# Targeted Substituted-Phenol Production by Strategic Hydrogenolysis of Sugar-Cane Lignin
## 3 Results and Discussion
### Sugar-Cane Lignin (SCL) Characterization
#### 3.2.8 Effect of Pt and Rh Noble Metal Catalysts  
From Figure 3 it can be seen that most products increased in yield by the addition of these catalysts. Distribution of guaiacyl and syringyl derived molecules were well balanced, with higher yields for S unit-products due to the nature of the starting lignin. The main products were 4-ethylphenol (2A) and 2,6-dimethoxyphenol (6A), with selectivities of \(\sim\)28% and \(\sim\)15% for Pt and \(\sim\)20% and \(\sim\)15% for Rh, respectively. These molecules highlighted similarities in these catalysts' ability to catalyse dealkylation and deoxygenation, especially Pt/Al2O3. In Figure 3, it is relevant to note that Pt increased the yield mainly of products 2A, 6A, 11 and 14 whereas Rh increased the yield more generally for most of the products. Thus, despite rhodium effectiveness, Pt was indeed more selective. Similarly, in experiments with an ammonia derived lignin [18] even with Pt and Rh giving similar selectivity towards alkylphenolics, Rh was suggested, in general, as more effective in cleaving alkyl-aryl linkages. This behaviour of higher selectivity for Pt with SCL, when compared to ammonia lignin, could lead to the association of selectivity not only to the metal, but also to the less condensed nature of a lignin.  
These variations found with Rh and Pt were evidenced also in other studies. [PERSON] and co-authors in their study of hydrodeoxygenation of \(p\)-methylguaiacol found different main products from these metals - platinum with greater selectivity to 4-methylcatechol while rhodium gave cresols [41]. An investigation of the use of these metals to produce biobased chemicals from Kraft lignin [42] showed best results by Rh, with 30 wt% of monomer yield. In addition, when studying biphenyl model compound, [PERSON] et.al.  
Figure 3: Estimated yield in g/100g of phenolic compounds in solvolysis (reference), reactions in the presence of (**a**) Pt/Al2O3 and (**b**) Rh/Al2O3 catalysts. Standard deviation value: 01. Products identified by GC-MS: (1) 2-methoxyphenyl, (2) 4-methyl-2-methoxyphenol, (2A) 4-ethylphenol, (3) 4-ethyl-2-methoxyphenol, (4) 4-propyl-2-methoxyphenol, (5) 1,2-dihydroxybenzene, (6A) 2,6-dimethoxyphenol, (7) 4-(3-hydroxypropyl)-2-methoxyphenol, (8) 4-(3-methoxypropyl)-2-methoxyphenol, (9) 4-methyl-2,6-dimethoxyphenol, (10) 4-(2-hydroxyethyl)-2,6-dimethoxyphenol, (11) 4-ethyl-2,6-dimethoxyphenol, (12) 4-propenyl-2,6-dimethoxyphenol, (13) 4-(2-hydroxyethyl)-2-methoxyphenol, (14) 4-propyl-2,6-dimethoxyphenol, (15) 4-(1-hydroxy-2-methyl-pent-3-enyl)-2,6-dimethoxyphenol. Conditions: 573 K, 20 barg H\({}_{2}\), solvent, acetone/water 50:50 \(\mathrm{\SIUnitSymbol\char 67}\).  
found an effective C-C cleavage by Rh [20]. Thus, rhodium was expected to give higher overall yield.  
Regarding lignin-type linkages, these metals can be involved in more than one reaction during depolymerisation [43]. For example, hydrogenolysis and hydrolysis were found as essential to the rupture of C-O in studies with \({}_{\text{sc}}\)CO\({}_{2}\)/water, Rh/C and diphenyl ether [44]. This is relevant considering the lignin complexity and the several steps to finally result in monophenolics from this biopolymer [23]. For SCL experiments, we found Pt selective, but Rh had a higher extent of C-C and C-O-C bond rupture, inferring greater intermediates stabilization by rhodium.