653
produced FAc (>85%) as the primary product. The residual acid sites in low Si/Al Y
zeolites caused fast dehydration of FAcOH forming FAc, whereas strong basic sites
of K-impregnated and high Si/Al ratio zeolites promote second condensation step to
produce F 2 Ac. In case of USY zeolite, K 2 O species were formed by thermal activation due to the presence of a lower amount of ion-exchangeable proton sites in
mesoporous and defective crystalline framework of USY. The K 2 O species as the
strong basic sites in K-impregnated USY causes higher activity in aldol condensation and occurrence of the second condensation step. Kikhtyanin et al. also studied
the aldol condensation reaction of FUR and acetone using K-containing BEA zeolite prepared by ion exchange and combined ion exchanged and impregnation methods [143]. The K-BEA zeolite prepared by ion-exchanged method showed low
activity than the K-BEA zeolite prepared by combined ion-exchanged and impregnation method. The strong basic sites were formed by the combined ion-exchanged
and impregnation method due to the formation of K 2 O cluster on the zeolite. The
strong basic sites exhibit higher activity for aldol condensation reaction. Moreover,
this K-BEA zeolite limits the deposition of carbonaceous species and offers better
catalyst stability during reaction. Li et al. studied the aldol condensation of FUR and
acetone using K-promoted Sn-MFI zeolites [144]. The basicity of Sn-MFI increases
by addition of K resulting in remarkable change in production distribution. The pure
Sn-MFI produces only C 8 (FAc) aldol product, whereas both C 8 (FAc) and C 13
(F 2 Ac) aldol products were formed with K-promoted Sn-MFI catalysts (Table 7).
Moreover, the addition of K improves the water resistance capability of K-promoted
Sn-MFI zeolite than the parent Sn-MFI zeolite. The K-promoted Sn-MFI promotes
the formation of C 18 product in the presence of water. Xiao-ming et al. studied the
aldol condensation reaction of FUR and acetone using MgO/NaY catalyst to produce jet fuel intermediates [145]. The performance of MgO/NaY catalysts depends
on the MgO loading, and 20% MgO/NaY showed higher activity with condensation
product yield of 98.6% at 99.6% FUR conversion. The selectivity of F 2 Ac enhances
with the increase of FUR-to-acetone ratio with a slight decline of the reaction rate.
This catalyst deactivates gradually due to the formation of inactive Mg(OH) 2 .
However, the spent catalyst showed good regeneration capability after heat treatment. CaO-loaded HZSM-5 (Ca/ZSM-5) catalyst was also studied for aldol condensation of FUR and acetone in the presence of lower dosages of water [146]. The
catalyst activity was related to the formation of CaO species. The Ca/ZSM-5 catalyst showed no activity in the absence of water. The excess water favors the formation of FAc and inhibits the formation of F 2 Ac. Highest yields of FAc (38.4 mol%)
and F 2 Ac (60.2 mol%) were obtained with acetone-to-FUR mole ratio of 0.8:1 and
water content of 29.7 wt%. The catalyst deactivated due to the leaching of CaO from
the Ca/ZSM-5 catalyst, and the catalyst activity was restored appreciably by reloading of CaO.
Tandem catalysis empowers multiple consecutive reactions to be performed in
one pot and one step at similar or identical conditions. This strategy is an example
of effective process intensification for chemical process by removing expensive
separation steps and enhancing energy efficiency [147]. The tandem reactions
require a catalytic material of two or more types of active sites to facilitate
Efficient Nanocomposite Catalysts for Sustainable Production of Biofuels and…
produced FAc (>85%) as the primary product. The residual acid sites in low Si/Al Y
zeolites caused fast dehydration of FAcOH forming FAc, whereas strong basic sites
of K-impregnated and high Si/Al ratio zeolites promote second condensation step to
produce F 2 Ac. In case of USY zeolite, K 2 O species were formed by thermal activation due to the presence of a lower amount of ion-exchangeable proton sites in
mesoporous and defective crystalline framework of USY. The K 2 O species as the
strong basic sites in K-impregnated USY causes higher activity in aldol condensation and occurrence of the second condensation step. Kikhtyanin et al. also studied
the aldol condensation reaction of FUR and acetone using K-containing BEA zeolite prepared by ion exchange and combined ion exchanged and impregnation methods [143]. The K-BEA zeolite prepared by ion-exchanged method showed low
activity than the K-BEA zeolite prepared by combined ion-exchanged and impregnation method. The strong basic sites were formed by the combined ion-exchanged
and impregnation method due to the formation of K 2 O cluster on the zeolite. The
strong basic sites exhibit higher activity for aldol condensation reaction. Moreover,
this K-BEA zeolite limits the deposition of carbonaceous species and offers better
catalyst stability during reaction. Li et al. studied the aldol condensation of FUR and
acetone using K-promoted Sn-MFI zeolites [144]. The basicity of Sn-MFI increases
by addition of K resulting in remarkable change in production distribution. The pure
Sn-MFI produces only C 8 (FAc) aldol product, whereas both C 8 (FAc) and C 13
(F 2 Ac) aldol products were formed with K-promoted Sn-MFI catalysts (Table 7).
Moreover, the addition of K improves the water resistance capability of K-promoted
Sn-MFI zeolite than the parent Sn-MFI zeolite. The K-promoted Sn-MFI promotes
the formation of C 18 product in the presence of water. Xiao-ming et al. studied the
aldol condensation reaction of FUR and acetone using MgO/NaY catalyst to produce jet fuel intermediates [145]. The performance of MgO/NaY catalysts depends
on the MgO loading, and 20% MgO/NaY showed higher activity with condensation
product yield of 98.6% at 99.6% FUR conversion. The selectivity of F 2 Ac enhances
with the increase of FUR-to-acetone ratio with a slight decline of the reaction rate.
This catalyst deactivates gradually due to the formation of inactive Mg(OH) 2 .
However, the spent catalyst showed good regeneration capability after heat treatment. CaO-loaded HZSM-5 (Ca/ZSM-5) catalyst was also studied for aldol condensation of FUR and acetone in the presence of lower dosages of water [146]. The
catalyst activity was related to the formation of CaO species. The Ca/ZSM-5 catalyst showed no activity in the absence of water. The excess water favors the formation of FAc and inhibits the formation of F 2 Ac. Highest yields of FAc (38.4 mol%)
and F 2 Ac (60.2 mol%) were obtained with acetone-to-FUR mole ratio of 0.8:1 and
water content of 29.7 wt%. The catalyst deactivated due to the leaching of CaO from
the Ca/ZSM-5 catalyst, and the catalyst activity was restored appreciably by reloading of CaO.
Tandem catalysis empowers multiple consecutive reactions to be performed in
one pot and one step at similar or identical conditions. This strategy is an example
of effective process intensification for chemical process by removing expensive
separation steps and enhancing energy efficiency [147]. The tandem reactions
require a catalytic material of two or more types of active sites to facilitate
Efficient Nanocomposite Catalysts for Sustainable Production of Biofuels and…