Luis Miguel Azofra

Promising prospects for 2D d2–d4 M3C2 transition metal carbides (MXenes) in N2 capture and conversion into ammonia

Density functional theory investigations of M3C2 transition metal carbides from the d2, d3, and d4 series suggest promising N2 capture behaviour, displaying spontaneous chemisorption energies that are larger than those for the capture of CO2 and H2O in d3 and d4 MXenes. The chemisorbed N2 becomes activated, promoting its catalytic conversion into NH3. The first proton–electron transfer is found to be the rate-determining step for the whole process, with an activation barrier of only 0.64 eV vs. SHE for V3C2.

Electro-synthesis of ammonia from nitrogen at ambient temperature and pressure in ionic liquids

Ammonia as the source of most fertilizers has become one of the most important chemicals globally. It also is being increasingly considered as an easily transported carrier of hydrogen energy that can be generated from “stranded” renewable-energy resources. However, the traditional Haber–Bosch process for the production of ammonia from atmospheric nitrogen and fossil fuels is a high temperature and pressure process that is energy intensive, currently producing more than 1.6% of global CO2 emissions. An ambient temperature, electrochemical synthesis of ammonia is an attractive alternative approach, but has, to date, not been achieved at high efficiency. We report in this work the use of ionic liquids that have high N2 solubility as electrolytes to achieve high conversion efficiency of 60% for N2 electro-reduction to ammonia on a nanostructured iron catalyst under ambient conditions.

Ionic liquid electrolytes for reversible magnesium electrochemistry

Mg has great potential as the basis for a safe, low cost energy storage technology, however, cycling of magnesium is difficult to achieve in most electrolytes. We demonstrate cycling of Mg from a novel alkoxyammonium ionic liquid. DFT calculations highlight the role that Mg coordination with [BH4](-) ions plays in the mechanism.

Feasibility of N2 Binding and Reduction to Ammonia on Fe-Deposited MoS2 2D Sheets: A DFT Study

Based on the structure of the nitrogenase FeMo cofactor (FeMoco), it is reported that Fe deposited on MoS2 2D sheets exhibits high selectivity towards the spontaneous fixation of N2 against chemisorption of CO2 and H2 O. DFT predictions also indicate the ability of this material to convert N2 into NH3 with a maximum energy input of 1.02 eV as an activation barrier for the first proton-electron pair transfer.

Hydrogenation of CO2‐Derived Carbonates and Polycarbonates to Methanol and Diols by Metal–Ligand Cooperative Manganese Catalysis

The first example of base-metal catalysed hydrogenation of the CO2-derived-carbonates to alcohols is presented. The reaction operates under mild conditions using a well-defined manganese complex with loading as low as 0.25 mol %. The nonprecious homogenous catalytic system provides an indirect route to convert CO2 to methanol with the co-production of the value-added vicinal diols with yields up to 99%. Experimental and computational studies indicate a metal ligand cooperative catalysis mechanism. Transition metal catalysed hydrogenation of polar bonds is a key technology in modern industrial chemistry. So far most of these catalytic systems rely on the use of precious metal catalysts.[1] However, the replacement of the rare-earth metal catalysis by the earth-abundant alternatives is a topic of current interest.[2] Accordingly, significant advances have been made to the hydrogenation of aldehydes,[3] ketones,[3] esters,[4]carboxylic acids[4d] and amides[5] using base-metal catalysts. On the other hand, the hydrogenation of the carbonic acid derivatives is significantly more difficult due to the resonance stabilisation effect of the adjacent alkoxy groups which lower the electrophilicity of the carbonyl group. To the best of our knowledge, catalytic hydrogenation of carbonic acid derivatives has never been reported using a homogenous non-precious metal catalyst.[6] Among the carbonic acid derivatives, the hydrogenation of cyclic organic carbonates (COCs) to alcohols is of particular interest, because COCs are industrially synthesised by the direct coupling between carbon dioxide and oxiranes or oxetanes. Hence, developing mild hydrogenation of the COCs would lead to a practical two–step route to convert CO2 to methanol, in addition to the production of the value added diols (Scheme 1). More specifically, the industrial production of ethylene glycol (EG) involves the use of the so called “omega process” in which CO2 is inserted into the ethylene oxide to produce ethylene carbonate, followed by catalytic hydrolysis of the former carbonate to (EG) and CO2.[7] The replacement of the catalytic hydrolysis by catalytic hydrogenation would lead to the formation of methanol instead of CO2, thus giving a great advantage in terms of sustainability. The catalytic production of methanol from CO2 is an elegant alternative option for the recycling of carbon and could lead to “methanol economy” which is a suggested future in which methanol might play the central role as a hydrogen storage material and C1 building block.[8] This reaction has been studied with heterogeneous catalysts. Nevertheless, these catalytic systems have to operate at elevated temperature (>200 °C) and suffer from the formation of several sideproducts.[9] In contrast, well-defined homogenous catalysts are potentially more active and can be tuned by mechanistic studies. In that regard only recently, seminal reports outlined preliminary results on the direct[10] and indirect[6,11] hydrogenation of CO2 to methanol. However, an efficient catalytic system based on an earthabundant metal remains an elusive goal. Thus a development of a base metal catalyst which could be used at low catalyst loadings for the reduction of CO2 derived organic carbonates to value added alcohols would be an important advancement in achieving the requirements of an ecologically and economically benign process (Scheme 1a). Besides, the successful development of such a process may also be extended to the recycling of polycarbonates with the simultaneous formation of valuable diols and methanol (Scheme 1b). Scheme 1. Unprecedented base-metal catalysed hydrogenation of organic carbonates. Inspired by the recent progress on manganese catalysis[12] and our interest on developing sustainable transformations using inexpensive base-metals stabilised by stable non-innocent ligands,[13-14] we herein present a new manganese complex that reduces COCs as well as recycles polycarbonates into methanol and vicinal diols under mild reaction conditions. For the first time, a combined experimental and computational study provides insight into the reaction mechanism and explains the role of the non-innocent ligand in the cascade hydrogenation of the CO2-derived COCs. In order to accomplish a practical reduction method for the rather challenging cyclic carbonates, we started our studies with [a] V. Zubar, Dr. O. El-Sepelgy Prof. Dr. M. Rueping Institute of Organic Chemistry RWTH Aachen University Landoltweg 1, 52074 Aachen (Germany) E-mail: Magnus.Rueping@rwth-aachen.de [b] Dr. Y. Lebedev, Dr. L. M. Azofra, Prof. Dr. L. Cavallo, Prof. Dr. M. Rueping KAUST Catalysis Center (KCC) King Abdullah University of Science and Technology (KAUST) Thuwal 23955-6900 (Saudi Arabia) Supporting information and the ORCID identification numbers(s) for the author(s) of this article can be found under: https://doi.org/10.1002/anie.2018XXXXX.

Experimental and Computational Study of an Unexpected Iron‐Catalyzed Carboetherification by Cooperative Metal and Ligand Substrate Interaction and Proton Shuttling

An iron-catalyzed cycloisomerization of allenols to deoxygenated pyranose glycals has been developed. Combined experimental and computational studies show that the iron complex exhibits a dual catalytic role in that the non-innocent cyclopentadienone ligand acts as proton shuttle by initial hydrogen abstraction from the alcohol and by facilitating protonation and deprotonation events in the isomerization and demetalation steps. Molecular orbital analysis provides insight into the unexpected and selective formation of the 3,4-dihydro-2H-pyran.

Energy-Efficient Nitrogen Reduction to Ammonia at Low Overpotential in Aqueous Electrolyte under Ambient Conditions

The electrochemical nitrogen reduction reaction (NRR) under ambient conditions is a promising alternative to the traditional energy-intensive Haber-Bosch process to produce NH3 . The challenge is to achieve a sufficient energy efficiency, yield rate, and selectivity to make the process practical. Here, we demonstrate that Ru nanoparticles (NPs) enable NRR in 0.01 m HCl aqueous solution at very high energy efficiency, that is, very low overpotentials. Remarkably, the NRR occurs at a potential close to or even above the H+ /H2 reversible potential, significantly enhancing the NRR selectivity versus the production of H2 . NH3 yield rates as high as ≈5.5 mg h-1  m-2 at 20 °C and 21.4 mg h-1  m-2 at 60 °C were achieved at a redox potential (E) of -100 mV versus the reversible hydrogen electrode (RHE), whereas a highest Faradaic efficiency (FE) of ≈5.4 % is achievable at E=+10 mV vs. RHE. This work demonstrates the potential use of Ru NPs as an efficient catalyst for NRR at ambient conditions. This ability to catalyze NRR at potentials near or above RHE is imperative in improving the NRR selectivity towards a practical process as well as rendering the H2 viable as byproduct. Density functional theory calculations of the mechanism suggest that the efficient NRR process occurring on these predominantly Ru (0 0 1) surfaces is catalyzed by a dissociative mechanism.

Molybdenum on solid support materials for catalytic hydrogenation of N₂-into-NH₃

Very stable in operando and low-loaded atomic molybdenum on solid-support materials have been prepared and tested to be catalytically active for N2 -into-NH3 hydrogenation. Ammonia synthesis is reported at atmospheric pressure and 400 °C with NH3 rates of approximately 1.3×103  μmol h-1  gMo -1 using a well-defined Mo-hydride grafted on silica (SiO2-700 ). DFT modelling on the reaction mechanism suggests that N2 spontaneously binds on monopodal [(≡Si-O-)MoH3 ]. Based on calculations, the fourth hydrogenation step involving the release of the first NH3 molecule represents the rate-limiting step of the whole reaction. The inclusion of cobalt co-catalyst and an alkali caesium additive impregnated on a mesoporous SBA-15 support increases the formation of NH3 with rates of circa 3.5×103  μmol h-1  gMo -1 under similar operating conditions and maximum yield of 29×103  μmol h-1  gMo -1 when the pressure is increased to 30 atm.