Ni-based nano-catalysts for the dry reforming of methane
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Development of a highly efficient and coke-resistant, nickel based nano-catalyst in the carbon dioxide reformation of methane is reported. The alumina supported Ni-based catalyst with a metal loading of 5wt% was prepared via the solution combustion synthesis (SCS) method as well as the conventional wetness impregnation method. The synthesized catalysts were thoroughly characterized by a combination of analytical techniques including high-resolution electron microscopy (HRTEM-SAED), X-ray diffraction (XRD), nitrogen physisorption (BET surface area), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H 2 -TPR) and temperature programmed oxidation (TPO). Compared to the conventional nickel-impregnated (Ni-I) catalyst, the Ni-SCS nano-catalyst was superior in activity and stability during dry reformation of methane. Ni-SCS catalyst exhibited higher percentage conversions of methane and carbon dioxide. The percentage yields of hydrogen and carbon monoxide over Ni-SCS catalyst were also significantly higher. During the investigated period on stream for 50 h, the Ni-I catalyst deactivated severely, by contrast the Ni-SCS stayed active. It was clear from the results of elemental carbon analysis and TPO that deactivation of the Ni-I catalyst was due to severe carbon deposition, whereas the Ni-SCS catalyst exhibited minor carbon deposition. These differences in the catalytic activities and stabilities between the Ni-I and Ni-SCS catalysts were attributed to the difference in their physicochemical properties and chemical structure, as obvious from the results of the above mentioned analysis techniques. The XRD and XPS analysis revealed that the Ni-SCS nanocatalyst resulted in the formation of uniformly distributed nickel aluminates (NiAl 2 O 4 ) nano-crystallite spinels together with nickel oxide. The results of H 2 - TPR analysis clearly distinguished between NiO and NiAl 2 O 4 . H 2 -TPR affirmed the formation of NiAl 2 O 4 and NiO species on the SCS nanocatalyst but only NiO within the impregnation catalyst. In this regards the exceptionally high catalytic activity and stability of Ni-SCS nanocatalyst during dry reformation was attributed to the presence of NiAl 2 O 4 nano-crystallites structures. On the other hand, the presence of weakly associated NiO species on the Ni-I catalyst was responsible for decaying its activity due to carbon formation during the dry reformation of methane.