Controllable growth of defect-free zeolite protective layer on the surface of Pd membrane for chemical stability enhancement

Abstract

Pd membranes play a critical role in hydrogen purification due to excellent hydrogen permeability and selectivity. However, the poor chemical stability of Pd membranes when exposed to inclusion gases or organic reactants severely restricts their commercial applications. Herein, a novel strategy is developed to synthesize a thin and compact zeolite layer on the surface of Pd membrane which acts as an “armor” to protect it from being damaged by poisoning species. The results show that the zeolite membrane was NaA type and defect-free when using Si/Al ratio of 7.5 and silica sol as Si source after two-step hydrothermal synthesis. The variations of H2 permeance is monitored when Pd and zeolite-Pd composite membranes are exposed to 40% (ethanol/H2O) or 0.2% tetrahydrofuran (THF)/10% N2 in hydrogen atmosphere. Reactions between ethanol and water on Pd active sites are undetected, indicating the reactants are completely out of contact with Pd membrane in the presence of zeolite protective layer. Especially, compared to pure Pd membrane, almost 80% H2 permeance decline is constrained by the zeolite “armor” at 350 °C and W/E = 6. Moreover, the zeolite protective layer obviously enhances the chemical stability of Pd membrane by suppressing THF cracking and Pd active sites coverage.