(122d) Preventing H2s Poisoning of Pd Membranes for H2 Purification Using Applied Electric Fields

Petroleum refining annually consumes approximately 26 million tons of Hydrogen at a cost of $30 billion. Most of this hydrogen is produced by methane or naphtha reformation, which simultaneously produces several contaminants (H₂S, H₂O, etc.). This H₂ then requires purification which constitutes roughly 1/5 of the total dollar cost and accounts for ~15% of total efficiency losses in the H₂ production process. Theoretically, the best separation process would consist of a single step, which could be achieved by a dense Pd metal membrane. However, the prevalence of contaminants, particularly H₂S, which poisons and corrodes Pd membranes, prevents their widespread adoption in petroleum refining despite their high H₂ flux and selectivity. Here, we use density functional theory to demonstrate a proof of concept for using an applied electric field (AEF) to prevent the decomposition of H₂S on the Pd(111) surface. We find that strong (2 V/Å) AEFs oriented toward and away from the Pd surface similarly reduce the adsorption energy of H₂S but have conflicting effects on the barrier of S-H scission such that a strong field oriented toward the surface reduces the rate of H₂S decomposition. These findings are integrated into a microkinetic analysis which shows no significant surface coverage of Sulfur adatoms at this field strength and orientation. Here, the overall effects of the AEF strength and orientation on the surface electronic density, reaction thermodynamics and kinetics, and surface coverage over time are reported.