n-Butane dehydrogenation over Ni-Sn/SiO2: Adsorption modes and reaction paths of n-butane and 1-butene

Compared with i-butane dehydrogenation over Ni-Sn/SiO2 catalyst, the conversion is higher for n-butane dehydrogenation, the selectivity to butenes is obviously lower, and the catalyst deactivates more rapidly. In order to clarify the difference, adsorption modes of n-butane and 1-butene along with desorption activation energy of 1-butene were determined by in-situ FTIR and TPD. n-Butane is adsorbed on Ni-Sn surface with a H atom in methyl, and the formed intermediates are prone to the rupture of C-C bonds, leading to the lower selectivity to butenes. In addition, secondary reactions of butenes also play an important role in decreased selectivity, but to a less extent due to the medium desorption activation of butenes (58 kJ mol(-)(1) for 1-butene, for example). The generation of coke is the third reason for lower selectivity. The rapid deactivation of Ni-Sn/SiO2 catalyst mainly results from the formation of 1,3-butadiene, coke precursor, by further dehydrogenation of butenes.