Integrated Stefan–Maxwell, Mean Field, and Single-Event Microkinetic Methodology for Simultaneous Diffusion and Reaction inside Microporous Materials

Abstract

The assessment of intrinsic reaction kinetics in the presence of diffusion limitations within a porous material remains one of the key challenges within the field of catalysis. The model-guided design of medium-pore zeolite catalysts which typically give rise to mass transport limitations would offer a feasible alternative to conventional trial-and-error procedures. Intracrystalline diffusion limitations during n-hexane hydroconversion on Pt/H-ZSM5 were assessed using an integrated Stefan–Maxwell, mean field, and Single-Event MicroKinetic (SEMK) methodology. The former theory quantifies multicomponent diffusion through a microporous substituent from pure component properties, while framework parameters inherent to the ZSM5 topology are incorporated via a mean field approximation. The complex chemistry involved in n-hexane hydroconversion was described by an SEMK model which is based upon the reaction family concept. Model regression against experimental data resulted in excellent agreement between the model and experiment. In addition, the estimated values for, among others, the component diffusion coefficients were physically meaningful. A sensitivity analysis of the catalyst descriptors demonstrated that especially the total acid site concentration and the crystallite geometry impact the catalyst activity and product distribution, establishing them as critical catalyst design parameters.

Impact of the Spatial Organization of Bifunctional Metal–Zeolite Catalysts on the Hydroisomerization of Light Alkanes

“…However,i ts hould be noted that the iso-butane-to-n-butane ratio over Pt-H-ZSM-5/Al 2 O 3 is significantly lower than over Pt-Al 2 O 3 /H-ZSM-5 ( Figure S18 c), indicating that the energetically unfavorable secondary-to-secondary cracking reactions ( Figure S9 b) tend to take place more extensively inside the H-ZSM-5 micropores.T herefore,t he platinum location still has an influence on product selectivities for H-ZSM-5 with a3 Dp ore structure.V andegehuchte et al reported that in n-hexane hydroconversion, branched isomers would suffer from strong intracrystalline diffusion limitations in H-ZSM-5 crystallites, but the limitations could be mitigated by decreasing the size of the H-ZSM-5 crystals. [29] In fact, decreasing the effective crystal sizes of zeolites and building hierarchical structures has often been employed to increase the isomer selectivity over H-MOR and H-beta catalysts without considering the platinum location. [30] We think that the detrimental effect on product selectivity imposed by placing platinum particles inside the zeolite crystals in hydroisomerization reactions is generalizable for zeolites with 1D pore systems and 3D zeolites with long diffusion channels.…”

Information-Driven Catalyst Design Based on High-Throughput Intrinsic Kinetics

“…By implementation of these models in an adequate reactor model accounting for transport phenomena [28,29], specific reactor configurations such as a riser reactor [30] or a slurry-bubble column [31] and catalyst deactivation [32], reliable, industrially relevant simulations can be made with these models. This also comprises the extension from model compound behavior, as typically measured at the laboratory scale, to realistic feeds [25,33].…”

Bifurcation and Pattern Symmetry Selection in Reaction-Diffusion Systems with Kinetic Anisotropy

“…Ordering and self-organization in reaction-diffusion systems are of great significance in determining the ordered patterns in chemistry, physics and biology 1–7 . Pioneered by Alan Turing, the mathematical description of reaction-diffusion systems are well established, and it has been recognized that the Turing instability originates from the reaction kinetics and the ordering is dictated by the breaking of continuous translational symmetry (i.e., the loss of homogeneity) 8,9 .…”