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<p>Fullerenes of different sizes (C₆₀, C₇₀, and C₈₀) were used to examine the cis–trans isomerization and unimolecular dissociation of formic acid using density functional theory. Confinement within the larger C₇₀ and C₈₀ cages stabilizes both conformers and lowers the trans-to-cis isomerization barrier, whereas C₆₀ induces steric destabilization. Confinement also modifies dissociation energetics. The cis-HCOOH→CO₂+H₂ pathway, which is slightly exothermic in the gas phase, becomes endothermic inside all fullerene cages, while the trans-HCOOH→CO + H₂O pathway, already endothermic, becomes increasingly unfavourable under confinement. Water-assisted dissociation of trans-formic acid, previously reported in the gas phase, remains possible inside C₇₀ and C₈₀; however, the energetic benefit of water catalysis is reduced compared to the gas phase, and the process is not feasible in C₆₀ due to spatial constraints. The effect of an external electric field was also studied. In the gas phase, as the field strength increases, both reaction energies (ΔE) and activation barriers rise steadily, with cis-formic acid showing a stronger response. Within fullerene cages, the influence of the electric field is reduced. However, the changes are small; in specific encapsulated systems, the electric field can lower reaction energies (ΔE) and activation barriers relative to the corresponding field-free confined states.</p>

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Environmental effects on formic acid isomerization and decomposition: a computational study of fullerene confinement, water catalysis, and external electric fields

  • 期刊论文

  • 发表日期：

    2026年3月11日

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  • Vasu Nagpal,
  • Vishal Sharma,
  • Aniruddha Chakraborty

摘要

Fullerenes of different sizes (C₆₀, C₇₀, and C₈₀) were used to examine the cis–trans isomerization and unimolecular dissociation of formic acid using density functional theory. Confinement within the larger C₇₀ and C₈₀ cages stabilizes both conformers and lowers the trans-to-cis isomerization barrier, whereas C₆₀ induces steric destabilization. Confinement also modifies dissociation energetics. The cis-HCOOH→CO₂+H₂ pathway, which is slightly exothermic in the gas phase, becomes endothermic inside all fullerene cages, while the trans-HCOOH→CO + H₂O pathway, already endothermic, becomes increasingly unfavourable under confinement. Water-assisted dissociation of trans-formic acid, previously reported in the gas phase, remains possible inside C₇₀ and C₈₀; however, the energetic benefit of water catalysis is reduced compared to the gas phase, and the process is not feasible in C₆₀ due to spatial constraints. The effect of an external electric field was also studied. In the gas phase, as the field strength increases, both reaction energies (ΔE) and activation barriers rise steadily, with cis-formic acid showing a stronger response. Within fullerene cages, the influence of the electric field is reduced. However, the changes are small; in specific encapsulated systems, the electric field can lower reaction energies (ΔE) and activation barriers relative to the corresponding field-free confined states.