High-performance mesoporous (AlN/Al2O3) for enhanced NH3 yield during chemical looping ammonia generation technology

Abstract

Chemical looping ammonia generation (CLAG), including the N-sorption/desorption steps of the N-carrier, is increasingly important due to the high demand for formation of carbon-free fuel. The N-sorption step, the synthesis of aluminum nitride (AlN) by the carbothermal reduction, has been widely studied for improving the purity and stability of aluminum nitride. However, there are few studies on how to enhance the porosity and thus N-desorption reactivity of AlN, one of the key issues for the CLAG. Therefore, in this paper, a supported Al-based nitrogen carrier (AlN/Al2O3) with mesoporous structure, in which 5% of Y2O3 was added as a catalyst, was developed with excess aluminum oxide (γ-Al2O3) and the corresponding N-desorption of the generated N-carrier was studied with a stationary bed reactor, X-ray diffraction (XRD), Brunner-Emmet-Teller (BET) measurements, Raman spectra and scanning electron microscope (SEM). The results showed that using the excess aluminum oxide in N-sorption step significantly led to the significant improvement in N-carrier's porosity and thus N-desorption reactivity, which did not vary with change in carbon types. Also, the N-sorption performance of γ-Al2O3 with carbon black was better than that with graphite due to their different carbon crystal structures. In addition, the effect of other parameters including the mole ratio of Al2O3:C, reaction temperature on the N-sorption performance of the N-carrier were studied. It was found that the specific surface area of the mesoporous structured Al-based AlN, synthesized with mole ratio of Al2O3: C being 3:3 at 1200 °C, reached to>70 m2/g, which was the best one for good NH3 synthesis performance.