Microstructure-based design and synthesis of surface-tailored bimetallic catalysts

The catalytic performance of supported bimetallic nanoparticles depends on their surface microstructure. Achieving an ideal surface microstructure results in a bimetallic catalyst that has enhanced activity and/or selectivity compared its monometallic components. This is commonly known as synergy. To identify a synergistic surface microstructure for the reduction of NO with H2, Pt-Rh/gamma-Al2O3 catalysts were prepared, evaluated for their catalytic performance, and characterized with in-situ FTIR spectroscopy and aberration-corrected scanning transmission electron microscopy (STEM). The microstructure-based design and synthesis method was developed to form and surface-tailor populations supported bimetallic nanoparticles using time-temperature atmosphere treatments. This method was applied to replace Rh with Co and Ni to produce new, synergistic Pt-Co and Pt-Ni catalysts for the reduction of NO with H2. Synergistic Pt-Co and Pt-Ni catalysts were prepared by coimpregnation, sequential impregnation, and sequential impregnation with an intermediate calcination step each followed by a defined series of thermal treatments. In-situ FTIR spectroscopy and aberration-corrected STEM were used to show that the catalysts exhibiting optimal synergistic performance had the desired surface microstructure. The microstructure-based design and synthesis method allowed the bulk composition and preparation procedure that resulted in synergy to be predicted, and time-temperature-atmosphere treatments were successfully used to control the surface microstructure of supported bimetallic nanoparticles.