Low Coke Research Articles

Co‐feeding CO2 for Methylfuran Aromatization over Bifunctional Zeolite‐supported ZnMoO4

Aromatization of biofuran offers promising approaches for sustainable biochemical production. However, this process is often hampered by low yields and severe coking on traditional zeolite catalysts. Herein, we report co‐feeding CO2 for 2‐methylfuran (MF) aromatization (CCMA) over bifunctional ZSM‐5 supported ZnMoO4. This bifunctional catalyst can achieve both MF and CO2 conversions of >97%, generating >85% carbon yield of target arenes and CO with negligible alkenes (0.05%). Meanwhile, coke formation is remarkably suppressed from 22.3% to 8.6%. ZnMoO4/ZSM‐5 is capable of selectively manipulating the reaction intermediates and pathways of the CCMA reactions, favoring the cyclopentenones‐ and alkenes‐based dehydro‐aromatization rather than the benzofurans‐based pathway. This finding challenges the prevailing understanding that MF aromatization follows a hydrocarbon pool mechanism. Moreover, the abundant surface oxygen vacancies of ZnMoO4 facilitate the adsorption of CO2 and its subsequent reaction with coke. These insights into reaction mechanism and catalyst design for co‐conversion of CO2 and biofuran can offer guidelines for process intensification in biomass utilization with a carbon‐negative manner.

Co-Feeding CO2 for Methylfuran Aromatization over Bifunctional Zeolite-Supported ZnMoO4.

Aromatization of biofuran offers promising approaches for sustainable biochemical production. However, this process is often hampered by low yields and severe coking on traditional zeolite catalysts. Herein, we report co-feeding CO2 for 2-methylfuran (MF) aromatization (CCMA) over bifunctional ZSM-5 supported ZnMoO4. This bifunctional catalyst can achieve both MF and CO2 conversions of >97 %, generating >85 % carbon yield of target arenes and CO with negligible alkenes (0.05 %). Meanwhile, coke formation is remarkably suppressed from 22.3 % to 8.6 %. ZnMoO4/ZSM-5 is capable of selectively manipulating the reaction intermediates and pathways of the CCMA reactions, favoring the cyclopentenones- and alkenes-based dehydro-aromatization rather than the benzofurans-based pathway. This finding challenges the prevailing understanding that MF aromatization follows a hydrocarbon pool mechanism. Moreover, the abundant surface oxygen vacancies of ZnMoO4 facilitate the adsorption of CO2 and its subsequent reaction with coke. These insights into reaction mechanism and catalyst design for co-conversion of CO2 and biofuran can offer guidelines for process intensification in biomass utilization with a carbon-negative manner.

Hydrodeoxygenation of Isoeugenol-Derived Model Compound over Carbon-Supported Pt and Pt-SnS Catalysts for the Production of Sustainable Jet Fuel.

This study focuses on the sustainable production of bio-jet fuel through the catalytic hydrodeoxygenation (HDO) of isoeugenol (IE). Sucrose-based activated carbon supported bimetallic Platinum-Tin metal sulphides (PtO-SnS/AC) catalyst was prepared for HDO process. Physicochemical properties of catalysts with different spraying synthesis methods (in situ and ex situ metal doping) and Pt loading (0.1-1.0 %) were further investigated. The PtO-SnS/AC catalysts were characterised using various techniques such as X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA). Both HRTEM and FESEM results show the successful preparation of a spherical nanoparticles doped over activated carbon, and Pt was dispersed on the outer shell of the particles. The catalytic HDO of IE was evaluated in a batch system and showed a high yield and conversion as follows: IE conversion of 100 %, liquid-phase mass balance of 95.92 %, dihydroeugenol (DH) conversion of 99.32 %, propylcyclohexane (PCH) yield of 88.94 % and 2-methoxy-4-propylcyclohexanol (HYD) yield of 76.19 %. Moreover, the PtO-SnS/AC catalyst exhibited high reusability with low metal leaching and high coke resistance for 10 cycles. The catalyst was evaluated in a continuous flow reactor for 100 h at different reaction temperatures, and interestingly, the catalyst showed low deactivation with a high half-time.

On‐Purpose Production of Light Olefins Through Oxidative Dehydrogenation: An Overview of Recent Developments

AbstractProducts made from light olefins play an important role in our daily lives. Traditional light olefins production based on steam cracking and fluid catalytic cracking suffer from high energy consumption and CO2 emissions. Thereby, the continually increasing demand for light olefins needs to be met through more environmentally sustainable procedures. On‐purpose production routes are preferred choice among petrochemicals manufacturers, being energy efficient and having lower carbon footprint. Among them, oxidative dehydrogenation (ODH) of light paraffins is a thermodynamically favourable exothermic process as compared to non‐oxidative routes. They can be operated at lower temperatures and have propensity of low coke deposition on catalyst, thereby resisting rapid catalyst deactivation. Herein, we have analysed various catalytic systems utilised in the oxidative dehydrogenation process. We have reviewed role of support, chemical composition of catalyst, presence of dopant, oxidation state of active metal, controlled surface modification by oxidative and reductive pretreatments, and reaction factors for each system. The performance of various catalytic systems for ODH of ethane, propane and butane in the presence of O2, CO2, N2O and special oxidants have been reviewed. A short critical overview on emerging on‐purpose routes for the production of renewable 1,3 butadiene has also been discussed.

Favorable formation of needle-shaped NiAl2O4 phase over macroporous Ni/CexZr1-xO2–Al2O3 catalysts in one-pot preparation and coke-resistant catalytic performance in dry reforming of methane

In this study, we report the formation of needle-shaped NiAl2O4 via favorable interactions between Ni and Al species over macroporous Ni/CexZr1-xO2–Al2O3 catalysts for dry reforming of methane (DRM) and its remarkable improvement in the catalytic performance. The macroporous catalysts prepared by a one-pot (OP) method promote a favorable interaction between Ni and Al species that results in the formation of unique needle-shaped NiAl2O4 due to easy access to each other compared with that by incipient wetness impregnation. The NiAl2O4 phase in the calcined catalysts transforms into highly dispersed Ni and defective Al2O3 via the Ni exsolution in the reduction step. The presence of oxygen vacancies near Ni0 species facilitates the CO2 activation and enhances the catalyst stability over DRM. The optimized distribution of active sites with abundant defects over macroporous Ni/CexZr1-xO2-Al2O3 catalysts (OP) result in high conversions of CH4 and CO2 and a low coking rate in DRM.

Structural design and electronic regulation of atomically dispersed Mo-S4 sites by second shell N species reconfiguration for intensifying hydrogen spillover

Intensifying hydrogen spillover by regulating the atomic local structures catalysts is crucial for improving the hydrogenation performance, but still hugely challenging. Herein, we report a robust single-atom catalyst featuring Mo-S4 sites in the first shell modulated with N atoms in the second shell (Mo-S4-N/C) by an efficient cyclodextrin supramolecular self-assembly pyrolysis strategy for intensifying hydrogen spillover in slurry-phase hydrocracking of vacuum residue (VR). We discovered that the H2 is activated at the single-atom Mo-S4 sites efficiently and the spillover of active hydrogen is accelerated by the reconfiguration of N species in the second shell. Remarkably, the Mo-S4-N/C catalyst demonstrates excellent catalytic hydrogenation activity with high turnover frequency calculated for total metals up to 0.46 s−1, the VR per pass conversion of 61 wt.%, liquid product yield of 94 wt.%, and the low coke content of 0.6 wt.%, along with good stability, respectively. Theoretical calculations revealed that the N species in the second shell regulated the electronic structure of Mo-S4 sites, promoting the migration of active hydrogen species by reducing the transfer energy barrier of hydrogen spillover, thus enhancing the hydrogenation performance. This work proposed a strengthened hydrogen spillover mechanism from the atomic scale for hydrogenation reaction, offering novel concepts for designing and developing high-performance hydrogenation catalysts.

Fluoride- and OSDA-free synthesis of ZSM-5 with controllable b-axis orientation: Insights into the role of medium alkalinity and seed induction

MFI-topology nanosheets with a b-axis-oriented structure are valuable catalysts in diffusion-controlled acid-catalyzed reactions. Therefore, b-axis-oriented ZSM-5 nanosheets were synthesized herein in a fluoride-free solution without using special additives and complex methods. The initial gel pH of mixed raw materials was adjusted to approximately 5–7 (weak acidity) to direct nanosheet structure formation. The target ZSM-5 zeolite with a b-axis-oriented structure was achieved through the synergistic effect between the involved gel pH and seed solution. The seed solution directed the formation of an MFI structure, and the low alkalinity of the gel limited crystal growth in the b plane, thereby affording b-axis-oriented thin sheets. The ratio of the lengths of the c and b axes of the obtained ZSM-5 could be effectively tuned by adjusting the pH of the initial gel. Compared with the nanosized hexagonal ZSM-5 sample synthesized in a strong-basic system, the as-synthesized b-axis-oriented ZSM-5 exhibited a lower coking rate and higher propylene yield during the considered 1-hexene cracking reaction.

Vitreous silica supported metal catalysts for direct non-oxidative methane coupling

Direct non-oxidative methane coupling (NMC) transforms methane into valuable chemicals and hydrogen, which is a promising pathway to boost industrial decarbonization. The reaction, however, is challenged by high C-H bond activation temperature, catalyst coking, and low selectivity towards hydrocarbon products. Here we studied the efficacy of five vitreous silica supported 3d transition metal (Mn, Fe, Co, Ni, and Cu) catalysts (denoted as M/SiO2-v) for NMC. These catalysts were prepared by flame fusion of mixtures of quartz and metal silicate precursors. The metal species in the as-synthesized catalysts were fully or partially oxidized, with their stability following the order of Mn > Fe ≈ Co > Ni > Cu in the NMC reaction. The Cu species has low methane reaction rate, due to the high adsorption and dissociation energies of methane. The Mn and Ni species have high methane reaction and coke formation rates, which is supported by easy kinetics of methane deep dehydrogenation to carbon. In contrast, Fe and Co species showed the best hydrocarbon product selectivity. Particularly, the Co species emerged as the optimal catalyst for NMC, showcasing a balanced methane activation, hydrocarbon formation, and low coke yield. The relationship between the evolved metal species under reaction conditions and their NMC performance was discussed. The present study screens and provides effective catalyst formulations for NMC reactions.

Reduction of the Low Zinc-containing EAF Dust and Coke

T his paper presents the result of reducing the pellets prepared from low zinc (Zn) containing electric arc furnace dust (EAFD) and coke. The temperature is predetermined in the 1000 to 1200 °C range, and the holding time varies from 30 to 90 minutes. The Zn and iron (Fe) content in the EAFD is analyzed by the ICP-OES method as 15.85 and 20.50 wt.%, respectively. Franklinite (ZnFe2O4) and zincite (ZnO) are the majority compounds of Zn. The experimental result shows that the reduced Zn vapors from the heated pellets increased the Zn removal with increasing temperature and time. The Zn removal from the pellets is significant at temperatures of 1100 and 1200 °C, at which the efficiencies reached about 95 % for the holding time of 90 minutes. The fact that the Fe content was around 31 wt.% and metallic Fe was thought to be present in the pellets heated at 1200 °C would be beneficial if further residue recycling could be done.

Exploring the superior mild temperature performance of nickel-infused fibrous titania silica for enhanced dry reforming of methane

Carbon (IV) oxide (CO2) and methane (CH4) contribute significantly to greenhouse gas emissions and global warming. One potential approach for reducing their environmental impact is transforming these gases into synthesis gas (CO + H2). This study illustrates the advancement of catalysts supported by fibrous titania silica (FTS), which have nickel loadings of 1%, 3%, and 5%. The FTS support, a modified variant of silica-titania, has a distinct fibrous structure and exhibits mesoporous material properties such as a type IV isotherm and an H1 hysteresis loop. After 72 h of operation, the 1Ni/FTS catalyst converted over 80% of CH4 and CO2 with low coke deposition, outperforming other catalysts. The bare FTS support had reduced CH4 conversion at 600°C, CO2 conversion at 650°C, and H2/CO ratio at 700°C. However, the 5Ni/FTS and 3Ni/FTS catalysts showed consistent increases in CH4 conversion at 600°C. The 1Ni/FTS catalyst, with a pore size of 7.39 nm, had strong metal-support interaction and moderate basicity sites, which helped with reactant dissociation and coke gasification. Despite the slightly higher CH4 conversion of the 3Ni/FTS catalyst and the high basicity of the 5Ni/FTS catalyst, the 1Ni/FTS catalyst demonstrated superior thermal stability and coking resistance, as evidenced by negligible weight loss during TGA analysis. Raman shifts revealed the presence of carbon synthesis and the buildup of disordered amorphous carbon. The Id/Ig ratios of FTS, 1Ni/FTS, 3Ni/FTS, and 5Ni/FTS were 1.01, 0.98, 1.01, and 1.01, respectively. The lower Id/Ig ratio of 1Ni/FTS suggests less disorder. The FTS support promises mild-temperature, carbon-neutral CH4 reforming with long-term catalytic applications. This study demonstrates the efficacy of FTS-supported catalysts in constructing long-term and efficient systems for converting greenhouse gasses.

Alumina lattice confined Niσ+ species as highly selective and anti-coking sites for sustainable propane dehydrogenation

Propane dehydrogenation (PDH) is a vital petrochemical process. As an alternative to Pt and Cr-based catalysts, Ni-based catalysts used in PDH, however, exhibit low propylene selectivity with severe coking. This work aims to understand the role of different Ni species in PDH and achieve high propylene selectivity by inhibiting coking. Specifically, we obtained NiOx/Al2O3 catalysts with solely tetrahedrally coordinated Ni2+ (NiIV) by selectively removing microcrystalline NiOx using the impregnation-complexation strategy. The Niσ+ species derived from NiIV exhibited high propylene selectivity (∼88 %) and low coke yield (2.26 %) in PDH. In contrast, reducing microcrystalline NiOx to Ni0 resulted in high methane selectivity and high coke yield (14.90 %). Theoretical calculations and experimental results indicate that this difference is attributed to the faster propylene desorption from Niσ+ as compared to that from Ni0. Therefore, catalysts with well-confined Niσ+ are selective in PDH. This study offers a rational strategy for designing Ni-based PDH catalysts.

Enhancement of non-thermal plasma-catalytic CO2 reforming of CH4 using Ni/Mg–Al2O3 catalysts in a parallel plate dielectric barrier discharge reactor

CO2 and CH4 are converted to syngas by dry reforming of methane (DRM) reaction. This research investigated the effects of the Mg promoter on Al2O3-supported Ni catalysts and Mg calcination temperature on the DRM performance in a parallel plate dielectric barrier discharge reactor. The Mg promoter played a crucial role in the DRM performance, as increasing the Mg calcination temperature from 700 °C to 800 °C significantly improved the DRM performance and catalyst properties, including increased specific surface area, decreased total acidity, reduced crystallite and particle sizes, and more uniform dispersion of the Ni nanoparticles. Under these conditions, the H2 and CO selectivity were 77.0 % and 70.7 %, the CH4 and CO2 conversion were 25.1 % and 20.6 %, and the energy efficiency was 8.4 %. In addition, the catalyst was associated with a lower coking rate (0.5 mg C/gcat h), a relatively low carbon deposit of 1.5 %, and a carbon loss of 2.8 %, possibly because the weak acidity hindered the Boudouard reaction and CH4 decomposition. However, increasing the Mg calcination temperature to 900 °C increased the total acidity and Ni particle size, decreasing H2 and CO selectivities and increasing carbon deposits on the catalyst surface.

Synthesis of HZSM-5@activated carbon for improving aromatic production from catalytic pyrolysis of biomass

HZSM-5 widely used for the catalytic pyrolysis of biomass exhibits the drawbacks of high diffusion resistance and large coke production. To effectively enhance the catalytic efficiency and alleviate the coke deposition, a novel promising catalyst, HZSM-5 coated activated carbon (HZSM-5@AC), was prepared for the first time for in-line upgrading the pyrolysis products of soybean straw. Various catalysts including HZSM-5, activated carbon, and the HZSM-5@AC catalysts with different HZSM-5 to activated carbon mass ratios were characterized. The results showed that the HZSM-5 was successfully coated on the surface of activated carbon and the addition of activated carbon introduced a mesoporous structure and more acidic sites to the catalyst. The catalytic performance on the biomass conversion showed that the catalyst with HZSM-5-to-activated carbon mass ratio of 18:5 (18HZSM-5@5AC) had the highest catalytic efficiency on the conversion of biomass into aromatics with a selectivity of 99.5%, including 75.68% of benzene, toluene, and xylenes (BTX) with a yield of 74.68 mg/g. Moreover, a possible pathway for HZSM-5@AC catalyzed biomass pyrolysis was proposed through analyzing the conversion of model compounds. The catalyst cycling experiments demonstrated the higher stability of HZSM-5@AC than the parent HZSM-5 and activated carbon. TG, FTIR, Raman and SEM showed that the spent HZSM-5@AC was hardly structurally changed with a low coke yield of 0.08%. However, the spent HZSM-5 was partly structurally deactivated by large aromatic ring systems with a coke yield of 3.74%. SEM results also showed that a large amount of polymerized material encapsulated the surface of the spent HZSM-5.

Performance of NiO doped on alkaline sludge from waste photovoltaic industries for catalytic dry reforming of methane.

Alkali sludge (AS) is waste abundantly generated from solar photovoltaic (PV) solar cell industries. Since this potential basic material is still underutilized, a combination with NiO catalyst might greatly influence coke resentence, especially in high-temperature thermochemical reactions (Arora and Prasad, RSC Adv. 6:108,668-108688, 2016). This paper investigated alkaline sludge containing 3CaO-2SiO2 doped with well-known NiO to enhance the dry reforming of methane (DRM) reaction. The wet-impregnation method was used to prepare the xNiO/AS (x = 5-15%) catalysts. Subsequently, all catalysts were tested by using X-ray diffraction (XRD), nitrogen adsorption/desorption (BET), temperature-programmed reduction of hydrogen (H2-TPR), temperature-programmed desorption of carbon dioxide (TPD-CO2), field emission scanning electron microscopy (FESEM-EDX), and X-ray photoelectron spectroscopy (XPS). The spent catalysts were analyzed by thermogravimetric analysis (TGA/DTG), transmission electron microscopy (TEM), and temperature-programmed oxidation (TPO). The catalytic performance of xNiO/AS catalysts was investigated in a fixed bed reactor connected with gas chromatography thermal conductivity detector (GC-TCD) at a CH4:CO2 flow rate of 30 mL-1 during a 10-h reaction by following (Shamsuddin et al., Int. J. Energy Res. 45:15,463-15,480, 2021d). For optimization parameters, the effects of NiO concentration (5, 10, and 15%), reaction temperature (700, 750, 800, 850, and 900 °C), catalyst loading (0.1, 0.2, 0.3, 0.4, and 0.5 g), and gas hourly space velocity (GHSV) range from 3000, 6000, 9000, 12,000, and 15,000 h-1 were evaluated. The results showed that physical characteristics such as BET surface area and porosity do not significantly impact NiO percentages of dispersion, whereas chemical characteristics like reducibility are crucial for the catalysts' efficient catalytic activity. Due to the active sites on the catalyst surface being more accessible, increased NiO dispersion resulted in higher reactant conversion. The catalytic performance on various parameters that showed 15%NiO/AS exhibited high reactant conversion up to 98% and 40-60% product selectivity in 700 °C, 0.2 g catalyst loading, and 12,000 h-1 GHSV. According to spent catalyst analyses, the catalyst was stable even after the DRM reaction. Meanwhile, increased reducibility resulted in more and better active site formation on the catalyst. Synergetic effect of efficient NiO as active metal and medium basic sites from AS enhanced DRM catalytic activity and stability with low coke formation.

Hydrothermally Ce modified HZSM-5 zeolite enhancing its strong acidity and Brønsted/Lewis acid ratio: Stably boosting ethylene/propylene ratio for cracking n-heptane

Modulating zeolite acidity by conventional metal impregnation is a challenge in preparing hydrocarbon cracking catalyst, which often eliminates its intrinsic strong acidity, resulting in reduced the hydrocarbon conversion capacity and low light olefins (C2=-C4=) yield. Here, the Ce/HZ5-HM and CeO2/HZ5-HM catalysts were readily prepared by hydrothermally modifying HZSM-5 zeolite (HZ5) with cerium salts (Ce3+) and cerium oxide (CeO2), respectively. Comparatively, Ce/HZ5-IW catalyst was obtained by modifying HZ5 with Ce3+ using the incipient wetness impregnation. It is revealed that, compared to HZ5, Ce/HZ5-HM and CeO2/HZ5-HM catalysts have an increased ratio of strong/weak (S/W) acid and Brønsted/Lewis (B/L) acid, while Ce/HZ5-IW sample has reduced strong acidity. Further, the Ce/HZ5-HM exhibits higher acid strength, acid density, and B/L value than that of CeO2/HZ5-HM sample. When applied to cracking n-heptane reaction, compared with HZ5 and Ce/HZ5-IW, heptane conversion and ethylene yield on Ce/HZ5-HM and CeO2/HZ5-HM catalysts increase by 6–11 % and 7–9 %, yielding the ratio of ethylene/propylene (E/P) more than 1. Moreover, Ce/HZ5-HM and CeO2/HZ5-HM catalysts perform a lifetime of 117 h and 150 h, with four-to-five times longer than that of HZ5 zeolite (∼29 h) and Ce/HZ5-IW catalyst (∼39 h). The characterization results demonstrate that, adopting hydrothermal method ensures more Ce3+ interacting with the silanol groups in Ce/HZ5-HM, generating the new Brønsted acid sites and makes CeOx species incorporating into the hydroxyl nest of zeolite, which can heal the defective sites and improve stabilization of acidity and framework structure of zeolite. Therefore, the above two catalysts can highlight the monomolecular cracking reaction, low coke deposit rate, long catalytic stability.

Hydrogen production by biogas reforming using Ni/MgO-Al2O3 catalysts

Hydrogen has been pointed out as a highly potential energy source for the future due to its flexibility in production and utilization. In order to obtain hydrogen sustainably, technologies that use renewable raw materials must be developed. In this context, this work proposes hydrogen production from biogas reforming. Ni/MgO-Al2O3 catalysts, containing 20 wt% of NiO and 10 wt% of MgO, were prepared by three methodologies (wet impregnation, coprecipitation, and citrate) and compared with Ni/Al2O3. The catalyst prepared by impregnation exhibited the highest Ni dispersion and basicity, with the highest activity in methane reforming with CO2 (CO2/CH4 = 1) at temperatures between 600 and 800 °C. This catalyst presented high stability during 100 h of reaction at 700 °C (92 % of CH4 conversion and 95 % of CO2 conversion), with a lower coking rate than Ni/Al2O3. Coke was predominantly graphitic for all catalysts, but the catalyst prepared by coprecipitation showed a higher proportion of amorphous coke and the lowest coking rate.

Kinetic implications of (hierarchical) zeolite fouling during liquid-phase aromatics upgrading

The kinetics of fouling in large pore zeolites (BEA, MOR), including those with hierarchical pore systems, were probed during the Brønsted acid catalyzed reaction of benzyl alcohol (BA) with 1,3,5-trimethylbenzene (TMB) by varying reactant driving force (i.e., [TMB]0/[BA]0; 11–119). In BEA, initial deactivation rate constants (kD,0) decreased exponentially with [TMB]0/[BA]0, highlighting the significance of oxygenates as deactivation precursors. Further, seeding pores with oxygenates completely suppressed measured rates in parent MOR and BEA, while seeding with TMB had no effect. Comparisons of mass accumulations of different organics (low molecular weight reaction species and coke) as functions of ln([TMB]0/[BA]0) revealed that coke (derived from oxygenate-seeded polyalkylation of TMB) disproportionately controlled deactivation rates by damping apparent (diffusion-controlled) and intrinsic (diffusion-corrected) rate constants through proton losses and/or altered molecule confinement within shrinking pores. These kinetic consequences were delayed upon introduction of mesopores, demonstrating how zeolite porosity impacts coke proliferation and behavior in liquid-phase reactions.

Zeolite Y-based catalysts for efficient epoxidation of R-(+)-Limonene: Insights into the structure-activity relationship

Parent, hierarchical, and metal-modified hierarchical zeolite Y were investigated as heterogeneous catalysts in the R-(+)-limonene epoxidation, a catalytic route for synthesizing precursors of bio-polycarbonates, an alternative to isocyanate polyurethanes. The fresh catalysts underwent detailed characterization using XRD, N2 physisorption, TEM, SEM-EDX, pyridine-FTIR, NH3-TPD, CO2-TPD, UV–Vis-DRS, and solid-state NMR. Spent materials were investigated by TPO-MS and TGA, confirming low coke formation on the catalytic surface. The most active material was K–Sn-modified dealuminated zeolite Y, reflected in a high turnover frequency (TOF) of 96 h−1. This material exhibited the lowest Brønsted to Lewis acidity ratio (0.1), the highest mesoporosity fraction (43%), and the lowest total surface area (465 m2 g−1). Aprotic polar solvents with high polarity and medium donor capacity appeared suitable for limonene epoxidation. Limonene conversion of ca. 97% was reached at 70 °C, H2O2: limonene molar ratio = 7, and acetonitrile as a solvent, while selectivity to total monoepoxides exhibited values up to 96% under different reaction conditions. Hydration of internal epoxides to limonene diol was favored at high temperatures and high H2O2/limonene molar ratios. The efficiency of H2O2 reached maximum values of about 85% at low H2O2 amounts, while no significant influence was observed for temperature, catalyst amount, and the initial concentration of limonene. A plausible reaction mechanism was proposed for the R-(+)-limonene epoxidation with H2O2 based on the experimental findings.

Co-pyrolysis coking characteristics of nC12H26 and DHN/MeOH/EtOH/MF/DMF/H2O/H2/CO2/CO/N2 under supercritical condition

The introduction of additives or carrier gases to change the physicochemical process of endothermic fuel in a regenerative cooling channel and then regulate the carbon deposition behavior is an important coking control method. In this work, the co-pyrolysis and coking behavior of several novel additives, such as alcohols, furans, flue gas, and syngas, is compared under the supercritical condition of n-dodecane (nC12H26) with the traditional hydrogen supply agent decalin (DHN) and inert nitrogen (N2) as the basis in a 304STS tube with an inner diameter of 2 mm. Results show that the addition of methanol (MeOH) / ethanol (EtOH) / 2-methylfuran (MF) / 2,5-dimethylfuran (DMF) promotes the pyrolysis of nC12H26 and shows a strong coking trend. The coking rate of carbon monoxide (CO) addition is higher than that of carbon dioxide (CO2) addition, and the system is prone to presenting an exothermic chemical effect. The addition of hydrogen (H2) does not contribute to the hydrogen source but leads to a high coking risk at a low blend ratio. Although water (H2O) and CO2 atmospheres exhibit coke inhibition potential, they weaken the heat absorption capacity of nC12H26. The co-pyrolysis of alcohols, furans, and hydrocarbon feedstock to CO needs to be controlled in a targeted manner, so that endothermic fuels have high heat sink and low coking tendency in regenerative cooling channels.

Synthesis of nanostructured titanium carbide (TiC) from bitumen coke by mechanical alloying process

AbstractThis study explored synthesizing titanium carbide (TiC) from bitumen coke using mechanical alloying. Initially, raw bitumen coke (5.9 wt.% sulphur) from delayed coking was desulphurized to produce low sulphur coke with a sulphur content of 0.2 wt.% for comparison purposes. Both high and low sulphur coke samples were mechanically alloyed with titanium (Ti) powder in a planetary ball mill under various conditions (milling time, milling speed, and ball‐to‐material ratios [BMR]). TiC was successfully produced from both high sulphur and low sulphur coke samples. The formation of TiC was confirmed by X‐ray diffraction (XRD) analysis. The effects of the experimental parameters on the production of TiC were evaluated. The experimental results showed that the high sulphur coke and Ti were converted into TiC after 10 h milling, whereas the low sulphur coke and Ti were converted into TiC much faster (after 5 h milling) at the same milling speed and BMR. Under the same milling time and BMR, the high sulphur coke and Ti were converted into TiC at 400 rpm, whereas the low sulphur coke and Ti were converted into TiC at 300 rpm. In addition, the high sulphur coke and Ti were converted into TiC when the BMR was 60:1, and the low sulphur coke and Ti were converted into TiC when the BMR was 40:1 under the same milling time and speed. Overall, preliminary results suggest that the conversion of low sulphur coke samples is easier and requires less energy to produce TiC compared to the high sulphur coke samples.