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Instruments / Technical Area	Publication Details	Published
I11-High Resolution Powder Diffraction	Enhancement of the catalytic activity of lithium amide towards ammonia decomposition by addition of transition metals Caitlin Brooker-Davis , Joshua Makepeace , Thomas Wood Journal Of Ammonia Energy 1 DOI: 10.18573/jae.11 Show Abstract ▼ Abstract: The catalytic decomposition of ammonia to hydrogen is a vital process in the use of ammonia as a zero-carbon energy store. However, the viability of current catalyst systems in terms of operating conditions, versatility, and cost efficiency has proven an issue. Catalytic and gravimetric studies were conducted considering mechanistic uncertainty surrounding the enhanced catalytic activity reported for lithium amide and imide composited with transition metals (Cr, Mn, Fe). Gas flow in excess of ammonia decomposition was quantified and used to differentiate the extent of formation of non-stoichiometric lithium imide amide from other competing processes. This analysis showed the initial compositional transition from lithium amide to an imide-rich phase was reduced in temperature by compositing with Mn and Cr, but not with Fe. The system is, therefore, best considered as promoted lithium imide, with Cr and Mn acting to reduce the formation temperature of the active imide-rich phase such that the catalytic activity is enhanced.	Jul 2023
I11-High Resolution Powder Diffraction	Compositional flexibility in Li–N–H materials: implications for ammonia catalysis and hydrogen storage Joshua W. Makepeace , Jake M. Brittain , Alisha Sukhwani Manghnani , Claire A. Murray , Thomas J. Wood , William I. F. David Physical Chemistry Chemical Physics 420 DOI: 10.1039/D1CP02440J Diamond Proposal Number(s): [14926] Open Access Show Abstract ▼ Abstract: Li–N–H materials, particularly lithium amide and lithium imide, have been explored for use in a variety of energy storage applications in recent years. Compositional variation within the parent lithium imide, anti-fluorite crystal structure has been related to both its facile storage of hydrogen and impressive catalytic performance for the decomposition of ammonia. Here, we explore the controlled solid-state synthesis of Li–N–H solid-solution anti-fluorite structures ranging from amide-dominated (Li4/3(NH2)2/3(NH)1/3 or Li1.333NH1.667) through lithium imide to majority incorporation of lithium nitride–hydride (Li3.167(NH)0.416N0.584H0.584 or Li3.167NH). Formation of these solid solutions is demonstrated to cause significant changes to the thermal stability and ammonia reactivity of the samples, highlighting the potential use of compositional variation to control the properties of the material in gas storage and catalytic applications.	Jul 2021
I11-High Resolution Powder Diffraction	Bulk phase behavior of lithium imide–metal nitride ammonia decomposition catalysts Joshua W. Makepeace , Thomas J. Wood , Phillip L. Marks , Ronald I. Smith , Claire Murray , William I. F. David Physical Chemistry Chemical Physics 1 DOI: 10.1039/C8CP02824A Diamond Proposal Number(s): [15226] Open Access Show Abstract ▼ Abstract: Lithium imide is a promising new catalyst for the production of hydrogen from ammonia. Its catalytic activity has been reported to be significantly enhanced through its use as a composite with various transition metal nitrides. In this work, two of these composite catalysts (with manganese nitride and iron nitride) were examined using in situ neutron and X-ray powder diffraction experiments in order to explore the bulk phases present during ammonia decomposition. Under such conditions, the iron composite was found to be a mixture of lithium imide and iron metal, while the manganese composite contained lithium imide and manganese nitride at low temperatures, and a mixture of lithium imide and two ternary lithium–manganese nitrides (LixMn2−xN and a small proportion of Li7MnN4) at higher temperatures. The results indicate that the bulk formation of a ternary nitride is not necessary for ammonia decomposition in lithium imide–transition metal catalyst systems.	Aug 2018
I11-High Resolution Powder Diffraction	Synthesis, PtS-type structure, and anomalous mechanics of the Cd(CN)2 precursor Cd(NH3)2[Cd(CN)4] Chloe S. Coates , Joshua W. Makepeace , Andrew G. Seel , Mia Baise , Ben Slater , Andrew L. Goodwin Dalton Transactions 47, 7263 - 7271 DOI: 10.1039/C8DT01128A Diamond Proposal Number(s): [17375, 13284] Show Abstract ▼ Abstract: We report the nonaqueous synthesis of Cd(CN)2 by oxidation of cadmium metal with Hg(CN)2 in liquid ammonia. The reaction proceeds via an intermediate of composition Cd(NH3)2[Cd(CN)4], which converts to Cd(CN)2 on prolonged heating. Powder X-ray diffraction measurements allow us to determine the crystal structure of the previously-unreported Cd(NH3)2[Cd(CN)4], which we find to adopt a twofold interpenetrating PtS topology. We discuss the effect of partial oxidation on the Cd/Hg composition of this intermediate, as well as its implications for the reconstructive nature of the deammination process. Variable-temperature X-ray diffraction measurements allow us to characterise the anisotropic negative thermal expansion (NTE) behaviour of Cd(NH3)2[Cd(CN)4] together with the effect of Cd/Hg substitution; ab initio density functional theory (DFT) calculations reveal a similarly anomalous mechanical response in the form of both negative linear compressibility (NLC) and negative Poisson's ratios.	May 2018
I11-High Resolution Powder Diffraction	Ammonia decomposition catalysis using lithium-calcium imide Joshua William Makepeace , Hazel M. A Hunter , Thomas J Wood , Ronald I Smith , Claire A. Murray , William I. F. David Faraday Discussions DOI: 10.1039/C5FD00179J Diamond Proposal Number(s): [11298] Show Abstract ▼ Abstract: 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 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.	Dec 2015
I11-High Resolution Powder Diffraction	n situ X-ray powder diffraction studies of hydrogen storage and release in the Li-N-H system Josh Makepeace , Martin O. Jones , Sam Callear , Peter Edwards , William I. F. David Physical Chemistry Chemical Physics 16 (9), 8972-8979 DOI: 10.1039/c4cp00087k Show Abstract ▼ Abstract: We report the experimental investigation of hydrogen storage and release in the lithium amide–lithium hydride composite (Li–N–H) system. Investigation of hydrogenation and dehydrogenation reactions of the system through in situ synchrotron X-ray powder diffraction experiments allowed for the observation of the formation and evolution of non-stoichiometric intermediate species of the form Li1+xNH2−x. This result is consistent with the proposed Frenkel-defect mechanism for these reactions. We observed capacity loss with decreasing temperature through decreased levels of lithium-rich (0.7 ≤ x ≤ 1.0) non-stoichiometric phases in the dehydrogenated material, but only minor changes due to multiple cycles at the same temperature. Annealing of dehydrogenated samples reveals the reduced stability of intermediate stoichiometry values (0.4 ≤ x ≤ 0.7) compared with the end member species: lithium amide (LiNH2) and lithium imide (Li2NH). Our results highlight the central role of ionic mobility in understanding temperature limitations, capacity loss and facile reversibility of the Li–N–H system.	Jan 2014

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