Synthesis of Nanosized ZSM-5 Zeolites by Different Methods and Their Catalytic Performance in the Alkylation of Naphthalene

Three nanosized ZSM-5 zeolites were successfully prepared from reactive gels with the same Si/Al ratios by different synthetic procedures that included the use of tetrapropylammonium hydroxide or n-butylamine as a template and a seeding method that did not use an organic additive. The effect of the synthetic method on the physicochemical properties of the prepared samples was investigated by XRD, XRF, XPS, N2 physisorption, SEM, TEM, 27Al MAS NMR, NH3-TPD, and Py-FTIR. The catalytic performance of the nanosized ZSM-5 zeolites in the alkylation of naphthalene with methanol was compared. The prepared samples were phase-pure, highly crystalline ZSM-5 zeolites, but they had different bulk and surface Si/Al ratios as well as textural and acidic properties. The study of the prepared catalysts in naphthalene methylation revealed that both the acid characteristics of the ZSM-5 nanosized zeolites and their textural properties were responsible for their activity in the reaction. A difference in the composition of monomethylnaphthalenes and dimethylnaphthalenes was attributed to the ability of the catalyst to isomerize the primary reaction products on acid sites located on the external surface of the zeolite crystals. 2,7-DMN was found to be the preferred reaction product over 2,6-DMN when formed at pore entrances to ZSM-5 channels due to the differences in their dimensions. In contrast, 2,6-dimethylnaphthalene could be produced on weaker external Brønsted acid sites, which are hydroxyls attached to octahedral Al atoms. The presented results show that the method used to synthesize nanoscale ZSM-5 zeolites is a critical factor that determines the physicochemical properties and catalytic performance of the resulting crystals.

Kinetic Behavior of Quaternary Ammonium Hydroxides in Mixed Methane and Carbon Dioxide Hydrates

This study evaluates the kinetic hydrate inhibition (KHI) performance of four quaternary ammonium hydroxides (QAH) on mixed CH4 + CO2 hydrate systems. The studied QAHs are; tetraethylammonium hydroxide (TEAOH), tetrabutylammonium hydroxide (TBAOH), tetramethylammonium hydroxide (TMAOH), and tetrapropylammonium hydroxide (TPrAOH). The test was performed in a high-pressure hydrate reactor at temperatures of 274.0 K and 277.0 K, and a concentration of 1 wt.% using the isochoric cooling method. The kinetics results suggest that all the QAHs potentially delayed mixed CH4 + CO2 hydrates formation due to their steric hindrance abilities. The presence of QAHs reduced hydrate formation risk than the conventional hydrate inhibitor, PVP, at higher subcooling conditions. The findings indicate that increasing QAHs alkyl chain lengths increase their kinetic hydrate inhibition efficacies due to better surface adsorption abilities. QAHs with longer chain lengths have lesser amounts of solute particles to prevent hydrate formation. The outcomes of this study contribute significantly to current efforts to control gas hydrate formation in offshore petroleum pipelines.

Removal of sulfate from aqueous solution using Mg–Al nano-layered double hydroxides synthesized under different dual solvent systems

Because of its priority to remove anions, nano-layered double hydroxide (LDH) was incorporated to improve the sulfate attack corrosion resistance of cement-based materials. Herein, the synthesis of high-efficiency LDH for removal of SO 4 2 − {\text{SO}}_{4}^{2-} is necessary. In this study, LDH with different Mg/Al ratios was synthesized under different dual solvent systems (water and ethylene glycol/ethanol/tetrapropylammonium hydroxide). Based on the adsorption experimental results, the LDH synthesized with n(Mg:Al) = 2:1 under water and ethanol solvent systems (ET2.0) exhibits the best adsorption capacity. The d (003) of LDH synthesized with n(Mg:Al) = 2:1 under different dual solvent systems are 0.7844, 0.7830, and 0.7946 nm, respectively. Three LDH belong to LDH- NO 3 − {\text{NO}}_{3}^{-} . The results indicated that their surface charges show obvious difference synthesized under different dual solvent systems, which leads to differences in adsorption performance. The adsorption experimental results show that ET2.0 followed pseudo second-order kinetics and Langmuir model. The ET2.0 removed SO 4 2 − {\text{SO}}_{4}^{2-} through anion substitution and electrostatic interaction and exhibited excellent adsorption rate with the maximum adsorption capacity of 95.639 mg/g. The effects of pore solution anion (OH−, Cl−, and CO 3 2 − {\text{CO}}_{3}^{2-} ) on the removal of SO 4 2 − {\text{SO}}_{4}^{2-} by the ET2.0 are limited.

Tetrapropylammonium Hydroxide as a Zinc Dendrite Growth Suppressor for Rechargeable Aqueous Battery

Zinc metal is widely used as an anode in various aqueous systems. However, zinc anode suffers from the dendrite formation on the surface upon cycling leading to a poor cyclability of a cell and its termination due to short circuit. In this work, the effect of tetrapropylammonium hydroxide (TPAH) was studied as an electrolyte additive for aqueous Zn//ZnCl2 + LiCl//LiFePO4 battery. TPAH additive prolongs the battery cycle life depending on its concentration (0.01–0.1 M). The better capacity retention over 350 cycles was observed for a symmetrical Zn//ZnCl2 + LiCl//Zn cell with 0.05 M TPAH whereas without additives the cell worked for only 110 cycles. The mechanism of TPAH influence on capacity retention is proposed based on the results of SEM and XRD analysis of the Zn anode and FTIR and NMR studies of the electrolyte. The XRD patterns of the negative electrode of the cell with TPAH indicates that zinc was preferentially deposited in a highly oriented (002) direction, which is more resistant against dendrite formation. These differences in deposited structure of Zn dendrites were confirmed by SEM images as well. FTIR and NMR spectra showed that TPAH decomposes to propylamine (RnN+H) and propene during cycling. TPAH also has an effect on the size and uniform distribution of Zn growth sides.

Uniform hierarchical MFI nanosheets prepared via anisotropic etching for solution-based sub–100-nm-thick oriented MFI layer fabrication

Zeolite nanosheets have shown unprecedented opportunities for a wide range of applications, yet developing facile methods for fabrication of uniform zeolite nanosheets remains a great challenge. Here, a facile approach involving anisotropic etching with an aqueous solution of tetrapropylammonium hydroxide (TPAOH) was developed for preparing uniform high–aspect ratio hierarchical MFI nanosheets. In addition, the mechanism associated with the formation of MFI nanosheets was proposed. In the next step, a dynamic air-liquid interface–assisted self-assembly method and single-mode microwave heating were used for b-oriented MFI nanosheets monolayer deposition and controlled in-plane solution-based epitaxial growth, respectively, ensuring the formation of well-intergrown b-oriented MFI layers with sub–100-nm thickness. Moreover, our study indicated that b-oriented ultrathin MFI layers could be fabricated on diverse substrates demonstrating excellent anticorrosion capacity, ionic sieving properties, and n-/i-butane isomer separation performance.

The Synthesis of Mesoporous TS-1 and Its Performance for Oxidation of Diphenyl Sulfide and Dibenzyl Sulfide

TS-1 zeolite has outstanding performance in the catalytic reactions with hydrogen peroxide as catalytic promoter. However, the narrow pore size (< 1.0 nm) of traditional TS-1 makes it difficult for bulky organic compounds to contact with the active sites in the pores, which seriously limits application of TS-1. Recently, the introduction of mesoporous structure into microporous TS-1 becomes a hot research topic. Meanwhile, the huge synthesis cost of TS-1 is another main reason hindering its industrial application. In this paper, mesoporous TS-1 was successfully synthesized using sodium silicate as silicon source and titanium trichloride as titanium source under the template conditions of tetrapropylammonium hydroxide (TPAOH) and cationic polymer. The mesoporous TS-1 was characterized by X-ray diffraction (XRD), N2 adsorption, scanning electric microscopy (SEM), transmitting electric microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and UV-Vis Spectrum spectra (UV-Vis). Results show that the synthesized TS-1 zeolites have good crystallinity and tetra-coordinated framework Ti atoms, and there are abundant mesoporous structures in the zeolite crystals. The results of oxidation experiments show that conversion of diphenyl sulfide and dibenzyl sulfide with mesoporous TS-1 are 97.3 % and 85.3 % respectively, while that conversion with microporous TS-1 are 75.7 % and 63.5 respectively.

Heterogeneity in the microstructure and dynamics of tetraalkylammonium hydroxide ionic liquids: insight from classical molecular dynamics simulations and Voronoi tessellation analysis

Microscopic structural and dynamic heterogeneities were investigated for three ionic liquids (ILs), tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and tetrabutylammonium hydroxide employing classical molecular dynamics (MD) simulations.