Promoting Effect of Sulfur Addition on the Catalytic Performance of Ni/MgAl2O4 Catalysts for Isobutane Dehydrogenation

Ni/MgAl2O4 catalysts with high NiO loadings were highly active for isobutane cracking, which led to abundant formation of methane, hydrogen and coke. The results of activity testing and XRD characterization jointly revealed that large ensembles of metallic nickel species formed during reaction notably catalyzed cracking instead of dehydrogenation. However, after introduction of sulfur into Ni/MgAl2O4 catalyst through impregnation with ammonium sulfate, undesired cracking reactions were effectively inhibited, and the selectivity to isobutene increased remarkably. Totally, up to ∼42 wt % isobutene could be obtained at 560 °C in a single pass after the modification. From the characterization results, it was also concluded that, after sulfur introduction, NiO particles became much smaller and better dispersed on the catalyst surface. NiS species, formed during the induction period of the reaction, not only facilitated isobutene desorption from the catalyst, but also constituted the active sites for isobutane dehydrogenation. In addition, due to the appearance of NiS species, Ni/MgAl2O4 catalyst after H2S/H2 sulfuration exhibited a high initial activity without experiencing an induction period, further confirming the crucial role that introduced sulfur played.