443
Ag-exchanged heteropoly tungstate [51] were prepared and examined for the dehydration of fructose. These catalysts gave 74 and 77.7% of HMF yield in the presence
of water/MIBK, respectively. Roy et al. reported Zn x TPA/γ-Al 2 O 3 via microwaveassisted hydrothermal method for fructose conversion to HMF [52].
Shun Zhao et al. reported bifunctional surfactant combined with heteropoly
tungstate catalyst for one-pot transformation of cellulose to HMF [53]. Yongshui
et al. reported sulphate-functionalized ionic liquid containing heteropoly tungstate
catalyst for fructose dehydration [54]. This catalyst showed an exceptional activity
with 99% of HMF yield in 2-butanol. Direct conversion of glucose to HMF was
disclosed by Lei Hu and co-workers [55]. They used the combination of boric acid
and tungstophosphoric acid as catalyst in ionic liquid solvent. This catalyst gave
52% HMF within 30 min of reaction time at 120 °C. Direct conversion of glucose
to HMF was reported over ionic liquid-exchanged HPW [MimAM]H 2 PW 12 O 40 catalyst [56]. In this report the maximum yield of 53% HMF was attained in THF/water
and NaCl mixture. Song-Bai Yu et al. successfully converted sucrose into HMF
using different ILs and heteropoly acid catalysts in DMSO/H 2 O mixture [57].
Among the combinations [Hmim][HSO 4 ]/Cs 2.3 H 0.7 PW 12 O 40 showed better HMF
yield of 91% from sucrose at 180 °C. Glucose and fructose are also examined with
this catalyst combination. Gomes et al. reported fructose conversion to HMF over
HPW dispersed on MCM-41. Around 80% HMF was observed in 1 h at 120 °C [58].
Our group reported Al-exchanged heteropoly tungstate (AlTPA) supported on
SnO 2 catalyst for fructose dehydration to HMF in DMSO [59]. The results suggested that the activity of the catalyst is guided by the acidity of the catalyst, which
varied with calcination temperature of the catalyst. 20%AlTPA/SnO 2 catalyst calcined at 400 °C showed 100% fructose conversion with around 90% yield of
HMF. We also reported heteropoly tungstate supported on Ta 2 O 5 catalyst for HMF
synthesis from fructose. The maximum yield of 85% HMF was achieved with
20%TPA/Ta 2 O 5 calcined at 300 °C [60]. The active catalyst in this study was
assessed with different oxide supports such as Nb 2 O 5 , SiO 2 and ZrO 2 , and the results
are displayed in Table 3. All these catalysts showed moderate HMF yields. In order
to know the activity difference in these catalysts, all the catalysts were characterized
by NH 3 -TPD analysis to know their acidity. The 20%TPA/Ta 2 O 5 catalyst had more
acidity than other catalysts, and it showed best activity. These results clearly indicate the dehydration of fructose was unambiguously proportionate to acidity of the
catalyst. The support nature also played an important role.
Mesoporous ZrO 2 -supported molybdophosphoric acid catalyst was also reported
by our group [61]. A high HMF yield of 80% within a reaction time of 30 min at
120 °C was achieved. The reason to get good yields in less reaction time is dependent on the dispersion of MPA on mesoporous ZrO 2 . The dispersion increased the
accessibility of active sites of the catalyst.
The above-discussed catalytic systems for the transformation of carbohydrates to
HMF were summarized in Table 4.
Carbohydrates to Chemicals and Fuel Additives over ModifiedPolyoxometalate Catalysts
Ag-exchanged heteropoly tungstate [51] were prepared and examined for the dehydration of fructose. These catalysts gave 74 and 77.7% of HMF yield in the presence
of water/MIBK, respectively. Roy et al. reported Zn x TPA/γ-Al 2 O 3 via microwaveassisted hydrothermal method for fructose conversion to HMF [52].
Shun Zhao et al. reported bifunctional surfactant combined with heteropoly
tungstate catalyst for one-pot transformation of cellulose to HMF [53]. Yongshui
et al. reported sulphate-functionalized ionic liquid containing heteropoly tungstate
catalyst for fructose dehydration [54]. This catalyst showed an exceptional activity
with 99% of HMF yield in 2-butanol. Direct conversion of glucose to HMF was
disclosed by Lei Hu and co-workers [55]. They used the combination of boric acid
and tungstophosphoric acid as catalyst in ionic liquid solvent. This catalyst gave
52% HMF within 30 min of reaction time at 120 °C. Direct conversion of glucose
to HMF was reported over ionic liquid-exchanged HPW [MimAM]H 2 PW 12 O 40 catalyst [56]. In this report the maximum yield of 53% HMF was attained in THF/water
and NaCl mixture. Song-Bai Yu et al. successfully converted sucrose into HMF
using different ILs and heteropoly acid catalysts in DMSO/H 2 O mixture [57].
Among the combinations [Hmim][HSO 4 ]/Cs 2.3 H 0.7 PW 12 O 40 showed better HMF
yield of 91% from sucrose at 180 °C. Glucose and fructose are also examined with
this catalyst combination. Gomes et al. reported fructose conversion to HMF over
HPW dispersed on MCM-41. Around 80% HMF was observed in 1 h at 120 °C [58].
Our group reported Al-exchanged heteropoly tungstate (AlTPA) supported on
SnO 2 catalyst for fructose dehydration to HMF in DMSO [59]. The results suggested that the activity of the catalyst is guided by the acidity of the catalyst, which
varied with calcination temperature of the catalyst. 20%AlTPA/SnO 2 catalyst calcined at 400 °C showed 100% fructose conversion with around 90% yield of
HMF. We also reported heteropoly tungstate supported on Ta 2 O 5 catalyst for HMF
synthesis from fructose. The maximum yield of 85% HMF was achieved with
20%TPA/Ta 2 O 5 calcined at 300 °C [60]. The active catalyst in this study was
assessed with different oxide supports such as Nb 2 O 5 , SiO 2 and ZrO 2 , and the results
are displayed in Table 3. All these catalysts showed moderate HMF yields. In order
to know the activity difference in these catalysts, all the catalysts were characterized
by NH 3 -TPD analysis to know their acidity. The 20%TPA/Ta 2 O 5 catalyst had more
acidity than other catalysts, and it showed best activity. These results clearly indicate the dehydration of fructose was unambiguously proportionate to acidity of the
catalyst. The support nature also played an important role.
Mesoporous ZrO 2 -supported molybdophosphoric acid catalyst was also reported
by our group [61]. A high HMF yield of 80% within a reaction time of 30 min at
120 °C was achieved. The reason to get good yields in less reaction time is dependent on the dispersion of MPA on mesoporous ZrO 2 . The dispersion increased the
accessibility of active sites of the catalyst.
The above-discussed catalytic systems for the transformation of carbohydrates to
HMF were summarized in Table 4.
Carbohydrates to Chemicals and Fuel Additives over ModifiedPolyoxometalate Catalysts