Supported β-Mo₂C on Carbon Materials for Kraft Lignin Decomposition into Aromatic Monomers in Ethanol

Abstract

The β-Mo 2 C on different carbon supports was prepared conveniently via direct H 2 reduction or self-reduction for catalytic conversion of Kraft lignin into aromatic hydrocarbons, aromatic alcohols, and aromatic aldehydes. The β-Mo 2 C on macroporous carbon (MC) with large pore size exhibits the highest activity with aromatic yield of 0.543 g/g Kraft lignin at 280 °C for 3 h, resulting from the accessibility of lignin fragments to β-Mo 2 C. Mo, MoO 2 , and MoO 3 possess relatively low activity. Higher calcination temperature is required to obtain β-Mo 2 C over graphite (Gr) support than MC and activated carbon (AC), and small grain size of Gr-supported catalysts is beneficial for high activity. The β-Mo 2 C on AC exhibits the highest selectivity to aromatic hydrocarbons, which are attributed to highly dispersed β-Mo 2 C in micropores.

Synthesis-Controlled α- and β-Molybdenum Carbide for Base-Promoted Transfer Hydrogenation of Lignin to Aromatic Monomers in Ethanol

“…The aromatic components are classified as aromatic hydrocarbons, aromatic alcohols, and aromatic aldehydes, which are produced from C−C and C−O scissions of lignin. Our previous work 39 showed that the yields of aromatic monomers (0.022 g/g Kraft lignin) without any catalyst are significantly lower than that in Figure 7, which confirms the benefit of MoC catalysts for the conversion of Kraft lignin to aromatic monomers. The esters are mainly produced via esterification of solvent ethanol and oxygenated compounds (such as alcohols, aldehydes, and acids from linkages and acid branches of lignin) with the hydrogen radical involved, and the long carbon-chain esters are highly related to aldol condensation of intermediate aldehydes.…”

Metal–Organic Framework-Mediated Synthesis of One-Dimensional Nitrogen-Doped Molybdenum Carbide for the Cleavage of Lignin and Dimeric Lignin Model Compounds

“…Compared to the higher yields of esters and alcohols from the depolymerization of Kraft lignin over a conventional Mo 2 C catalyst, the main products identified here are C 6 –C 11 monophenols such as sinapyl, coniferyl, p -coumaryl alcohols, and their derivatives. Moreover, the overall yield of the mono-oxygenated phenolics detected by GC is 10.1 wt %, based on the weight of the enzymatic hydrolysis lignin loaded into the reactor, which is much higher than that obtained from the one-pot lignin depolymerization over Mo 2 C catalysts having been reported so far, as shown in Figure b. − , …”

“…When the reaction of an enzymatic hydrolysis lignin sample obtained from corncob with a weight-average molecular weight (M w ) of 10,650 was carried out at the optimized reaction conditions (Figures S13 and S14), that is, 300 °C and 9.6 MPa for 4 h, over N-Mo 2 C@C-700, the maximum yield of the liquid products was 93.5% with a M w of 573 and a polydispersity index (PDI) of 1.57, much lower than that obtained over hydrogenation catalysts, confirming that the lignin depolymerization is well performed in this process (Figure S15). 44,45 Also, some chemicals with m/z of 300−900 were also detected by LC-MS (Figures S16−20). The total-ion chromatogram (TIC) derived from a gas chromatography− mass spectrometry (GC−MS) is shown in Figure 3a.…”

“…Moreover, the overall yield of the monooxygenated phenolics detected by GC is 10.1 wt %, based on the weight of the enzymatic hydrolysis lignin loaded into the reactor, which is much higher than that obtained from the onepot lignin depolymerization over Mo 2 C catalysts having been reported so far, as shown in Figure 3b. [13][14][15]45 The 2D HSQC NMR and FT-IR techniques were employed to better estimate the C−O bond change of lignin before and after the reaction. The relative contents of the linkages in lignin such as β-O-4, α-O-4/β-5, β-β, syringyl units (S y ), and guaiacyl units (G) are listed in Figure 4 and Figure S21, as well as in Tables S5 and S6.…”

“…Given the excellently catalytic results on lignin model compounds, enzymatic hydrolysis lignin was further used to prove the valorization activity of N-Mo 2 C@C-700 in supercritical ethanol, which has been proven to be an effective solvent in the depolymerization of lignin over Mo 2 C-based catalysts because of being a hydrogen donor in nature with high molecule diffusivity and proper polarity under these supercritical conditions. − , Fragments with m / z of 194, 232, 262, and 292 were obtained at 300 °C in Ar, indicating that the fragmentation of lignin without a catalyst is possible (Figure S12). When the reaction of an enzymatic hydrolysis lignin sample obtained from corncob with a weight-average molecular weight ( M w ) of 10,650 was carried out at the optimized reaction conditions (Figures S13 and S14), that is, 300 °C and 9.6 MPa for 4 h, over N-Mo 2 C@C-700, the maximum yield of the liquid products was 93.5% with a M w of 573 and a polydispersity index (PDI) of 1.57, much lower than that obtained over hydrogenation catalysts, confirming that the lignin depolymerization is well performed in this process (Figure S15).…”