Carbon-dioxide activation by methane with iron-doped barium zirconate in chemical looping cracking system

Abstract

• Fe-doped BaZr 0.9 Y 0.1 O 3−δ (BZFY) was developed as highly active catalyst. • BZFY40 exhibited the highest methane cracking activity with tubular carbon growth. • Deposited carbon removal reaction with CO 2 was completed quickly. • Cracks generated in BZFY during reduction reaction was self-repaired with BaCO 3 . • The three-reactors system was proposed as an efficient CLMC system with BZFY40. Highly efficient carriers are developed for hydrogen production by methane cracking with carbon-dioxide activation in a chemical looping system. The carrier materials comprise BaZr 0.9 Y 0.1 O 3−δ (BZY) with a high proton conductivity and Fe as a base metal, and they are prepared by doping Fe into BZY. Thermal gravimetric analysis (TGA) showed that Fe-doped BZY (BaZr 0.9− x Fe x Y 0.1 O 3−δ , BZFY) with x = 0.4 (BZFY40) exhibited a high activity for carbon deposition with methane thermal decomposition. Surface observation and kinetic analysis suggested that the high activity for carbon deposition results from the promotion of tubular carbon growth with growth-mode transition from horizontal to vertical direction for the tubular carbon on reduced BZFY40. The rapid growth of carbon tubes proceeded with the base-growth mechanism, which can provide an advantage in the stable cycle reactions. The carbon removal reaction with carbon dioxide was also investigated. In BZFY, the removal reaction was completed in ~10 min. BZFY reacted with carbon dioxide under carbon dioxide flow to generate barium carbonate. From the BZFY surface observation before and after the reactions, the BZFY plate that was mechanically broken during the carbon deposition and removal cycles could be repaired by filling cracks with carbonate in the BZFY that was generated via the reduction reaction with methane. Therefore, carbon removal from the BZFY surface with carbon dioxide contributes to maintaining the BZFY particle shape during cycles with the self-healing scheme. The BZFY40 carrier has a high activity and durability for the carbon deposition and removal cycle and provides an effective system design for carbon dioxide-free hydrogen generation.