Development of metal catalysts for the transformation of biomass-derived furans to value-added chemicals

Abstract

Production of fuel and different value-added chemicals from widely distributed renewable biomass provides a facile path to reduce global dependence on the fossil resources. Different platform compounds isolated or produced from biomass such as sugars and furans are getting outstanding considerations for the synthesis of different industrially applicable chemicals and fuel components. As biomass-derived furans such as 2-furfuraldehyde (furfural), 5-hydroxymethyl-2-furfural (5-HMF) and others have highly reactive -CHO and/or -CH2OH side chains with furan ring, these can be explored for the production of several valuable chemicals. In recent years, catalysts (homogeneous and heterogeneous catalysts) have provided efficient upgradation of biomass-derived furans through diverse catalytic reactions. This thesis comprises seven chapters. The first chapter narrates brief introduction about catalysis and biomass-derived compounds along with biomass-derived furans. This chapter includes thorough literature survey for the catalytic upgradation of biomass-derived furans and the importance of different transformed compounds in diverse fields. Successive chapters elucidate the detail studies on the syntheses and characterizations of homogeneous metal complexes (Ru-based complexes) and heterogeneous metal nanoparticles (Ni, Cu, Co and Pd) based catalysts for the catalytic upgradation of biomass-derived furans. The main objectives of the present study are,  To develop simple, water soluble and highly active metal complexes for catalytic transformation of biomass-derived furans to valuable ketoacid and diketones under environmental benign reaction conditions and study the mechanistic pathway of catalytic transformations.  Design and synthesis of cost-effective high-performance supported and unsupported bimetallicM-Pd (M = Ni, Cu or Co) alloy nanoparticle catalysts (nano-catalyst) for oxidative and hydrogenating upgradation of biomass-derived furans and study the mechanistic aspects.To study the effect of synergistic interaction (between two metals of alloy bimetallic nano-catalyst) on the catalytic oxidation and hydrogenation of biomass-derived furans. The contents of each chapter included in the thesis are, briefly, as follows: Chapter 1. Introduction and Background In this chapter, a brief introduction about catalysis and biomass-derived compounds along with biomass-derived furans is described. The chapter is summarized background of the catalytic upgradation of biomass-derived furans and the importance of different transformed compounds in the diverse fields. Chapter2. Materials and Instrumentation In this chapter, materials and instruments employed in the different projects of the thesis are discussed. Chapter 3. Catalytic transformation of biomass-derived furans to valuable ketoacid and diketones using water-soluble arene-ruthenium catalysts In this work, we designed and developed water-soluble 8-aminoquinoline coordinated arene-ruthenium(II) complexes and exploredtheir activity for the catalytic transformation of biomass-derived furans such as furfural, 5-HMF and 5-methyl-2-furfural (5-MF) to ketoacid (levulinic acid; LA) and diketones (1-hydroxyhexane-2,5-dione; 1-HHD, 3-hydroxyhexane-2,5-dione; 3-HHD and hexane-2,5-dione; HD) under moderate reaction conditions. Complete conversion of furfural to LA with >99% selectivity was attained with 1 mol% catalyst and 12 equivalents of formic acid at 80-100 °C. Different experimental observations and 1H NMR studies have given more insights into the mechanistic pathway for the catalytic transformation of furans to open ring compounds. Furthermore, studies carried out with structural analogues of the active catalyst revealed a structure-activity relationship for the observed higher catalytic performance of arene-ruthenium(II) complex having 8-aminoquinoline ligand. Results inferred that -NH moiety of 8-aminoquinoline ligand assisted the transfer hydrogenation where, probably, -NH moiety form hydrogen bonding with formyl group to bring the furfural in close vicinity of the ruthenium center and transfer H+ ion to formyl group to facilitate the formic acid driven transfer hydrogenation of furfural to furfuryl alcohol (a key intermediate). Moreover, high water-solubility of the studied catalyst resulted in high recyclability (up to 4 catalytic runs) without any remarkable loss in the catalytic activity. Molecular characterizations of the studied arene-ruthenium(II) complexes were also confirmed by different spectroscopic technique such as NMR, ESI-MS and single-crystal X-ray diffraction studies.Chapter 4. Catalytic aerial oxidation of biomass-derived furans to furan carboxylic acids in water over bimetallic Ni-Pd alloy nanoparticles In this chapter, we designed and synthesized bimetallic Ni1-xPdx (0.10 ≤ x ≤ 0.75) alloy nano-catalysts and explored their activity for the catalytic aerial oxidation of different biomass-derived furans such as furfural, 2-furfuryl alcohol, 5-HMF, 5-MF and 5-methyl-2-furfuryl alcohol to corresponding furan carboxylic acids (2-furoic acid, furan-2,5-dicarboxylic acid (FDCA), 5-methyl-2-furoic acid (MFCA)) at 80 °C under aqueous reaction conditions. Among all, Ni0.90Pd0.10 nano-catalyst (having very low Pd content) resulted in superior catalytic activity to attain high yields of corresponding furan carboxylic acid. Furthermore, results revealed that presence of Ni in the bimetallic Ni1-xPdx catalysts not only increased the catalytic performance for facile oxidation of biomass-derived furans (with high catalytic turnover) using aerial oxygen but also followed to high stability of Ni0.90Pd0.10 nano-catalyst in the presence of air and water which led to high recyclability up to 10 catalytic runs. The high-performance of studied bimetallic Ni1-xPdx catalysts was assigned to charge transfer from Ni (less ionization energy as compare to Pd) to Pd. Further, we also achieved a one-pot direct transformation of fructose to furan carboxylic acid products (such as FDCA) using Ni0.90Pd0.10 nano-catalyst. The studied catalysts were characterizedusing different techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and powder X-ray diffraction (P-XRD).Chapter 5. Catalytic aerial oxidation of 5-hydroxymethyl-2-furfural (5-HMF) to furan-2,5-dicarboxylic acid (FDCA) over Ni-Pd nanoparticles supported on Mg(OH)2 nanoflakes for the synthesis of furan diesters In this chapter, different bimetallic M0.90Pd0.10 (M = Ni, Co or Cu) alloy nanoparticles supported on in situ prepared Mg(OH)2 nanoflakes were synthesized and explored for the catalytic aerial oxidation of biomass-derived 5-HMF to the industrially important FDCA without using any external base additive. Among different M0.90Pd0.10/Mg(OH)2, Ni0.90Pd0.10/Mg(OH)2 displayed higher catalytic activity. Furthermore, studies with Ni0.90Pd0.10 supported on different supports such as SiO2, Al2O3, ZnO and Mg(OH)2 inferred that the basic nature of the Mg(OH)2 facilitated the efficient oxidation of 5-HMF and avoids the usage of an external base additive. Moreover, reactions carried out with Ni1-xPdx/Mg(OH)2 (x = 0.10 to 1) and a physical mixture of Ni/Mg(OH)2 and Pd/Mg(OH)2 revealed that the remarkable synergistic interaction between Ni and Pd (attributed to electronic charge transfer) plays an important role in the achieved high catalytic performance of Ni0.90Pd0.10/Mg(OH)2 towards the oxidation of 5-HMF to FDCA. Notably, Ni0.90Pd0.10/Mg(OH)2 catalyst could be employed to the gram-scale oxidation of 5-HMF to FDCA. Thereafter, the prepared FDCA was explored for the synthesis of different furan diesters, to be utilized as precursors for the synthesis of bio-based polymers and plastics materials. Furthermore, structural and chemical characterization of Ni0.90Pd0.10/Mg(OH)2 (highly active catalyst) was confirmed using P-XRD, TEM, EDS, SEM, elemental mapping, XPS and ICP-AES analysis. Chapter 6. Bimetallic Ni-Pd alloy nanoparticles: An efficient catalyst for the room temperature hydrogenation of biomass-derived furans and furan/acetone aldol adducts In thischapter, an efficient and environmental benign hydrogenation of biomass-derived furans and furan/acetone aldol adducts (having C5-C15 carbon) has been explored over simple, cost-effective and highly active bimetallic Ni-Pd alloy nanoparticles catalysts under aqueous reactionconditions at room temperature using H2 gas at atmospheric pressure. For the optimization of reaction conditions, 2-furfuryl alcohol (furfuryl alcohol) was used as a model substrate. Among all studied bimetallic Ni1-xPdx (x = 0.10 to 0.75) as well as monometallic nanoparticles catalysts, Ni0.90Pd0.10 (having only 10% Pd in comparison to Ni) outperformed and displayed the highest TON for the hydrogenation of furfuryl alcohol to tetrahydro-2-furfuryl alcohol (THFAL). Time-scale analyses for the hydrogenation of aldol adducts revealed that Ni0.90Pd0.10 catalysts show high efficiency towards the hydrogenation of C=C over C=O bond. Furthermore, studied Ni0.90Pd0.10 catalyst could be scaled to the gram-level hydrogenation of aldol adduct. Moreover, Ni0.90Pd0.10 catalyst displayed high stability under the employed reaction conditions and could be reused for five catalytic runs without any significant loss in the catalytic activity.Chapter 7. Conclusions and future scopes Conclusions The conclusions of different projects included in this thesis are as follows: 1) We developed high-performing water-soluble arene-ruthenium(II) complexes (having 8-aminoquinoline, 2,2′-bipyridine or 8-hydroxyquinoline ligand) catalysts for the catalytic transformation of different biomass-derived furans such as furfural, 5-HMF and 5-methyl-2-furfural (5-MF) to value-added ketoacid and diketones under moderate reaction conditions. Our findings revealed that N-H moiety of 8-aminoquinoline facilitated the enhanced catalytic activity of the Ru-complex where, probably, N-H moiety form hydrogen bonding with furfural and bring it in close vicinity of ruthenium centre. Furthermore, N-H moiety may also transfer a H+ ion to a formyl group and resulted to facile transfer hydrogenation of furfural to furfuryl alcohol in the presence of formic acid.2) We also developed cost-effective high-performing bimetallic Ni1-xPdx (0.10 ≤ x ≤ 0.75) alloy nanocatalysts (heterogeneous catalyst) for the oxidation of biomass-derived furans. Results inferred that high synergisticinteraction between Ni and Pd, due to the electronic charge transfer from Ni to Pd, contributed significantly in the observed high catalytic performance with low leaching and high reusability of Ni0.90Pd0.10 catalyst. 3) Different bimetallic M-Pd (M = Ni, Cu or Co) alloy nanoparticles supported over in situ generated Mg(OH)2 have also synthesized and explored for an efficient oxidation of 5-HMF to FDCA without addition of an external base. Results attained with Ni0.90Pd0.10 supported on different supports such as SiO2, Al2O3, ZnO and Mg(OH)2 suggested that the basic nature of Mg(OH)2 was favourable for efficient oxidation of 5-HMF and to avoid the usage of an external base additive. 4) Bimetallic Ni-Pd alloy nano-catalysts were alsoexplored for the room temperature hydrogenation of biomass-derived furans and aldol adduct of furan, where we studied the effect of alloying of non-noble metal (Ni) with noble metals (Pd) on the catalytic hydrogenation of furans derivatives. In conclusion, diverse homogeneous and heterogeneous catalytic systems were developed and extensively employed during various projects (catalytic upgradation of biomass-derived furans) included in this thesis. The studied catalysts represent a class of low-cost high-performance, stable (towards air, water and other reaction conditions), recyclable catalysts and hence can also be explored for several other catalytic reactions and approaches.Future scope The relevant future scope of the work included in this thesis has been discussed briefly.