Cobalt catalysts for COx-free hydrogen production: Effect of catalyst type on ammonia decomposition in gliding discharge plasma reactor

Abstract

Hydrogen is considered the cleanest, most environmentally friendly fuel and energy carrier required for the gradual decarbonisation of many industrial sectors. Using ammonia as a Cox-free source of hydrogen is the most reasonable and most applicable method. This paper studies the properties and activity of cobalt catalysts in the ammonia decomposition reaction using a plasma-catalytic system. The effect of catalyst type (supported versus bulk) was evaluated. The catalysts were examined using XRD, STEM-EDX, and sorption techniques (N2 physisorption, TGA-TPR, H2-TPD, CO2-TPD) to reveal the influence of physicochemical properties of these two types of catalysts on the efficiency of NH3 decomposition in the plasma-catalytic process using a gliding discharge plasma. The results disclose that the supported-type catalyst (Ba-Co/CeO2) decomposed NH3 more effectively than the bulk-type catalyst (Co/Ce/Ba). At discharge power of 300 W and flow rate of 180 dm3 h–1 of NH3:N2 mixture (50/50 vol%), the ammonia conversion over the Ba-Co/CeO2 catalyst was 70%, whereas over the Co/Ce/Ba catalyst it was only 21%. The favourable performance of the supported-type catalyst was attributed to a more thermally stable surface area compared with the bulk-type catalyst. Smaller and more stable cobalt nanoparticles (NPs) with numerous weak hydrogen adsorption sites were also seen. Meanwhile, the strong basic sites were generated, improving the electron-donating ability of the surface active sites. High ammonia conversion and relatively low-energy consumption of the plasma-catalytic ammonia decomposition over Ba-Co/CeO2 make it suitable for practical hydrogen production applications, such as fuel cells and hydrogen storage.