Engineering Tandem Catalysis for Direct CO₂-Enabled N-Methylaniline Synthesis With a Fixed-Bed Flow Reaction Process

Integrated tandem catalysis within a continuous fixed-bed reactor represents a promising yet underexplored strategy for process intensification in advanced amine synthesis via CO₂ utilization. Here, we demonstrate the direct conversion of nitrobenzene and CO₂ with H₂ into N-methylaniline in a continuous fixed-bed reactor over a CuZnZrO_x catalyst, achieving 99% conversion and 95% selectivity with stable operation exceeding 100 h. Mechanistic studies identify Cu-ZnO interfaces in the form of Cu⁺-O_v-Zn^2-δ serve as active sites for CO₂ hydrogenation to key intermediate formaldehyde (CH₂O*), which couples the CO₂ hydrogenation and methylation of aniline derived from nitrobenzene hydrogenation in kinetics. The tandem configuration provides intrinsic heat-management benefits, recovering 0.341 kg of steam (1.5 MPa, 201°C) per mole of nitrobenzene-far superior to the methanol consumption characteristic of the conventional three-step route. This work highlights tandem catalysis as an effective reactor-level strategy that bridges atomic-scale active-site engineering with kinetic synergies, advancing continuous-flow CO₂ valorization toward higher-value amines.