# Targeted Substituted-Phenol Production by Strategic Hydrogenolysis of Sugar-Cane Lignin
## 4 Post-Reaction Catalyst Evaluation  
Stability of alumina in the presence of water at high pressure and temperature could be affected by hydration and Al2O3 phase transition. This has been found [53] in studies with \(\gamma\)-alumina undergoing transformations to beohmite at 473 K. Here, \(\theta\)-alumina, which is considered more stable [18] was used, nevertheless it was of interest to investigate whether chemical or physical changes occurred with the catalysts. Elemental analysis of post-reaction Al2O3, Pt/Al2O3 and Ni/Al2O3 revealed that there was carbon laydown but also traces of hydrogen and nitrogen (Table S1, Supplementary Materials), confirming  
Figure 1: Possible reaction pathways for the formation of 4-ethylphenol. (**A**) Catalytic demethylation-alation of 4-ethyl-2-methoxyphenyl resulting in 4-ethylphenol, (**B**) (i) hydrogenolysis of a \(p\)-coumaryl alcohol lignin fragment (ii) decarboxylation and formation of 4-vinylphenol-type specie as intermediate, (iii) hydrogenation resulting in 4-ethylphenol.  
the interaction of lignin and catalyst during the reaction. Following these results, TPO analysis (Figure 6) also showed the presence of carbonaceous deposits. It is noticeable that compared to Al\({}_{2}\)O\({}_{3}\) (Figure S1, Supplementary Materials), the metal catalysts had a higher mass loss (\(\sim\)15%) which would be expected if the carbon deposit was associated with enhanced interaction between lignin and metal-support system. Looking in detail at the TPO plots (Figure S1, Figure S2, Supplementary Materials), there was a similar profile for all catalysts with an initial weight loss at 250 K-380 K, associated with physisorbed water. Subsequently, a main weight loss between \(\sim\)400 K and 800 K, which was related to CO\({}_{2}\) evolution, as shown in Figure 6. At this temperature, the adsorbed species could be pseudo-molecular [41]. There were small events below 700 K for all catalysts indicating more than one type of carbonaceous deposit. As no further weight loss was observed above 800 K, no recalcitrant species were present on the surface. In agreement with these results, Raman spectroscopy revealed (Figure S3, Supplementary Materials) low intensities of disordered and graphitic bands in the used catalysts. They were associated to D and G bands [54,55] at \(\sim\)1380 cm\({}^{-1}\) and \(\sim\)1600 cm\({}^{-1}\), respectively and the D/G ratio of 0.1 suggested that there was more slightly ordered carbon species in nature. Previous studies using Al\({}_{2}\)O\({}_{3}\) and Pt/Al\({}_{2}\)O\({}_{3}\) at the same reaction conditions of this study (with Kraft lignin) gave no modification in the support's XRD patterns after reaction [26]. This stability could be associated to a synergistic effect between the metals and the support [54] preventing phase transition and the presence of oxygenates in the reaction medium, interacting with the alumina surface, inhibiting hydrolysis. Finally, BET analysis (Table S2, Supplementary Materials) revealed an increase in the surface area and decrease of pore volume due to the deposit of carbon species.