Conversion Of N-dodecane Research Articles

Engineering oxygen vacancies on Tb-doped ceria supported Pt catalyst for hydrogen production through steam reforming of long-chain hydrocarbon fuels

Steam reforming of long-chain hydrocarbon fuels for hydrogen production has received great attention for thermal management of the hypersonic vehicle and fuel-cell application. In this work, Pt catalysts supported on CeO2 and Tb-doped CeO2 were prepared by a precipitation method. The physical structure and chemical properties of the as-prepared catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, H2 temperature programmed reduction, and X-ray photoelectron spectroscopy. The results show that Tb-doped CeO2 supported Pt possesses abundant surface oxygen vacancies, good inhibition of ceria sintering, and strong metal-support interaction compared with CeO2 supported Pt. The catalytic performance of hydrogen production via steam reforming of long-chain hydrocarbon fuels (n-dodecane) was tested. Compared with 2Pt/CeO2, 2Pt/Ce0.9Tb0.1O2 and 2Pt/Ce0.5Tb0.5O2, the 2Pt/Ce0.7Tb0.3O2 has higher activity and stability for hydrogen production, on which the conversion of n-dodecane was maintained at about 53.2% after 600 min reaction under 700 oC at liquid space velocity of 9 ml·(g cat)–1∙h–1. 2Pt/CeO2 rapidly deactivated, the conversion of n-dodecane was reduced to only 41.6% after 600 min.

N-dodecane partial oxidative reforming in gliding arc discharge plasma and kinetic model

A gliding arc discharge (GAD) plasma reactor was developed for partial oxidative reforming (POR) H2 production. Air was used as carrier gas and oxidant. The effects of the molar ratio of oxygen to carbon(O/C), input power and residence time on POR reaction were investigated. Under O/C ratio 0.75, input power 35 W and residence time 35 s, the energy yield of H2 was 68.7 L/kWh and the main products were H2 and CO. The GAD plasma was diagnosed with OES. A zero-dimensional(0-D) reaction kinetic model of was established. The simulation results were consistent with the experimental ones. The mechanism of C12H26 conversion, the generation and consumption of products were discussed in detail. The experiment results were in good agreement with the simulated ones. The primary path of n-dodecane conversion was the direct cracking reaction and H2 mainly derived from the recombination reaction between H atom and CH4, C3H6 and C2H6.

Dehydrogenation of cycloalkanes over Pt/SBA-15 for endothermic cooling

Dehydrogenation of cyclohexane, methylcyclohexane, and decalin was studied on Pt/SBA-15 between 773 and 873 K for application to engine cooling in hypersonic aircraft. While the reactions were unstable at 1 bar, the reactions showed no evidence for deactivation at pressures of 20 and 60 bar for at least 4 h. Selectivities for dehydrogenation of cyclohexane to benzene and methylcyclohexane to toluene were greater than 90% in all cases. The reaction of decalin proceeded sequentially, forming primarily tetralin at low reactor space times and naphthalene at higher space times. The reaction of 50% mixtures of n-dodecane and decalin at 773 K showed negligible conversion of n-dodecane but the reaction of decalin was similar to what was observed for a pure decalin feed. Heat measurements gave endothermicities that were in good agreement with standard reaction enthalpies.

Catalytic conversion of n-Dodecane to lower olefins hydrogen carriers over bran-shaped modified MCM-22 zeolite catalyst: SiO2/Al2O3 ratio effects

The demand-supply gap for light olefins and aromatics has been enormous in recent years. This imbalance is anticipated to grow exponentially due to their extensive use in manufacturing plastics, textiles, pharmacological intermediates, climate-neutral synthetic fuels, and hydrogen carriers. Production of light olefins through the catalytic cracking of naphtha is widely regarded as one of the most prestigious methods. Despite this, selecting an effective and efficient catalyst is one of the most challenging aspects of the scaling-up process. In this study, a highly active, modified MCM-22 catalyst has been synthesized by a hydrothermal method. Various techniques are used for the characterization of catalysts, including scanning electron microscopy (SEM), X-ray diffraction (XRD), N2 adsorption-desorption, temperature-programmed desorption of ammonia (NH3-TPD), and solid-state nuclear magnetic resonance experiments (NMR) with Al and Si. The cracking of n-dodecane to lower olefins was performed, and it was found that the conversion rates were highly correlated with the SiO2/Al2O3 ratio of the MCM-22 samples. Sample Si0.5 (SiO2/Al2O3 ∼ 28.9) showed a typical photograph of the MWW phase with a bran or flake shape in a stacking mode. The Si0.5 sample has a superior external surface area than other samples (up to ca. 130 m2/g) caused by a smaller particle with an average crystal size of around 15 nm, resulting in maximum catalytic performance towards light olefins. It was discovered that Si0.5 had a diminishing tendency in the paraffinic selectivity but had a robust selectivity for olefins (propylene and butylene in particular). This research may provide academics and the industry with new prospects for improving the catalytic cracking of n-dodecane into light olefins.

Superior activity and isomerization selectivity in n-dodecane hydroisomerization over Ni clusters on ZSM-22 zeolite with structural defects

Developing nonnoble catalysts with high performance for the selective hydroisomerization of long-chain n-alkanes to isoalkanes that are comparable to commercial Pt catalysts is important but challenging. We report a low-loading nickel catalyst on structure-defective nanosized ZSM-22 zeolite (Ni/SD-HZSM-22, 1.0 wt%) with superior activity and isomerization selectivity for n-dodecane hydroisomerization than a commercial Pt catalyst (Pt, 0.5 wt%). The developed Ni/SD-HZSM-22 catalyst achieves 86.0–88.6 % n-dodecane conversion and 80.0–81.3 % C12-isomer yield, outperforming the conventional ZSM-22–supported Ni catalyst (Ni/HZSM-22; 50.4 % and 41.1 %, respectively) and the commercial Pt catalyst (56.8 % and 52.4 %, respectively) under the same reaction conditions, with high durability for 120 h. This is because SD-HZSM-22 with abundant surface structural defects increased available 10-membered ring openings, anchoring the small-sized Ni species and enhancing the isomerization activity and selectivity, endowing Ni/SD-HZSM-22 with good synergy between metal and acid functions.

Influence of nickel loading on the hydroisomerization of n-dodecane with nickel-tungsten oxide-alumina supported catalysts

Heterogeneous catalysts based on alumina-supported tungsten oxides (15 wt% W) with different loadings of nickel (0.5, 1, 2, 4, 6, 8 and 10 wt% Ni) were selected to study the influence of Ni loading on the hydroisomerization of n-dodecane. The catalysts were prepared by applying the wetness impregnation method on the supports to introduce W and Ni. The characterization techniques applied for determining physicochemical properties of the catalysts were N2 adsorption-desorption at 77 K (textural properties), X-ray diffraction (structure and crystalline phases), H2-TPR (redox properties), FTIR, NH3-TPD (acid sites analyses) and XPS (chemical surface analysis). The catalytic properties of such catalysts were found to be crucial in the n-dodecane conversion. The NH3-TPD profiles indicate that the medium acid sites are the main sites responsible for the reaction performance. The formation of bulky crystal structures of nickel species in the high nickel loading catalyst (10 wt% Ni) was confirmed by XRD and XPS results, resulting in the largest cracking activity. The conversion of n-dodecane and selectivity to i-C12+branched C12 tend to increase with Ni loading until the catalyst contains 6 wt% Ni (28% n-C12 conversion and 94% of branched C12 selectivity). The lower selectivity at high nickel loading is due to metal-based cracking reaction. An optimum balance between metal and acid centers is needed to achieve a compromise between conversion and selectivity, avoiding or minimizing cracking reactions.

Influence of W loading, support type, and preparation method on the performance of zirconia or alumina-supported Pt catalysts for n-dodecane hydroisomerization

Catalysts based on zirconia and alumina-supported tungsten oxides (3–18 wt% W) with a small loading of platinum (0.3 wt% Pt) were selected to study the influence of W loading, support type, and preparation methods on the hydroisomerization of n-dodecane. The alumina- and zirconia-supported catalysts show different catalytic properties that play an important role in n-dodecane conversion. Specific surface area and acidity of the alumina-supported catalysts are clearly higher than those of zirconia-supported counterparts. The 15 wt% W loaded catalysts were found to exhibit the best catalytic performance for the hydroisomerization of n-dodecane for both zirconia and alumina (67% of n-C12 conversion and 87% of i-C12 selectivity) based catalysts. Catalysts prepared by a single-step wet impregnation method were more active in the hydroisomerization of n-dodecane than catalysts prepared via several consecutive steps.

Acidity tuning of HZSM-5 zeolite by neutralization titration for coke inhibition in supercritical catalytic cracking of n-dodecane

Reducing the acid density and strength of HZSM-5 zeolite are typical strategies to inhibit coke deposition during catalytic cracking reactions. Herein, direct titration of HZSM-5/H2O suspension using dilute NaOH aqueous solution at room temperature was introduced to neutralize excessive Brønsted acid sites of HZSM-5 zeolite (Si/Al = 25). SEM, XRD, N2 adsorption and n-propylamine temperature-programmed decomposition confirmed that simultaneous acid strength weakening and acid density reducing were achieved without obvious influence on crystalline or textural property. The evolution of the surface charge during the titration process tracked by Zeta-potential measurement reveals that the mechanism of such neutralization is: liquid phase neutralization between H+ and OH− & solid phase ion exchange between Na+ and H+. Supercritical catalytic cracking of n-dodecane over a series of partial neutralized HZSM-5 catalysts showed that moderate neutralization can enhance the conversion of n-dodecane by alleviating both the coke amount and harmfulness per unit mass of coke.

Steam reforming of surrogate diesel model over hydrotalcite-derived MO-CaO-Al2O3 (M = Ni & Co) catalysts for SOFC applications

Catalytic steam reforming of diesel fuel has the potential for producing syngas or hydrogen that can be feed to a fuel cell (especially SOFC) for portable power generation. Cost-effective, highly active reforming catalysts with resistance towards carbon formation and sulfur poisoning are critically needed to commercialize such technologies successfully. Thus in the present work, we have explored CaO-Al2O3 based hydrotalcite structure derived catalyst precursors for syngas production via steam reforming of a diesel model compound (n-dodecane). The steam reforming of n-dodecane reactions was also carried out in the presence of 100 ppm of sulfur compounds at a steam-to-carbon ratio of 2. Among all the catalysts tested, the Co-CaO-Al2O3 catalyst gave the best catalytic performance with respect to n-dodecane conversion, stability, and carbon suppression. At 700 °C, the Co-CaO-Al2O3 catalyst possesses > 90% of n-dodecane conversions with a negligible carbon formation (1.04 mg C/g.h) for a period of 24 h. It is also observed that upon deactivation due to sulfur poisoning, the Co-CaO-Al2O3 catalyst can be regenerated by a simple thermal treatment at 750 °C, which is due to the considerably low decomposition temperature behavior of CoSx and CaS species formed for this catalyst. Lower carbon deposition over the Co-CaO-Al2O3 catalyst can be attributed to the better oxygen affinity of Co species and higher normalized basicity than other catalysts.

Study of CA-treated ZSM-22 zeolite with enhanced catalytic performance in the hydroisomerization of long-chain n-dodecane

Pt catalysts on citric acid treated ZSM-22 zeolites exhibited enhanced n-dodecane conversion (89.7%) and C12-isomer yield (68.8%) compared with the parent ZSM-22 zeolite (19.6% and 16.4%).

Design and synthesis of Pt catalyst supported on ZSM-22 nanocrystals with increased accessible 10-MR pore mouths and acidic sites for long-chain n-alkane hydroisomerization

Abstract Synthesis of ZSM-22 with more accessible 10-membered ring (10-MR) openings is important for the preparation of highly active and selective hydroisomerization catalyst. Herein, we synthesized ZSM-22 nanocrystals (HZSM-22-NA) with more 10-MR openings and a mesoporous structure on a large scale. The prepared Pt/HZSM-22-NA catalyst (4.74 × 10−6 mol·g−1·s−1) exhibited higher intrinsic activity than conventional HZSM-22-supported Pt catalyst (Pt/HZSM-22, 2.65 × 10-6 mol·g−1·s−1) in the hydroisomerization of n-dodecane. Additionally, Pt/HZSM-22-NA had higher C12 isomer selectivity (93.5%) and lower cracking selectivity (6.5%) than Pt/HZSM-22 (79.8% and 20.2%) at the same n-dodecane conversion level (~90%). These features could be due to the change in the porous structure and acidity between HZSM-22-NA and HZSM-22. HZSM-22-NA composed of nanocrystals at c-axis could double the number of accessible 10-MR openings and acidic sites, thus enhancing the isomerization activity of Pt/HZSM-22-NA. Furthermore, the mesoporosity of HZSM-22-NA facilitated mass transfer of the intermediates and products, thus inhibiting cracking reaction.

N-Dodecane steam reforming over Ni catalysts supported on ZrO2–KNbO3

Coke-resistant Ni catalyst supports are evaluated for steam reforming (SR) n-dodecane, the alkane used as a surrogate for diesel fuel in this study. Reactions are conducted at 800 °C for 5 h, with a molar steam-to-carbon ratio of 3.0 and a gas hourly space velocity of 20000 h−1. Thermally stable, coke-resistant supports loaded with 15 wt% Ni are prepared using the following potassium oxides: K2Ti2O5 (KTI), K4Zr5O12 (KZR), KNbO3 (KNB), KTaO3 (KTA), and K2WO4 (KW). Ni/KZR and Ni/KW show the best catalytic performance in the SR reaction due to their moderate-to-strong acidities and lack of porosity, which are necessary features for hydrocarbon cracking. Unfortunately, these catalysts are poorly stable under the defined operating conditions. KNB is the most suitable support due to its excellent thermal stability and coke-resistance; however, it lacks acidity. The acidity of KNB is enhanced by impregnation with ZrO2, which transforms it into an acidic oxide (ZR-KNB). ZR-KNB features high thermal stability and high coke-resistance during the SR of n-dodecane under the applied test conditions. The Ni/ZR-KNB catalyst delivers excellent SR performance with respect to both n-dodecane conversion and hydrogen selectivity.

Synthesis of pillared nanosheet HZSM-5 zeolite films for catalytic cracking of supercritical n-dodecane

The chemical heat sink yielded by the catalytic cracking of supercritical hydrocarbons facilitates the thermal management of hypersonic aircraft. The objective of this study was to alleviate the diffusion restriction of supercritical hydrocarbons in conventional microporous zeolite films. A dual template method involving different n (C22-6-6)/n (TPAOH) values was adopted to prepare pillared nanosheet HZSM-5 zeolite films by using seed assisted secondary growth. Compared with those of the parent nanosheet HZSM-5 zeolite film (ZN) prepared using only C22-6-6 as the structure directing agent (SDA), the zeolite film prepared using n (C22-6-6)/n (TPAOH) of 10/4 (DZN-4) after pillaring exhibited a higher surface area (525 m2 g−1) and mesoporous volume (0.453 cm3 g−1). A larger amount of TPAOH in the synthesized solution (n (C22-6-6)/n (TPAOH) < 10/6) induced the formation of a bulky microporous MFI crystal phase, thereby sacrificing the mesoporous structure. At 550 °C and 4 MPa, the DZN-4 zeolite film yielded the highest n-dodecane conversion rate (76.8%) and TOF value (130.9 s−1), due to the presence of highly accessible Brønsted acid sites and ordered mesoporous structures, leading to a heat sink of 2.99 MJ kg−1, which is 32% higher than that under ZN. Restricted secondary reactions, such as hydride transfer and aromatization, were observed in the presence of highly connected mesopores designed by pillaring, leading to high and low selectivities toward olefins and aromatic compounds, respectively. Amorphous coke was detected on the external mesopore surface of DZN-4, and the adhesive strength was significantly enhanced, resulting in a higher catalytic stability.

Coconversion of n-Dodecane and 2-Methylthiophene in the Presence of Dual-Zeolite Cracking Catalysts Containing Different Amounts of Rare-Earth Elements

The effect of the rare-earth element (REE) content in dual-zeolite cracking catalysts on the conversion of n-dodecane and an n-dodecane–2-methylthiophene mixture (5000 ppm S) has been studied. The catalysts have been synthesized using zeolites Y and ZSM-5 modified with REEs and phosphorus, respectively, as the active component. It has been shown that the presence of REE oxides in zeolite Y (at a constant SiO2/Al2O3 ratio) affects the catalytic activity of cracking catalysts based on this zeolite. The dependence of the light olefin yield on the REE oxide content in zeolite Y passes through a maximum at 2–3 wt %. The presence of a sulfur compound in an amount of 5000 ppm (in terms of sulfur) in the feedstock leads to a decrease in the model hydrocarbon conversion and the C2–C4 olefin yield. In the presence of a sulfur compound, the change in the C2–C4 olefin yield as a function of REE oxide content in zeolite Y is less pronounced than that in the case of individual n-dodecane cracking.

Supercritical catalytic cracking of n-dodecane over air-oxidized activated charcoal

The direct conversion of n-dodecane to light alkenes with an efficient catalyst can enhance the combustion efficiency and cooling performance of endothermic heat sinks for the development of propellants suitable for supersonic vehicles. In this work, a pretreated activated charcoal showed excellent performance as a novel cracking catalyst superior to the conventional ZSM-5 zeolite catalyst. Activated charcoal was oxidized at 298, 473, and 673 K, leading to surface modification, and n-dodecane cracking experiments were carried out at 4 MPa and 723 K. The activated charcoal exhibited a higher light alkene selectivity and heat sink capacity compared with the conventional ZSM-5. The charcoal oxidized at 673 K showed the highest light alkene selectivity of 28% among the tested catalysts, exceeding that of the reference ZSM-5 by 18%. The oxidizing pretreatment of the charcoal at high temperatures was found to generate carboxylic functional groups acting as Brӧnsted acid sites based on characterization by X-ray photoelectron spectroscopy, FT-IR, and temperature-programmed desorption with NH3. The activated charcoal oxidized at 673 K had the largest amount of strong acid sites and Brӧnsted acid sites, which led to the highest conversion of n-dodecane and the selectivity of light alkene.

Tuning metal-support interaction and oxygen vacancies of ceria supported nickel catalysts by Tb doping for n-dodecane steam reforming

Hydrogen is a green and efficient energy carrier that can be applied directly in fuel cell system. On-board/on-site hydrogen production for a portable fuel cell is urgently required, and catalytic steam reforming of liquid hydrocarbons is a promising pathway. In this context, Ni catalysts supported on various Tb-doped ceria were synthesized by a citric-acid-assisted sol-gel method. The textural and physicochemical properties of the fresh and spent catalysts were characterized by different techniques including XRD, N2 physical adsorption, H2-TPR, H2-TPD, TEM, SEM, XPS, EPR, TG and Raman. Catalytic performance of the as-prepared catalysts was evaluated in steam reforming of n-dodecane. The conversion of n-dodecane and hydrogen production rate were measured at LHSV of 10 ml/gcat·h and H2O/C = 2 and 4 in a fixed-bed tubular reactor. The reaction data showed that Tb dopant affected both the conversion of n-dodecane and the gas product composition. The origins of the improved performance by Tb doping were investigated, in which the moderate interaction between metal and support, highly dispersed Ni particles, increased basicity sites and abundant surface oxygen vacancies play key roles.

Catalyst-free low temperature conversion of n-dodecane for co-generation of COx-free hydrogen and C2 hydrocarbons using a gliding arc plasma

In this study, plasma reforming of n-dodecane for the co-generation of COx-free hydrogen and C2 hydrocarbons at low temperature and ambient pressure has been investigated in a gliding arc discharge (GAD) reactor. The selective synthesis of H2, C2H2 and C2H4 and the energy efficiency for n-dodecane conversion can be tuned by changing different processing parameters including the gas flow rate, n-dodecane concentration and input voltage. The highest selectivities of H2 (76.7%), C2H2 (41.4%) and C2H4 (12.0%) were achieved with an n-dodecane conversion of 68.1%. The generation of mixed hydrogen, acetylene and ethylene offers the possibility for in-situ hydrogenation to enhance the selectivity of light olefins (e.g., ethylene) without prior gas separation. The plausible reaction mechanism and pathways in the plasma cracking of n-dodecane have been discussed through plasma emission spectroscopic diagnostics coupled with a comprehensive analysis of gas and liquid products. A strong correlation between the yield of C2 hydrocarbons and the relative intensity of C2 Swan bands was found, which suggests that C2 Swan bands could be used as a valuable probe to understand the generation of C2 hydrocarbons in the plasma reforming of hydrocarbon oils.

Effect of Metal Precursors on the Performance of Pt/SAPO-11 Catalysts for n-Dodecane Hydroisomerization.

Pt(NH3)4(NO3)2, Pt(NH3)4(Ac)2, (NH4)2PtCl4, and H2PtCl6 were used to prepare Pt/SAPO-11 catalysts to investigate the effect of Pt precursors on the hydroisomerization of n-dodecane. The catalyst derived from Pt(NH3)4(NO3)2 displays the best hydroisomerization activity and selectivity among these precursors. The hydroisomerization conversion of n-dodecane is affected by the platinum particle size, platinum dispersion, the location of platinum, and the valence state of platinum. The selectivity of n-dodecane is determined by the number of Brønsted acid sites and Pt crystal planes. These conclusions are verified by combining transmission electron microscopy, high-resolution transmission electron microscopy, hydrogen temperature programmed reduction, NH3-temperature programmed desorption, and Py-IR studies. The catalyst prepared with Pt(NH3)4(NO3)2 as the precursor exhibits the smallest platinum particle size and the highest platinum dispersion. Most of the platinum particles are supported on the external surface of SAPO-11 with the Pt(111) crystal face. Such a catalyst also possesses a suitable number of Brønsted acid sites and then displays the best catalytic performance. Obviously, the use of various precursors for the Pt-based catalyst can significantly affect the performance of Pt/SAPO-11 for the hydroisomerization of n-dodecane.

Platinum‐promoted fibrous silica Y zeolite with enhanced mass transfer as a highly selective catalyst for n ‐dodecane hydroisomerization

A fibrous silica zeolite Y (HY@KCC-1) catalyst with a high surface area of 568 m2/g and unique core-shell morphology was successfully synthesized via a modified KCC-1 synthesis method. Characterization of the catalysts was achieved with X-ray powder diffraction (XRD), field emission scanning microscope (FESEM), N2 adsorption/desorption, and 2,6-dimethylpyridine adsorbed Fourier-transform infrared spectroscopy (FTIR). The Pt/HY@KCC-1 has displayed complete n-dodecane conversion coupled with an incredibly enhanced isomer yield of 72% at 350°C, nearly two-fold higher than that of unmodified Pt/HY catalyst. Remarkably, Pt/HY@KCC-1 had an internal effectiveness factor (η) of unity and negligible internal diffusion limitation, thus suggesting its potential application in hydroisomerization of higher hydrocarbons for enhancing fuel properties.

N-Dodecane steam reforming catalyzed by Ni-Ce-Pr catalysts. Part 1: Catalyst preparation and Pr doping

Catalytic steam reforming of long-chain hydrocarbons has drawn great attention for hydrogen production, which can be used for on-board/on-site fuel cell. In this study, various ceria (or Pr-doped ceria) supported Ni catalysts have been prepared by two different methods (impregnation method and sol-gel method), which are denoted as 10Ni/Ce1-xPrxO2 and 10Ni-Ce1-xPrxO2 (x = 0 or 0.2) respectively. Steam reforming of n-dodecane has been carried out to evaluate catalytic performance of the obtained catalysts at high LHSV (15 ml/gcat h), low temperature (600 °C) and low mole ratio of water-to-carbon (2) in a fixed-bed tubular reactor. Results show that both the formation of nickel-ceria strong metal support interaction and Pr doping increase its catalytic performance. 10Ni-Ce0.8Pr0.2O2 prepared by sol-gel method exhibits the highest activity (100% conversion of n-dodecane) and stability of hydrogen production (5917.1 μmol/min) together with lowest coke deposition (0.0251 g/gcat h). Various techniques including XRD, nitrogen adsorption-desorption, H2-TPR, TEM/STEM, SEM-EDS, XPS, TG/DTG and Raman spectra have been employed to characterize the fresh and spent catalysts. The evaluated activity and stability of ceria supported Ni catalyst is ascribed to the strong interaction between metal and support. In addition, the oxidation of deposited coke on metal is enhanced by the doping of Pr due to its high oxygen storage-release capability.