Dendrimer-derived bimetallic platinum-copper catalysts: Synthesis, characterization, and evaluation

In this work, we aim to develop nanostructured supported bimetallic Pt-Cu catalysts using poly (amido amine) dendrimer metal nanocomposites (DMNs). Conventional approaches for catalyst preparation by deposition of metal salt precursors typically result in the formation of metal particles with large sizes and broad size distributions. In contrast, catalysts prepared using DMNs as precursors show great potential for better control over particle formation and metal exposure on supports, allowing for more efficient use of noble metals.; The first part focuses on the synthesis of liquid phase Pt DMNs to understand the fundamentals of dendrimer-metal complexation and the possible mechanisms for the nanoparticle formation using dialysis, UV-Visible Spectroscopy (UV-VIS), Atomic Force Microscopy (AFM), High Resolution Transmission Electron Microscopy (HR-TEM) and Atomic Adsorption Spectroscopy (AA) techniques.; The second part investigates the formation of metal carbonyl species and nanoclusters in solution and on supports in the presence of dendrimer before and after H2 treatment using Attenuated Total Reflection Infrared Spectroscopy (ATR-IR), UV-VIS and HRTEM. These results suggest the formation of Chini-type Pt carbonyls and a possible core-shell structure for the bimetallic Pt-Cu nanoclusters with a Cu-enriched shell.; The third part considers the preparation of supported catalysts, including the deposition of DMNs onto mesoporous supports followed by dendrimer decomposition and catalyst activation. These were studied using transmission Fourier Transform IR (FT-IR), leading to the identification of an optimal treatment protocol for DD catalyst preparation that yielded the greatest exposure of the metal. Further Scanning-TEM (STEM) measurements reveal the formation of smaller particle sizes with narrower size distributions for the DD catalysts than their conventional counterparts. No obvious electronic modification between Cu and Pt in the bimetallic Pt-Cu catalysts was concluded from the isotope 12CO/ 13CO FTIR studies.; Finally, the catalytic activity and selectivity of a series of Pt-Cu catalysts with varying compositions prepared via dendrimer and conventional approaches were examined using ethane hydrogenolysis and hydrodechlorination of 1,2-dichloroethane reactions. The results of these experiments indicate that the activity and selectivity differ substantially with the metal compositions. The formation of a bifunctional Pt-Cu catalyst was observed for the hydrodechlorination reaction.