Hierarchical silica monoliths with submicron macropores as continuous-flow microreactors for reaction kinetic and mechanistic studies in heterogeneous catalysis

Abstract

The proposed scheme enables academic laboratories to prepare hierarchical silica monoliths as continuous-flow microreactors for kinetic studies in heterogeneous catalysis.

Kinetics Studies on a Multicomponent Knoevenagel−Michael Domino Reaction by an Automated Flow Reactor

“…To address the intrinsic kinetics of a heterogeneous catalytic reaction, we introduced benchmarked, commercially available, hierarchical (macro–mesoporous) silica‐based monoliths as high‐performance catalyst supports . Their use allows to shift the solid–liquid operation from diffusion‐limited to reaction‐controlled conditions by combining unhindered access to a large mesopore surface area (∼250 m 2 g −1 ) inside the monolith skeleton with hydrodynamic plug‐flow behavior in the macropore space of the microreactor.…”

“…[6,7] We have recently presented an automated flow system that relies on an efficient combination of a continuous-flow micro-reactor and an online coupled HPLC analysis system to rapidly collect data on heterogeneous catalytic reactions. [8,9] However, we did not focus on optimization, but on investigating the selected reaction process in detail to derive mechanistic conclusions from the reaction kinetics (rate constants, reaction orders, and activation energies) and to characterize the catalyst support (e.g., transport versus reaction limitations, catalyst effectiveness). Based on our previous reports, this work presents a follow-up study where the derived kinetic information is directly implemented into process optimization.…”

“…To address the intrinsic kinetics of a heterogeneous catalytic reaction, we introduced benchmarked, commercially available, hierarchical (macro-mesoporous) silica-based monoliths as high-performance catalyst supports. [8][9][10] Their use allows to shift the solid-liquid operation from diffusion-limited to reactioncontrolled conditions by combining unhindered access to a large mesopore surface area (~250 m 2 g À 1 ) inside the monolith skeleton with hydrodynamic plug-flow behavior in the macropore space of the microreactor. Although mesopore space and macropore space are microscopically disordered, their threedimensional physical reconstruction combined with morphological analysis as well as fluid flow and mass transport simulations yielded quantitative morphology-transport relationships for these materials.…”

Influence of Pore Space Hierarchy on the Efficiency of an Acetylcholinesterase‐Based Support for Biosensorics

“…This operation will also allow to move from the apparent to the intrinsic reaction kinetics (as transport limitations are removed) and access parameters like the reaction order, rate constants, and activation energies. [ 30 ] On the other hand, with an adequate enzyme loading in the macropores, a purely macroporous material may suffice as functional component in biosensor applications and at the same time take full advantage of the fast mass transfer due to forced advection in a flow‐through design. If required, the surface area (and thus, enzyme loading) of the macropores can be increased to some extent by reducing the macropore size and increasing the macroporosity.…”

Silica Monolith for the Removal of Pollutants from Gas and Aqueous Phases

“…Nakanishi and coworkers synthesized silica gel monoliths with macro-mesoporous hierarchical structure via a spontaneous sol–gel process from silicon alkoxide using a structure-directing agent and a micellar swelling agent [ 5 ]. Kohns et al obtained silica monoliths with submicrometric macropores, introducing urea as an agent to control the size of macropores, mesopores and skeleton thickness [ 6 ]. Fotoohi et al prepared mesoporous silica monoliths using a simple one-pot sol–gel synthesis with subsequent atmospheric evaporation [ 1 ].…”