Nitric Acid-Pretreated Natural Halloysite Nanotubes as Ni Nanoparticle Catalyst Supports for CO2 Methanation

The CO2 methanation reaction has attracted more and more attention, which can achieve a carbon cycle and high-valued chemicals, but the development of efficient catalysts remains a big challenge. Herein, the natural halloysite nanotubes (HNTs) pretreated with different concentrations of nitric acid solutions (4, 6, 8, and 10 mol/L) were used as supports for the first time to synthesize Ni-based CO2 methanation catalysts through the impregnation method. The results revealed that the catalysts prepared with acid-pretreatment HNTs demonstrated more excellent catalytic activity due to the improved dispersion of Ni nanoparticles and more basic sites, which efficiently adsorb and activate the reaction gases H2 and CO2. Moreover, the effects of metal loading on the catalytic performance were also studied. The optimized (Ni(30%)/HNTs-8AC) catalyst with a Ni loading of 30 wt % showed significantly superior CO2 conversion (95.8%) at 350 °C with CH4 selectivity of 100% at 15,000 mL/g/h and did not show significant deactivation during a 50 h stability test because of excellent resistance to coking and sintering. This work provides a support of natural materials for preparing a CO2 methanation catalyst.