4 research outputs found
Mesoporous MFI Zeolite Nanosponge as a High-Performance Catalyst in the Pechmann Condensation Reaction
A zeolite nanosponge possessing <b>MFI</b> framework type
was hydrothermally prepared by a seed-assisted synthesis method using
C<sub>22</sub>H<sub>45</sub>–N<sup>+</sup>(CH<sub>3</sub>)<sub>2</sub>–C<sub>6</sub>H<sub>12</sub>–N<sup>+</sup>(CH<sub>3</sub>)<sub>2</sub>–C<sub>6</sub>H<sub>13</sub> as a structure-directing
agent. The nanosponge morphology was composed of a three-dimensional
disordered network of <b>MFI</b> nanolayers with 2.5 nm thickness
supporting each other. Catalytic performance of the <b>MFI</b> nanosponge was investigated in the Pechmann condensation of bulky
reactants (pyrogallol and resorcinol) with ethyl acetoacetate and
compared with conventional zeolites <b>MFI</b>, <b>BEA</b>, and USY) and also layered <b>MFI</b>, pillared <b>MFI</b>, and self-pillared <b>MFI</b>. The investigation revealed
outstanding catalytic performance of the <b>MFI</b> nanosponge,
which can be attributed to the contribution of strong acid sites located
on the external surfaces accessible for the reaction of bulky reactants
Adsorption and Diffusion of C<sub>1</sub> to C<sub>4</sub> Alkanes in Dual-Porosity Zeolites by Molecular Simulations
We employ grand canonical Monte Carlo
and molecular dynamics simulations to systematically study the adsorption
and diffusion of C<sub>1</sub> to C<sub>4</sub> alkanes in hierarchical
ZSM-5 zeolite with micropores (∼1 nm) and mesopores (>2
nm). The zeolite is characterized by a large surface area of active
sites on the microporous scale with high permeability and access to
the active sites, which arises from the enhanced transport at the
mesoporous scale. We model this zeolite as a microporous Na<sup>+</sup>-exchanged alumino-sillicate zeolite ZSM-5/35 (Si/Al = 35) in which
cylindrical mesopores with a diameter of 4 nm have been built by deleting
atoms accordingly. We use the TraPPE and Vujić–Lyubartsev
force fields along with the Lorentz–Berthelot combining rules
to describe adsorbate–adsorbate and adsorbate–adsorbent
interactions. The performance of the force fields is assessed by comparing
against experimental single-component adsorption isotherms of methane
and ethane in microporous ZSM-5/35, which we measured as part of this
work. We compare the adsorption isotherms and diffusivities of the
adsorbed alkanes in the dual-porosity zeolite with those in microporous
ZSM-5/35 and discern the specific behavior at each porosity scale
on the overall adsorption, self-diffusion, and transport behavior
in zeolites with dual micro/mesoporosities
Ru-Based Complexes with Quaternary Ammonium Tags Immobilized on Mesoporous Silica as Olefin Metathesis Catalysts
Ruthenium olefin metathesis catalysts
bearing a polar quaternary
ammonium group in N-heterocyclic ligand were immobilized on silica
and siliceous mesoporous molecular sieves with different pore sizes
(SBA-15 and MCM-41). The activity of the heterogeneous catalysts was
found to increase with an increase in pore size of the support used,
with the best results observed for SBA-15-supported catalyst. The
influence of reaction conditions (temperature, solvent, catalyst,
and substrate concentration) on the efficiency of new heterogeneous
catalysts was established. A significant influence of the counterion
present in the ruthenium complex on the activity of immobilized catalysts
was also found: those derived from chloride containing ion exhibited
the highest activity. High activity in ring-closing metathesis of
substrates as citronellene, 1,7-octadiene, and diallyl compounds as
well as in cross-metathesis of unsaturated aliphatic compounds with
methyl acrylate was observed under optimized conditions. In some cases,
heterogenization led to catalysts with efficiency higher than those
observed for corresponding homogeneous complexes
Microporous Lead–Organic Framework for Selective CO<sub>2</sub> Adsorption and Heterogeneous Catalysis
A novel
microporous metal–organic framework, {[Pb<sub>4</sub>(μ<sub>8</sub>-MTB)<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>]·5DMF·H<sub>2</sub>O}<sub><i>n</i></sub> (<b>1</b>; MTB = methanetetrabenzoate
and DMF = <i>N</i>,<i>N</i>′-dimethylformamide),
was successfully synthesized by a solvothermal reaction and structurally
characterized by single-crystal X-ray diffraction. The framework exhibits
a unique tetranuclear [Pb<sub>4</sub>(μ<sub>3</sub>-COO)(μ<sub>2</sub>-COO)<sub>6</sub>(COO)(H<sub>2</sub>O)<sub>4</sub>] secondary
building unit (SBU). The combination of the SBU with the tetrahedral
symmetry of MTB results in a three-dimensional network structure,
with one-dimensional jarlike cavities having sizes of about 14.98
× 7.88 and 14.98 × 13.17 Å<sup>2</sup> and propagating
along the <i>c</i> axis. Due to the presence of four coordinately
unsaturated sites per one metal cluster, an activated form of compound <b>1</b> (i.e., desolvated form denoted as <b>1′</b>) was tested in gas adsorption and catalytic experiments. The studies
of gas sorption revealed that <b>1′</b> exhibits a surface
area (Brunauer–Emmett–Teller) of 980 m<sup>2</sup>·g<sup>–1</sup>. This value is the highest reported for any compound
from the MTB group. Interactions of carbon dioxide (CO<sub>2</sub>) molecules with the framework, confirmed by density functional theory
calculations, resulted in high CO<sub>2</sub> uptake and significant
selectivity of CO<sub>2</sub> adsorption with respect to methane (CH<sub>4</sub>) and dinitrogen (N<sub>2</sub>) when measured from atmospheric
pressure to 21 bar. The high selectivity of CO<sub>2</sub> over N<sub>2</sub> is mostly important for capturing CO<sub>2</sub> from the
atmosphere in attempts to decrease the greenhouse effect. Moreover,
compound <b>1′</b> was tested as a heterogeneous catalyst
in Knoevenagel condensation of active methylene compounds with aldehydes.
Excellent catalytic conversion and selectivity in the condensation
of benzaldehyde and cyclohexanecarbaldehyde with malononitrile was
observed, which suggests that accessible lead(II) sites play an important
role in the heterogeneous catalytic process