Selective Hydrogenation of Acetylene over Pd-Mn/Al(2)O(3)Catalysts

Novel bimetallic Pd-Mn/Al(2)O(3)catalysts are designed by the decomposition of cyclopentadienylmanganese tricarbonyl (cymantrene) on reduced Pd/Al(2)O(3)in an H(2)atmosphere. The peculiarities of cymantrene decomposition on palladium and, thus, the formation of bimetallic Pd-Mn catalysts are studied. The catalysts are characterized by N(2)adsorption, H(2)pulse chemisorption, temperature-programmed desorption of hydrogen (TPD-H-2), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The modified catalysts show the changed hydrogen chemisorption properties and the absence of weakly bonded hydrogen. Using an organomanganese precursor provides an uniform Mn distribution on the catalyst surface. Tested in hydrogenation of acetylene, the catalysts show both higher activity and selectivity to ethylene (20% higher) compared to the non-modified Pd/Al(2)O(3)catalyst. The influence of the addition of Mn and temperature treatment on catalyst performance is studied. The optimal Mn content and treatment temperature are found. It is established that modification with Mn changes the route of acetylene hydrogenation from a consecutive scheme for Pd/Al(2)O(3)to parallel one for the Pd-Mn samples. The reaction rate shows zero overall order by reagents for all tested catalysts.