Understanding water-induced zeolite dealumination is crucial for control of the hydrothermal stability of zeolite-based catalyst materials. Here we explore the dealumination process, focusing on the first Al–O­(H) bond-breaking step in a density functional theory model of a ZSM-5 crystal in the presence of a single and two water molecules per active site. We identify a set of four possible reaction mechanisms consisting of two different types of reactions. In the first three proposed mechanisms, Al–O­(H) bond breaking is induced by adsorption and dissociation of an incoming water molecule. The fourth mechanism is different and leads to a different reaction product, suggesting an alternative follow-up mechanism. In this energetically very favorable case, the breaking of the Al–O­(H) bond is induced by nondissociative adsorption of two water molecules. We therefore assume that the proposed mechanism is a viable first dealumination step. This implies that all Al–O­(H) bond-breaking mechanisms are initiated from metastable water adsorption modes, and water reorganization from the most stable mode needs to occur prior to hydrolysis of the Al–O­(H) bond. We suggest that the feasibility of this rearrangement (Al accessibility) is one of the determining factors for the relative occurrence of dealumination at different sites. We further establish a correlation between the Al site susceptibility toward dealumination and reaction conditions, which can be further used during postsynthetic treatment of the zeolite to control Al distribution and thus hydrothermal stability of the catalyst.

Establishing structure–reactivity relationships for specific channel orientations of zeolites is vital to developing new, superior materials for various applications, including oil and gas conversion processes. Herein, a well‐defined model system was developed to build structure–reactivity relationships for specific zeolite‐channel orientations during various catalytic reaction processes, for example, the methanol‐ and ethanol‐to‐hydrocarbons (MTH and ETH) process as well as oligomerization reactions. The entrapped and effluent hydrocarbons from single‐oriented zeolite ZSM‐5 channels during the MTH process were monitored by using operando UV/Vis diffuse reflectance spectroscopy (DRS) and on‐line mass spectrometry (MS), respectively. The results reveal that the straight channels favor the formation of internal coke, promoting the aromatic cycle. Furthermore, the sinusoidal channels produce aromatics, (e.g., toluene) that further grow into larger polyaromatics (e.g., graphitic coke) leading to deactivation of the zeolites. This underscores the importance of careful engineering of materials to suppress coke formation and tune product distribution by rational control of the location of zeolite acid sites and crystallographic orientations.

In this work, we use quantum-mechanical calculations to examine a number of possible dealumination routes in a model reminiscent of a commercial Y zeolite (Si/Al ratio of 3) as used in fluid catalytic cracking. First, we determine the distribution of Al over the zeolite lattice. The thermodynamically most stable distribution found in our calculations does not match the aluminum distribution found experimentally with NMR. We then describe the design of a periodic structure model to better fit the experimental distribution for zeolite Y with a Si/Al ratio of 3. This new model is used to determine the mechanism of dealumination in the absence and presence of stabilizing La3+ ions. It was found that the dealumination pathways with La3+ present in this model lead to higher activation energies, supporting a stabilizing effect of rare earth ions on the dealumination. The local environment (with both Brønsted and Lewis acid sites) has a large effect on the transition states and intermediates. While the local environment destabilizes pathways that involve protonation of oxygen atoms near another Brønsted acid site, it reduces the barriers of other pathways by coordinating newly formed OH groups in the transition states. These findings imply that the realistic aluminum distributions provided by our model are a prerequisite for this type of study.

A novel route for the production of the versatile chemical building block phthalide from biorenewable furfuryl alcohol and acrylate esters is presented. Two challenges that limit sustainable aromatics production via Diels-Alder (DA) aromatisation-an unfavourable equilibrium position and undesired regioselectivity when using asymmetric addendswere addressed using a dynamic kinetic trapping strategy. Activated acrylates were used to speed up the forward and reverse DA reactions, allowing for one of the four DA adducts to undergo a selective intramolecular lactonisation reaction in the presence of a weak base. The adduct is removed from the equilibrium pool, pulling the system completely to the product with a fixed, desired regiochemistry. A single 1,2-regioisomeric lactone product was formed in up to 86 % yield and the acrylate activating agent liberated for reuse. The lactone was aromatised to give phthalide in almost quantitative yield in the presence of Ac 2 O and a catalytic amount of strong acid, or in 79 % using only catalytic acid.

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