Ammonia deep chemical looping combustion on perfect and reduced Fe ₂ O ₃ : A theoretical account

Abstract

Summary Chemical looping combustion (CLC) between Fe2O3 and NH3 can lead to the generation of H2O, H2, NO, and N2 as the main product under different reaction stages, reasonable control of which can realize effective conversion and utilization of NH3. To initiate the CLC reaction, NH3 is chemically adsorbed on the perfect Fe2O3 surface with a hybrid between N and Fe, leading to the dehydrogenation of NH3 into *NH2 as the first reaction step. Then the second dehydrogenation step (*NH2→*NH) acts as the speed‐control step for the oxidation of NH3 into H2O and N2, leading to the reduction of Fe2O3. The reduction of Fe2O3 promotes the further adsorption of NH3, especially the intermediate species *NH2, *NH, and *N, which favors the generation of H2O and N2. Further reduction of Fe2O3 into the oxidation state lower than ~Fe2O2.25 shows lower surface oxygen potential, which is beneficial to the formation of H2 and N2. Results suggest that reasonable control of the oxidation state of iron oxide can optimize the NH3 CLC process for H2 production.

Review and Outlook of Theoretical Understanding on Pollutants Reaction Mechanism during Chemical Looping Combustion

“…The reduction of oxygen carrier is conducive to the effective conversion and utilization of NH 3 in CLC. It was found that NH 3 was mainly oxidized to H 2 O and N 2 on the Fe 2 O 3 surface . H 2 O can be formed by the reactions of OH* + NH 3 * → NH 2 * + H 2 O and 2OH* → H 2 O + O*, and the corresponding energy barriers are 0.77 and 1.90 eV, respectively.…”