Continuous OME _n Synthesis: Supported ionic liquid phase (SILP)-catalysts open the tap for the novel continuous and anhydrous synthesis of oxymethylene dimethyl ethers (OME _n ) by reaction of dimethoxymethane (OME₁) with molecular gaseous formaldehyde (FA) as catalyzed by M[NTf₂] _x salts, most favorably for M=Cu⁺, Co²⁺ and Mg²⁺.

Abstract

Oxymethylene dimethyl ethers (OME _n ; CH₃(−OCH₂) _n −OCH₃) are promising sustainable synthetic fuels when produced from CO₂ and green H₂. The synthesis pathway presented here overcomes synthetic problems and includes the reaction of dimethoxymethane (OME₁) with molecular gaseous formaldehyde in a novel continuous, anhydrous reaction setup. An initially performed wide batch-catalyst screening highlighted the salts M[NTf₂] _x with M=Cu⁺, Co²⁺ and Mg²⁺ as especially interesting catalysts (NTf₂=N(SO₂CF₃)₂). Supported ionic liquid phase (SILP)-catalysts were prepared on this basis and demonstrated the successful synthesis of OME _n in a continuous process. The SILP-catalysts immobilized in the IL EMIM[BF₄] showed a fast and strong deactivation, but those with the IL EMIM[NTf₂] showed excellent catalytic performance and stable results in continuous operations exceeding 19 h. The influence of the weight hourly space velocity (WHSV), the reaction temperature as well as the storage conditions of the catalysts (inert vs non-inert) were investigated. 90 °C was identified as ideal reaction temperature. High feed-gas flows (WHSV=15.8 h⁻¹) are preferable in terms of product selectivity S _OME2-5>90 mol- % with an OME₁ conversion X _OME1=5.10 mol- % at the same time. We also demonstrated that the catalysts can be stored in air for 50 days without loss of activity. The SILP-catalysts were analyzed by NMR and IR spectroscopy. Furthermore, the thermodynamics of the reaction mechanism of some selected catalysts was calculated by DFT theory to this reaction.

Photosensitation of fungal melanin provides photo-excited electrons and H₂O₂-cosubstrate to fungal AA9-LPMO enzymes. An example of natural photobiocatalytic system with component sorted all from the same organism.

Abstract

Melanin is a class of hetero-polymer pigments commonly found in nature and widely in fungi. Often referred to as the “animal lignin“, melanin is a very abundant bioresource and features many catalytically interesting properties. We conceived that, upon light absorbance, the polymer could promote long-distance electron donation to fuel redox enzymatic catalysis or controlled in-situ generation of H₂O₂. Here, we report on a fungal photo-biocatalytic system extracted from the commercially relevant A. nidulans, where photoactivated melanin acts as an electron donor for the cellulose-degrading AnAA9A and TtAA9E metalloenzymes. Furthermore, there was a stable and significant accumulation of H₂O₂ when melanin was irradiated by visible light; having the peroxide functioning as a co-substrate for the AA9 LPMO enzymes. Oxidized cellulose-derived oligosaccharides were detected in the dark and under light conditions, confirming the potential of melanin to reduce AA9s. When placed under light conditions, they provided hydrogen peroxide as a co-substrate for AA9s. The use of light to tune the in-situ generation of H₂O₂ by natural pigments might be pivotal to enable also another peroxide-dependent enzymatic catalysis.

Porous metal phosphonates and their oxide derivatives for electrochemical water oxidation: four different transition metal-based oxides have been synthesized under pyrolysis which have been explored for electrochemical water oxidation reaction in alkaline KOH solution.

Abstract

The development of low cost-effective and highly efficient heterogeneous electrocatalysts is most appreciable in the research community. A newly designed microporous organic-inorganic hybrid iron cobalt phosphonate (FeCoDPAM) is synthesized using diphenylphosphinamide as an organophosphorus ligand through a hydrothermal pathway without any template. To synthesize N, P-codoped bimetallic oxides (NP/FeCoO350, NP/FeCoO550, and NP/FeCoO750), the as-synthesized material FeCoDPAM has undergone pyrolysis at three different temperatures, i. e., 350, 550, 750 °C, respectively. The high specific surface area and a regular microporous array of N, P-codoped iron cobalt oxide (NP/FeCoO350) material provide excellent oxygen evolution reaction (OER) activity. The NP/FeCoO350 material catalyzes OER with the overpotential of 331 mV at a current density of 10 mAcm⁻² and Tafel slope of 56.7 mV dec⁻¹ in 1.0 M KOH solution. The inclusion of iron in the cobalt phosphonate framework can change the electronic structure, and electron transfer can be feasible to the d-orbital of cobalt. Due to the doping of heteroatoms such as N and P into the bimetallic oxide matrix, a synergistic effect can occur, which is the driving force for the efficient electrocatalytic OER activity. Also, the FeCoO350 displays stability with outstanding oxidative current up to 50 h time in chronoamperometry measurement.

Titanium nitride (TiN) shows desirable properties for use as an electrocatalyst and catalyst support, as it possesses high electrical conductivity and excellent corrosion resistance. However, the effect of oxygen content in the nitride lattice on its ability to drive the hydrogen evolution reaction (HER) is not well understood. Here, a series of titanium oxynitrides (TiNxO1-x) with varied nitrogen occupancy (0.53 ≤ x ≤1.0) in the bulk have been fabricated by ammonolysis. Their specific activities towards the HER were normalised by the surface areas determined by BET and electrochemical methods. We show that the specific activities of these oxynitrides are strongly correlated with the bulk nitrogen occupancy, despite the similar surface composition derived from XPS analysis. Furthermore, a removal of the oxygen content in the bulk or at the surface was attributed to the upgraded performance (up to 25% increase) seen during extended chronoamperometry (CA) tests. Our results show that minimising bulk oxygen content in this class of material is critical to achieve a more conductive and active material for the HER.

Polysaccharide oxidative depolymerization is highly desirable to achieve recalcitrant biomass valorization. Inspired by recently discovered Lytic Polysaccharide Monooxygenases, mononuclear copper complexes have been prepared and studied in the literature. However, the activities were evaluated on different substrates and under various conditions. In this work we intended to establish a robust and reproducible activity assay, in aqueous solution at a pH close from neutrality and under mild conditions. We have evaluated several complexes on substrates of increasing complexity: the model substrate para-nitrophenyl-β-D-glucopyranoside (p-NPG), cellobiose (glucose dimer), as well as on extended substrates (chitin, cellulose and bagasse from agave). The different assays were compared and proof-of-concept that bioinspired complexes can oxidatively promote polysaccharide depolymerization was obtained. Finally, we measured level of hydroxyl radicals released by the complexes under comparable experimental conditions and mechanistic pathways are discussed.

In this work, a series of N-doped carbon supported FeCo bimetallic catalysts with plentiful FeCo alloy-FeO interfaces, which are derived from metal-organic frameworks (MOFs) ZIF-67, are designed for the one-pot direct conversion of methyl levulinate to 1,4-pentanediol. The FeCo alloy-FeO interfaces are precisely controlled via tuning the reduction temperatures and Fe/Co ratios. The optimal catalyst gives a high 1,4-pentanediol yield of 90.5% along with complete conversion of methyl levulinate. These catalysts are carefully characterized by multiple techniques, such as HRTEM, XRD, XPS, NH3-TPD, Py-IR and so on. It is found that Co presents in electron deficiency caused by the electron transference from Co to Fe in FeCo alloy, which in turn enhances the heterolysis of H2. In addition, plentiful Lewis acid sites derived from interfacial FeO species favour the re-adsorption and the ring-opening reaction of GVL. With the synergy between FeCo alloy and Lewis acid, the FeCo alloy-FeO interfaces exhibit excellent catalytic activity for selective hydrogenation of methyl levulinate to 1,4-pentanediol.

The present review emphases on the strategy for development of trifunctional double perovkite electrocatalysts for water splitting reaction. Synergistic effect of multiple cationic redox sites and structural distortions in double perovskites can tailor the ORR/OER/HER activities concurrently in single material. This review highlights recent observations of trifunctional activity of few double perovskite and motivate further to obtain improved efficiency.

Abstract

In the present scenario, the paramount significant roles of various heterogeneous catalysts stimulate the modern technologies to underpin the benchmark requirements for the generation of sustainable energy by reducing toxic fossil fuel emissions. Such critical role necessitates further development of cost-effective highly efficient and earth-abundant multifunctional or trifunctional electrocatalysts to promote the advancement of electrochemical overall water splitting performances, yet it is extremely desirable. In this review context, we present the development of double perovskite (DP) oxides as robust trifunctional catalysts for electrochemical oxygen evolution reaction (OER), oxygen reduction reaction (ORR) and hydrogen evolution reactions (HER) by rational design of multiple cationic redox sites with stoichiometric oxygen amount. Particularly, we highlight the importance of the structural modifications via doping, surface structure and oxygen stoichiometry as key parameters to tune the electrocatalytic activities and understand the insight into activity and mechanism of this oxide family. This perspective also describes controlled synthesis protocols including the surface structure of double perovskite oxides are key techniques for realizing a correlation between structure-activity relationships of these materials. Finally, it is concluded by outlining the several aspects of optimization strategies and computational opportunities can expand the future scope of double perovskite oxides as robust trifunctional electrocatalysts.

Two tungsten-based catalysts have been selectively immobilized within the pores of ordered mesoporous silica materials. X-ray absorption spectroscopy confirm the structural integrity of the catalysts. Compared to the homogenous analogues, the immobilized tungsten-catalysts exhibit a substantially increased macrocyclization- and Z-selectivity, which allow for the use of high substrate concentrations.

Abstract

Macrocyclization reactions are still challenging due to competing oligomerization, which requires the use of small substrate concentrations. Here, the cationic tungsten imido and tungsten oxo alkylidene N-heterocyclic carbene complexes [[W(N-2,6-Cl₂-C₆H₃)(CHCMe₂Ph(OC₆F₅)(pivalonitrile)(IMes)⁺ B(Ar^F)₄ ⁻] (W1) and [W(O)(CHCMe₂Ph(OCMe(CF₃)₂)(IMes)(CH₃CN)⁺ B(Ar^F)₄ ⁻] (W2) (IMes=1,3-dimesitylimidazol-2-ylidene; B(Ar^F)₄ ⁻=tetrakis(3,5-bis(trifluoromethyl)phenyl borate) have been immobilized inside the pores of ordered mesoporous silica (OMS) with pore diameters of 3.3 and 6.8 nm, respectively, using a pore-selective immobilization protocol. X-ray absorption spectroscopy of W1@OMS showed that even though the catalyst structure is contracted due to confinement by the mesopores, both the oxidation state and structure of the catalyst stayed intact upon immobilization. Catalytic testing with four differently sized α,ω-dienes revealed a dramatically increased macrocyclization (MC) and Z-selectivity of the supported catalysts compared to the homogenous progenitors, allowing high substrate concentrations of 25 mM. With the supported complexes, a maximum increase in MC-selectivity from 27 to 81 % and in Z-selectivity from 17 to 34 % was achieved. In general, smaller mesopores exhibited a stronger confinement effect. A comparison of the two supported tungsten-based catalysts showed that W1@OMS possesses a higher MC-selectivity, while W2@OMS exhibits a higher Z-selectivity which can be rationalized by the structures of the catalysts.

Catalytic hydrogenation and oxidative dehydrogenation of N-heterocycles to produce tetrahydroquinoline and quinoline derivatives are important reactions of particular importance in the agrochemical and pharmaceutical industries. Herein, we report earth-abundant cobalt nanoparticles supported on hydroxyapatite (HAP) as an inexpensive and efficient catalyst for the hydrogenation and reverse oxidative dehydrogenation of N-heterocycles. The optimal nanocatalyst exhibits excellent activity in both reactions for a wide range of substrates including (iso)quinolines, acridine, benzo[h]quinoline, quinoxaline and indole. Reactions proceed under relatively mild conditions without requiring any additives.

Chemicals with a four-carbon chain (C4 chemicals), like succinic acid, maleic acid, 1,4-butanediol, and tetrahydrofuran are extensively used as commodity chemicals and polymer precursors. Currently, these chemicals are commercially synthesized from petrochemical based feedstocks. There is a growing interest in catalytic pathways for producing these and other C4 chemicals from biomass. However, biomass is mainly composed of hexose and pentose sugars and the natural abundance of a C4 feedstock is low. This review summarizes the current development in catalytic pathways for C4 chemical synthesis from biomass derived sugars and its derivatives and suggests future direction of research.