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

Abstract

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.

Insight into the structure evolution and the associated catalytic behavior of highly dispersed Pt and PtSn catalysts supported on La2O2CO3 nanorods

“…Therefore, it is plausible that the heat-treatment in air can easily induce the phase segregation of PtSn alloys and further result into the loss of SnO x layers, assuming that a weak interaction between lanthanum and tin oxides. 43 Moreover, ICP-OES results in Table S2 † clearly indicate a decrease of Sn content (0.46 wt%) and Sn/Pt molar ratio (0.73) in PtSn 0.94 /LOC-C compared to the fresh PtSn 0.94 /LOC, which provides further evidence on the leaching of Sn during the cycle experiment. Above results lead us to a conclusion that the phase segregation of PtSn alloys and the loss of SnO x patches in the vicinity of Pt centers during the cycle experiments, may be the primary reason responsible for the catalyst deactivation of the PtSn 0.94 /LOC.…”

Kinetics of Lifetime Changes in Bimetallic Nanocatalysts Revealed by Quick X‐ray Absorption Spectroscopy

“…The zero‐order process approaches a zero activation energy (Supporting Information, section S6). Notably, the order of magnitude of the rate coefficients of Pt surface oxidation accords with an earlier study, assessing Pt NP oxidation only.…”

Catalysts for Methanol Oxidation

“…Here is a brief example. Very fresh investigations [56] with in situ time-resolved energy-dispersive X-ray Absorption Fine Structure (DXAFS) and quick XAFS (QXAFS) techniques discover structural changes of the Pt x Sn nanocatalyst during the progress of the oxidation reaction. 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.…”