Carbon dioxide reforming of methane over cobalt supported on activated carbon catalysts for syngas production

Abstract

Carbon dioxide reforming of methane (CDRM) utilizes two major greenhouse gases (GHG) of methane (CH4) and carbon dioxide (CO2) for syngas production. The transformation of GHG satisfies the requirements of synthesis processes and is a great interest for reducing gas emission. In this work, cobalt catalysts were synthesized by wet impregnation method onto oil palm shell activated carbon (OPS‒AC) and zeolite socony mobil-5 (ZSM‒5). The characterizations of supported cobalt catalysts were performed by elemental analysis, Brunauer-Emmett- Teller, thermogravimetric analysis, x-ray diffraction, temperature programmed reduction, temperature programmed desorption, scanning electron microscope, field emission scanning electron microscopy and transmission electron microscopy analysis. In comparison of both supported cobalt catalysts, OPS‒AC supported catalysts exhibited superiority in physical and chemical properties than that of ZSM‒5. Four manipulated parameters of the micro reactor system namely operating pressure, operating temperature, feedstock ratio of CH4/CO2 and gas hourly space velocity (GHSV) were investigated. In catalyst screenings, cobalt 14wt% of OPS‒AC (OPS-AC(14)) gave better catalytic performance than cobalt 14wt% of ZSM‒5 (ZSM‒5 (14)) with 15 % conversion and 60 % yield at 1023 K. The feedstock gases and products of syngas were analyzed by gas chromatography with thermal conductivity detector for yield of hydrogen (H2) and carbon monoxide (CO) and conversion (CH4 and CO2). Then, activity testings of OPS-AC(14) showed high temperature at 1173 K which favoured the conversion (CH4, 15 %; CO2, 12 %) and yield (H2, 80 %; CO, 47 %). However, conversion and yield disfavoured at high pressure of 7 bar and less effect by CH4/CO2 ratio and GHSV. Multi-responses of both yields (H2 and CO) were optimized at 903 °C, 0.88 bar, 1.31 CH4/CO2 and 4488 mL/h.g-catalyst for a global optimum value by desirability function analysis. Kinetics study of CDRM was performed for OPS-AC(14) using a power law, Arrhenius plot and equation. The reaction orders of CH4 and CO2 were 0.92 and 0.88, respectively which are close to the first order. The average activation energy of CO2 was lower (66.0 kJ/mol) than that of CH4 (77.3 kJ/mol). The potential side reactions were graphically plotted using Mathematica.