Monolithic Ni₅Ga₃/SiO₂/Al₂O₃/Al-fiber catalyst for CO₂ hydrogenation to methanol at ambient pressure

A series of Ni₅Ga₃/m-SiO₂/Al₂O₃/Al-fiber (m = 0, 0.5, 1.0, 3.0 and 5.0 wt%) catalysts have been developed for CO₂ hydrogenation to methanol at ambient pressure. Microfibrous-structured SiO₂/Al₂O₃/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 H₂O (2 Al + 4H₂O → 2 AlOOH + 3H₂), followed by calcination and SiO₂-modification using silica sol. The bimetallic Ni₅Ga₃ nanoparticles are then placed onto the pore surface of as-obtained SiO₂/Al₂O₃/Al-fiber support by co-impregnation method using Ni and Ga nitrates as precursors followed by reduction in H₂ at 630 °C. The promising Ni₅Ga₃/1-SiO₂/Al₂O₃/Al-fiber catalyst is capable of converting 2.3% CO₂ into CH₃OH with a high selectivity of 86.7% as well as 10.3%/3.0% selectivities to CO/CH₄ at 210 °C, for a feed of CO₂/H₂/N₂ (2/6/1, molar ratio). Such microfibrous-structured catalyst design combines the promising catalytic performance of Ni₅Ga₃ with the enhanced heat transfer and high permeability of the Al₂O₃/Al-fiber support. The effect of SiO₂ loading on the formation of Ni₅Ga₃ alloy nanoparticles is also discussed.