Genesis and Evolution of Surface Species during Pt Atomic Layer Deposition on Oxide Supports Characterized by in Situ XAFS Analysis and Water-Gas Shift Reaction

Platinum atomic layer deposition (ALD) using MeCpPtMe3 was employed to prepare high loadings of uniform-sized, 1-2 nm Pt nanoparticles on high surface area Al2O3, TiO2, and SrTiO3 supports. X-ray absorption fine structure was utilized to monitor the changes in the Pt species during each step of the synthesis. The temperature, precursor exposure time, treatment gas, and number of ALD cycles were found to affect the Pt particle size and density. Lower-temperature MeCpPtMe3 adsorption yielded smaller particles due to reduced thermal decomposition. A 300 degrees C air treatment of the adsorbed MeCpPtMe3 leads to PtO. In subsequent ALD cycles, the MeCpPtMe3 reduces the PtO to metallic Pt in the ratio of one precursor molecule per PtO. A 200 degrees C H-2 treatment of the adsorbed MeCpPtMe3 leads to the formation of 1-2 nm, metallic Pt nanoparticles. During subsequent ALD cycles, MeCpPtMe3 adsorbs on the support, which, upon reduction, yields additional Pt nanoparticles with a minimal increase in size of the previously formed nanoparticles. The catalysts produced by ALD had identical water-gas shift reaction rates and reaction kinetics to those of Pt catalysts prepared by standard solution methods. ALD synthesis of catalytic nanoparticles is an attractive method for preparing novel model and practical catalysts.