Effect of Confinement on Chemical Reactions

Abstract

Molecular simulation studies of chemical equilibrium for several reactions in pores of slit-like and cylindrical geometry have shown a significant effect of the confinement on the equilibrium compositions, with differences of several orders of magnitude with respect to the bulk fluid phase in some cases. As a first step towards the calculation of rate constants in confinement, we have studied the reaction mechanisms for several reactions involving small organic molecules in slit-like pores. We show results for the rotational isomerization of 1,3-butadiene and the unimolecular decomposition of formaldehyde obtained using plane wave pseudopotential density functional theory (DFT). These examples show the influence that confinement can have through both geometrical constraints and fluid-wall interactions.

Adsorption and diffusion of argon in disordered nanoporous carbons

“…In many cases, the accessible range of time and length scales of these methods is sufficient such that the calculated quantities can be directly compared with empirical measurements. For these reasons, such approaches have been widely applied to study adsorption (Cracknell et al 1993;Do and Do 2004;Cruz and Müller 2009a), diffusion (Cruz and Müller 2009b;Liu et al 2010) and even chemical reactions (Turner et al 2001;Santiso et al 2005;Lísal et al 2006) in idealized models of nanoporous carbons that consist of regularly-shaped, isolated pores. The challenge in extending these methods to study confinement effects in DNCs has been the lack of realistic structural models for these materials with features such as variable pore sizes and morphologies, chemical and structural surface heterogeneities and pore-pore connectivity.…”

Confinement effects on chemical reactions—Toward an integrated rational catalyst design

“…The latter is usually considered to be the actual catalytic effect, and it is the one that has the most obvious www.elsevier.com/locate/apsusc Applied Surface Science 253 (2007) [5570][5571][5572][5573][5574][5575][5576][5577][5578][5579] influence on the reaction rates, as it alters the reaction mechanism. However, the first and second type of effects can also have a strong influence on both the rates and equilibrium yields, as has been shown in several recent theoretical calculations [2][3][4][5][6][7][8][9][10][11] and experimental studies [12][13][14].…”

“…More details about these calculations can be found in Refs. [1,5,6]. The reaction pathways for the unimolecular decomposition of formaldehyde and the dissociation of water both in the gas phase and in confinement were obtained using the Nudged Elastic Band (NEB) method [31,32] with the climbing image modification [33] to obtain the structure of the transition states.…”

Isomerization kinetics of small hydrocarbons in confinement

“…The latter effect is the one most often studied, as it has the most patent influence on reaction rates. The other two effects, however, can have a significant impact on the rates and equilibrium yields of many chemical reactions, as discussed in several recent experimental (Byl et al 2003;Kaneko et al 1989;Imai et al 1991) and theoretical (Lisal et al 2006;Travis and Searles 2006;Halls and Schlegel 2002;Santiso et al 2005aSantiso et al , 2005bSantiso et al , 2006Santiso et al , 2007aSantiso et al , 2007bTurner and Gubbins 2003;Turner et al 2001aTurner et al , 2001bTurner et al , 2002 studies.…”

“…Our recent work has been focused on understanding the relative impact of the different effects mentioned above on reactions happening within graphitic carbon pores and nanostructures (Santiso et al 2005a(Santiso et al , 2005b(Santiso et al , 2006(Santiso et al , 2007a(Santiso et al , 2007bKostov et al 2005). Our choice of carbon as the confining material is due to several reasons: (1) A detailed study of chemical reactions often requires the use of ab initio methods, since reactions involve changes in the electronic states of the atoms involved.…”