Acid Strength Distribution Research Articles

Zeolite-templated carbon synthesized with ion-exchanged FAU-zeolite using alkaline earth metal ions for the selective adsorption of C2 hydrocarbons over C1 hydrocarbon

In this study, zeolite-templated carbon (ZTC) was synthesized using ion-exchanged faujasite-Y (FAU, NaY) zeolites with different alkali earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) to investigate the effects of these metals on the synthesis, characteristics, and C2/C1 hydrocarbon separation performance of ZTC. Thermogravimetric and temperature-programmed desorption of NH3 (TPD-NH3) analyses showed that carbon deposition tends to occur outside the pores because of the increasing number of moderate acid sites as the atomic number increases. In particular, in the case of FAU-ZTC(Ca) synthesized using CaY as the ZTC template, carbon accumulated inside the pores owing to the distribution of the appropriate acid strength, resulting in the highest specific surface area of 2,835 m2/g among the synthesized ZTCs. The combined X-ray photoelectron and Raman spectroscopy results confirm that these defect sites of ZTC act as adsorption sites for large molecules such as C2H4 and C2H6. The isothermal adsorption of CH4, C2H4, and C2H6 showed that FAU-ZTC(Ca) exhibited the highest adsorption capacity ratios of C2H4 and C2H6 to CH4, with a C2H6/CH4 ratio of 5.897 and C2H4/CH4 ratio of 5.288, respectively. The effective pore size ranges affecting the adsorption of CH4, C2H4, and C2H6 determined using linear regression analysis are 0.4 to 0.6 nm for CH4 and 0.6 to 1.1 nm for C2H4 and C2H6. Molecular simulations confirmed that the adsorption energy was maximized by the interaction between the hydrogen atoms of the hydrocarbons and the carbon atoms of ZTC. Furthermore, C2H4 and C2H6 require larger pores than CH4 adsorption because C2H4 and C2H6 prefer to lie horizontally rather than vertically in the pores of the ZTC.

MOX-TiO2 (M=Pt, Pd, Ru) for alcoholysis reaction from furfuryl alcohol to ethyl levulinate

Simple noble metal oxides (PtOx, PdOx, RuOx) based titanium dioxide (Pt–TiO2, Pd–TiO2, Ru–TiO2) were prepared using a facile sol-gel method. The conversion of furfuryl alcohol (FAL) to ethyl levulinate (EL) was studied. Full characterizations were performed using XRD, XPS, Raman and in situ FT-IR. An in-depth study of acidic strength and sites distribution (Brønsted or Lewis) was conducted by NH3-TPD, pyridine-IR. The profiles of H2-TPR and O2-TPD suggested enhanced reducibility and optimum oxygen storage capacity in Pt–TiO2. Remarkable FAL conversion (94.4%), EL yield (89.6%) with productivity (21.3 × 103 molEL/mmolPt h) and TOF (22.5 × 103 molFAL/mmolPt h) were obtained. Metal productivity follows the order: Pt (21.3 × 103 molEL/mmolPt h) > Ru (11.5 × 103 molEL/mmolRu h) > Pd (3.6 × 103 molEL/mmolPd h). Two different reaction pathways were proposed. From computational calculations of charge density differences and Ead value, a robust electron transfer capacity was found in Pt–TiO2, as well as an advantageous FAL adsorption as compared to other catalytic systems.

ZSM‐5@KIT‐6‐encapsulated composite molecular sieves for the catalytic cracking of waste cooking oil model compound to produce light olefins

AbstractBACKGROUNDA series of ZSM‐5@KIT‐6 composite molecular sieve catalysts was prepared by encapsulating ZSM‐5 as a substrate in the mesoporous material KIT‐6. The intent was to use these catalysts to promote the catalytic cracking of a waste cooking oil model compound (WCOMC) to produce light olefins.RESULTSThe morphology, structural characteristics and acidity of each of the resulting catalysts were characterized by X‐ray diffraction, transmission electron microscopy, N2‐Brunauer–Emmett–Teller (N2‐BET) surface area analysis and temperature‐programmed ammonia desorption. The results showed that ZSM‐5 was successfully coated with KIT‐6. The BET surface areas of these catalysts ranged from 345 to 792 m2 g−1 and the specimens had average pore sizes in the range of 2.37–5.51 nm. Total acidity increased with increases in the mass‐based proportion of ZSM‐5 in the material.CONCLUSIONThe catalytic cracking of WCOMC was studied in a lab‐scale fixed‐bed apparatus. Trials at a reaction temperature of 600 °C using the material having a mass‐based ZSM‐5 proportion of 80.0% (ZK‐80) gave the highest gas‐phase yield of light olefins of 43.8%. After 6000 min, the catalytic performance of this material remained stable, demonstrating a resistance to carbon deposits. The superior activity of the present composite catalysts can be ascribed to improvements in pore structure and acid strength distribution. © 2023 Society of Chemical Industry (SCI).

Extend ethylene aromatization single-event kinetic modeling with physical and chemical descriptor based on ZSM-5 catalyst

The ethylene aromatization is critical for the methanol to aromatics and light alkane dehydroaromatization process. The single-event microkinetic (SEMK) model combining the linear free energy theory and solid acid distribution concept were established and extend for the ethylene aromatization process, which can reduce the kinetic parameters and simplify the reaction network by comparison with the SEMK model including subtype elementary steps based on the type of carbenium ions. Further introducing deactivation parameters φ into the model and applying the linear free energy model to the deactivation experimental data, the obtained deactivation parameters φ indicate that the carbon deposition precursors have the greatest impact on reducing the reaction rate of single-molecular reactions and the smallest impact on the hydrogen transfer reaction. Meanwhile, according to the change of reaction enthalpy, effect of carbenium ion structure on methylation, ethylation, cyclization and endo-β scission was investigated by introducing linear free energy concept into the SEMK model. The effect of different acid strengths on elementary steps was investigated based on the acid strength distribution model, it was found that the methylation and oligomerization reactions, the ali-β scission reaction, endo-β scission reaction and the cyclization reaction were more sensitive to strong acidity sites. The physisorption and chemisorption heat are separated from the protonation heat in the linear free energy kinetic model and the acid strength distribution kinetic model, and the absolute values of the obtained physisorption and chemisorption heat increase with the carbon number of carbenium ions. Furthermore, the parameters of the acid strength distribution kinetic model were applied to propane dehydroaromatization on H-ZSM-5 and the ethane dehydroaromatization on Zn/ZSM-5 to confirm the independence of parameters in the SEMK model with the similar reaction network.

Highly efficient catalytic conversion of biomass-derived 2,5-dimethylfuran into renewable p-xylene over zirconium phosphate catalysts

A series of zirconium phosphates (ZrP-x) with various P/Zr ratios were prepared. Among the catalysts, ZrP-2.5 with a high specific surface area of 410.9 m2·g−1 and abundant mesopores exhibited outstanding catalytic performance in the synthesis of p-xylene (PX) from 2,5-dimethylfuran (DMF) and ethylene. A high PX yield of 89.2% and a productivity of 72.3 mmolPX·gcat−1·h−1 were achieved at 250 °C using a small amount of catalyst. The excellent catalytic performance of ZrP-2.5 was attributed to the synergy between the large quantities of acidic sites with appropriate acid strength distribution, balanced Brønsted and Lewis acidity, and abundant mesopores. In addition, the catalyst had excellent recyclability and stability. In-situ FT-IR spectra of adsorbed DMF and ethylene revealed the crucial roles of P-OH and the coordinately unsaturated Zr(IV) in the adsorption and reaction process, which is beneficial to understanding the reaction mechanism and designing highly efficient catalysts.

Evidence of Surface Properties by Isopropanol Decomposition Reaction and NH3‐TPD over Ni−Fe Spinel Nanoparticles Prepared via Hydrothermal Route

AbstractIn this work, surface properties evaluated by catalytic conversion of isopropanol and by ammonia Temperature Programmed Reduction (NH3‐TPD) over ferrite spinel nanoparticles was investigated. Bulk NiFe2O4 with specific surface area 114 m2/g and crystallites size 6 nm was prepared by hydrothermal synthesis using nitrates as precursors. X‐ray diffraction (XRD), Raman spectroscopy, specific surface area by B.E.T, Scanning Electron Microscopy (SEM) and X‐ray energy dispersive microanalysis (EDS), Transmission Electron Microscopy (TEM) and X‐ray Photoelectron Spectroscopy (XPS) techniques were used for their structural and textural characterizations. The reducibility by hydrogen at variable temperatures was investigated by Temperature Programmed reduction (H2‐TPR) and Thermal Gravimetric Analysis‐ Differential Scanning Calorimetry (TGA‐DSC). The total acidity and acid strength distribution was determined by NH3‐TPD. The synthesized oxide showed the presence of mixed phases containing the inverse spinel structure NiFe2O4 as the major phase and iron oxide α‐Fe2O3 as an additional phase. It was shown that the surface of the powder was richer in Ni2+ species. The surface acidity (Brönsted and Lewis) determined by NH3‐TPD showed that the number of acidic sites increased dramatically with the temperature. The catalytic conversion of isopropanol yields both acidic and redox/basic sites were available. A good correlation between textural, structural, redox and acid‐base properties of catalyst is established.

Effect of Preparation Method on the Catalytic Performance of HZSM-5 Zeolite Catalysts in the MTH Reaction.

A kind of nano-ZSM-5 zeolite crystal was synthesized by the hydrothermal method, and HZSM-5 zeolite powder was obtained via acid exchange. By using pseudoboehmite as a binder, a series of HZSM-5 zeolite catalysts for methanol-to-hydrocarbons (MTH) were prepared through adjusting the binder content between 20 and 50% in addition to the molding method of wet extrusion and mechanical mixing. XRD, 27Al NMR, SEM-EDS, ICP, low-temperature N2 adsorption and desorption, NH3-TPD, Py-FTIR, FT-IR, TG and elemental analyses were used to characterize the properties of fresh catalysts and coke-deposited catalysts. Then, MTH catalytic performance was evaluated in a continuous-flow fixed-bed reactor. The characterization and evaluation results showed that the addition of dilute nitric acid during the molding process increased the amount of moderate-strength acid and formed a hierarchical pore distribution, which helped to reduce the reaction ability of cracking, aromatization and hydrogen transfer, improve the diffusion properties of the catalyst and slow down the coke deposition rate. The catalyst with a binder content of 30% made by wet extrusion with dilute nitric acid had the best performance, whose activity stability of MTH increased by 96 h, higher than other catalysts, and the coke deposition rate was slower, which was due to the most suitable distribution of acid strength and B/L ratio as well as the most obvious hierarchical pore structure.

Engineering the Distinct Structure Interface of Subnano-alumina Domains on Silica for Acidic Amorphous Silica-Alumina toward Biorefining.

Amorphous silica–aluminas (ASAs) are important solid catalysts and supports for many industrially essential and sustainable processes, such as hydrocarbon transformation and biorefining. However, the wide distribution of acid strength on ASAs often results in undesired side reactions, lowering the product selectivity. Here we developed a strategy for the synthesis of a unique class of ASAs with unvarying strength of Brønsted acid sites (BAS) and Lewis acid sites (LAS) using double-flame-spray pyrolysis. Structural characterization using high-resolution transmission electron microscopy (TEM) and solid-state nuclear magnetic resonance (NMR) spectroscopy showed that the uniform acidity is due to a distinct nanostructure, characterized by a uniform interface of silica–alumina and homogeneously dispersed alumina domains. The BAS population density of as-prepared ASAs is up to 6 times higher than that obtained by classical methods. The BAS/LAS ratio, as well as the population densities of BAS and LAS of these ASAs, could be tuned in a broad range. In cyclohexanol dehydration, the uniform Brønsted acid strength provides a high selectivity to cyclohexene and a nearly linear correlation between acid site densities and cyclohexanol conversion. Moreover, the concerted action of these BAS and LAS leads to an excellent bifunctional Brønsted–Lewis acid catalyst for glucose dehydration, affording a superior 5-hydroxymethylfurfural yield.

Preparation of n-amyl acetate via esterification of acetic acid and n-amyl alcohol using [HSO3-pmim][HSO4]/SiO2 as catalyst: Catalyst preparation, characterization and reaction kinetics

In order to present a green method to produce n-amyl acetate, a novel supported ionic liquids (ILs) catalyst [HSO3-pmim][HSO4]/SiO2 was synthesized by sol–gel method and was used to catalyze the esterification reaction of acetic acid and n-amyl alcohol. The kinetic equations for the esterification were established based on ideal quasi homogeneous (IQH) model and Langmuir-Hinshelwood-Hougen-Watson (LHHW) model. The parameters in the equations were obtained from kinetic experimental data fit using fourth order to fifth order Runge-Kutta algorithm. The morphology, surface elements, structural stability, pore diameter, specific surface area, thermal stability and distribution of acid strength of the fabricated catalysts were characterized in detail, while immobilization yield, corrosiveness and stability of the catalyst were also evaluated. The reaction kinetic performances of [HSO3-pmim][HSO4]/SiO2 were compared with conventional catalysts like sulfuric acid, P-toluenesulfonic acid, [HSO3-pmim][HSO4] and [HSO3-pmim][HSO4]/Silica gel by the reaction kinetic experiments. The equilibrium conversion of acetic acid in the presence of [HSO3-pmim][HSO4]/SiO2 was increased by 10.8% after immobilization. The mean absolute squared error of the kinetic equations of the esterification based on LHHW model and IQH model were 3.87 × 10-5 and 1.49 × 10-4 respectively. LHHW model based on the solid–liquid reaction mechanism were in better agreement with the experimental results. This concept of recyclable supported IL catalyst provides promising applications prospects for the industrial production of n-amyl acetate.

Thermal desorption of trimethylphosphine (TMP) on the HY zeolite followed by FT-IR and 31P MAS NMR

Characterization of the acidic properties of solid acid catalysts is essential to understanding their catalytic performance with respect to activity, deactivation rate and product selectivity. In this work, trimethylphosphine (TMP) was used as a probe molecule for the study of acidity in a HY zeolite activated at 773 ​K. The variations in type, concentration and acid strength with the desorption temperature of the probe molecule were followed by infrared spectroscopy (FT-IR) and solid-state Nuclear Magnetic Resonance (ss-NMR). Oxidation of TMP to trimethylphosphine oxide (TMPO) provided additional information about Brønsted (BAS) and Lewis (LAS) acid sites with different acid strengths. The variation in acid strength of certain species determined by calculating the concentration percentage of the desorption and reabsorption of the majority species by increasing the desorption temperature. The 31P ss-NMR chemical shifts at δ=-62, −32 to −58, 45 and 51 ​ppm correspond to weak acid sites (<423 ​K). The peaks at δ= 54 and 55 ​ppm arose from medium acid sites (423–623 ​K). The strong acid sites at δ= 58, 61, 63, 64, 65, 67, 70, 73, 76 and 80 ​ppm correspond to sites with different acid strengths (>623 ​K). Our results demonstrated differences in the concentrations of acid and the distribution of acid strengths of extra-framework (EFAl) aluminum species in different cavities by varying the desorption temperature of the probe molecule. The developed methodology provides more detailed information about acidic properties and can be used for solid acid catalysts using alkylphosphines and their oxides as probe molecules.

A study on the alkylation of m-cresol with 1-decene over mesoporous silica supported tungstophosphoric acid (HPW)

Linear alkylcresols were synthesized in high yield by the alkylation of m-cresols with 1-decene in the presence of 25%HPW/SBA-15 catalyst. The physicochemical properties of the catalyst were investigated by means of N2 adsorption/desorption measurements (textural properties: surface area, pore volume and average pore diameter) and thermal desorption of diethyl-amine (acidity and the acid strength distribution). HPW-loaded acid as well as the SBA-15 support displayed a mesoporous structure. The effects of the reaction time and the catalyst amount on the reaction were studied. The main monitored parameters were the conversion of m-cresol, yield of decylcresol isomers (ortho- and para-) and yield of polyakylated cresol. The results indicates that 25%HPW/SBA-15 catalyst has high catalytic activity, with the m-cresol conversion of 93.8% , at 160 °C with a reaction time of 150 min and a catalyst loading of 0.5 wt% m-Cresol was alkylated preferably in the para-position, the yield of 4-(decan-2yl)-3-methylphenol, after 150 min reaction time was 54.5%.

Optimization of Supports in Bifunctional Supported Pt Catalysts for Polystyrene Hydrocracking to Liquid Fuels

A series of bifunctional platinum catalysts were prepared, supported on alumina or different zeolites, some of which were submitted to either desilication or dealumination in order to modify their acidic properties. The catalysts were characterized for their structural and textural properties, their acidic properties, including distribution of acid strength and Bronsted and Lewis acidity, their metallic properties, and used in the hydrocracking of polystyrene under kinetic control, where activity in end-of-chain scission and random scission of the polymer has been quantified as well as the distribution of products. Activation energies and pre-exponential factors have been calculated from the kinetic data, and analyzed in terms of compensation effect, in order to extract conclusions on activity, active centers and reaction pathways. Finally, activation energies, both of end-of-chain and random scissions, yield to gasoline fraction and percentage of aromatics in the gasoline fraction have been correlated with catalytic properties in order to extract conclusions on the major catalytic properties affecting catalytic performance in this process, from the point of view of catalytic design.

Synthesis and Evaluation of Levulinic Ester as Biodiesel Additives

In this study, the SO42-/TiO2-La2O3-Fe2O3 catalyst was prepared and tested in the conversion of fructose to ethyl levulinate . The catalyst was characterized from the point of view of the textural analysis, FT-IR analysis, acid strength distribution, X-ray powder diffraction and pyridine adsorption IR spectra. The influence of the reaction parameters on the ethyl levulinate yield was study. The maximum yield of 37.95% in levulinate esters was obtained at 180 �C, 2 g catalyst and 4 h reaction time. The effect of ethyl levulinate addition to diesel-biodiesel blend in different rates, i.e, 0.5, 1, 2.5, 5 (w.t %) on density, kinematic viscosity and flash point was evaluated and compared with the European specification.

Dehydrogenative Coupling of Methanol for the Gas-Phase, One-Step Synthesis of Dimethoxymethane over Supported Copper Catalysts.

Oxymethylene dimethyl ethers (OMEs), CH3-(OCH2)n-OCH3, n = 1-5, possess attractive low-soot diesel fuel properties. Methanol is a key precursor in the production of OMEs, providing an opportunity to incorporate renewable carbon sources via gasification and methanol synthesis. The costly production of anhydrous formaldehyde in the typical process limits this option. In contrast, the direct production of OMEs via a dehydrogenative coupling (DHC) reaction, where formaldehyde is produced and consumed in a single reactor, may address this limitation. We report the gas-phase DHC reaction of methanol to dimethoxymethane (DMM), the simplest OME, with n = 1, over bifunctional metal-acid catalysts based on Cu. A Cu-zirconia-alumina (Cu/ZrAlO) catalyst achieved 40% of the DMM equilibrium-limited yield under remarkably mild conditions (200 °C, 1.7 atm). The performance of the Cu/ZrAlO catalyst was attributed to metallic Cu nanoparticles that enable dehydrogenation and a distribution of acid strengths on the ZrAlO support, which reduced the selectivity to dimethyl ether compared to a that obtained with a Cu/Al2O3 catalyst. The DMM formation rate of 6.1 h-1 compares favorably against well-studied oxidative DHC approaches over non-noble, mixed-metal oxide catalysts. The results reported here set the foundation for further development of the DHC route to OME production, rather than oxidative approaches.

Renewable Butene Production through Dehydration Reactions over Nano-HZSM-5/γ-Al2O3 Hybrid Catalysts

The development of new, improved zeolitic materials is of prime importance to progress heterogeneous catalysis and adsorption technologies. The zeolite HZSM-5 and metal oxide γ-Al2O3 are key materials for processing bio-alcohols, but both have some limitations, i.e., HZSM-5 has a high activity but low catalytic stability, and vice versa for γ-Al2O3. To combine their advantages and suppress their disadvantages, this study reports the synthesis, characterization, and catalytic results of a hybrid nano-HZSM-5/γ-Al2O3 catalyst for the dehydration of n-butanol to butenes. The hybrid catalyst is prepared by the in-situ hydrothermal synthesis of nano-HZSM-5 onto γ-Al2O3. This catalyst combines mesoporosity, related to the γ-Al2O3 support, and microporosity due to the nano-HZSM-5 crystals dispersed on the γ-Al2O3. HZSM-5 and γ-Al2O3 being in one hybrid catalyst leads to a different acid strength distribution and outperforms both single materials as it shows increased activity (compared to γ-Al2O3) and a high selectivity to olefins, even at low conversion and a higher stability (compared to HZSM-5). The hybrid catalyst also outperforms a physical mixture of nano-HZSM-5 and γ-Al2O3, indicating a truly synergistic effect in the hybrid catalyst.

Hydrogenation of levulinic acid to γ-valerolactone over bifunctional Ru/(AlO)(ZrO)n catalyst: Effective control of Lewis acidity and surface synergy

A bifunctional Ru/(AlO)(ZrO)n catalyst was reported for efficient hydrogenation of levulinic acid to γ-valerolactone, an important and environmental-benign upgrading process of bio-platform compound. The optimal Ru/(AlO)(ZrO)0.1 catalyst showed 100% yield to γ-valerolactone in water at 120 °C under 1 MPa H2, one of the best performances among Ru catalysts under mild conditions. And this catalyst also presented good stability and reusability. PXRD, TEM, XPS, CO chemisorption, CO adsorption DRIFT-IR, NH3-TPD and pyridine adsorption IR gave insights into the acidic property and surface synergy of the catalysts. Highly active electron-rich Ru0 sites stabilized by strong metal-support interaction (SMSI) can effectively adsorb and activate molecular H2 and CO bond in levulinic acid. Varying Zr/Al ratio and calcination temperature can rationally control the acid strength and acid sites distribution of support, and (AlO)(ZrO)0.1 calcined at 400 °C exhibited the maximal proportion of Lewis acid sites. Ru0 species and Lewis acid sites synergistically enhanced the conversion of levulinic acid and facilitated the intramolecular dehydration of 4-hydroxypentanoic acid as intermediate to γ-valerolactone (i.e., the rate-limiting step).

A facile solvent-free synthesis strategy for Co-imbedded zeolite-based Fischer-Tropsch catalysts for direct gasoline production

A series of Co-imbedded zeolite-based catalysts were synthesized following a facile solvent-free grinding route. The catalytic performance for direct syngas conversion to gasoline range hydrocarbons was compared with their counterpart Co-impregnated zeolite-based catalysts. Successful transformation of solid raw materials to targeted zeolite was confirmed by XRD, SEM, STEM, and N 2 physisorption analysis. An in-depth study of acidic strength and acidic site distribution was conducted by NH 3 -TPD and Py-IR spectroscopy. Acidic strength showed a pivotal role in defining product range. Co@S1, with the weakest acidic strength of silicalite-1 among three types of zeolites, evaded over-cracking of product and exhibited the highest gasoline and isoparaffin selectivity (≈70% and 30.7%, respectively). Moreover, the solvent-free raw material grinding route for zeolite synthesis accompanies several advantages like the elimination of production of wastewater, high product yield within confined crystallization space, and elimination of safety concerns regarding high pressure due to the absence of the solvent. Facileness and easiness of the solvent-free synthesis route together with promising catalytic performance strongly support its application on the industrial scale. A facile and green solvent-free solid raw material grinding route was used to prepare Co-imbedded zeolite-based catalysts for direct gasoline production from syngas via Fischer-Tropsch synthesis.

Quantitative Relationship Between Activity and Acid Site Distribution in the Oligomerization of Ethylene Over MCM-41 Catalyst

Nickel ion exchanged MCM-41 samples with different Si/Al ratios and Ni-ZSM-5/MCM-41 were prepared and used to catalyze ethylene oligomerization which was performed in a fixed bed model (T = 523 K, P = 2 MPa). A temperature programmed desorption of ammonia (NH3-TPD) method was employed to quantitatively determine the acid strength distribution of Ni-MCM-41 samples with different Si/Al ratios and Ni-ZSM-5/MCM-41. The TPD spectrum was analyzed by an interrupted-TPD method with desorption-control (dc-method) to obtain the desorption activation energy of ammonia, which can be used as acid strength scale for the purpose of correlation with catalytic activity. A quantitative relationship between catalyst acidity and catalytic activity was established by a Bronsted type equation. The site with desorption activation energy of ammonia E = 124 kJ mol−1 was found as the most suitable site for ethylene oligomerization. An approximate linear relationship is obtained between the activity of the ethylene oligomerization reaction and the acid amount corresponding to the acid site with E = 124 kJ mol−1.

Hydrodesulfurization of Dibenzothiophene on a CoNiMo Catalyst

In order to evaluate the performance of CoNiMo/g-Al2O3, the hydrogenolysis of dibenzothiophene was carried out. The conversion of dibenzothiophene, the yields of the reaction products and the unconverted sulfur content, expressed in ppm, were determined, at different temperatures in the catalytic layer (300�C-360�C), pressures (40 bar-60 bar) and liquid hourly space velocity (1-4h-1). The hydrodesulphurization catalyst was characterized by: determining the textural characteristics (BET specific surface area, mean pore diameter and pore volume), the acidic strength distribution, morphological analysis (scanning electron microscopy - SEM) and by identification of the species (X-ray diffraction � XRD). The analysis of the textural characteristics results in an ordered mesoporous structure of the catalyst, with a specific area of 280 m2/g and a medium pore diameter of 4.42 nm. At high temperature of 360�C and pressure of 60bar, the CoNiMo/ g-Al2O3 exhibit a good activity in hydrodesulphurization, with a 100% conversion of dibenzotiophene.

Kinetics of thiophene hydrodesulfurization over a supported Mo–Co–Ni catalyst

In this study, the kinetics of thiophene (TH) hydrodesulfurization (HDS) over the Mo–Co–Ni-supported catalyst was investigated. Trimetallic catalyst was synthesized by pore volume impregnation and the metal loadings were 11.5 wt % Mo, 2 wt % Co, and 2 wt % Ni. A large surface area of 243 m 2 /g and a relatively large pore volume of 0.34 cm 3 /g for the fresh Mo–Co–Ni-supported catalyst indicate a good accessibility to the catalytic centers for the HDS reaction. The acid strength distribution of the fresh and spent catalysts, as well as for the support, was determined by thermal desorption of diethylamine (DEA) with increase in temperature from 20 to 600 °C. The weak acid centers are obtained within a temperature range between 160 and 300 °C, followed by medium acid sites up to 440 °C. The strong acid centers are revealed above 440 °C. We found a higher content of weak acid centers for fresh and spent catalysts as well as alumina as compared to medium and strong acid sites. The catalyst stability in terms of conversion as a function of time on stream in a fixed bed flow reactor was examined and almost no loss in the catalyst activity was observed. Consequently, this fact demonstrated superior activity of the Mo–Co–Ni-based catalyst for TH HDS. The activity tests by varying the temperature from 200 to 275 °C and pressure from 30 to 60 bar with various space velocities of 1–4 h −1 were investigated. A Langmuir–Hinshelwood model was used to analyze the kinetic data and to derive activation energy and adsorption parameters for TH HDS. The effect of temperature, pressure, and liquid hourly space velocity on the TH HDS activity was studied.