Understanding the Hydrodenitrogenation of Heteroaromatics on a Molecular Level

Structural Design of Single-Atom Catalysts for Enhancing Petrochemical Catalytic Reaction Process

Petroleum, as the "lifeblood" of industrial development, is the important energy source and raw material. The selective transformation of petroleum into high-end chemicals is of great significance, but still exists enormous challenges. Single-atom catalysts (SACs) with 100% atom utilization and homogeneous active sites, promise a broad application in petrochemical processes. Herein, the research systematically summarizes the recent research progress of SACs in petrochemical catalytic reaction, proposes the role of structural design of SACs in enhancing catalytic performance, elucidates the catalytic reaction mechanisms of SACs in the conversion of petrochemical processes, and reveals the high activity origins of SACs at the atomic scale. Finally, the key challenges are summarized and an outlook on the design, identification of active sites, and the appropriate application of artificial intelligence technology is provided for achieving scale-up application of SACs in petrochemical process.

Elucidation of the Pyridine Ring-Opening Mechanism of 2,2'-Bipyridine or 1,10-Phenanthroline Ligands at Re(I) Carbonyl Complexes

The cleavage of the C-N bonds of aromatic heterocycles, such as pyridines or quinolines, is a crucial step in the hydrodenitrogenation (HDN) industrial processes of fuels in order to minimize the emission of nitrogen oxides into the atmosphere. Due to the harsh conditions under which these reactions take place (high temperature and H2 pressure), the mechanism by which they occur is only partially understood, and any study at the molecular level that reveals new mechanistic possibilities in this area is of great interest. Herein, we unravel the pyridine ring-opening mechanism of 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen) ligands coordinated to the cis-{Re(CO)2(N-RIm)(PMe3)} (N-RIm= N-alkylimidazole) fragment under mild conditions. Computational calculations show that deprotonation of the pyridine ring, once dearomatized, is crucial to induce ring contraction, triggering extrusion of the nitrogen atom from the ring and cleavage of the C-N bond. It is noteworthy that different products (regioisomers) are obtained depending on whether the ligand used is bipy or phen due to the additional rigidity and stability conferred by the central ring of the phen ligand, an issue also addressed and clarified computationally. Strong support for the proposed mechanism is provided by the characterization and isolation, including three single-crystal X-ray diffraction structures, of several of the proposed reaction intermediates.

Adsorptive denitrogenation of model oil by MOF(Al)@GO composites: remarkable adsorption capacity and high selectivity

An as-synthesized recyclable Al-NDC@GO composite exhibited remarkable adsorption capacity and high selectivity for pyridine, quinoline and indole.

Investigating the Effects of Organonitrogen Types on Hydrodearomatization Reactions over Commercial NiMoS Catalyst

The hydrogenation of polyaromatic compounds (PACs) present in mineral oils is of great importance when it comes to the desired product properties and the minimization of health hazards; however, the presence of organonitrogen inhibits the conversion of these compounds. In this study, the inhibition effects of different types of organonitrogen compounds (acridine (ACR) and carbazole (CBZ)-basic and nonbasic organonitrogen) on the hydrodearomatization (HDA) of phenanthrene over a sulfided commercial NiMo/Al2O3 catalyst were investigated in a microflow trickle-bed reactor at a temperature range of 280 to 320 °C and at a total pressure of 120 barg. Analysis of the experimental results shows that the hydrogenation of phenanthrene is significantly decreased in the presence of organonitrogen, with acridine showing stronger inhibiting effects. The extent of hydrodenitrogenation (HDN) is shown to correlate with the inhibition degree with a higher extent of HDN being achieved for carbazole than for acridine. Results from co-feeding different nitrogen types (acridine and carbazole) indicate that basic nitrogen is the dominating type of organonitrogen inhibitor. Recovery of catalyst activity in the absence of organonitrogen indicates fully reversible deactivation suggesting that inhibition relates to competitive adsorption and slower reaction rate of HDN compared to HDA.

Carbon-Based Materials for Oxidative Desulfurization and Denitrogenation of Fuels: A Review

Sulfur (S) and nitrogen (N) are elements naturally found in petroleum-based fuels. S- and N-based compounds in liquid fuels are associated with a series of health and environmental issues. Thus, legislation has become stricter worldwide regarding their content and related emissions. Traditional treatment systems (namely hydrodesulfurization and hydrodenitrogenation) fail to achieve the desired levels of S and N contents in fuels without compromising combustion parameters. Thus, oxidative treatments (oxidative desulfurization–ODS, and oxidative denitrogenation-ODN) are emerging as alternatives to producing ultra-low-sulfur and nitrogen fuels. This paper presents a thorough review of ODS and ODN processes applying carbon-based materials, either in hybrid forms or as catalysts on their own. Focus is brought to the role of the carbonaceous structure in oxidative treatments. Furthermore, a special section related to the use of amphiphilic carbon-based catalysts, which have some advantages related to a closer interaction with the oily and aqueous phases, is discussed.

Syntheses, Structures, Reactivities, and Basicities of Quinolinyl and Isoquinolinyl Complexes of an Electron Rich Chiral Rhenium Fragment and Their Electrophilic Addition Products

Reactions of Li⁺ [(η⁵ -C₅ H₅ )Re(NO)(PPh₃ )]^- with 2- and 4-chloroquinoline or 1-chloroisoquinoline give the corresponding σ quinolinyl and isoquinolinyl complexes 3, 6, and 8. With 3 and 8 there is further protonation to yield HCl adducts, but additions of KH give the free bases. Treatment of 3 with HBF₄ ⋅OEt₂ or H(OEt₂ )₂ ⁺ BAr_f ^- gives the quinolinium salts [(η⁵ -C₅ H₅ )Re(NO)(PPh₃ )(C(NH)C(CH)₄ C(CH)(CH))]⁺ X^- (3-H⁺ X^- ; X^- =BF₄ ^- /BAr_f ^- , 94-98 %). Addition of CF₃ SO₃ CH₃ to 3, 6, or 8 affords the corresponding N-methyl quinolinium salts. In the case of [(η⁵ -C₅ H₅ )Re(NO)(PPh₃ )(C(NCH₃ )C(CH)₄ C(CH)(CH))]⁺ CF₃ SO₃ ^- (3-CH₃ ⁺ CF₃ SO₃ ^- ), addition of CH₃ Li gives the dihydroquinolinium complex (S_Re R_C ,R_Re S_C )-[(η⁵ -C₅ H₅ )Re(NO)(PPh₃ )(C(NCH₃ )C(CH)₄ C(CHCH₃ )(CH₂ ))]⁺ CF₃ SO₃ ^- ((S_Re R_C ,R_Re S_C )-5⁺ CF₃ SO₃ ^- , 76 %) in diastereomerically pure form. Crystal structures of 3-H⁺ BAr_f ^- , 3-CH₃ ⁺ CF₃ SO₃ ^- , (S_Re R_C , R_Re S_C )-5⁺ Cl^- , and 6-CH₃ ⁺ CF₃ SO₃ ^- show that the quinolinium ligands adopt Re⋅⋅⋅C conformations that maximize overlap of their acceptor orbitals with the rhenium fragment HOMO, minimize steric interactions with the bulky PPh₃ ligand, and promote various π interactions. NMR experiments establish the Brønsted basicity order 3>8>6, with K_a (BH⁺ ) values >10 orders of magnitude greater than the parent heterocycles, although they remain less active nucleophilic catalysts in the reactions tested. DFT calculations provide additional insights regarding Re⋅⋅⋅C bonding and conformations, basicities, and the stereochemistry of CH₃ Li addition.

Hydrodenitrogenation of pyridines and quinolines at a multinuclear titanium hydride framework

Investigation of the hydrodenitrogenation (HDN) of aromatic N-heterocycles such as pyridines and quinolines at the molecular level is of fundamental interest and practical importance, as this transformation is essential in the industrial petroleum refining on solid catalysts. Here, we report the HDN of pyridines and quinolines by a molecular trinuclear titanium polyhydride complex. Experimental and computational studies reveal that the denitrogenation of a pyridine or quinoline ring is easier than the ring-opening reaction at the trinuclear titanium hydride framework, which is in sharp contrast with what has been reported previously. Hydrolysis of the pyridine-derived nitrogen-free hydrocarbon skeleton at the titanium framework with H2O leads to recyclization to afford cyclopentadiene with the generation of ammonia, while treatment with HCl gives the corresponding linear hydrocarbon products and ammonium chloride. This work has provides insights into the mechanistic aspects of the hydrodenitrogenation of an aromatic N-heterocycle at the molecular level.

C–N bond hydrogenolysis of aniline and cyclohexylamine over TaOx–Al2O3

Aniline denitrogenation over TaO_x–Al₂O₃ leads to chemically inert Ta-imido species.