Nanocomposites and nanomaterials

Preparation and characterization of Ni–Co/SiO2 nanocomposite catalysts for CO2 methanation
Dyachenko А.G.1, Ischenko O.V.1, Lisnyak V.V.1, Goncharuk O.V.2, Borysenko M.V.2, Mischanchuk O.V.2, Gun’ko V.M.2, Dariusz Sternik3
1Taras Shevchenko National University of Kyiv, 64/13 Volodymyrs’ka Str, Kyiv, 01601, Ukraine
2O.O. Chuiko Institute of Surface Chemistry National Academy of Science of Ukraine, 17 General Naumov Str, Kyiv, 03164, Ukraine
3Maria Curie-Sklodowska University, M.C. Sklodowska Sq.3, 20031 Lublin, Poland.
E-mail: dyachenko.alla@yahoo.com

A set of mono and bimetallic Ni100–xCox/SiO2 nanocomposites have been prepared for highly effective carbon dioxide (CO2) methanation. Mentioned nanocomposites were synthesized by the method of solvate stimulated modification of silica surface with nitrate solution of corresponding metals, further thermal decomposition and chemical reduction in the H2/He flow. All samples were characterized with SEM EDX, N2 adsorption and XRD analysis. The prepared samples before and after hydrogen treatment have similar mesoporous structure in contrast to the pristine nanosilica. SEM images of nanocomposites demonstrated equally distributed bimetallic particles on the silica surface with the small individual particle (d≈30 nm) and large agglomerate of them (d≈220 nm). XRD results have shown the smallest bimetallic crystallites (≈13 nm) estimated from the Scherrer equation, and obtained by substitution of Ni for Co in metal nanoparticles, having a positive synergistic effect and caused the best catalytic performance. 
The samples were tested in the reaction of СО2 hydrogenation. The main reaction product was methane and co-product was carbon monoxide. Maximum CO2 conversion was achieved at 400 0C with CH4 yield 85%. Up to 5% of CO was also observed in the temperature range 200-350 0С.
Thermoprogrammed desorption mass spectrometry method was applied to investigation of the surface state of Ni-Co/SiO2 nanocomposites after catalytic test of them. TD profiles of H2O (m/z 18), CO (m/z 28), COH* (m/z 29), CO2 (m/z 44) species were registered. It showed that the catalytic process of CO2 methanation have passed through the formation of intermediates compounds over the active sites of Ni-Co particles and silica functional groups.