Highly selective aromatic ring hydrogenation of lignin-derived compounds over macroporous Ru/Nb2O5 with the lost acidity at room temperature

Selective Cleavage of the Diphenyl Ether C–O Bond over a Ni Catalyst Supported on AC with Different Pore Structures and Hydrophilicities

“…Obtaining chemicals from renewable energy has attracted plenty of attention due to the declining fossil fuels. , Lignocellulosic biomass provides a potential alternative in place of fossil fuels to produce chemicals. , Lignin is a potential renewable feedstock, containing a large number of aromatic backbones and organic carbon, making it an ideal renewable energy source of aromatic compounds for a large number of applications. − Due to the improvement of the reduction catalytic fractionation (RCF) process (also known as lignin-first biorefinery), a complete valorization of lignin into liquid fuels and chemicals has been widely investigated. − In the process of RCF, it is important to cleave a large number of C–O bonds for the basic catalysis of lignin depolymerization. There are several types of C–O bonds in the structure of lignin, consisting of β-O-4, α-O-4, and 4-O-5 bonds, which account for 45–62, 3–12, and 4–9% of the ether bonds in lignin, respectively. − Among them, the order of the bond dissociation energy is as follows: 4-O-5 (314 kJ/mol) > β-O-4 (289 kJ/mol) > α-O-4 (218 kJ/mol), and the 4-O-5 bond is the strongest in lignin. , Therefore, selective cleavage of the 4-O-5 C–O bonds to obtain chemicals is a challenging step .…”

Catalytic Hydrodeoxygenation of Lignin and Its Model Compounds to Hydrocarbon Fuels over a Metal/Acid Ru/HZSM-5 Catalyst

“…The selectivity of cyclohexane was up to 100 and 95.8%, respectively. In addition to the higher solubility of H 2 in alkanes than that of alcohols, an important fact was that alcohols as solvents could easily compete for adsorption on the surface of the acidic Ru/HZSM-5 catalyst to undergo the dehydration reaction, thereby reducing the surface coverage of substrates. ,, Therefore, the active sites for DPE to undergo the HDO reaction were greatly reduced. The conversion of DPE in isopropanol was higher than that of methanol and ethanol, which could be explained by the factor that apart from the dehydration reaction of isopropanol, the dehydrogenation reaction could also provide a small amount of hydrogen source. , Moreover, the diffusion rate of H 2 in different solvents was different.…”

“…Moreover, support is also an important part of enhancing the activity and stability, especially during the HDO process. Common supports are mainly composed of HZSM-5, activated carbon, Al-SBA-15, carbon nanotubes, metal–organic framework, hydrotalcite, and Nb 2 O 5 . , The HDO reaction requires the active sites where hydrogenolysis, hydrogenation, and deoxidation are feasible as well as acid sites. ,, Generally, bifunctional catalysts containing Brønsted acid sites and Lewis metal sites such as HZSM-5, HY, and Hβ zeolites are regarded as promising catalysts. ,, The unitization of metal-impregnated zeolite in the HDO is widely explored due to its strong acidity, uniform pore size, and crystal structure, suggesting the high activity for the HDO. Additionally, compared with other oxide supports, high-surface-area zeolite supports are considered as the better choice for catalytic reactions because they allow higher dispersion of active metals and provide a higher contact area between the catalyst and the substrate. , …”

“…20,21 The HDO reaction requires the active sites where hydrogenolysis, hydrogenation, and deoxidation are feasible as well as acid sites. 18,22,23 as promising catalysts. 16,24,25 The unitization of metalimpregnated zeolite in the HDO is widely explored due to its strong acidity, uniform pore size, and crystal structure, suggesting the high activity for the HDO.…”

More than a support: the unique role of Nb2O5 in supported metal catalysts for lignin hydrodeoxygenation

“…The study suggested that the abundant acidic sites on Nb 2 O 5 promoted the C–O cleavage. Jiang et al 41 prepared a macroporous Ru/Nb 2 O 5 catalyst with reduced acidity and applied the catalyst in the HDO of diphenyl ether. They found that only the benzene ring hydrogenation reaction occurred, whereas the HDO reactions did not, which further confirmed that the acidic properties of Nb 2 O 5 affected the cleavage of the C–O bond.…”