Abstract
High throughput experimentation has the capability to generate massive, multidimensional datasets, allowing for the discovery of novel catalytic materials. Here, we show the synthesis and catalytic screening of over 100 unique Ru-Metal-K based bimetallic catalysts for low temperature ammonia decomposition, with a Ru loading between 1–3 wt% Ru and a fixed K loading of 12 wt% K, supported on γ-Al2O3. Bimetallic catalysts containing Sc, Sr, Hf, Y, Mg, Zr, Ta, or Ca in addition to Ru were found to have excellent ammonia decomposition activity when compared to state-of-the-art catalysts in literature. Furthermore, the Ru content could be reduced to 1 wt% Ru, a factor of four decrease, with the addition of Sr, Y, Zr, or Hf, where these secondary metals have not been previously explored for ammonia decomposition. The bimetallic interactions between Ru and the secondary metal, specifically RuSrK and RuFeK, were investigated in detail to elucidate the reaction kinetics and surface properties of both high and low performing catalysts. The RuSrK catalyst had a turnover frequency of 1.78 s−1, while RuFeK had a turnover frequency of only 0.28 s−1 under identical operating conditions. Based on their apparent activation energies and number of surface sites, the RuSrK had a factor of two lower activation energy than the RuFeK, while also possessing an equivalent number of surface sites, which suggests that the Sr promotes ammonia decomposition in the presence of Ru by modifying the active sites of Ru.
Highlights
Ammonia has proven to be a promising COx -free candidate for hydrogen storage and transportation [1,2]
We demonstrated the utilization of high throughput screening to determine low cost substitutional materials for low temperature ammonia decomposition
This screen concluded that substitution of Ru with Mg, Ca, Sr, Sc, Y, Ta, Hf, and Zr resulted in catalyst formulations that were more active than a baseline 4,12 RuK catalyst with less Ru content
Summary
Ammonia has proven to be a promising COx -free candidate for hydrogen storage and transportation [1,2]. H2 from these materials requires harsh operating conditions and often suffers from poor H2 sorption reversibility [1]. These materials have lower hydrogen storage capabilities than ammonia. Despite the obvious advantages of H2 storage through ammonia, on-site power generation via hydrogen fuel cells requires the catalytic decomposition of ammonia, and limited by the performance of the catalytic material. This process requires a highly active ammonia decomposition catalyst that can generate H2 from ammonia at moderate to low temperatures (below 450 ◦ C) in order
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