One‐Click Flow Transition Enables MnO ₂ Crystal Phase Engineering for Enhanced Catalytic Oxidation of HMF to DFF

ABSTRACT Traditional microreactors are limited by fixed flow regimes, which restrict their multifunctional applications in both catalyst synthesis and the production of high value‐added chemicals. Here, we introduce a click‐activated microreactor that enables a rapid and facile transition between laminar and turbulent flow modes through a switch‐like mechanism. In the context of laminar flow conditions, the reactor successfully synthesizes α‐MnO 2 catalysts, characterized by their substantial surface area and abundance of oxygen vacancies, with a concurrent reduction in energy consumption of 68.6%. Conversely, when switched to turbulent mode via a “click‐switch” operation, the reactor enhances mass transfer, enabling the efficient selective oxidation of 5‑hydroxymethylfurfural (HMF) to 2,5‑diformylfuran (DFF), achieving a DFF yield of up to 23.8 mmol/g/h, which was beyond the yield limit of conventional thermocatalytic oxidation. This innovative design overcomes the conventional “Single‐Purpose Reactor” paradigm, providing a versatile platform for integrated chemical manufacturing.