Low temperature-high selectivity carbon monoxide methanation over yttria-stabilized zirconia-supported Pt nanoparticles

The high purity hydrogen, free from any traces of carbon monoxide is crucial for the efficient operation of hydrogen proton exchange membrane fuel cells (PEMFCs). In this study we report the low temperature (25-120 °C) carbon monoxide methanation in hydrogen-rich streams over 1 wt. % Pt nanoparticles supported on yttria-stabilized zirconia (YSZ) support. Pt nanoparticles with four average particle sizes 1.9, 3.0, 4.4 and 6.7 nm are investigated. The turnover frequency at 30 °C of CO methanation reaction rate doubles with decreasing Pt mean particle size from 6.7 to 1.9 nm. The high activity of Pt/YSZ catalyst is due to the backspillover of ionic species Oδ− from YSZ support to Pt active sites. Under the reaction conditions, Oδ− forms an “effective” double layer at the catalyst surface that weakens CO (electron acceptor) adsorption and strengthens H2 (electron donor) adsorption bonds and this effect becomes more pronounced as nanoparticle size decreases.