N-Butane isomerization on Ni-promoted sulfated zirconia catalysts

Abstract

A few years ago, Hsu et al . found that Fe and Mn oxides were able to promote sulfated zirconia making it active for the isomerization of n-butane at temperatures much lower than those typically needed on unpromoted sulfated zirconia. Even though the interpretation of this promotion is still a matter of discussion, the idea that the presence of the transition metal oxides promotes an inter-molecular reaction path is gaining strong support. Previous reports on FMSZ catalysts have indicated that, in the absence of added H 2 , the isomerization activity exhibited a typical pattern when measured as a function of time on stream. In all cases, the initial activity was very low, but as the reaction proceeded, the conversion slowly increased, reached a maximum, and then started to decrease. In a recent paper, it was described that the time evolution, in terms of a simple mathematical model, includes induction and deactivation periods. This model predicts the existence of two types of sites with different reactivity and stability. One type of site was responsible for most of the activity observed during the first few minutes on stream, but it rapidly deactivated. For the second type of site, both, the induction and deactivation processes, were significantly slower. This chapter presents new evidence to support this hypothesis for the particular case of Ni-promoted catalysts. This chapter analyzes the promoting effects of Ni with and without the addition of H 2 , the activity induction, the catalyst deactivation, and its regeneration in air.