Conversion of Sugars to Lactic Acid using Homogeneous Niobium-Substituted Polyoxometalate Catalysts.

The catalytic conversion of biomass into high-value chemicals is an increasing field of research. This study uniquely investigates the use of various Keggin-type heteropoly salts (HPS) for the chemical conversion of sugars into lactic acid under mild conditions of 160 °C and 20 bar N. In the first phase, Nb- and V-substituted HPSs were employed to synthesize lactic acid from dihydroxyacetone, an intermediate in the conversion of sugars to lactic acid.

Supported HPVMoO on activated carbon: Synthesis and Investigation of influencing factors for catalytic performance.

Polyoxometalates (POMs), in particular the Keggin-type HPA-5 (HPVMoO) are widely established as effective catalysts for acid- and redox-catalyzed reactions. Yet, they are mainly used as homogeneous catalysts, which poses challenges regarding catalyst separation. This study explores the synthesis of supported HPA-5, and its application as a heterogeneous catalyst for biomass conversion, focusing on activated carbons with diverse chemical and physical properties as support materials.

Heteroelements in polyoxometalates: a study on the influence of different group 15 elements on polyoxometalate formation.

In the field of polyoxometalate (POM) chemistry, different heteroelements are integrated into the cage-like structures, to obtain different structural types of so-called heteropolyanions (HPAs). While it is generally accepted, that some elements favor certain types of structure, a systematic study is still missing. In this article, we present a systematic investigation of the influence of the group 15 elements nitrogen, phosphorous, arsenic, and antimony on the formation of different POM structure types.

Effect of Conversion, Temperature and Feed Ratio on In O /In(OH) Phase Transitions in Methanol Synthesis Catalysts: A Combined Experimental and Computational Study.

Catalytic hydrogenation of CO to methanol has attracted lots of attention as it makes CO useable as a sustainable carbon source. This study combines theoretical calculations based on the dummy catalytic cycle model with experimental studies on the performance and degradation of indium-based model catalysts for methanol synthesis. In detail, the reversibility of phase transitions in the In O /In(OH) system under industrial methanol synthesis conditions are investigated depending on conversion, temperature and feed ratio.

H [PV Mo O ] - A Unique Polyoxometalate for Acid and RedOx Catalysis: Synthesis, Characterization, and Modern Applications in Green Chemical Processes.

Polyoxometalates (POMs) are a fascinating group of anionic metal-oxide clusters with a broad variety of structural properties and several catalytic applications, especially in the conversion of bio-derived platform chemicals. H [PV Mo O ] (HPA-5) is a unique POM catalyst that ideally links numerous fascinating research fields for the following reasons: a) HPA-5 can be synthesized by rational design approaches; b) HPA-5 can be well characterized using multiple analytical tools explaining its catalytic properties; and c) HPA-5 is suitable for multiple important catalytic transformations of bio-based feedstock. This Review combines the fields of synthesis, spectroscopic, electrochemical, and crystallographic characterization of HPA-5 with those of sustainable catalysis and green chemistry.

Revealing the nitrogen reaction pathway for the catalytic oxidative denitrification of fuels.

Aside from the desulfurisation, the denitrogenation of fuels is of great importance to minimze the environmental impact of transport emissions. The oxidative reaction pathway of organic nitrogen in the catalytic oxidative denitrogenation could be successfully elucidated. This is the first time such a pathway could be traced in detail in non-microbial systems.

Spectroscopic, Crystallographic, and Electrochemical Study of Different Manganese(II)-Substituted Keggin-Type Phosphomolybdates.

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.

Switchable Catalytic Polyoxometalate-Based Systems for Biomass Conversion to Carboxylic Acids.

We present the Keggin-type polyoxometalate H[PVMoO] as a switchable catalyst being able to catalyze the transformation of both glucose and glyceraldehyde to formic acid (42%) and lactic acid (40%), respectively, within 1 h reaction time by simply changing the reaction atmosphere at 160 °C from oxygen to nitrogen in one reactor setup. In detail, we report the influence of different gas atmospheres and reaction temperatures on various vanadium-containing catalysts in the selective transformation of several biogenic substrates to carboxylic acids with a special emphasis on reaction pathways and switchability of the catalyst systems. All investigations were carried out in parallel using either an oxygen or a nitrogen atmosphere of 20 bar performing time-resolved experiments between 0.

Combining Cost-Efficient Cellulose and Short-Chain Carboxylic Acid Production: The Polyoxometalate (POM)-Ionosolv Concept.

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.

Catalytic Low-Temperature Dehydration of Fructose to 5-Hydroxymethylfurfural Using Acidic Deep Eutectic Solvents and Polyoxometalate Catalysts.

HMF synthesis typically requires high temperature and is carried out in aqueous solutions. In this work, the low-temperature dehydration of fructose to HMF in different deep eutectic solvents (DES) was investigated. We found a very active and selective reaction system consisting of the DES tetraethyl ammonium chloride as hydrogen bond acceptor (HBA) and levulinic acid as hydrogen bond donor (HBD) in a molar ratio of 1:2 leading to a maximum HMF yield of 68% after 120 h at 323 K.

Combining autoclave and LCWM reactor studies to shed light on the kinetics of glucose oxidation catalyzed by doped molybdenum-based heteropoly acids.

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.

Ru-Doped Wells-Dawson Polyoxometalate as Efficient Catalyst for Glycerol Hydrogenolysis to Propanediols.

A Ru-doped phospho-tungstic Wells-Dawson polyoxometalate (POM) was successfully applied as homogeneous catalyst for glycerol hydrogenolysis in aqueous media. The synthesized compound showed superior catalytic activity compared to classical homogeneous/heterogeneous Ru catalysts like RuCl and Ru/C under identical reaction conditions, whereas the analogous POM doped with Pd or Pt proved far less activity. Detailed characterization of the POMs was performed using P-NMR to identify characteristic phosphorous peaks of the heteroatoms, infrared spectroscopy (ATR-FTIR) to confirm characteristic P-O and W-O-W vibrations, powder XRD for comparison of crystal structures, and X-ray fluorescence (XRF) and inductive-coupled plasma (ICP) analysis to determine elemental composition.

Highly Selective Synthesis of Acrylic Acid from Lactide in the Liquid Phase.

A new reaction system for the highly selective, hydrobromic acid catalyzed conversion of lactide into acrylic acid under mild conditions is reported. The applied liquid reaction system consists of a temperature-stable bromide-containing ionic liquid and 2-bromopropionic acid as a source of dry HBr, with no volatile organic solvent being used. This allows for the in situ removal of the formed acrylic acid, leading to an unmatched acrylic acid selectivity of over 72 % at full lactide conversion.

Zwitterionic Hydrobromic Acid Carriers for the Synthesis of 2-Bromopropionic Acid from Lactide.

A convenient and highly efficient way of synthesizing 2-bromopropionic acid (2-BrPA) from lactide is presented. The procedure uses ionic liquids obtained from the addition of HBr to ammonium-based zwitterions as the solvent and bromination agent. The buffered HBr acidity, high polarity, and charge stabilizing character of the ionic liquid (IL) enable the synthesis of 2-BrPA with excellent selectivity.

Measuring and Predicting the Extraction Behavior of Biogenic Formic Acid in Biphasic Aqueous/Organic Reaction Mixtures.

The distribution coefficients and selectivities required for extraction purposes were predicted with a thermodynamic equation of state for the ternary system formic acid/water/extraction solvent. These predictions were validated with experimental data from the literature and experimental data from the oxidation of biomass to formic acid process measured in this work. Extraction solvents discussed in this work are 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 1-decanol, ethyl -butyl ether, diisopropyl ether, di--butyl ether, benzyl formate, and heptyl formate.

Selective oxidation of lignocellulosic biomass to formic acid and high-grade cellulose using tailor-made polyoxometalate catalysts.

The main goal of this project was to identify and optimize tailor-made polyoxometalate catalysts for a fractionated oxidation of lignocellulosic biomass (i.e. wood and residues from sugar or paper industries) to produce formic acid (FA) and high-grade cellulose for further processing e.