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Understanding and Controlling Light Alkane Reactivity on Metal Oxides: Optimization Through Doping

  • Author(s): Derk, Alan
  • Advisor(s): McFarland, Eric
  • Metiu, Horia
  • et al.
Abstract

Metal oxide catalysts have numerous industrial applications and have garnered research

attention. Although oxides catalyze many important reactions, their yields to products are

too low to be of economic value due to low conversion and/or low selectivity. For example,

some oxides can catalyze the conversion of methane to intermediates or products that are

liquefiable at yields no higher than 30%. With improved yield, such a process could help

reduce the trillions of cubic feet of natural gas flared every year, saving billions of dollars

and millions of tonnes of greenhouse gases. To this end, one goal of this work is to

understand and improve the catalytic activity of oxides by substituting a small fraction of the

cations of a "host oxide" with a different cation, a "dopant." This substitution disrupts

chemical bonding at the surface of the host oxide, which can improve reactant and lattice

oxygen activation where the reaction takes place. Another goal of this work is to combine

catalysts with metal oxides reactants to improve thermodynamic limitations. Outstanding

challenges for the study of doped metal oxide catalysts include (1) selection of dopants to

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synthesize within a host oxide and (2) understanding the nature of the surface of the doped

oxide during reaction.

Herein, strongly coupled theoretical calculations and experimental techniques are

employed to design, synthesize, characterize, and catalytically analyze doped oxide catalysts

for the optimization of light alkane conversion processes. Density Functional Theory

calculations are used to predict different energies believed to be involved in the reaction

mechanism. These parameters offer valuable suggestions on which dopants may perform

with highest yield and activity and why. Synthesis is accomplished using a combination of

wet chemical techniques, suited specifically for the preparation of doped (rather than

supported or mixed) metal oxide catalysts of high surface area and high reactivity.

Characterization is paramount in any doped-oxide investigation to determine if the catalyst

under reaction conditions is truly doped or merely small clusters of supported catalyst. With

that goal, diffraction, X-ray, electron microscopies, infrared spectroscopy, and chemical

probes are used to determine the nanoscopic nature of the catalysts. Additional novel

measurement techniques, such as transient oxidation reaction spectroscopy, determined the

nature of the active site's oxidation state.

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