Several catalysts with 1 w% Pd + x w% Ag (x=0, 0.1, 1, 2) have been supported on αAl2O3 or Na modified Na-Al2O3, and tested for the selective hydrogenation of 1,3-butadiene (BD) in the presence of 1-butene (1-B). With all catalysts the activity decreases markedly with aging due to accumulation of carbonaceous residue on the surface. Alloying the Pd with Ag and neutralising the acid sites on the support with Na both have significant effects on the selectivity, i.e. converting BD directly to n-butenes without isomerizing or hydrogenating significant quantities of the 1-butene. Addition of Ag to the Pd decreases the hydrogenation activity but increases the selectivity for BD conversion to butenes, although solid state and chemisorption measurements indicated that mixing of the two metals is limited under these conditions. Experiments with 13C-BD demonstrated that the major reaction pathway is to 1-B (〉50%). When normalized to the same pressure, much more of the product n-butane is formed from the BD than from 1-B. Alternate exposure to 13C-labeled and unlabeled BD showed that the surface residue does not mix significantly with the reactants and is formed predominantly from the BD, not the n-butenes. The presence of Na in the support seems to inhibit Pd/Ag mixing and results in decreased selectivity; some of the Pd or Ag may be encapsulated in the Na2O.
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry