Combined steam and CO₂ reforming of CH₄ using coke oven gas on nickel-based catalyst: Effects of organic acids to nickel dispersion and activity

Combined steam and carbon dioxide reforming with CH₄ (CSCR) has been investigated using Ni/Al₂O₃ catalysts, where γ-Al₂O₃ support was previously modified with four different organic acids before nickel impregnation, to verify the effects of different nickel distributions induced from the modified acid sites to the catalytic activity. The CSCR reactions were performed at T=750°C, P=1.0MPa, space velocity of 36,000L(total mixed gas)/(kg_cat·h), and CH₄/CO₂/CO/H₂/H₂O molar ratio=1/0.38/0.29/2.09/1.2, which is the typical compositions of the coke oven gas in steel industry. The Ni/Al₂O₃ prepared by formic acid for the pretreatment of γ-Al₂O₃ showed a higher catalytic activity due to the maintenance of smaller nickel particles even after a high temperature CSCR reaction. The types of organic acids significantly changed the surface properties of γ-Al₂O₃ by varying the isoelectric points, which are strongly depending on pKa values of organic acids, and it concomitantly alters the dispersion of nickel precursor with the different deposition depths in γ-Al₂O₃ pores by largely changing the particle size distribution and the metal-support interaction. The surface-enriched nickel containing Ni/Al₂O₃ pretreated with oxalic acid was also applied to derive the kinetic parameters using Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism by showing an activation energy of ~240kJ/mol for the CSCR reaction.