Constructing highly dispersed Ni based catalysts supported on fibrous silica nanosphere for low-temperature CO2 methanation. (15th October 2020) - Lv, Chufei
Graphical abstract: Highlights: Fibrous silica nanosphere (KCC-1) is prepared by improved microemulsion strategy. KCC-1 has large surface area and multi-dimensional dendrimeric mesoporous channel. Highly dispersed Ni obtained over KCC-1 due to good accessibility of surface area. Ni/KCC-1 performs excellent low-temperature catalytic activity of CO2 methanation. TPSR and in-situ DRIFTS of CO2 methanation reveal reaction kinetics and mechanism. Abstract: In this work, we reported that the fibrous silica nanosphere, also called as KCC-1, was facilely synthesized by the improved microemulsion hydrothermal fabrication strategy. The obtained KCC-1 was investigated as the support of the Ni based catalysts toward CO2 methanation. The obtained catalysts with unique dendrimeric mesopore structure and outstanding structural properties could provide easily accessible as well as highly dispersed Ni nanoparticles to the gaseous reactants. Besides, the Ni based catalysts with commercial SiO2 and MCM-41 as supports were also prepared as the reference catalysts to demonstrate the advantages of the dendrimeric mesoporous channels. Various techniques, such as X-ray powder diffraction (XRD), N2 physisorption, transmission electron microscopy (TEM), H2 temperature programmed reduction (H2 -TPR), CO2 temperature programmed desorption (CO2 -TPD), X-ray photoelectron spectroscopy (XPS), etc., were used to characterize the catalytic supports and corresponding catalysts. It was found that the metallic Ni nanoparticles could be highly dispersed over the catalysts supported on fibrous KCC-1 with dendrimeric mesoporous channels. Furthermore, the catalytic performances toward CO2 methanation had been further evaluated over these catalysts at different temperatures. It was found that the KCC-1 supported catalyst performed much higher low-temperature catalytic activities than the reference catalysts supported on commercial SiO2 and MCM-41, suggesting that the fibrous and dendrimeric mesoporous channels displayed distinctive advantages by accommodating enough metallic Ni active sites. The kinetic study also revealed that the topology of the mesoporous channel could obviously influence the apparent activation energy in the CO2 methanation reaction. Besides, the temperature programmed surface reaction (TPSR) and in-situ Diffused Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) of the CO2 methanation were also carried out to reveal the possible reaction pathway and mechanism. We also found that the fibrous silica nanosphere (KCC-1) supported catalyst demonstrated much better sintering-proof property of the metallic Ni nanoparticles than the reference catalysts during the 40 h stability tests at 400 °C. Therefore, the present fibrous silica nanosphere (KCC-1) could be considered as the promising support for Ni based catalysts toward CO2 methanation.