Nickel Nanoparticles Decorated Nitrogen-Doped Carbon Nanotubes (Ni/N-CNT); a Robust Catalyst for the Efficient and Selective CO₂ Methanation

Carbon dioxide (CO2) hydrogenation to methane (CH4) is a way of great significance from an energy-saving viewpoint that consists in the direct conversion of a natural and abundant waste into a fuel of added value. Indeed, it can be used to provide synthetic CH4 as an alternative source to natural gas to be potentially injected in the existing gas grid. This contribution describes the synthesis of a robust catalyst for the efficient and selective CO2 methanation, based on Nickel nanoparticles (Ni-NPs) grown on N-doped carbon nanotubes (Ni/N-CNT). The high thermal conductivity of N-CNT ensures a good dispersion of the reaction heat throughout the catalyst bed while N-doping lists a number of key and distinctive catalyst features: a) it provides preferential binding sites for the Ni-NPs stabilization, b) it contributes to generate CO2 concentration gradients in proximity of the catalyst active phase and c) it largely prevents the formation of coke deposits (catalyst passivation) on stream. The as prepared catalyst shows superior methanation activity and selectivity compared to those claimed for the most representative Ni-based composites reported so far in the literature. Importantly, the Ni/N-CNT displays its better performance in CO2 methanation under severe reaction conditions, that is, high temperatures and GHSV (up to 120 000 mL g–1 h–1) where it unveils an excellent stability as a function of time-on-stream.