(547d) Selective Oxidation of Methane to Methanol Using Pd/Au Bimetallic Nanoparticles

Selective Oxidation
of Methane to Methanol using Pd/Au Bimetallic Nanoparticles

Cody Wrasman¹,
Joshua J. Willis¹, Jong Suk Yoo¹, Jens K. Nørskov¹,
Matteo Cargnello¹

¹Department
of Chemical Engineering and SUNCAT Center for Interface Science and Catalysis, Stanford
University, Stanford, CA 94305, USA

                Methane, which makes up the largest fraction of
natural gas, is an underutilized natural resource.  In petroleum operations,
byproduct natural gas is often flared rather than collected.  The difficulty in
utilizing methane fully lies in transporting gases from scattered wells to a
central location for processing.  Therefore, a method to convert methane to
liquid products must be developed to fully utilize this resource.  One
promising liquid product is methanol, which is already used in the industrial
chemical industry in massive quantities, can be converted into gasoline or
other transportation fuels, and has potential to serve as a future
transportation fuel itself.  Despite significant research efforts, methods to
convert methane to methanol at economically viable conditions, (T<300 ^oC
and near ambient pressure) none have been identified.  One of the largest
challenges in developing processes to carry out this conversion is the fact
that the oxidation of the first C-H bond in methane is the least energetically
favorable step in the methane total combustion reaction that converts methane
to carbon dioxide.  Once one C-H bond is oxidized, the others are increasingly
easy to oxidize, thus creating the undesired byproduct carbon dioxide.  One
possible way to address this is to synthesize a catalyst with active regions
small enough to only activate and oxidize a single C-H bond in methane per
catalytic cycle.  Computational simulations predict that this may be accomplished
by dispersing Pd onto Au nanoparticles.

            In
this work, controlled amounts of Pd are added to monodisperse Au nanoparticles
of several sizes using colloidal synthesis methods.  Pd is one of the most
active methane oxidation catalysts while Au is relatively inert to the
reaction.  The aim of the syntheses was to add controlled coverages of Pd to Au
NPs from atomic dispersion to complete Pd shells.  These particles were
deposited onto porous TiO₂ supports and tested for their catalytic
activity for the gas phase methane to methanol reaction. These experiments
allow for the elucidation of structure-activity relationships for Pd/Au systems
in the methane to methanol reaction and provide a starting point for future
catalyst design.