Review on the Macro-Transport Processes Theory for Irregular Pores able to Perform Catalytic Reactions

Abstract

We review and generalize a recent theoretical framework that provides a sound physicochemical basis to describe how volume and surface diffusion are affected by adsorption and desorption processes, as well as by catalytic conversion within the space defined by the irregular geometry of the pores in a material. The theory is based on two single-dimensional mass conservation equations for irregular domains deduced for the volumetric (bulk) and surface mass concentrations. It offers a powerful tool for analyzing and modeling mass transport across porous media like zeolites or artificially build materials, since it establishes how the microscopic quantities that refer to the internal details of the geometry, the flow and the interactions within the irregular pore can be translated into macroscopic variables that are currently measured in experiments. The use of the theory in mass uptake experiments is explained in terms of breakthrough curves and effective mass diffusion coefficients which are explicitly related to the internal geometry of the pores.

Connecting theory and simulation with experiment for the study of diffusion in nanoporous solids

“…This literally means "shapeless" in Greek. Nevertheless, at larger scales, there are often various degrees of order that allow us to describe amorphous porous materials-from the structure of the pore walls to the organization of the pores or the particles that constitute the materials [289][290][291][292][293][294][295][296][297][298][299][300][301][302][303][304]. Fully atomistic descriptions are not often used for amorphous mesoporous materials, due to the absence of crystalline periodicity and, thus, the very large number of atoms required to represent the material.…”

“…The mesopores are the negative space, the voids in between these building blocks, which are typically simple shapes, like spheres, platelets or fibers, which do or do not overlap. This representation attempts to conform to the packing, aggregation, agglomeration, fusing or sintering of particles by which the porous material is synthesized experimentally [292][293][294][295][296][297][298][299][300][301][306][307][308][309][310][311][312][313][314][315][316][317][318][319].…”

Entropic Effects of Interacting Particles Diffusing on Spherical Surfaces

“…Using this tool, we can identify how the change of perspective, confinement and crowding are incorporated in an effective diffusion coefficient that takes into account the entropic confinement and the anomalous diffusion. The model used here was derived in the context of mesoscopic non-equilibrium thermodynamics (MNET) and has been widely used in order to obtain kinetic equations for transport phenomena, like diffusion-adsorption processes, anomalous diffusion, activated processes, diffusion in pores, and diffusion in the presence of entropic barriers [35][36][37][38][39]. In particular for our purposes, MNET has been successful in describing diffusion on other confined systems [38,[40][41][42].…”

Ultrathin nanoporous metal electrodes facilitate high proton conduction for low-Pt PEMFCs

“…Dealloying is known as an efficient fabrication technique to various functional nanoporous metals (NPMs), albeit in less well-defined structural periodicity. Because of their ease in the control of composition, pore dimension, and porosity, there are growing interests in developing nanostructured NPMs for PEMFC-associated applications [20][21][22][23][24][25]. While NPMs possess natural advantages of being highly conductive for electron transfer and bicontinuously porous for mass transportation, the construction of efficient proton transfer channels can be simplified or even ignored by concentrating all catalytic sites into an ultrathin CLs, if its thickness is much smaller than the Debye length of proton transfer (~ 1 μm) [26,27].…”