Highly selective Pd composite membrane on porous metal support for high-purity hydrogen production through effective ammonia decomposition

In this study, an alumina sol assisted pretreatment method for porous metal supports was investigated for a highly selective Pd composite membrane for ammonia decomposition. Alumina sol made of boehmite was applied to an yttria-stabilized zirconia (YSZ) filled porous Inconel support. Additionally, a vacuum-assisted, two-step electroless plating of Pd drastically increased the hydrogen selectivity. The hydrogen permeation flux and selectivity (H2/N2) measured at 723 K and a transmembrane pressure difference of 100 kPa were 3.40 × 10−1 mol m−2 s−1 and 8,050, respectively. A highly selective Pd composite membrane was applied to a membrane reactor combined with a Ru/Al2O3 catalyst to efficiently produce high-purity hydrogen by ammonia decomposition. The ammonia decomposition test showed that the membrane reactor was able to achieve a high ammonia conversion (99.6%) and a high hydrogen purity (99.99%) with a hydrogen production rate of 0.25 Nm3 h−1 at 745 K and a gauge pressure of 500 kPa. The Pd composite membrane reactor has the advantage of being able to selectively removing hydrogen, increasing the ammonia conversion rate and high-purity hydrogen production via a one-step reaction combined with purification.