Atomic layer deposited Co/gamma-Al2O3 catalyst with enhanced cobalt dispersion and Fischer-Tropsch synthesis activity and selectivity

摘要

Co/gamma-Al2O3 catalysts were prepared by atomic layer deposition (ALD) of Co(acac)(2) and impregnation of Co(NO3)(2), characterized by HRTEM, XRD, XPS, TPR, H-2-TPD, O-2 titration, and Raman spectroscopy methods, and used for Fischer-Tropsch synthesis (FTS). The ALD temperature window for self-limited chemisorption of Co(acac)(2), rather than its condensation at lower or decomposition at higher temperatures, is 175-205 degrees C. The period for Co(acac)(2) saturated chemisorption and its complete reaction with ozone are also determined. Smaller cubic Co3O4 nanoparticles are formed in the ALD method, while spherical ones are developed in the impregnation method. The ALD catalysts have up to 2.3 times higher dispersions at the lower number of ALD cycles. However, more cobalt aluminates are formed on the ALD catalysts. In FTS, the catalyst with 6 ALD cycles shows 38% higher conversion, 30% higher C5+ selectivity, 28% less methane selectivity, and stabilizes at earlier time on stream, as compared to the impregnation catalyst with the same loading. (C) 2015 Elsevier B.V. All rights reserved.