Alkaline modification of ZSM-5 catalysts for methanol aromatization: The effect of the alkaline concentration

Recent Progress on In Situ Catalytic Conversion Catalysts for Oil Shale

With the gradual depletion of oil resources, it is urgent to vigorously develop unconventional and renewable energy sources. As an unconventional resource with abundant resources, the rational and efficient development of oil shale is of great significance to alleviating the national energy crisis. The main methods of oil shale development are surface dry distillation and in situ transformation. In situ catalytic conversion technology, as an emerging mining method, has the potential to improve efficiency, reduce costs, and environmental impact and is an important direction for future oil shale development. As a key component in the in situ conversion process, catalysts play a crucial role in the rate, selectivity, and product quality of the reaction. However, the research on oil shale pyrolysis catalysts is still in the laboratory stage and is difficult to translate into practical applications. Therefore, this paper reviews recent progress of catalyst research in the in situ catalytic conversion of oil shale, including the types, design principles, and reaction mechanisms of catalysts, and looks forward to the future development direction. It provides a certain reference for the discovery of new catalysts that can improve yield and reduce environmental pollution in the process of oil shale extraction and also provides a valuable technical reference for the green development and utilization of unconventional and strategic alternative energy sources in the world and the transformation and sustainable development of the global energy structure.

Recent advances in bifunctional synthesis gas conversion to chemicals and fuels with a comparison to monofunctional processes

In order to meet the climate goals of the Paris Agreement and limit the potentially catastrophic consequences of climate change, we must move away from the use of fossil feedstocks for the production of chemicals and fuels. The conversion of synthesis gas (a mixture of hydrogen, carbon monoxide and/or carbon dioxide) can contribute to this. Several reactions allow to convert synthesis gas to oxygenates (such as methanol), olefins or waxes. In a consecutive step, these products can be further converted into chemicals, such as dimethyl ether, short olefins, or aromatics. Alternatively, fuels like gasoline, diesel, or kerosene can be produced. These two different steps can be combined using bifunctional catalysis for direct conversion of synthesis gas to chemicals and fuels. The synergistic effects of combining two different catalysts are discussed in terms of activity and selectivity and compared to processes based on consecutive reaction with single conversion steps. We found that bifunctional catalysis can be a strong tool for the highly selective production of dimethyl ether and gasoline with high octane numbers. In terms of selectivity bifunctional catalysis for short olefins or aromatics struggles to compete with processes consisting of single catalytic conversion steps.

Resource Utilization of Waste Cooking Oil Catalyzed by Na2CO3/ZSM-5

A catalyst with a simple synthetic process and good catalytic performance was prepared using Na2CO3 as the active component and ZSM-5 as the carrier for the resource utilization of waste cooking oil. The structure of Na2CO3/ZSM-5 was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, and the effects of parameters such as Na2CO3 loading, catalyst percentage, and reaction time on the yield of fatty acid methyl esters were investigated. The results showed that the conversion of waste cooking oil to fatty acid methyl esters yielded up to 96.89% when the Na2CO3 loading was 35%, the reaction temperature was 65 °C, the reaction time was 2 h, and the catalyst percentage was 1 wt %. The Na2CO3/ZSM-5 catalyst could be used to replace H2SO4 or NaOCH3 in the industrial treatment of waste cooking oil for its resource utilization.

Xylene and n-Hexane Adsorption Performance of a Waste Methanol-to-Propylene Catalyst under Acid-Base Treatment

Spent methanol-to-propylene (MTP) catalysts have a large specific surface area and high porosity but are usually directly disposed of in landfills, and recycling is rare. In this study, spent MTP catalyst was moderately dealuminized with acids and etched with an alkali solvent to increase its specific surface area. A novel adsorbent was obtained. XRD, SEM, FT-IR, XRD, XRF, and MAS-NMR characterization shows that the adsorbent maintains a typical ZSM-5 zeolite structure, and the dealumination effect of H2C2O4 is better than that of HCl. HCl mainly removes the framework aluminum of the molecular sieve; H2C2O4 not only removes the framework aluminum but also dissolves some of the nonframework aluminum, which increases the BET-specific surface area and pore diameter. The spent catalyst maintains an irregular ellipsoidal shape. After alkali treatment, the surface of the spherical particles becomes rough. With increasing alkali concentration, the damage degree increases. After treatment with 4 mol/L H2C2O4 and 0.1 mol/L NaOH, the p-xylene and n-hexane adsorption capacities reach the maximum, with values of 141.04 mg/g and 106.87 mg/g, respectively, 20.7% and 16.2% greater than those before treatment. These findings indicate that modified spent MTP catalyst has the potential for application in the removal of VOCs from the air.

Microwave-responsive SiC foam@zeolite core-shell structured catalyst for catalytic pyrolysis of plastics

Catalytic pyrolysis is a promising chemical recycling technology to supplement mechanical recycling since plastics can be broken down into monomers or converted to the required fuels and chemicals. In this study, a microwave (MW) -responsive SiC foam@zeoltie core-shell structured catalyst was proposed for the catalytic pyrolysis of polyolefins. Under microwave irradiation, the SiC foam core works as both microwave adsorber and catalyst support, thus concentrating the generated heat energy on the ZSM-5 zeolite shell, where the catalytic reaction takes place. SiC foam with an open cellular structure can also improve the global transport of mass and heat during plastics pyrolysis. In this work, the effects of the SiO₂/Al₂O₃ ratio and alkaline treatment of ZSM-5 zeolite coated SiC foam under MW irradiation on the variations in product distribution from low-density polyethylene (LDPE) pyrolysis were investigated at 450 °C. The results indicated that the appropriate acidity and pore structure were crucial to upgrading gas and liquid products. Particularly, the creation of a mesoporous structure in ZSM-5 zeolite via alkaline treatment could improve the diffusion of large molecules and products, thus significantly increasing the selectivity of high-valued light olefins and aromatics while inhibiting the formation of unwanted alkanes, which are expected in the chemical industry. Concretely, the concentration of olefins in gas increased to 51.0 vol% for ZSM-5(50)-0.25AT, and 65.6 vol% for ZSM-5 (50)-0.50AT, compared with 45.2 vol% for the parent ZSM-5(50). The relative concentration of aromatics in liquid decreased from 96.6% for ZSM-5(50) to 75.9% for ZSM-5(50)-0.25AT, and 71.1% for ZSM-5(50)-0.50AT. Given the respective yield of gas and liquid, the total selectivity of C2-C4 olefins and aromatics for mesoporous ZSM-5 zeolites could reach 58.6-64.9% during LDPE pyrolysis, which were higher than that for the parent ZSM-5 zeolite.

The effect of hierarchical single-crystal ZSM-5 zeolites with different Si/Al ratios on its pore structure and catalytic performance

Hierarchical single-crystal ZSM-5 zeolites with different Si/Al ratios (Hier-ZSM-5-x, where x = 50, 100, 150 and 200) were synthesized using an ordered mesoporous carbon-silica composite as hard template. Hier-ZSM-5-x exhibits improved mass transport properties, excellent mechanical and hydrothermal stability, and higher catalytic activity than commercial bulk zeolites in the benzyl alcohol self-etherification reaction. Results show that a decrease in the Si/Al ratio in hierarchical single-crystal ZSM-5 zeolites leads to a significant increase in the acidity and the density of micropores, which increases the final catalytic conversion. The effect of porous hierarchy on the diffusion of active sites and the final catalytic activity was also studied by comparing the catalytic conversion after selectively designed poisoned acid sites. These poisoned Hier-ZSM-5-x shows much higher catalytic conversion than the poisoned commercial ZSM-5 zeolite, which indicates that the numerous intracrystalline mesopores significantly reduce the diffusion path of the reactant, leading to the faster diffusion inside the zeolite to contact with the acid sites in the micropores predominating in ZSM-5 zeolites. This study can be extended to develop a series of hierarchical single-crystal zeolites with expected catalytic performance.

High-Impact Promotional Effect of Mo Impregnation on Aluminum-Rich and Alkali-Treated Hierarchical Zeolite Catalysts on Methanol Aromatization

A systematic change of HZSM-5 (HZ5) as a catalyst of the methanol to aromatics (MTA) reaction was undertaken by employing a fixed-bed tubular-type reactor under ambient pressure, applying a weight hourly space velocity (WHSV) of 2 h^-1 at 375 °C, as the first report on the application of low-Si/Al-ratio alkaline-[Mo,Na]-HZSM-5 in the MTA process. To characterize the surface and textural properties of the catalysts, powder X-ray diffraction (PXRD), nitrogen adsorption/desorption, temperature-programmed desorption of ammonia (NH₃-TPD), pyridine-infrared spectroscopy (Py-IR), thermogravimetric analysis (TGA), and energy-dispersive X-ray (EDX) methods were employed. Gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) measurements demonstrated a selectivity of up to 86 wt % (65.7 wt % for benzene, toluene, and xylene (BTX)) over 2[Mo]HZ5. NH₃-TPD and Py-IR results indicated a sensible decrease of strong acid sites on the impregnated samples, while the surface analyses revealed the highest Lewis acid sites (LAS) together with the largest mesopore surface area for 2[Mo]alk-HZ5, supporting the migration of Mo species to the bulk of the catalysts. Mo impregnation had a minor effect on the observed coke formation in the promoted catalyst.

Highly Selective Hierarchical ZnO/ZSM-5 Catalysts for Propane Aromatization

Hierarchical ZnO/ZSM-5 catalysts were prepared by desilication and impregnation with 2 wt % metallic ZnO. X-ray diffraction and Fourier transform infrared (FTIR) results showed that the structures of the hierarchical zeolites were relatively preserved despite desilication but were accompanied with sequential loss in crystallinity, likewise Bro̷nsted acidity causing decline in conversion or activity of the catalyst. However, pyridine FTIR shows enhancement of the Bro̷nsted acidic sites. Throughout the activity test, the hierarchical ZnO/ZSM-5 catalysts showed an outstanding performance within 5 h on stream with the average aromatic (benzene, toluene, and xylenes) selectivity trend, represented by their NaOH concentrations 0.3 M > 0.4 M > 0.2 M > 0.1 M corresponding to 61.0, 53.5, 40.3, and 36.8%, respectively. Their average propane conversions within the same period followed a consecutive trend 0.1 M > 0.2 M > 0.3 M > 0.4 M conforming to 34.1, 24.8, 17.3, and 10.2%, respectively. These were compared with that of the reference (ZnO/ZSM-5), which exhibited an average aromatic selectivity of 25.2% and propane conversion of 39.7%. Furthermore, the hierarchical catalyst generally displayed a low amount of C9+ heavier aromatics with the ZnO/ZSM-5(0.3 M) catalyst having the lowest C9+ selectivity of 23.7% compared to the reference catalyst with 72.7% at the same time on stream.

Optimized preparation and regeneration of MFI type base catalysts ford-glucose isomerization in water

Eco-friendly solid bases possessing hierarchical MFI structure ford-glucose isomerization tod-fructose. Optimizing catalyst synthesis and composition for enhanced stability.

Biomass-Derived Renewable Aromatics: Selective Routes and Outlook for p-Xylene Commercialisation

Methylbenzenes are among the most important organic chemicals today and, among them, p-xylene deserves particular attention because of its production volume and its application in the manufacture of polyethylene terephthalate (PET). There is great interest in producing this commodity chemical more sustainably from biomass sources, particularly driven by manufacturers willing to produce more sustainable synthetic fibres and PET bottles for beverages. A renewable source for p-xylene would allow achieving this goal with minimal disruption to existing processes for PET production. Despite the fact that recently some routes to renewable p-xylene have been identified, there is no clear consensus on their feasibility or implications. We have critically reviewed the current state-of-the-art with focus on catalytic routes and possible outlook for commercialisation. Pathways to obtain p-xylene from a biomass-derived route include methanol-to-aromatics (MTA), ethanol dehydration, ethylene dimerization, furan cycloaddition or catalytic fast pyrolysis and hydrotreating of lignin. Some of the processes identified suggest near-future possibilities, but also more speculative or longer-term sources for synthesis of p-xylene are highlighted.