657
873 K. Huber et al. performed crossed aldol condensation reaction with acetone
using mixed Mg-Al oxide catalyst at room temperature [153]. The aldol products
were then hydrogenated and dehydrogenated to produce alkanes, and more than
40% carbon selectivity of C 9 product and 25% carbon selectivity of C 8 product were
achieved. Bohre et al. studied the aldol condensation reaction of 5-HMF and acetone using series of basic magnesium and lanthanum (Mg-La) mixed oxides of different Mg/La molar ratio for the production of green diesel and jet fuel intermediates
[154]. Among the various Mg-La catalysts, Mg-La catalyst of Mg/Al molar ratio of
3 (ML-3) exhibits superior catalyst activity, and 99% 5-HMF conversion and 89%
yield of C 9 (HAc) product was achieved. The higher activity of ML-3 mixed oxide
was attributed to the higher basic strength, moderate surface area, and strong interaction between Mg and Al in mixed oxide. Cueto et al. demonstrated the catalytic
performance of basic mixed oxides (Mg-Al and Mg-Zr) for aqueous-phase 5-HMF
and acetone aldol condensation [155]. MgZr showed the superior performance for
aldol condensation reaction and selectivity of dimer aldol product (H 2 Ac) was
higher for this catalyst (Table 8). The high activity of this catalyst was attributed to
the presence of optimum concentration of medium-strength acid-base sites. The
stronger basic site promotes the retro-aldolization reaction which was identified as
an important side reaction.
Suttipat et al. developed a highly efficient composite of hierarchical faujasite
nanosheets and zeolite imidazolate framework-8 (Hie-FAU-ZIF-8) by stepwise
deposition of ZIF-8 on modified zeolite surface and tested this nano-composite
catalyst for the aldol condensation of 5-HMF and acetone [156]. The designed hierarchical nano-composite showed excellent acid-base catalytic properties for aldol
condensation reaction with a yield of HAc of 66.8% in comparison to the isolated
FAU and ZIF-8 (Table 8). The stepwise deposited Hie-FAU-ZIF-8 nano-composite
develops a synergistic effect between the Na
+
-stabilized zeolite framework and
ZIF-8 catalytic functions, which causes higher activity and selectivity to target
product. Malkar et al. reported a novel composite catalyst of aluminum-exchanged
heteropoly acid (HPA) encapsulated inside the cage of ZIF-8 (Al0.66-DTP@ZIF-8)
(DTP = dodecatungstophosphoric acid; ZIF = zeolitic imidazolate framework) for
selective synthesis of HAc product by aldol condensation of 5-HMF and acetone
[157]. The higher concentration of acid sites in HPA moiety and the smaller pore
diameter of ZIF-8 in Al0.66-DTP@ZIF-8 composite catalyst lead to the selective
formation of the HAc aldol product at high 5-HMF conversion of 98% in 10 h
(Table 8). Bohre et al. reported a composite solid base (Zr(CO 3 ) x ) and bifunctional
metal acid catalyst (Pd/Zeolite β) for the production of biofuel from 5-HMF in two
steps [158]. The zirconium carbonate exhibits high catalytic activity and water tolerance for aldol condensation reaction of 5-HMF and acetone. Ninety-two percent
yield of HAc aldol product was achieved at 100% 5-HMF conversion in the first
step (Table 8). The bifunctional Pd/zeolite-β catalyst quantitatively converted the
aldol product in ethanol to n-nonane and 1-ethoxynonane with 40 and 56% selectivity, respectively. The amine-grafted hierarchical FAU zeolite nanosheets with basic
sites were also tested for aldol condensation of 5-HMF and acetone [159]. In this
study, the synergistic effects of hierarchical porosity and the basicity of various
Efficient Nanocomposite Catalysts for Sustainable Production of Biofuels and…
873 K. Huber et al. performed crossed aldol condensation reaction with acetone
using mixed Mg-Al oxide catalyst at room temperature [153]. The aldol products
were then hydrogenated and dehydrogenated to produce alkanes, and more than
40% carbon selectivity of C 9 product and 25% carbon selectivity of C 8 product were
achieved. Bohre et al. studied the aldol condensation reaction of 5-HMF and acetone using series of basic magnesium and lanthanum (Mg-La) mixed oxides of different Mg/La molar ratio for the production of green diesel and jet fuel intermediates
[154]. Among the various Mg-La catalysts, Mg-La catalyst of Mg/Al molar ratio of
3 (ML-3) exhibits superior catalyst activity, and 99% 5-HMF conversion and 89%
yield of C 9 (HAc) product was achieved. The higher activity of ML-3 mixed oxide
was attributed to the higher basic strength, moderate surface area, and strong interaction between Mg and Al in mixed oxide. Cueto et al. demonstrated the catalytic
performance of basic mixed oxides (Mg-Al and Mg-Zr) for aqueous-phase 5-HMF
and acetone aldol condensation [155]. MgZr showed the superior performance for
aldol condensation reaction and selectivity of dimer aldol product (H 2 Ac) was
higher for this catalyst (Table 8). The high activity of this catalyst was attributed to
the presence of optimum concentration of medium-strength acid-base sites. The
stronger basic site promotes the retro-aldolization reaction which was identified as
an important side reaction.
Suttipat et al. developed a highly efficient composite of hierarchical faujasite
nanosheets and zeolite imidazolate framework-8 (Hie-FAU-ZIF-8) by stepwise
deposition of ZIF-8 on modified zeolite surface and tested this nano-composite
catalyst for the aldol condensation of 5-HMF and acetone [156]. The designed hierarchical nano-composite showed excellent acid-base catalytic properties for aldol
condensation reaction with a yield of HAc of 66.8% in comparison to the isolated
FAU and ZIF-8 (Table 8). The stepwise deposited Hie-FAU-ZIF-8 nano-composite
develops a synergistic effect between the Na
+
-stabilized zeolite framework and
ZIF-8 catalytic functions, which causes higher activity and selectivity to target
product. Malkar et al. reported a novel composite catalyst of aluminum-exchanged
heteropoly acid (HPA) encapsulated inside the cage of ZIF-8 (Al0.66-DTP@ZIF-8)
(DTP = dodecatungstophosphoric acid; ZIF = zeolitic imidazolate framework) for
selective synthesis of HAc product by aldol condensation of 5-HMF and acetone
[157]. The higher concentration of acid sites in HPA moiety and the smaller pore
diameter of ZIF-8 in Al0.66-DTP@ZIF-8 composite catalyst lead to the selective
formation of the HAc aldol product at high 5-HMF conversion of 98% in 10 h
(Table 8). Bohre et al. reported a composite solid base (Zr(CO 3 ) x ) and bifunctional
metal acid catalyst (Pd/Zeolite β) for the production of biofuel from 5-HMF in two
steps [158]. The zirconium carbonate exhibits high catalytic activity and water tolerance for aldol condensation reaction of 5-HMF and acetone. Ninety-two percent
yield of HAc aldol product was achieved at 100% 5-HMF conversion in the first
step (Table 8). The bifunctional Pd/zeolite-β catalyst quantitatively converted the
aldol product in ethanol to n-nonane and 1-ethoxynonane with 40 and 56% selectivity, respectively. The amine-grafted hierarchical FAU zeolite nanosheets with basic
sites were also tested for aldol condensation of 5-HMF and acetone [159]. In this
study, the synergistic effects of hierarchical porosity and the basicity of various
Efficient Nanocomposite Catalysts for Sustainable Production of Biofuels and…