Syngas production for steelmaking applications via dry reforming of methane using rare earth-containing aerogel catalysts: Evaluation of resistance to deactivation by coke deposition

Abstract The dehydrogenation of propane to propylene is an important process, with great significance for meeting the growing market demand for propylene. Platinum (Pt) ‐based catalysts exhibit excellent activity in the propane dehydrogenation (PDH) reaction, owing to their high affinity for C─H bonds, but suffer from problems such as easy coke deposition and deactivation. Herein, PtCu‐xCa/MSN catalysts were prepared by using Ca‐modified mesoporous silica nanoparticles (Ca/MSN) as support. The experimental results showed that the addition of Ca acts as an electronic promoter, providing electrons to Pt and enhancing its electron density, promotes the migration of coke deposition from active sites to the support, significantly enhancing the activity and stability of the catalyst. Among the synthesized catalysts, the PtCu‐0.5Ca/MSN catalyst exhibited the highest performance, with initial propane conversion and propylene selectivity reaching 56.1% and 96.1%, respectively, along with the lowest deactivation rate constant (0.03 h −1 ).

Abstract Propane dehydrogenation (PDH) is a pivotal technology for propylene production. Supported Pt catalysts for PDH are often subjected to nanoparticle agglomeration and coke deposition, thus limiting their stability and efficiency. Herein, we constructed a high‐performance Pt‐Ce catalyst consisting of CeO x with redox properties and active Pt species with the regulated electronic properties. Through the controllable impregnation, the unique structure of adjacent Pt‐CeO x sites were elaborately supported on the Mn‐modified Silicalite‐1 (Mn‐S‐1). Characterization results reveal that the generated Ce 3+ /V O species contribute to the formation of electron‐deficient Pt 0 ‐V O ‐Ce 3+ active sites via hydrogen spillover and electron transfer. Benefiting from the high dispersion of active components, appropriate acidity, redox activity of V O , and electron‐deficient Pt 0 sites, the optimal 0.5Pt0.2Ce/Mn‐S‐1 catalyst exhibits superior propane conversion of 38.23%, propylene selectivity of 88.45%, and excellent coke resistance. This study not only reveals the intrinsic correlation between active Pt and CeO x species but also provides valuable guidance for designing highly efficient catalysts.

Abstract Fluid catalytic cracking (FCC) is the major process for heavy oil conversion in current refineries and is explored for the intake of renewable feedstocks, like biomass and plastic waste. Due to coke deposition, FCC catalysts undergo continuous reaction‐regeneration cycles. However, many gas pollutants are generated in the FCC regeneration process, and their emission characteristics and formation mechanisms are poorly understood. Here, we conducted stack tests of three industrial FCC units to monitor pollutant emissions. The spent catalysts were characterized to identify the carbon deposits formed. We developed a method to correlate the decomposition of carbon deposits and the formation of gas pollutants in regeneration experiments using in situ Raman spectroscopy, operando FT‐IR spectroscopy, and online gas‐phase FT‐IR spectroscopy. The evolution of coke species is significantly influenced by the oxygen content of the regeneration gas, leading to differences in emission concentration and formation temperature of various gas pollutants. The experimental results are compared with density functional theory (DFT) calculations to explain the formation of the major gas pollutants. This work is expected to advance pollutant emission prediction and control in FCC regeneration, thereby laying the foundation of future work in which different fossil‐based and renewable feedstock compositions can be compared, including their effect on gas pollutant formation.

Fluid catalytic cracking (FCC) is the major process for heavy oil conversion in current refineries and is explored for the intake of renewable feedstocks, like biomass and plastic waste. Due to coke deposition, FCC catalysts undergo continuous reaction-regeneration cycles. However, many gas pollutants are generated in the FCC regeneration process, and their emission characteristics and formation mechanisms are poorly understood. Here, we conducted stack tests of three industrial FCC units to monitor pollutant emissions. The spent catalysts were characterized to identify the carbon deposits formed. We developed a method to correlate the decomposition of carbon deposits and the formation of gas pollutants in regeneration experiments using in situ Raman spectroscopy, operando FT-IR spectroscopy, and online gas-phase FT-IR spectroscopy. The evolution of coke species is significantly influenced by the oxygen content of the regeneration gas, leading to differences in emission concentration and formation temperature of various gas pollutants. The experimental results are compared with density functional theory (DFT) calculations to explain the formation of the major gas pollutants. This work is expected to advance pollutant emission prediction and control in FCC regeneration, thereby laying the foundation of future work in which different fossil-based and renewable feedstock compositions can be compared, including their effect on gas pollutant formation.

Particle-resolved lattice Boltzmann simulations for sedimentation of catalyst particles involving coke deposition

This study explores the catalytic performance of solutioncombustion-synthesizeddoped defective fluorite catalysts, La2–xSrxCe2–yNiyO7, for the dry reforming of methane. A comprehensive structuralanalysis, supported by theoretical calculations, revealed that theadopted synthetic methodology enabled Ni doping beyond a criticalconcentration, leading to its occupation of the interstitial latticesites. The optimally doped Ni-containing defective fluorite oxideLa1.9Sr0.1Ce1.7Ni0.3O7 exhibited superior catalytic activity with more than 70%conversion of CO2 and CH4 with an H2/CO ratio of 0.7 for a 50-h reaction at 700 °C. The prolongedreforming reaction also resulted in minimal coke deposition (11 μgc gcat–1 h–1), primarily due to the oxidative dissociation pathway of methane,as revealed through mechanistic analysis. Detailed surface studieshighlighted the crucial role of metal–support interactions,wherein facile electron transfer from Ni to Ce during the reactioncontributed significantly to the enhanced catalytic performance. Thus,this study establishes a strategic framework for designing and developingdefect-engineered oxide catalysts, paving the way for advanced materialsin dry methane reforming.

Catalyst deactivation has drawn continuing concern from both the academia and industry. Preventing deactivation and optimizing the regeneration process necessitate molecular deciphering of coke deposits. Key to achieving this goal is to identify previously less unexplored, more condensed coke species. Herein, taking commercially relevant HZSM-5 zeolite-catalyzed methanol-to-hydrocarbon as a prototypical reaction, we decode the "structural code" of the previously elusive coke molecules. This is made possible by integrating multiple techniques, especially scanning tunneling microscopy (STM) and noncontact atomic force microscopy (nc-AFM) techniques, which enables the single-molecule direct imaging of coke species with atomic resolution in real space. Combined with complementary techniques, such as gas chromatograph-mass spectrometry and matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry, coke species with an explicit molecular structure covering soluble and insoluble ranges are identified. With this, their molecular routes are consequently unveiled. Molecular imaging with atomic precision resolves the previous ambiguity about "average structures" of "ensemble coke" given by the traditional means with group-based structural identification. This work showcases the potential of STM and nc-AFM as powerful mechanistic tools for resolving mechanistic hypotheses in catalysis.

This study investigates the mineralogical and textural controls on coke deposition during in-situ combustion in reservoir sandstones, with implications for low-carbon energy recovery applications. Experimental simulations using feldspar-bearing, quartz-cemented Penrith Sandstone demonstrate that coke formation, the key requirement of high temperature combustion, occurs heterogeneously, primarily at grain contacts, along dissolved feldspar cleavage planes, and on rough detrital surfaces, but is largely absent from the flat faces of quartz cement. Quantitative X-ray computed tomography and scanning electron microscopy reveal that feldspar-rich zones experience greater porosity reduction through coke deposition, which is influenced by local specific surface area and mineral–fluid interactions. These findings indicate that feldspathic, poorly cemented, and fine-grained sandstones are more favourable substrates for coke formation, enhancing the thermal output potential during in-situ combustion and supporting the stable propagation of combustion fronts. The results provide a petrographic framework for reservoir screening aimed at optimising the selection of lithologies for geothermal energy recovery and related low-carbon strategies.

Alkali metal-modified M-ZSM-5 zeolites (M: Li+, Na+, K+) were synthesized by cationic exchange and characterized using ICP-MS, XRD, N2 adsorption–desorption, Py-IR and NH3-TPD techniques to evaluate their elemental composition, structure, textural and acidic properties. In addition, XPS and DFT calculations were employed to study the effects of metal ion doping on the electronic structure and catalytic behavior. The latter catalytic performance was assessed in the methanol-to-olefin (MTO) reaction. The results showed that alkali metal doping facilitated the enhancement of the zeolite structural stability, adjustment of acid density, and increase in the adsorption energy of light olefins onto the active sites. During the reaction, olefin products shifted from Brønsted acid sites to alkali metal sites, effectively minimizing hydrogen transfer reactions. This change in the active site nature promoted the olefin cycle, resulting in higher yields in propylene and butylenes, reduced coke deposition, and prolonged catalyst lifetime. Among all zeolites, Li-exchanged ZSM-5 exhibited the best and extending the catalyst lifetime by 5 h.

In the chemical industry, an elaborated design of catalysts for propane dehydrogenation (PDH) should be capable of high propane conversion and propylene selectivity, strong resistance to sintering and coke deposition, and easy regeneration. Here, we report a unique design of fluorinated siliceous MFI zeolite-clothed PtSn for PDH, where the fluorination induces the formation of "holes" in all-silica molecular sieves and the position of ultrasmall PtSn nanoclusters as a result of high activity, selectivity, and especially remarkable resistance to sintering during PDH over 5000 h. The present catalyst displays a near-thermodynamic-limited propane conversion and 94% propylene selectivity in pure propane, respectively, under industrially relevant conditions. Impressively, the coked catalyst can be simply regenerated by H2 treatment at the same temperature for PDH, avoiding the complicated, poisonous, and corrosive oxychlorination process in the conventional method for regeneration, which will contribute to the extensive application of the industrial PDH process. Detailed investigations demonstrate that the strong synergy between F-modified PtSn nanoclusters and MFI zeolite can promote the selective PDH to propylene and stabilize PtSn nanoclusters against sintering and coke deposition. The unique design of the catalyst and the enhanced performance will provide a feasible strategy to solve the current difficulties in the industrial PDH process.

Dry reforming ofmethane (DRM) offers an efficient pathway forthe simultaneous utilization of CO2 and CH4,two of the most impactful greenhouse gases, through their conversioninto valuable synthesis gas. Nevertheless, the practical deploymentof DRM remains challenged by catalyst deactivation, predominantlycaused by carbon accumulation and metal sintering. In this work, weexplore the impact of group 9 metal promoters, specifically iridium(Ir), cobalt (Co), and rhodium (Rh), on the catalytic behavior andstability of nickel-based materials derived from hydrotalcite precursors.The catalysts were synthesized via a coprecipitation method and thoroughlycharacterized using a combination of structural, morphological, andsurface analytical techniques, alongside hydrogen temperature-programmedreduction (H2-TPR) and temperature-programmed desorptionanalyses for CO2 (CO2-TPD) and NH3 (NH3-TPD). Catalytic testing was conducted at 750 °Cover a 20-h period. The addition of Ir and Rh was found to markedlyenhance Ni dispersion, strengthen metal–support interactions,and increase the abundance of strong basic sites, all contributingto reduced carbon formation. Among the catalysts, NiHT-Ir demonstratedthe highest stability and activity, maintaining CH4 andCO2 conversions above 80% with minimal deactivation. NiHT-Rhsimilarly exhibited excellent catalytic performance and coke resistance.By contrast, NiHT-Co showed a decline in performance associated withsevere Ni sintering, while the monometallic NiHT catalyst sufferedrapid deactivation. Post-reaction analyses confirmed that Ir and Rheffectively limited coke deposition and metal aggregation, whereasCo promoted Ni particle growth. Density functional theory (DFT) calculationswere carried out to elucidate the variations in adsorption behaviorof CH4 and CO2 across the different catalystsurfaces. This study underscores the beneficial role of group 9 metals,particularly Ir and Rh, in enhancing the catalytic efficiency, stability,and resistance to the deactivation of hydrotalcite-derived Ni-basedcatalysts for DRM.

This work examines the effect of gadolinium (Gd) promotion on nickel-based SBA-16 catalysts for the dry reforming of methane (DRM), with the goal of improving syngas production by optimizing catalyst composition and operating conditions. Catalysts with varying Gd loadings (0.5–3 wt.%) were synthesised using co-impregnation. XRD, N2 physisorption, FTIR, XPS, and H2-TPR–CO2-TPD–H2-TPR were used to examine the structural features, textural properties, surface composition, and redox behaviour of the catalysts. XPS indicated formation of enhanced metal–support interactions, while initial and post-treatment H2–TPR analyses showed that moderate Gd loadings (1–2 wt.%) maintained a balanced distribution of reducible Ni species. The catalysts were tested for DRM performance at 800 °C and a gas hourly space velocity (GHSV) of 42,000 mL g−1 h−1. 1–2 wt.% Gd-promoted catalysts achieved the highest H2 (~67%) and CO yield (~76%). Response surface methodology (RSM) was used to identify optimal reaction conditions for maximum H2 yield. RSM predicted 848.9 °C temperature, 31,283 mL g−1 h−1 GHSV, and a CH4/CO2 ratio of 0.61 as optimal, predicting a H2 yield of 96.64%, which closely matched the experimental value of H2 yield (96.66%). The 5Ni–2Gd/SBA-16 catalyst exhibited minimal coke deposition, primarily of a graphitic character, as evidenced by TGA–DSC and Raman analyses. These results demonstrate the synergy between catalyst design and process optimization in maximizing DRM efficiency.

JP-10 (exo-tetrahydrodicyclopentadiene) is a high-energy-density hydrocarbon broadly used in advanced aerospace propulsion as a regenerative cooling fluid; in this study, we aimed to clarify how fuel pressure affects its thermal degradation (oxidative and pyrolytic) in near-isothermal flowing reactor. Experiments were performed under oxidative conditions (wall temperature 623.15 K, p = 0.708–6.816 MPa) and pyrolytic conditions (wall temperature 793.15 K, p = 2.706–7.165 MPa); carbon deposits were quantified by LECO analysis, oxidation activity was assessed by temperature-programmed oxidation (TPO), and morphology was performed by FESEM and EDS. Results show that oxidative coking is minimal (5.37–14.95 μg·cm2) and largely insensitive to pressure in the liquid phase (1.882–6.816 MPa), whereas at 0.708 MPa (gas/phase-change conditions), deposition increases, implicating phase and local heat-transfer effects. Under oxidative conditions, deposits are predominantly amorphous carbon with a disordered structure, formed at relatively low temperatures, with only a few fiber-like metal sulfides identified by EDS. In contrast, under pyrolysis conditions, the deposits are predominantly carbon nanotubes, exhibiting well-defined tubular morphology formed at elevated temperatures via metal-catalyzed growth. The pyrolysis coking yield is substantially higher (66.88–221.89 μg·cm−2) and increases with pressure. The findings imply that the pressure influences the coking of JP-10 via phase state under oxidative conditions and residence time under pyrolytic conditions, while basic morphologies of coke deposits remain similar; operationally, maintaining the working pressure higher than the saturated vapor pressure can mitigate oxidation coking associated with phase transitions, and minimizing residence time can mitigate pyrolytic coking.

Abstract Recycling CO2 to light olefins (C2 ‐ C4 ) is a promising strategy for long‐term carbon storage. However, selective hydrogenation to light olefins while suppressing alkane formation remains a challenge. This work presents an optimized ZnZrOx/SAPO‐18 tandem catalyst, which achieves 88.7% light olefins selectivity at 9.5% CO2 conversion with C3 +C4 dominating 68.4% of the hydrocarbons. The catalyst exhibits resistance to over hydrogenation, yielding the (C2 −C4 )/(C20−C40) (O/P) ratio of 17.7 and only 1.4% CH4 selectivity. Furthermore, the catalyst shows good stability over 100 h on stream without obvious deactivation, owing to the synergistic effect between ZnZrOx and the reaction conditions, which facilitates the elimination of coke deposition. Hydrothermal treatment brings more Zn─O─Zr active sites and oxygen vacancies (Ov) on ZnZrOx, as well as the modulated Brønsted acid sites (BAS) in SAPO‐18 suppresses the over‐hydrogenation of olefins, and the AEI‐type cage can contain expanded hydrocarbon pool (HCP) intermediates for enhanced C3 +C4 formation. This study advances the development of selective CO2‐to‐olefin conversion technologies.

Recycling CO2 to light olefins (C2 - C4 ) is a promising strategy for long-term carbon storage. However, selective hydrogenation to light olefins while suppressing alkane formation remains a challenge. This work presents an optimized ZnZrOx/SAPO-18 tandem catalyst, which achieves 88.7% light olefins selectivity at 9.5% CO2 conversion with C3 +C4 dominating 68.4% of the hydrocarbons. The catalyst exhibits resistance to over hydrogenation, yielding the(C2 -C4 )/(C2 0-C4 0) (O/P) ratio of 17.7 and only 1.4% CH4 selectivity. Furthermore, the catalyst shows good stability over 100h on stream without obvious deactivation, owing to the synergistic effect between ZnZrOx and the reaction conditions, which facilitates the elimination of coke deposition. Hydrothermal treatment brings more Zn─O─Zr active sites and oxygen vacancies (Ov) on ZnZrOx, as well as the modulated Brønsted acid sites (BAS) in SAPO-18 suppresses the over-hydrogenation of olefins, and the AEI-type cage can contain expanded hydrocarbon pool (HCP) intermediates for enhanced C3 +C4 formation. This study advances the development of selective CO2-to-olefin conversion technologies.

The increasing concentration of greenhouse gases, such as CH4 and CO2, in the environment is pushing the planet to the next level of global warming, where living creatures are becoming extinct one after another. The catalytic conversion of CH4 and CO2 together into syngas, known as dry reforming of methane (DRM), not only depletes the concentration of these gases but also provides an industrially important synthesis gas. Herein, the active sites (metallic Ni) supported over calcium-stabilized zirconia (Ni-xCaSZ; x = 8, 10, 12, 14 mol%) are investigated toward DRM reaction. Catalysts are characterized by X-ray diffraction, surface area and porosity, X-ray photoelectron spectroscopy, Raman spectroscopy, H2-temperature-programmed reduction, and thermogravimetry. Calcium stabilizes the cubic phases of ZrO2 and surges mixed oxide phases like cubic CaZrO3 and monoclinic CaZr4O9. At high mol% of Ca, the interaction between CaO and ZrO2 is grown, the covalence character about oxygen in MOM' bond is raised, the surface area of catalyst is increased, and coke deposition is restricted. Upon increasing mol% of Ca from 8 to 12 mol%, the moderate-level interaction of NiO over support is established, weak interaction of NiO is declined, and overall concentration of active sites is grown. As a result, 5Ni-12CaSZ achieves the highest 66% CH4 conversion, 73% CO2 conversion, and 0.86 H2/CO ratio at 700 °C reaction temperature. An excess amount of calcium (14 mol%) changes the surface composition of CaZrOx, as well as it may also block the oxide vacancy, which may inhibit the CO2 activation vis-à-vis catalytic activity.

Abstract In industrial zeolite catalysis, high‐temperature (>650°C) air combustion is commonly used to restore the activity of catalysts deactivated by coke deposition. Herein, we propose a low‐temperature (440–500°C) air regeneration strategy that harnesses spatially restructured coke in SAPO‐34 catalysts for enhanced performance in the methanol‐to‐olefins reaction. The resulting “tight‐outside, loose‐inside” coke distribution expands accessible reaction volumes, improves product transport, and enhances exposure of confined naphthalene species, key intermediates for ethylene formation. Compared to conventional high‐temperature air regeneration that substantially removes coke, the proposed strategy repurposes it as a functional promoter, enabling prolonged catalyst lifetime and markedly improved ethylene selectivity. The practical viability of this strategy was further confirmed by pilot‐scale fluidized bed reactor‐regenerator experiments and process simulations in terms of both catalyst stability and thermal utilization efficiency. This work reveals an alternative approach to enhance shape‐selective zeolite catalysis via rationally modulating coke by controlling the regeneration strategy.

The application of EDTA exerted a governing effect on the synthesis of ZSM-5 zeolites. Analytical results revealed that EDTA presented as EDTA4- and EDTA3- in alkaline systems. Herein, EDTA4- served as the mineralized agent for dissolving amorphous gel into soluble Si-Al species, while EDTA3- acted as an electrostatic cross-linker, assembling with n-butylamine+ and soluble Si-Al species into "Inorganic-Organic Hybrid Sphere." Significantly, the objective of controlling the crystallization process and product morphology can be achieved by adjusting the EDTA4-/EDTA3- ratio. The appearance of sole EDTA4- (pH ≥ 13) altered the crystallization mechanism from the solid hydrogel one into a solution-mediated one, shifting the zeolite morphology from aggregates into large crystals. Under the cooperativity of EDTA4-/EDTA3- (pH 8.5-10.5), the synthesis gel assembled into an "Inorganic-Organic Hybrid Sphere" and then crystallized into a hollow ZSM-5 capsule. Next, when tested in the methanol-to-aromatics (MTA) reaction, the enhanced stability (186h) and improved aromatics selectivity (40.2%) were directly attributed to the hollow structure, which not only elevated the coke-admitting capacity and suppressed the coke deposition rate but also increased the contact time of the intermediate products with the ZSM-5 shell. These findings established structure-property relationships governing zeolite crystallization mechanisms, product morphologies, and catalytic performances, as well as simplified the preparation procedure of hollow capsules.

Transforming waste into resources: Pyrometallurgical recovery of copper and zinc from spent CuO-ZnO-Al2O3 catalysts.