Date of Award
Open Access Dissertation
John R. Regalbuto
Polyvinyl chloride (PVC) is the third most-produced plastic polymer world-wide by volume after polypropylene and polyethylene. Vinyl chloride monomer, which is polymerized into PVC, is produced via mercuric chloride catalysts that deactivate as mercury sublimes into the atmosphere from the catalyst surface, resulting in substantial environmental concerns.
In an effort to rationally synthesize non-mercuric catalysts, strong electrostatic adsorption (SEA) was used to prepare highly dispersed and active gold nanoparticles over low point of zero charge (PZC) carbon to increase the active metal surface area. The use of <1.5nm gold clusters did not lead to large increases in activity as there was an increased degree of particle coalescence during reaction for activated carbon supported samples. A pronounced support effect was observed in which oxide supports completely prevented Au sintering, but was virtually inactive. This suggests that the active site for the hydrochlorination reaction involves the carbon surface.
The stabilization of carbon supported gold nanoparticles in the HCl-rich reaction environment was achieved by “high surface free energy anchoring” shells of Au onto stable cores of high surface free energy metals. The synthesis of core-shell nanoparticles with high dispersion is possible by coupling electroless deposition (ED) with SEA. Highly dispersed Pt or Ru cores, which were stable in presence of HCl at elevated temperature (180°C), were prepared via SEA. ED was used to selectively deposit gold at various surface coverages onto the stable cores. The gold, which had a lower surface free energy than that of either the Pt or Ru, remained on the base metal after 20 hours of reaction time, as no gold (or Pt or Ru) sintering was observed. However, catalytic activity of the core-shell catalysts remained low, even though the amount of exposed Au surface was on the order of twenty times higher than the pure, sintered Au catalyst.
Efforts in catalyst design and synthesis have become increasingly important to ensure high metal utilization in catalysts employing expensive metals such as platinum group metals, and to maintain an active surface at high temperatures and/or extreme chemical environments. The ability to exploit differences in surface free energy of metal species coupled with SEA and ED to control particle morphology opens up a new vein of synthesis to stabilize particles through rational catalyst design that gives unparalleled control over particle morphology and size control.
O'Connell, K. C.(2016). Characterization, Synthesis And Stabilization Of AU Based Bimetallic Catalysis For The Hydrochlorination Of Acetylene. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/3438