Influence of Step-Edge vs Terrace Sites on Temperature-Dependent C2H2 Hydrogenation with Ag-Doped Pt Nanoparticles

Abstract

Ag-doped Pt nanoparticles (NP) were tested for continuous-flow C2H2 hydrogenation reactivity and CO adsorption–desorption from 100 to 300 °C to investigate how submonolayer levels of an insoluble metal dopant can distribute on steps and terraces of a NP surface and modify reactivity. High Ag coverage (0.5 monolayer, ML) on Pt promoted selective hydrogenation of C2H2 at T < 200 °C; at higher temperatures, both low (0.06 ML) and high (0.5 ML) Ag coverages were seen to increase selective C2H4 formation. Ag incorporation onto Pt step and terrace sites, and resultant temperature-dependent desorption behavior, were probed using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) with CO. At low coverage, Ag appeared to occupy Pt step sites; for higher coverage, Ag occupied both step and terrace sites, which lowered the CO desorption temperature. Highly correlated reactivity and DRIFTS data show the importance of step site blocking and desorption from Pt during selective C2H2 hydrogenation. Multiple reaction cycles from 100 to 300 to 100 °C demonstrate how immiscible metal dopants can preferentially modify nanoparticle surface compositions and promote active, selective, and stable catalysts over large temperature operating windows.