Understanding the Influence of Temperature On H2 Flux in the Presence of H2S On Pd-Based Ternary Alloy Membranes

摘要

Palladium (Pd) based membranes are appealing for hydrogen separation applications [1-4]. The use of pure Pd has been limited due to poor chemical tolerance in the presence of carbon monoxide and hydrogen sulfide (H2S), which are stream contaminants commonly found in coal-derived syngas [5-7]. Carbon species deactivate hydrogen dissociation sites on the Pd surface [8, 9]. H2S can block hydrogen dissociation sites, and cause Pd-sulfide formation, which has lower hydrogen permeability than Pd [3, 10, 11]. The hydrogen flux of a pure Pd membrane was reduced by 71 % in a gas mixture with only 4 ppm of H2S in hydrogen [7], In order to enhance chemical stability, Pd is alloyed with other metals such as gold, copper, and platinum [7, 9,12-18]. Although Pd-based binary alloys have been studied for over 50 years and have a presence in current literature, recent research has focused on Pd-based ternary alloys for improved chemical tolerance [19-21]. Fabrication and testing of these ternary alloys is in its infancy, but there are a few compositions with notably enhanced properties. Pd_(80)Au_(10)Pt_(10) alloy membranes fabricated by magnetron sputtering had a flux reduction of 21% when 20 ppm H2S was added to a water-gas shift mixture at 673 K and 1.27 MPa feed pressure [20]. Pd_(74)Ag_(14)Au_(12) showed no sulfide formation when exposed to 1000 ppm H2S in hydrogen at 623 K [19].