
- 全文大小：797K
- 年卷期：v.115,no.48(December 8, 2011)
- ISSN：1520-5207
文摘
The reversible decomposition of formic acid (HCOOH CO2 + H2) 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鈥揙ppenheimer (BO) molecular dynamics (MD) calculations have been performed to explore the mechanism involved in hydrogen (H2) 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 (H2) and carbon dioxide (CO2) 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鈥揌 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 CO2 by the strong electrostatic field of the ionic liquid solvent.