Metal oxide and bimetallic nanoparticles in ionic liquids: synthesis and application in multiphase catalysis

Ionic liquids (ILs) are well established as solvents and stabilizing agents for the synthesis of metallic nanoparticles (NPs) in general. The physicochemical properties of ILs and the supramolecular organization in the liquid state are capable of directing the growth of transition metal NPs generated in situ and to subsequently protect and stabilize them. Until now, many different NPs have been successfully synthesized within these media; however, the synthesis of metal oxide and bimetallic alloy or core-shell NPs in ILs is still relatively rare. Herein, we summarize the current state-of-the-art of the synthetic methods for these materials and their application in the broad field of catalysis, including multiphase systems, hydrogenation, dehydrogenation, functionalization, as well as defunctionalization reactions

Methanol-Driven Oxidative Rearrangement of Biogenic Furans - Enzyme Cascades vs. Photobiocatalysis

The oxidative ring expansion of bio-derived furfuryl alcohols to densely functionalized six-membered O-heterocycles represents an attractive strategy in the growing network of valorization routes to synthetic building blocks out of the lignocellulosic biorefinery feed. In this study, two scenarios for the biocatalytic Achmatowicz-type rearrangement using methanol as terminal sacrificial reagent have been evaluated, comparing multienzymatic cascade designs with a photo-bio-coupled activation pathway.Peer reviewe

Transfer Hydrogenation Employing Ethylene Diamine Bisborane in Water and Pd- and Ru-Nanoparticles in Ionic Liquids

Herein we demonstrate the use of ethylenediamine bisborane (EDAB) as a suitable hydrogen source for transfer hydrogenation reactions on C-C double bonds mediated by metal nanoparticles. Moreover, EDAB also acts as a reducing agent for carbonyl functionalities in water under metal-free conditions

Chemoenzymatic Hydrogen Production from Methanol through the Interplay of Metal Complexes and Biocatalysts

Microbial methylotrophic organisms can serve as great inspiration in the development of biomimetic strategies for the dehydrogenative conversion of C1 molecules under ambient conditions. In this Concept article, a concise personal perspective on the recent advancements in the field of biomimetic catalytic models for methanol and formaldehyde conversion, in the presence and absence of enzymes and co-factors, towards the formation of hydrogen under ambient conditions is given. In particular, formaldehyde dehydrogenase mimics have been introduced in stand-alone C1-interconversion networks. Recently, coupled systems with alcohol oxidase and dehydrogenase enzymes have been also developed for in situ formation and decomposition of formaldehyde and/or reduced/oxidized nicotinamide adenine dinucleotide (NADH/ NAD+). Although C1 molecules are already used in many industries for hydrogen production, these conceptual bioinspired low-temperature energy conversion processes may lead one day to more efficient energy storage systems enabling renewable and sustainable hydrogen generation for hydrogen fuel cells under ambient conditions using C1 molecules as fuels for mobile and miniaturized energy storage solutions in which harsh conditions like those in industrial plants are not applicable.Peer reviewe

New insights into the catalytic cleavage of the lignin beta-O-4 linkage in multifunctional ionic liquid media

Ionic liquids are attractive reaction media for the solubilisation and depolymerisation of lignin into value-added products. However, mechanistic insight related to the cleavage of specific linkages relevant for efficient lignin depolymerisation in such solvents is still lacking. This study presents important insight into the scission of the most abundant lignin β-O-4 motif in Brønsted acidic ionic liquids. Using relevant model compounds, cleavage products were identified and undesired side reactions examined carefully. Stabilization of reactive intermediates was achieved in ionic liquids comprising both Brønsted acidic function as well as stabilized nanoparticles that comprise hydrogenation activity in order to supress undesired side reactions. Especially, the in situ hydrogenation of the aldehyde intermediate originating from acid catalysed cleavage of lignin beta-O-4 model compounds into more stable alcohols was investigated. This is the first time that such products have been systematically targeted in these multifunctional reaction media in relation to lignin depolymerization

The Role of Ionic Liquids in Hydrogen Storage

Ionic liquid (IL) based H-2 storage for H-2 generation from NH3BH3 derivatives is shown. These systems promote H-2 generation at low temperature, with good reaction rates and high total H-2 yields. The effects of ILs and the H-2 yield in correlation with the basicity, the cations of the ILs, and the role of carbenes are discussed. Furthermore, mechanistic findings on the dehydrogenation are described. IL material blends are competitive with conventional H-2 storage materials with experimental efficiencies of at least 6.5 wt% H-2

Selective conversion of alcohols in water to carboxylic acids by in situ generated ruthenium trans dihydrido carbonyl PNP complexes

In this work, we present a mild method for direct conversion of primary alcohols into carboxylic acids with the use of water as an oxygen source. Applying a ruthenium dihydrogen based dehydrogenation catalyst for this cause, we investigated the effect of water on the catalytic dehydrogenation process of alcohols. Using 1 mol% of the catalyst we report up to high yields. Moreover, we isolated key intermediates which most likely play a role in the catalytic cycle. One of the intermediates was identified as a trans dihydrido carbonyl complex which is generated in situ in the catalytic process

Selective and mild hydrogen production using water and formaldehyde

With the increased efforts in finding new energy storage systems for mobile and stationary applications, an intensively studied fuel molecule is dihydrogen owing to its energy content, and the possibility to store it in the form of hydridic and protic hydrogen, for example, in liquid organic hydrogen carriers. Here we show that water in the presence of paraformaldehyde or formaldehyde is suitable for molecular hydrogen storage, as these molecules form stable methanediol, which can be easily and selectively dehydrogenated forming hydrogen and carbon dioxide. In this system, both molecules are hydrogen sources, yielding a theoretical weight efficiency of 8.4% assuming one equivalent of water and one equivalent of formaldehyde. Thus it is potentially higher than formic acid (4.4 wt%), as even when technical aqueous formaldehyde (37 wt%) is used, the diluted methanediol solution has an efficiency of 5.0 wt%. The hydrogen can be efficiently generated in the presence of air using a ruthenium catalyst at low temperature