Highly-efficient and magnetically-separable ZnO/Co@N-CNTs catalyst for hydrodeoxygenation of lignin and its derived species under mild conditions

• Published in: Green chemistry : an international journal and green chemistry resource : GC 2019-03, Vol.21 (5), p.121-142
• Main Authors: Ranaware, Virendra, Verma, Deepak, Insyani, Rizki, Riaz, Asim, Kim, Seung Min, Kim, Jaehoon
• Format: Article
• Language: English
• Subjects: Acetosyringone; Aqueous solutions; Bimetals; Biofuels; Byproducts; Carbon nanotubes; Catalysis; Catalysts; Chemical composition; Cinnamaldehyde; Cobalt; Cyclohexanone; Deoxygenation; Dislocations; Furfural; Green chemistry; Hydroxymethylfurfural; Isoeugenol; Lignin; Metal-organic frameworks; Monomers; Nanoparticles; Nanotechnology; Nanotubes; Noble metals; Organic chemistry; Reaction time; Roasting; Species; Syringaldehyde; Vanillin; Wettability; Zinc; Zinc oxide
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/c8gc03623c

A catalyst comprising highly-efficient and magnetically-separable bimetallic ZnO and Co nanoparticles (NPs) deposited on N-doped carbon nanotubes (ZnO/Co@N-CNTs) was synthesized by the direct calcination of the bimetallic Zn/Co zeolitic imidazolate framework (Zn/Co-ZIF) for the effective hydrogenation (HD) and hydrodeoxygenation (HD) of lignin and its derived species. During the calcination of Zn/Co-ZIF, Zn was dislocated from the framework to the particle surface to form amorphous ZnO NPs and metallic Co NPs, which activated the growth of the N-CNTs. Because of the highly Lewis acidic amorphous ZnO, high HD/HDO ability of metallic Co NPs, and high wettability of the N-CNT, an almost complete conversion of vanillin into its corresponding deoxygenated species, creosol, was achieved in an aqueous medium without the production of byproducts under mild reaction conditions (150 °C, 0.7 MPa H 2 , a reaction time of 2 h). When kraft lignin and bio-oil derived from concentrated strong acid hydrolysis lignin were converted over ZnO/Co@N-CNTs, high degrees of deoxygenation of 74.2% and 34.4%, respectively, could be achieved at 350 °C, 5.0 MPa H 2 , and a reaction time of 6 h in water. A detailed chemical composition analysis of the deoxygenated bio-oil revealed that cyclohexanone and its alkyl group-substituted derivatives were the major species. To gain insight into the HD/HDO mechanisms, various types of lignin-derived monomers (syringaldehyde, acetovanillone, acetosyringone, 2-phenoxy-1-phenylethanol, cinnamaldehyde, isoeugenol) and holocellulose-derived monomers (furfural and 5-hydroxymethyl furfural), different types of catalysts, and various reaction parameters were tested. The mild reaction conditions, use of a non-noble metal catalyst, and use of water as the solvent make it possible to develop a cost-effective, easy to scale up, and environmental-benign process for biofuel and biochemical production. An efficient bimetallic ZnO/Co@N-CNT catalyst was designed for selective hydrogenation and hydrodeoxygenation of lignin and its derived components in water.