334
authors clearly explained the mechanism of HMF to FDCA using metal-supported
functionalized CNT (M/CNT) catalyst. Initially, the hydroxyl group of HMF is
adsorbed on the surface of M/CNT catalyst, followed by C–H activation. Two
hydrogen atoms (H of CH 2 and OH) were abstracted by the support and removed by
oxygen molecule favouring the formation of DFF. The functional groups on the
CNT interacted with the aldehyde group (of DFF) which undergo hydrolysis and
form FFCA intermediate. Finally, FFCA easily converts into FDCA with similar
hydrolysis mechanism as mentioned above. This work also successfully investigated the adsorption behaviour of substrate and product on CNT surface. Among
these catalysts, noble metals have more selectivity and activity towards FDCA formation because of their excellent ability to attract the β-H atom from the methyl side
chain of HMF. The catalyst ability for the attraction of β-H group is in the order
Pt > Pd > Ru on CNT; accordingly, FDCA product selectivity also varied.
4 Conclusion and Challenges
4.1 Conclusions
The importance of biomass conversion and primary building blocks of carbohydrates is discussed at the beginning of this chapter. The application and importance
of levulinic and furan-based molecules were explained with pertinent examples. A
brief outline of levulinic acid synthesis and its catalytic conversion to various valuable products such as γ-valerolactone, arylated-γ-lactones and 4,4-disubstituted
pentanoic acid/esters was covered. Prior art on hydrocyclization of levulinic acid to
γ-valerolactone in the presence of different hydrogen sources using layered double
hydroxide-based catalysts is discussed along with their catalytic performances.
Preparation of arylated-γ-lactones (levulinic acid and aromatics) was introduced in
this chapter using various homogeneous and heterogeneous (zeolite) catalysts. The
acid-catalysed conversion of levulinic acid with aromatics into 4,4-disubstituted
pentanoic acid/esters is disclosed such as diphenolic acid, γ,γ-di-2-methylfuran
pentanoic acid (4,4-bis(5-methylfuran-2-yl)pentanoic acid) and (4,4-bis(5methylthiophen- 2-yl)pentanoic acid. The possible applications of 4,4-disubstituted
pentanoic acid/esters were also mentioned.
A brief discussion on 5-hydroxymethylfurfural (HMF) synthesis preferably from
fructose dehydration has been covered using various acid catalysts including mineral/organic acids, metal salts, metal oxides, heteropolyacids, ion-exchange resins,
functionalized carbon materials, clay and zeolitic materials. We focused on the performance of mentioned catalysts by considering conversion of fructose, yield of
HMF, stability, reusability, etc.. Finally, brief outline of the results of selective oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid is discussed with
emphasis on Ru-based catalyst for this conversion under base-free aqueous medium
using O 2 /air as the oxidant.
S. Gundekari et al.
authors clearly explained the mechanism of HMF to FDCA using metal-supported
functionalized CNT (M/CNT) catalyst. Initially, the hydroxyl group of HMF is
adsorbed on the surface of M/CNT catalyst, followed by C–H activation. Two
hydrogen atoms (H of CH 2 and OH) were abstracted by the support and removed by
oxygen molecule favouring the formation of DFF. The functional groups on the
CNT interacted with the aldehyde group (of DFF) which undergo hydrolysis and
form FFCA intermediate. Finally, FFCA easily converts into FDCA with similar
hydrolysis mechanism as mentioned above. This work also successfully investigated the adsorption behaviour of substrate and product on CNT surface. Among
these catalysts, noble metals have more selectivity and activity towards FDCA formation because of their excellent ability to attract the β-H atom from the methyl side
chain of HMF. The catalyst ability for the attraction of β-H group is in the order
Pt > Pd > Ru on CNT; accordingly, FDCA product selectivity also varied.
4 Conclusion and Challenges
4.1 Conclusions
The importance of biomass conversion and primary building blocks of carbohydrates is discussed at the beginning of this chapter. The application and importance
of levulinic and furan-based molecules were explained with pertinent examples. A
brief outline of levulinic acid synthesis and its catalytic conversion to various valuable products such as γ-valerolactone, arylated-γ-lactones and 4,4-disubstituted
pentanoic acid/esters was covered. Prior art on hydrocyclization of levulinic acid to
γ-valerolactone in the presence of different hydrogen sources using layered double
hydroxide-based catalysts is discussed along with their catalytic performances.
Preparation of arylated-γ-lactones (levulinic acid and aromatics) was introduced in
this chapter using various homogeneous and heterogeneous (zeolite) catalysts. The
acid-catalysed conversion of levulinic acid with aromatics into 4,4-disubstituted
pentanoic acid/esters is disclosed such as diphenolic acid, γ,γ-di-2-methylfuran
pentanoic acid (4,4-bis(5-methylfuran-2-yl)pentanoic acid) and (4,4-bis(5methylthiophen- 2-yl)pentanoic acid. The possible applications of 4,4-disubstituted
pentanoic acid/esters were also mentioned.
A brief discussion on 5-hydroxymethylfurfural (HMF) synthesis preferably from
fructose dehydration has been covered using various acid catalysts including mineral/organic acids, metal salts, metal oxides, heteropolyacids, ion-exchange resins,
functionalized carbon materials, clay and zeolitic materials. We focused on the performance of mentioned catalysts by considering conversion of fructose, yield of
HMF, stability, reusability, etc.. Finally, brief outline of the results of selective oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid is discussed with
emphasis on Ru-based catalyst for this conversion under base-free aqueous medium
using O 2 /air as the oxidant.
S. Gundekari et al.