2022, Drabo, Peter, Fischer, Matthias, Emondts, Meike, Hamm, Jegor, Engelke, Mats, Simonis, Marc, Qi, Long, Scott, Susannah L., Palkovits, Regina, Delidovich, Irina

Rational catalyst design and optimal solvent selection are key to advancing biorefining. Here, we explored the organocatalytic isomerization of D-fructose to a valuable rare monosaccharide, D-allulose, as a function of solvent. The isomerization of D-fructose to D-allulose competes with its isomerization to D-glucose and sugar degradation. In both water and DMF, the catalytic activity of amines towards D-fructose is correlated with their basicity. Solvents impact the selectivity significantly by altering the tautomeric distribution of D-fructose. Our results suggest that the furanose tautomer of D-fructose is isomerized to D-allulose, and the fractional abundance of this tautomer increases as follows: water < MeOH < DMF ≈ DMSO. Reaction rates are also higher in aprotic than in protic solvents. The best D-allulose yield, 14 %, was obtained in DMF with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst. The reaction kinetics and mechanism were explored using operando NMR spectroscopy.

2018, Artz, Jens, Delidovich, Irina, Pilaski, Moritz, Niemeier, Johannes, Kübber, Britta Maria, Rahimi, Khosrow, Palkovits, Regina

Covalent triazine-based frameworks (CTFs) were synthesized in large scale from various monomers. The materials were post-synthetically modified with acid functionalities via gas-phase sulfonation. Acid capacities of up to 0.83 mmol g−1 at sulfonation degrees of up to 10.7 mol% were achieved. Sulfonated CTFs exhibit high specific surface area and porosity as well as excellent thermal stability under aerobic conditions (>300 °C). Successful functionalization was verified investigating catalytic activity in the acid-catalyzed hydrolysis of cellobiose to glucose at 150 °C in H2O. Catalytic activity is mostly affected by porosity, indicating that mesoporosity is beneficial for hydrolysis of cellobiose. Like other sulfonated materials, S-CTFs show low stability under hydrothermal reaction conditions. Recycling of the catalyst is challenging and significant amounts of sulfur leached out of the materials. Nevertheless, gas-phase sulfonation opens a path to tailored solid acids for application in various reactions. S-CTFs form the basis for multi-functional catalysts, containing basic coordination sites for metal catalysts, tunable structural parameters and surface acidity within one sole system.