Carbon nanotube as catalyst support for monometallic and bimetallic Nanostructures: Unexpectedly high efficiency of supported bimetallic bare metals

Bimetallic catalysts have emerged as a pivotal innovation in catalysis, offering enhanced activity, selectivity, and stability compared to their monometallic counterparts. Developing simple methods to prepare efficient bimetallic catalysts is currently a major challenge for scientists. Comparison of the catalytic activity of heterogenized monometallic and bimetallic nanocatalysts prepared by immobilizing metalloporphyrins (iron porphyrin and manganese porphyrin) or bare metals (iron chloride and manganese acetate) onto the surface of functionalized multi-walled carbon nanotubes (MWCNT-COOHs) is reported. Supported nanocatalysts are characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), atomic absorption spectroscopy (AAS), and Fourier-transform infrared spectroscopy (FT-IR). The catalytic study focused on the aerobic oxidation of olefins under mild conditions. The role of porphyrin ligand on the catalytic efficiency of the prepared bimetallic heterogenized nanocatalysts was compared with metal salts as well as monometallic catalysts, and the results show higher catalytic activity of bimetallic nanostructures compared to the monometallic catalysts. Although among monometallic nanohybrids, supported metalloporphyrins exhibited much higher efficiency than immobilized bare-metals; unexpectedly, the supported bare-metals show higher (or at least equal) catalytic activity compared to the porphyrin-based nanocatalyst in the case of bimetallic nanostructures. All the prepared nanocatalysts were reusable for at least four catalytic cycles.