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

Abstract

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 % H2/N2 flow. The characterizations such as N2 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 °C under N2 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 Caryl–OCH3 bond, and the moderate acid amounts enhanced the alkylation reaction.

Solvent Effect on the Hydroconversion of Lignin-Related Model Compounds over MoO3

“…As shown in Figure , the Mo 3d doublet is contributed from a large amount of Mo 4+ , Mo 5+ , and Mo 6+ with the 3 d 5/2 bands located at 229.5, 230.8, and 232.7 eV, respectively. The Mo 5+ species formation can be caused by the conversion of MoO 3 to MoO x C y H z and/or oxygen vacancy (OV) produced by the MoO 3 reduction. , The Mo 5+ contents of the used catalysts in the solvents at 250 °C via the deconvolution of XRPES decrease in the order: E (51%) > M (46%) > IP (27%) > EA (25%) > H (1%). The Mo 5+ content of the used catalyst in H and EA increased dramatically to 53 and 55%, respectively, with raising temperature to 300 °C.…”

Catalytic Depolymerization of Lignin for the Selective Production of Phenolic Monomers over Cobalt-Supported Calcium Catalysts

“…Various research groups have proposed several heterogeneous catalytic systems (noble or transition metals) for the selective cleavage of lignin and have been reviewed extensively. , However, the design of an appropriate catalyst is still far from ideal and continues to be a challenging topic of research. , Currently, the reported methodologies in the literature for lignin utilization are pyrolysis, , catalytic oxidative depolymerization, hydrogenolysis, , and acid–alkali hydrolysis . The procedure of hydrogenation can increase product stability considerably.…”

Lignin Catalytic Depolymerization for Phenolic Monomers: Boosting the Selective Cleavage of β-O-4 Bonds of Lignin by Mo═O and Al(IV)–O–BO2 Interfacial Sites in B–Mo/Sepiolite

“…Under the influence of angle strain, Ar-OH bond fracture and alkyl group substitution were easily realized. Recently, based on the properties of molybdenum and sepiolite clay, our team prepared a series of sepiolite-supported Mo-based catalysts and investigated the effects of Mo content, reduction treatment, calcination temperature, and transition metal and nonmetal modification , on lignin depolymerization for liquid fuels and aromatic compounds. These results confirmed that the metal constituents, oxygen species, and surface functional groups (MoO, Mo–O) of Mo-based catalysts can be changed through the above-mentioned modification methods to achieve the regulation of the acid–base sites and electron-rich/electron-poor sites, which accordingly maximize the polarization of β-O-4 bonds, reduce the dissociation energy of C–O bonds, and produce more oxygen-containing phenolic intermediates.…”