Simultaneous production of hydrogen and carbon nanotubes from cracking of a waste cooking oil model compound over Ni-Co/SBA-15 catalysts

Hydrogen is considered an ideal energy carrier. However, the use of fossil fuels to produce hydrogen depletes natural resources and causes environmental problems. Therefore, there is an urgent need to find alternative raw materials and technologies for the production of hydrogen. Waste cooking oil (WCO) is a renewable energy source that has emerged as a potential raw material for hydrogen production. This study describes the production of hydrogen and carbon nanotubes (CNTs) by catalytic cracking of a WCO model compound (WCOMC) performed in a lab-scale fixed bed using Ni-Co/SBA-15 catalysts. The phase, structure and reduction properties of the catalyst were analysed by using different characterisation methods. The effects of the nickel-cobalt metal content and the reaction temperature on both the hydrogen production and the quality of the CNTs were investigated. The deposited carbonaceous products were characterised to analyse their external appearance, internal structure, oxidation stability and graphitisation degree. The results indicated that the catalyst containing 20% Ni and 30% Co showed the highest activity. When reaction temperature was 800°C, the instantaneous volume fraction of hydrogen was close to 43.5 vol% and the content of hydrogen in the gas product was close to 66.5 vol%. A few multi-walled CNTs having a small diameter and some CNTs with an open-topped structure were deposited on 10%Ni-40%Co/SBA-15 and 30%Ni-20%Co/SBA-15, respectively. Thermogravimetric analysis and Raman spectroscopic analysis indicated that all CNTs showed high oxidation stability and a high degree of graphitisation.