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] |