Trimethylphosphine (TMP) is demonstrated as a suitable 31 P MAS NMR probe molecule for determining accessibility, environment, and spatial distribution of oxidation-active oxidic metal species on solid catalysts quantitatively. It oxidizes to trimethylphosphine oxide (TMPO) at oxygen donor sites, which is demonstrated for oxides of copper, manganese, cobalt, and molybdenum. At loadings <2 wt % of Mo a direct quantitative correlation between TMPO quantity and accessible metal oxide content is observed. Exceeding 2 wt % results in a gradual agglomeration and thus decreases the amount of available oxidative sites, probed as a decay of the amount of TMPO formed. Additionally, the spatial distribution of oxides neighboring species could be inferred. The solid TMPO deposited near MoO x species was very sensitive to extra framework aluminum (EFAL) as well as Brønsted acid sites in close proximity, depending on Mo loading. Thus, the TMP method provides unprecedented insights into the surface chemistry of oxidative metal oxide catalysts.
The Cover Feature shows a possible pathway for the application of ammonia as a renewable hydrogen and energy vector. Ammonia is an easily available and transportable compound with high hydrogen content. In their Concept, S. Peters et al. highlight the current state of thermocatalytic ammonia decomposition. The COx‐free hydrogen released by this process can be used in fuel cells and chemical processes. Reaction kinetics and catalytically active materials are reviewed, with a focus on both Ru‐based and non‐noble catalyst systems and their respective developments. Several key aspects for rational catalyst design by elucidation of structure‐reactivity relationships are discussed. Furthermore, a future strategy for incorporation of renewably produced ammonia into the world's energy infrastructure by flexible combination of ammonia synthesis and decomposition is proposed.More information can be found in the Concept by S. Peters et al.
Hydrogen storage materials and technologies are deemed as the cornerstone towards a world economy less reliant on, and ultimately independent of fossil resources. Ammonia is considered among the most efficient carbon‐free hydrogen carriers because of its relatively high gravimetric and volumetric hydrogen storage capacities and, equally important, ease of transport and storage. In addition, the well‐established chemical production of ammonia (preferably a green Haber‐Bosch process) would accelerate the immediate introduction of hydrogen into energy infrastructure. Thermocatalytic decomposition of ammonia yields clean, COx‐free hydrogen, but is energy intensive and currently performed with expensive Ru‐based catalysts. The development of more efficient catalysts based on more abundant and cheaper elements is indispensable for future wide‐scale industrial application. Therefore, the conceptualization of strategies and challenges for material developments, study and optimization of ammonia decomposition catalysts as well as their in situ/operando characterizations are pivotal aspects to be considered.
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