Paper NS+AS+SS-TuA10
Development of New Nanocatalysts through Restructuring of Co₃O₄ Nanorods Anchored with Pt Atoms

Tuesday, November 11, 2014, 5:20 pm, Room 304

Low-temperature water-gas shift (WGS) reaction is crucial for low-temperature fuel cell technology as it provides a solution for on-board hydrogen purification near operational temperature. Design of catalysts with lower activation energy and higher activity is critical for a practical application. Significant effort has been devoted to development of new WGS catalysts with high activity at low temperatures. Most of them are metal nanoparticles supported on reducible oxides such as CeO₂ or TiO₂.

Here we reported two nanocatalysts, PtCo_n/Co₃O₄ and Pt_mCo_m’/CoO_1-x that are highly active for low-temperature WGS reaction. They were prepared by restructuring singly dispersed Pt atoms supported on Co₃O₄ nanorods through a controlled reduction. The single dispersion of Pt atoms on cobalt oxide nanorods was confirmed with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Photoemission feaures of Co2p and Pt 4d_5/2 of these catalysts during catlaysis were tracked with ambient pressure x-ray photoelectron spectroscopy (AP-XPS) using monochromated Al Kα. Coordiantion environment of Pt atoms was tracked with in-situ extended x-ray absorption fine structure spectroscopy (EXAFS). These ex-situ and in-situ studies show that two new active phases, PtCo_n/Co₃O₄ and Pt_mCo_m’/CoO_1-x were formed in the temperature ranges of 150 ^oC – 200 ^oC and 280 ^oC – 350 ^oC in the mixture of 3 Torr CO, 1 Torr H₂O, respectively. The formation of singly dispersed bimetallic sites PtCo_n anchored on Co₃O₄ was confirmed with in-situ EXAFS studies. The formed Pt_mCo_m’ nanoclusters supported on CoO_1-x in the temperature range of 280 ^oC – 350 ^oC was identified with HAADF-STEM. Kinetics studies in the gas mixture of carbon monoxide and water vapor with a ratio of 3:1 revealed that activation barriers for PtCo_n/Co₃O₄ at 150-200 ^oC and Pt_mCo_m’/CoO_1-x at 150-250 ^oC are 50.1±5.0 kJ/mol and 29.6±4.0 kJ/mol, respectively. Turn-over frequencies (TOFs) of the two new catalysts PtCo_n/Co₃O₄ and Pt_mCo_m’/CoO_1-x at 150 ^oC are larger than those of Pt and Au nanoparticles supported on CeO₂ and TiO₂ catalysts by one magnitude. The excellent activities of the new catalytic phases PtCo_n/Co₃O₄ and Pt_mCo_m’/CoO_1-x formed through restructuring the singly dispersed Pt atoms on Co₃O₄ suggest a method of developing new catalysts through restructuring singly dispersed catalyst atoms such as noble metals on an oxide support.