Monolithic Ni5Ga3/SiO2/Al2O3/Al-fiber catalyst for CO2 hydrogenation to methanol at ambient pressure
A series of Ni 5 Ga 3 / m -SiO 2 /Al 2 O 3 /Al-fiber ( m = 0, 0.5, 1.0, 3.0 and 5.0 wt%) catalysts have been developed for CO 2 hydrogenation to methanol at ambient pressure. Microfibrous-structured SiO 2 /Al 2 O 3 /Al-fiber supports are obtained though endogenous growth of free-standing boehmite (AlOOH) nanosheets onto a three-dimensional (3D) network of 60 μm-Al-fiber thin felt with the aid of steam-only hydrothermal oxidation reaction between Al metal and H 2 O (2 Al + 4H 2 O → 2 AlOOH + 3H 2 ), followed by calcination and SiO 2 -modification using silica sol. The bimetallic Ni 5 Ga 3 nanoparticles are then placed onto the pore surface of as-obtained SiO 2 /Al 2 O 3 /Al-fiber support by co-impregnation method using Ni and Ga nitrates as precursors followed by reduction in H 2 at 630 °C. The promising Ni 5 Ga 3 /1-SiO 2 /Al 2 O 3 /Al-fiber catalyst is capable of converting 2.3% CO 2 into CH 3 OH with a high selectivity of 86.7% as well as 10.3%/3.0% selectivities to CO/CH 4 at 210 °C, for a feed of CO 2 /H 2 /N 2 (2/6/1, molar ratio). Such microfibrous-structured catalyst design combines the promising catalytic performance of Ni 5 Ga 3 with the enhanced heat transfer and high permeability of the Al 2 O 3 /Al-fiber support. The effect of SiO 2 loading on the formation of Ni 5 Ga 3 alloy nanoparticles is also discussed.
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