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

摘要

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 K(2)CO(3)via 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 PdxCuy 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 Pd1Cu0.6 catalyst. Furthermore, the catalyst could be recycled and reused owing to the magnetic nature of the Fe3O4 support.