Alumina-grafted macro-/mesoporous silica monoliths as continuous flow microreactors for the Diels–Alder reaction

Bimodal macro-/mesoporous silica monoliths (6 mm diameter, 1–4 cm length) were functionalized with aluminum oxide allowing the preparation of a new solid Lewis acid catalyst named Al-MonoSil. Al-MonoSil was used as catalytic microreactor for the in-flow implementation of the Diels–Alder reaction. Due to the interconnected and homogeneous system of macropores of 5 μm within the monolith, the Al-MonoSil shows high conversion and productivity in continuous flow without pressure drop. The external mass transfer limitations and the productivity were controlled by adjusting monolith length and flow rate. Al-MonoSil is a stable microreactor for long time productivity for Lewis acid–catalyzed reactions.