| Bimetallic interactions of Pd supported catalysts are of importance due to their wide industrial application, in particular in the reactions that involve the selective hydrogenation of alkynes to alkenes. Pd bimetallic catalysts exhibit enhanced activity and selectivity than their monometallic counterparts. The effects of the method of the synthesis, support and pretreatment were studied. A detailed study of the bimetallic interaction of Pd with Ag and Zn using diverse techniques was performed, both monometallic and bimetallic catalysts were studied and compared, the effect of support was explored, as well as the effect of synthesis procedures. In monometallic impregnated catalysts, the major source of variations in terms of ethylene and oligomers selectivity, among the different catalysts, is the type of support on which the Pd is loaded; minor effect was related to the pretreatment procedure. In the bimetallic impregnated catalysts, both (support type and pretreatment procedure) modify the ethylene and oligomers selectivity of the catalysts. XRD shows that in the monometallic impregnated catalysts, the active site is metallic Pd. In the bimetallic impregnated catalyst, the active site is a function of support and pretreatment procedure: metallic Pd when reduced at 100°C, alloy after reduced at 500°C. Temperature programmed reduction results allow us to relate the pretreatment effect to the amount of Hz acquired by the catalyst during the PdO reduction, released during beta-PdHx decomposition and the amount of irreversible adsorbed hydrogen, with the catalyst selectivity. There is a clear beneficial effect of the inclusion of Ag in the catalyst prepared by impregnation; however not only is the inclusion of Ag necessary to enhance that catalyst performance, but the pretreatment also plays a significant role.; Plasma torch synthesis was probed as a novel way to prepare tailor designed micro alloy particles. However, the plasma torch prepared catalyst presents almost the same activity and selectivity as the monometallic impregnated catalyst, even after Ag has been added. XRD results reveal no formation of Pd-Ag alloy while PdZn formation was obtained. The morphology and phase composition shows a dependency on the intensity of the interaction of the particle within the plasma zone. Plasma torch synthesis methods affected the total surface area of the support, especially in the case of Al2O3. |
