Peter J. C. Hausoul

Hydrogenolysis of Cellulose over Cu-Based Catalysts—Analysis of the Reaction Network

A series of polyols, carbohydrates, and cellulose were tested in the aqueous, CuO/ZnO/Al2O3-catalyzed hydrogenolysis reaction at 245u2009°C and 50u2005bar H2. The compositions of liquid-phase products were analyzed; based on these results a unified reaction mechanism is proposed that accounts for the observed product distribution. Elementary transformations such as dehydration, dehydrogenation/hydrogenation, Lobryu2005deu2005Bruyn-vanu2005Ekenstein isomerization and retro-aldol cleavage were identified as most important for controlling the selectivity of simple polyols and carbohydrates. For cellulose the product distribution is considerably different than for glucose or sorbitol, indicating a change in the reaction pathway. Therefore, next to the traditional hydrolysis of the glycosidic bond, an additional depolymerization mechanism involving only the reducing ends of cellulose oligomers is proposed to account for this observation.

Unravelling the Ru-Catalyzed Hydrogenolysis of Biomass-Based Polyols under Neutral and Acidic Conditions.

The aqueous Ru/C-catalyzed hydrogenolysis of biomass-based polyols such as erythritol, xylitol, sorbitol, and cellobitol is studied under neutral and acidic conditions. For the first time, the complete product spectrum of C2 C6 polyols is identified and, based on a thorough analysis of the reaction mixtures, a comprehensive reaction mechanism is proposed, which consists of (de)hydrogenation, epimerization, decarbonylation, and deoxygenation reactions. The data reveal that the Ru-catalyzed deoxygenation reaction is highly selective for the cleavage of terminal hydroxyl groups. Changing from neutral to acidic conditions suppresses decarbonylation, consequently increasing the selectivity towards deoxygenation.

Solid Molecular Phosphine Catalysts for Formic Acid Decomposition in the Biorefinery

The co-production of formic acid during the conversion of cellulose to levulinic acid offers the possibility for on-site hydrogen production and reductive transformations. Phosphorus-based porous polymers loaded with Ru complexes exhibit high activity and selectivity in the base-free decomposition of formic acid to CO2 and H2 . A polymeric analogue of 1,2-bis(diphenylphosphino)ethane (DPPE) gave the best results in terms of performance and stability. Recycling tests revealed low levels of leaching and only a gradual decrease in the activity over seven runs. An applicability study revealed that these catalysts even facilitate selective removal of formic acid from crude product mixtures arising from the synthesis of levulinic acid.

Catalytic upgrading of α-angelica lactone to levulinic acid esters under mild conditions over heterogeneous catalysts

Butyl levulinate was prepared starting from α-angelica lactone and butanol over Amberlyst® 36. Different reaction conditions were optimized, which resulted in full conversion and 94% selectivity toward the ester at 75 °C. A reaction network analysis reveals pseudo-butyl levulinate and levulinic acid as intermediates in the preparation of butyl levulinate. The mild protocol was successfully applied for different alcohols and compared with the esterification of levulinic acid. Overall, this study identifies α-angelica lactone as a better candidate than levulinic acid for the heterogeneously catalysed preparation of levulinic acid esters. A catalyst screening shows that also zeolites and zirconia-based catalysts are able to catalyse the reaction. However, the transformation of the intermediate pseudo-butyl levulinate into butyl levulinate requires acid sites of sufficient strength to proceed.

Kinetics study of the Ru/C-catalysed hydrogenolysis of polyols – insight into the interactions with the metal surface

The aqueous Ru/C-catalysed hydrogenolysis of xylitol and sorbitol was studied in a temperature range between 393–443 K under 6 MPa H2. For the three main reactions, stereoisomerisation, decarbonylation and deoxygenation, kinetic models were formulated and fitted to the experimental data. The obtained rate constants were used to determine apparent activation enthalpies via the Eyring method. The data reveals a clear dependence of the type and position of the reacting hydroxyl group as well as the length of the polyol on the activation energies. It is proposed that these differences are the result of increased stabilisation due to polydentate interactions with the metal surface.

Selective production of glycols from xylitol over Ru on covalent triazine frameworks – suppressing decarbonylation reactions

Ru on covaltent triazine frameworks (CTF) are highly active and selective catalysts for the conversion of xylitol to glycols (80% C-yield) in basic media. With increasing N-content decarbonylation reactions are suppressed leading to high glycol selectivity. The suppression can be attributed to the presence of N in the support and to metal-support interactions. The catalysts exhibit high stability and could be recycled 5 times with minor loss of activity.

Hydrogenation of CO2 to Formate over Ruthenium Immobilized on Solid Molecular Phosphines

Formic acid is a promising hydrogen storage medium and can be produced by catalytic hydrogenation of CO2 . Molecular ruthenium complexes immobilized on phosphine polymers have been found to exhibit excellent productivity and selectivity in the catalytic hydrogenation of CO2 under mild conditions. The polymeric analog of 1,2-bis(diphenylphosphino)ethane exhibited the highest activity and turnover numbers up to 13u2009170 were obtained in a single run. This catalyst was already active at 40u2009°C and with a catalyst loading of only 0.0006u2005molu2009%. Recycling experiments revealed a loss of activity after the first run, followed by a gradual decrease during the subsequent runs. This is attributed to a change in the catalytically active complex during the hydrogenation reaction. High selectivity towards formate and low leaching were maintained in the absence of CO formation. Based on the catalyst characterization, a mechanism for the CO2 hydrogenation is proposed.

Mechanistic Studies of the Cu(OH)+-Catalyzed Isomerization of Glucose into Fructose in Water

The isomerization of glucose to fructose is a crucial interim step in the processing of biomass to renewable fuels and chemicals. This study investigates the copper-catalyzed glucose-fructose isomerization in water, focusing on insights into the roles of the dissolved copper species. Depending on the pH, the thermodynamic equilibrium shifted towards one or a few copper species, namely Cu2+ , Cu(OH)+ , and Cu(OH)2 . According to thermodynamics, the highest concentration of Cu(OH)+ is at pHu20055.3, at which the highest fructose yield of 16u2009% is achieved. The obtained fructose yields strongly correlate with the concentration of Cu(OH)+ . A pH decrease of 2-3u2005units was observed during the reaction, resulting in the deactivation of the catalyst through hydrolysis in acidic media. Based on the results of the catalytic experiments, as well as spectroscopic and spectrometric studies, we propose Cu(OH)+ as an active Lewis-acidic species following an intramolecular 1,2-hydride shift.

Solid Molecular Frustrated Lewis Pairs in a Polyamine Organic Framework for the Catalytic Metal-free Hydrogenation of Alkenes

We report for the first time a metal‐free heterogeneously catalyzed hydrogenation using a semi‐solid frustrated Lewis pair (FLP). The catalyst consists of a solid polyamine organic framework and molecular tris(pentafluorophenyl)borane (BCF) that form a semi‐immobilized FLP inu2005situ in the catalytic hydrogenation of diethyl benzylidenemalonate. 11Bu2005NMR spectroscopy proves the successful hydrogen activation by the FLP. Furthermore, the B−N interactions between the polyamine and BCF are investigated by IR and solid state NMR spectroscopy. The FLP 1,4‐diazabicyclo[2.2.2]octane (DABCO)/BCF, which combines the features of a FLP and a classical Lewis adduct, functions as molecular reference in both, catalysis and characterization. Furthermore, computational studies enable a better insight into the hydrogen activation through DABCO/BCF and polyamine/BCF.