CO2 Methanation on Ni Catalysts Supported over Activated Carbons Derived from Cork Waste

Abstract

Activated carbons (ACs) derived from cork wastes were for the first time used as supports for CO2 methanation catalysts. Cork wastes (natural-N and processed-P) were physically activated under N2/H2O(v) atmosphere at 800 °C to obtain the corresponding AC supports (ACN and ACP, respectively). Ni and Ni-CeO2 catalysts were prepared by loading the ACs with 15 wt % Ni (Ni/AC) or 15 wt % Ni and 15 wt % Ce (NiCe/AC) by incipient wetness impregnation or co-impregnation, respectively, using 2-propanol as the solvent. For comparison purposes, a commercial activated carbon (ACC) was impregnated with the same metals and loadings. The catalysts were characterized by N2 and CO2 sorption, XRD, TGA, SEM, and TEM, and finally tested at atmospheric pressure under CO2 methanation conditions (86 100 mL·h–1·gcat–1, H2/CO2 = 4:1). Microporous activated carbons with high surface areas (757–903 m2·g–1) were obtained from natural and processed cork wastes. While nickel was incorporated as Ni0 over the materials, CeO2 phases were detected on Ni-CeO2 catalysts. The incorporation of these metal species over the activated carbons induced a decrease of the textural properties, while the affinity toward CO2 was promoted by CeO2. In terms of average Ni0 particle sizes, while the smallest ones were detected on Ni/ACC (8 nm) for Ni/AC samples, the addition of CeO2 led to a remarkable decrease of this parameter on cork-derived materials (from 20 to 7 nm and from 33 to 16 nm on ACN and ACP, respectively). Higher CH4 yields were exhibited by CeO2-containing catalysts, with relative CH4 yield increases of 210–670% using Ni samples as the basis being observed. This was ascribed to CeO2’s ability to activate CO2 and promote Ni0 dispersion. The best results (CH4 yield of 73% at 400 °C) were obtained for the NiCe/ACN catalyst, its performance being similar to or higher than that reported in the literature for similar systems, thus motivating further development and optimization of these materials for CO2 methanation.