Deciphering the rational design of the early transition metals for ammonia synthesis

Designing the catalyst that can favor both N2 activation and N species hydrogenation is essential for ammonia production. In October issue of Chem Catalysis, Guo et al. report a new strategy through “activation” inactive Cr-based synthesis by creating [BaCrHN] structure. Main textCatalytic second largest industrial chemical manufacture volume. Ammonia from nitrogen hydrogen an exothermic reaction.1Foster S.L. Bakovic S.I.P. Duda R.D. Maheshwari S. Milton Minteer S.D. Janik M.J. Renner J.N. Greenlee L.F. Catalysts reduction to ammonia.Nat. Catal. 2018; 1: 490-500Google Scholar From thermodynamic point view, low-temperature high-pressure formation. However, high temperature pressure have be utilized overcome kinetic barriers rearrangement bonds achieve desired production rate in industry. traditional Haber-Bosch process, reaction usually operates at range 300°C–500°C 10–30 MPa. addition, low-cost iron-based metal oxide major catalyst. According calculations Jacobsen al.,2Jacobsen C.J.H. Dahl Clausen B.S. Bahn Logadottir A. Nørskov J.K. Catalyst design interpolation periodic table: bimetallic catalysts.J. Am. Chem. Soc. 2001; 123: 8404-8405Google highly correlated with adsorption energy its derivates. Optimum benefits productivity. The optimum means small barrier dissociation but weak derivates following hydrogenation. Thus, catalytic surface two active sites will benefit synthesis, one site conversion intermediates ammonia. As mentioned, combination Mo Co close theoretical synthesis. there are still many issues should addressed practical use catalyst.In co-workers activate quaternary barium chromium nitride-hydride structure composed [CrN4] tetrahedral units [HBa6] octahedral units. general, early transition metals forming bulk nitrides easily. But lattice difficult further hydrogenated. light reports,3Guo J. Wang P. Wu G. Hu D. Xiong Z. Yu Chang F. Chen Lithium imide synergy 3d transition-metal leading unprecedented activities decomposition.Angew. Int. Ed. Engl. 2015; 54: 2950-2954Google Scholar, 4Kitano M. Kujirai Ogasawara K. Matsuishi Tada T. Abe H. Niwa Y. Hosono Low-temperature perovskite oxynitride-hydrides as 2019; 141: 20344-20353Google 5Kobayashi Tang Kageyama Yamashita Masuda N. Hosokawa Titanium-based hydrides heterogeneous catalysts synthesis.J. 2017; 139: 18240-18246Google 6Wang Gao W. He Breaking scaling relations LiH-mediated transfer hydrogenation.Nat. 9: 64-70Google introducing alkali or hydride into Also, were proposed involved process Mars-van Krevelen mechanism. this work, was synthesized hydrodenitrogenation amide precursor condition. Ar-TPD-MS, FTIR, H-NMR, XRD, PDF applied reveal composition amorphous sample.PDF ability distinguish short-range ordering complex suggests probably mixture Ba5CrN4H, BaH2, CrN (Figure 1A). activity proved correlate Ba5CrN4H nitride-hydride. forms Ba-N-Ba bond Ba and/or Ba-N-Cr Cr, Cr coordinated tetrahedrally resides distorted Ba6 octahedra unit Ba-H length (2.80–3.00 Å) much longer than BaH2 (2.50–2.75 Å), implying higher reactivity H which agreement FTIR H-D isotope exchange results 1B).In all comparisons, highest 6,860 μmol gcat−1 h−1 achieved over (Cr:Ba = 1:2) sample under condition weight hourly space velocity (WHSV) 60,000 mL h−1, 573 K, 10 bar syngas. work ca. 4 times benchmark Cs-promoted Ru/MgO superior most recently reported Ru 1C). Based on experimental results, scheme showing possible mechanism 1D). has been adsorbed either hydridic function electron proton donor facilitate NHx species. formed bonded hydrogenated H2 via heterolytic pathway release NH3 mechanism, simultaneously, regenerated fulfill cycle.Introducing paper provides effective This ready extended metals, turnover frequency studied. guide rational synthesize bifunctional Catalytic sample. 1B). cycle. Introducing Barium synthesisGuan al.Chem CatalysisSeptember 27, 2021In BriefEarly such very low catalysis. formation leads great change, resulting enhancement more three orders magnitude compared nitride. comprising reactive ( - ) creates environment favorable mild conditions. Full-Text Open Archive