Catalytic Deactivation and Regeneration of Nickel Microparticles in a Home‐Built Microchannel‐Coupled Millireactor: Substrate Specificity and Multiphase Flow Dependency

Substrate‐assisted product desorption often proposed in heterogeneous catalysis (nanozymes) denounces the catalytic deactivation of these catalysts. On the contrary, the catalytic deactivation of rigid heterogeneous catalyst becomes noticeable in a continuous flow reactor. Surprisingly, it has been addressed inadequately and in an isolated manner. In this study, we have developed a cost‐effective non‐lithographic method for the fabrication of a PDMS‐based microchannel‐coupled‐millreactor. Immobilized nickel particles are resistant to leaching in the flow process. During continuous operation, millireactors show a strong catalytic activity for reduction of resazurin and p‐nitrophenol with a conversion rate of almost 100 %. Catalytic poisoning is ubiquitous and gets gradually prominent whereas complete catalytic deactivation of magnetic Ni‐microparticles is found to be an instantaneous process. Relatively large‐sized resorufin binds predominantly to the surface and thereby blocks the access of the substrate to the Ni‐particles. The dissociations of product molecules ‐ resorufin and p‐aminophenol are the rate‐limiting steps that caused the abrupt deactivation of Ni‐microparticle. The kinetic mechanism of heterogeneous derived from the Langmuir‐Hinshelwood mechanism satisfactorily explains the catalytic poisoning and deactivation of nickel microparticles. This study sheds light on the intricacies of catalytic activity and poisoning of magnetic nickel microparticles. A microchannel‐coupled‐millireactor has been fabricated to eradicate the catalyst leaching frequently present in flow chemistry studies.