Key Takeaways & Executive Findings
- •• • Phosphorus and tungsten co-modified ZSM-5 achieved the highest ethylene yield, with L acid amount of 18.3 μmol/g, strong Brønsted acid amount of 31.3 μmol/g, and L_T/B_T ratio of 0.37, demonstrating an optimal balance for mild dehydrogenation and cracking. • • An excessively high L/B acid ratio (e.g., >0.37) promotes hydrogen and coke formation, leading to pore blockage and reduced conversion, thereby lowering ethylene and propylene yields; this underscores the need for precise acid-site engineering. • • Reactant conversion follows the order n-heptane > 3-methylhexane > methylcyclohexane, correlating with molecular size and diffusional constraints in ZSM-5 micropores; efficient conversion of branched and cyclic C7 hydrocarbons requires high specific surface area and micropore surface area. • • Modification with phosphorus and transition metals (except Cu and La) increased total Brønsted acid amount, while L acid sites were predominantly weak; this tunability allows optimization of dehydrogenation versus cracking pathways for enhanced light olefin production.
Abstract
Phosphorus and transition metal-modified ZSM-5 zeolites were prepared via incipient wetness impregnation and characterized by XRD, N2 adsorption-desorption, and pyridine-IR spectroscopy. The effects of modified zeolites on catalytic pyrolysis of n-heptane, 3-methylhexane, and methylcyclohexane were systematically investigated, revealing the structure-activity relationship between acid properties and catalytic performance. Results indicate that phosphorus and transition metal modification can regulate the L/B acid ratio of ZSM-5, which significantly influences product distribution. An excessively high L/B acid ratio promotes hydrogen and coke formation, leading to pore blockage and reduced conversion, whereas an appropriate L/B acid ratio facilitates mild dehydrogenation, enhancing ethylene and propylene yields. Reactant conversion followed the order: n-heptane > 3-methylhexane > methylcyclohexane. Efficient conversion of 3-methylhexane and methylcyclohexane requires catalysts with high L acid amount, strong Brønsted acid amount, optimized L/B acid ratio, as well as high specific surface area and micropore specific surface area. This study provides critical insights for designing high-efficiency alkane pyrolysis catalysts.
1. Introduction
Steam cracking of naphtha remains the dominant route for ethylene and propylene production, but its high energy intensity (operating temperatures of 800–850 °C) and substantial CO2 emissions have driven interest in catalytic cracking alternatives that operate at lower temperatures (~675 °C). However, conventional ZSM-5 catalysts suffer from rapid deactivation due to coke deposition and insufficient selectivity to light olefins when processing complex naphtha fractions rich in C6–C10 alkanes and cycloalkanes. The challenge lies in tailoring the acid site distribution—specifically the ratio of Lewis (L) to Brønsted (B) acid sites—to promote desired dehydrogenation and cracking reactions while suppressing hydrogen transfer and coke formation.
This study addresses this bottleneck by systematically modifying ZSM-5 with phosphorus and various transition metals (e.g., W, Cu, La) via incipient wetness impregnation. The authors demonstrate that such dual modification allows precise control over the L/B acid ratio, which critically influences product yields. By correlating acid properties with catalytic performance for three C7 hydrocarbons of different structures (n-heptane, 3-methylhexane, methylcyclohexane), they identify optimal catalyst formulations that maximize ethylene and propylene yields. The findings provide a rational basis for designing next-generation naphtha catalytic cracking catalysts with enhanced selectivity and stability.
Loading authentic research manuscript (Pages 1–5)...
HOU Kaijun, LIU Meijia, WANG Zhifeng, CAI Jinjun, GUO Rong, GAO Jinsen, WANG Gang, MA An (2026). Effect of Phosphorus and Transition Metal-Modified ZSM-5 on Catalytic Pyrolysis of C7 Hydrocarbons with Different Structures. Journal of Fuel Chemistry and Technology. https://doi.org/10.3724/2097-213X.2026.JFCT.0003
Research & Educational Purpose Only: The translations, structured abstracts, analytical annotations, and data reports provided by SinoGreenTechare intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoGreenTech claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the optimal L/B acid ratio for maximizing ethylene yield in catalytic cracking of C7 hydrocarbons?
The optimal L_T/B_T ratio was found to be 0.37, achieved with phosphorus and tungsten co-modified ZSM-5, which exhibited the highest ethylene yield. This ratio balances mild dehydrogenation (promoted by L acid sites) with cracking activity (from strong B acid sites), minimizing hydrogen and coke formation.
How does the molecular structure of C7 hydrocarbons affect their conversion over modified ZSM-5?
Conversion decreases in the order n-heptane > 3-methylhexane > methylcyclohexane, attributed to increasing molecular size and diffusional limitations in ZSM-5 micropores. Branched and cyclic hydrocarbons require catalysts with higher specific surface area and micropore surface area to achieve efficient conversion.
What are the deactivation mechanisms when L acid sites are excessive?
Excessive L acid sites promote dehydrogenation and hydrogen transfer reactions, leading to increased hydrogen and coke formation. Coke deposits block zeolite pores, reducing accessibility to active sites and causing a decline in conversion and light olefin yields.
Can phosphorus and transition metal modification improve hydrothermal stability of ZSM-5?
While this study focuses on catalytic performance, phosphorus modification is known to enhance hydrothermal stability by preventing dealumination. The combination with transition metals may further stabilize the framework, though stability tests under steam conditions are not reported here.
What are the implications for industrial naphtha catalytic cracking processes?
The findings suggest that tailored ZSM-5 catalysts with optimized L/B acid ratios can operate at lower temperatures (~675 °C) compared to steam cracking, offering energy savings and reduced CO2 emissions. The identification of phosphorus-tungsten modified ZSM-5 as a promising candidate provides a basis for pilot-scale testing and process development.
Related Chinese Research & Cross-Citations
Recent Advances in Carbon-Based Materials for CO2 Capture and Utilization
CO2 capture and utilization (CCU) technologies are critical for mitigating global warming and promoting resource circularity. Carbon-based materials, with tunable pore structures, abundant active sites, high specific surface area, and excellent chemical stability, show significant potential for CO2 capture and conversion. This review systematically analyzes the adsorption behaviors and performance variations of activated carbon, porous carbon, graphene, and carbon nanotubes in CO2 capture. For utilization, recent advances in catalytic applications for methanation, reverse water-gas shift (RWGS), dry reforming of methane (DRM), and alcohol synthesis are emphasized. The benefits and drawbacks of carbon materials regarding adsorption capacity, catalytic activity, and stability are evaluated, and their potential in integrated CCU technologies is discussed. Key strategies for enhancing performance through structural modulation and surface modification are elucidated. This review provides theoretical guidance for future development and large-scale implementation of carbon-based materials in CCU.
Fabrication and Microwave Absorption Performance of FexOy/TiO2/C Composites Derived from Red Mud
Red mud, an industrial solid waste from alumina production, poses severe environmental challenges. This study presents a resource-efficient strategy to convert red mud into high-performance microwave absorbing materials. FexOy/TiO2/C composites were synthesized via a sol-gel method using starch as carbon source, followed by carbothermal reduction. The phase composition and microstructure were optimized by adjusting calcination temperature and raw material ratio. The optimal sample, RmCT-5.4-700, exhibited a minimum reflection loss (RLmin) of -30.2 dB at 14.0 GHz with an effective absorption bandwidth (EAB) of 5.3 GHz at a coating thickness of 2.0 mm. The superior absorption performance is attributed to the synergistic effects of dielectric components (TiO2, graphitized carbon) and magnetic components (Fe3O4/Fe). Carbothermal reduction introduces defects that induce dipole polarization, while the conductive network formed by graphitized carbon and Fe3O4/Fe particles enhances conductive loss. Heterogeneous interfaces between Fe3O4, Fe, TiO2, and the red mud matrix promote interfacial polarization. The magnetic loss of Fe3O4/Fe improves impedance matching, facilitating electromagnetic wave penetration and absorption. This work not only provides a novel route for red mud valorization but also contributes to the high-value utilization of solid wastes.
Damage Mechanism of High Chromia Refractory in the Slag Tapping Hole of Commercial Entrained-Flow Gasifiers
The service life of refractory bricks in the slag tapping hole of entrained-flow gasifiers is a critical bottleneck for long-term stable operation. This study investigated the damage mechanism of high chromia refractories in four commercial coal-water slurry gasifiers by analyzing gasification coal samples and corroded refractory bricks. Slag characteristics, including crystallization and viscosity-temperature behavior, were evaluated. Results revealed that low-viscosity slag induces more severe refractory damage. To mitigate slag crystallization risk, a safe slag tapping temperature range is recommended as tICT−t2.5 when tICT exceeds t25. Interior morphology of corroded bricks exhibited cracks, primarily attributed to molten slag penetration and subsequent reactions with refractory material. SEM-EDS analysis of slag-aggregate and slag-matrix interfaces identified reduction in Cr2O3 content as the earliest damage characteristic. XRD detected no zirconium-containing spinel in cracks, indicating that thermal expansion mismatch between newly formed phases and the refractory matrix drives crack propagation. A damage mechanism is proposed: initial Cr2O3 depletion compromises both matrix and aggregate, facilitating slag ingress and new phase formation, ultimately leading to structural failure. Early detection or prevention of Cr2O3 reduction is essential to prolong refractory service life.
Research advances in the pyrolysis recycling of waste wind turbine blades
The global energy landscape is undergoing a profound transformation, with wind energy gaining increasing prominence due to its clean and renewable nature. However, as installed wind power capacity expands, disposal of waste wind turbine blades (WWTB) has emerged as a significant challenge. These blades are predominantly composed of epoxy resin (EP) polymers, carbon fibers (CFs), and glass fibers (GFs). Improper disposal exacerbates environmental concerns and leads to loss of valuable resources, particularly carbon-based materials. Pyrolysis technology, a versatile and environmentally sustainable method for resource recovery, has garnered considerable attention for WWTB disposal. This work presents a comprehensive review of pyrolytic recycling of WWTB, focusing on principles and classifications of pyrolysis technology, key factors influencing the pyrolysis process, as well as pyrolysis methods, equipment, products, and their applications. Through in-depth analysis of current research, this review identifies critical unresolved issues and provides a forward-looking perspective on emerging research trends. The review highlights that pyrolysis can effectively recover glass fibers and carbon fibers with mechanical property retention depending on process conditions, and that catalytic pyrolysis can enhance the quality of recovered products. Economic analysis indicates that collaborative disposal methods can improve cost-effectiveness. Future research should focus on optimizing process parameters for large-scale industrial application and developing more efficient catalysts to improve product selectivity and fiber quality.
Citric Acid-Modified HUSY Zeolite Catalyzes Alkylation of Phenol with Cyclohexanol for High-Density Aviation Fuel Precursors
Lignin-derived oxygenated aromatics, particularly phenols and aromatic ethers, are promising feedstocks for synthesizing high-density, high-heat-sink aviation fuels via alkylation-hydrogenation processes. This study systematically evaluates the catalytic performance of various zeolites (Hβ, HZSM-5, MCM-41, and HUSY) in the alkylation of phenol with cyclohexanol. Characterization demonstrates that HUSY zeolite exhibits superior catalytic activity due to its favorable pore architecture and well-balanced acid site distribution, which synergistically facilitate molecular diffusion and catalytic transformations. To further enhance catalytic properties, HUSY was modified with citric acid at various concentrations and compared with NaOH and oxalic acid treatments. Results reveal that citric acid treatment preserves crystallinity while modulating acidity and pore structure. All modified zeolites enhance phenol alkylation activity. Notably, HUSY-0.5M, exhibiting the highest medium-strong acid to total acid ratio, achieves superior performance: 80.4% phenol conversion and 99.6% selectivity for alkylation products. The catalyst also shows high activity for various lignin-derived compounds (p-cresol, anisole, guaiacol), demonstrating broad applicability. This work provides a new strategy for valorizing lignin-derived phenols into high-value fuel precursors through alkylation.
Hydrogen Production and Structure Evolution Mechanism during Thermochemical Conversion of Microalgae Pellet in Molten Hydroxide Salts
This study investigates the thermochemical conversion behavior of microalgae pellets in a molten hydroxide salt (80% NaOH-20% Na2CO3) system and its influence on hydrogen production. By comparing temperature evolution, gas release characteristics, and structural evolution of pellets with and without molten salt, and integrating char alkalization experiments, the regulatory mechanism of molten salt on reaction pathways and hydrogen production was systematically analyzed. Results indicate that molten salt significantly enhances internal heat transfer efficiency, achieving a central heating rate of 177 °C/s, effectively alleviating thermal hysteresis. Concurrently, molten salt promotes pore development through penetration, erosion, and catalytic effects, resulting in a porosity increase of 53.2%–104.3% after 10 s of reaction. Conversion efficiency is markedly improved, with the dominant reaction pathway shifting to char alkalization after only 70 s. Furthermore, when heating rate is increased above 600 °C, hydrogen yield from char alkalization improves more significantly, primarily attributed to the synergistic promotion of molten salt catalysis and rapid heating on volatiles reforming. This study provides a theoretical foundation for understanding efficient hydrogen production from biomass in molten hydroxide salts.