Synthesis and Regeneration of Ni-Phyllosilicate Catalysts Using a Versatile Double-Accelerator Method: A Comprehensive Study

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.