Study of C/Doped δ-Bi2O3 Redox Reactions by in Operando Synchrotron X-ray Diffraction: Bond Energy/Oxygen Vacancy and Reaction Kinetics Relationships

Abstract

One major technical and economic hurdle on the sequestration of CO2 is its separation from nitrogen when fossil fuels are burned in air. An alternative, thermodynamically equivalent approach is to use a metal oxide as an oxygen carrier (oxidizer) and then recycle the carrier following its reduction by exothermic reoxidation in air. This process, termed chemical looping combustion (CLC), places many requirements on the oxygen carrier. Here, we explore how to evaluate the relationship between the microscopic properties of an oxygen carrier and its performance in CLC. In this paper, systematically doped Bi2O3 were synthesized as oxygen carriers for the oxidation of carbon. In operando synchrotron X-ray diffraction and online mass spectrometry enable us to monitor both the phase evolution in the solid and the production of gaseous products. Initiation temperature and reaction kinetics were deduced on the basis of the X-ray diffraction peak intensity change. Results show that lower metal–oxygen bond energy and higher oxygen vacancy concentration of doped Bi2O3 led to lower onset temperature, faster reaction rate, and smaller activation energy for carbon oxidation. These results provide important insights into manipulating the atomic properties of oxygen carrier for CLC applications.