The Preparation And Performance Of Ni-based Oxygen Carriers In Chemical Looping Reforming For Hydrogen Production

Chemical looping reforming is a new and promising process for hydrogen production.The process can achieve auto-thermal condition and eliminate the effect of carbon deposition on oxygen carriers.But the performance of oxygen carriers is crucial for efficient hydrogen production.The Ni-based oxygen carrier is considered to be efficient in chemical looping reforming process.The paper focuses on the effect of the support and CeO2 promoter on the performance of oxygen carriers.The performance of Ni-based oxygen carriers over different supports was investigated in chemical looping reforming of ethanol for hydrogen production in a fixed-bed reactor.The Ni-based oxygen carri ers possessi ng di ff erent supports were synthesized,incl uding alloy Ni/Al2O3,lamellar Ni/MMT,mesoporous support Ni/Al-MCM-41 and Ni/SBA-15.The oxygen carriers were characterized by means of N2 adsorption-desorption,XRD,TEM,H2-TPR,H2 pulse chemisorption and TG-DTG.It was observed that Ni/SBA-15 exhibited most efficient confinement effect followed by Ni/AI-MCM-41,Ni/MMT and Ni/Al2O3,via:1)achieving smaller nickel partials and high dispersion as well as strengthened metal-support interaction;2)sintering resistance by spatial restriction of support;3)anti-coke ability by offering diffusion routes and reducing the C-species absorption on Ni partials.The ’dead time’ and amounts of oxygen transformation reflect superior redox performance in the following order:Ni/SBA-15,Ni/AI-MCM-41,Ni/MMT and Ni/Al2O3.Ni/AI-MCM-41 exhibited excellent activity in initial cycle of CL SR but the collapse of the Ni/AI-MCM-41 structure for its weak thermostability I eaded to the deactivati on and si nteri ng of active phrase.T he N i/S B A-15 and lamel lar Ni/MMT OCs exhibited stable and superior activity and stability but the performance of Ni/Al2O3 OCs was mediocre.Chemical looping steam reforming of ethanol using xCeNi/SBA-15 oxygen carriers was carried out at 650°C under atmospheric pressure in a fixed-bed reactor.The xCeNi/SBA-15 oxygen carriers were prepared by encapsulating CeO2 and NiO nanoparticles in SBA-15 using surfactant-assisted iso-volumetric impregnation method.Some techniques were conducted to characterize the oxygen carriers,including N2 adsorption-desorption,X RD,T EM,H2-TPR and DSC-TGA.It was observed that all the oxygen carriers exhibited high specific surface area(>435 m2/g).12CeNi/SBA-15 oxygen carrier achieved small Nio particle size(3.2 nm for),high dispersion and strengthened metal-support interaction.Meanwhile,superior redox performance and shorter ’dead time’ were achieved on account of easier reducibility of NiO particles with increasing amount of CeO2.The oxygen carriers exhibited superior sinter resistance capacity and high activity and stability in CLR process.The highest ethanol conversion(90.0%)and hydrogen selectivity(84.7%)were obtained for 12CeNi/SBA-15 even after 14 cycl e stability test.