Molecular-level simulations of chemical reaction equilibrium for nitric oxide dimerization reaction in disordered nanoporous carbons

Abstract

We report a molecular-level simulation study of the effects of confinement on chemical reaction equilibrium for the NO dimerization reaction, 2NO ⇌ (NO) 2, in disordered nanoporous carbons. We use the Reaction Ensemble Monte Carlo (RxMC) method [W.R. Smith, B. Tříska, J. Chem. Phys. 100 (1994) 3019–3027; J.K. Johnson, A.Z. Panagiotopoulos, K.E. Gubbins, Mol. Phys. 81 (1994) 717–733] to investigate the effects of temperature and bulk pressure on the reaction conversion in three models of disordered nanoporous carbons obtained from sucrose in equilibrium with a vapor reservoir. Atomistic models of the carbons used [S.K. Jain, R.J.-M. Pellenq, J.P. Pikunic, K.E. Gubbins, Langmuir 22 (2006) 9942–9948] were constructed using the Hybrid Reverse Monte Carlo method, differing by the processing conditions used in the preparation of the corresponding real material. In addition to the RxMC simulations, we test conventional macroscopic adsorption models, such as the Langmuir–Freundlich, multisite Langmuir, vacancy solution and ideal adsorption solution models, in connection with the ideal-gas model for the vapor reservoir to model the reaction equilibrium. Pure fluid adsorption isotherms needed as input to the macroscopic models for mixture adsorption are generated using the Gibbs Ensemble Monte Carlo or Grand Canonical Monte Carlo simulations. We analyze the effects of the confinement, temperature and bulk pressure on the NO dimerization reaction equilibrium in terms of the reactive adsorption isotherms. The RxMC simulations and thermodynamic modeling show that the sucrose-based carbons substantially increase the conversion of NO to (NO) 2 with respect to the vapor reservoir, where the conversion is less than a few percent.