Dynamic Structural Changes of SiO₂ Supported Pt-Ni Bimetallic Catalysts over Redox Treatments Revealed by NMR and EPR

Journal Article · Tue Aug 18 00:00:00 EDT 2015 · Journal of Physical Chemistry C, 119(36):21219-21226

DOI:https://doi.org/10.1021/acs.jpcc.5b06344· OSTI ID:1222898

Xu, Suochang; Walter, Eric D.; Zhao, Zhenchao; Hu, Mary Y.; Han, Xiuwen; Hu, Jian Z.; Bao, Xinhe

SiO₂ supported Pt-Ni bimetallic catalysts with different nickel loadings were prepared and their structural changes after redox treatments were studied by XRD, NMR, and EPR. It is found that the paramagnetic Ni species are mainly located on the surface of silica lattice. The relaxation of detected ²⁹Si nuclei in our samples is mainly governed by a spin-diffusion mechanism. The paramagnetic effects are reflected in the spin-lattice relaxation of Q₄ species, with the oxidized samples presenting faster relaxation rates than the corresponding reduced ones. Meanwhile the Q₃ species, which are in close contact with the paramagnetic nickel ions, are “spectrally invisible”. In reducing atmosphere Ni gradually diffuses into Pt NPs to form PtNi alloys. While under oxidization treatment, the alloyed Ni atoms migrate outward from the core of Pt NPs and are oxidized. The main EPR spectrum results from reduced nickel species, and the reduced samples show stronger EPR signal than the corresponding oxidized ones. However, in the reduced samples, the superparamagnetic or ferromagnetic metallic Ni particles were inside the PtNi NPs, making their influence on the ²⁹Si relaxation in the SiO₂ support weaker than the oxidized samples.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1222898
• Report Number(s): PNNL-SA-112670; 47841; KC0302010
• Journal Information: Journal of Physical Chemistry C, 119(36):21219-21226, Journal Name: Journal of Physical Chemistry C, 119(36):21219-21226
• Country of Publication: United States
• Language: English

Related Subjects

Environmental Molecular Sciences Laboratory