René Wölfel

Selective catalytic conversion of biobased carbohydrates to formic acid using molecular oxygen

A new and straightforward method to transform carbohydrate-based biomass to formic acid (FA) by oxidation with molecular oxygen in aqueous solution using a Keggin-type H5PV2Mo10O40 polyoxometalate as catalyst is presented. Several water-soluble carbohydrates were fully and selectively converted to formic acid and CO2 under very mild conditions. It is worth noting, even complex biomass mixtures, such as poplar wood sawdust, were transformed to formic acid, giving 19 wt% yield (11% based on the carbon atoms in the feedstock) under non-optimized conditions.

Selective oxidation of complex, water-insoluble biomass to formic acid using additives as reaction accelerators

The oxidation of complex, water-insoluble biomass to formic acid is reported using a Keggin-type polyoxometalate (H5PV2Mo10O40) as the homogeneous catalyst, oxygen as the oxidant, water as the solvent and p-toluenesulfonic acid as the best additive. The reaction proceeds at 90 °C and 30 bar O2 and transforms feedstock like wood, waste paper, or even cyanobacteria to formic acid and CO2 as the sole products. The reaction obtains up to 53% yield in formic acid for xylan as the feedstock within 24 h. Besides the role of the additive as a reaction promoter, the formic acid isolation and the recycling of catalyst and additive are demonstrated.

Catalytic production of hydrogen from glucose and other carbohydrates under exceptionally mild reaction conditions

A catalytic reaction system for the production of hydrogen from sugars and even water-insoluble biomass like cellulose is presented. The reaction system is based on an ionic liquid that has the role to dissolve the carbohydrate feedstock and a ruthenium catalyst. As hydrogen dissolves in this media at very low level, hydrogen consuming side reactions have been hindered, leading to a gaseous product mixture consisting mainly of hydrogen and carbon dioxide. Investigations with isotopic labelling suggest a reaction sequence in which glucose first thermally decomposes to formic acid followed by Ru-catalyzed decomposition of the latter to hydrogen and CO2.

Ligand‐Modified Rhodium Catalysts on Porous Silica in the Continuous Gas‐Phase Hydroformylation of Short‐Chain Alkenes–Catalytic Reaction in Liquid‐Supported Aldol Products

Ligand‐modified Rh complexes were physically adsorbed on the surface of porous silica. The resulting materials were subjected to the continuous gas‐phase hydroformylation of C2 and C4 alkenes. The ligands used for catalyst modification were bidentate phosphorus ligands known from the literature, namely, sulfoxantphos (1) and a benzopinacol‐based bulky diphosphite 2. The tested catalyst materials were active and, in particular, selective as in comparable homogeneous liquid‐phase experiments. Long‐term stability experiments over 1000 h on stream showed minor deactivation. A significant increase in the catalyst mass after the reaction was detected by weighing and thermogravimetric analysis. By using headspace‐GC–MS, the mass increase could be attributed to high‐boiling compounds, which are formed in situ during the catalytic reaction itself and accumulate inside the pores of the support. Evidence is given that the initially physisorbed catalyst complexes dissolve in the high‐boiling aldol side‐products, which are suitable solvents for the active catalyst species and provide a liquid‐phase environment held by capillary forces on the support.