Study on the Synthesis of Ni–Al2O3 Catalysts via Topological Transformation and Their Structure–Activity Relationship

Nitrohydrogenation is a common process in industry. Here, a highly efficient Ni–Al₂O₃ catalyst derived from Ni–Al layered double hydroxide synthesized in a rotating packed bed (RPB) was first applied in the hydrogenation of 3,4-dichloronitrobenzene (3,4-DCNB) to 3,4-dichloroaniline (3,4-DCA). Leveraging the enhanced mass transfer and micromixing performances by applying RPB, the phenomenon of particle agglomeration and uneven size distribution occurring during catalyst synthesis has been effectively mitigated. The effects of Ni mass fraction, reduction temperature, and time on the physical properties and catalytic performance of the catalyst were investigated. Results showed that the Ni–Al₂O₃ catalysts prepared under optimal conditions (Ni mass fraction of 78 wt %, reduction temperature of 500 °C, reduction time of 4 h) have small Ni particle sizes and high dispersion. When applied to 3,4-DCNB hydrogenation under optimized conditions (65 °C, 1.5 MPa of H₂, 60 min, catalyst loading 12.55 mg/g), both conversion and 3,4-DCA selectivity approached 100%. Furthermore, the kinetic study on the 3,4-DCNB hydrogenation revealed that the reaction has an activation energy of 39.91 kJ/mol and a pre-exponential factor of 2.54 × 10⁴ min^–1. This finding presents an innovative approach for preparing a highly efficient Ni-based catalyst for the hydrogenation of 3,4-DCNB to 3,4-DCA.