Synthesis, performance, and application of bimetallic composite nanocatalysts: A novel highly efficient and recyclable PtNix nanoparticles supported on multi-walled carbon nanotubes for catalytic hydrogenation of unsaturated copolymers

The catalytic hydrogenation of polymers and copolymers is an efficient method to produce high value hydrogenated products. Here, we successfully synthesized monometallic (Pt/MWCNTs) and bimetallic (PtNi x /MWCNTs) composite nanocatalysts using a simple chemical reduction method for the selective hydrogenation of styrene-butadiene-styrene (SBS) copolymer. The bimetallic composite nanocatalysts with Pt-to-Ni ratios of 1:1, 1:2, 1:3, and 1:4 showed a higher catalytic activity compared with monometallic composite nanocatalysts. The crystal structure and elemental analysis of the synthesized nanocatalysts are characterized by XRD and XPS. The change of binding energy due to the transfer of valence electrons between Pt and Ni was verified via XPS analysis. The PtNi x nanoparticles were firmly anchored on the MWCNTs, as observed by TEM and HRTEM analysis. The nanocatalysts are also with a mesoporous, face-centered cubic structure and high thermal stability. As a result, the nanocatalysts showed excellent performance, stability, and recyclability towards the benzene rings and unsaturated double bonds hydrogenation in the SBS copolymer, implying that the bimetallic composite nanocatalysts have effectively eliminated diffusion limitations and enhanced SBS molecules accessibility to active sites. Simultaneously, GPC, FTIR, NMR, TG, and DSC analysis were used to characterize the SBS and its hydrogenated product (cyclic block copolymer). Thermogravimetric analysis proved that cyclic block copolymer possesses a higher heat resistance (426 °C) compared to SBS (416 °C).