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

Abstract

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.

Enhanced CO2 Methanation over Ni/Na-HNTs: Effect of Pretreatment with NaOH

“…The halloysite nanotubes (HNTs) were first reacted with different concentrations of NaOH solution. Typically, 4 g acid-pretreated HNTs were added into NaOH solution (100 mL, 0.5, 1.0, and 1.5 mol/L), respectively. The mixture was then heated in a water bath at 60 °C for 4 h with continuous stirring.…”

“…Halloysite nanotubes (HNTs) are a naturally hollow-structured aluminosilicate material with chemical formula [Al 2 (OH) 4 Si 2 O· n H 2 O] . Due to HNTs possessing the high specific surface area and porous structure, the metal nanoparticles can be highly dispersed, which is critical in catalytic applications. , In our previous work, we discovered that treating HNTs with acid solution can increase the number of defective sites on the surface, resulting in highly dispersed metal particles and enhanced catalytic activity at low temperatures. However, the acid solution would not significantly activate the outer surface of the HNTs, which is composed of chemically inert Si–O–Si groups.…”