On the Role of Promotors in Pd Catalysts for Methanol Synthesis

Resume Plusieurs catalyseurs au Palladium sur silice avec ou sans promoteurs (Mg2+ et La3+) ont ete prepares et etudies. La selectivite pour l'hydrogenation de CO en methanol ainsi que l'activite sont plus elevees pour les catalyseurs contenant des ajouts. Par l'application de plusieurs techniques experimentales (extraction des especes Pdn+ par l'acetylacetone; M.E.; spectroscopies: U.V.-visible, R.P.E., I.R.) il a ete demontre que la promotion du Palladium par Mg ou La, provoque la formation ou la stabilisation des centres positifs: Pdn+, qui comme nous le suggerons, sont essentiels pour la production de methanol a partir de CO et H2. Abstract Several Palladium catalysts on silica with and without promotors (Mg2+ and La3+) were prepared and studied. By catalytic activity measurements of the synthesis gas reaction over these catalysts it was found that the addition of the promotors increases both the selectivity for methanol and the activity of the Palladium catalysts. Using several experimental techniques (extraction of Pdn+ by acetylacetone; E.M.;U.V./VIS;E.P.R.;I.R.) it was shown that promotion of Palladium with Mg2+ or La3+ gives rise to the formation and stabilization of positive centres: Pdn+, which we suggest are essential for the production of methanol from synthesis gas.