Table 27. Processes for the Catalytic Oxidation of Technical Lignins.

Entry	Lignin	Oxidant	Catalyst	Conditions	Major product(s)	Yields	Ref
1	Enzymatic hydrolysis of steam explosion corn stalk	O2	LaFe0.8Cu0.2O3/ LaMnO3	Aqueous NaOH, 120 °C, 30–120 min	p-hydroxybenzaldehyde/vanillin, syringaldehyde	Up to 2.5%/5.6 /11.5, respectively	(471−473)
2	Alkali lignin	O2	MoPO/ CeO2	Aqueous NaOH, 150 °C, 3 h	Vanillin	9%	(495)
3	Wheat straw organosolv lignin	10% O2 in N2	CoFe (1:1) mixed oxides	Water, 200 °C, 4 h	Vanillin/syringaldehyde (17%/50% selectivity as part of the total monomers)	19.6% identified aromatic monomers	(474)
4	Kraft lignin	H2O2	CuMn mixed oxides (1:3)	Aqueous NaOH, 180 °C, 60 min, 26 h	p-hydroxybenzaldehyde /vanillin/vanillic acid /acetovanillone	About 17%	(475)
5	Softwood Kraft (Indulin AT)	NaOCl	TEMPO immobilized on iron magnetic beads	Aqueous NaBr, 25 °C, 4 h	Vanillin (78% selectivity)	Up to 28.5%	(476)
6	Milled softwood Kraft (Indulin AT)	a) t-BuOOH	a) TPPFeCl	a) Phosphate buffer (pH = 3): MeCN 3:1, rt	Methyl vanillate, 5-carbomethoxy-vanillate	10%	(496)
		b) H2O2	b) –	b) HCOOH/H2O, 50 °C, 70 h
7	Acid milled alkali lignin	Visible light	TiO2	Water, 250 W/m2 light	Vanillin, homovanillic acid, acetovanillone, guaiacol, and vanillic acid	22.8 wt%	(480)
8	Kraft lignin (Indulin AT)	O2	H3PMo12O40·xH2O	1:4 H2O:MeOH, 170 °C, 20 min	Vanillin/methyl vanillate (70% of total mon.)	10% monomers	(481)
9	Organosolv lignin	O2	Au/CeO2	MeOH	Vanillin/methyl vanillate/methyl syringate	About 21 wt%	(482)
10	Softwood Kraft (Indulin AT)	O2	Au/Li-AlLDH	a) DMF, 120 °C, 1 h	Vanillin/vanillic acid	Around 10%	(483)
				b) 0.1 M NaOH (aq.)
11	Sodium lignosulfonate	Air	–	Bu4NOH·30H2O, 120 °C, 43–70 h	Vanillin/vanillic acid	6.5%	(484)
12	Soda lignin	Air	–	Bu4NOH·30H2O, 120 °C, 43–70 h	Vanillin/vanillic acid	6.7%	(484)
13	Alkali lignin	[Pro]2[MnCl4]	–	Ethyl ammonium nitrate, 35 °C, 4 h	Vanillin/acetovannillone	18–20% vanillin	(485)
14	Alkali lignin	O2	[HC4im]3PMo12O40	([HC4im]HSO4) 80%, 150 °C, 5 h	Complex mixture of phenolic monomers	Up 15 wt%	(486)
15	Beech organosolv lignin	Air	Mn(NO3)2	[EMIM][CF3SO3], 100 °C, 24 h	Depending on the catalyst concentration, syringaldehyde or DMBQ as main product	11.5 wt% isolated yield of DMBQ	(487)
16	Softwood Kraft (Indulin AT)	Electric current	Ni electrodes	Aqueous NaOH, 160 °C	Vanillin and acetovanillone	Up to 7 wt%	(497)
17	Lignosulfonate	Electric current	Ferrate	Aqueous NaOH	Vanillic acid	7.2 wt%	(498)
18	Butanosolv lignin	Electric current	Lead/mercury electrodes	Aqueous NaOH	Phenolic carboxylic acids	23.5 wt%	(494)
19	Spruce lignosulfonate	Electric current	Nickel mesh	Aqueous NaOH	Vanillin	9.6 wt%	(493)
20	Bamboo lignin	Electric current	Cu and Pb/PbO2 electrode	Aqueous NaOH	Vanillin/syringaldehyde/p-coumaric acid	3.6/5.7/3.0 wt%, respectively	(493)