369
materials in terms of hydrothermal stability (due to introduction of zeolite building
blocks on the surface of mesoporous walls), which leads to improved reusability of
the catalyst in many organic reactions’ regeneration cycles, and zeolitic acidity,
which creates new possibilities for applications of mesoporous zeolites in the catalytic reactions demanding strong acidity [171]. Due to such positive attributes, hierarchical zeolites are preferable and gaining attention as heterogeneous catalysts/
supports to execute various organic transformations involving demanding acidity
and bulkier entities (which is generally the case with fine chemical synthesis) over
conventional zeolites due to their improved catalytic activity. One can envisage the
wide utility of mesozeolites and their functionalized derivatives for biomass-derived
chemical synthesis. Verboekend and Pérez-Ramírez [178] have provided in-depth
discussion on the catalyst design aspect of mesoporous zeolites for catalytic applications from the point of view of synthesis-property-function relationship. They
suggested that the functionalization of mesopores can exposed zeolites to novel
applications; however, one has to think of large-scale synthesis of mesozeolites/
hierarchical zeolites in which the shape of the catalyst is a key factor, as each size
has its different role to play. Activity, intracrystalline mass transport, and practical
implementation for mesozeolite synthesis are key functions of micropores, mesopores, and shape-geometry, respectively. Further, the authors suggested that, for
large-scale industrial success, one has to look into the economic aspect critically
while keeping in mind both the production cost and advantage in catalysis which
demands for close collaborations between inventors and industrial partners.
Zeolites have extensively been used for the preparation of numerous ester derivatives, an important one being alkyl levulinates. Since the last decade, our research
group has been engaged on research related to the development of environmentally
benign methods for the synthesis of complex drug molecules via multicomponent
reactions and the conversion of biomass-based derivatives into value-added chemicals, especially esterification of biomass-derived levulinic acid to produce n-butyl
levulinates using hierarchical zeolite catalysts.
Initially, attempts have been made for the development of mesozeolite BEA (via
desilication approach using alkali-treated zeolite precursors) and employing them
in biologically active drug-like molecules [derivatives of dihydopyridinones
(DHPMs), dialkylpyrimidinones (DAPMs), amino alkyl naphthols (AANs), etc.]. In
this research, the success of mesozeolites is realized as improved catalytic activity
is observed in case of the synthesis of bulkier products as compared to parent zeolite
H-BEA catalyst. In the subsequent research, several mesoporous zeolites (mesoZSM- 5 and meso-H-BEA) have been developed after employing a series of synthetic modifications in terms of change in reaction conditions, use of varied
templates [surfactants: [cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB)], rice husk, pH, stirring period, etc.], etc. [179,
180]. The resulting hierarchical materials were characterized for their morphology
(by SEM/TEM/low- and wide-angle XRD,
27
Al and
29
Si-MAS-NMR), thermal stability (by TG-DTA), elemental analysis (by ICP-AES), surface area (by BET), pore
volume (by BJH), acidity (by NH 3 -TPD), etc. using several sophisticated analytical
techniques [181, 182].
Solid Acid-Catalyzed Esterification of Levulinic Acid for Production of Value-Added…
materials in terms of hydrothermal stability (due to introduction of zeolite building
blocks on the surface of mesoporous walls), which leads to improved reusability of
the catalyst in many organic reactions’ regeneration cycles, and zeolitic acidity,
which creates new possibilities for applications of mesoporous zeolites in the catalytic reactions demanding strong acidity [171]. Due to such positive attributes, hierarchical zeolites are preferable and gaining attention as heterogeneous catalysts/
supports to execute various organic transformations involving demanding acidity
and bulkier entities (which is generally the case with fine chemical synthesis) over
conventional zeolites due to their improved catalytic activity. One can envisage the
wide utility of mesozeolites and their functionalized derivatives for biomass-derived
chemical synthesis. Verboekend and Pérez-Ramírez [178] have provided in-depth
discussion on the catalyst design aspect of mesoporous zeolites for catalytic applications from the point of view of synthesis-property-function relationship. They
suggested that the functionalization of mesopores can exposed zeolites to novel
applications; however, one has to think of large-scale synthesis of mesozeolites/
hierarchical zeolites in which the shape of the catalyst is a key factor, as each size
has its different role to play. Activity, intracrystalline mass transport, and practical
implementation for mesozeolite synthesis are key functions of micropores, mesopores, and shape-geometry, respectively. Further, the authors suggested that, for
large-scale industrial success, one has to look into the economic aspect critically
while keeping in mind both the production cost and advantage in catalysis which
demands for close collaborations between inventors and industrial partners.
Zeolites have extensively been used for the preparation of numerous ester derivatives, an important one being alkyl levulinates. Since the last decade, our research
group has been engaged on research related to the development of environmentally
benign methods for the synthesis of complex drug molecules via multicomponent
reactions and the conversion of biomass-based derivatives into value-added chemicals, especially esterification of biomass-derived levulinic acid to produce n-butyl
levulinates using hierarchical zeolite catalysts.
Initially, attempts have been made for the development of mesozeolite BEA (via
desilication approach using alkali-treated zeolite precursors) and employing them
in biologically active drug-like molecules [derivatives of dihydopyridinones
(DHPMs), dialkylpyrimidinones (DAPMs), amino alkyl naphthols (AANs), etc.]. In
this research, the success of mesozeolites is realized as improved catalytic activity
is observed in case of the synthesis of bulkier products as compared to parent zeolite
H-BEA catalyst. In the subsequent research, several mesoporous zeolites (mesoZSM- 5 and meso-H-BEA) have been developed after employing a series of synthetic modifications in terms of change in reaction conditions, use of varied
templates [surfactants: [cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TTAB)], rice husk, pH, stirring period, etc.], etc. [179,
180]. The resulting hierarchical materials were characterized for their morphology
(by SEM/TEM/low- and wide-angle XRD,
27
Al and
29
Si-MAS-NMR), thermal stability (by TG-DTA), elemental analysis (by ICP-AES), surface area (by BET), pore
volume (by BJH), acidity (by NH 3 -TPD), etc. using several sophisticated analytical
techniques [181, 182].
Solid Acid-Catalyzed Esterification of Levulinic Acid for Production of Value-Added…