Design of 3D printed Mg doped Ni-Co-containing biowaste-derived porous silica as highly-effective catalysts for CO2 methanation

Abstract

Mesoporous silica (MS) derived from rice husk was doped with Mg and additionally modified with Ni and/or Co by incipient wetness impregnation method. 3D printing technology was applied before or after the modification with metal precursors for better performance of the obtained catalysts in a larger scale CO₂ hydrogenation. The initial silica and the modified materials were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), N₂ physisorption, temperature-programmed reduction (TPR-TGA), and X-ray photoelectron spectroscopy (XPS). The formation of a rock salt (Ni,Mg,Co)O phase and a highly dispersed spinel (Ni,Mg,Co)₃O₄ phase was registered. It was found that optimal Mg doping significantly influences the dispersion of the formed metal oxide species. The peculiarities of the applied mesoporous silica could influence metal dispersion as well. The obtained catalysts are active in CO₂ hydrogenation to methane. The optimal Ni-Co ratio and the moderate-strength basic sites promote high CO₂ conversion and CH₄ selectivity. Among them, powder 5Mg5Ni5Co/MS material was selected for 3D printing based on its high activity and the optimal content of nickel from an economical point of view. The stabilization of Ni dispersion in the 3D-printed samples is beneficial for long-term catalytic performance. The advantage of the 3D printed catalysts was demonstrated showing their higher activity in CO₂ hydrogenation than that of their powder analog, keeping high CO₂ conversion of around 3.8 mol CO₂ g cat ⁻¹ h⁻¹ in 6 hours reaction time. The favorable catalytic properties of the 3D printed catalysts, their stability and reusability indicate their potential for commercialization.