Low-temperature water-gas shift on Pt/Ce0.8La0.2O2-δ-CNT: The effect of Ce0.8La0.2O2-δ/CNT ratio

Hybrid materials of (100-x)wt% Ce0.8La0.2O2-delta-x wt% CNT composition (x=0, 7.5, 20.5, 32.5, 44.1 and 100) were synthesized using the urea-assisted co-precipitation method and used as supports of 0.5 wt% Pt toward the low-temperature WGS (LT-WGS) reaction. The main focus of this work was to provide fundamental understanding of the effect of Ce0.8La0.2O2-delta/CNT ratio on the LT-WGS catalytic activity of such materials. It was found that the material containing 44.1 wt% CNT presented the best catalytic activity (kinetic rate and CO conversion), result that is correlated with the following parameters: (i) Pt-CO bond strength (TPD-CO), (ii) extent of dispersion of the Ce0.8La0.2O2-delta phase in the hybrid support system and, thus of the Pt phase; the larger dispersion of the Ce0.8La0.2O2-delta phase had a direct impact on its reducibility ability (labile oxygen species), (iii) concentration of surface Ce3+ species (XPS), indication for an increased concentration of oxygen vacant sites, (iv) Pt-H bond strength (H-2-TPD studies), and (v) concentration of active carbon-containing intermediates, C-pool formed around each Pt nanoparticle (SSITKA studies). WGS kinetic studies at 300 degrees C revealed that the reaction order with respect to CO was 0.17 and 0.13 for the catalysts containing 20.5 and 44.1 wt% CNT, respectively, while the reaction order with respect to H2O was 1.40 for the latter CNT loading. Oxidation of CNTs over the catalyst containing 44.1 wt% of CNTs occurred at temperatures larger than 400 degrees C, result of practical importance for the LT-WGS reaction. The proposed WGS reaction mechanism over the present catalytic materials is that of redox in parallel with the associative with OH group regeneration mechanism. (C) 2015 Elsevier B.V. All rights reserved.