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Ni(OH) 2 and H 4 SiO 4 are the two key intermediates for the synthesis of Ni-phyllosilicate, and the purpose of this work is to reveal which one is more efficient. The silica (D) was extracted from distillers' grains, which was used as the sacrificial template for Ni-phyllosilicate. The formation of Ni(OH) 2 and H 4 SiO 4 was enhanced by NaOH and NH 4 F, respectively, and Ni/D-S (assisted by sodium hydroxide) and Ni/D-A (assisted by ammonium fluoride) were obtained. Although the amount of NaOH and NH 4 F and hydrothermal synthesis procedures were identical, there was a significant difference of their Ni contents. The Ni content of Ni/D-S and Ni/D-A was 17.7 wt% and 2.5 wt%, respectively. As a result, Ni/D-S was more active for CO 2 methanation, whose CH 4 yield reached 61.6% at 450 °C, 0.1 MPa, 60 L g−1·h−1, while the maximum CH 4 yield of Ni/D-A was only 16.4% at 500 °C. However, the formation of Ni-phyllosilicate could also be improved after addition of more NH 4 F, and the increased amount of H 4 SiO 4 led to the high Ni content (33.4 wt%) of Ni/D-A-M (M refers to the addition of more ammonium fluoride) and enhanced catalytic performance for CO 2 methanation. It was concluded that Ni(OH) 2 and H 4 SiO 4 were both important for the synthesis of Ni-phyllosilicate, while Ni(OH) 2 was the more efficient one. [Display omitted] • NaOH was used to accelerate the formation of Ni(OH) 2. • NH 4 F was used to accelerate the formation of H 4 SiO 4. • Ni(OH) 2 or H 4 SiO 4 were both important for the synthesis of Ni-phyllosilicate. • Ni(OH) 2 was the more efficient intermediate compared with H 4 SiO 4. [ABSTRACT FROM AUTHOR]

In order to achieve green synthesis of MCM-41 and address the sintering problem of Ni-based catalyst supported on silica material, MCM-41 with regular spherical morphology was prepared using sodium silicate extracted from renewable equisetum fluviatile as silicon source, and then a group of nickel phyllosilicates were synthesized via the reaction of MCM-41 sphere and nickel nitrate under hydrothermal condition. Much denser nanosheets corresponding to lamellar nickel phyllosilicate were formed on the surface of MCM-41 sphere with the raise of hydrothermal temperature in the range of 180–220 °C, resulting in the nickel content varying from 17.2 to 41.8 wt%. Fine Ni particles with size smaller than 6 nm could be obtained on the 750oC-reduced catalyst owing to the strong nickel-silica interaction derived from Ni-phyllosilicate. After the addition of V 2 O 5 promoter, Ni particle size was further reduced to around 4.5 nm at high Ni loading above 30 wt%. Vanadium species was in the mixed valence state of V(III), V(IV) and V(V) after reduction, which increased the electron cloud density of Ni0, resulting in high catalytic activity of the VO x -modified Ni-phyllosilicate catalyst for CO 2 methanation. In a 100 h-400oC-lifetime test and 600 °C-steam hydrothermal treatment, the VO x -modified Ni-phyllosilicate catalyst also showed high long-term stability, excellent sintering resistance of metallic nickel particles and high hydrothermal stability due to the strong surface confinement effect of nickel phyllosilicate and promotion of VO x species. In all, this work provided a green synthesis of MCM-41 as well as an efficient Ni/SiO 2 catalyst derived from nickel phyllosilicate for CO 2 methanation. This work provides a green synthesis of MCM-41 as well as an efficient Ni/SiO 2 catalyst derived from nickel phyllosilicate for CO 2 methanation. [Display omitted] • Mesostructured silica nanoparticles with regular spherical morphology were prepared using renewable biomass. • VO x modified nickel phyllosilicate catalyst improved its methanation activity. • Nickel phyllosilicate catalysts were facilely prepared using hydrothermal method. • Nickel phyllosilicate catalysts exhibited high activity and stability for CO 2 methanation. • Nickel phyllosilicate catalysts exhibited highly hydrothermal stability in 100% steam at 600 °C. [ABSTRACT FROM AUTHOR]

In order to compare the effect of preparation method on the catalytic performance over Ni/3D-SBA-15 catalyst for CO 2 methanation, one-pot and two-pot synthesis strategies were used in this work. 3D-SBA-15-derived Ni-phyllosilicate catalyst could be obtained via a two-pot hydrothermal synthesis using 3D-SBA-15 and nickel nitrate as precursors at 180 °C. This Ni-phyllosilicate catalyst with a monolithic macromorphology and a microcosmic appearance of 3D-networked framework covered by nanosheets, was also achieved via a one-pot hydrothermal method with elimination of the preparation and pretreatment of 3D-SBA-15. The one-pot-synthesized Ni/S–O catalyst not only showed high catalytic activity due to the small-sized Ni particles, but also exhibited excellent anti-sintering property owing to the strong metal-support interaction derived from Ni-phyllosilicate. Compared with the two-pot synthesis, many advantages were observed for one-pot synthesis including monolithic appearance, high convenience, large Ni-phyllosilicate amount and low cost. [Display omitted] • 3D-SBA-15 was used as the sacrificial template to synthesized nickel phyllosilicate. • One-pot and two-pot synthesis strategies were used to prepare Ni-phyllosilicate. • One-pot synthesis was more facile and efficient than two-pot synthesis. • Ni-phyllosilicate with monolithic appearance and high Ni content was obtained via one-pot synthesis. • One-pot Ni-phyllosilicate exhibited higher catalytic activity for CO 2 methanation. [ABSTRACT FROM AUTHOR]

In this work, nickel phyllosilicate was prepared through the hydrothermal reaction of rice husk-derived silica (SR) and nickel nitrate. Owing to the loss of surface silanol group on SR during the calcination process, a small amount of Ni-phyllosilicate with Ni content of 10.2 wt% was obtained on N 220 /SR, which was prepared under a very severe hydrothermal condition of 220 °C for 48 h. After the addition of urea, the dense flower-like nanosheets attributing to Ni-phyllosilicate were observed on the surface of N 180 /SR-U-24 with high Ni content of 22.6 wt%, which was prepared under a much milder hydrothermal temperature of 180 °C and a shorter reaction time of 24 h. This was because urea could facilitate the formation of an important intermediate (Ni(OH) 2) and leaching of SiO 2 , resulting in the quick formation of Ni-phyllosilicate. N 180 /SR-U-24 exhibited both good catalytic activity and high long-term stability for CO 2 methanation due to the relatively high Ni content, fine Ni particles and the strong metal-support interaction derived from Ni-phyllosilicate. [Display omitted] • Renewable rice-husk-derived SiO 2 was prepared. • Ni-phyllosilicate was synthesized using two hydrothermal methods with or without urea. • Urea-assisted hydrothermal method was efficient for synthesis of Ni-phyllosilicate. • Urea could facilitate the formation of Ni(OH) 2 and leaching of SiO 2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni-phyllosilicate was synthesized by a modified hydrothermal method for CO 2 methanation. • NH 4 F and urea were used as double accelerators to form Ni-phyllosilicate. • NH 4 F could improve the formation of important intermediate of H 4 SiO 4. • Urea could facilitate the formation of intermediate of Ni(OH) 2. • Ni-phyllosilicate showed high catalytic performance for CO 2 methanation. Nickel phyllosilicate materials were usually prepared by the hydrothermal method under severe conditions with high hydrothermal temperature and long hydrothermal time. In order to obtain Ni-phyllosilicate under mild hydrothermal conditions, a modified hydrothermal method assisted by double accelerators of ammonium fluoride and urea was proposed in this work. The N/F-A 100 -12 catalyst was prepared by the modified hydrothermal method at 100 °C for 12 h with similar Ni content and morphology as N/F-H 220 -48 prepared by the conventional hydrothermal method at 220 °C for 48 h. The improvement derived from that ammonium fluoride accelerated the etching of FDU-12 to form the intermediate of H 4 SiO 4 , and urea could facilitate the formation of Ni(OH) 2 , resulting in the quick formation of Ni-phyllosilicate under mild conditions. N/F-A 100 -12 exhibited high TOF CO2 (220 °C) value of 3.05 × 10−3 s−1 and low activation energy of 96.5 kJ mol−1 for CO 2 methanation due to the small Ni particle size and enhanced CO 2 and H 2 adsorption property. In addition, N/F-A 100 -12 also displayed high long-term stability and anti-sintering property. In all, the modified hydrothermal method was highly efficient to synthesize Ni-phyllosilicate material under mild hydrothermal conditions. [ABSTRACT FROM AUTHOR]

An impregnated Ni/CeO 2 catalyst with an array structure and a phyllosilicate-based Ni/SiO 2 catalyst prepared by hydrothermal method were designed for CO 2 methanation. The as-synthetized Ni/SiO 2 catalyst exhibits a high Ni content of 25.9 wt%, while its CO 2 conversion at low temperature is far lower than that of Ni/CeO 2 , whose Ni content is only 10.0 wt%. TEM and XRD results show that the Ni/CeO 2 catalyst possesses very tiny Ni particle size of around 1.2 nm, which leads to large H 2 uptake capacity. XPS and Raman analyses indicate that Ni/CeO 2 obtains more oxygen vacancies resulting in promotion of the CO 2 activation. The combined effect of the Ni/CeO 2 catalyst to enhance chemisorption of H 2 and CO 2 leads to high low-temperature activity. [Display omitted] • The catalytic activity of Ni/CeO 2 and Ni/SiO 2 was compared for CO 2 methanation. • The Ni/CeO 2 catalyst possessed smaller Ni particle size and larger H 2 chemisorption capacity. • The Ni/CeO 2 catalyst exhibited more oxygen vacancies and enhanced CO 2 activation property. • Enhanced H 2 and CO 2 activation properties of Ni/CeO 2 led to higher activity. [ABSTRACT FROM AUTHOR]