Bifunctional Mechanism of Pyridine Hydrodenitrogenation

Marzari, J.A.; Rajagopal, S.; Miranda, R.

doi:10.1006/jcat.1995.1252

Cited by 23 publications

(7 citation statements)

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“…On phosphides similar studies have not been carried out, but it is likely that again no single rate-limiting step is involved, and that CNH will be one of the key steps. The CNH reaction is a complex reaction and requires multiple sites [79][80][81] among them an acid site to bind the nitrogen compound and a proximal basic site to carry out a β-H attack. Thus, the reaction is structure sensitive [67], and is expected to be influenced by the substitution of Fe for Ni at the surface.…”

Section: Infrared Spectroscopy Of Adsorbed Comentioning

confidence: 99%

Nature of active sites in Ni2P hydrotreating catalysts as probed by iron substitution

Zhao

Oyama

Freund

et al. 2015

Applied Catalysis B: Environmental

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A series of NiFeP/SiO 2 catalysts with different Ni:Fe molar ratios (1:0, 3:1, 1:1, 1:3, 0:1) was investigated for the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene.The Fe component is a good probe for active sites because Ni 2 P and Fe 2 P adopt the same hexagonal crystal structure, yet Fe 2 P is completely inactive for HDS. X-ray diffraction analysis and FTIR spectroscopy of adsorbed CO indicated the formation homologous alloys. At 3.1 MPa and 613 K (340 o C) the activity of the alloys was similar to that of Ni 2 P, which was very high. There was also unprecedented selectivity towards direct desulfurization (DDS). A reconstruction of the NiFe phase occurred to expose more Ni sites, likely driven by the formation of surface Ni-S bonds as observed by EXAFS. The analysis showed that Ni(2) pyramidal sites responsible for hydrogenation were largely replaced by Fe. This left behind Ni(1) tetrahedral sites which favor DDS and explains the reactivity results.

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Section: Infrared Spectroscopy Of Adsorbed Comentioning

confidence: 99%

Nature of active sites in Ni2P hydrotreating catalysts as probed by iron substitution

Zhao

Oyama

Freund

et al. 2015

Applied Catalysis B: Environmental

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“…The work is described in a comprehensive discussion of the mechanism of piperidine HDN by Hadjiloizou et al, an in-depth review of catalytic denitrogenation by Perot, and a more recent, insightful monograph by Prins . In many cases for sulfides, carbides, and nitrides, the C−N bond cleavage proceeds by a β-elimination mechanism catalyzed by a Brønsted acid−Lewis base site. , Although there is some uncertainty about the rate-limiting step, ,, there is agreement that HDN involves a multi-functional mechanism with hydrogenation and C−N cleavage carried out on different active sites, − depending on the structure of the nitrogen-containing heterocyclic compound, the reaction conditions, and the type of catalyst.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Hydrodenitrogenation on Phosphides and Sulfides

Oyama

Lee

2004

J. Phys. Chem. B

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The mechanism of hydrodenitrogenation (HDN) of 2-methylpiperidine was studied over a silica-supported nickel phosphide catalyst (Ni2P/SiO2, Ni/P = 1/2) and a commercial Ni-Mo-S/Al2O3 catalyst in a three-phase trickle-bed reactor operated at 3.1 MPa and 450-600 K. Analysis of the product distribution as a function of contact time indicated that the reaction proceeded in both cases predominantly by a substitution mechanism, with a smaller contribution of an elimination mechanism. Fourier transform infrared spectroscopy (FTIR) of the 2-methylpiperidine indicated that at reaction conditions a piperidinium ion intermediate was formed on both the sulfide and the phosphide. It is concluded that the mechanism of HDN on nickel phosphide is very similar to that on sulfides. The mechanism on the nickel phosphide was also probed by comparing the reactivity of piperidine and several of its derivatives in the presence of 3000 ppm S. The relative elimination rates depended on the structure of the molecules, and followed the sequence: 4-methylpiperidine approximately piperidine > 3-methylpiperidine > 2,6-dimethylpiperidine > 2-methylpiperidine. [Chemical structure: see text] This order of reactivity was not dependent on the number of alpha-H or beta-H atoms in the molecules, ruling out their reaction through a single, simple mechanism. It is likely that the unhindered piperidine molecules reacted by an S(N)2 substitution process and the more hindered 2,6-dimethylpiperidine reacted by an E2 elimination process.

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“…Low-temperature reduction could be associated with the partial reduction of heteropolymolybdates (octahedral Mo species) or multilayered Mo oxides that are highly defective and amorphous, and this phenomenon generally relates to the presence of the active Ni–Mo–S precursor type-II phase. , On the other hand, the high-temperature reduction is evident in the reduction of tetrahedral Mo species such as Mo oxides, which requires intense reduction as well as the reduction of a highly dispersed MoO 3 monolayer plus the reduction of the crystalline phases of orthorhombic MoO 3 and Al 2 (MoO 4 ) that get formed as a result of strong metal–support interaction. The pattern in Figure suggests a Mo 6+ to Mo 4+ reduction for the first peak followed by a reduction of Mo 4+ to Mo 0+ in the second peak. − For the NiMo/γ-Al 2 O 3 catalyst, the first reduction peak was centered at 472 °C, whereas the second reduction peak of much higher intensity continued to develop at the experimental cut-off temperature close to 800 °C. The intermediate reduction peak at about 570 °C from the NiMo/γ-Al 2 O 3 catalyst can be assigned to separate Ni oxide phases as previously reported by Brito and Laine (1993) for similar NiMo/γ-Al 2 O 3 catalysts …”

Section: Results and Discussionmentioning

confidence: 96%

Comparative Studies of Carbon Nanomaterial and γ-Alumina as Supports for the Ni–Mo Catalyst in Hydrotreating of Gas Oils

et al. 2021

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Carbon nanohorns (CNH), other carbon particles (OCP), fine fractions of other carbon particles (OCPf), carbon nanotubes (CNT), and γ-alumina (γ-Al2O3) were utilized as support materials for the Ni–Mo catalyst in this study to test the influence of the support on hydrotreating efficiency using light gas oil (LGO) and identify the cause of disparity in activity from these various catalyst supports. OCP and OCPf are the main byproducts obtained during the production of CNH. The influence of the support on the hydrotreating catalyst is significant and includes enhancement of textural properties, active phase dispersion, and catalyst reducibility. The hydrodenitrogenation activities of all of the different supported catalysts with light gas oil are presented and correlated with their physicochemical properties. Among all of the carbon-supported catalysts used, the NiMo/CNH catalyst exhibited outstanding physicochemical properties, and as such, its hydrodesulfurization activity of 89% dominated that of NiMo/OCPf (78%), NiMo/OCP (67%), and NiMo/CNT (73%) catalysts. The pore volume, pore diameter, and surface area of the NiMo/CNH catalyst was 0.42 cm3/g, 10.9 nm, and 350 m2/g, respectively. The percentage metal dispersion of the NiMo/CNH catalyst was 8.0% and was about twice that of the NiMo/OCPf and NiMo/CNT catalysts. X-ray absorption spectroscopy (XAS) analysis confirmed that the carbon-supported catalysts exhibited a distorted octahedral Mo coordination environment, whereas the NiMo/γ-Al2O3 catalyst exhibited a mixture of octahedral and tetrahedral Mo environment. From XAS results, it was apparent that the possession of a Mo octahedral coordination environment does not always translate to attainment of highest hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities.

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Bifunctional Mechanism of Pyridine Hydrodenitrogenation

Cited by 23 publications

References 0 publications

Nature of active sites in Ni2P hydrotreating catalysts as probed by iron substitution

Nature of active sites in Ni2P hydrotreating catalysts as probed by iron substitution

Mechanism of Hydrodenitrogenation on Phosphides and Sulfides

Comparative Studies of Carbon Nanomaterial and γ-Alumina as Supports for the Ni–Mo Catalyst in Hydrotreating of Gas Oils

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