Extra-Large Pore Titanosilicate Synthesized via Reversible 3D–2D–3D Structural Transformation as Highly Active Catalyst for Cycloalkene Epoxidation

Double Four Ring Units-Containing Zeolites: Synthesis, Structural Modification and Catalytic Applications

In zeolite frameworks, double four-ring (d4r) configurations are among the most frequent composite building units. The composition variations in d4r units greatly influence the energy and structural modifiability of the zeolitic framework. The introduction of germanium, with a larger ionic radius than silicon or aluminum, not only reduces the energy constraints of d4r in the nucleation and crystal growth of zeolites, but also opens a new window for constructing novel crystalline structures, especially with large or extra-large pores and channels. Ge-enriched d4r units endow germanosilicates with structure diversity readily for post treatments. Promising catalytic materials have been gradually developed and increasingly studied by direct synthesis or post-synthetic isomorphous substitution for Ge. This review focuses on the recent progress in the synthesis, modification, and catalytic application of d4r-containing zeolites, including germanosilicates, aluminosilicates, and silicates.

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.

OUP accepted manuscript

The rational design synthesis of zeolite catalysts with effective, environmentally benign and atom-economic routes is a major topic in the field of microporous materials, as it would avoid the high labor cost and inefficiency of traditional trial-and-error methods in developing new structures and dispel environmental concerns regarding the industrial mass production of zeolites. Catalytic applications of zeolite materials have expanded from conventional single functionalities, such as solid acids or selective oxidation catalysts to bi/multifunctionalities through combination with metals or metal oxides. This is a response to new requirements from petrochemical and fine chemical industries, such as precise control of product distribution, conversion of low-carbon resources for chemical production, and solutions to increasingly severe environmental problems related to CO₂ and NO_x. Thus, based on the systematic knowledge of zeolite chemistry and science that researchers have acquired in the past half-century and the development requirements, remarkable progress has been made in zeolite synthesis and catalysis in the past 10 years. This includes the manipulation of zeolitic monolayers derived from layered zeolites and germanosilicates to construct novel zeolite materials and effective and green zeolite syntheses as well as the synergistic interaction of zeolites and metal/metal oxides with different space distributions in the conversion of low-carbon resources. With many zeolite catalysts and catalytic processes being developed, our understanding of the close relationship between zeolite synthesis, structure and catalytic properties has deepened. Researchers are gradually approaching the goal of rationally designing zeolite catalysts with precisely controlled activity and selectivity for particular applications.

Dealumination-controlled strategy mediates Ti–Y zeolite with cooperative active sites for selective oxidations

Hierarchical Ti–Y zeolite, with dual active sites containing framework-substituted Ti and tri-coordinated Al species, was successfully constructed via a dealumination-controlled strategy, which synergistically catalyzed selective oxidations.