Selective Hydrogenation of Phenylacetylene on Bimetallic Pd-Cu and Pt-Cu Catalysts.
Cladaras, George.
2013
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Abstract: The
development of selective catalysts has become a key concept in improving the efficiency
of processes. Controlling the product distribution of a reaction can result in fewer
by-products and reduce energy requirements for process equipment downstream. The
selective hydrogenation of alkynes to alkenes is of major importance to industrial
polymerization processes where alkyne/diene ... read moreimpurities can poison the polymerization
catalyst and have an unwanted inhibiting effect on the growth of the polymer chain. In
many circumstances, bimetallic catalysts have proved to have superior catalytic
properties such as greater activity, selectivity or stability compared to their
monometallic analogs. A study by the Sykes group (Chemistry, Tufts) in collaboaration
with our group has shown that in ultra-high vacuum (UHV), the addition of Pd minority
species (0.01 ML) onto an otherwise inert Cu(111) single crystal surface can activate
the Cu surface for selective hydrogenation reactions. This thesis work is an extension
of the surface science study to the preparation of bimetallic catalysts at the nanoscale
and their testing in hydrogenation reactions at ambient reaction conditions. The overall
aim of this work was to develop single atom alloy Pd-Cu and Pt-Cu catalysts which are
highly active and selective for the selective hydrogenation reaction of phenylacetylene
to styrene. The bimetallic catalysts were prepared by a colloidal synthesis of Cu
nanoparticles immobilized on γ-alumina support and the precious metals as a
minority species were deposited by galvanic replacement. The prepared materials and
synthesis technique were characterized with electron microscopy (TEM), UV-Vis
spectroscopy, X-Ray diffraction (XRD), temperature programmed reduction (TPR), BET
surface area measurements, chemisorption experiments and X-ray photoelectron
spectroscopy (XPS). The resulting catalysts can be described as γ-Αl2O3
supported Cu nanoparticles with a narrow size distribution. The Pt/Pd species are
alloyed and well-dispersed on the surface of the nanoparticles. The bimetallic catalysts
were tested for the liquid phase hydrogenation of phenylacetylene and were compared to
their monometallic analogs for reactivity and selectivity. Both the Pt-Cu and Pd-Cu
bimetallic catalysts display a significant improvement of the selectivity to styrene,
especially at high conversions. Based on the rate data, activation energy measurements
and the model study done in UHV, it is concluded that the reaction mechanism has been
altered in the bimetallic samples. Pt and Pd serve as sites for molecular hydrogen
dissociation to hydrogen atoms, which in turn spillover onto the Cu surface where the
hydrogenation reaction occurs. In summary, this work has demonstrated how Pd-Cu and
Pt-Cu bimetallic catalysts can serve as both active and highly selective hydrogenation
catalysts, where the Pd and Pt entities promote the hydrogenation activity of a Cu
surface which maintains high selectivity for phenylacetylene hydrogenation to
styrene.
Thesis (M.S.)--Tufts University, 2013.
Submitted to the Dept. of Chemical and Biological Engineering.
Advisor: Maria Flytzani-Stephanopoulos.
Committee: Matthew Panzer, and Charles Krueger.
Keywords: Chemical engineering, Chemistry, and Nanoscience.read less - ID:
- 6395wk51h
- Component ID:
- tufts:21877
- To Cite:
- TARC Citation Guide EndNote
