Enhanced Selectivity and Stability of Finned Ferrierite Catalysts in Butene Isomerization

Amino-Acid-Assisted Synthesis of Hollow Hierarchical FER Zeolite with Improved Catalytic Performance

Hierarchical zeolites are highly-desired catalysts in the petrochemical industry due to their shorter diffusion length, faster diffusion rate, and better accessibility to active acid sites compared with conventional zeolites. Herein, we report a simple amino-acid-assisted method to synthesize urchin-like hollow hierarchical FER zeolites with abundant mesopores and macroporous inner cavities. An amino acid (i. e. L-lysine) is used to facilitate the agglomeration of primary gel nanoparticles. The preferential nucleation and crystal growth at the external surfaces together with the lagged crystallization of the inner core of the agglomerates results in the formation of hollow inner cavities after the exhaustion of interior materials. Thanks to the unique hierarchical structure and more accessible acid sites, the hollow hierarchical FER zeolite exhibits improved catalytic performance over the conventional one in the skeletal isomerization of 1-butene to isobutene.

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

Metal substitution of molecular sieve systems is a major driving force in developing novel catalytic processes to meet current demands of green chemistry concepts and to achieve sustainability in the chemical industry and in other aspects of our everyday life. The advantages of metal-substituted molecular sieves include high surface areas, molecular sieving effects, confinement effects, and active site and morphology variability and stability. The present review aims to comprehensively and critically assess recent advances in the area of tetra- (Ti, Sn, Zr, Hf) and pentavalent (V, Nb, Ta) metal-substituted molecular sieves, which are mainly characterized for their Lewis acidic active sites. Metal oxide molecular sieve materials with properties similar to those of zeolites and siliceous molecular sieve systems are also discussed, in addition to relevant studies on metal-organic frameworks (MOFs) and some composite MOF systems. In particular, this review focuses on (i) synthesis aspects determining active site accessibility and local environment; (ii) advances in active site characterization and, importantly, quantification; (iii) selective redox and isomerization reaction applications; and (iv) photoelectrocatalytic applications.

Influence of the Synthesis Protocol on the Catalytic Performance of PHI-Type Zeolites for the Dehydration of Lactic Acid

Acrylic acid is an important basic chemical and a key starting compound for a variety of consumer products. Today, acrylic acid is still produced from fossil-based propene. If acrylic acid were produced from bio-based lactic acid, this would be an important step towards sustainability. The gas-phase dehydration reaction of lactic acid to acrylic acid was performed over eight-membered ring PHI-type zeolites in the Na+ and K+-form. A few variations in the synthesis procedure of PHI-type zeolite made a big difference in the performance during the catalytic reaction due to differences in the physical and chemical properties, especially the accessibility of the pores. The catalysts were characterized with ICP-OES, XRD, CO2 physisorption, SEM and 27Al MAS NMR. The calcination resulted in a partial collapse of the PHI structure. In the case of Na,K-PHI with a low surface area, the catalysis tends to take place on the outer surface, while in the case of Na,K-PHI with a high surface area the catalysis can also take place within the pore system. This has a considerable influence on the selectivity of the catalysts.

Tracking Structural Deactivation of H-Ferrierite Zeolite Catalyst During MTH with XRD

We used the methanol-to-hydrocarbon (MTH) reaction as a shape-selective model reaction to investigate coke formation in zeolite H-Ferrierite. Despite being a 2D topology in terms of channel propagation, the FER framework displays a lattice expansion in all three dimensions of space upon deactivation. Therefore, the volume of the unit cell is an excellent X-Ray diffraction (XRD) descriptor for the catalyst deactivation. A model with dummy atoms added, also proved to be an accurate approach to measure the amount of internal coke and/or water inside the pore network correlated with thermogravimetric analysis results. While the catalyst deactivation of the H-Ferrerite during the MTH was fast, a comparably long induction period was observed. We were able to track such fast deactivation with the aforementioned descriptors by means of an operando XRD study by a standard laboratory diffractometer.

Metal Sites in Zeolites: Synthesis, Characterization, and Catalysis

Zeolites with ordered microporous systems, distinct framework topologies, good spatial nanoconfinement effects, and superior (hydro)thermal stability are an ideal scaffold for planting diverse active metal species, including single sites, clusters, and nanoparticles in the framework and framework-associated sites and extra-framework positions, thus affording the metal-in-zeolite catalysts outstanding activity, unique shape selectivity, and enhanced stability and recyclability in the processes of Brønsted acid-, Lewis acid-, and extra-framework metal-catalyzed reactions. Especially, thanks to the advances in zeolite synthesis and characterization techniques in recent years, zeolite-confined extra-framework metal catalysts (denoted as metal@zeolite composites) have experienced rapid development in heterogeneous catalysis, owing to the combination of the merits of both active metal sites and zeolite intrinsic properties. In this review, we will present the recent developments of synthesis strategies for incorporating and tailoring of active metal sites in zeolites and advanced characterization techniques for identification of the location, distribution, and coordination environment of metal species in zeolites. Furthermore, the catalytic applications of metal-in-zeolite catalysts are demonstrated, with an emphasis on the metal@zeolite composites in hydrogenation, dehydrogenation, and oxidation reactions. Finally, we point out the current challenges and future perspectives on precise synthesis, atomic level identification, and practical application of the metal-in-zeolite catalyst system.