Comparison of Ni and Ni-Ce/Al2O3 catalysts in granulated and structured forms: Their possible use in the oxidative dehydrogenation of ethane reaction

Abstract

Ni and Ni-Ce/Alumina catalysts in structured form were prepared, characterized by different techniques and tested in the oxidative dehydrogenation of ethane (ODE). In order to gain further insight into active species, catalysts in granulated form were also synthesized, characterized and evaluated in the same reaction test. The results indicated that the Ni and Ni-Ce/Al2O3 granulated catalysts were active and selective for this reaction. The addition of cerium using two atomic ratios (Ce/Ni = 0.11 and 0.25) significantly increased the ethylene productivity by kg of nickel mainly motivated by the marked increment in ethane conversion. This behavior could be explained by the smaller nickel oxide crystallite size and the incorporation of nickel into the ceria lattice. The structured systems showed similar active species but achieved a better performance in terms of ethane conversion and ethylene productivity, compared with the granulated forms. The higher catalytic activity could be associated with the presence of lower crystallite sizes of the active phases and also related to a better utilization of active sites due to a higher accessibility of the reagents to the catalyst surface. The existence of certain species (mainly chromium oxide) in the coverage also contributed to obtain higher conversion even though the selectivity to ethylene decreased. Lower temperature treatments applied to the structured support (550°C instead of 700°C) reduced the amount of these undesired species that favor the total oxidation of ethane.