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

Abstract Hybrid materials of (100 −  x ) wt% Ce 0.8 La 0.2 O 2− δ – 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 Ce 0.8 La 0.2 O 2− δ /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 Ce 0.8 La 0.2 O 2− δ phase in the hybrid support system and, thus of the Pt phase; the larger dispersion of the Ce 0.8 La 0.2 O 2− δ phase had a direct impact on its reducibility ability (labile oxygen species), (iii) concentration of surface Ce 3+ 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 °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 H 2 O 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 °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.