Gas‐solid catalytic reactions with an extendedDSMCmodel

Abstract

An algorithm of diffusive gas transport in porous solids based on random collisions of molecules (DSMC) is extended to include basic heterogeneous reaction mechanisms (adsorption, coadsorption, desorption, and reaction of gas species on the surface of the solid). With this model, we study the catalytic oxidation of CO inside highly porous nanoparticle layers in the transition regime using kinetic parameters from Pd(111) surfaces at ultra high vacuum conditions. Investigation of the reaction at different temperatures reveals a clear transition between a kinetic limit (low temperatures) and a diffusion limit (high temperatures). At high temperatures and under steady‐state conditions, the porous layer shows three distinct regions with different reaction rates (reactor poisoning, an effective reaction region, and a region with CO depletion), whose extends are determined by CO concentration and mass‐transport limitation. We expect that similar investigations help optimizing the structure of gas sensor elements based on nanoparticle layers fabricated with flame spray pyrolysis. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2092–2103, 2015

Computational optimization of catalyst distributions at the nano-scale

“…The governing processes in applications where the bounding geometry is of micro-or nanometer size typically span several orders of magnitude in spatial and temporal scales [10][11][12]. Consequently, there are many inherent difficulties involved in performing non-intrusive, non-destructive experimental investigations of the processes occurring on the smallest scales in such systems.…”

“…Furthermore, the DSMC method has the additional advantages of allowing treatment of inverse collisions and ternary chemical reactions, which becomes especially problematic in attempts at solving the Boltzmann equation directly [19]. The DSMC method is therefore well suited to describe reactive nanoscale systems [12,22]. It is, in fact, the most widely used numerical algorithm in kinetic theory [23,24] and has been experimentally validated for a great number of applications, including nonequilibrium gas flows (e.g.…”

“…shocks) [24], rarefied gas dynamics (e.g. velocity, temperature and concentration slip) [25], near-vacuum flow of high-temperature gas at supersonic speeds [26], low-pressure deposition processes [27] and temperature-programmed desorption in heterogeneous catalysis [12].…”

Simulation of atomic layer deposition on nanoparticle agglomerates

“…[22][23][24][25] However, some of these studies only focus on the molecular diffusion regime (Kn ( 1), [22][23][24] whereas others do not address self-limiting reactions in fractal geometries. [22][23][24][25] On the other hand, self-limiting ALD reactions and rarefied gas diffusion have been studied inside very simple pore geometries such as narrow trenches and cylindrical pores. In the present paper, we develop and demonstrate a computational model for the rarefied reaction-diffusion problem in ALD coating of agglomerated nanoparticles which, in deviation from all previous studies, combines models for (1) a fully resolved fractal agglomerate; (2) self-limiting half cycle ALD reactions; and (3) diffusion in the transition regime.…”

On governing equations and closure relations for the multiscale modeling of concentration polarization in solid-oxide fuel cells: mass transfer and concentration-induced voltage losses.

“…Thus, at steady state, values of surface coverage must be such that the net production rate due to chemistry is zero for every surface species (i.e., ̇ , = 0 when is a surface species). Evidently, this is a corollary assumption within the mean-field approximation, but it does not mean it is a good approximation for the real problem being solved [ 296,132,55] .…”