Improvement of catalytic performance of MCM-22 in the cracking of n-hexane by controlling the acidic property

Modulation of Al Distribution in High-Silica ZSM-5 Zeolites for Enhancing Catalytic Performance

The spatial distribution of framework Al (AlF) has been one of the important factors that affect the catalytic properties of zeolites in diverse chemical reactions; however, the synthesis of high-silica zeolites with special AlF distribution remains a challenge. In this study, we successfully synthesized high-silica ZSM-5 zeolites with a unique AlF distribution by employing pentaerythritol (PET) as an additive in the presence of a few tetrapropylammonium hydroxide (TPAOH). The results demonstrated that the introduction of PET led to a higher proportion of Al atoms located at the sinusoidal and/or straight channels. It was observed that the addition of PET prevented the interaction between TPA+ and tetrahedral [AlO4]- during the crystallization process, resulting in enhanced availability of TPA species in the form of ion-paired TPA+. This effect leads to AlF atoms dominantly distributed away from the intersection and located in narrow channels, where acidic sites more effectively inhibit hydrogen transfer and coke formation. In the reaction of dimethyl ether (DME) to olefins, the catalyst with a unique Al distribution exhibited a significant prolonged catalytic lifetime, surpassing traditional TPA-ZSM-5 by more than 2-fold and maintaining DME conversion above 90% for a maximum of 148 h. The results of multiple pulse experiments also showed that these PET-assisted ZSM-5 zeolites significantly enhanced the selectivity of propene and butene. This approach provides an effective strategy to regulate AlF distribution in high-silica ZSM-5 catalysts with the assistance of neutral alcohol. It holds great potential for application in the synthesis of other high-silica zeolites, thereby enriching the diversity of zeolite catalysis.

Catalytic Performance of One-Pot Synthesized Fe-MWW Layered Zeolites (MCM-22, MCM-36, and ITQ-2) in Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

The application of layered zeolites of MWW topology in environmental catalysis has attracted growing attention in recent years; however, only a few studies have explored their performance in selective catalytic reduction with ammonia (NH3-SCR). Thus, our work describes, for the first time, the one-pot synthesis of Fe-modified NH3-SCR catalysts supported on MCM-22, MCM-36, and ITQ-2. The calculated chemical composition of the materials was Si/Al of 30 and 5 wt.% of Fe. The reported results indicated a correlation between the arrangement of MWW layers and the form of iron in the zeolitic structure. We have observed that one-pot synthesis resulted in high dispersion of Fe3+ sites, which significantly enhanced low-temperature activity and prevented N2O generation during the reaction. All of the investigated samples exhibited almost 100% NO conversion at 250 °C. The most satisfactory activity was exhibited by Fe-modified MCM-36, since 50% of NO reduction was obtained at 150 °C for this catalyst. This effect can be explained by the abundance of isolated Fe3+ species, which are active in low-temperature NH3-SCR. Additionally, SiO2 pillars present in MCM-36 provided an additional surface for the deposition of the active phase.

The Role of Organic and Inorganic Structure-Directing Agents in Selective Al Substitution of Zeolite

Organic and inorganic structure-directing agents (SDAs) impact Al distributions in zeolite, but the insights into how SDAs manipulate Al distribution have not been elucidated yet. Herein, the roles of different SDAs such as cyclohexylamine (CHA), hexamethylenimine (HMI), and Na⁺ in selective Al substitution of MCM-49 zeolite are investigated comprehensively by multinuclear solid-state NMR. The results demonstrate that MCM-49 synthesized with HMI shows relatively more T₆ and T₇ Al, while more T₂ Al is observed using CHA. The formation of T₂ Al in both MCM-49(HMI) and MCM-49(CHA) is derived from Na⁺, while protonated HMIs show bias in incorporation of T₆ and T₇ Al. Most HMIs are occluded in protonated status, and about half of CHAs are occluded in nonprotonated status. The close spatial proximity between nonprotonated CHAs and Na⁺ synergistically promotes the formation of zeolite structure, leading to more Na⁺ ions occluded in the zeolite channel with preferential T₂ Al substitution.

Activation and conversion of alkanes in the confined space of zeolite-type materials

Microporous zeolite-type materials, with crystalline porous structures formed by well-defined channels and cages of molecular dimensions, have been widely employed as heterogeneous catalysts since the early 1960s, due to their wide variety of framework topologies, compositional flexibility and hydrothermal stability. The possible selection of the microporous structure and of the elements located in framework and extraframework positions enables the design of highly selective catalysts with well-defined active sites of acidic, basic or redox character, opening the path to their application in a wide range of catalytic processes. This versatility and high catalytic efficiency is the key factor enabling their use in the activation and conversion of different alkanes, ranging from methane to long chain n-paraffins. Alkanes are highly stable molecules, but their abundance and low cost have been two main driving forces for the development of processes directed to their upgrading over the last 50 years. However, the availability of advanced characterization tools combined with molecular modelling has enabled a more fundamental approach to the activation and conversion of alkanes, with most of the recent research being focused on the functionalization of methane and light alkanes, where their selective transformation at reasonable conversions remains, even nowadays, an important challenge. In this review, we will cover the use of microporous zeolite-type materials as components of mono- and bifunctional catalysts in the catalytic activation and conversion of C₁⁺ alkanes under non-oxidative or oxidative conditions. In each case, the alkane activation will be approached from a fundamental perspective, with the aim of understanding, at the molecular level, the role of the active sites involved in the activation and transformation of the different molecules and the contribution of shape-selective or confinement effects imposed by the microporous structure.

Synthesis, characterization and catalytic testing of MCM-22 derived catalysts for n-hexane cracking

Layered zeolites and their delaminated structures are novel materials that enhance the catalytic performance of catalysts by addressing diffusion limitations of the reactant molecules. n-Hexane catalytic cracking was observed over MCM-22 layered zeolite and its derivative structures over the temperature range of 450–650 °C for the production of olefins. MCM-22, H-MCM-22, and ITQ-2 zeolites were prepared by the hydrothermal method. Oxalic acid was used as a dealuminating reagent to obtain H-MCM-22 with various Si/Al ratios ranging from 09–65. The prepared samples were characterized by XRD, SEM, TGA, and BET. The cracking of n-hexane was carried out by Pyro/GC–MS. It was observed that the selectivity for olefins was improved by increasing the Si/Al ratio. H-MCM-22–10% produced the highest relative olefinic concentration of 68% as compared to other dealuminated structures. Moreover, the product distribution showed that higher reaction temperature is favorable to produce more olefins. Furthermore, a comparison between ITQ-2 and MCM-22 derived structures showed that ITQ-2 is more favorable for olefins production at high temperatures. The concentration of relative olefins was increased up to 80% over ITQ-2 at 650 °C.

Catalytic Performances of Cu/MCM-22 Zeolites with Different Cu Loadings in NH3-SCR

The NH₃-SCR activities and hydrothermal stabilities of five xCu/MCM-22 zeolites with different Cu loadings (x = 2–10 wt%) prepared by incipient wetness impregnation method were systematically investigated. The physicochemical properties of xCu/MCM-22 zeolites were analyzed by XRD, nitrogen physisorption, ICP-AES, SEM, NH₃-TPD, UV-vis, H₂-TPR and XPS experiments. The Cu species existing in xCu/MCM-22 are mainly isolated Cu²⁺, CuO_x and unreducible copper species. The concentrations of both isolated Cu²⁺ and CuO_x species in xCu/MCM-22 increase with Cu contents, but the increment of CuO_x species is more distinct, especially in high Cu loadings (>4 wt%). NH₃-SCR experimental results demonstrated that the activity of xCu/MCM-22 is sensitive to Cu content at low Cu loadings (≤4 wt%). When the Cu loading exceeds 4 wt%, the NH₃-SCR activity of xCu/MCM-22 is irrelevant to Cu content due to the severe pore blockage effects caused by aggregated CuO_x species. Among the five xCu/MCM-22 zeolites, 4Cu/MCM-22 with moderate Cu content has the best NH₃-SCR performance, which displays higher than 80% NO_x conversions in a wide temperature window (160–430 °C). Furthermore, the hydrothermal aging experiments (xCu/MCM-22 was treated at 750 °C for 10 h under 10% water vapor atmosphere) illustrated that all the xCu/MCM-22 zeolites exhibit high hydrothermal stability in NH₃-SCR reactions.

Modification of MCM-22 Zeolite and Its Derivatives with Iron for the Application in N2O Decomposition

Layered 2D zeolite MCM-22 and its delaminated derivative, ITQ-2, were modified with iron, by different methods (ion-exchange and direct synthesis), and with the use of different precursors (FeSO4∙7H2O, Fe(NO3)3∙9H2O, and [Fe3(OCOCH3)7∙OH∙2H2O]NO3 oligocations. The applied modifications were aimed at optimization of iron form in the samples (aggregation, amount, location, and reducibility), in order to achieve the highest catalytic activity in the N2O decomposition. The synthesis of the samples was verified with the use of XRD (X-Ray Diffraction), N2-sorption and ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy) techniques, while the form of iron in the samples was investigated by UV–vis-DRS (UV–vis diffuse reflectance spectroscopy), H2-TPR (Hydrogen Temperature-Programmed Reduction) and HRTEM (High-Resolution Transmission Electron Microscopy). The highest activity in the N2O decomposition presented the sample Fe(O,IE)MCM-22, prepared by ion-exchange of MCM-22 with Fe3(III) oligocations. This activity was related to the oligomeric FexOy species (the main form of iron in the sample) and the higher loading of active species (in comparison to the modification with FeSO4∙7H2O).

Investigation of a Ni-Modified MCM-41 Catalyst for the Reduction of Oxygenates and Carbon Deposits during the Co-Pyrolysis of Cellulose and Polypropylene

Catalytic fast co-pyrolysis of biomass and plastic is an effective method to achieve high-quality bio-oil production. In this work, (Ni)-MCM-41 catalysts with different Ni loadings were prepared and characterized in detail by using a variety of advanced analytical techniques, and the effects on the catalytic performance were analyzed by micropyrolysis with gas chromatography mass spectrometry (Py-GC/MS) and thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) methods. The results showed that an appropriate amount of Ni addition can effectively modulate the physicochemical properties of MCM-41. For a Ni loading of 25.1 wt % (Cat-C), the catalyst showed an optimal catalytic performance, a decrease in the proportion of oxygenated compounds in the product from 35.6 (MCM-41) to 13.4%, and an increase in the relative total amount of olefins plus aromatics from 62.2 (MCM-41) to 84.6%. The excellent catalytic performance of Cat-C can be ascribed to a balancing of its proper physical structural properties, appropriate acidity, strong metal-carrier interaction, high metal dispersion, and excellent compatibility balance between active and acidic sites.

Excellent performance of one-pot synthesized Fe-containing MCM-22 zeolites for the selective catalytic reduction of NOx with NH3

One-pot synthesized OP-Fe/M22 zeolites exhibit excellent performances in NH₃-SCR reactions.

Fast and deep oxidative desulfurization of dibenzothiophene with catalysts of MoO3–TiO2@MCM-22 featuring adjustable Lewis and Brønsted acid sites

The synthesis of high-performance and recyclable catalysts for oxidative desulfurization (ODS) from fuels has been a significant challenge.

Theta-1 zeolite catalyst for increasing the yield of propene when cracking olefins and its potential integration with an olefin metathesis unit

Theta-1 zeolite with secondary mesoporosity improves propene selectivity with respect to ZSM-5 for cracking of olefins.