Publication: Catalytic hydrogenolysis of lignin into aromatic compounds over mesoporous ni-based bimetallic catalysts in the presence of hydrogen donor solvent
Loading...
Date
2024-05-01
Authors
Ewuzie Nnadozie Remigius
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Lignin, a renewable biopolymer is the most common source of aromatics and carbon on the Earth. Valorization of lignin into aromatic compounds has received limited attention due to its intricate structure. Lignin hydrogenolysis holds huge potential to produce aromatic compounds. This study focused on the development of promoted Ni-based bimetallic catalysts, specifically Ni-Co/C, and Ni-Cu/C, on activated carbon support. Also, Ni-Co/HZSM-5 and Ni-Cu/HZSM-5 on zeolite support. And to evaluate their performance on lignin hydrogenolysis reaction in an 80 mL stainless-steel batch reactor under internal hydrogen donor solvents (isopropanol and methanol), and to compare their performance with their corresponding monometallic catalysts. Their promotional effect on lignin hydrogenolysis was evaluated. The catalysts were synthesized by the incipient wetness impregnation method. BET, SEM, EDX, and XPS measurements revealed their physicochemical properties and promotional effects. This promotional effect led to improved hydrogen transformation ability and enhanced hydrogenolysis activity, resulting in high lignin conversion and yield of monomeric products. Effects of reaction parameters such as temperature (220-260 ℃), pressure (2-5 MPa), time (2-5 h), stirring speed (500-800 rpm), and catalyst dosage (0.05 to 0.3 g) on lignin hydrogenolysis were elucidated. Catalyst reusability and high heating values were also investigated, and the kinetic parameters were elucidated. The addition of cobalt and copper to nickel as promoters enhanced the lignin conversion and monomeric product yield because they providedmore active sites for catalyst-lignin interaction. Activated carbon support demonstrated better dispersion and stability of the active components compared to zeolite support due to its larger surface area of 537.6 m2/g. 20%Ni-10%Co/C bimetallic catalysts achieved the highest lignin conversion and yield of monomer products of 94.2% and 53.1 wt.%, while Ni-Co/HZSM-5 bimetallic catalysts achieved 91.2% lignin conversion and 44.9 wt.% yield of monomer products in isopropanol solvent. Similarly, Ni-Cu/HZSM-5 bimetallic catalysts achieved a remarkable lignin conversion of 90.6% and a significant monomer product yield of 40.8 wt.% in methanol solvent. Meanwhile, Ni-Cu/C bimetallic catalysts achieved 84.7 % lignin conversion affording 33.0 wt.% monomer product in isopropanol solvent under optimal reaction conditions at 250 ℃, 4 MPa, 4 h, 700 rpm, and 0.3 g. GC-MS, GC-FID, FT-IR, GPC, and elemental analysis were employed to investigate the volatile and non-volatile products. The effective depolymerization of alkali lignin was revealed by GPC analysis. A total of 20 aromatic compounds were successfully identified by the GC-MS analysis. Based on the excellent results obtained, possible reaction mechanisms were proposed to elucidate the catalytic pathways involved. The results demonstrated that Ni-based bimetallic catalysts exhibited superior catalytic performance, enhanced stability, and product selectivity than their corresponding
monometallic catalysts.