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The evolution of soliton pulses into noise-like pulses in a nonlinear fiber externally to the laser oscillator is demonstrated at 1.9 µm, for the first time. Soliton collapse based mechanisms induce noise-like pulses with varying properties as a function of nonlinear fiber length without requiring any laser cavity feedback. The proposed method allows the generation of noise-like pulses with a sub-300 fs spike and sub-40 ps pedestal duration. Power scaling of the noise-like pulses is demonstrated in a double-clad thulium-doped fiber amplifier with amplification up to an average power of 5.19 W, corresponding to a pulse energy of 244 nJ. This method provides an alternative route for generating fully synchronized noise-like pulses and solitons in the same system, without relying on the conventionally used mechanism of changing the intracavity nonlinearity within the laser cavity.

Zeolite with crystal intracrystalline pore structure with less acid on the outer surface.

MOR zeolites were synthesized using a series of Gemini-type dications as high-efficiency novel OSDAs. The prepared MOR zeolites exhibit superior catalytic activity for DME carbonylation, due to the preferential siting of Al and Brønsted acid sites in its 8-MR side pockets.

The dynamic evolution of Al species in the hydrothermal dealumination process of CHA zeolite was investigated by multiple solid-state NMR methods. Two types of Al–OH species were clearly distinguished by 1H–1H DQ-SQ MAS NMR.

The traditional zeolites used in air separation are generally N2-selective adsorbents. It was found for the first time that the O2/N2 adsorption selectivity can be reversed by directly decorating the Ce metal ion sites of a traditional Y zeolite with imidazole molecules, which results in a novel O2 adsorbent. The O2/N2 selectivity changes from 0.9 to 1.6 under normal conditions, and most importantly, the O2 adsorbent is recyclable. The in situ XPS characterization results indicate that the imidazole modification can change the electronic state of Ce in the Y zeolite and increase its affinity for O2, which is confirmed by theoretical calculations. Dynamic breakthrough adsorption experiments show that the adsorbent has significant application potential in air separation.

Seed-assisted synthesis shows great potentials to modify the properties of inorganic microporous materials and enhance synthetic efficiency. However, the understanding on the related mechanism is insufficient, especially in silicoaluminophosphate (SAPO)...

Summary The first C–C bond formation mechanism in the methanol-to-hydrocarbons (MTH) process has always been a highly controversial issue. Using solid-state NMR spectroscopy, the initial C1 reactants and C1 intermediates were observed on the HSSZ-13 zeolite surface. In particular, for the first time, the highly reactive ethene precursor, surface ethoxy species, was directly captured under a real MTH reaction. These findings and in situ captured activated C1 reactants linked C1 species and initially generated ethene, in which C1 intermediates activate methanol/DME to form the first C–C bond. For such a difficult-to-detect and extremely initial reaction process, the advanced ab initio molecular dynamics technology simulated the complete process from C1 reactants to product. The visualized reaction process vividly shows methanol/DME in the gas phase approaching SMS/TMO on zeolite, being activated via effective collision and methylation to generate an ethene precursor. The zeolite catalyst and active C1 intermediates contribute together to the first C–C bond formation in a synergistic manner.

The adsorption and diffusion of adsorbates or reactants are the most essential steps in zeolite-based processes for gas separation and catalysis. An explicit description of the relationship between...

Direct observation of the activation and transformation of reactant molecules is extremely attractive but very challenging in the study of most chemical processes. Here is reported the first case of dynamic activation of C1 molecules in zeolite-catalyzed chemistry. During the methanol conversion over the HZSM-5 zeolite, a sequence of progressive activation states of dimethyl ether (DME) evoked by the special catalysis from CH3-Zeo, a hybrid supramolecular catalytic system formed by the organic methylic species growing on the inorganic silico-aluminate zeolite framework, has been directly observed by in situ ssNMR spectroscopy at programmed temperatures. Operando simulations visually display the variability of this hybrid supramolecular system of which the C–O bond property goes through a dynamic transition from covalent to ionic with the temperature increase, and thus the gradually enhanced electrophilicity of CH3δ+ and nucleophilicity of Zeoδ− lead to the dynamic activation of DME. This dynamic transition is generally reflected in the alkyl-Zeo system with other alkoxy groups, which linked the alkoxy species and carbocations in zeolite catalysis. Consequently, this work not only sheds light on the key issue of the first carbon–carbon (C–C) bond formation in the methanol to hydrocarbons (MTH) process but also brings a new awareness on the essence of acid catalysis in zeolite mediated chemical processes., In zeolite-catalyzed chemistry, dynamic activation of C1 molecules by CH3-Zeo catalysis has been first revealed by the combination of in situ ssNMR spectroscopy and AIMD simulation.

Part of tetrahedral framework aluminum in a protonic mordenite (HMOR) will convert geometry to distorted tetrahedral and octahedral coordination. High-field

A series of Fe-substituted ZSM-5 zeolite samples with an almost constant Si/(Fe + Al) molar ratio of 50 but varied levels of Fe substitution were synthesized via an in situ seed-induced hydrotherma...

ZIF-8 membranes have emerged as the most promising candidate for propylene/propane (C3 H6 /C3 H8 ) separation through its precise molecular sieving characteristics. The poor reproducibility and durability, and high cost, thus far hinder the scalable synthesis and industrial application of ZIF-8 membranes. Herein, we report a semi-solid process featuring ultrafast and high-yield synthesis, and outstanding scalability for reproducible fabrication of ZIF-8 membranes. The membranes show excellent C3 H6 /C3 H8 separation performance in a wide temperature and pressure range, and remarkable stability over 6 months. The ZIF-8 membrane features dimethylacetamide entrapped ZIF-8 crystals retaining the same diffusion characteristics but offering enhanced adsorptive selectivity for C3 H6 /C3 H8 . The ZIF-8 membrane was prepared on a commercial flat-sheet ceramic substrate. A prototypical plate-and-frame membrane module with an effective membrane area of about 300 cm2 was used for efficient C3 H6 /C3 H8 separation.

Methanol-to-olefins(MTO) reaction is one of the important non-petroleum routes to produce light olefins over acidic molecular sieves. In this study, the complete reaction course of MTO on SAPO-34 molecular sieve with retained organics evolution from induction period to deactivation period was investigated systematically at different weight hourly space velocities(WHSV) of methanol. By the aid of 12C/13C-methanol isotopic switch experiment, the dual cycle mechanism involving aromatics-based cycle and alkenes-based cycle was evaluated during the whole reaction process. The detailed reaction route varied with the evolution of the retained organics in the catalyst at different reaction stages. The aromatics-based cycle and alkenes-based cycle alternately dominate the reaction process. In the efficient reaction period, aromatics-based cycle is the main reaction mechanism, while in the induction and deactivation periods, the contribution of alkenes-based cycle mechanism will become more important.

Water is the most important substance in nature. Imitating the formation of natural materials, molecular sieves have been synthesized under hydrothermal conditions and applied in industry. Herein, we reveal an unforeseen observation on a very special water-induced structural dynamic process of these materials. Dynamic and reversible breaking and forming of T-O-T bonds in silicoaluminophosphate (SAPO) occurs through interactions between gaseous water and the molecular-sieve framework under mild hydrothermal conditions and is confirmed by detection of the incorporation of 17 O from H2 17 O into molecular-sieve framework. Encapsulation of the bulky molecules trimethylphosphine and pyridine (kinetic diameters much larger than the pore size of SAPO-34) into CHA cavities consolidated the water-induced dynamic process. Consequently, new insights into the dynamic features of molecular sieves in water are provided. The ship-in-a-bottle strategy based on these findings also open new fields for fine acidity identification and gives extra boost in shape-selective catalysis.

A reconstruction strategy has been developed to synthesize Cu-SAPO-34 with a wide crystallization phase region, high solid yield, and tunable Si and Cu contents. Cu-rich SAPO-34 was prepared from a Cu-amine complex, which acted as a precursor and Cu source for the reconstruction synthesis. The role of the Cu-amine complex as a template was restricted, which allowed easier control over the Cu and Si contents than in the previously reported “one-pot” synthesis method. Characterization of the material revealed that the Si(4Al) coordination environment dominates the synthesized Cu-SAPO-34 catalysts. High-temperature hydrothermal treatment increased the isolated Cu2+ content slightly, and the acid sites in the low-silica catalyst are more resistant to hydrothermal treatment than those of the existing catalysts. The obtained materials, especially the low-silica Cu-SAPO-34 sample, exhibit excellent catalytic activity and hydrothermal stability for the selective catalytic reduction of NOx by NH3 (NH3-SCR). In addition, the influence of the catalyst acidity on the NH3-SCR reaction was also investigated and is discussed. The high synthetic efficiency and outstanding catalytic performance make Cu-SAPO-34 synthesized by the reconstruction method a promising catalyst for the NH3-SCR process.

Ball milling modification was performed on Cs/X catalysts before or after cesium ion exchange. Multiple characterization results (such as pyridine-FTIR, XPS, and solid-state NMR) demonstrated that ball milling played a distinct role in these two different preparation procedures of the catalyst. Ball milling performed after the cesium modification has a strong influence on the Cs/X structure and acid–base properties, which results in the enhancement of the catalytic performance for side-chain methylation of toluene with methanol. Detailed studies revealed that ball milling intensified the interactions between oxides and molecular sieves, which not only increased the dispersion of the Cs species but also generated some weaker basic centers. It is proposed that the new basic centers could be Si–O–Cs and Al–O–Cs, which are produced by breaking of the Si–O–Al bonds of the zeolite framework under the synergetic effect of ball milling and alkali treatment. These new active sites may help to promote the side-chain methylation reaction. However, excessive ball milling will lead to the vanishing of zeolite micropores, thus deactivating side-chain methylation activity, which indicates that microporosity plays a key role in side-chain methylation and individual basic centers cannot catalyze this reaction.

Methylcyclopentenyl cations (MCP+) have been regarded as active intermediates during methanol conversion, however, their function mode in the reaction are still uncertain. In our recent report, trimethylcyclopentenyl cation (triMCP+) and its deprotonated counterpart (trimethylcyclopentadiene, triMCP) were directly captured on H-RUB-50 catalyst with small cavity by the aid of in situ 13C MAS NMR spectroscopy, and their higher catalytic reactivity were clarified by 12C/13C-CH3OH isotopic switch experiment. In this contribution, an alternative route—cyclopentadienes-based cycle was applied on methanol conversion catalyzed on the H-RUB-50, in which ethene was produced with the participation of triMCP+ as critical intermediate. Then the cyclopentadienes-based cycle was predicted to be energetically favorable for ethene formation by density functional theory (DFT) calculations. The energetic comparison of paring mechanism in the aromatics-based cycle and cyclopentadienes-based cycle with the involvements of trimethylcyclopentadienyl (triMCPdi+) and triMCP+ as the corresponding active intermediates suggests that cyclopentadienes-based cycle is a feasible route for ethene formation. Furthermore, this work highlights the importance of the steric constraint and the host-guest interaction induced by the zeolite with cavity structure in the formation of intermediates and reaction pathway.

Calcium-metal batteries (CMBs) provide a promising option for high-energy and cost-effective energy-storage technology beyond the current state-of-the-art lithium-ion batteries. Nevertheless, the development of room-temperature CMBs is significantly impeded by the poor reversibility and short lifespan of the calcium-metal anode. A solvation manipulation strategy is reported to improve the plating/stripping reversibility of calcium-metal anodes by enhancing the desolvation kinetics of calcium ions in the electrolyte. The introduction of lithium salt changes the electrolyte structure considerably by reducing coordination number of calcium ions in the first solvation shell. As a result, an unprecedented Coulombic efficiency of up to 99.1 % is achieved for galvanostatic plating/stripping of the calcium-metal anode, accompanied by a very stable long-term cycling performance over 200 cycles at room temperature. This work may open up new opportunities for development of practical CMBs.

Manipulation of zeolite composition through judicious choice of an organic structure-directing agent (OSDA) is essential to regulate its physicochemical properties. ZSM-48 is a unidimensional zeoli...

This paper reports a new strategy for the structural reconstruction of biomass carbon sulfonic acid (BCSA) to its solid superacid counterpart. In this approach, a cheap layered biomass carbon (BC) source is chemically exfoliated by cetyltrimethyl ammonium bromide and then converted to silica-isolated carbon nanosheets (CNSs) by a series of conversion steps. The state of the silica-isolated CNSs and the stacking density of their nanoparticles are regulated by the dehydration temperature. Only the highly isolated and non-crosslinked CNSs with loose particle stacking structures obtained upon dehydration at 250 °C can be turned into superacid sites (with stronger acidity than that of 100% H2SO4) after sulfonation. This is accompanied by the creation of abundant hierarchical slit pores with high external surface area, mainly driven by the strong hydrogen bonding interactions between the introduced sulfonic acid groups. In typical acid-catalyzed esterification, etherification, and hydrolysis reactions, the newly formed superacid exhibits superior catalytic activity and stability compared to those of common BCSA and commercial Amberlyst-15 catalysts, owing to its good structural stability, highly exposed stable superacidic sites, and abundance of mesoporous/macroporous channels with excellent mass transfer rate. This groundbreaking work not only provides a novel strategy for fabricating bio-based solid superacids, but also overcomes the drawbacks of BCSA, i.e., unsatisfactory structural stability, acidity, and porosity.

In the conversion of methanol to hydrocarbon (MTH), hydrocarbon pool (HCP) species have been observed and demonstrated as important intermediates for efficient formation of olefins in the steady-st...

High-silica zeolite Y (FAU) plays a vital role in (petro)chemical industries. However, the slow nucleation and growth kinetics of the high-silica FAU framework limit its direct synthesis and the improvement of framework SiO

We report a thulium-doped all-fiber mode-locked laser that can be switched between stable conventional and dissipative soliton regimes. Periodic soliton explosions with oscillatory recovery dynamics are observed in the transition between the two stable regimes.