Organosilane Surfactant-Directed Synthesis of Hierarchical ZSM-5 Zeolites with Improved Catalytic Performance in Methanol-to-Propylene Reaction

The synergistic interplay of hierarchy, crystal size, and Ga-promotion in the methanol-to-aromatics process over ZSM-5 zeolites

In the context of advancing social modernization, the projected shortfall in the demand for renewable aromatic hydrocarbons is expected to widen, influenced by industries like high-end materials, pharmaceuticals, and consumer goods. Sustainable methods for aromatic production from alternative sources, particularly the methanol-to-aromatics (MTA) process using zeolite ZSM-5 and associated with the "methanol economy", have garnered widespread attention. To facilitate this transition, our project consolidates conventional strategies that impact aromatics selectivity-such as using hierarchical zeolites, metallic promoters, or altering zeolite physicochemical properties-into a unified study. Our findings demonstrate the beneficial impact of elongated crystal size and heightened zeolite hierarchy on preferential aromatics selectivity, albeit through distinct mechanisms involving the consumption of shorter olefins. While metallic promoters enhance MTA performance, crystal size, and hierarchy remain pivotal in achieving the maximized aromatics selectivity. This study contributes to a deeper understanding of achieving superior aromatics selectivity through physicochemical modifications in zeolite ZSM-5 during MTA catalysis, thereby advancing the field's comprehension of structure-reactivity relationships.

Critical layer in liquid-solid system influencing the remediation of chromium using zeolite-supported sulfide nano zero-valent iron

Sulfidated nano zero-valent iron particles were immobilized on ZSM-5 zeolite (Z/S-nZVI) and used for hexavalent chromium (Cr(VI)) remediation. The performance of Z/S-nZVI improved with the increase in Cr(VI) concentration (< 60 mg/L), while the performance significantly decreased for a Cr(VI) concentration of more than 60 mg/L. The adsorption behavior for Cr(VI) was different from that reported in previous studies. The improved performance can be tailored for increasing efficiency of nano zero-valent iron (nZVI) corrosion, while the degree of corrosion of nZVI was affected by the concentration of the pollutant as discussed by kinetics, X-ray diffraction (XRD) and X-ray photoelectron spectrometer (XPS) analyses. The experiments for the dissolution of ferrous ions and the dosage of adsorbent demonstrated that the critical layer in the liquid-solid system changed with the increase in the concentration of Cr(VI) (Cr(VI): Z/S-nZVI > 0.6). Moreover, the removal mechanisms of Cr(VI) were elucidated through XRD, transmission electron microscopy (TEM) and XPS techniques. This results demonstrate that the species of chromium in the critical layer changed from Cr(III) to Cr(VI) as the concentration of chromium increased from low to high. Furthermore, the critical layer was composed of Cr(VI), Fe(II), O and H elements. Additionally, the experiments of coexisting ions and aging time confirmed that Z/S-nZVI possessed high selectivity and stability to ensure efficiency and cost-effectiveness in practical applications.

Capturing Cu2+ and recycling spent Cu-adsorbents as catalyst for eliminating Rhodamine B: reactivity and mechanism

The thorny problem of adsorption is the disposing of spent adsorbent. In this manuscript, the exhaust adsorbent of efficient capture Cu(II) over ZSM-5 that supported zero-valent iron (nZVI) was reused as a catalyst for eliminating Rhodamine B (RhB). Batch experiments were used to evaluate the removal performance of Cu2+ and RhB. The results demonstrated that the Cu2+ adsorption process obeyed pseudo-second-order kinetics, and the adsorption performance was dependent on solution pH. The maximum adsorption capacity at the optimal pH 4.0 was 375.9 mg/g; equilibrium was reached rapidly within 35 min. From XPS, the reduction-oxidation between Fe0 and Cu2+ was occurred in the adsorption process, and Fe2+, Fe3+, and Cu0 was formed. In the recycling experiments, RhB was removed by the spent Cu adsorbent, with the removal performance being dependent on the initial Cu concentration, in the order of 5 mg/L > 20 mg/L > 0 mg/L > 100 mg/L > 500 mg/L. RhB removal also improved with increasing H2O2 concentration. More than 99.9% of the RhB was degraded within 8 min using 1.75 mM H2O2, which was a large improvement over the previously used catalyst. The hydroxyl radical was found to be the main free radical responsible for RhB degradation.

Realizing of ZSM-5 microspheres with enhanced catalytic properties prepared from iron ore tailings via solid-phase conversion method

The comprehensive utilization of iron ore tailings (IOTs) not only resolved environmental problems but also brought huge economic benefits. In this study, the synthetic route presented herein provides a novel method for the synthesis of ZSM-5 microspheres from IOTs. The effects of Si/Al molar ratios and the pH of the precursor solution on the formation of zeolite was evaluated by various analytical methods. The catalytic performance of the catalyst prepared by the solid-phase conversion method (denoted as MP-ZSM-5) was evaluated by methanol-to-propylene (MTP) reaction. Compared with the zeolite catalyst that synthesized via the conventional hydrothermal method (denoted as HM-ZSM-5), MP-ZSM-5 not only prolongs catalytic lifetime from 18.7 to 36.0 h but also has higher selectivity for propylene by MP-ZSM-5 (43.7%) than that for HM-ZSM-5 (38.6%). In addition, Kissinger-Akahira-Sunose (KAS) model is applied to the TG result to study the template removal process kinetics. The average activation energy values required for the removal of CTAB and TPABr are 201.11 ± 13.42 and 326.88 ± 16.91 kJ∙mol^-1, respectively. Furthermore, this result is well coupled with the model-free kinetic algorithms to determine the conversion and isoconversion of the TPABr and CTAB decomposition in ZSM-5, which serves as important guidelines for the industrial production process.

Constructing single-crystalline hierarchical plate-like ZSM-5 zeolites with short b-axis length in the synthesis for catalyzing MTO reaction

ZSM-5 zeolite with hierarchical and lamellar structure is highly desired in industrial application. This paper reports an efficient additive, tetramethylguanidine (TMG), modifying crystal growth of the zeolite to this morphology....

Mechanism on redistribution synthesis of dichlorodimethylsilane by AlCl3/ZSM-5(3T)@γ-Al2O3 core-shell catalyst

The redistribution method plays an important role in addressing the issue of organosilicon by-products in the direct synthesis of dichlorodimethylsilane, and the redistribution mechanism is still a topic of debate. The redistribution mechanism by the ZSM-5(3 T)@γ-Al₂O₃ core-shell catalyst and post-modified AlCl₃/ZSM-5(3 T)@γ-Al₂O₃ catalyst was technically performed using the Density functional theory (DFT) at the level of B3LYP/6-311 +  + G(3df,2pd). The results show that no. 1 active site of ZSM-5(3 T)@γ-Al₂O₃ core-shell structure has a significant effect on the activity of the catalyst. Indicating that the active center involved in the reaction is H provided by the Al-O-H bond, which is an obvious catalytic active center of Bronsted acid. Furthermore, the post-modified AlCl₃/ZSM-5(3T)@γ-Al₂O₃ catalyst is in more favor of redistribution reaction comparing with the ZSM-5(3 T)@γ-Al₂O₃ core-shell catalyst. It ascribes to the robust Lewis site of aluminum chloride favorable modification. The redistribution synthesis mechanism of dichlorodimethylsilane on the ZSM-5(3 T)@γ-Al₂O₃ core-shell catalyst and post-modified AlCl₃/ZSM-5(3 T)@γ-Al₂O₃ catalyst had been investigated by using the Density functional theory (DFT) method at the level of B3LYP/6-311 +  + G(3df,2pd). The former active center was Bronsted acidic center, while the latter one was Lewis acidic center, ascribing to the Lewis site of aluminum chloride favorable modification. The catalytic activity of the post-synthesis AlCl₃/ZSM-5(3 T)@γ-Al₂O₃ catalyst completely was consistent with experimental results.

Controlled direct synthesis of single- to multiple-layer MWW zeolite

The minimized diffusion limitation and completely exposed strong acid sites of the ultrathin zeolites make it an industrially important catalyst especially for converting bulky molecules. However, the structure-controlled and large-scale synthesis of the material is still a challenge. In this work, the direct synthesis of the single-layer MWW zeolite was demonstrated by using hexamethyleneimine and amphiphilic organosilane as structure-directing agents. Characterization results confirmed the formation of the single-layer MWW zeolite with high crystallinity and excellent thermal/hydrothermal stability. The formation mechanism was rigorously revealed as the balanced rates between the nucleation/growth of the MWW nanocrystals and the incorporation of the organosilane into the MWW unit cell, which is further supported by the formation of MWW nanosheets with tunable thickness via simply changing synthesis conditions. The commercially available reagents, well-controlled structure and the high catalytic stability for the alkylation of benzene with 1-dodecene make it an industrially important catalyst.

One-Pot Synthesis of Ultra-Small Pt Dispersed on Hierarchical Zeolite Nanosheet Surfaces for Mild Hydrodeoxygenation of 4-Propylphenol

The rational design of ultra-small metal clusters dispersed on a solid is of crucial importance in modern nanotechnology and catalysis. In this contribution, the concept of catalyst fabrication with a very ultra-small size of platinum nanoparticles supported on a hierarchical zeolite surface via a one-pot hydrothermal system was demonstrated. Combining the zeolite gel with ethylenediaminetetraacetic acid (EDTA) as a ligand precursor during the crystallization process, it allows significant improvement of the metal dispersion on a zeolite support. To illustrate the beneficial effect of ultra-small metal nanoparticles on a hierarchical zeolite surface as a bifunctional catalyst, a very high catalytic performance of almost 100% of cycloalkane product yield can be achieved in the consecutive mild hydrodeoxygenation of 4-propylphenol, which is a lignin-derived model molecule. This instance opens up perspectives to improve the efficiency of a catalyst for the sustainable conversion of biomass-derived compounds to fuels.

A Mechanistic Investigation of Sustainable Solvent-Free, Seed-Directed Synthesis of ZSM-5 Zeolites in the Absence of an Organic Structure-Directing Agent

The solvent-free, seed-directed synthesis using natural precursors has emerged as a sustainable route for the synthesis of zeolite. Albeit the significant progress in the synthesis techniques, the crystallization behaviors of zeolites are somewhat elusive. Herein, we performed a detailed investigation of the crystallization behaviors of ZSM-5 zeolites synthesized through the solvent-free, seed-directed route using rice husk silica as starting materials. The crystallization at 180 °C is completed rapidly in 10 h, with an ultrahigh zeolite yield of at least 95%. Moreover, we evaluated the crystallization kinetics at different temperatures using the nonlinear Avrami equation and found instantaneous nucleation with three-dimensional growth in the studied temperature range, with activation energies for nucleation, transition, and crystal growth of 137, 51, and 51 kJ mol-1, respectively, indicating that nucleation is the rate-determining step. Further investigation of the structural and morphological evolution revealed a preference for secondary nucleation over the seed-growth mechanism. Crystallization proceeds via structural rearrangement within the solid system. We anticipate that our work will provide extensive insights that increase the understanding of zeolite crystallization and expand the highly sustainable production of zeolites.

Hierarchical Ti-beta with a three-dimensional ordered mesoporosity for catalytic epoxidation of bulky cyclic olefins

Hierarchical beta zeolites with a three-dimensionally ordered mesoporous-imprinted (3DOm-i) structure and post-synthetic Ti grafting for catalytic epoxidation of cyclic olefins.

Facile Synthesis of Proton-Type ZSM-5 by Using Quasi-Solid-Phase (QSP) Method

Herein, a simple and green quasi-solid-phase (QSP) method for facile synthesis of proton-type ZSM-5 avoiding use of excessive water, dry gel, Na⁺ cation and fluoride is reported. Crystallization by using the stoichiometric amount of TPAOH (tetrapropylammonium hydroxide) at 180 °C for only 12 h gave well-structured HZSM-5 crystals with high specific surface area of 429 m²  g^-1 and high thermal stability. 5MRs was observed to closely relate the formation of MFI structure and QSP method exhibits shorter induction period (t₀ ), higher nucleation rate (V_n ), and faster growth rate (V_g ). Moreover, HZ-12-180 showed extremely better and rather stable catalytic activity for methanol-to-propylene reaction by comparison with commercial HZSM-5.

Bolaform surfactant-directed synthesis of TS-1 zeolite nanosheets for catalytic epoxidation of bulky cyclic olefins

Hierarchical TS-1 nanosheets were hydrothermally synthesized by using a bolaform surfactant as the structure-directing agent and exhibited improved catalytic performance and superior recyclability in the epoxidation of cyclohexene and cyclooctene.

Direct synthesis of [B,H]ZSM-5 by a solid-phase method: AlF siting and catalytic performance in the MTP reaction

[B,H]ZSM-5 directly synthesized by a solid-phase method with tuned Al_F siting and acidity exhibited a longer lifetime in the MTP reaction.