Doping effects of Ni–MgO on the structure and performance of carbon nanotube-supported Pt catalysts for preferential oxidation of CO in a H 2 stream

Abstract

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, TiO 2, SiO 2 and Al 2O 3 followed by identical treatment. The CNT-supported Pt 0.3Ni 1.0Mg 2.4 (Pt 0.3Ni 1.0Mg 2.5/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 Pt 0.3Ni 1.0Mg 2.4 ones perform very low or insufficient activities under the same reaction conditions. Further, the Pt 0.3Ni 1.0Mg 2.4/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 H 2O vapor and CO 2. The deactivation of the catalyst is largely due to the accumulation of H 2O/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.