This paper presents a new type of process for the cracking of ammonia (NH3) that is an alternative to the use of rare or transition metal catalysts. Effecting the decomposition of NH3 using the concurrent stoichiometric decomposition and regeneration of sodium amide (NaNH2) via sodium metal (Na), this represents a significant departure in reaction mechanism compared with traditional surface catalysts. In variable-temperature NH3 decomposition experiments, using a simple flow reactor, the Na/NaNH2 system shows superior performance to supported nickel and ruthenium catalysts, reaching 99.2% decomposition efficiency with 0.5 g of NaNH2 in a 60 sccm NH3 flow at 530 °C. As an abundant and inexpensive material, the development of NaNH2-based NH3 cracking systems may promote the utilization of NH3 for sustainable energy storage purposes.
The non-stoichiometric lithium imide–amide system effectively decomposes ammonia to its constituents, hydrogen and nitrogen. Isotopic studies show that this bulk catalytic reaction has the potential to generate high-purity hydrogen for future energy and transport applications.
Mesoporous silica, SBA-2, has been investigated by using high-resolution transmission electron microscopy
supported by computer image simulations. The complete pore structure connecting the discrete supercages
of which the silica is composed has been determined. In addition, unexpected well-defined cubic-hexagonal
(polytypic) intergrowths have been uncovered, involving a hitherto unknown mesoporous structure that we
designate STAC-1. It was found that both SBA-2 and STAC-1 contain a two-dimensional pore system and
that the symmetry of the SBA-2 structure must be lower than that (space group P63/mmc) determined previously
on the basis of X-ray powder diffraction methods. Polytypic irregularities in these mesoporous materials
indicate that, similar to microporous zeolitic systems, a range of solids with structures intermediate between
end members SBA-2 and STAC-1 might be prepared.
Lithium-calcium imide is explored as a catalyst for the decomposition of ammonia. It shows the highest ammonia decomposition activity yet reported for a pure light metal amide or imide, comparable to lithium imide-amide at high temperature, with superior conversion observed at lower temperatures. Importantly, the post-reaction mass recovery of lithium-calcium imide is almost complete, indicating that it may be easier to contain than the other amide-imide catalysts reported to date. The basis of this improved recovery is that the catalyst is, at least partially, solid across the temperature range studied under ammonia flow. However, lithium-calcium imide itself is only stable at low and high temperatures under ammonia, with in situ powder diffraction showing the decomposition of the catalyst to lithium amide-imide and calcium imide at intermediate temperatures of 200-460 °C.
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