Pyridine Hydrodenitrogenation Research Articles

Catalytic Hydrodenitrogenation of Pyridine under Hydrothermal Conditions: A Comprehensive Study

This article focuses on the kinetic modeling and catalytic performance of hydrodenitrogenation of pyridine under hydrothermal conditions. Piperidine derivatives are the major nitrogen-containing intermediates, including 1-piperidinecarboxaldehyde, 1-piperidineethanol, and alkyl piperidines. Catalysts overall improved the formation of N-free products including 1-pentanol and 2-methyl-1-pentanol. Commercial Pd/C provided the highest pyridine conversion rate at 350 °C, while the homemade Ni–Ru bimetallic catalyst provided a prominent denitrogenation activity at 400 °C, leading to the highest 1-pentanol yield as a major denitrogenated product. Conversion of pyridine over the Ni50Ru50/C catalyst led to formation of three major alkyl piperidines (1-ethyl piperidine, 1-methyl piperidine, and 1-pentyl piperidine). These alkyl piperidine intermediates could further be converted into amino and N-free compounds. A kinetic model was developed to mathematically describe the hydrothermal HDN reaction of pyridine over the Ni50Ru50/C catalyst, which clearly captured all data trends and fitted the temporal variation of all major products. Sensitivity analysis suggested that dehydrogenation from piperidine to pyridine has a strong impact on the whole reaction pathways.

One-step synthesis of ultrafine MoNiS and MoCoS monolayers as high-performance catalysts for hydrodesulfurization and hydrodenitrogenation

A one-step facile strategy is developed to prepare highly disordered MoS2-based monolayers via the thermal organometallic decomposition in the presence of elemental sulfur and oleylamine. Characterizations including TEM, SEM, XRD, Raman spectroscopy, XPS, and nitrogen adsorption–desorption confirm the monolayer structure of the MoS2-based sulfides with similar ultrasmall lateral sizes of 4.2–4.6 nm and the successful doping of Ni and Co atoms in MoNiS and MoCoS. Due to the abundant active sites enabled by the ultrafine monolayer structure, these sulfides exhibit significantly improved activity in the hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyridine compared to the commercial multilayer MoS2. Rational comparison of these catalysts justified by almost the same size, morphology, specific surface area confirms the superior promoting roles of Co for the HDS while Ni for the HDN, and further demonstrates that pyridine is a competitive inhibitor for thiophene in binding to the active sites of the catalysts. Moreover, excellent reusability for five consecutive cycles in the HDS and HDN is exhibited by MoCoS and MoNiS, respectively, which is attributed to their well-retained monolayer structure during the tests. This study highlights the significance of advanced synthetic strategy for improving the catalytic performance of Mo-based sulfides as industrial HDS and HDN catalysts.

Pyridine hydrodenitrogenation kinetics over a sulphided NiMo/γ-Al2O3 catalyst

Gas phase pyridine hydrodenitrogenation (HDN) kinetics have been determined over a commercial, sulphided NiMo/γ-Al2O3 catalyst in a Berty type Continuous Stirred Tank Reactor (CSTR). Temperatures and total pressures varied from 573 to 633K and from 1.5 to 4.0MPa, in a space time range from 350 to 1800kgcatsmol−1P. Pyridine was first hydrogenated into piperidine. The subsequent denitrogenation went via piperidine ring opening to pentyl amine followed by the actual nitrogen removal, yielding C5 hydrocarbons and ammonia as end products. The C–N bond scission rate was enhanced by the presence of H2S, which could be rationalized based on a substitution mechanism. Langmuir Hinshelwood reaction mechanisms accounting for two types of sites, i.e., coordinatively unsaturated sites (∗) and sulphur anions (S2−), have been developed to assess the experimentally measured kinetics. These models explicitly accounted for the substitution mechanism in the C–N bond scission in terms of elementary steps. Model discrimination has allowed assessing the importance of hydrogen addition to pyridine through heterolytically or homolytically chemisorbed hydrogen and hydrogen sulphide, as well as of sulphydril or hydrogen assisted C–N bond scission in piperidine denitrogenation. Chemisorption entropies were calculated a priori such that, in addition to the kinetic parameters, only chemisorption enthalpies had to be estimated by regression. The third hydrogen addition and the naphthenic C–N bond breaking were found to be rate determining in pyridine hydrogenation and piperidine denitrogenation, with activation energies amounting to 41kJmol−1 and 185kJmol−1. A distinct linear relationship was established between the proton affinity of the various nitrogen components and their free energy of chemisorption.

Hydrodenitrogenation of pyridine on MoP(0 1 0): Competition between hydrogenation and denitrification

Periodic density functional theory (DFT) calculations were performed to investigate the hydrodenitrogenation (HDN) mechanism of pyridine on MoP(010). The geometries and energies for the adsorbed pyridine were first described, and then the competition between hydrogenation and denitrification of pyridine were analysed to elaborate the HDN mechanism. Our results show that pyridine has side-on and end-on adsorption modes on MoP(010), in which the most stable η4(N1,C2,C3,C5) configuration of the side-on mode facilitates the hydrogenation of pyridine. The favourable HDN pathway of pyridine proceeds along the pyridine→4-Monohypyridine→3,4-Dihydropyridine→1,3,4-Trihydropyridine→1,3,4,5-Tetrahydropyridine→CH(CH2)3CHNH route. The denitrification process could not exhibit the competitive advantage until after the fourth hydrogenation step of 1,3,4,5-Tetrahydropyridine. This theoretical work provides further information on the HDN mechanism of pyridine on MoP(010), and also provides insight into the understanding of competition between hydrogenation and denitrification.

Pyridine hydrodenitrogenation over industrial NiMo/γ-Al2O3 catalyst: Application of gas phase kinetic models to liquid phase reactions

A systematic methodology for simulating gas–liquid–solid kinetics starting from a gas–solid kinetics model has been developed and applied to pyridine hydrodenitrogenation over an industrial NiMo/γ-Al2O3 catalyst. Data have been acquired in two independent, dedicated experimental programmes: i.e. an extended set of gas phase experiments that were previously carried out in a Berty type reactor setup at 573–633K, 1.5–4.0MPa and space times between 0.36 and 1.8kgcats/mmol and a more limited set of liquid phase experiments that were performed as part of the present work in a Robinson–Mahoney reactor setup at 543–613K, 6.0–8.0MPa and space times between 0.65 and 3.0kgcats/mmol. At liquid phase conditions the pyridine conversion ranged from 47% to 70%, while at gas phase conditions the pyridine conversion ranged from 17% to 72%. The reaction temperature and H2S inlet partial pressure were found to be most significantly affecting the selectivity to intermediates and products in both experimental programmes. 1-pentylpiperidine formation, a bimolecular reaction product exclusively observed at liquid phase conditions, could be ascribed to the differences in phases present during the kinetic measurements as well as to the differences in molar H2 and H2S to pyridine inlet ratios used and the resulting surface concentrations. A kinetic model constructed using the gas phase data was extended to liquid phase conditions by accounting for (i) liquid phase non-ideality, (ii) solvent adsorption effects and (iii) the additionally observed response, i.e. 1-pentylpiperidine. The latter was found to be produced via condensation between piperidine and pentylamine.

Comprehensive kinetic study for pyridine hydrodenitrogenation on (Ni)WP/SiO2 catalysts

In this work the reaction kinetics for pyridine hydrodenitrogenation on (Ni)WP/SiO2 catalysts were determined. The experiments were conducted at 17.2bar and between 573K and 633K for various flow rates of hydrogen and pyridine. Adding Ni to the WP/SiO2 catalyst enhanced the hydrogenation reaction and gave higher pentane and pentylamine yields. A trend in terms of selectivity was not evident on either catalyst. The results were fit to several models and a Bayesian approach was applied for parameter estimation and model discrimination. Adding Ni to the WP/SiO2 catalyst did not change the reaction mechanism – both catalysts favor the same Langmuir–Hinshelwood model with different active sites for hydrogenation and CN bond cleavage. Ni did, however, influence the type of adsorbed species, the heat of adsorption and the activation energies.

Ni Promotion of WP/SiO2 Catalysts for Pyridine Hydrodenitrogenation

WP/SiO2 catalysts promoted with Ni were prepared by wet impregnation with various molar ratios of Ni to W and then evaluated in the reaction of pyridine hydrodenitrogenation for pyridine conversion and product selectivity. The addition of Ni to the WP/SiO2 catalysts resulted in increased pyridine conversion and selectivity to pentane. The molar ratios of Ni:W:P are important, because nickel and tungsten compete for phosphorous and form WP, W3O, Ni2P and/or W crystals.

Catalytic hydrothermal hydrodenitrogenation of pyridine

We herein report on the hydrothermal catalytic conversion of pyridine to hydrocarbons. The catalytic activity of several supported noble metal (5wt%) catalysts (Pt/C, Pd/C, Ru/C and Rh/C, sulfided Pt/C, and Pt/γ-Al2O3), a traditional hydrodenitrogenation (HDN) catalyst (sulfided CoMo/γ-Al2O3), a transition metal carbide (Mo2C) and sulfide (MoS2), and a noble metal oxide (PtO2) toward the HDN of pyridine in a hydrothermal reaction medium between 250 and 400°C was determined. The Pt/γ-Al2O3 catalyst proved to be the most active for hydrothermal HDN of pyridine, and we report the effects of batch holding time, reaction temperature, catalyst loading, initial hydrogen pressure, and water density on the Pt/γ-Al2O3-catalyzed HDN of pyridine in supercritical water. The latter two process variables had the greatest influence on the product yields and distribution. Conditions were identified that lead to essentially 100% conversion of pyridine to N-free hydrocarbons. The catalyst shows some modest loss in activity upon being reused. An HDN reaction network for pyridine under hydrothermal conditions was proposed. The main HDN products are n-butane and n-pentane. Nitrogen was removed as ammonia.

Preparation and Ultra-Deep Hydrorefining Performance of Ni-P/Al<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> Catalysts

A series of Al2O3-ZrO2 (AZ-X) composite oxides with different ZrO2 contents were prepared by a chemical precipitation method. Ni-P/AZ-X catalysts were prepared by temperature-programmed reduction. The supports and catalysts were extensively characterized by X-ray diffraction (XRD) and BET. The effects of support composition and P/Ni molar ratios on the catalytic performance of the catalysts were investigated by thiophene hydrodesulfurization (HDS) and pyridine hydrodenitrogenation (HDN). In comparison with Al2O3, Al2O3-ZrO2 (20 wt% ZrO2) composite oxide supported Ni-P catalyst exhibited higher activity and the activities of HDS and HDN increased by 7.5 % and 11.1 %, respectively. Studies of Ni-P/AZ-X catalysts with varying initial P/Ni molar ratios indicated that oxidic precursors with molar ratios of P/Ni = 2/1 yielded catalyst containing phase-pure Ni2P which exhibited optimal activity.

PREPARATION, CHARACTERIZATION, AND CATALYTIC ACTIVITY TEST OF Ni-Mo/NATURAL ZEOLITE ON PYRIDINE HYDRODENITROGENATION

Preparation, characterization, and catalytic activity test of Ni-Mo/natural zeolite on pyridine hydrodenitrogenation were carried out. Preparation of catalyst was conducted by impregnation method using nickel nitrate hexahydrate and ammonium heptamolibdate precursor as Ni and Mo source respectively. Characterization of catalyst was conducted by using gravimetry, atomic absorption spectrophotometry, and X-ray diffraction method. Catalytic activity test on pyridine hydrodenitrogenation was carried out by using flow system reactor with hydrogen flow rate variable. The research results showed that the catalyst's total acidity and crystallinity are increased with level of impregnation success of 96.71% and 90.08% respectively. Ni-Mo/natural zeolites able to increase the catalytic conversion up to 71.78% at 350 °C and hydrogen flow rate of 10 mL/min with more highly varied product distribution. Assuming that the pyridine hydrodenitrogenation follows the pseudo first order kinetics.

Ni//Mo synergism via hydrogen spillover, in pyridine hydrodenitrogenation

The pyridine hydrodenitrogenation (HDN) over physically separated stacked Ni//Mo beds was investigated using a continuous-flow high pressure (3 MPa) stainless steel microreactor. Results prove the existence of synergism between physically separated beds of Ni-/γ-Al2O3 and Mo/γ-Al2O3 catalysts for the pyridine hydrodenitrogenation reaction. This synergism is explained by the formation of hydrogen spillover. Product analysis of the pyridine hydrodenitrogenation over Ni//Mo stacked beds suggested that the hydrogen spillover modified the active sites of the MoS2 by increasing the hydrogenation sites.

Effect of citric acid on the synthesis of tungsten phosphide hydrotreating catalysts

The effect of using citric acid in the synthesis of unsupported tungsten phosphide (WP) hydrotreating catalyst was investigated by synthesizing WP using varying amounts of citric acid. Catalyst characterization was done using nitrogen physisorption, CO chemisorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The activities of the catalysts were tested on a high pressure kinetics rig using the hydrodenitrogenation of pyridine as a test reaction. The use of citric acid in the preparation resulted in smaller WP particles—1–10 μm versus >100 μm when no citric acid was used. The characterization results suggest that the citric acid formed complexes with the W ions and limited the agglomeration of these ions during calcination. The smaller WP particles were more active catalysts for pyridine conversion on both per volume and per site basis.

A general method for determining the role of spectroscopically observed species in reaction mechanisms: Analysis of coverage transients (ACT)

A kinetic method is described to determine the role of adsorbed intermediates in heterogeneous reaction mechanisms. The method, denoted as analysis of coverage transients (ACT), involves comparing the time response of a spectroscopically observed species in an inert gas and a reactive gas to differentiate between adsorption–desorption processes and reaction. The method is applied in a kinetic study of pyridine hydrodenitrogenation (HDN) on a 12.2 wt% silica-supported nickel phosphide (Ni 2P/SiO 2) catalyst at 423 K and atmospheric pressure. In situ Fourier transform infrared spectroscopy (FTIR) measurements of pyridine adsorbed on Ni 2P revealed the formation of a pyridinium surface intermediate. The concentration of the pyridinium intermediate increased with pyridine partial pressure and decreased in the presence of hydrogen, suggesting that it was a reaction intermediate. However, transient and steady-state kinetic measurements showed that the rate of reaction of the intermediate did not correspond to the overall reaction rate, and it is concluded that the pyridinium intermediate is not directly involved in the HDN reaction of pyridine over Ni 2P. The studies demonstrate that mere observation of an adsorbed surface species at reaction conditions is not sufficient to prove that it is a reaction intermediate. The ACT method has potential as it can be used with any type of spectroscopy, as long as the surface coverage can be calibrated.

Kinetic Modeling of Hydrodenitrogenation of Pyridine

This study is aimed at developing a kinetic model for the hydrodenitrogenation (HDN) of pyridine. The developed model deals with the selectivity of piperidine, one of the products obtained from the HDN of pyridine and with the conversion of pyridine to piperidine. Kinetic parameters were estimated from the results of the experimental data obtained from literature sources where the reactions were carried out in a trickle-bed reactor in the liquid phase over Mo2C, NbMo2C, and MoS2/SiO2 catalysts at temperatures of 480 to 590 K. POLYMATH 5.0 software was used to solve the proposed first-order model. It was shown that during the course of the HDN reaction of pyridine the conversion increases exponentially with temperature while selectivity of piperidine with respect to pyridine decreases with temperature. The changes in activation energies evaluated for the catalysts were 80.30 kJ/mol, 55.10 kJ/mol, and 40.85 kJ/mol for Mo2C, NbMo2C, and MoS2/SiO2, respectively.

Mesoporous silica–alumina as support for Pt and Pt–Mo sulfide catalysts: Effect of Pt loading on activity and selectivity in HDS and HDN of model compounds

The potential of mesoporous silica–alumina (MSA) material as support for the preparation of sulfided Pt and Pt–Mo catalysts of varying Pt loadings was studied. The catalysts were characterized by their texture, hydrogen adsorption, transmission electron microscopy, temperature programmed reduction (TPR) and by activity in simultaneous hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyridine. Sulfided Pt/MSA catalysts with 1.3 and 2wt.% Pt showed almost the same HDS and higher HDN activities per weight amounts as conventional CoMo and NiMo/Al2O3, respectively. The addition of Pt to sulfided Mo/MSA led to promotion in HDS and HDN with an optimal promoter content close to 0.5wt.%. The results of TPR showed strong positive effect of Pt on reducibility of the MoS2 phase which obviously reflects in higher activity of the promoted catalysts. The activity of the MSA-supported Pt–Mo catalyst containing 0.5wt.% Pt was significantly higher than the activity of alumina-supported Pt–Mo catalyst. Generally, Pt–Mo/MSA catalysts promoted by 0.3–2.3wt.% Pt showed lower HDS and much higher HDN activities as compared to weight amounts of CoMo and NiMo/Al2O3. It is proposed that thiophene HDS and pyridine hydrogenation proceed over Pt/MSA and the majority of Pt–Mo/MSA catalysts on the same type of catalytic sites, which are associated with sulfided Pt and MoS2 phases. On the contrary, piperidine hydrogenolysis takes place on different sites, most likely on metallic Pt fraction or sites created by abstraction of sulfur from MoS2 in the presence of Pt.

Hydrotreating catalysts supported on organized mesoporous alumina: Optimization of Mo deposition and promotional effects of Co and Ni

Abstract The deposition of Mo over organized mesoporous alumina with a surface area of 344 m 2 g −1 and pore-size radius 2.3 nm was investigated. The impregnation of the support from a solution of molybdenum dioxide diacetylacetonate in methanol yielded catalysts that are highly active in the hydrodesulfurization of benzothiophene. The sulfidic Mo catalysts supported on the organized mesoporous alumina were successfully promoted by Co and Ni from solutions of acetylacetonates of these metals in methanol as shown by increased hydrodesulfurization of benzothiophene and of thiophene in parallel with hydrodenitrogenation of pyridine, and by an increase in the relative selectivity C S hydrogenolysis/C C hydrogenation.

On the Formation of Pentylpiperidine in the Hydrodenitrogenation of Pyridine

The hydrodenitrogenation of 2-methylpiperidine and 2-methylpyrrolidine was studied over sulfided NiMo/γ-Al2O3 in the presence of dialkylamines, alkylamines, and alkenes to determine why N-pentylpiperidine is formed in the hydrodenitrogenation of pyridine. N-alkylated 2-methylpiperidine and 2-methylpyrrolidine were only formed as primary products by reaction with alkylamines and not by reaction with 2-methylpiperidine and 2-methylpyrrolidine, or by reaction with an alkene. This indicates that, in the hydrodenitrogenation of pyridine, N-pentylpiperidine is formed by the reaction of the secondary intermediate pentylamine with the primary intermediate piperidine, and not by reaction of two primary piperidine intermediates or by reaction of pentene, one of the final products, with piperidine.

Synthesis, characterization and hydrotreating performance of supported tungsten phosphide catalysts

Supported tungsten phosphide catalysts were prepared by temperature-programmed reduction of their precursors (supported phospho-tungstate catalysts) in H2 and characterized by X-ray diffraction (XRD), BET, temperature-programmed desorption of ammonia (NH3-TPD) and X-ray photoelectron spectroscopy (XPS). The reduction-phosphiding processes of the precursors were investigated by thermogravimetry and differential thermal analysis (TG-DTA) and the suitable phosphiding temperatures were defined. The hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities of the catalysts were tested by using thiophene, pyridine, dibenzothiophene, carbazole and diesel oil as the feedstock. The TiO2, γ-Al2O3 supports and the Ni, Co promoters could remarkably increase and stabilize active W species on the catalyst surface. A suitable amount of Ni (3%–5%), Co (5%–7%) and V (1%–3%) could increase dispersivity of the W species and the BET surface area of the WP/γ-Al2O3 catalyst. The WP/γ-Al2O3 catalyst possesses much higher thiophene HDS and carbazole HDN activities and the WP/TiO2 catalyst has much higher dibenzothiophene (DBT) HDS and pyridine HDN activities. The Ni, Co and V can obviously promote the HDS activity and inhibit the HDN activity of the WP/γ-Al2O3 catalyst. The G-Ni5 catalyst possesses a much higher diesel oil HDS activity than the sulphided industrial NiW/γ-Al2O3 catalyst. In general, a support or promoter in the WP/γ-Al2O3 catalyst which can increase the amount and dispersivity of the active W species can promote its HDS and HDN activities.

Solution synthesis of the unsupported Ni–W sulfide hydrotreating catalysts

Three solution synthesis routes for the preparation of unsupported Ni–W–S hydrotreating catalysts were compared. In all of them WO 2S 2 2− core was applied as precursor, but the reaction between Ni and W species was done in different ways. The preparation methods included solution reaction between WO 2S 2 2− and nickel species in the presence of organic surfactant (liquid–liquid route), reaction of amorphous high surface area nickel compound with aqueous WO 2S 2 2− species (liquid–solid route) and reaction of amorphous WOS 2 solid with aqueous solution of nickel salt (solid–liquid route). The catalysts were characterized by several techniques including X-ray powder diffraction, specific surface area and pore volume measurements, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The catalytic activities were evaluated in thiophene hydrodesulfurization (HDS), toluene hydrogenation (HYD) and pyridine hydrodenitrogenation (HDN) reactions. It has been shown that highly active unsupported sulfides can be obtained from three routes. The highest weight activity was observed for the most finely dispersed liquid–liquid preparation. However, the relation between catalytic activity and texture is not linear and the preparation having low surface area and containing NiS bulky particles covered by curved WS 2 slabs showed the highest activity per unit of surface area.

A comparative study of the catalytic performance of Co-Mo and Co(Ni)-W carbide catalysts in the hydrodenitrogenation (HDN) reaction of pyridine

In this contribution the HDN catalytic behaviour of Co-Mo carbide catalysts and Co(Ni)-W carbide catalysts is compared in order to establish a rational effect of cobalt (or nickel) over Mo and W carbide HDN catalysts. The bimetallic and trimetallic catalysts were characterized by using elemental analysis, X-ray diffraction (XRD), infrared spectroscopy, Raman spectroscopy, thermo-gravimetric analysis and measurements of BET specific surface area. The catalytic performance was evaluated in a continuous flow reactor using hydrodenitrogenation of pyridine as model reaction. The incorporation of cobalt onto the structure of Mo2C reached an optimal Co/Mo ratio of 0.43 (i.e. Co4Mo6Cx catalyst), whose HDN activity and stability was markedly higher than industrial catalysts (i.e. CoMoS/Al2O3 and NiMoS/Al2O3). Higher molar ratios facilitated the segregation of promoter. This was reflected in a poor catalytic stability not only on Co-Mo carbide catalysts, but also on the Co(Ni)-W carbide catalysts. The CoWCx bimetallic catalyst was more active in the steady state than Ni-containing catalysts. Two modes of pyridine adsorption may occur in the HDN reaction, the end-on mode appears to be the more favourable at low temperatures whereas the side-on mode is more favourable at higher temperatures. Further increasing reaction temperature over 400 °C leads to an increase in the hydrogenolysis reaction so more methane is produced, while the percentage of other hydrocarbon products decreased.