Structure–Reactivity Relationship of β‐O‐4 Linkers in Lignin Model Compound Catalytic Pyrolysis

Understanding the catalytic pyrolysis mechanism of lignin is essential for developing efficient biomass valorization strategies. How does the bond structure influence reactivity, product selectivity, and side reactions? By using photoionization mass spectrometry (PIMS) with synchrotron vacuum ultraviolet radiation, intermediates as well as products are identified, and pyrolysis mechanisms are unveiled. The dimers studied here feature different functionalization at the β‐O‐4 linkage, connecting aromatic rings in 2‐phenylethyl phenyl ether (PPE), 2‐phenoxy‐1‐phenylethanone (Ppone), and 2‐phenoxy‐1‐phenylethanol (Ppol). Major products during the catalytic pyrolysis include phenol, styrene, phenylacetylene, and benzene; however, their abundances vary significantly due to differently pronounced mechanisms. Dehydration as the primary reaction dominates in Ppol and Ppone, yielding phenylacetylene and phenol or phenanthrenols, respectively, which are potent coke precursors responsible for catalyst deactivation. Moreover, Ppone is the only model compound producing bibenzyl. Retro‐ene and Maccoll eliminations are proposed as major pathways in PPE, while their contribution is reduced in Ppol and Ppone due to the outcompeting dehydration. Our mechanistic analysis shows that the decomposition pathways of β‐O‐4 linkages are sensitive to their substitution pattern. This dependence may be exploited by choosing lignins from specific processes, since these yield characteristic substitution motifs and therefore influence the product distributions.