A bimetallic PdCu–Fe3O4 catalyst with an optimal d-band centre for selective N-methylation of aromatic amines with methanol

Abstract

Catalytic methylation utilising methanol as a sustainable C1 building block and hydrogen source continues to attract attention due to its atom-economical, cost-effective, and simple one-pot method. So far, research on heterogeneous systems has been limited to noble monometallic catalysts such as Ir, Pd, and Pt. A bimetallic catalyst containing a non-noble metal can be an ideal tool to modulate the reactivity and economic feasibility. Reported herein is a bimetallic PdCu–Fe₃O₄ nanoparticle (NP) catalyst for the selective N-methylation of aniline with methanol as a carbon source in the presence of K₂CO₃via a “hydrogen-borrowing strategy”. The PdCu alloy showed synergistic catalytic activity, superior to monometallic Pd and Cu catalysts. The best catalytic activity for N-methylation of aniline was achieved when the Pd/Cu metal ratio was 1 : 0.6 and on an Fe₃O₄ support. To explain the details of the synergistic effect according to the metal composition, we investigated the electronic properties of the catalytic surface of Pd_xCu_y on Fe₃O₄ NPs through the density functional theory (DFT). DFT calculation and kinetic studies successfully delineated the catalytic activities of N-methylation depending on varying Pd/Cu ratios. Highly efficient monomethylation of a wide range of aromatic amines was possible using the optimally chosen Pd₁Cu_0.6 catalyst. Furthermore, the catalyst could be recycled and reused owing to the magnetic nature of the Fe₃O₄ support.