Hydrogen-Selective Pd-Ag-Ru Membranes and the Secret of High Permeability: The Influence of the Morphology of the Nano-Structured Coating on the Rate of Surface Processes

The efficiency of membrane reactors for steam reforming of hydrocarbons depends critically on the performance and selectivity of hydrogen-permeable membranes. In this work, a strategy for controlling the catalytic and gas-transport characteristics of Pd-Ag-Ru membranes by modifying the surface and controlling the morphology of nanostructured coatings was developed. It was found that as the process temperatures approached ~200 °C and the membrane thickness decreased, a transition to limitation of the hydrogen transfer process by surface stages was observed. Surface modification with pyramidal nanoparticles resulted in a significant increase in the hydrogen flux by up to 1.5 times compared to membranes with spiked nanoparticles and up to 2 times compared to membranes with spherical nanoparticles. The maximum difference in fluxes of up to 12 times was achieved compared to uncoated membranes. The achieved result is due to a significant increase in the active surface area associated with a systematic change in the morphology of the coatings. This aspect was a key factor in improving the catalytic activity of the material, reducing the energy barrier of sorption and accelerating the stages of hydrogen transfer through the developed membranes. Thus, modification with shape-controlled nanoparticle coatings presents an effective strategy for overcoming the limitations of the permeability of palladium-based membranes under conditions of small thickness and low temperatures. The use of the developed membranes in steam reforming reactors of alcohols can provide increased energy efficiency, conversion and purity of hydrogen.