Self-pillared hierarchical Silicalite-1 zeolites for enhanced Suzuki-Miyaura coupling reactions

Hierarchical zeolites comprising orthogonally stacked bundles of zeolite nanosheets for catalytic and adsorption applications

Hierarchical zeolite enveloping Pd-CeO2 nanowires: An efficient adsorption/catalysis bifunctional catalyst for low temperature propane total degradation

Fundamental understanding of the mass transport of petrochemical and biomass derived molecules in microporous and mesoporous solid catalysts is important for developing the next generation of heterogeneous catalysts for traditional hydrocarbon processing including biomass pyrolysis and upgrading. Hierarchical zeolites with both micropores and mesopores exhibit enhanced mass transport and unique catalytic performance in reactions involving large molecules. However, quantitative description of mass transport in such materials remains elusive, owing to the complicated structure of hierarchical pores and difficulty in the synthesis of the materials with controllable structures. In this work, zero length column chromatography (ZLC) was used to study temperature-dependent diffusion of cyclohexane in silicalite-1, self-pillared pentasil (SPP) zeolite, and three-dimensionally ordered mesoporous imprinted (3DOm-i) silicalite-1. The samples were synthesized with controllable characteristic diffusion lengths from micrometer scale (ca. 20 μm) to nanometer scale (ca. 2 nm), allowing systematic study of the effect of mesoporosity on the mass transport behavior of hierarchical zeolites. The results show that the introduction of mesoporosity can indeed significantly facilitate the mass transport of cyclohexane in hierarchical silicalite-1 by reducing diffusional time constants, indicating rapid overall adsorption and desorption. However, when the length scale of the material approaches several nanometers, the contribution from the surface resistance, or "surface barrier", to overall mass transfer becomes dominant.

Disulfide is an important organic reagent and synthetic intermediate that is widely used in organic synthesis, polymers, and other fields, but its synthesis still suffers from many environmental pollution and economic problems. Here, we present an environmentally friendly and efficient base-free aerobic oxidative thiol coupling catalyzed by heterogeneous CoOx nanoclusters entrapped in hierarchical silicalite-1 zeolite, synthesized by combining silane pore expansion and metal coordination methods under hydrothermal conditions. It is confirmed that open hierarchical channels favor mass diffusion, and the chemical valence of Co species in CoOx/h-S-1-H is +2, which is different from that of Co3O4 particles in CoOx/h-S-1-I. CoOx nanoclusters, are strongly fixed in the channels of silicalite-1 zeolite via Co-O-Si bonds, which is of great importance for the high catalytic activity in both symmetrical and unsymmetrical oxidative thiol coupling reactions. After recycling experiments four times, the CoOx/h-S-1-H used has almost the same chemical state and the same distribution of Co(II) species as the fresh catalysts. Based on DFT calculations and inhibition experiments, the oxidative coupling of thiols undergoes a free radical mechanism in which Co(III) causes RS-H cleavage into RS· and H· species. Subsequently, two RS· radicals are coupled to disulfides, while H· radicals react with the O species to form H2O molecules. This work not only provides guidance on catalyst design and parameter optimization for oxidative thiol coupling but also advances the understanding of the aerobic oxidation mechanism.

Faster transport in hollow zeolites

Hierarchical silicalite-1 zeolites were obtained from the direct conversion of a mixture of ground solid raw materials via a steam-assisted crystallization(SAC) method without involvement of any mesoscale template. Only a trace amount of water was necessary during the crystallization, implying that the amount of water can be dramatically reduced, which still offers easy separation and high yields. The simple procedure involved only grinding and heating, which not only saves resources and energy, but also significantly reduces the discharge of eco-friendly synthesis of zeolites for practical applications. Compared to conventional bulk silicalite-1, the nanosized hierarchical zeolites with MFI structure show enhanced removal capabilities for methylene blue owing to their hierarchical porosity.

Hierarchical zeolites are advanced materials possessing the catalytic and adsorption properties of conventional zeolites while eliminating their transport limitations through the introduction of mesopores. Recent experiments comparing the adsorption in hierarchical self-pillared pentasils (SPP) and silicalite-1 (MFI) revealed an interesting crossover in sorbate loading for branched or long-chain alkanes but not for shorter linear alkanes, but an explanation for this behavior is not readily available through experimental probes due to the complications arising from the presence of multiple adsorption sites. Here we present a molecular simulation study on the adsorption of alkane isomers and show that a multi-step mechanism, found here for all molecules, is responsible for the observed phenomena.

Tungsten-substituted Silicalite-1 with an interconnected hollow structure for catalytic epoxidation of cyclohexene

Three synthetic strategies for the construction of tert-butyl (E)-3-arylprop-2-en-1-ol carbonates are described. Complementary approaches employing Suzuki-Miyaura coupling and cross-metathesis reaction gave moderate yields of the title compounds in one-step, both methods are suitable for high-throughput and parallel chemistry. A detailed investigation into the Suzuki-Miyaura coupling reaction is provided along with the studies on the synthesis of pinacolyl 1-(tert-butyloxycarbonyl)propenol-3-ylboronate, the key building block. Conventional synthesis of the title compounds via the Horner-Wadsworth-Emmons reaction as a key step in a three-step-one-purification protocol was optimized and the results are compared with those of the latter reactions.

5-Nitrobenzimidazole containing Pd(II) catalyzed C[sbnd]C cross-coupling reactions: The effect of the N-substituent of the benzimidazole structure on catalyst activity

A reliable protocol for fast and facile constructing multi-hollow silicalite-1 and encapsulating metal nanoparticles within the hierarchical zeolite

Synthesis of hierarchical titanium silicalite-1 by seed silanization for selective oxidation reactions

Hollow hierarchical silicalite-1 zeolite encapsulated Pt and PtNi bimetals (Pt@HS-1 and PtNi@HS-1) were successfully synthesized via a ship-in-bottle strategy and employed for hydroconversion of me...

Palladium complexes containing 2,7-bis(mesitylimidazolylidenyl)naphthyridine (NHC-NP) have been synthesized and characterized. Reaction of [{Ag(3)(NHC-NP)(2)}(PF(6))(3)] with [Pd(PhCN)(2)Cl(2)] provided an unusual dipalladium complex bridged by two NHC-NP units, forming a 20-membered dinuclear metallacycle [{Pd(2)(NHC-NP)(2)Cl(2)}(PF(6))] (2) in high yield. Treatment of 2 with KI in acetone yielded a neutral species [Pd(2)(NHC-NP)I(4)] (3). Meanwhile, the pyridinyl N-heterocyclic carbene (NHC-Py) precursor, 1-(2-pyridinyl)-3-mesitylimidazolium chloride, reacted with Pd(2)(dba)(3) directly to form the mononuclear palladium complex [Pd(NHC-Py)Cl(2)] (4). These complexes were characterized by elemental analyses as well as NMR spectroscopy, and the structures of 3 and 4 were further identified by X-ray diffraction analysis. The use of these palladium complexes for Suzuki-Miyaura and Kumada-Corriu coupling reactions has been examined. There is no significant difference in catalytic activities between 2 and 4 in Suzuki-Miyaura coupling reactions. However, the catalytic activity of 2 in the Kumada-Corriu coupling of ArBr with cyclohexylmagnesium bromide is quite different from that of 4. Thus complex 2 is active for the cross coupling, but complex 4 is active for the reduction of aryl halides.

Synthesis of biphenyl via sustainable Suzuki-Miyaura coupling reaction using mesoporous MCF-supported tin-palladium nanoparticles