Table 5.

Recent progresses of catalysts used in lignin catalytic pyrolysis, and their selectivity

Lignin	Catalyst	Catalytic pyrolysis	Reaction conditions	Products yield	Important findings	Product selectivity	Ref.
Kraft lignin	Aluminosilicate	In situ	450, 550, and 650 °C, 12,500–40,625 °C/s, 6 s, He	N/A	HZSM5-30 showed the most promising anti-coking performance and the highest selectivity to desired products, HZSM5-500 showed good diffusion and high reaction rate, and the anti-coking performance of HY/MCM41 was weaker than HZSM5	Hydrocarbons selectivity: HZSM5-30 > HY > HZSM5-300/MCM41-40/MCM41-Si	[311]
Beech wood lignin	Micro/meso porous ZSM-5	In/Ex situ	400, 500, and 600 °C, 20 min, N2	Organic phase: 15–35 wt%; char: ~ 40 wt%; gas: < 20 wt%	Both two catalysts exhibited excellent dealkoxylation/aromatization reactivity to yield more aromatics. Meso-ZSM-5 induces higher dealkoxylation reactivity, leading to higher selectivity to BTX aromatics without the increase of PAHs	MAHs selectivity: meso-ZSM-5 > ZSM-5	[312]
Cellulolytic enzyme lignin	Micro-meso ZSM-5	In-situ	873 K, 30 s	Char: ~ 30 wt% > coke: ~ 15 wt% > aromatics: ~ 8 wt% > phenolics: ~ 3 wt% > catechols: ~ 2 wt%	Mesoporous structure was beneficial for the diffusion of heavy phenols and modulation of pyrolysis products	AHs selectivity: C6 > C8 > C10+ ≈ C7 > C9+ > C14+	[281]
Rice straw lignin	Modified ZSM-5	In situ	450, 500, 550, and 600 °C	N/A	These ZSM-5 catalysts showed shape selectivity and acidity, beneficial for pyrolytic products distribution, and demethoxylation and dehydroxylation of oxygenates	Hydrocarbons selectivity: (without catalyst) oxygenates > phenols > PAHs > MAHs; (with ZSM-5) PAHs > MAHs ≈ oxygenates ≈ phenols; (with alkali ZSM-5) PAHs > MAHs > phenols > oxygenates; (with Ni-ZSM-5) MAHs ≈ PAHs > oxygenates > phenols. MAHs: naphthalenes with 40–60%	[47]
Commercial lignin	Modified HZSM-5	Ex situ	500 °C (I) and 450–600 °C (II), 20 °C/min, N2	Organic liquid: 17.5–22.7 wt%; solid: 42.7–43.2 wt%; gas: 19.2–19.8 wt%	HZSM-5 treated by organic alkali exhibited a coordinated micro/meso-proportion with proper size and acidity, of which the acidity would be further enhanced after cobalt incorporation, exhibiting better MAHs selectivity	Alkali treated HZSM-5 preferred phenols, while Co-alkali-HZSM-5 exhibited much higher selectivity to MAHs (38%) than phenols (23%)	[313]
Commercial lignin	HZSM-5/biochar	Ex situ	500 °C, 10 min, N2	Oil: 35 wt%; total AHs: 50 mg/g (maximum)	LC (lignin carbon) incorporating lignin depolymerization produced more phenols, which can be further transformed into aromatic hydrocarbons through HZSM-5	The production of AHs from lignin/LC/HZSM-5 was almost two times higher than lignin/HZSM-5 (from 30 to 50 mg/g)	[297]
Alkali lignin	ZSM-5/biochar	In situ	500 °C, 10 min, N2	Oil: ~ 20 wt%; char: ~ 40 wt%; gas: < 20 wt%; aromatics: > 30 mg/g	The addition of biochar enhanced bond breaking of lignin to yield more oils, and ZSM-5 acted as a selective aromatization to obtain higher content of aromatics	Total aromatics (12.32%) > methoxyphenols (5.17%) > alkylphenols (4.4%) > phenols (2.42%) > acid (0.85%)	[314]
Corn cob lignin	HZSM-5@Al-SBA-15	In situ	550 °C, 10 °C/min, N2	Gas: ~ 35 wt%, water: < 10 wt%; organic liquid: < 15 wt%	Mixed zeolite with tailored properties of acidity and porosity regulated the composition of AHs by pre-cracking and enhanced diffusion	AHs selectivity: MAHs (~ 40%) > PAHs (~ 25%) > phenols (~ 13%) > aliphatics (~ 8%) > methoxyphenols (~ 0%)	[293]
Commercial lignin	Pine-Mo2C	In situ	300, 400, and 500 °C, WHSV = 1 h−1, H2(N2)	Total AHs: 12.36 wt%; light gases: 29.68 wt% (maximum)	Pine carbon supported Mo2C catalyst showed good selective deoxygenation targeting C-O cracking to produce more monocyclic aromatic hydrocarbons	Deoxygenation rate: pine-Mo2C (100%); MAHs selectivity: toluene (98%) > others (benzene and xylenes, < 2%)	[298]
Enzymatic hydrolysis lignin	Nb2O5	In situ	500–650 °C, 0.5 min	Phenols: ~ 4 wt%; MAHs: ~ 6 wt%	Nb2O5 exhibited excellent deoxygenation ability to convert lignin into AHs, especially for MAHs	AHs selectivity: C6+C7+C8+C9+C9+ (MAHs, up to 90%) > C10+C11+C12+C12+ (PAHs, up to 8%)	[303]
Kraft lignin	Biochar, activated carbon	In situ	550 °C, 5 min, N2	Oil: 13.15 wt%; char: 58.76 wt%; gas: 39.74 wt% (maximum)	The catalytic effect of biochar was derived from surface sodium and alkali metals. The addition of AC resulted in the high-phenol-concentration oils production	Products selectivity: phenols > PAHs > oxygenates	[296]
Bagasse lignin	Ca0.5Pr0.5FeO3	In situ	20 °C/min, 2 h, N2	Oil: ~ 25 wt%; char: > 50 wt%; gas: > 40 wt% (maximum)	Guaiacols, syringols, and phenols were the main component in pyrolytic oils, and the content of light aliphatic hydrocarbons increased after catalysts addition	Products selectivity: Guaiacols > syringols > phenyl ethers > phenolics > phenyl ketones	[306]
Bagasse lignin	La0.8M0.2FeO3 (M = La, Ca, Sr, Ba)	In situ	600 °C, 10 °C/min, 2 h, N2	Oil: ~ 25.73 wt%; char: > 40.65 wt%; gas: > 42.89 wt% (maximum)	Perovskites improved the generation of aliphatic hydrocarbons via inhibiting decarboxylation and decarbonylation, and increased aryl oxygen-containing compound yield	LaFeO3, La0.8Ca0.2FeO3, La0.8Sr0.2FeO3, and La0.8Ba0.2FeO3 produced the maximum selectivity of phenolics (24.59%), syringols (25.78%), guaiacols (23.79%), syringols (22.47%), respectively	[307]