Development of Pd-Ag Compostie Membrane for Separation of Hydrogen at Elevated Temperature

Abstract

Pd-based membrane reactor offers the possibility of combining reaction and separation in a single operation at high temperatures to overcome the equilibrium limitations experienced in conventional reactor configurations. In this project to develop a defect-free and thermally-stable Pd-film on microporous stainless steel (MPSS) support for H 2 -separation and membrane reactor applications, the electroless plating process was revisited with an aim to improve the membrane morphology. Specifically, this study includes; (a) an improvement of activation step using Pulse Laser Deposition (PLD), (b) development of a novel surfactant induced electroless plating (SIEP) for depositing robust Pd-film on microporous support, and (c) application of Pd-membrane as membrane reactor in steam methanol reforming (SMR) reactions.In conventional sensitization/activation steps, Pd-seed deposition is uneven and penetration in the pore is problematic. To address this, PLD developed Pd-nuclei directly onto microporous substrate was explored. EDX (Energy Dispersive X-ray) and SEM (Scanning Electron Microscopy) results showed significant improved in Pd-nuclei deposition.In electroless plating, it was identified that the gas bubbles (ammonia and nitrogen) that released due to autocatalytic reactions tend to adhere to the substrate surface and result in poor Pddeposition. Incorporation of cationic surface active agents with favorable structures into the plating bath appears to be a promising remedy of surface to prevent gas bubbles from growing within the vicinity of the plating substrate. More importantly, suitable cationic charge and concentration would be useful to tailor the Pd-grain size and subsequent agglomeration. The surface morphology and compositional microstructures were examined using SEM coupled with in-situ EDS (Energy Dispersive Spectroscopy).Steam methanol reforming (SMR) was carried out in a Pd-MPSS membrane reactor fabricated by SIEP method. Experimental results along with modeling work revealed that the Pd-based membrane reactor was superior to conventional non-membrane reforming reactors with respect to conversion, selectivity and hydrogen productivity.In summary, we demonstrated that by using suitable surfactant in electroless plating, the Pd-film morphology can be significantly improved. This is a significant development in electroless plating method. This work resulted in an US patent filing. The Pd-MPSS membrane fabricated by SIEP showed excellent H 2 -permselectivity. The application of Pd-MPSS membrane as membrane reactorseparator is demonstrated by running SMR reaction.iv