High-performance monoliths in heterogeneous catalysis with single-phase liquid flow†
Hierarchical, macro-mesoporous silica monoliths with domain sizes (sum of mean macropore size and skeleton thickness) of ∼1 μm are highly efficient supports in heterogeneous catalysis with single-phase liquid flow. Their unprecedented performance regarding low backmixing, the elimination of internal and external diffusive transport limitations, as well as the simultaneous realization of a large (internal and external) surface area of the monolith skeleton allow reactor operation under exclusive reaction control. For experimental characterization, the Knoevenagel condensation was employed with an aminopropylated silica monolith integrated into an on-line coupled, high-pressure reaction–analysis system. It allows precise, fully automated adjustment and control of all relevant reaction parameters and promises a boost in the rapid, reproducible determination of the intrinsic reaction kinetics, in general. Hydrodynamic and reaction kinetic parameters identify extreme plug-flow conditions with this high-surface-area, compact type of microreactor and quasi-homogeneous operation in continuous-flow mode.