Hierarchical Beta Zeolites As Catalysts in α-Pinene Oxide Isomerization

Abstract

Hierarchical beta zeolites obtained in the concentrated reaction mixtures (H 2 O/Si = 2.5) and micromesoporous materials synthesized using a dual-template approach from a zeolite beta precursor were rigorously characterized and tested in a sustainable and environmentally friendly process of α-pinene oxide isomerization. The highest yield of trans-carveol (42%) with chemopreventive activity of mammary carcinogenesis was achieved over low crystalline micromesoporous materials characterized by well-developed mesoporosity, an increased fraction of weak-to-medium Brønsted acid sites and low Brønsted and Lewis acid sites (BAS/LAS) ratio. In turn, highly crystalline hierarchical beta zeolites with a lower mesopore volume and the mesopore surface area, stronger Brønsted acidity, and a higher BAS/LAS ratio favored the formation of campholenic aldehyde (31% yield). The mechanism of the desired product and byproducts formation was discussed and its feasibility was confirmed by kinetic modeling.

Florol synthesis via Prins cyclization over hierarchical beta zeolites

“…The micelles of cetyltrimethylammonium bromide were shown to additionally limit the growth of zeolite nanoparticles during the hydrothermal treatment [15,16]. Resulting materials with a high concentration of acid sites on the external surface demonstrated enhanced catalytic activity in the Prins-Friedel-Crafts reaction of butyraldehyde with 3-buten-1-ol and anisole [12], Prins cyclisation of (-)-isopulegol with acetone [17], α-pinene oxide isomerization [18], as well as tetrahydropyranylation of bulk alcohols [15]. In this study, a simple, straightforward and cost efficient method for the synthesis of hierarchical beta zeolites with a variable Si/Al ratio, nanoparticle sizes, textural properties (micropore and mesopore volumes, mesopore diameter, total specific surface area, external surface area) and acid site concentrations is proposed.…”

Kinetics of Heterogeneous Single‐Site Catalysis

“…One of the descriptors of the catalytic activity in acidcatalysed reactions besides the acid strength is also the acid site density. [57,58] While in some cases, like gas-phase n-pentane cracking or 1-propanol dehydration, analysis of primary experimental data does not display any dependence of turnover frequency TOF calculated per acid site on the acid site density, [57] there are several cases where not only TOF, [58,59] but also selectivity depends on this descriptor. [60] For the methanol to hydrocarbons reaction, it was found [58] that the increase of acid site density can accelerate formation of initial active species and decrease the apparent activation energy for the autocatalysis step elevating formation of the species in the "hydrocarbon" pool.…”

“…Thus resulting in hierarchical beta zeolites and CB-1 conventional beta zeolite (reproduced from permission, [59] Copyright 2022, The Authors).…”

“…One of the descriptors of the catalytic activity in acid‐catalysed reactions besides the acid strength is also the acid site density [57,58] . While in some cases, like gas‐phase n ‐pentane cracking or 1‐propanol dehydration, analysis of primary experimental data does not display any dependence of turnover frequency TOF calculated per acid site on the acid site density, [57] there are several cases where not only TOF, [58,59] but also selectivity depends on this descriptor [60] …”

“…Figure12. Isomerization of α-pinene oxide (APO): a) reaction scheme, where the products are campholenic (CA) and fencholenic (FA) aldehydes, pinocarveol (PC), trans-carveol, 2,8-menthadien-1-ol (MD), and p-cymene (PCY); b) TOF for different catalysts as a function of the total acid site concentration according to pyridine adsorption, where MZ-1-MZ-5 denote hierarchical beta zeolites and CB-1 conventional beta zeolite (reproduced from permission,[59] Copyright 2022, The Authors).…”