464480 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.
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