Diffusion Kinetics of Gold and Copper Atoms on Pristine and Reduced Rutile TiO₂ (110) Surfaces

Statistical mechanics and transition-state theory have been used to investigate the diffusion kinetics of gold and copper atoms on pristine and various reduced surfaces of rutile TiO₂ (110). A DFT+<i>U</i> approach has been employed to calculate potential energy maps and to evaluate the required diffusion activation barriers. The role of the support reducibility has been examined on the adsorption properties (optimal structures, energetics, and spin polarization) and diffusion kinetics, especially for the reduced support presenting a single subsurface oxygen vacancy. This approach has allowed us to demonstrate key discrepancies between Au and Cu atoms and to sketch out a comparative scenario for the early-stage nucleation of Au and Cu nanoparticles on the various surface states of TiO₂ (110)

Promoter Effect of Early Stage Grown Surface Oxides: A Near-Ambient-Pressure XPS Study of CO Oxidation on PtSn Bimetallics

The knowledge of the catalyst active phase on the atomic scale under realistic working conditions is the key for designing new and more efficient materials. In this context, the investigation of CO oxidation on the bimetallic Pt₃Sn­(111) surfaces by near-ambient-pressure X-ray photoelectron spectroscopy and density functional theory calculations illustrates how combining advanced methodologies allows the determination of the nature of the active phase. Starting from 300 K and 500 mTorr of oxygen, the progressive formation of surface oxides is observed with increasing temperature: SnO, PtO units first, and SnO₂, PtO₂ units afterward. For CO oxidation on the (2 × 2) surface, the activity gain is assigned to the build-up of ultrathin domains composed of SnO and SnO₂ units. The formation of these early stage surface oxides is entirely supported by a density functional theory analysis. More generally, this study demonstrates how the catalyst surface oxidation and transformation can be better controlled by a relevant choice of environmental conditions