Date of Award
Open Access Dissertation
John R. Regalbuto
Catalysts play an important role in many chemical reactions. However, simple impregnated monometallic catalysts are often limited in their function. One way to overcome this limitation is through the incorporation of a secondary metal to the catalysts. These bimetallic catalysts often have synergistic benefits not observed in the monometallic analogues. Here, we focused on the synthesis of bimetallic catalysts using rational methods in order to improve catalyst function; specifically by tuning the particle size, morphology, and composition. The two methods of interests were Strong Electrostatic Adsorption (SEA) and Electroless Deposition (ED). An adaptation of SEA to bimetallic catalysts (coSEA) was use to synthesize ultrasmall highly dispersed alloyed nanoparticles on high surface area oxide supports (alumina and silica). Bimetallic catalysts of Pt, Pd, Co, Cu, and Ni having ~1nm nanoparticles were synthesized over silica, and Pt-Pd bimetallics were synthesized over aluminosilicates. These co-SEA catalysts have improved bimetallic interactions due to the close proximity and well-mixing of atoms. The Pt-Pd catalysts were evaluated as diesel oxidation catalysts using a simulated diesel exhaust at ORNL. The coSEA catalysts were more active and stable compared to conventional co-impregnated catalysts. Moreover, these highly alloyed co-SEA catalysts remained more alloyed after high temperature treatments (>700°C) when compared to typical co-impregnation catalysts. Core-shell catalyst stabilization using surface free energy (SFE) principles was investigated through annealing treatments followed by catalyst characterization. The principle of anchoring low SFE metals on high SFE cores was demonstrated through the coupling of SEA for the nanoparticle cores and ED for the nanoparticle shells. The Ag-Ir core-shell materials resisted sintering with particle size growing only twofold for the bimetallic catalysts compared to over a tenfold size increase in the monometallic catalysts. This work demonstrated the effectiveness of using rational synthesis methods for bimetallic catalysts over simple co-impregnations. Having precise control on particle morphology, whether core-shell or alloyed, and size are important in catalyst design where high metal utilization and intimate bimetallic interaction are desired to reduce the amount of expensive precious group metals. By utilizing ED and SEA, we demonstrated new possibilities in improved bimetallic catalyst design that were unachievable with current conventional methods.
Phillip Wong, A.(2018). The Rational Synthesis of Bimetallic Catalysts on Oxide Supports. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/4511