Table 1.
Summary of catalytic conversion of various plastic and biomass substrates via activating C–C, C–O and C–N bonds
| Bonds | Feedstocks | Methods | Catalysts | Products | |
|---|---|---|---|---|---|
| C–C | Caliph–Caliph | Ubiquitous in biomass and plastic | Catalytic cracking | Brønsted acid | Paraffins, light olefins and bio-oils |
| Hydrogenolysis | Metal | Paraffins and aromatics | |||
| Hydrocracking | Metal–acid | iso-Paraffins | |||
| Metathesis (requiring C═C bond) | Homogeneous and heterogeneous metathesis catalysts | Hydrocarbons | |||
| Retro-aldol reaction (requiring β-hydroxy carbonyl unit) | Metal–Lewis acid | Polyols and alcohols | |||
| Carom–Caliph | Lignin fragments featuring β–5, β–1, β–β and α–1 linkages, PS, PC and PF | Catalytic cracking | Brønsted acid | Aromatics and phenolics | |
| Reductive cleavage | Metal and metal–acid | Aromatics, cycloalkanes and phenolics | |||
| Oxidation–hydrogenation (requiring β-O–4 linkages) | Combination of metal and oxidant | Phenol | |||
| Carom–Carom | Lignin fragments featuring 5-5′ linkages | Reductive cleavage | Homogeneous and heterogeneous metal catalysts, and metal–acid | Phenolics | |
| Aromatics and cycloalkanes | |||||
| C–O | Ether bond | Cellulose, chitin, lignin, epoxy resins and PPO | Reductive cleavage using H2 | Metal and metal–acid | Phenolics, aromatics and cycloalkanes |
| Reductive cleavage using other reagents (for example, amine, organosilane and LiAlH4) | Metal | Phenolics and N-containing chemicals | |||
| Oxidative | Acid, base and metal–organic | Aromatic oxygenated chemicals | |||
| Hydrolysis (requiring a glycosidic bond) | Metal halides and acid | Carbohydrates | |||
| Ester bond | Triglyceride, PET and PC | Solvolysis | Acid, base, metal halides and acetates | Alcohol and carboxylic acids | |
| Hydrogenolysis | Metal and metal–acid | Alcohol, carboxylic acids and hydrocarbons | |||
| C–N | Amide bond | Protein, PA and PU | Solvolysis | Strong acid, strong base and transition metal salts | Amino acids and aliphatic ester/aminocaproic acid |
| Hydrogenolysis | Metal and metal-centred pincer catalysts | Amides, amino alcohols and polyols | |||
PA, polyamide; PC, polycarbonate; PET, polyethylene terephthalate; PPO, poly(p-phenylene oxide); PU, polyurethane.