Search

The oxidative reaction pathway of organic nitrogen in the catalytic oxidative denitrogenation could be successfully elucidated.

Adjusting the RedOx activity of polyoxometalate catalysts is a key challenge for the catalysis of selective oxidation reactions. For this purpose, the possibility of influencing the RedOx potential by the introduction of an additional RedOx-active element was investigated. Thereby, Keggin-type polyoxometalates (POMs) with up to three different elements in the metal framework were created. An advanced and reproducible synthetic procedure to incorporate Mn

The recently developed polyoxometalate (POM)–ionosolv concept offers an interesting strategy to generate two valuable product streams from lignocellulosic biomass, a solid cellulose-rich pulp and short-chain carboxylic acids like formic acid and acetic acid in a simple and cost-efficient manner. This study aimed to find optimum parameters for the two steps of the transformation by performing a sensitivity analysis on the initial ionosolv fractionation step as well as kinetic investigations of the following POM-catalyzed oxidation step. The results were transferred to the POM–ionosolv concept to find the overall process optimum. Beech wood was used as an industrially relevant substrate for ionosolv fractionation with the low-cost ionic liquid triethylammonium sulfate, [TEA][HSO4], and the HPA-5 [H8PV5Mo7O40] POM catalyst for the oxidation of the dissolved components in an oxygen atmosphere. As the most seminal finding, we defined optimum conditions of 125 °C, 1200 rpm, 30 bar oxygen, and 24 h reaction time in ionic liquid containing 70% water, achieving 72% xylose extraction from beech wood, which resulted in a 39% formic acid yield. We suggest that the fractionation and catalytic conversion are carried out at different water contents for maximum conversion efficiency for each step.

ACS omega 5(30), 19082-19091 (2020). doi:10.1021/acsomega.0c02430, Published by ACS Publications, Washington, DC

In this contribution, we present for the first time a continuous production of formic acid under industrially relevant conditions using real biomass as a feedstock. A scale up to 2 L of reaction vo...

The triphasic aerobic extractive desulfurization of benzothiophene (BT) using an aqueous H8PV5Mo7O40 solution as catalyst and O2 as oxidant was investigated. A time-resolved analysis of all reaction products in the gas, organic and aqueous phase, is given. The organic sulfur in BT is mainly converted to sulfuric acid. Mass transport limitations can be excluded. The reaction orders are 1 with regard to BT, and 0.5 both for HPA-5 and O2. Calculated data derived from this mechanism with a power law kinetic approach show good agreement to the experimental data for conversions below 60 \%. At higher BT conversions, significant deviations are found, suggesting that acidic products formed in the BT oxidation affect the catalyst and therefore the initial kinetics of the BT oxidation.

A liquid core waveguide membrane microreactor is a novel concept that allows in situ spectroscopy to be carried out in an optical microreactor, while enabling a very high gas-to-liquid mass transfer. The potential of this reactor concept to derive kinetics in gas/liquid reactions is demonstrated using the heteropoly acids catalyzed oxidation of biomass to formic acid (the ‘OxFA process’). For vanadium-substituted, Keggin-type heteropoly acids, the kinetics of the reduction and reoxidation step of the catalyst cycle was deduced using in situ UV/Vis spectroscopy. Reduction was studied from 40 to 80 °C: a strong dependency of the reduction kinetics was deduced. In combination with additional cyclic voltammetry and EPR characterization, it can be assumed that two active centers promote this reaction, while the existence and proportions of both types depends on the degree of vanadium substitution. The rapid mass transfer allowed transient response experiments to be carried out for the reoxidation step, which was studied up to 150 °C. Switching from anaerobic to aerobic conditions, an even stronger dependency of the reoxidation kinetics on the degree of vanadium substitution was revealed.

The main objective of this contribution was to optimize the process conditions for a fractionated oxidation of lignocellulosic biomass (e.g., wood) to produce formic acid and cellulose for further ...

Synthesis of bulk chemicals from biogenic resources is gaining increasing interest in industry and academia. In the present study, we demonstrate the continuous production of acrylic acid (AA) from...

For the first time, a selective catalytic conversion of thermally induced side products (humins) from biomass valorization to short-chain carboxylic acids like formic acid and acetic acid is reported. Very interestingly, we found that homogeneous polyoxometalate catalysts could selectively oxidize humins from sugar-derived levulinic acid production to formic acid and acetic acid under very mild conditions in a simple monophasic aqueous approach. This green and sustainable process offers a very cost-effective and sustainable way for the conversion of undesired humins and benefits from its low reaction temperature (90-120 °C) and its tunable product distribution. By variation of process parameters and chemical composition of the POM structures, we could control both product selectivity and humin conversion. Furthermore, catalyst recycling over three batches has been successfully carried out.

A detailed kinetic analysis of the selective catalytic oxidation of different biogenic model substrates to formic acid (OxFA process) is presented using two different polyoxometalate catalysts, HPA-2 (H5PV2Mo10O40) and HPA-5 (H8PV5Mo7O40). By using high oxygen pressures (30–60 bar) and temperatures of 80–90 °C in aqueous solution, we were able to investigate the rate-determining substrate oxidation step catalyzed by the oxidized form of the polyoxometalates (POMs) by keeping the concentration of the catalytic active species constant. Under these conditions, kinetic parameters like effective reaction order and reaction rate constants could be determined by the differential method for model substrates like glucose, fructose, sorbitol, and gluconic acid. Furthermore, kinetic experiments using the two different catalysts showed a different behavior for various functionalities within the carbon framework of the substrate with the tendency of higher reaction rates with the HPA-5 catalyst. This effect was more p...

Our contribution demonstrates a new way of fuel desulfurization, namely selective oxidation of organic S-compounds present in fuels to water-soluble sulfur compounds followed by in situ extraction of the latter into an aqueous phase. Different from common oxidative desulfurization (ODS) processes, we demonstrate a technique that converts sulfur compounds in fuel to a large extent to sulfate (60–70%) using oxygen as the oxidant and an aqueous H8PV5Mo7O40 (HPA-5) solution as the catalyst phase. Other water-soluble desulfurization products are sulfoacetic acid (SAA) with a share of 10–20%, 2-sulfobenzoic acid (2-SBA), and 2-(sulfooxy)benzoic acid (2-SOBA), the latter two with a share of

Full cost‐effective exploitation of all wood components is key to growing a commercially successful biorefining industry. An innovative process is reported that combines fractionation of lignocellulosic biomass using a low‐cost ionic liquid (Ionosolv) and production of bio‐derived formic acid using polyoxometalates and molecular oxygen (OxFA process). We show that the hemicellulose and part of the lignin were selectively dissolved into the ionic liquid triethylammonium hydrogen sulfate and oxidised in situ to short‐chain, distillable carboxylic acids by a Keggin‐type polyoxometalate with high yields and selectivities. Characterization by several techniques, including ICP‐OES, FTIR, GC, HPLC and NMR spectroscopy confirmed stability of the catalyst over three consecutive POM‐Ionosolv recycles and stable formic acid yields.High formic acid yields of 26 % (pine chips), 23 % (beech chips), and 18 % (Miscanthus ) were obtained with respect to the initial carbon content of the biomass, with unprecedented oxidation selectivities for formic acid of 54–62 % depending on vanadium substitution in the polyoxometalate, the processing temperature and the water content in the reaction mixture.. We also demonstrate that the cellulose rich pulp is a suitable source of glucose via enzymatic saccharification. We report cellulose yields of 37% for Miscanthus (from originally 48% glucan content), 33% for pine (from originally 49%) and 31% for beech (from originally 41%) were achieved, and a saccharification yield of up to 25% without optimisation. With further optimisation, this concept has the potential to generate two chemical products directly from lignocellulose in high yields and selectivities and hence a novel avenue for full utilisation of cellulose, hemicellulose and lignin.

In this work we combined kinetic studies for aqueous-phase glucose oxidation in a high-pressure autoclave setup with catalyst reoxidation studies in a liquid-core waveguide membrane reactor. Hereby, we investigated the influence of Nb- and Ta-doping on Mo-based Keggin-polyoxometalates for both reaction steps independently. Most importantly, we could demonstrate a significant increase of glucose oxidation kinetics by Ta- and especially Nb-doping by factors of 1.1 and 1.5 compared to the classical HPA-Mo. Moreover, activation energies for the substrate oxidation step could be significantly reduced from around 80 kJ mol−1 for the classical HPA-Mo to 61 kJ mol−1 for the Ta- and 55 kJ mol−1 for the Nb-doped species, respectively. Regarding catalyst reoxidation kinetics, the doping did not show significant differences between the different catalysts.

While the production of hydrocarbons by Fischer–Tropsch synthesis (FTS) is a widely recognized, yet technically quite complex way to transform biomass via syngas (mostly from biomass gasification) into liquid fuels, we here present an alternative route transforming biomass first into formic acid (FA) followed by syngas formation by decomposition of FA and finally FTS using regenerative hydrogen (or if needed H2 from the stored FA) to balance the C:H ratio. The new method builds on the recently developed, selective oxidation of biomass to formic acid using Keggin-type polyoxometalates of the general formula (H3+x[PVxMo12–xO40]) as homogeneous catalysts, oxygen as the oxidant, and water as the solvent. This method is able to transform a wide range of complex and wet biomass mixtures into FA as the sole liquid product at mild reaction conditions (90 °C, 20–30 bar O2). We propose to convert FA with hydrogen from water electrolysis—the electrolysis step producing also the oxygen for the biomass oxidation to FA...

A series of Lindqvist-isopolyoxometalates [M6O19]n− (M=W, V) were synthesized under one-pot conditions and were applied in the homogeneous oxidation of glucose as a model substrate for lignocellulosic biomass to formic acid (FA), which offers a new field for application of isopolyoxometalates (IPA) in catalysis. Their low molecular weight and facile accessibility in aqueous solution together with their tuneable redox properties offers a new and straightforward path for optimized precious metal free oxidation catalysts. We have systematically synthesized and characterized a series of vanadium- and tungsten-based Lindqvist structures and verified their applicability in the selective oxidation of glucose to FA. Maximum FA-yields of 39 % in aqueous solution under non-optimized conditions were observed for Cs4[V2W4O19] and it is shown that reactivity and selectivity can be tuned by metal substitution of the cluster: FA formation is favoured with increasing V-substitution of the [W6O19]2−-framework. Moreover, the influence of different inorganic counter cations was investigated.