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Mo2N is trigonal omega-like structured and crystallizes in the trigonal R-3m space group. The structure is two-dimensional and consists of three Mo2N sheets oriented in the (0, 0, 1) direction. Mo is bonded in a 3-coordinate geometry to three equivalent N atoms. All Mo–N bond lengths are 2.16 Å. N is bonded to six equivalent Mo atoms to form edge-sharing NMo6 octahedra.
Mo2N is Anatase structured and crystallizes in the tetragonal I4_1/amd space group. The structure is three-dimensional. Mo is bonded in a T-shaped geometry to three equivalent N atoms. There are one shorter (2.10 Å) and two longer (2.13 Å) Mo–N bond lengths. N is bonded to six equivalent Mo atoms to form a mixture of edge and corner-sharing NMo6 octahedra. The corner-sharing octahedral tilt angles are 4°.
Ethanol is the smallest molecule containing C–O, C–C, C–H, and O–H bonds present in biomass-derived oxygenates. The development of inexpensive and selective catalysts for ethanol reforming is important towards the renewable generation of hydrogen from biomass. Transition metal nitrides (TMN) are interesting catalyst support materials that can effectively reduce precious metal loading for the catalysis of ethanol and other oxygenates. Herein theoretical and experimental methods were used to probe platinum-modified molybdenum nitride (Pt/Mo 2 N) surfaces for ethanol reforming. Computations using density-functional theory and machine learning predicted monolayer Pt/Mo 2 N to be highly active and selective for ethanol reforming. Temperature-programmed desorption (TPD) experiments verified that ethanol primarily underwent decomposition on Mo 2 N, and the reaction pathway shifted to reforming on Pt/Mo 2 N surfaces. Additionally, high-resolution electron energy loss spectroscopy (HREELS) results further indicated that while Mo2N decomposed the ethoxy intermediate by cleaving C–C, C–O, and C–H bonds, Pt-modification preserved the C–O bond, resulting in ethanol reforming.
The conversion of biomass compounds into fuels and chemicals is an important step towards a more sustainable future. This work combines results from model surfaces and powder catalysts to demonstrate Cu-modified mo- lybdenum nitride (Cu/Mo 2 N) as a selective catalyst for dehydrogenation of the biomass model compounds, ethanol and isopropanol. Results from model surfaces showed that while Mo2N led to unselective decomposition via both dehydrogenation and dehydration, the addition of Cu increased the dehydrogenation activity and selectivity. DFT calculations showed how Cu influenced the structures of active sites, adsorbate interactions, and thus the product selectivity. Batch reactor studies on corresponding powder catalysts confirmed the trend that Cu modification increased dehydrogenation activity, and in situ X-ray absorption spectroscopy elucidated the Cu oxidation state under reaction conditions. Further, this work demonstrates a strategy for promoting dehydrogenation over Mo 2 N-based catalysts, as well as the feasibility of using model surfaces to guide the design of industrially relevant catalysts.
Mo2N(C) is Tungsten Carbide-derived structured and crystallizes in the orthorhombic Pmm2 space group. The structure is three-dimensional. there are two inequivalent Mo+3.50+ sites. In the first Mo+3.50+ site, Mo+3.50+ is bonded to four equivalent C4- and two equivalent N3- atoms to form a mixture of distorted edge, face, and corner-sharing MoC4N2 pentagonal pyramids. All Mo–C bond lengths are 2.20 Å. Both Mo–N bond lengths are 2.20 Å. In the second Mo+3.50+ site, Mo+3.50+ is bonded to two equivalent C4- and four equivalent N3- atoms to form distorted MoC2N4 pentagonal pyramids that share corners with twelve MoC4N2 pentagonal pyramids, edges with six MoC4N2 pentagonal pyramids, and faces with two equivalent MoC2N4 pentagonal pyramids. Both Mo–C bond lengths are 2.19 Å. All Mo–N bond lengths are 2.20 Å. C4- is bonded to six Mo+3.50+ atoms to form distorted CMo6 pentagonal pyramids that share corners with four equivalent CMo6 pentagonal pyramids, corners with eight equivalent NMo6 pentagonal pyramids, edges with two equivalent CMo6 pentagonal pyramids, edges with four equivalent NMo6 pentagonal pyramids, and faces with two equivalent CMo6 pentagonal pyramids. N3- is bonded to six Mo+3.50+ atoms to form distorted NMo6 pentagonal pyramids that share corners with four equivalent NMo6 pentagonal pyramids, corners with eight equivalent CMo6 pentagonal pyramids, edges with two equivalent NMo6 pentagonal pyramids, edges with four equivalent CMo6 pentagonal pyramids, and faces with two equivalent NMo6 pentagonal pyramids.
A common route for the synthesis of molybdenum nitrides is through the temperature-programmed reaction of molybdenum oxides with NH3, or ammonolysis. In this work, the role of precursor phase, gas phase chemistry (impact of H2O), and temperature profile on the reaction outcome (700 °C) was examined, which resulted in varying amounts of MoO2, H2MoO5, and the nitride phases—cubic γ (nominally Mo2N) and hexagonal δ (nominally MoN). The phase fraction of the δ phase increased with precursor in the sequence MoO2 > MoO3 > H2MoO5. Steam in the reaction gas also favored the production of δ over γ, but with too much steam, MoO2 was obtained in the product. Synthesis conditions for obtaining nearly phase-pure δ were identified: MoO2 as the precursor, 2% H2O in the gas stream, and a moderate heating rate (3 °C/min). In situ X-ray diffraction provided insights into the reaction pathway. Extensive physico-chemical analysis of the δ phase, including synchrotron X-ray and neutron diffraction, electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and prompt gamma activation analysis, revealed its stoichiometry to be MoO0.108(8)N0.892(8)H0.012(5), indicating non-trivial oxygen incorporation. The presence of N/O ordering and an impurity phase Mo5N6 were also revealed, detectable only by neutron diffraction. Notably, a computationally predicted MoON phase (doi: 10.1103/PhysRevLett.123.236402), of interest due to its potential to display a metal-insulator transition, did not appear under any reaction condition examined.