Mechanistic Study of the Selective Methanation of CO over Ru/TiO2 Catalysts: Effect of Metal Crystallite Size on the Nature of Active Surface Species and Reaction Pathways

Molybdenum complexes supported by tridentate pincer ligands are exceptional catalysts for dinitrogen fixation using chemical reductants, but little is known about their prospects for electrochemical reduction of dinitrogen. The viability of electrochemical N2 binding and splitting by a molybdenum(III) pincer complex, (pyPNP)MoBr3 (pyPNP = 2,6-bis(tBu2PCH2)-C5H3N)), is established in this work, providing a foundation for a detailed mechanistic study of electrode-driven formation of the nitride complex (pyPNP)Mo(N)Br. Electrochemical kinetic analysis, optical and vibrational spectroelectrochemical monitoring, and computational studies point to two reaction pathways: in the “reaction layer” pathway, the molybdenum(III) precursor is reduced by 2e– and generates a bimetallic molybdenum(I) Mo2(-N2) species capable of N–N bond scission. In the “bulk solution” pathway the precursor is reduced by 3e– at the electrode surface to generate molybdenum(0) species that undergo chemical redox reactions via comproportionation in the bulk solution away from the electrode surface to generate the same bimetallic molybdenum(I) species capable of N2 cleavage. The comproportionation reactions reveal the surprising intermediacy of dimolybdenum(0) complex trans,trans-[(pyPNP)Mo(N2)2](-N2) in N2 splitting pathways. The same “over-reduced” molybdenum(0) species was also found to cleave N2 upon addition of lutidinium, an acid frequently used in catalytic reduction of dinitrogen.

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Reaction pathways and roles of N-alkylmorpholine in amine·alane transamination: A mechanistic study

International Journal of Hydrogen Energy ◽

10.1016/j.ijhydene.2014.01.088 ◽

2014 ◽

Vol 39 (10) ◽

pp. 5003-5009 ◽

Cited By ~ 1

Author(s):

Chengbao Ni ◽

Liu Yang

Keyword(s):

Reaction Pathways ◽

Mechanistic Study

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Mechanistic Study of Hydroamination of Alkyne through Tantalum-Based Silica-Supported Surface Species

ACS Catalysis ◽

10.1021/acscatal.9b02184 ◽

2019 ◽

Vol 9 (9) ◽

pp. 8719-8725 ◽

Cited By ~ 3

Author(s):

Maha A. Aljuhani ◽

Ziyun Zhang ◽

Samir Barman ◽

Mohamad El Eter ◽

Laura Failvene ◽

...

Keyword(s):

Mechanistic Study ◽

Surface Species

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Mechanistic study of a manganese porphyrin catalyst for on-demand production of chlorine dioxide in water

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424615500376 ◽

2015 ◽

Vol 19 (01-03) ◽

pp. 492-499 ◽

Cited By ~ 3

Author(s):

Scott D. Hicks ◽

Silei Xiong ◽

Curt J. Bougher ◽

Grigori A. Medvedev ◽

James Caruthers ◽

...

Keyword(s):

Electron Transfer ◽

Chlorine Dioxide ◽

Transfer Reaction ◽

Water Soluble ◽

Reaction Pathways ◽

Mechanistic Study ◽

Manganese Porphyrin ◽

Oxygen Atom Transfer ◽

On Demand ◽

Proton Coupled Electron Transfer

A water-soluble manganese porphyrin complex was examined for the catalytic formation of chlorine dioxide from chlorite under ambient temperature at pH 5.00 and 6.90. Quantitative kinetic modeling allowed for the deduction of a mechanism that accounts for all experimental observations. Catalysis is initiated via an OAT (Oxygen Atom Transfer) reaction resulting in formation of a putative manganese(V) oxo species, which undergoes ET (Electron Transfer) with chlorite to form chlorine dioxide. As chlorine dioxide accumulates in solution, chlorite consumption slows down and ClO 2 reaches a maximum as the system reaches equilibrium. In phosphate buffer at pH 6.90, manganese(IV) oxo accumulates and its reaction with ClO 2 gives ClO 3-. However, at pH 5.00 acetate buffer proton coupled electron transfer (PCET) from chlorite to manganese(IV) oxo is fast and irreversible leading to chlorate formation only via the putative manganese(V) oxo species. These differences underscore how PCET rates affect reaction pathways and mechanism. The ClO 2 product can be collected from the aqueous reaction mixture via purging with an inert gas, allowing for the preparation of chlorine dioxide on-demand.

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