Molecular sieves (zeolites, mesoporous materials, hierarchic systems, two-dimensional zeolites) are important acid catalysts for transformations of biomass into required products. This article covers ...the upgrading potential of different types of biomass based on their source and discusses the reaction pathways of their transformations emphasizing the role of molecular sieve catalysts. As typical examples, catalytic pyrolysis, deoxygenation, transesterification, dehydration, isomerization, and condensation reactions were chosen. Properties and chemical/textural characteristics of the most important molecular sieve catalysts are briefly discussed and related to their catalytic behavior in biomass transformations. Finally, potential of novel molecular sieve catalysts towards biomass upgrading is highlighted and some examples of novel zeolitic materials are addressed.
The assembly–disassembly–organization–reassembly (ADOR) process has been used to disassemble a parent zeolite with the UOV structure type and then reassemble the resulting layers into a novel ...structure, IPC‐12. The structure of the material has previously been predicted computationally and confirmed in our experiments using X‐ray diffraction and atomic resolution STEM‐HAADF electron microscopy. This is the first successful application of the ADOR process to a material with porous layers.
A germane assembly: The synthesis of a new zeolite IPC‐12 using the assembly–disassembly–organization–reassembly (ADOR) transformation of a germanosilicate zeolite with the UOV topology is reported.
Carbon-templated mesoporous ZSM-5 have been synthesized by microwave irradiation. The nature of acid sites both in the micropores and on the surface of mesopores was investigated by in situ FTIR.
...Carbon-templated mesoporous ZSM-5 zeolites were synthesized directly avoiding a drying process. Carbon nanoparticles were simply mixed into synthesis precursor of ZSM-5 and hydrothermally treated by microwave irradiation. The amount of mesopores formed inside the ZSM-5 single crystals was controllable by adjusting the amount of carbon used. For comparison, mesoporous ZSM-5 zeolites have also been synthesized under hydrothermal conditions. The influence of microwave irradiation on mesoporous ZSM-5 materials was thoroughly investigated by using nitrogen adsorption/desorption studies and
27Al MAS NMR. The nature of acid sites both in the micropores (internal) and on the surface of mesopores (external) was investigated by in situ FTIR spectroscopy using pyridine (Py) and 2′,6′-di-tert-butylpyridine (DTBPy) as a probe molecules. Mesoporous ZSM-5 prepared by microwave synthesis showed higher catalytic activity in the bulky molecular reaction of 2′,4′-dimethoxyacetophenone (2′,4′-DMAP) with 4-methoxybenzaldehyde as a model reaction in comparison with the results obtained over hydrothermally prepared ZSM-5. The further catalytic behavior has been studied in condensation reaction and cracking of substituted benzene.
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Porous materials are outstanding catalysts in various reactions using confinement and shape selectivity effects. Unsurprisingly, extensive research has been conducted on zeolites, ...pillared clays, metal oxides, metal organic frameworks, and mesoporous materials. In particular, selective oxidation of hydrocarbons stands out an important class of reactions, but the ability to avoid over-oxidation remains a challenge. Thus, the present review highlights the latest findings on octahedral and tetrahedral catalytic materials in oxidation reactions, primarily focusing on types of reactive oxygen species and approaches to their investigation, on the incorporation of different heteroatoms (Ti, Sn) into silica matrices for catalytic purposes and corresponding types of reactions and on surface engineering and design of “single-site catalysts”. In addition, composite catalysts for one-pot selective oxidation reactions are reviewed, providing examples from photochemistry including “single-site photocatalysis”, electrocatalysis, and integration of metal complexes with functional solid materials. Ultimately, the end goal of this review is to discuss current state-of-the-art approaches that are being used in the area of selective catalytic oxidations with some novel porous materials. This includes methods that are being used to study mechanistic details as well as new catalysts and new substrates for such oxidations.
This contribution reports new methodology we have developed for the disassembly of 3-D UTL framework into 2-D lamellae followed by structure modification including pillaring. This may be widely ...applicable, particularly to other zeolites that have D4R units present, and so should have great impact also on other porous solids. Specifically, controlled hydrolysis of D4R units in the interlayer space provides individual ultrathin layers with UTL structure by a chemically selective method. Further manipulation of the layers gives a completely novel approach (3D to 2D to pillared) offering hitherto unprecedented opportunities for the preparation of modified zeolites with diverse chemical and structural properties.
High-silica zeolites, some of the most important and widely used catalysts in industry, have potential for application across a wide range of traditional and emerging technologies. The many ...structural topologies of zeolites have a variety of potential uses, so a strong drive to create new zeolites exists. Here, we present a protocol, the assembly-disassembly-organization-reassembly (ADOR) process, for a relatively new method of preparing these important solids. It allows the synthesis of new high-silica zeolites (Si/Al >1,000), whose synthesis is considered infeasible with traditional (solvothermal) methods, offering new topologies that may find novel applications. We show how to identify the optimal conditions (e.g., duration of reaction, temperature, acidity) for ADOR, which is a complex process with different possible outcomes. Following the protocol will allow researchers to identify the different products that are possible from a reaction without recourse to repetitive and time-consuming trial and error. In developing the protocol, germanium-containing UTL zeolites were subjected to hydrolysis conditions using both water and hydrochloric acid as media, which provides an understanding of the effects of temperature and pH on the disassembly (D) and organization (O) steps of the process that define the potential products. Samples were taken from the ongoing reaction periodically over a minimum of 8 h, and each sample was analyzed using powder X-ray diffraction to yield a time course for the reaction at each set of conditions; selected samples were analyzed using transmission electron microscopy and solid-state NMR spectroscopy.
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•Different structural types of zeolites (mostly 10-ring) were tested as additives increased VGO conversion.•Increased rate of hydrogen transfer reactions decreased the yield of ...propylene.•Maximum propylene yield of 10.9wt.%, was achieved over ferrierite.•Higher rate of cracking of iso-paraffins and olefins decreased gasoline yield.•Kinetic parameters obtained over zeolite SSZ-74 showed lower activation energy.
Catalytic cracking of vacuum gas oil (VGO) was carried out in a microactivity test (MAT) unit. Commercial FCC USY catalyst (E-Cat) is used and modified by various zeolites with different pore structures, namely SSZ-74, SSZ-33, MCM-22, MCM-36, ZSM-5, TNU-9, IM-5, and ferrierite to enhance propylene yield. Adding zeolite additives to E-Cat increased catalyst activity. The highest propylene yield of ∼11wt.% was achieved over ferrierite and MCM-36 compared with 7wt.% over E-Cat. An increase in light olefins yield over all additives was associated with a decrease in gasoline yield due to the cracking of gasoline-range reactive species (mainly olefins and iso-paraffins). Zeolite SSZ-74 showed a good enhancement in light olefins yield up to 21.3wt.% compared with 16.1wt.% over E-Cat. It is found that additives with lower ability to carry bimolecular reactions are more selective to light olefins. Gasoline quality was improved as the octane number increased over E-Cat with all additives except MCM-36.
Zeolites are often investigated as potential adsorbents for CO2 adsorption and separation. Depending on the zeolite topology and composition (Si/Al ratio and extra‐framework cations), the CO2 ...adsorption heats at low coverages vary from −20 to −60 kJ mol−1, and with increasing surface coverage adsorption heats either stay approximately constant or they quickly drop down. Experimental adsorption heats obtained for purely siliceous porous solids and for ion‐exchanged zeolites of the structural type MFI, FER, FAU, LTA, TUN, IMF, and ‐SVR are discussed in light of results of periodic density functional theory calculations corrected for the description of dispersion interactions. Key factors influencing the stability of CO2 adsorption complexes are identified and discussed at the molecular level. A general model for CO2 adsorption in zeolites and related materials is proposed and data reported in literature are evaluated with regard to the proposed model.
Adsorb or not adsorb? The role of different factors that determine the gas–solid interaction energy, such as zeolite topology and zeolite chemical composition, is analyzed based on a combination of accurate ab initio descriptions of CO2 interactions with zeolites and experimental investigations of adsorption heats (see scheme).
Sievilized chemistry: Molecular sieves are highly active and selective catalysts with industrial potential for acylation reactions. Zeolites are the catalysts of choice when shape‐selectivity ...influences the preferential formation of some products, while high conversions are achieved over mesoporous catalysts with enhanced diffusion rates of reactants and products.
Friedel–Crafts acylation reactions play an important role in the manufacture of aromatic ketones, which are used as intermediates or products in fine‐chemical synthesis. Molecular sieves are highly active and selective catalysts with industrial potential for acylation reactions. Zeolites are the catalysts of choice when shape selectivity influences the preferential formation of some products, while high conversions are achieved over mesoporous catalysts with enhanced diffusion rates of reactants and products. In this Minireview, we focus on the understanding of the relationship among the structure of molecular sieve, type and concentration of acid sites and activity/selectivity in various acylations of aromatic and olefinic hydrocarbons. The products of these acylation reactions are important compounds for the pharmaceutical industry, fragrance and flavor materials, dyes, polymers, agrochemicals, and other applications.
Sievilized chemistry: Molecular sieves are highly active and selective catalysts with industrial potential for acylation reactions. Zeolites are the catalysts of choice when shape‐selectivity influences the preferential formation of some products, while high conversions are achieved over mesoporous catalysts with enhanced diffusion rates of reactants and products.
Owing to the significant difference in the numbers of simulated and experimentally feasible zeolite structures, several alternative strategies have been developed for zeolite synthesis. Despite their ...rationality and originality, most of these techniques are based on trial-and-error, which makes it difficult to predict the structure of new materials. Assembly-Disassembly-Organization-Reassembly (ADOR) method overcoming this limitation was successfully applied to a limited number of structures with relatively stable crystalline layers (UTL, UOV, *CTH). Here, we report a straightforward, vapour-phase-transport strategy for the transformation of IWW zeolite with low-density silica layers connected by labile Ge-rich units into material with new topology. In situ XRD and XANES studies on the mechanism of IWW rearrangement reveal an unusual structural distortion-reconstruction of the framework throughout the process. Therefore, our findings provide a step forward towards engineering nanoporous materials and increasing the number of zeolites available for future applications.
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