Pyrolysis-assisted catalytic hydrogenolysis of lignin at temperatures greater than 250 degrees C includes pyrolytic degradation prior to catalytic conversion. This study investigated the reactivities of various intermediate prod-ucts from lignin pyrolysis using Pd/C and H2 in anisole at 300 and 350 degrees C. Saturated alkyl side chains (methyl, ethyl, and propyl) were very stable, whereas side chains containing functional groups were hydrogenated and/or fragmented into saturated alkyls or unsubstituted H-, presumably by efficient adsorption onto the polar Pd surface. Specifically, unsaturated C--C bonds were hydrogenated to saturated alkyls. Conjugated alpha-ketone changed to-CH2-, while conjugated aldehydes underwent deformylation through alpha-scission along with the above deoxydation. Deformylation also proceeded for side chains bearing OH groups. Lignin pyrolysis intermediates containing conjugated C--C and C--O groups had particularly high affinity for Pd/C, allowing successive transformations (e.g., coniferyl alcohol -> dihydroconiferyl alcohol -> ethyl guaiacol) before desorption. Therefore, the composition of side-chain alkyls of monomers, including unsubstituted ones, depends on the chemical composition of intermediates produced by pyrolysis.
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