This paper explores how the visible features of segmented flow, under reaction conditions, can be used in lab-scale multiphase heterogeneous catalysis. Continuous-flow microreactors are now routinely used in bench-scale synthesis and optimization applications, owing to their small reactant inventory, negligible heat effects at small scales, and fast mixing. However, miniaturizing multiphase heterogeneous catalysis on chips is considerably more difficult than homogeneous liquid phase chemistry. Several applications of gas–liquid and gas–liquid–solid reactions have been reported. In these continuous- flow devices, the catalyst was immobilized on the wall of the channel or incorporated as powder. A powder packed-bed gas–liquid microreactor may appear ideal for off-the-shelf catalysts, but in practice such reactors are cumbersome: critical packing parameters vary from one instance to the next and channeling and flow hysteresis abound, as we have recently visualized. For immobilized catalysts, Kobayashi et al. have advocated creating a thin film of liquid on the walls, sheared along by a fast-flowing gas stream. A drawback of this system is that it is hard to control or visualize how long the reactants are in contact with the catalyst, because both phases each move at their own velocity. Especially for more complex pathways, the spread in residence time reduces yields.
The article is published online in the journal ChemCatChem and is free to access.