Achieving equilibrium conversions for low-temperature NH3 decomposition: Synergy between catalyst and electric field effects

초록

In the advent of an energy shift towards renewable energy sources, ammonia is considered a promising energy carrier for convenient hydrogen storage and transport. However, ammonia decomposition requires temperatures higher than 500 °C to achieve 100% conversion. Here, we present the facile synthesis and use of nanocluster RuCeO2 catalysts for the low-temperature electric field-assisted ammonia decomposition reaction. The catalysts obtained desirable properties and achieved high conversions for ammonia decomposition under conventional conditions. Interestingly, catalyst activities significantly increased upon exposure to an electric field, achieving 100% conversion at 450 °C and obtaining exceptional conversions of up to 34% at a low temperature of 200 °C and a high GHSV of 30,000 mLNH3/gcath. Optimization of reaction parameters effectively increased NH3 conversions, allowed highly stable long-term activities, and enabled the catalyst to achieve equilibrium conversions at remarkably lower temperatures. Further studies reveal that the electric field essentially reduces apparent activation energies and boosts the ammonia decomposition reaction by promoting the recombinative desorption of N2 and H2, thereby alleviating the rate-determining step and preventing deactivation due to H2 poisoning. The occurrence of surface protonics as a result of N-H bond scission and transport of H+ species to the support, along with increased NH3 activation and oxygen vacancy migration improves charge transfer between the support and the Ru active sites, thereby resulting in increased desorption of N2 and H2 products. Thus, an energy-efficient route toward economical hydrogen production is achieved by combining electric field effects with a highly active RuCeO2 catalyst.

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