The Role of the Nanoscale in Nanocatalysis

There are many cases where catalytic reactions occur efficiently only if the catalyst is a nanoparticle below a critical diameter. In other cases, size does not matter and, in some cases, nanoparticles smaller than a critical diameter exhibit decreased catalytic activity. This talk will cover three examples in which results of first-principles quantum mechanical calculations are used to elucidate the specific nanoscale features that are responsible for the enhanced catalytic reaction: Fixation of CO2 by CdSe nanoparticles smaller than ~5 nm (CdS works independent of size, including in bulk form); oxidation of CO by gold nanoparticles (gold becomes highly reactive for nanoparticles smaller than ~5 nm, but Pt becomes less reactive at such dimensions); and oxidative dehydrogenation of saturated hydrocarbons by CrOx nanoparticles (formation of Cr2O3 inhibits catalysis). Z-contrast atomic-resolution imaging and electron-energy-loss spectroscopy by S. J. Pennycook's group are used to highlight features of the first two examples and are combined with theory in the third example as conclusive evidence for the role of the nanoscale.