n-butane dehydrogenation on PtSnIn and PtSnGa trimetallic catalysts supported on structured materials prepared by washcoating

Abstract

The aim of this work was to evaluate PtSnIn and PtSnGa catalysts supported on structured materials, composed of a thin layer of γ- Al2O3 deposited on compact spheres of α-Al2O3, in the non-oxidative dehydrogenation of n-butane to n-butene. The trimetallic catalysts supported on γ-A-wc showed better catalytic behaviour in terms of activity, selectivity to all butenes, and a low deactivation along the reaction time, compared to the monometallic catalyst. PtSnIn/γ-A-wc and PtSnGa/γ-A-wc catalysts with the highest In or Ga loading showed better performance than those with a lower content of promoters. The results of the pulse experiments clearly indicated the important effect of the promoters added to Pt, both by sharply increasing the selectivity to butenes and by decreasing the carbon formation during the first steps of the reaction. The characterization of the metallic phase showed that the addition of promoters such as Sn and In or Sn and Ga produce geometric effects, dilution and blocking effects on Pt atoms. XPS results confirmed the presence of surface metallic Pt(0), In(0) or Ga(III), Sn(II)/Sn(IV) species in a high concentration and minor amounts of surface Sn(0), probably forming alloy particles with Pt and the third metal. The PtSnIn (0.5)/γ-A-wc catalyst which showed the best catalytic behaviour in flow experiments was submitted to successive reaction-regeneration cycles in order to determine its catalytic stability. There was a small yield decrease in the first two cycles, but from the third cycle onwards the yields to butenes proved to be more stable. These results were very promising mainly if compared to those obtained for the monometallic Pt catalyst. Characterization results of the catalyst after cycles showed that the metallic phase did not undergo significant modifications.