From First Principles Design to Realization of Bimetallic Catalysts for Ultrahigh Selectivity - Final Project Report

Abstract

(A) Synthesis, Characterization, and Fundamental Properties of Bimetallic DENs. AuAg alloy and core/shell bimetallic DENs were synthesized and characterized. Selective extraction was used as a structural characterization tool for these bimetallic nanoparticles. This is significant because there are few easily accessible methods for structure elucidation of bimetallic nanoparticles in this size regime. As a first step towards the synthesis of catalytically active, bimetallic heterogeneous materials we reported the incorporation of Au and Pd monometallic DENs and AuPd bimetallic DENs into amorphous titania networks. The compositional fidelity of the original DENs, and to some extent their size, is retained following dendrimer removal. Gas-phase catalytic activity for CO oxidation is higher for the bimetallic catalysts than for the corresponding Pd-only and Au-only monometallics. (B) Electrocatalysts based on dendrimer-encapsulated nanoparticles. Platinum dendrimer-encapsulated nanoparticles (DENs) were prepared within fourth-generation, hydroxyl-terminated, poly(amidoamine) dendrimers and immobilized on glassy carbon electrodes using an electrochemical immobilization strategy. X-ray photoelectron spectroscopy, electron microscopy, and electrochemical experiments confirm that the Pt DENs are about 1.4 nm in diameter and that they remain within the dendrimer following surface immobilization. The resulting Pt DEN films were electrocatalytically active for the oxygen reduction reaction (ORR). The films are also robust, surviving up to 50 consecutive cyclic voltammograms and sonication. Monometallic Pd DENs were also prepared and found to have little catalytic activity for the ORR. However, PtPd bimetallic DENs had catalytic activity nearly identical to that found for Pt-only DENs. This indicates an overall catalytic enhancement for the bimetallic electrocatalysts.