Dinitrogen cleavage and hydrogenation by transition-metal centers to produce ammonia is central in industry and in Nature. After an introductory section on the thermodynamic and kinetic challenges linked to N2 splitting, this tutorial review discusses three major classes of transition-metal systems (homogeneous, heterogeneous and biological) capable of achieving dissociation and hydrogenation of dinitrogen. Molecular complexes, solid-state Haber-Bosch catalytic systems, silica-supported tantalum hydrides and nitrogenase will be discussed. Emphasis is focused on the reaction mechanisms operating in the process of dissociation and hydrogenation of dinitrogen, and in particular on the key role played by metal hydride bonds and by dihydrogen in such reactions.

… the intersection of carbon materials and catalysis--is the use of large-area, metal-free carbon to facilitate chemical reactions. In their Communication on page 6813 ff., C. Bielawski and co-workers demonstrate that graphene-based materials may be used as carbocatalysts to facilitate a number of synthetically useful transformations, including the oxidation of alcohols and alkenes into their respective aldehydes and ketones, as well as the hydration of alkynes.

No abstract

No abstract

No abstract

The hydrothermal reactions of trivacant Keggin A-alpha-XW(9)O(34) polyoxoanions (X=P(V)/Si(IV)) with transition-metal ions (Ni(II)/Cu(II)/Fe(II)) in the presence of amines result in eight novel high-nuclear transition-metal-substituted polyoxotungstates [{Ni(7)(mu(3)-OH)(3)O(2)(dap)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))][{Ni(6)(mu(3)-OH)(3)(dap)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))][Ni(dap)(2)(H(2)O)(2)]4.5 H(2)O (1), [Cu(dap)(H(2)O)(3)](2)[{Cu(8)(dap)(4)(H(2)O)(2)}(B-alpha-SiW(9)O(34))(2)]6 H(2)O (2), (enH(2))(3)H(15)[{Fe(II) (1.5)Fe(III) (12)(mu(3)-OH)(12)(mu(4)-PO(4))(4)}(B-alpha-PW(9)O(34))(4)]ca.130 H(2)O (3), [{Cu(6)(mu(3)-OH)(3)(en)(3) (H(2)O)(3)}(B-alpha-PW(9)O(34))]7 H(2)O (4), [{Ni(6)(mu(3)-OH)(3)(en)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))]7 H(2)O (5), [{Ni(6)(mu(3)-OH)(3)(en)(2)(H(2)O)(8)}(B-alpha-PW(9)O(34))]7 H(2)O (6), [{Ni(6)(mu(3)-OH)(3)(dap)(2)(H(2)O)(8)}(B-alpha-PW(9)O(34))] 7 H(2)O (7), and [{Ni(6)(mu(3)-OH)(3)(en)(3)(H(2)O)(6)}(B-alpha-SiW(9)O(34))][Ni(0.5)(en)] 3.5 H(2)O (8) (en=ethylenediamine, dap=1,2-diaminopropane). These compounds have been structurally characterized by elemental analyses, IR spectra, diffuse reflectance spectra, thermogravimatric analysis, and X-ray crystallography. The double-cluster complex of phosphotungstate 1 simultaneously contains hepta- and hexa-Ni(II)-substituted trivacant Keggin units [{Ni(7)(mu(3)-OH)(3)O(2)(dap)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))](2-) and [{Ni(6)(mu(3)-OH)(3)(dap)(3)(H(2)O)(6)}(B-alpha-PW(9)O(34))]. The dimeric silicotungstate 2 is built up from two trivacant Keggin [B-alpha-SiW(9)O(34)](10-) fragments linked by an octa-Cu(II) cluster. The main skeleton of 3 is a tetrameric cluster constructed from four tri-Fe(III)-substituted [Fe(III) (3)(mu(3)-OH)(3)(B-alpha-PW(9) O(34))](3-) Keggin units linked by a central Fe(II) (4)O(4) cubane core and four mu(4)-PO(4) bridges. Complex 4 is an unprecedented three-dimensional extended architecture with hexagonal channels built by hexa-Cu(II) clusters and trivacant Keggin [B-alpha-PW(9)O(34)](9-) fragments. The common feature of 5-8 is that they contain a B-alpha-isomeric trivacant Keggin fragment capped by a hexa-Ni(II) cluster, very similar to the hexa-Ni(II)-substituted trivacant Keggin unit in 1. Magnetic measurements illustrate that 1, 2, and 5 have ferromagnetic couplings within the magnetic metal centers, whereas 3 and 4 reveal the antiferromagnetic exchange interactions within the magnetic metal centers. Moreover, the magnetic behavior of 4 and 5 have been theoretically simulated by the MAGPACK magnetic program package.

The hydrothermal reactions of [A-alpha-SiW(9)O(34)](10-)/[A-alpha-PW(9)O(34)](9-) with NiCl(2) x 6H(2)O and amines yielded four unprecedented hybrid high-nuclear Ni-subsituted polyoxotungstates.

A novel method of redox precipitation was applied for the first time to synthesize a Au-doped α-MnO catalyst with high dispersion of the Au species. Au nanoparticles (NPs) can be downsized into approximate single atoms by this method, thereby realizing highly efficient utilization of Au element as well as satisfying low-temperature oxidation of formaldehyde (HCHO). Under catalysis of the optimal 0.25% Au/α-MnO catalyst, a polluted stream containing 500 ppm HCHO can be completely cleaned at 75 °C with the condition of a weight hourly space velocity (WHSV) of 60000 mL/(g h). Meanwhile, the catalyst retains good activity for removal of low-concentration HCHO (about 1 ppm) at ambient temperature with a high WHSV, and exhibits a high tolerance to water and long-term stability. Our characterization of Au/α-MnO and catalytic performance tests clearly demonstrate that the proper amount of Au doping facilitates formation of surface vacancy oxygen, lattice oxygen, and charged Au species as an active site, which are all beneficial to catalytic oxidation of HCHO. The oxidation of HCHO over Au-doped α-MnO catalyst obeys the Mars-van Krevelen mechanism as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy.