Applied Catalysis B: Environmental, Vol.234, 279-289, 2018
Methane steam reforming in water deficient conditions on Ir/Ce0.9Gd0.1O2-x catalyst: Metal-support interactions and catalytic activity enhancement
This work reports on the study of steam reforming of methane under water deficient conditions over Ir/Ce0.9Gd0.1O2-x (Ir/CGO) catalyst with very low Ir loading (0.1 wt% Ir). The catalyst surface was studied before and after testing by X-ray photoelectron spectrometry (XPS) and aberration-corrected high-resolution transmission electron microscopy (HRTEM) with 1 angstrom best resolution. Ir/CGO was pretreated at 1173 K in He flow with less than 0.5 ppm O-2 prior to catalytic testing. This led to the formation of Ir metal nanoparticles (NPs) with narrow-size distribution (2.5-6 nm, mean size of 4 nm in diameter). Ir/CGO slowly activated during reaction until reaching a steady state with tenfold increase of CH4 conversion rate. The initial catalytic activity was consistent with surface metal sites being the main active sites and the CGO support having no effect on the CH4 conversion rate except the inhibiting influence on the thermodynamically favoured carbon accumulation. After completion of the activation during reaction, Ir was present in the form of metallic NPs with smaller mean size (ca. 1.7 nm) than before testing, and oxidized Ir in 3 + /4 + states. Metal support interactions were thought to be responsible for Ir oxidation and redispersion at the CGO surface during reaction. It is proposed that the improved catalytic activity is due to a synergy between highly dispersed Ir species and the CGO substrate through delocalization of the catalytic reactions in the vicinity of the Ir metal particles.