Doping effects of Ni-MgO on the structure and performance of carbon nanotube-supported Pt catalysts for preferential oxidation of CO in a H2 stream

The preferential oxidation of CO (CO-PROX) in a H-2-rich stream is performed on a series of supported Pt catalysts doped with Ni-MgO. The characterizations of the catalysts by means of in situ X-ray diffraction, high resolution transmission electron microscopy, and scanning transmission electron microscopy-energy dispersive spectroscopy reveal that the nanocomposites of Pt-Ni alloys that intimately adjoined Ni-MgO solid solution are present on the surfaces of carbon nanotube (CNT). However. the Pt-Ni alloying is hardly detected when the same compositions are supported on other carriers like active carbon, graphite, TiO2. SiO2 and Al2O3 followed by identical treatment. The CNT-supported Pt0.3Ni1.0Mg2.4 (Pt0.3Ni1.0Mg2.5/CNT, the data at subscript stand for the Pt/Ni/Mg atomic ratio) catalyst with overall metal loading of 15 wt% affords 100% CO conversion and 50% O-2 selectivity in H-2 at temperatures ranging from 333 to 453 K. whereas the CNT-supported Pt catalyst and the other carriers-supported Pt0.3Ni1.0Mg2.4 ones perform very low or insufficient activities under the same reaction conditions. Further, the Pt0.3Ni1.0Mg2.4/CNT catalyst with a mean Pt-Ni particle size about 7.3 nm shows negligible drop in CO-PROX performance at 373 K for longer than 40 h on the streams either with or without H2O vapor and CO2. The deactivation of the catalyst is largely due to the accumulation of H2O/OH- species and carbonates, which can be removed by calcination and reduction to get the regeneration of the CO-PROX performance as a result. The high performance of the catalysts is ascribed to the interaction between Pt and Ni with the formation of Pt-Ni alloy which is strongly interacted with Ni-MgO solid solution. (C) 2011 Elsevier B.V. All rights reserved.