Incidence of the preparation method of the support on the behavior in n-butane dehydorgenation of Pt/MgAl2O4, PtSn/ MgAl2O4 y PtPb/ MgAl2O4 catalysts

SONIA BOCANEGRA; ALBERTO CASTRO; OSVALDO SCELZA; SERGIO DE MIGUEL

Braga-Portugal

Congreso; CHEMPOR 2008; 2008

Universidade do Minho

Two preparation methods of MgAl2O4 have been used: ceramic and co-precipitation. The supports were characterized by measurements of the textural properties (BET isotherms), XRD and 2-propanol dehydration. The XRD characterization shows the formation of MgAl2O4 spinel for both materials.The textural properties indicated that the specific surface of MgAl2O4 obtained by co-precipitacion was much higher than that obtained by the ceramic method. The results of 2-propanol dehydration reaction show a scarce activity for both MgAl2O4, mainly for MgAl2O4co-precipitation. This means that these materials have very low acidity. The monometallic catalysts were prepared by impregnation of both supports with solution of H2PtCl6 such as to obtain a Pt loading of 0.3 wt%. The bimetallic catalysts (PtSn and PtPb) were obtained by impregnation of the corresponding monometallic ones with an aqueous solution of SnCl2 or Pb(NO3)2. The Sn contents were 0.3 and 0.5 wt%. The Pb contents were 0.52 and 0.87 wt%. These catalysts were characterized by H2 chemisorption, TEM, TPR, XPS, test reactions of the metallic phase (cyclohexane dehydrogenation and cyclopentane hydrogenolysis) and evaluated in the n-butane dehydrogenation reaction at 530 ºC. The H2 chemisorption and TEM results show that Pt/MgAl2O4co-precipitation displays a lower metallic dispersion than the Pt supported on MgAl2O4ceramic. The characterizations carried out by TPR, XPS and test reactions show good interaction for bimetallic catalysts, except for PtPb/MgAl2O4co-precipitation. The evaluation of catalysts in n-butane dehydrogenation displays a lower activity of Pt(0,3)/MgAl2O4co-precipitation than  Pt(0,3)/MgAl2O4ceramic and a similar selectivity to all butenes. The bimetallic catalysts that contain Sn showed better activities and selectivities with regard to the monometallic ones, but the PtPb catalysts did not show the above mentioned behavior. Likewise, the PtSn(0.3)/MgAl2O4ceramic shows the best catalytic performance