Yield and distribution of products of lignin liquefaction catalyzed by molybdenum-vanadium-phosphorus heteropolyacids

This paper focuses on the performance of Molybdenum-vanadium-phosphorus heteropolyacids (PMo_12-xV_x) with different V-doped amounts in catalyzing the conversion of lignin to bio-oil, and the distribution of liquefied products. Molybdenum-vanadium-phosphorus heteropolyacids (PMo₁₁V₁, PMo₁₀V₂, PMo₉V₃) with different amount (0, 2.5, 5, 10 w_t%) were used to catalyze lignin liquefaction. The experimental results showed that PMo_12-xV_x could effectively catalyze the depolymerization of lignin to bio-oil, and the doping amount of the V atom in PMo_12-xV_x affects the distribution of lignin depolymerization products. The highest bio-oil yield (53.62w_t%) and conversion (57.83w_t%) could be obtained from lignin liquefaction at 2.5 w_t% PMo₉V₃. With the increase of PMo_12-xV_x V-atom doped amount, the content of aliphatic hydrocarbons increased from 3.14% to 40.58%, the content of vanillin increased from none to 8.9%. Based on the analysis of bio-oil, FT-IR data, and DFT simulation results, it was found that the selective cleavage of the C_α-C_β bond and the ring-opening of the carbon at the methyl end of lignin were the main reasons for the high yield of vanillin and aliphatic hydrocarbons during the depolymerization of lignin catalyzed by PMo_12-xV_x. Finally, a possible reaction pathway for the PMo_12-xV_x-catalyzed depolymerization of lignin to vanillin and aliphatic hydrocarbons was proposed.

本研究围绕不同钒掺杂量的钼钒磷杂多酸（Molybdenum-vanadium-phosphorus heteropolyacids，记为PMo₁₂₋ₓVₓ）催化木质素转化制备生物油的催化性能，以及液化产物的分布规律展开。我们选用不同投加量（0、2.5、5、10 质量百分比，wt%）的钼钒磷杂多酸（包括PMo₁₁V₁、PMo₁₀V₂、PMo₉V₃）催化木质素液化反应。实验结果表明，PMo₁₂₋ₓVₓ可高效催化木质素解聚生成生物油，且其中钒原子的掺杂量会显著调控木质素解聚产物的分布。当投加2.5 wt%的PMo₉V₃作为催化剂时，木质素液化可获得最高的生物油产率（53.62 wt%）与木质素转化率（57.83 wt%）。随着PMo₁₂₋ₓVₓ中钒原子掺杂量的提升，脂肪烃类物质的含量从3.14%升至40.58%，香兰素的含量则从无提升至8.9%。结合生物油组分分析、傅里叶变换红外光谱（FT-IR）数据以及密度泛函理论（Density Functional Theory，DFT）模拟结果，研究发现：在PMo₁₂₋ₓVₓ催化木质素解聚的过程中，Cα-Cβ键的选择性断裂与木质素甲基端碳原子的开环反应，是香兰素与脂肪烃类物质高产率生成的核心机制。本研究最终提出了PMo₁₂₋ₓVₓ催化木质素解聚生成香兰素与脂肪烃类物质的可行反应路径。