MgAl2O4 spinel prepared by novel mechanochemical synthesis used as a support of multimetallic catalysts for paraffin dehydrogenation

Abstract

The catalytic performance in nbutane dehydrogenation of bimetallic PtSn, PtGa and PtIn, and tri metallic PtSnIn and PtSnGa catalysts (with low metal contents) supported on a MgAl2O4 prepared by a novel mechanochemical synthesis was evaluated both in flow and pulse equipment. The influence of the addition of different promoters (Sn, Ga and In) to Pt on the activity, selectivity and deactivation in the nbutane dehydro genation reaction was studied. Stability experiments through successive reactionregeneration cycles were car ried out for selected catalysts. In order to correlate the properties of the metallic phase of the catalysts with the catalytic behavior, several characterization techniques were used, such as test reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis), TPR, XPS, H2 chemisorption and TEM. Bimetallic PtSn catalyst has a better catalytic behavior than PtIn and PtGa ones. For PtSnM (M: In or Ga) cat alysts, whereas Ga addition to the bimetallic catalyst does not practically modify the dehydrogenation perform ance, the addition of In produces an increase of the activity and the selectivity to butenes. Characterization results indicate the presence of geometric effects for the PtSn catalyst, and geometric and electronic effects for PtIn and PtGa ones. For trimetallic catalysts, the presence of a close contact between Pt, Sn and In or Ga in both trimetallic catalysts was found, mainly due to geometric effects like blocking and dilution of the active sites by the promoters. In stability experiments, the trimetallic PtSnIn/MgAl2O4 catalyst clearly displays the best cat alytic performance along reactionregeneration cycles, though PtSnGa and PtSn catalysts also showed a very good behavior through the successive cycles. The characterization of these catalysts after cycles shows that their metallic phases are slightly modified along the cycles.