Two-dimensional zeolites in catalysis: current state-of-the-art and perspectives

Synthesis and Catalytic Applications of Advanced Sn- and Zr-Zeolites Materials

The incorporation of isolated Sn (IV) and Zr (IV) ions into silica frameworks is attracting widespread attention, which exhibits remarkable catalytic performance (conversion, selectivity, and stability) in a broad range of reactions, especially in the field of biomass catalytic conversion. As a representative example, the conversion route of carbohydrates into valuable platform and commodity chemicals such as lactic acid and alkyl lactates, has already been established. The zeotype materials also possess water-tolerant ability and are capable to be served as promising heterogeneous catalysts for aqueous reactions. Therefore, dozens of Sn- and Zr-containing silica materials with various channel systems have been prepared successfully in the past decades, containing 8 membered rings (MR) small pore CHA zeolite, 10-MR medium pore zeolites (FER, MCM-56, MEL, MFI, MWW), 12-MR large pore zeolites (Beta, BEC, FAU, MOR, MSE, MTW), and 14-MR extra-large pore UTL zeolite. This review about Sn- and Zr-containing metallosilicate materials focuses on their synthesis strategy, catalytic applications for diverse reactions, and the effect of zeolite characteristics on their catalytic performances.

Surface Modification of Synthetic Zeolites with Ca and HDTMA Compounds with Determination of Their Phytoavailability and Comparison of CEC and AEC Parameters

Zeolites obtained from fly ash are characterized by very good anion- and cation-exchange properties and a developed porous structure. This paper presents the results of surface modification studies of synthetic zeolites obtained from calcined coal shale (clay materials). Calcium compounds and hexadecyltrimethylammonium bromide (HDTMA) were used as modifying substances. The characteristics of the raw material and the zeolite obtained as a result of its synthesis are presented. The surface modification method is described. Furthermore, the results of sorption and desorption of NO₃, PO₄, and SO₄ from raw and modified samples are presented. The results of anion- and cation-exchange capacities for other zeolite types were also compared. Modification of the materials with Ca ions and HDTMA surfactant only improved the sorption of sulfates. The 90% desorption of nitrates, phosphates, and sulphates from the zeolite material without modification indicates a good release capacity of these compounds and their potential use as fertilizer additives.

A Review on the Effects of Organic Structure-Directing Agents on the Hydrothermal Synthesis and Physicochemical Properties of Zeolites

The study on the synthesis of zeolites, including both the development of novel techniques of synthesis and the discovery of new zeolitic frameworks, has a background of several decades. In this context, the application of organic structure-directing agents (SDAs) is one of the key factors having an important role in the formation of porous zeolitic networks as well as the crystallization process of zeolites. There are various elements that are needed to be explored for elucidating the effects of organic SDAs on the final physicochemical properties of zeolites. Although SDAs were firstly used as pore generators in the synthesis of high-silica zeolites, further studies proved their multiple roles during the synthesis of zeolites, such as their influences on the crystallization evolution of zeolite, the size of the crystal and the chemical composition, which is beyond their porogen properties. The aim of this mini review is to present and briefly summarize these features as well as the advances in the synthesis of new SDAs during the last decades.

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.