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Conversion of hemicellulose streams and the constituent monosaccharides, xylose, arabinose, glucose, mannose, and galactose, was conducted to produce value‐added chemicals, including furfural, hydroxymethylfurfural (HMF), levulinic acid and anhydrosugars. The study aimed at developing a kinetic model relevant for direct post‐Organosolv hemicellulose conversion. Monosaccharides served as a tool to in detail describe the kinetic behavior and segregate contribution of hydrothermal decomposition and acid catalyzed dehydration at the temperature range of 120–190 °C. Catalyst free aqueous media demonstrated enhanced formation of furanics, while elevated temperatures led to significant saccharide isomerization. The introduction of sulfuric and formic acids maximized furfural yield and significantly reduced HMF concentration by facilitating its rehydration into levulinic acid (46 mol%). Formic acid additionally substantially enhanced formation of anhydrosaccharides. An excellent correlation between modeled and experimental data enabled process optimization to maximize furanic yield in two distinct hemicellulose streams. Sulfuric acid‐containing hemicellulose stream achieved the highest furfural yield after 30 minutes at 238 °C, primarily due to the high Ea for pentose dehydration (150–160 kJ mol−1). Contrarily, formic acid‐containing hemicellulose stream enabled maximal furfural yield at more moderate temperature and extended reaction time due to its lower Ea for the same reaction step (115–125 kJ mol−1). [ABSTRACT FROM AUTHOR]

Combining carboxylation reactions using carbon dioxide (CO2) as a reactant with phenol results in creation of new C-C bonds, and represents one of the most promising routes in sustainable utilization of ubiquitous and readily available resources for production of highly valuable products. This study provides a detailed and well-structured investigation of the effect of various reaction conditions (reactant loading, reaction duration, temperature, CO2 pressure) on the carboxylation of phenol. Sodium phenoxide carboxylation showed well-resolved trends with variation of temperature and time, and resulted in production of salicylic acid (SA) in the range of 11.4 to 47.8%, 4-hydoxybenzoic acid (4HBA) in the range of 2.0 to 8.2%, while the dicarboxylated 4-hydroxyisophthalic acid (4HiPh) was only detected in trace amounts. The effect of the variation of reactant content was shown to be significantly influenced by the reactor size, solid/vessel and gas/solid contact area, as well as the efficiency of the stirring. CO2 pressure was shown to be a crucial element, where reactions carried out below 2 MPa CO2 did not show any activity. While investigating the reaction mechanism, it was shown that the salt analogues of potential products could be acidified in situ by the moisture present, and immediately degraded back to phenol, thus lowering yields of potentially obtained products. The experimental results were successfully used to compose a kinetic model, which very well describes the experimentally obtained results. As such, this study provides a valuable dataset for valorization of lignocellulosic aromatic compounds as well as highly abundant and environmentally detrimental carbon dioxide into industrially valuable mono- and dicarboxylic acids. [ABSTRACT FROM AUTHOR]

Commercial SSZ‐13 zeolite with different n(Si)/n(Al) ratios and from different suppliers were subjected to a post‐synthetic treatment in order to create mesopores of up to 15 nm. Furthermore, the materials were modified with copper ions and thoroughly physico‐chemically characterized. The modified textural properties varied the nature of copper species, and thus, activity in the selective catalytic reduction of NOx with ammonia (NH3‐SCR‐DeNOx). Pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) studies with hexane as probe liquid revealed improved intracrystalline diffusion for some Cu‐containing SSZ‐13 materials. The NH3‐SCR‐DeNOx pathways are verified via in situ DR UV‐Vis, in situ FT‐IR and EPR, temperature‐programmed studies as well as SSITKA studies that provide a mechanistic understanding of the reaction. Kinetic modelling results demonstrate the highest NH3‐SCR‐DeNOx reaction rates and up to 20 % lower energy barriers with n(Si)/n(Al) ratio of 6.5 for all modified forms (i. e., (NH4)Cu‐SSZ‐13_6.5 and Cu‐SSZ‐13_6.5_NaOH/0.1) and cause only negligible parasitic ammonia oxidation. The modelling of the stop‐flow experiments further demonstrates that the SCR pathway via the HONO surface intermediate is present but barely contributes to the overall NO conversion compared to the dominant path between adsorbed NH3 and NO from the gas phase. [ABSTRACT FROM AUTHOR]

The natural aromatic polymer lignin and its lignin-like oligomeric fragments have attracted attention for their antioxidant capacity and free radical scavenging activities. In this study, a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was employed to assess the antioxidant capacity of fractionated and partially depolymerized organosolv lignin by electron paramagnetic resonance (EPR) and UV-Vis spectroscopy. The results show significant antioxidant activity for both the lignin and oligomeric fragments, with the EPR measurements demonstrating their efficiency in quenching the free radicals. The EPR data were analyzed to derive the kinetic rate constants. The radical scavenging activity (RSA) of lignins was then determined by UV-Vis spectroscopy and the results were compared with the EPR method. This two-method approach improves the reliability and understanding of the antioxidant potential of lignin and its derivatives and provides valuable insights for their potential applications in various industries, including pharmaceuticals, food preservation, and cosmetics. [ABSTRACT FROM AUTHOR]