No abstract

The development of an economic and sustainable catalytic system was crucial for lignin-based biorefinery. Herein, we reported a low-cost Cu/CuMgAlO x catalyst with promising activity toward lignin hydrodeoxygenation (HDO) through a H2-free method. Supercritical methanol was used as the hydrogen donor, solvent, and reactant simultaneously. Guaiacol was employed as a representative lignin model compound to reveal the HDO mechanism of lignin derivatives. HDOs of guaiacol performed at 250, 275, 300, and 350 °C with durations ranging from 15 to 120 min indicated a high HDO efficiency of the catalytic system. The obtained liquid products were categorized to oxygen-containing unsaturated products (OUPs), oxygen-containing saturated products (OSPs), and cycloalkanes. A kinetic model based on a simplified reaction process containing the three following conversion steps was established: guaiacol transformed to OUPs through the initial HDO, then hydrogenated to OSPs (medium HDO), and eventually turned to cycloalkanes by the deep HDO. The deep HDO was the rate-determining step, and the apparent activation energies of the three steps were all lower than those in the literature. Phenol, 1,2-cyclohexanediol, anisole, and veratrole were the major intermediates, the HDOs of which were programed for pathway verification. Remarkably, catechol (the culprit of condensation) was not produced in this system. Overall, a detailed reaction network of guaiacol HDO was established, and the veil of Cu/CuMgAlO x -catalyzed lignin-derivatives HDO in supercritical methanol was revealed. This work paved the way for the application of Cu/CuMgAlO x catalyst in lignin-derivatives upgrading.

No abstract

No abstract

The fundamental understanding of the catalytic performance of copper-based catalysts for lignin hydroconversion is delayed compared with the empirical optimization of the catalyst preparation. Herein, we investigate the interplay between the lignin-abundant oxygen-containing functional groups and Cu active species via the catalytic β-O-4 lignin linkage hydrogenolysis. Catalyst performance data and elemental spectra characterizing the catalyst demonstrate the dominance of Cu0 in the catalysis. Remarkably, Cα–OH and CαO in the aliphatic chain play critical roles in this process, without which the linkage cannot be broken. These groups markedly accelerate the linkage cleavage by decreasing both the chemisorption energy between Cβ–O and Cu0 and the bond dissociation energy of the linkage. On the contrary, the methoxyl groups attached to the aromatic rings hinder the bond cleavage as a result of the steric effect. Such hindrance is significantly affected by the amount and position of the methoxyl groups. The results of this work highlight the importance of the unique structures of lignin in its reductive depolymerization catalyzed by copper-based catalysts, which appear to offer an opportunity for tailoring efficient copper-based catalysts for lignin hydrogenolysis.

Production of jet fuel precursors from waste kraft lignin through a depolymerization and hydrodeoxygenation (DHDO) method with a complex copper acid catalyst is reported. The kraft lignin undergoes a high degree of depolymerization, deoxygenation, hydrogenation, and C–C coupling. Monomers and dimers with molecular weights in the ranges of <200 Da and 354–452 Da are obtained with optimized yields reaching 93.29 and 39.30 C% at 360 °C for 8 h, while trimers and oligomers with higher molecular weights are also generated with lower contents. The high carbon yields of monomers and dimers are given by the incorporation of methanol solvent. The double bond equivalent (DBE) and polydispersity index (PDI) decrease from 14.77 and 2.77 in kraft lignin to 9.05 and 1.35 in the products, while the high heating value (HHV) increases from 24.53 to 36.47 MJ/kg after reaction. Furthermore, over 45% of the optimized products have boiling points in the range of that of commercial jet fuel (60–280 °C). All these results demonstrate the appropriate properties of the products from kraft lignin DHDO as potential jet fuel precursors.

No abstract

In the field of photocatalysis, the crystal phase engineering of titanium dioxide is a research hotspot. Titanium dioxide heterojunctions often exhibit better photocatalytic performance than single-phase TiO2. Here, a two-step hydrothermal and calcination method is used to build the phase interface between TiO2 (B) and rutile for the first time, and a narrow band gap heterojunction TiO2 material is synthesized. The heterojunction TiO2 material is characterized by transmission electron microscopy (TEM), ultraviolet (UV), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR). The two phases are connected by a corner-sharing at the phase interface. The different positions of the conduction bands and valence bands between the two phases result in the effective separation of photogenerated electrons and holes through the phase interface. Under light, the photogenerated holes are transferred to the rutile phase and quickly consumed by the sacrificial agent, and the surplus photogenerated electrons participate in the H2 evolution reaction. When the ratio of TiO2 (B) to rutile is about 2/1, the TiO2 (B)/rutile heterojunction exhibits the highest photocurrent and the best H2 evolution performance under the present experimental conditions.