Hydroconversion Of N-heptane Research Articles

Illuminating the impact of the proximity communication modes between redox metallic and acidic zeolite sites during hydro-conversion of n-heptane

The unique physicochemical properties of “redox-acid” bifunctional zeolites make them an essential tool in the petrochemical industry, especially in the hydro-conversion of linear alkanes to deliver high-octane fuels. The current research activities in this domain are primarily tailored towards evaluating the “intimacy/proximity” criteria among two catalytically active sites and minimizing the loading of noble metals (e.g., Pd or Pt) in catalysis. However, the chemistry behind the communication mode (i.e., “through-space” or “through-bond” interaction between metallic and acid sites) has remained vastly underexplored during the hydro-conversion of n-alkanes over Pt or Pd/zeolites. To dig deeper into this uncharted territory, this work demonstrates that both “through-space” (cf. metals in extra-framework position in/on zeolite) and “through-bond” (cf. metals on the zeolite framework) bifunctionality favors the hydroisomerization step, while the later partially also promote the hydro-cracking. Their working protocol was probed by the diverse material characterization techniques that improved the understanding of the zeolite-catalyzed hydrocarbon conversion processes.

Experimental and Kinetic Modeling of n-Heptane Hydroconversion over Mesoporous Pt/MSU Catalyst. Effect of Site Activity and Residence Time

A zeolite-based mesostructured (MSU) molecular sieve material was synthesized, characterized, and used in the preparation of Pt (0.6 and 1 wt %) supported catalysts for hydroconversion of n-heptane under the experimental conditions of 300–450°C and 760 mmHg. Samples were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherm, and NH3-TPD (temperature-programmed deposition) techniques. The activity test shows that catalysts have good activity and selectivity for isomerization reaction. Also, increasing metal sites, selectivity tends to the production of aromatization reaction in the heterogeneous catalytic process. Based on experimental results, a kinetic model of this reaction was carried out. Based on other publications and combining the examined features, a network of the reaction was proposed. It can be claimed that the results of converging the feed from the kinetic model are in good agreement with the experimental results. Some of the superiorities of this model compared to other models are the determination of kinetics parameters, source of isomers, aromatic, and cracked products distinctly with emphasis on the effect of site activity and residence time over metal-acid sites.

Experimental and Kinetic Modeling of n-Heptane Hydroconversion over Mesoporous Pt/MSU Catalyst. Effect of Site Activity and Residence Time

Experimental and Kinetic Modeling of n-Heptane Hydroconversion over Mesoporous Pt/MSU Catalyst. Effect of Site Activity and Residence Time

Multiscale Modeling as a Tool for the Prediction of Catalytic Performances: The Case of n-Heptane Hydroconversion in a Large-Pore Zeolite

The optimization of predictive kinetic models for catalytic processes is a topical challenge. In the present work, a predictive multiscale single-event microkinetic model based on the data obtained by density functional theory (DFT) calculation for n-heptane hydroconversion in large-pore zeolites has been obtained. It was validated by a large set of kinetic data obtained by high-throughput kinetic experiments, performed with a well-balanced Pt/Beta zeolite catalyst. DFT calculations show that secondary cations are much less stable than tertiary cations and adsorbed alkenes. This is of prime importance in the quantification of type B isomerization reaction barriers depending on the type of the carbenium ion. Cracking reaction barriers are also strongly affected by the nature of the cation that cracks and that of the cracking products. The agreement between simulated and experimental kinetic data is satisfactory, showing the reliability of the multiscale kinetic approach. Only a few parameters were adjusted to improve the correspondence with experiments. The analysis of the simulated coverage demonstrates a very low proportion of acidic sites involved in the adsorption and further reactions in the relevant experimental conditions. When these occur, tertiary carbenium ion intermediates appear in a significantly higher concentration with respect to other species. This works opens the route to a better prediction of the catalytic performance of large-pore zeolites in alkane hydroconversion.

NiCu bimetallic catalysts derived from layered double hydroxides for hydroconversion of n-heptane

Supported NiCu bimetallic catalysts have been produced in-situ on commercial Al2O3 by using layered double hydroxides as precursors. The resulting catalysts show a uniform Ni and Cu distribution, thus providing good activity and selectivity in the reforming reaction of n-heptane. The catalytic performance has been found to depend on the Cu/Ni ratio, revealing the synergic catalysis between homogeneously dispersed Ni and Cu sites. The good catalysis of NiCu bimetallic catalysts makes it possible to partly or even completely replace Pt with NiCu bimetallic catalysts.

Hydroconversion of n-Heptane over Bifunctional Pt–Ti–MSU/Al–Ti–MSU Catalysts in a Micro Reactor

Cracking and isomerization of n-alkanes, employing bifunctional catalysts, are vital reactions in various refinery processes for producing different high-quality fuels. These catalysts consist of a specific metal component and a specific acid function. The metal component is used for dehydrogenation and hydrogenation constituted from a specific noble metal such as palladium and platinum. The acid function, on the other hand, is used for cracking and isomerization aims. In this work, a number of mesoporous catalysts with different ratios of Si/Ti based on MSU containing Platinum were synthesized and characterized with XRF, XRD, NH3–TPD, and BET tests. These catalysts were applied in n-heptane hydroconversion process in a fixed bed microreactor to see their performance in an actual process. In the microreactor, the pressure was constant (atmospheric), and the temperature varies in the range of 250–600°C. The performance of each of the catalysts was investigated in different ratios of hydrogen to hydrocarbon (5, 10, 15, 20, and 25) and in two values of Weight Hour Space Velocity (WHSV) (1.5 and 2.5 h–1). Products analysis carried out to check out the activity and selectivity of each of the catalysts. The result showed that all samples have a high surface area, favorable pore distribution, and high acidity. The outcome of the study showed that the CAT-D catalyst has the highest activity for normal heptane conversion. This catalyst also has the highest selectivity for isomerization products at moderate temperatures (350°C) and WHSV = 1.5 h–1.

Toward estimation of upgrading of n-heptane over catalysts using robust technique

Catalytic reforming in the presence of metal-acid bifunctional catalysts is a widely used reaction in refinery industry to improve some properties of products like temperature performance of diesel and octane number of gasoline. So the ability of the prediction of Iso-C7 selectivity during n-heptane hyroconversion is a key issue. In this study, a data set which was collected from previous publications are put in an artificial neural network-multi layer perceptron (ANN-MLP) model. Properties used as input parameters are: temperature, pressure, WHSV (weight hourly space velocity), catalysts acidity and pore volume of the catalysts, and Iso-C7 selectivity used as the output parameter. Based on results, the MLP-ANN has great ability to estimate n-heptane hydroconversion. Root mean squared error (RMSE) and R-squared (R2) error were calculated for training, test and total set of data. For training set, test set and total set RMSE are 97915, 5.1607, and 3.9441, respectively and corresponding R2 are 0.97915, 0.9334, and 0.9746, respectively.

Procedure for the synthesis of AlSBA-15 with high aluminium content: Characterization and catalytic activity

Abstract In this study, AlSBA-15 materials with low nSi/nAl ratio were hydrothermally prepared by using three different acids, i.e. HCl, HNO3 and H2SO4, aiming to investigate the effect of the synthesis environment on their physicochemical properties. The resulting aluminium substituted molecular sieves were used as a supports for Pt catalysts. The AlSBA-15 materials and the Pt/AlSBA-15 catalysts were characterised by different techniques (N2 sorption, XRD, Py–FTIR, 27Al MAS NMR, CO chemisorption, TEM and SEM) and tested in n-heptane hydroconversion. It was found that the crystallisation of AlSBA-15 structure under the use of HNO3 led to the formation of AlSBA-15 with the highest amount of Al atoms in tetrahedral coordination. Depending on the AlSBA-15 preparation conditions, the Pt/AlSBA-15 catalysts displayed different physicochemical features, especially in term of acidity. As a consequence of the highest substitution of Al in tetrahedral positions in AlSBA-15 sample synthesised under the use of HNO3, the corresponding Pt catalyst exhibited the highest Bronsted acid sites concentration. The results of n-heptane hydroconversion showed that, this catalyst provided the highest yield of the most desired high-octane number products, i.e. multibranched heptane isomers. At the same time it was less selective towards hydrocarbons displaying the boiling temperatures higher than this of n-heptane (they are produced in cyclisation and aromatization) which are the precursors of carbonaceous deposits.

Prediction of catalytic hydro conversion of normal heptane over catalysts using multi-layer perceptron artificial neural network (ANN-MLP)

Catalytic reforming in the presence of metal-acid bifunctional catalysts is a widely used reaction in refinery industry to improve some properties of products like temperature performance of diesel and octane number of gasoline. So the ability of the prediction of Iso-C7 selectivity during n-heptane hyroconversion is a key issue. In this study, a data set which was collected from previous publications are put in an artificial neural network-multi layer perceptron (MLP-ANN) model. Properties used as input parameters are: temperature, pressure, WHSV (weight hourly space velocity), catalysts acidity and pore volume of the catalysts, and Iso-C7 selectivity used as the output parameter. Based on results, the MLP-ANN has great ability to estimate n-heptane hydroconversion. Root mean squared error (RMSE) and R-squared (R2) error were calculated for training, test and total set of data. For training set, test set and total set RMSE are 97915, 5.1607 and 3.9441, respectively and corresponding R2 are 0.97915, 0.9334 and 0.9746 respectively.

Influence of Molybdenum Loadings on the Properties of MoO3/Zirconia Catalysts

An ideal hydroisomerisation reaction is expected to take place over a bifunctional catalyst, in which a balance between the number of metal sites and acid sites might lead to an optimal performance. In order to assess this relationship and the implications for n-heptane hydroisomerisation, various loadings of molybdenum oxide (1–10 wt%) were impregnated on zirconia with a view to producing samples with a range of acid and metal-like properties. The nature and amounts of the acid sites were determined using quantitative FTIR of pyridine adsorption, while the metal-like properties were determined using CO chemisorption. It was observed that zirconia alone contained only Lewis acid sites (1440 cm−1), while addition of MoO3 generated Bronsted acidity (1536 cm−1). The ratio of Bronsted to Lewis acid sites increased with loadings. Similarly, the amounts of CO taken up by the samples increased with MoO3 loadings; hence, the addition of MoO3 resulted in an improved metal like behaviour. The ratio of Bronsted acid to metal-like sites were found to range between 0.009 and 1.180 on going from 1 to 10 wt% MoO3. The materials were used for n-heptane hydroconversion. The sample with the highest amount of Bronsted acid site, which also consumed the highest amount of CO showed the highest activity. Hence, it could be concluded that the addition of MoO3 improves the Bronsted acid to metal-like site ratio, which resulted in a pronounced improvement in the activity of the samples.

Synthesis and functionalization of ordered mesoporous carbons supported Pt nanoparticles for hydroconversion of n-heptane

Reaction pathway of n-heptane hydroconversion.

N-Heptane hydroconversion over sulfated-zirconia-supported molybdenum carbide catalysts

Molybdenum carbide on sulfated zirconia was prepared by impregnation of MoO3 on sulfated zirconia to give a loading of 5 wt% followed by carburisation at 923 K in a mixture of CH4/H2 (4:1). The resulting catalyst was characterised by N2 adsorption–desorption, CO chemisorption, FTIR of pyridine adsorption, XRD, TPR, TGA, Raman and SEM–EDX. This combination of characterisation studies suggests formation of a well-dispersed Mo2C phase over tetragonal zirconia. When employed in the hydroconversion of n-heptane, high temperature and low space velocity lead to substantial cracking. However, under some conditions, an increase in the research octane number (RON) from 0 (n-heptane) to ca. 50 was attained. Between 723 and 873 K, n-heptane is mainly cracked to iso-pentane and ethane. The product distribution as a function of conversion suggests that the reaction did not simply follow a consecutive reaction pathway, but that other parallel routes were involved.

N-Heptane hydroconversion over nickel-loaded aluminum- and/or boron-containing BEA zeolites prepared by recrystallization of magadiite varieties

Phase-pure [Al]BEA and [Al,B]BEA zeolites, prepared by solid-state recrystallization of synthetic aluminum-containing magadiites and conventionally synthesized [B]BEA, were tested, after ion exchange with nickel, as bifunctional catalysts for hydroconversion of n-heptane. The reducibility of nickel ions incorporated into BEA zeolites by ion exchange was investigated by temperature-programmed reduction (TPR). The acidity of the samples was characterized with strong (pyridine (Py) and ammonia (NH3)) and weak (nitrogen) bases. The adsorbed bases were studied by transmission FT-IR (Py), diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy (N2), and temperature-programmed ammonia evolution (TPAE, NH3). Over Ni/H-[B]BEA the reactants were completely converted via fast hydrogenolysis, whereas this reaction pathway plays only a negligible role in the hydroconversion over Ni/H-[Al]BEA and Ni/H-[Al,B]BEA zeolites. Boron-containing BEA zeolites were less active catalysts than the boron-free catalyst in the principal unimolecular hydroconversion reactions. However, incorporation of boron into the framework of BEA zeolite results in a considerable selectivity shift toward isomerization. Results suggest that the acid strength of bridged hydroxyls, probed with weak (N2) and strong basis (pyridine), was found to be similar in the boron-free and boron-containing BEA samples. The decrease in the isomerization rate and the increase of the apparent activation energy upon incorporation of boron may be attributed to the decrease in the heat of n-heptane adsorption.

Synthesis, characterization and catalytic application of bi- and trimetallic Al-HMS supported catalysts in hydroconversion of n-heptane

Bi (Pt–Sn and Pt–Re) and trimetallic (Pt–Sn–Re) catalysts supported on Al-HMS material (Si/Al=10) were prepared and characterized by X-ray diffraction, N2 adsorption–desorption and temperature programmed reduction techniques. TPR results showed the interaction between metal species and mesoporous framework that can affect the acidity of mesoporous materials. Catalytic performance of samples was investigated for hydroconversion of n-heptane. A comparison of Pt–Re and Pt–Sn catalysts supported on Al-HMS-10 and Al2O3–Cl under the same conditions is made. Mesoporous catalysts exhibited better activity in comparison with Al2O3–Cl supported catalysts. Performance of trimetallic catalysts is better than bimetallic catalysts.

Hydroisomerization of n-Heptane over Pt-Loaded USY Zeolites. Effect of Steaming, Dealumination, and the Resulting Structure on Catalytic Properties

The hydroconversion of n-heptane was studied on five USY zeolite samples loaded with 1 wt % Pt. Experiments were performed on a continuous fixed-bed stainless steel reactor at 210-310 ??C and pressures up to 15 bar. Three in-house samples were subjected to steaming treatment, and the remaining were acid-leached from a commercial source. The study aimed to evaluate the effect of acid leaching, and its subsequent extraframework alumina (EFAL) species removal, on the performance of bifunctional USY zeolite catalysts during n-heptane transformation. Results have shown that steamed samples generate more cracked products at higher conversions when compared to acid-leached ones, more than likely due to a high presence of EFAL species. The degree of steaming played a role in decreasing cracking tendency at higher pressures, which is attributed to pore structure change and decreasing acidity. In addition, steaming resulted in a catalyst sample capable of generating isomers with blended research octane numbers close to those achieved with a robust commercial catalyst. However, poisoning experiments have shown that these two catalysts are highly sensitive to sulfur and require sulfur-free feeds in order to demonstrate their full capacities.

Thermal Stability of Pt Nanoparticles Supported on WOx/Al2O3 for n-Heptane Hydroconversion

AbstractThe thermal stabilization of γ-Al2O3 using W+6 ions has been found useful to the synthesis of Pt/Al2O3 catalysts. The sequential impregnation method was used to study the effect of W6+ upon Pt/ γ-Al2O3 reducibility, Pt dispersion, Raman spectroscopy and n-heptane hydroconversion. The W/Pt atomic ratios varied from 3.28 to 75. We found that the W6+ ions delayed reduction of a fraction of Pt+4 atoms beyond 773 K. At the same time, W6+inhibited sintering of the metallic crystallites once they were formed on the surface. For the sample with a W/Pt atomic ratio of 3.28, W6+ did not inhibit the H2 reduction of Pt oxides even below of 773 K, the Pt oxides were reduced completely, however, the Pt dispersion decreased for this sample with respect to the Pt/γ-Al2O3 catalyst. After reduction at 1073 K, sequential samples impregnating Pt on WOx/γAl2O3 were more active and stable during n-heptane hydroconversion than monometallic Pt/γAl2O3 catalyst. Selectivities for dehydrocyclization, isomerization and Hydrocracking changed significantly when the W/Pt atomic ratio and reduction temperature increased. Initial and final reaction rates were more sensitive to reduction temperature. W6+ ions promoted high thermal stability of Pt crystallites when sequential catalysts were reduced at 1073 K and deactivation of bimetallic catalysts reduced at 773 K and 1073 K was less than the deactivation of Pt/Al2O3 catalyst.

Hydroconversion of n-heptane over Pt/Al-MCM-41 mesoporous molecular sieves

Pt/Al-MCM-41 samples with constant metal loading but various pore sizes were hydrothermally synthesized using cetyltrimethylammonium bromide (CTAB) surfactant with different alkyl chain length (pore diameters ranging from 1.7 to 2.7 nm). These samples were carefully characterized by X-ray diffraction, N 2 physisorption, the infrared spectra, temperature-programmed desorption of ammonia, and solid-state MAS NMR. Hydroconversion of n-heptane was carried out over these Pt/Al-MCM-41 samples. It was found that the steric restrictions are negligible for this catalytic system and high catalytic activity and high isomer yield were achieved. Another finding was that the radius of curvature of pore wall surface had effect on the hydroconversion of n-heptane. It was speculated that the main reason for the curvature effect in this particular model system was that the formation of alkylcarbenium ions, also denoted as the transfer of proton, was affected by the distribution of acid sites on the pore wall surface.

Synthesis of pillared clays with aluminum by means of concentrated suspensions and microwave radiation

Starting from clay suspensions in water at 2% and 30% and also from dry clay, aluminum pillared clays were synthesized by applying microwave radiation both during the maturation of the aluminum polyhydroxication and in the intercalation, in order to reduce the time and the amounts of water with respect to the conventional synthesis of pillared clays. The intercalation was carried out by means of a direct mixture of the pillaring solution and the clay. The X-ray diffraction analyses, the cationic exchange capacity and the catalytic assessment in the n-heptane hydroconversion, showed that the solids synthesized exhibited better characteristics and catalytic behavior than the solid obtained through the conventional method of synthesis.

An improved route for the synthesis of Al13-pillared montmorillonite catalysts

The distribution of Al13 pillars and the process of intercalation in montmorillonite can be enhanced through the application of an ultrasonic treatment. This paper describes the results of ultrasonic treatment in the preparation of Al-pillared montmorillonite with and without prior exchange with Na+. The resulting materials have been characterised by X-ray diffraction (XRD), N2 adsorption/desorption, Scanning Electron Microscopy and Atomic Force Microscopy (AFM). The catalytic activity was tested with the n-heptane hydroconversion test. Optimum results were obtained after ultrasonic treatment up to 20 min without prior Na-exchange before the Al13 intercalation. Longer ultrasonic treatment resulted in partial destruction of the pillared structure. The pore size diameter also increased with increasing ultrasonic treatment up to 20 min with values in the range of 4 nm. This behaviour can be explained by the loss of the typical house of cards structure after prolonged ultrasonic treatment. AFM showed that the pillars in the interlayer of the montmorillonite resulted in a distortion of the tetrahedral sheets of the clay. At atomic scale resolution it was clear that the pillar distribution is not homogenous, confirming earlier results using high resolution TEM. The effects of ultrasonic treatment on the catalytic activity is rather limited, although the pillared clays prepared with short ultrasonic treatments of 5 and 10 min performed slightly better.

Selective Hydroconversion of <i>n</i>-Heptane over Pd-supported Zeolites and Pd-containing Hybrid Catalyst

Hydroconversion of n-heptane was investigated over Pd-supported H-zeolite and hybrid catalyst consisting of Pd/SiO 2 and USY. Highly selective hydrocracking occurred over Pd/ZSM-5 whereas hydroisomerization dominated over Pd/USY and Pd/β. Skeletal isomerization occurred before the cracking reactions. The zeolite used and hydrogen spillover onto the zeolite were important in determining the isomerization selectivity. Experiments over hybrid catalysts suggested that close contact and the balance of metal and acidic sites are crucial in determining the activity and selectivity of isomerization and cracking. A reaction scheme based on the concept of hydrogen spillover was proposed.