Date of Award

Spring 2022

Document Type

Open Access Dissertation

Department

Chemical Engineering

First Advisor

John Regalbuto

Second Advisor

Christopher Williams

Abstract

Well-defined single-atom catalytic sites with unique geometric and electronic properties are at the forefront of catalyst research. One type of SAC is a so-called dilute limit alloy (DLA), where single metal atom sites are supported on (or in) the surface of a second metal. This category of well-dispersed atoms alloyed on a metal surface has shown to be effective in reactions like selective hydrogenation of alkynes and dienes to alkenes, ethanol dehydrogenation, and the Ullmann reaction of aryl chlorides. In biomass conversion, this type of catalyst may find its way to address and improve conversion and yield that are crucial for it to be economically feasible, given that the cost of production is greatly dependent on catalyst cost and catalyst life cycle. In this work, the generalizable, scalable, and facile synthesis method of strong electrostatic adsorption (SEA) is pushed to the limit of metal dilution to prepare single atom alloy catalysts. It is evaluated for the upgrading of a bio-oil model compound.

First, silica-supported dilute limit alloy (DLA) bimetallic catalysts (Y1X/SiO2, Y=Pt, Pd and Ru; X=Cu, Co and Ni) were prepared using modified simultaneous strong electrostatic adsorption (co-SEA) with controllable metal ratio deposition to obtain ultrasmall nanoparticles of the abundant metal X alloyed with an isolated atom Y on the surface. Monometallic catalysts (Pd, Pt, Ru, Cu, Co, and Ni) were also prepared by SEA. H2-TPR of dried DLA catalysts suggest close interaction between the two metals involve even at high dilution and the diffraction patterns of as-synthesized reduced catalysts implies ultrasmall nanoparticle. Confirming the existence of this isolated atom was the next step with the application of CO probe Fourier transform infrared (CO-FTIR) spectroscopy on a two-metal surface where a convoluted spectra complicates the analysis. A summary of CO vibration frequencies adsorbed on these isolated atoms were made. Finally, these DLA catalysts were evaluated in aqueous phase furfural hydrogenation reaction in a batch reactor. Monometallic nickel was activated with the addition of single atom sites on the surface. Also, changes in product selectivity were observed for cobalt- and copper-based catalyst with the addition of single atom sites. It was observed that Pd-X DLA and Y-Co based DLA are resistant to sintering after 10 hours of aqueous-phase reaction (150 °C, 430 psig H2) . Minimal dissolution of the abundant metal was observed for Cu-based DLA

Rights

© 2022, Leandro Tagum De Castro

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