Naoto Kamiuchi

In situ time-resolved XAFS study on the structural transformation and phase separation of Pt3Sn and PtSn alloy nanoparticles on carbon in the oxidation process

The dynamic behavior and kinetics of the structural transformation of supported bimetallic nanoparticle catalysts with synergistic functions in the oxidation process are fundamental issues to understand their unique catalytic properties as well as to regulate the catalytic capability of alloy nanoparticles. The phase separation and structural transformation of Pt(3)Sn/C and PtSn/C catalysts during the oxidation process were characterized by in situ time-resolved energy-dispersive XAFS (DXAFS) and quick XAFS (QXAFS) techniques, which are element-selective spectroscopies, at the Pt L(III)-edge and the Sn K-edge. The time-resolved XAFS techniques provided the kinetics of the change in structures and oxidation states of the bimetallic nanoparticles on carbon surfaces. The kinetic parameters and mechanisms for the oxidation of the Pt(3)Sn/C and PtSn/C catalysts were determined by time-resolved XAFS techniques. The oxidation of Pt to PtO in Pt(3)Sn/C proceeded via two successive processes, while the oxidation of Sn to SnO(2) in Pt(3)Sn/C proceeded as a one step process. The rate constant for the fast Pt oxidation, which was completed in 3 s at 573 K, was the same as that for the Sn oxidation, and the following slow Pt oxidation rate was one fifth of that for the first Pt oxidation process. The rate constant and activation energy for the Sn oxidation in PtSn/C were similar to those for the Sn oxidation in Pt(3)Sn/C. In the PtSn/C, however, it was hard for Pt oxidation to PtO to proceed at 573 K, where Pt oxidation was strongly affected by the quantity of Sn in the alloy nanoparticles due to swift segregation of SnO(2) nanoparticles/layers on the Pt nanoparticles. The mechanisms for the phase separation and structure transformation in the Pt(3)Sn/C and PtSn/C catalysts are also discussed on the basis of the structural kinetics of the catalysts themselves determined by the in situ time-resolved DXAFS and QXAFS.

Electrochemical CO Oxidation and Microstructure in Pt / Co3O4-Based Catalysts

The metal-support interaction in a platinum catalyst supported on cobalt oxide (Pt/Co 3 O 4 ) was investigated. In the as-calcined catalysts prepared by the impregnation method, platinum particles were highly dispersed on the surface of cobalt oxide with the strong interaction. The as-calcined catalysts were sensitive to the reduction treatment. After the pretreatment with hydrogen, the formation of the intermetallic compound of Pt 3 Co was observed, accompanied with a significant change in the surface composition and microstructure. Furthermore, the reduced surface species were readily oxidized after exposure to an oxidizing atmosphere. These behaviors were induced by the strong chemical interaction between platinum and cobalt oxide. As a model case study, the electrocatalytic activity for CO oxidation was studied for the applications to polymer electrolyte fuel cells.

Catalytic Combustion of Methane

The combustion of methane has been investigated for production of heat and for removal of unburnt fuel. Achievement of complete methane oxidation at lower temperatures has been desired in every application. In this chapter, studies for methane combustion over catalyst are summarized from a perspective of catalyst materials. The development of catalysts with high activity at low temperatures and long-term durability under reaction conditions is required. Therefore, this chapter deals with the studies on low-temperature catalytic combustion of methane, while the hexaaluminate-related compounds for high-temperature combustion are described. In the case of low-temperature combustion, a large number of previous researches are classified into four kinds of catalysts: Pd, Pt, CeO2–ZrO2 mixed oxide, and perovskite-type oxide. The catalytic activities, durabilities, reaction mechanism, and degradation phenomena, the influence of support material, the effect of addition of other components, and so on are discussed.