Conversion of ethanol to hydrocarbons on hierarchical HZSM-5 zeolites

Benzenoid Aromatics from Renewable Resources

In this Review, all known chemical methods for the conversion of renewable resources into benzenoid aromatics are summarized. The raw materials that were taken into consideration are CO2; lignocellulose and its constituents cellulose, hemicellulose, and lignin; carbohydrates, mostly glucose, fructose, and xylose; chitin; fats and oils; terpenes; and materials that are easily obtained via fermentation, such as biogas, bioethanol, acetone, and many more. There are roughly two directions. One much used method is catalytic fast pyrolysis carried out at high temperatures (between 300 and 700 °C depending on the raw material), which leads to the formation of biochar; gases, such as CO, CO2, H2, and CH4; and an oil which is a mixture of hydrocarbons, mostly aromatics. The carbon selectivities of this method can be reasonably high when defined small molecules such as methanol or hexane are used but are rather low when highly oxygenated compounds such as lignocellulose are used. The other direction is largely based on the multistep conversion of platform chemicals obtained from lignocellulose, cellulose, or sugars and a limited number of fats and terpenes. Much research has focused on furan compounds such as furfural, 5-hydroxymethylfurfural, and 5-chloromethylfurfural. The conversion of lignocellulose to xylene via 5-chloromethylfurfural and dimethylfuran has led to the construction of two large-scale plants, one of which has been operational since 2023.

One-Step Conversion of n-Butanol to Aromatics-free Gasoline over the HZSM-5 Catalyst: Effect of Pressure, Catalyst Deactivation, and Fuel Properties as a Gasoline

Sustainable production of gasoline-range hydrocarbon fuels from biomass is critical in evading the upgradation of combustion engine infrastructures. The present work focuses on the selective transformation of n-butanol to gasoline-range hydrocarbons free from aromatics in a single step. Conversion of n-butanol was carried out in a down-flow fixed-bed reactor with the capability to operate at high pressures using the HZSM-5 catalyst. The selective transformation of n-butanol was carried out for a wide range of temperatures (523-563 K), pressures (1-40 bar), and weight hourly space velocities (0.75-14.96 h-1) to obtain the optimum operating conditions for the maximum yields of gasoline range (C5-C12) hydrocarbons. A C5-C12 hydrocarbons selectivity of ∼80% was achieved, with ∼11% and 9% selectivity to C3-C4 paraffin and C3-C4 olefins, respectively, under optimum operating conditions of 543 K, 0.75 h-1, and 20 bar. The hydrocarbon (C5-C12) product mixture was free from aromatics and primarily olefinic in nature. The distribution of these C5-C12 hydrocarbons depends strongly on the reaction pressure, temperature, and WHSV. These olefins were further hydrogenated to paraffins using a Ni/SiO2 catalyst. The fuel properties and distillation characteristics of virgin and hydrogenated hydrocarbons were evaluated and compared with those of gasoline to understand their suitability as a transportation fuel in an unmodified combustion engine. The present work further delineates the catalyst stability study for a long time-on-stream (TOS) and extensive characterization of spent catalysts to understand the nature of catalyst deactivation.

Bioethanol Upgrading to Renewable Monomers Using Hierarchical Zeolites: Catalyst Preparation, Characterization, and Catalytic Studies

Bioethanol is one of the most promising renewable resources for the production of important monomers. To date, there have been various processes proposed for bioethanol conversion to renewable monomers. In this review, the catalytic bioethanol upgrading to various types of monomers using hierarchical zeolites as catalysts is illustrated, including the recent design and preparation of hierarchical zeolites for these catalytic processes. The characterizations of catalysts including textural properties, pore architectures, acidic properties, and active species are also exemplified. Moreover, the catalytic studies with various processes of monomer production from bioethanol including bioethanol dehydration, bioethanol to hydrocarbons, and bioethanol to butadiene are revealed in terms of catalytic activities and mechanistic studies. In addition, the future perspectives of these catalytic circumstances are proposed in both economic and sustainable development contexts.

Comparison of catalytic effect on upgrading bio-oil derived from co-pyrolysis of water hyacinth and scrap tire over multilamellar MFI nanosheets and HZSM-5

Catalytic co-pyrolysis of water hyacinth and scrap tire experiments were performed to evaluate the feasibility of improving the monocyclic aromatic hydrocarbons production. The production of monocyclic aromatic hydrocarbons increased from 5.31% (sole pyrolysis of water hyacinth) to 13.11% (co-pyrolysis with scrap tire). With use of zeolites, the highest production of monocyclic aromatic hydrocarbons can reach up to 69.18%. Comprehensive comparison on catalytic effects of HZSM-5 and multilamellar MFI nanosheets were provided. With the material to multilamellar MFI nanosheets ratios changes from 2:1 to 1:4, the production of monocyclic aromatic hydrocarbons increases significantly from 37.15-69.18%. The average production of monocyclic aromatic hydrocarbons produced by using multilamellar MFI nanosheets were 12.07% higher than that using HZSM-5, indicating the better performance of multilamellar MFI nanosheets in producing monocyclic aromatic hydrocarbons. This work provided a reference for the reuse of water hyacinth and scrap tire over multilamellar MFI nanosheets in energy field.

Methanol, ethanol, propanol, and butanol adsorption on H-ZSM-5 zeolite: an ONIOM study

The search for renewable raw materials less harmful to the environment, such as methanol, ethanol, 1-propanol, and 1-butanol has become attractive. These products are obtained more rapidly and efficiently by specific solid catalysts, mainly the zeolites. The Brønsted acid sites distributed over the sinusoidal and the straight channels are important for the alcohol dehydration reaction that produces widely used chemicals. Therefore, the ONIOM method was used to study methanol, ethanol, propanol, and butanol adsorption in H-ZSM-5 zeolite. PM6 and DFT levels were used for the high layer ONIOM, while the low layer was calculated using the UFF force field. DFT was calculated using the B3LYP global hybrid GGA, M06-2X hybrid meta-GGA, and the hybrid range separated ωB97X-D functionals at 6-31+G(d) basis set. The high layer ONIOM was completely relaxed. The binding energy shows dependence on the relaxed tetrahedra and position of acid site. The Si/Al ratio was also studied. Graphical Abstract HOMO orbital of adsorbed alcohols showing the main contribution of zeolite for small alcohols.

In Situ Fabrication of Hierarchical MTW Zeolite via Nanoparticle Assembly by a Tailored Simple Organic Molecule

Amphiphilic surfactants are widely used as templates to synthesize hierarchically structured zeolites due to their multiple functions; however, piloting such new dual-functional templates is limited by their time-consuming nature and high cost. Herein, a simple organic molecule, without a long hydrophobic alkyl chain, was tailored from a gemini-type, poly-quaternary ammonium surfactant, and effectively used as a dual-porogenic template to synthesize hierarchical MTW zeolite. Upon a range of synthesis parameter optimizations, our detailed characterization suggested that the hierarchical MTW zeolite would completely crystallize within 36 hours from the surface to the inside of quasi-spherical particles through in situ consumption of amorphous silicon and aluminum species; much faster than most of the hierarchical MTW zeolites generated by conventional methods. Moreover, the as-prepared hierarchical MTW zeolite exhibited 4 times higher catalytic performance and lifetime of benzene-propene alkylation compared to conventional MTW zeolite, while the introduced crystalline mesopores are of benefit to diffuse reactants, products, and coke depositions. Our strategy broadens the design of new templates in more effective ways to facilely synthesize versatile hierarchical zeolites for diverse applications, especially for those in which macromolecules are involved.

Catalytic test reactions for the evaluation of hierarchical zeolites

Hierarchical zeolites have received increasing attention in the last decade due to their outstanding catalytic performance. Several types of hierarchical zeolites can be prepared by a large number of different techniques. Hierarchical zeolites combine the intrinsic catalytic properties of conventional zeolites and the facilitated access and transport in the additional meso- or macropore system. In this tutorial review, we discuss several test reactions that have been explored to show the benefit of the hierarchical pore system with respect to their suitability to prove the positive effects of hierarchical porous zeolites. It is important to note that positive effects on activity, stability and less frequently selectivity observed for hierarchically structured catalysts not necessarily are only a consequence of the additional meso- or macropores but also the number, strength and location of active sites as well as defects and impurities. With regard to these aspects, the test reaction has to be chosen carefully and potential changes in the chemistry of the catalyst have to be considered as well. In addition to the determination of conversion, yield and selectivity, we will show that the calculation of the activation energy and the determination of the Thiele modulus and the effectiveness factor are good indicators of the presence or absence of diffusion limitations in hierarchical zeolites compared to their parent materials.

Discerning the Location and Nature of Coke Deposition from Surface to Bulk of Spent Zeolite Catalysts

The formation of carbonaceous deposits (coke) in zeolite pores during catalysis leads to temporary deactivation of catalyst, necessitating regeneration steps, affecting throughput, and resulting in partial permanent loss of catalytic efficiency. Yet, even to date, the coke molecule distribution is quite challenging to study with high spatial resolution from surface to bulk of the catalyst particles at a single particle level. To address this challenge we investigated the coke molecules in HZSM-5 catalyst after ethanol conversion treatment by a combination of C K-edge X-ray absorption spectroscopy (XAS), ¹³C Cross polarization-magic angle spinning nuclear magnetic resonance (CP-MAS NMR) spectroscopy, and atom probe tomography (APT). XAS and NMR highlighted the aromatic character of coke molecules. APT permitted the imaging of the spatial distribution of hydrocarbon molecules located within the pores of spent HZSM-5 catalyst from surface to bulk at a single particle level. ²⁷Al NMR results and APT results indicated association of coke molecules with Al enriched regions within the spent HZSM-5 catalyst particles. The experimental results were additionally validated by a level-set–based APT field evaporation model. These results provide a new approach to investigate catalytic deactivation due to hydrocarbon coking or poisoning of zeolites at an unprecedented spatial resolution.

Heterobimetallic Zeolite, InV-ZSM-5, Enables Efficient Conversion of Biomass Derived Ethanol to Renewable Hydrocarbons

Direct catalytic conversion of ethanol to hydrocarbon blend-stock can increase biofuels use in current vehicles beyond the ethanol blend-wall of 10–15%. Literature reports describe quantitative conversion of ethanol over zeolite catalysts but high C₂ hydrocarbon formation renders this approach unsuitable for commercialization. Furthermore, the prior mechanistic studies suggested that ethanol conversion involves endothermic dehydration step. Here, we report the complete conversion of ethanol to hydrocarbons over InV-ZSM-5 without added hydrogen and which produces lower C₂ (<13%) as compared to that over H-ZSM-5. Experiments with C₂H₅OD and in situ DRIFT suggest that most of the products come from the hydrocarbon pool type mechanism and dehydration step is not necessary. Thus, our method of direct conversion of ethanol offers a pathway to produce suitable hydrocarbon blend-stock that may be blended at a refinery to produce fuels such as gasoline, diesel, JP-8, and jet fuel, or produce commodity chemicals such as BTX.