Boric Acid as a Novel Homogeneous Catalyst Coupled with Ru/C for Hydrodeoxygenation of Phenolic Compounds and Raw Lignin Oil

Hydrodeoxygenation of Lignin-Based Compounds over Ruthenium Catalysts Based on Sulfonated Porous Aromatic Frameworks

Bifunctional catalysts are a major type of heterogeneous catalytic systems that have been widely investigated for biomass upgrading. In this work, Ru-catalysts based on sulfonated porous aromatic frameworks (PAFs) were used in the hydrodeoxygenation (HDO) of lignin-derived compounds: guaiacol, veratrole, and catechol. The relationship between the activity of metal nanoparticles and the content of acid sites in synthesized catalysts was studied. Herein, their synergy was demonstrated in the Ru-PAF-30-SO3H/5-COD catalyst. The results revealed that this catalytic system promoted partial hydrogenation of lignin-based compounds to ketones without any further transformations. The design of the Ru-PAF-30-SO3H/5-COD catalytic system opens a promising route to the selective conversion of lignin model compounds to cyclohexanone.

Efficient depolymerization of lignin through microwave-assisted Ru/C catalyst cooperated with metal chloride in methanol/formic acid media

Lignin, an abundant aromatic biopolymer, has the potential to produce various biofuels and chemicals through biorefinery activities and is expected to benefit the future circular economy. Microwave-assisted efficient degradation of lignin in methanol/formic acid over Ru/C catalyst cooperated with metal chloride was investigated, concerning the effect of type and dosage of metal chloride, dosage of Ru/C, reaction temperature, and reaction time on depolymerized product yield and distribution. Results showed that 91.1 wt% yield of bio-oil including 13.4 wt% monomers was obtained under the optimum condition. Yields of guaiacol-type compounds and 2,3-dihydrobenzofuran were promoted in the presence of ZnCl₂. Formic acid played two roles: (1) acid-catalyzed cleavage of linkages; (2) acted as an in situ hydrogen donor for hydrodeoxygenation in the presence of Ru/C. A possible mechanism for lignin degradation was proposed. This work will provide a beneficial approach for efficient depolymerization of lignin and controllable product distribution.

Selectively Producing Acetic Acid via Boric Acid-Catalyzed Fast Pyrolysis of Woody Biomass

Boric acid is recently proved to be a good substitute for conventional acidic catalytic materials. However, few studies used boric acid as a catalyst in biomass pyrolysis. This study focused on the catalytic effects of boric acid (BA) on pyrolysis behaviors of woody biomass. The birch wood flour (WF) was used as feedstock and treated by impregnation of boric acid solution. Both untreated and boric acid-treated samples (BW) were characterized by FTIR and SEM. Thermogravimetry (TG) and pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS) techniques were used for studying mass loss, composition, and distribution of evolved volatiles formed from pyrolysis process. Additionally, a small fixed-bed pyrolyzer with an amplificated loading amount was used to prepare liquid products, and further, GC/MS were used to analyze the composition of these liquid products. Different pyrolysis temperatures and boric acid/wood flour mass ratios were also studied. The main results are as follows. Boric acid infiltrated into both cell cavity and cell wall through impregnation treatment. FTIR analysis showed that boric acid reacted with wood flour to form B-O-C bond during the treatment. After the treatment of boric acid, the initial degradation temperatures and residual carbon contents were increased, while the maximum weight loss rates were decreased. Boric acid significantly altered the composition and distribution of volatile pyrolysis products of wood flour. It significantly increased the contents of small molecule compounds such as acetic acid and furfural but, decreased the contents of phenol derivatives with high molecular weights. And these changes became more pronounced as the temperature increased. When mass ratio of boric acid (BA) to wood flour (WF) was 2, the acetic acid accounted for 91.28% of the total product in the pyrolysis liquid, which was 14 times higher than that of untreated wood flour. Boric acid effectively catalyzed fast pyrolysis of woody biomass to selectively produce acetic acid