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

Activated carbons (ACs) derived from cork wastes werefor the firsttime used as supports for CO2 methanation catalysts. Corkwastes (natural-N and processed-P) were physically activated underN(2)/H2O(v) atmosphere at 800 degrees Cto obtain the corresponding AC supports (AC(N) and AC(P), respectively). Ni and Ni-CeO2 catalysts wereprepared by loading the ACs with 15 wt % Ni (Ni/AC) or 15 wt % Niand 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 (AC(C)) was impregnated withthe same metals and loadings. The catalysts were characterized byN(2) and CO2 sorption, XRD, TGA, SEM, and TEM,and finally tested at atmospheric pressure under CO2 methanationconditions (86 100 mL center dot h(-1)center dot g(cat) (-1), H-2/CO2 = 4:1).Microporous activated carbons with high surface areas (757-903m(2)center dot g(-1)) were obtained from naturaland processed cork wastes. While nickel was incorporated as Ni-0 over the materials, CeO2 phases were detectedon Ni-CeO2 catalysts. The incorporation of these metalspecies over the activated carbons induced a decrease of the texturalproperties, while the affinity toward CO2 was promotedby CeO2. In terms of average Ni-0 particle sizes,while the smallest ones were detected on Ni/AC(C) (8 nm)for Ni/AC samples, the addition of CeO2 led to a remarkabledecrease of this parameter on cork-derived materials (from 20 to 7nm and from 33 to 16 nm on AC(N) and AC(P), respectively).Higher CH4 yields were exhibited by CeO2-containingcatalysts, with relative CH4 yield increases of 210-670%using Ni samples as the basis being observed. This was ascribed toCeO(2)'s ability to activate CO2 and promoteNi(0) dispersion. The best results (CH4 yieldof 73% at 400 degrees C) were obtained for the NiCe/AC(N) catalyst,its performance being similar to or higher than that reported in theliterature for similar systems, thus motivating further developmentand optimization of these materials for CO2 methanation.