Date of Award
Open Access Dissertation
John R. Regalbuto
In heterogenous catalysis, metallic nanomaterials play vital roles in numerous chemical processes. However, monofunctional catalysts are greatly impeded in their applications especially in the systems including tandem and/or sequential reaction steps. Besides, the catalytic performance can also be greatly influenced by the particle size, morphology, and geometry of the surface metal atoms.
The goal of this work is to synthesize bifunctional or bimetallic nanoparticles with high metal dispersion and homogenous alloys by rational synthetic strategies to facilitate the catalyst function. Strong electrostatic adsorption (SEA) is an effective and facile methodology to produce well dispersed and uniform nanoparticles. Metal-acid bifunctional catalysts with ultra-small Pd nanoparticles (< 2nm) and tunable amount of acid sites were synthesized by using SEA protocol over metal (Zr, Nb)-doped silicas with hierarchically large mesopores. These bifunctional catalyst with varied metal/acid ratios were evaluated by hydrodeoxygenated (HDO) reaction of methyl-guaiacol under mild conditions. The resultant catalytic performance showed Nb-containing bifunctional catalysts with ultra-small Pd nanoclusters benefited the reactivity (97% conversion, 100% hydrogenation and >20% selectivity to deoxygenated products) due to the optimal Pd/acid balance.
Addition of a secondary metal to prepare bimetallic catalysts is another promising strategy to overcome the limitations of mono-metallic/functional materials taking into consideration of the electronic and geometric effects in the alloying nanoparticles. Simultaneous strong electrostatic adsorption (co-SEA) was used to prepared bimetallic PdAu alloys with three atomic ratio (Pd:Au=3:1, 1:1, 1:3) on high surface area silica and g-Al2O3. The principle of preparing PdAu alloys with varied compositions was governed by controlling the concentration of Pd and Au complex precursors in co-SEA synthetic procedure. Highly dispersed and homogenously alloyed PdAu nanomaterials were successfully achieved (<1.6 nm). The presence of Pd oxide species co-SEA synthesized alloys with higher loadings of Pd is due to the ultra-small nanoparticles, the amount of which can be tuned by controlling the alloy composition. Further work was conducted to extend co-SEA synthetic procedure for yielding dilute limit of Pd into Au nanocluster (atomic Pd/Au=1:1, 0.23:1, 0.08:1, 0.04:1, ......, 0.01:1) on silica and estimated their catalytic function in the partial oxidation of 1-phenalethanol. Isolated Pd species in Au clusters were obtained over Pd/Au < 0.08. Significant improvement in the activity of 1- phenyethanol oxidation were acquired over PdAu homogenous alloys with Pd monomers due to the electronic and geometric effects.
Dong, A.(2022). Supported Metal Bifunctional and Bimetallic Catalysts With Precisely Controlled Structures and Properties. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/7105