Synthesis and Regeneration of Ni-Phyllosilicate Catalysts Using a Versatile Double-Accelerator Method: A Comprehensive Study
Yaqi Chen, Qing Liu
Abstract
Nickel phyllosilicate materials were usually prepared by the conventional hydrothermal method under severe conditions and ammonia evaporation method with unavoidable ammonia emission. To address these problems, a versatile double-accelerator method was proposed in this work, which could successfully synthesize nickel phyllosilicates through the hydrothermal treatment of silica and nickel nitrate at a quite low temperature of 40 °C or in an open system at 80 °C without autogenous pressure assisted by ammonium fluoride (NH4F) and urea. NH4F could accelerate the etching of silica to form the intermediate H4SiO4, and urea could facilitate the formation of a Ni(OH)2 intermediate, resulting in the quick formation of Ni-phyllosilicates. In addition, this method exhibited high universality to prepare various metal (Ni, Co, and Cu) phyllosilicates, and both silica materials and sodium metasilicate could be the potential silicon-containing precursors to prepare Ni-phyllosilicates. Furthermore, the sintered Ni/SiO2 catalyst could also be regenerated after in situ acid pickling and double-accelerator synthesis without decline of catalytic activity. The optimal Ni-phyllosilicate catalyst (N/D-120-12) prepared by the double-accelerator method exhibited a high CO2 conversion of 78.4% and a CH4 yield of 74.5% at 400 °C, which also obtained a low Ea of 63.93 kJ·mol–1 and a high TOFCO2 (160 °C) of 3.1 × 10–2 s–1 for CO2 methanation. In situ DRIFTS results demonstrated that the presence of more m-HCOO– species on N/D-120-12 resulted in its high catalytic performance. Moreover, N/D-120-12 also exhibited high long-term and hydrothermal stability with an excellent anti-sintering property.