Exploring the chemistry of metal/metal oxide catalysts: an insight into nanoscale surface interactions
Date
2023
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Publisher
University of Delaware
Abstract
The work outlined in this dissertation is dedicated to the surface chemistry of promoted metal nanoparticle catalysts for dry reforming of methane (DRM). The main part of this work focuses on the effect of promoters on platinum and nickel active catalysts and understanding how the change in surface chemistry affects the mechanism of the DRM reaction. We have identified several promoters that improve the DRM activity by tuning the surface chemistry; boron promoter with platinum catalyst and transition metal promoters with nickel catalyst. The addition of promoter sites led to the migration of coke deposits away from active sites, improved surface activation of CO2, and morphological control over the coke deposits. This work is necessary because growing concern over the effects of climate change has necessitated research into potential fossil fuel replacements. The current energy infrastructure already supports hydrocarbon fuel sources. However, researchers' current challenge is the ability to produce fuel in a carbon-neutral process using inexpensive catalytic materials. Heterogeneous catalysis is paramount to solving the energy problem, and the chemistry of catalytic surfaces must be optimized to achieve carbon-based fuel production that can replace fossil fuels long term. Noble metals and transition metals are highly active to hydrocarbon conversion. The dry reforming of methane (DRM) is a promising reaction because it converts methane and carbon dioxide into a "synthesis gas", or syngas, which can be processed to produce fuels and other value-added chemicals. When in the form of a nanoparticle supported on metal oxide, the active surface area of the metal is maximized, and less metal is required for catalysis. However, nanoparticle catalysts are readily deactivated by coking (carbon deposits) and sintering (nanoparticle agglomeration). Noble metals are highly active to DRM due to their high selectivity and resistance to deactivation, but they are typically too costly for practical use. Nickel is a promising DRM catalyst because of its low cost and high activity but is more susceptible to deactivation, therefore nickel is often paired with a second "promoter" metal to optimize the material and prevent deactivation. The development of active, stable bimetallic catalysts requires a detailed understanding of the chemistry at the surface during the reaction. In this work, we have identified the role of promoter sites using surface characterization techniques which provide better understanding of the catalytic mechanism.
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Keywords
Catalysis, Methane reforming, Surface chemistry, Metal nanoparticle catalysts, Coke deposits