Catalytic synthesis of biogenic multi-walled carbon nanotubes and hydrogen from manure

Abstract

Synthesis of biogenic multi-walled carbon nanotubes (MWCNTs) and H2 recovery via pyrolysis-CO2 capture-chemical vapor deposition (CVD) are examined for the valorization of various animal farm wastes (chicken, horse, goat, and cow manures). To this end, the suitability of various catalysts − Co-Mo/MgO, Co-Ni-Mo/MgO, and Co-Fe-Mo/MgO − was evaluated at a CVD temperature of 700 °C. The results indicate that all manures are suitable for MWCNT and H2 production, with cow manure yielding the highest output: 2.4 ± 0.3 wt% MWCNTs and 161 ± 4 mL H2 per gram of feedstock when using Co-Ni-Mo/MgO as the catalyst. This superior performance is attributed to the higher levels of hydrocarbon precursors in the pyrolysis gas and the reduced crystallinity and particle size of the Ni-Co alloy in Co-Ni-Mo/MgO. Additionally, Co-Ni-Mo/MgO catalyzed the synthesis of MWCNTs with more uniform diameters, enhanced thermal stability, and the highest surface area (227 m2/g). The study also demonstrates effective nitrogen (2.2–2.8 at%) and sulfur (1.5–1.9 at%) doping of MWCNTs, which can be tailored depending on the manure type and catalyst. These findings highlight the strong potential of the trimetallic Co-Ni-Mo/MgO catalyst in the pyrolysis-CVD process for animal wastes.