Surface modification of Ni catalysts with trace Pt for oxidative steam reforming of methane

Abstract

Hysteresis of catalytic performance with respect to temperature increasing and decreasing in oxidative steam reforming of methane (CH 4/H 2O/O 2/Ar = 40/30/20/10) over the monometallic Ni catalysts disappeared by the modification with Pt, and the additive effect of Pt by the sequential impregnation method (Pt/Ni) was much more significant than that by the co-impregnation method (Pt + Ni) in terms of catalytic performance and catalyst bed temperature profile. Characterization results by means of TEM, TPR, EXAFS, and FTIR suggest that the Pt atoms on the Pt/Ni catalysts were located more preferably on the surface to form a Pt Ni alloy than those on the Pt + Ni catalysts. The modification of Ni with Pt suppressed the oxidation of Ni species near the bed inlet in the oxidative steam reforming of methane at 1123 K, although the species on the monometallic Ni catalysts were oxidized under similar conditions. This can be due to the decreased oxidation rate of the species and the increased reduction rate caused by the surface modification of Ni with Pt. Consequently, the Pt Ni species can be maintained in the metallic state near the bed inlet, and the species can be the active site for the reforming reaction as well as the combustion reaction, which this leads to a lower bed temperature and smaller temperature gradient than those seen for the monometallic Ni catalysts.