CrHZSM-5 Zeolites – Highly Efficient Catalysts for Catalytic Cracking of Isobutane to Produce Light Olefins

Cr- and Ga-Modified ZSM-5 Catalyst for the Production of Renewable BTX from Bioethanol

Light aromatics (benzene, toluene, and xylene, collectively known as BTX) are essential commodity chemicals in the petrochemical industry. The present study examines the aromatization of bioethanol with Cr- and Ga-modified ZSM-5. Both Cr and Ga were incorporated by the ion-exchange method. Cr-modified ZSM-5 outperforms the Ga-modified ZSM-5 and H-ZSM-5 catalysts. Cr-H-ZSM-5 almost doubled the carbon yield of aromatics compared to H-ZSM-5 at an optimum reaction temperature of 450 °C. Cr-H-ZSM-5 produced aromatics with a yield of ~40 %. The effect of dilution in feed on BTX production is also studied. Cr-H-ZSM-5 was found to be more active than H-ZSM-5. Complete ethanol conversion was obtained with both pure and dilute bioethanol. The Bronsted-Lewis acid (BLA) pair formed after metal incorporation is responsible for dehydrogenation followed by aromatization, leading to increased aromatic production.

Synergetic Regulation of the Microstructure and Acidity of HZSM-5/MCM-41 for Efficient Catalytic Cracking of n-Decane

Alkane catalytic cracking is regarded as one of the most significant processes for light olefin production; however, it suffers from serve catalyst deactivation due to coke formation. Herein, HZSM-5/MCM-41 composites with different Si/Al₂ ratios were first prepared by the hydrothermal method. The physicochemical properties of the prepared catalysts were analyzed by a series of bulk and surface characterization methods, and the catalytic performance was tested in n-decane catalytic cracking. It was found that HZSM-5/MCM-41 showed a higher selectivity to light olefins and a lower deactivation rate compared with the parent HZSM-5 due to an enhanced diffusion rate and decreased acid density. Moreover, the structure-reactivity relationship revealed that conversion, light olefin selectivity, and the deactivation rate strongly depended on the total acid density. Furthermore, HZSM-5/MCM-41 was further extruded with γ-Al₂O₃ to obtain the catalyst pellet, which showed an even higher selectivity to light olefins (∼48%) resulting from the synergy effect of the fast diffusion rate and passivation of external acid density.

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.

Direct Ink Writing of Metal Oxide/H-ZSM-5 Catalysts for n-Hexane Cracking: A New Method of Additive Manufacturing with High Metal Oxide Loading

Previously, 3D printing of porous materials and metal oxides was limited to low loading metal loadings, as increasing the nitrate salt concentrations, which are used to generate the oxide component, gave rise to poor rheological properties beyond 10 wt %. In this study, we addressed this problem by directly printing insoluble oxides alongside H-ZSM-5 zeolite, which allowed for increased oxide loadings. Various metal oxides such as V₂O₅, ZrO₂, Cr₂O₃, and Ga₂O₃ were doped onto H-ZSM-5 through the additive manufacturing method. Characterization and correlation between the X-ray diffraction, NH₃-temperature-programmed desorption, O₂-temperature programmed oxidation, temperature-programmed reduction, scanning electron microscopy-energy dispersive spectroscopy, and in situ CO₂ DRIFTS experiments revealed that directly 3D printing metal oxides/H-ZSM-5 inks leads to significant modification in the surface properties and oxide bulk dispersion, thereby enhancing the composites' reducibility and giving rise to widely differing product distributions in n-hexane cracking reaction. The obtained metal oxide/zeolite structured materials were used as bifunctional structured catalysts for the selective formation of light olefins from hexane at 550-600 °C and GHSV = 9000 mL/g_catalst·h in a packed-bed reactor. Among the various compositions of metal oxides/H-ZSM-5 examined (i.e., 15 wt % Ga₂O₃, 15 wt % ZrO₂, 15 wt % V₂O₅, 15 wt % Cr₂O₃, or 5 wt % Cr/10 wt % ZrO₂/10 wt % V₂O₅/10 wt % Ga₂O₃ balanced with H-ZSM-5), the 15 wt % Cr/ZSM-5 monolith displayed the best n-hexane cracking performance, as it achieved 80-85% conversion of hexane with a 40% selectivity toward propylene, 30% selectivity toward ethylene, and 10% selectivity toward butene at 550 °C. The sample also showed zero benzene/toluene/xylene selectivity and no deactivation after 6 h. This study represents a proof-of-concept for tailoring customizable heterogeneous structured catalysts by directly 3D printing high loading of metal oxides/porous zeolite and is a breakthrough in material science.

Creation of CuOx/ZSM-5 zeolite complex: healing defect sites and boosting acidic stability and catalytic activity

CuO_x/ZSM-5 was achieved by hydrothermally disintegrating CuO nanoparticle into zeolite. Further studies proved that stable clusters formed and connected with internal silanol, which leads to optimal acidity and high stability in hexane cracking.

Comparison and assessment of zeolite catalysts performance dimethyl ether and light olefins production through methanol: a review

The present review focuses on a comparison and assessment of zeolite catalyst performance of dimethyl ether and light olefin production through methanol. Dimethyl ether is a clean fuel which needs diverse processes to be produced. Methanol to dimethyl ether is a very novel process which offers considerable advantages versus additional processes for the production of dimethyl ether. The corresponding fixed-bed reactors compose the most important section of such a process. Production of dimethyl ether by the mentioned process is of high importance since it can be catalytically transferred to a substance with the value of propylene. Furthermore, in case of capability to transfer low-purity methanol into dimethyl ether, less expensive methanol can be consequently achieved with higher value added. In the petrochemical industry, light olefins, for example, ethylene and propylene, can be used as raw materials for the production of polyolefin. The present review aims to produce dimethyl ether in order to reach olefin substances, initially conducting a compressive assessment on production methods of olefin substances.

Heterogeneous catalysts for gas-phase conversion of ethylene to higher olefins

The reduced availability of propylene and C4 products from steam crackers continues to provoke on-purpose technologies for light olefins such that almost 30% of propylene in 2025 is predicted to be supplied from unconventional sources. Furthermore, the recent discoveries of natural gas reservoirs have urged interest in the conversion of surplus alkanes and alkenes, especially ethane and ethylene. The direct conversion of ethylene to propylene or a combination of value-added chemicals, including butylenes and oligomers in the range of gasoline and diesel fuel, provides the capability of responding to the fluctuations in the balance between supply and demand of the main petrochemicals. A comprehensive review of heterogeneous catalysts for the gas-phase conversion pathways is presented here in terms of catalytic performances (ethylene conversion and product selectivities), productivities, lifetimes, active sites, physicochemical properties, mechanisms, influence of operating conditions, deactivation and some unresolved/less-advanced aspects of the field. The addressed catalysts cover both zeolitic materials and transition metals, such as tungsten, molybdenum, rhenium and nickel. Efforts in both experimental and theoretical studies are taken into account. Aside from the potential fields of progress, the review reveals very promising performances for the emerging technologies to produce propylene, a mixture of propylene and butenes, or a liquid fuel from ethylene.

Crude oil to chemicals: light olefins from crude oil

The possibility to fulfill the increasing market demand and producers' needs in processing straightforwardly crude oil, a cheap and universally available feedstock, to produce petrochemicals appears to be a very attractive strategy.