In Silico Screening of Zeolites for the Highly Selective Adsorption of Central C–C Bonds toward More Effective Alkane Cracking

Pervaporation Separation of Isopropanol/Water Using Zeolite Nanosheets: A Molecular Simulation Study

Reducing greenhouse gas emissions plays a crucial role in slowing down the rise of the global temperature. One of the viable options is to employ renewable energy sources such as alcohols that can be produced from biomass. Specifically, one of the most common alcohols is isopropanol (IPA). Energy-intensive distillation processes are however involved in its production because of the rather low product concentration from fermentation. Membrane technologies, specifically pervaporation (PV), represent a promising alternative to the IPA/water separation. Particularly, employing zeolite nanosheets as PV membranes may provide great opportunities to extract IPA owing to their ultrathin and hydrophobic nature. By employing molecular dynamics simulations, this study conducts a systematic study on a diverse set of nanosheet candidates with the aim of exploring their potential and identifying top-performing structures. The best candidate among structures studied herein is predicted to offer an exceptional IPA/water selectivity of more than 400 with an unprecedentedly large flux. Structure-property-performance relationships have also been established to offer insights into the rational design of PV membranes with improved performance.

Molecular Views on Mechanisms of Brønsted Acid-Catalyzed Reactions in Zeolites

The Brønsted acidity of proton-exchanged zeolites has historically led to the most impactful applications of these materials in heterogeneous catalysis, mainly in the fields of transformations of hydrocarbons and oxygenates. Unravelling the mechanisms at the atomic scale of these transformations has been the object of tremendous efforts in the last decades. Such investigations have extended our fundamental knowledge about the respective roles of acidity and confinement in the catalytic properties of proton exchanged zeolites. The emerging concepts are of general relevance at the crossroad of heterogeneous catalysis and molecular chemistry. In the present review, emphasis is given to molecular views on the mechanism of generic transformations catalyzed by Brønsted acid sites of zeolites, combining the information gained from advanced kinetic analysis, in situ, and operando spectroscopies, and quantum chemistry calculations. After reviewing the current knowledge on the nature of the Brønsted acid sites themselves, and the key parameters in catalysis by zeolites, a focus is made on reactions undergone by alkenes, alkanes, aromatic molecules, alcohols, and polyhydroxy molecules. Elementary events of C-C, C-H, and C-O bond breaking and formation are at the core of these reactions. Outlooks are given to take up the future challenges in the field, aiming at getting ever more accurate views on these mechanisms, and as the ultimate goal, to provide rational tools for the design of improved zeolite-based Brønsted acid catalysts.

Computational Study of Alkane Adsorption in Brønsted Acid Zeolites for More Efficient Alkane Cracking

Alkane cracking using Brønsted acid zeolites, catalytically converting long-chain molecules into smaller ones, is critical to fuel and chemical production. To enable more energy-efficient cracking processes, developing zeolite catalysts with enhanced performance (i.e., a faster reaction rate with reduced methane formation) plays a substantial role. Given the adsorption thermodynamics of alkanes onto the protons of Brønsted acid zeolites is a key step in the overall cracking reactions; therefore, catalysts possessing a more negative Gibbs free energy of adsorption for alkanes with a larger central-to-terminal bond adsorption selectivity to promote central cracking are of particular interest. This Feature Article discusses recent computational developments and discoveries by Lin and co-workers in studying the adsorption of alkanes in Brønsted acid zeolites. Their developed approach, employing configurational bias Monte Carlo with domain decomposition, with a newly parametrized molecular potential to compute the adsorption properties is first introduced. With these developments, the roles of the Si/Al ratio and Al sitting are explored and discussed. Subsequently, the Feature Article discusses the key findings obtained from a large-scale computational screening of studying more than 100 000 possible zeolite structures. The performance of identified top candidates and associated key structural features leading to desirable adsorption properties are highlighted.