Hydrogen Production via Chemical Looping Steam Reforming of Ethanol: Effect of Ce and La on Ni-based Oxygen Carrier Performance

Abstract

Chemical looping steam reforming of ethanol for hydrogen production has been studied. In this process, the high hydrogen content compound, ethanol, was reacted with steam and oxygen carriers (OCs) through the redox reaction cycle to produce the clean fuel H2. The effects of the different promoters, CeO2 and La2O3, in Al2O3-supported Ni-based OCs were investigated. The mixed promoters Ni-Al2O3 OCs were synthesized by wet impregnation method. The fresh OCs were characterized by X-ray powder diffraction (XRD), N2 adsorption-desorption, H2-temperature programmed reduction (H2-TPR) and Scanning electron microscope/Energy dispersive x-ray spectroscopy (SEM/EDX) technique. The redox activity test was performed in a fixed bed reactor by alternating between fuel and air feeds at isothermal condition of 500°C. The fuel feed was composed of ethanol and steam with steam to ethanol (S/E) mole ratio of 3. It was found that addition of CeO2 and La2O3 on Ni/Al2O3 improved the metal dispersion, reduced the crystallite size and enhanced reducibility of NiO. The La2O3 promoted (Ni/La2O3-Al2O3) and CeO2 and La2O3 co-promoted (Ni/La2O3-CeO2-Al2O3) OCs showed high performance and stability in chemical looping steam reforming of ethanol with the maximum ethanol conversion of 98.3 and 92.5 %, respectively, with maximum H2 yield of 2.9 and 3.2 mol/mol ethanol, respectively. In addition, forming of La2O3-CeO2 solid solution phase in Ni/La2O3-CeO2-Al2O3 oxygen carriers enhanced the oxygen storage capacity (OSC) and high oxygen mobility (OM) of OCs, resulting in a lower carbon deposition.