Hydroxylation of Platinum Surface Oxides Induced by Water Vapor

With its high stability and well-tuned binding strength for adsorbates, platinum is an excellent catalyst for a wide range of reactions. In applications like car exhaust purification, the oxidation of hydrocarbons, and fuel cells, platinum is exposed to highly oxidizing conditions, which often leads to the formation of surface oxides. To reveal the structure of these surface oxides, the oxidation of Pt in O2 has been widely studied. However, in most applications, H2O is also an important or even dominant part of the reaction mixture. Here, we investigate the interaction of H2O with Pt surface oxides using near-ambient-pressure X-ray photoelectron spectroscopy. We find that reversible hydroxylation readily occurs in H2O/O2 mixtures. Using time-resolved measurements, we show that O–OH exchange occurs on a time scale of seconds

Structural model for transient Pt oxidation during fuel cell start-up using electrochemical X-ray photoelectron spectroscopy

Catalysis and Surface Chemistr

Surface and structural properties of Pt/CeO2 catalyst under preferential CO oxidation in hydrogen (PROX)

Preferential oxidation of CO in the presence of excess hydrogen was studied on Pt/CeO2 with 5% metal loading. Catalytic data were similar to those observed on 1% Pt/CeO2 earlier [Wootsch et al. J. Catal. 225 (2004) 259]. The optimum temperature region is T373 K; conversion and selectivity of CO oxidation strongly decreased at higher temperatures. High-pressure XPS indicated CO adsorbed on platinum particles and significant amount of water on the ceria surface. The top-most ceria surface re-oxidized as small amount of oxygen (3%) was introduced into the H2/CO feed. Despite this surface re-oxidation, high-resolution TEM after reaction indicated oxygen deficient ceria bulk structure, in which the defects formed a super-cell, with CeO1.695 structure. The defective ceria is suggested to play an important role stabilizing the hydrogen bonded surface water, which (i) suppresses further hydrogen oxidation and (ii) reacts at the metal/support interface with linearly adsorbed CO in a low temperature water-gas-shift type reaction to produce CO2