Development and Evaluation of Hydrophobic Catalysts for Deuterium Enrichment in a Gas-Vapor Reactor

Abstract

Deuterium, an isotope of hydrogen, has found diverse applications in pharmaceutical, nuclear, and analytical fields owing to its chemical similarity to protium, but distinct mass which gives rise to the kinetic isotope effect. The water-hydrogen catalysis method offers a clean route for deuterium enrichment from its natural abundance (0.015 %). This process can achieve industrial-grade purity (> 99 %) in the presence of a hydrophobic catalyst. However, the industrially used Pt/C/PTFE catalyst is costly, making the initial capital requirement for deuterium enrichment high. Further, limited documentation on the synthesis and performance of Pt/C/PTFE hinders the development of viable alternatives. This thesis develops a co-current gas-phase reactor and tests its ability to directly study kinetics for catalysts that perform deuterium enrichment through isotopic exchange between H2/H2O. A protocol for a Pt/C/PTFE catalyst was developed and standardized. This catalyst was used to establish benchmark catalytic performance metrics for deuterium enrichment of H2O by catalytic exchange between a blended H2/D2 and H2O vapor stream. A series of Ni-Pt alloys were then explored as low-Pt alternatives to this industry standard catalyst. The reaction temperature and reaction time required for alloying of NiPt with stoichiometric ratios of 1Ni:3Pt, 1Ni:1Pt and 3Ni:1Pt were established. The resultant alloy nanoparticles were prepared into Ni-Pt/C/PTFE catalysts, analogous to the industry standard Pt catalyst, and their catalytic properties were tested. A reliable evaluation method for assessing catalytic activity was developed, through which mass-transfer coefficients and activation energies were determined. Comparative analysis showed the NiPt/C/PTFE alloy to successfully catalyze the isotopic exchange reactions but not outperform Pt/C/PTFE. Mechanistic analysis provides evidence for OH* oversaturating the surface at elevated temperatures in the reaction, which may be responsible for lower-than-anticipated catalytic performance. Further investigations into temperature-dependent kinetics may guide the rational design of cost-effective catalyst for deuterium enrichment.