Acceleration of Zeolite Crystallization: Current Status, Mechanisms, and Perspectives.

Zeolites are important classes of crystalline materials and possess well-defined channels and cages with molecular dimensions. They have been extensively employed as heterogeneous catalysts and gas adsorbents due to their relatively large specific surface areas, high pore volumes, compositional flexibility, definite acidity, and hydrothermal stability. The zeolite synthesis normally undergoes high-temperature hydrothermal treatments with a relatively long crystallization time, which exhibits low synthesis efficiency and high energy consumption. Various strategies, e.g., modulation of the synthesis gel compositions, employment of special silica/aluminum sources, addition of seeds, fluoride, hydroxyl (·OH) free radical initiators, and organic additives, regulation of the crystallization conditions, development of new approaches, etc., have been developed to overcome these obstacles. And, these achievements make prominent contributions to the topic of acceleration of the zeolite crystallization and promote the fundamental understanding of the zeolite formation mechanism. However, there is a lack of the comprehensive summary and analysis on them. Herein, we provide an overview of the recent achievements, highlight the significant progress in the past decades on the developments of novel and remarkable strategies to accelerate the crystallization of zeolites, and basically divide them into three main types, i.e., chemical methods, physical methods, and the derived new approaches. The principles/acceleration mechanisms, effectiveness, versatility, and degree of reality for the corresponding approaches are thoroughly discussed and summarized. Finally, the rational design of the prospective strategies for the fast synthesis of zeolites is commented on and envisioned. The information gathered here is expected to provide solid guidance for developing a more effective route to improve the zeolite crystallization and obtain the functional zeolite-based materials with more shortened durations and lowered cost and further promote their applications.

Zn Single-Atom Catalysts Enable the Catalytic Transfer Hydrogenation of α,ß-Unsaturated Aldehydes.

Highly active nonprecious-metal single-atom catalysts (SACs) toward catalytic transfer hydrogenation (CTH) of α,ß-unsaturated aldehydes are of great significance but still are deficient. Herein, we report that Zn-N-C SACs containing Zn-N3 moieties can catalyze the conversion of cinnamaldehyde to cinnamyl alcohol with a conversion of 95.5% and selectivity of 95.4% under a mild temperature and atmospheric pressure, which is the first case of Zn-species-based heterogeneous catalysts for the CTH reaction. Isotopic labeling, in situ FT-IR spectroscopy, and DFT calculations indicate that reactants, coabsorbed at the Zn sites, proceed CTH via a "Meerwein-Ponndorf-Verley" mechanism. DFT calculations also reveal that the high activity over Zn-N3 moieties stems from the suitable adsorption energy and favorable reaction energy of the rate-determining step at the Zn active sites. Our findings demonstrate that Zn-N-C SACs hold extraordinary activity toward CTH reactions and thus provide a promising approach to explore the advanced SACs for high-value-added chemicals.

Multimetal Incorporation into 2D Conductive Metal-Organic Framework Nanowires Enabling Excellent Electrocatalytic Oxidation of Benzylamine to Benzonitrile.

As an important organic intermediate, benzonitrile (BN) is widely involved in organic synthetic chemistry and pharmaceutical and dyestuff industries. However, the exploration of a more efficient and controllable synthesis technique and the corresponding greener catalysts for the synthesis of BN still poses a great challenge. Herein, with multimetallic two-dimensional conductive metal-organic frameworks (2D cMOF) as anodic electrocatalysts, we develop a green, convenient, and highly efficient electrochemical synthesis strategy for BN. Thanks to the intrinsic 2D electrically conductive structure and the optimized the multimetallic coupling catalytic effect, the resulting multimetallic 2D cMOFs exhibit excellent benzylamine (BA) electrooxidation performance. Especially, the trimetallic 2D cMOF (NiCoFe-CAT) requires an ultralow potential of 1.29 V vs reversible hydrogen electrode (RHE) to achieve a 10 mA·cm-2 current density, which indicates the fastest reaction and the most favorable thermodynamic condition. A very high yield (0.058 mmol·mg-1·h-1) and faradic efficiency (∼87%) of benzonitrile are both achieved during the BA electrooxidation reaction at 1.45 V. The reaction mechanism investigations indicated that the various redox mediators of MII/MIII (Ni, Co, Fe) may be regarded as multimetal active species to promote BA conversion. Also, the excellent cycling durability of multimetallic 2D cMOFs further promotes their potential practical applications. These electrocatalytic performances are considered excellent and nearly surpass all other reported Ni-based inorganics or MOF-based electrocatalysts for the electrocatalytic oxidation of benzylamine.

Dendritic and Core-Shell-Corona Mesoporous Sister Nanospheres from Polymer-Surfactant-Silica Self-Entanglement.

Mesoporous nanospheres are highly regarded for their applications in nanomedicine, optical devices, batteries, nanofiltration, and heterogeneous catalysis. In the last field, the dendritic morphology, which favors molecular diffusion, is a very important morphology known for silica, but not yet for carbon. A one-pot, easy, and scalable co-sol-gel route by using the triphasic resol-surfactant-silica system is shown to yield the topologies of dendritic and core-shell-corona mesoporous sister nanospheres by inner radial phase speciation control on a mass-transfer-limited process, depending on the relative polycondensation rates of the resol polymer and silica phases. The trick was the use of polyolamines with different catalytic activities on each hard phase polycondensation. The self-entanglement of phases is produced at the {O- , S+ , I- } organic-surfactant-inorganic interface. Mono- and biphasic mesoporous sister nanospheres of carbon and/or silica are derivatized from each mother nanospheres and called "syntaxic" because of similar sizes and mirrored morphologies. Comparing these "false twins", or yin and yang mesoporous nanospheres, functionalized by sulfonic groups provides evidence of the superiority of the dendritic topologies and the absence of a shell on the diffusion-controlled catalytic alkylation of m-cresol.

Mononuclear-dinuclear equilibrium of grafted copper complexes confined in the nanochannels of MCM-41 silica.

Following the structural concept of copper-containing proteins in which dinuclear copper centers are connected by hydroxide bridging ligands, a bidentate copper(II) complex has been incorporated into nano-confined MCM-41 silica by a multistep sequential grafting technique. Characterization by a combination of EPR spectroscopy, X-ray photoelectron spectroscopy (XPS), UV/Vis spectroscopy, IR spectroscopy , and solid-state (13)C and (29)Si cross-polarization magic-angle spinning (CP-MAS) NMR suggests that dinuclear Cu complexes are bridged by hydroxide and other counterions (chloride or perchlorate ions), similar to the situation for EPR-undetectable [Cu(II)···Cu(II)] dimer analogues in biological systems. More importantly, a dynamic mononuclear-dinuclear equilibrium between different coordination modes of copper is observed, which strongly depends on the nature of the counterions (Cl(-) or ClO(4)(-)) in the copper precursor and the pore size of the silica matrix (the so-called confinement effect). A proton-transfer mechanism within the hydrogen-bonding network is suggested to explain the dynamic nature of the dinuclear copper complex supported on the MCM-41 silica.