This work reports an innovative route for biomass upgrading via hydrodeoxygenation (HDO) reactions which avoids external high-pressure hydrogen supply and harsh conditions (such as high-temperature or additives). A novel Pd/CFR catalyst with controllable oxygen groups and defects was synthesized with low-load Pd supported on resorcinol–formaldehyde resin carbon spheres (CFR) for selective hydrodeoxygenation of vanillin under mild conditions. The as-prepared Pd/CFR-800 catalyst shows excellent activity (>99.5% yield of 2-methoxy-4-methylphenol) using polymethylhydrosiloxane (PMHS) as green hydride source within 1 h at 70 °C, in the absence of additives. According to spectral analyses, the concentration of carbon skeleton defects and hydroxyl functional groups on the catalyst can be adjusted by the carbonization temperature. Combined with experimental results and mechanistic studies, the synergistic effect of hydroxyl groups and adjacent defects was deemed as the main reason for the strong adsorption of the substrate, which significantly facilitated the key hydrogenolysis step. Furthermore, the as-prepared Pd/CFR-800 catalyst has shown excellent recyclability after used for five times. The in situ regulation of functional groups and defects on carbon materials provides new ideas for designing high-performance catalysts for the catalytic transformation of various lignin derivatives.

The substitution of green hydrogen donors for replacing high-pressure H 2 to achieve biomass derived ketone and aldehyde hydrodeoxygenation (HDO) under mild conditions has attracted widespread attention. However, it remains a considerable challenge to get rid of acid additives and control product selectivity. Herein, a series of bimetallic Pd−M/HZSM-5 catalysts (M = Zr, Mn, Zn, or La) were fabricated for controlled hydrodeoxygenation of biobased ketones and aldehydes (acetophenone, benzophenone, 4-hydroxyacetophenone, vanillin, furfural) using polymethylhydrosiloxane (PMHS) as the green H-donor, in which >99% conversion and >99% selectivity to ethylbenzene were achieved for hydrodeoxygenation of acetophenone as the probe within 3 h at 35 °C over the as-prepared 0.5%Pd−2.0%Zr/HZSM-5 catalyst with a Pd/ Zr mass ratio of 1:4. According to characterizations of TEM-HAADF, XPS, ESR, and H 2 -TPR, the Pd−Zr alloy structure was formed on the bimetallic Pd−Zr/HZSM-5 catalyst, promoting the transform of Pd−O−Zr solid solution to PdO−ZrO 2 and the generation of oxygen vacancy. Moreover, the abundant of oxygen vacancies on the alloyed Pd−Zr/HZSM-5 catalysts enhance the dissociation of silanes to provide the abundance of hydrogen protons, greatly accelerating the hydrogenation of biobased ketones and aldehydes, and then the acid site of the Pd−Zr/HZSM-5 catalyst promotes the dehydration of the intermediates (alcohols) to hydrocarbons. Furthermore, the as-fabricated Pd−Zr/HZSM-5 alloy catalyst can achieve an excellent recycling capability after six uses and exhibits universality toward various biobased ketones and aldehydes at 35 °C. The present findings provide new insights into the design of selective HDO of biomass in a green process.

Research on biomass decomposition and transformation has attracted widespread attention from academia to industry worldwide, aiming to harvest bio-aromatics from the abundant renewable biomass resource. However, the complexity of the structure and composition of biomass makes its conversion into bio-aromatics a very challenging task. Hence, it is necessary to understand in depth the mechanism of biomass conversion to bio-aromatics with higher selectivity. Although considerable progress has been achieved on the development of bio-aromatics from biomass, the detailed process and reaction mechanism for the bioaromatics synthesis has lacked a complete summary. This work reviews the recent advances in the conversion of biomass to bioaromatics, including biomass gasification, pyrolysis, and hydrolytic fermentation, etc. Various biomass sources and biomass-derived model compounds as examples were used to illustrate the effect of different raw materials on the yield of bio-aromatics. Subsequently, this review summarizes the influence of different catalysts on the synthesis of bio-aromatics and the metal-modified HZSM-5 catalysts exhibited a higher bio-aromatics yield compared with those of other catalysts. Finally, the reaction mechanism of biomass to bio-aromatic hydrocarbons via different reaction routes was discussed in detail. The aim is for the conversion mechanism presented in this work to provide a reference for the efficient conversion of bio-aromatics from biomass in the future.

Various advantages of sustainable biomass hydrodeoxygenation in water-oil biphasic systems.

Herein, a defective zeolite–carbon (CFR@HZSM-5) nanocomposite-supported nano-scale Pd catalyst (Pd/CFR@HZSM-5) was facilely synthesized for selective “H2-free” hydrodeoxygenation (HDO) of vanillin (VL) under mild conditions. The optimal Pd/CFR@HZSM-5(2:1) catalysts show excellent activity (the 99% yield to 2-methoxy-4-methylphenol) and high turnover frequency in polymethylhydrosiloxane at 60 °C. According to spectral analysis, there is an abundant carbon defect structure on the surface of the CFR@HZSM-5 nanocomposite, which can provide unique sites for capturing Pd metal nanoparticles (NPs) and serve as active sites to promote the adsorption of substrates. The stable and high-dispersion Pd NPs are fastened with carbon atoms in the vacancy defect through strong electronic metal–support interactions, which improved the activity of VL HDO up to four times higher than that of other catalysts under mild conditions. The unique high-dispersion Pd structure and abundant surface defects of Pd/CFR@HZSM-5 catalysts are significant features to brilliant catalytic activity for biomass-derived molecule HDO. Meanwhile, the abundance of acidic sites in the composite carrier catalyst replaces the use of acidic additives in previous catalytic systems. The optimal Pd/CFR@HZSM-5(2:1) catalysts showed good recovery even after five uses. The catalytic system was also applied for various biomass HDO models under mild conditions. This methodology opens new ideas for designing catalysts with high activity and high efficiency for selective HDO of biomass under green and mild conditions.