Effect of Reduction Treatments of Mo/Sepiolite Catalyst on Lignin Depolymerization under Supercritical Ethanol

摘要

Depolymerization of lignin to produce high yield lignin oil is one of the prospective methods to achieve the sustainable and economic development for human society. Molybdenum-based sepiolite (Mo/SEP) catalyst presented a promising performance for lignin depolymerization under supercritical ethanol (LDSE). Herein, the influence of reductive treatments for calcined Mo/SEP (C-Mo/SEP) catalyst on lignin depolymerization was systematically investigated under supercritical ethanol. Two reduced catalysts N-Mo/SEP and H-Mo/SEP was obtained respectively through the reduction process by NaBH4 and 10 vol % H-2/N-2 flow. The characterizations such as N-2 adsorption-desorption, SEM, XRD, FTIR, XPS, NH3-TPD, and Py-FTIR were employed to investigate the variation of microcosmic structure and property of Mo/SEP affected by reductive treatments. The results exhibited that reduction treatment optimized the distributions of Mo5+ species and B/L acidic sites of Mo/SEP catalysts. During the LDSE process at 290 degrees C under N-2 atmosphere for 3 h, lignin oil produced over N-Mo/SEP catalyst gave a higher heating value of 34.92 MJ/kg, which slightly decreased from 36.07 MJ/kg that was obtained over C-Mo/SEP. But N-Mo/SEP catalyst generated the highest yields of lignin oil (112.0%) and petroleum ether soluble (PES) product (74.6%). According to the GC-MS results, the possible mechanism of N-Mo/SEP catalytic LDSE was proposed. The synergistic effect between Mo5+ species and B/L acid sites promoted the cracking of the C-aryl-OCH3 bond, and the moderate acid amounts enhanced the alkylation reaction.