Carbon cycle using the CO2 conversion to methane as environmental feasibility on Ni/TiO2-Na nanotubes catalysts

Abstract

xNi/TiO2-Na nanotubes catalysts were evaluated in CO2-methanation. The catalysts were characterized by FE-SEM, TEM, XRD, MS, CO2-TPD, DRIFTS and TPR. 50Ni/TiO2-Na catalyst showed better CO2 conversion and high CH4 selectivity while, the 5Ni/TiO2-Na catalyst that showed high CO selectivity, low CO2 methanation and Ni species in intimate contact with the support. In this latter, the difficulty of CO2 hydrogenation can be associated with the strength of the catalyst basic sites, which is influenced by the Ni species in intimate contact with the support, promoting the SMSI effect. According with TPD results, the CO2 is retained on the surface of the catalysts with 5 and 20 wt% Ni, and needs higher temperature than in the 50Ni/TiO2-Na nanotube sample to desorb it and liberate the active sites blocked for the reaction to proceed. Although, a high amount of the Ti0.75Ni0.23O cubic phase was observed on the 50Ni/TiO2-Na sample, a large number of metallic Ni particles remained supported on the TiO2-Na which could reduce the SMSI effect on this catalyst. DRIFTs studies showed that Ni impregnation to TiO2-Na nanotubes generated new sites for CO2 adsorption and H2 is necessary to produce carbonates, bicarbonates, formate and carboxilates as intermediaries of the reaction during CO2-hydrogenation.