Single Atom Alloys for Efficient and Selective Bond Activations: A Model Surface Chemistry Approach
Abstract: Heterogeneous catalysis is extensively utilized in the fabrication
of chemicals and materials. Finding a catalyst that exhibits high selectivity and activity
for a given process is often difficult as surfaces tend to be more active with strong
binding of adsorbates, but more selective with weak binding. Typical heterogeneous
catalysts utilize reactive metals such as Pd, Pt, Ir, and ... read moreRu. Not only are many of these
metals expensive and rare, but they also frequently suffer from less than ideal catalytic
selectivity. In addition, it is often difficult to determine the reaction mechanisms of
heterogeneous catalysts, due the diversity of surface sites. New strategies are needed to
efficiently use these expensive metals, and to improve catalytic selectivity. This thesis
uses a surface science approach to test the catalytic viability and map the reaction
mechanism of single atom sites for a variety of industrially relevant reactions. We
fabricate single atom alloys (SAAs), where Pd or Pt atoms exist as single isolated sites
substituted into a Cu(111) lattice. The economically friendly SAA approach use allows for
the activation of reactants using very small amounts of the expensive dopant metals, while
still maintaining the high selectivity and low cost typical of Cu catalysts. The
practicality of SAAs for a number of important reactions including H2 activation,
hydrogenations, dehydrogenations of O-H bonds, and C-H activation is examined. These
reactions are relevant to a number of fields including the petrochemical, pharmaceutical,
food, fine chemicals, and environmental industries. Using a combination of scanning
tunneling microscopy and temperature programmed desorption/reaction, the elementary steps
of the reaction mechanisms can be mapped out at an atomic level. In general, it is found
that SAAs are more active than pure Cu, with greater selectivity compared to Pd and Pt
catalysts. The SAA approach allows for a catalyst where the best properties of the dopant
metals and Cu are apparent, and can be widely applied to a number of catalytically relevant
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Chemistry.
Advisor: Emile Sykes.
Committee: Arthur Utz, Samuel Thomas, and Yuriy Roman.
Keywords: Chemistry, and Physical chemistry.read less