International Journal of Hydrogen Energy, Vol.44, No.33, 18093-18102, 2019
On the use of an in situ magnetometer to study redox and sintering properties of NiO based oxygen carrier materials for chemical looping steam methane reforming
Two NiO based oxygen carrier materials (OCMs) were synthesized and tested for use as potential materials in chemical looping reforming applications. Redox properties of these materials were evaluated in successive methane reduction - air oxidation (redox) cycles in a thermogravimetric analyzer unit (TGA) and an in situ magnetometer. Zirconia supported (Ni-Zr) OCM exhibited excellent redox activity (high degree of reduction and oxidation) and stability during ten CH4 reduction-air oxidation cycles. The degree of reduction of the alumina supported (Ni-Al) OCM increased gradually during cycling experiments, due to the formation of easily reducible NiO from nickel aluminate species with successive reduction/re-oxidation. The Ni-Al OCM exhibited excellent stability with respect to oxidation resulting in nearly complete oxidation of reduced Ni in all cycles. Results from measurements in the magnetometer were in good agreement with those in the TGA for the Ni-Zr OCM (both with regards to the degree of reduction and oxidation) and the degree of oxidation of the Ni-Al OCM. A moderate crystallite growth with cycling was observed for Ni-Al, whereas a decrease in nickel crystallite size was observed for Ni-Zr. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.