Tuning the Brønsted and Lewis acid nature in HZSM-5 zeolites by the generation of intracrystalline mesoporosity—Catalytic behavior for the acylation of anisole

Catalytic Advantages of SO3H-Modified UiO-66(Zr) Materials Obtained via Microwave Synthesis in Friedel-Crafts Acylation Reaction

The catalytic activity and stability of sulfonic-based UiO-66(Zr) materials were tested in the Friedel-Crafts acylation of anisole with acetic anhydride. The materials were prepared using microwave-assisted synthesis, producing microporous materials with remarkable crystallinity and physicochemical features as acid catalysts. Different ratios between both organic ligands, terephthalic acid (H2BDC) and monosodium 2-sulfoterephthalic acid (H2BDC-SO3Na), were used for the synthesis to modulate the sulfonic content. The sulfonic-based UiO-66(Zr) material synthesized with a H2BDC/H2BDC-SO3Na molar ratio of 40/60 exhibited the best catalytic performance in the acidic-catalyzed Friedel-Crafts acylation reaction. This ratio balanced the number of sulfonic acid sites and their accessibility within the UiO-66 microporous structure. The catalytic performance of this material increased remarkably at 200 °C, outperforming reference acids and commercial heterogeneous catalysts such as Nafion-SAC-13 and Amberlyst-70. Additionally, the best sulfonic-based UiO-66(Zr) material proved to be stable in four successive reaction cycles, maintaining both its catalytic activity and its structural integrity.

Insights into Sorption and Molecular Transport of Aqueous Glucose into Zeolite Nanopores

Liquid-phase heterogeneous catalysis using zeolites is important for biomass conversion to fuels and chemicals. There is a substantial body of work on gas-phase sorption in zeolites with different topologies; however, studies investigating the diffusion of complex molecules in liquid medium into zeolitic nanopores are scarce. Here, we present a molecular dynamics study to understand the sorption and diffusion of aqueous β-d-glucose into β-zeolite silicate at T = 395 K and P = 1 bar. Through 2-μs-long molecular dynamics trajectories, we reveal the role of the solvent, the kinetics of the pore filling, and the effect of the water model on these properties. We find that the glucose and water loading is a function of the initial glucose concentration. Although the glucose concentration increases monotonically with the initial glucose concentration, the water loading exhibits a nonmonotonic behavior. At the highest initial concentration (∼20 wt %), we find that the equilibrium loading of glucose is approximately five molecules per unit cell and displays a weak dependence on the water model. Glucose molecules follow a single-file diffusion in the nanopores due to confinement. The dynamics of glucose and water molecules slows significantly at the interface. The average residence time for glucose molecules is an order of magnitude larger than that in the bulk solution, while it is about twice as large for the water molecules. Our simulations reveal critical molecular details of the glucose molecule's local environment inside the zeolite pore relevant to catalytic conversion of biomass to valuable chemicals.

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.

Friedel-Crafts alkylation of benzene with benzyl alcohol over H-MCM-22

MCM-22 was synthesized by using silicic acid powder as a silica source under the static hydrothermal condition and characterized by X-ray diffraction, nitrogen adsorption-desorption isotherms, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, and temperature-programmed desorption of ammonia. The liquid phase benzylation of benzene with benzyl alcohol to diphenylmethane was investigated over H-MCM-22. The effects of reaction parameters on the conversion of benzyl alcohol and product distribution were determined. Under optimal reaction conditions, diphenylmethane yield of 92.1% was achieved for 99.3% conversion of benzyl alcohol in 3 h of reaction period. The reusability of the catalyst was also investigated after calcination of the catalyst in stagnant air at 500 °C for 4 h. The results show that the organic species produced during the reaction deposited in the catalyst lead to the deactivation of the catalyst and the calcination of the deactivated catalyst causes catalyst dealumination.