Functional Nanocomposites DOI: 10.1002/ange.201206542 Biomimetic Oxygen Activation by MoS 2 /Ta 3 N 5 Nanocomposites for Selective Aerobic Oxidation** Qingsheng Gao,* Cristina Giordano, and Markus Antonietti The selective oxidation of petroleum-based feedstocks to useful functionalized chemicals is an important family of chemical transformations. [1] Of these transformations, the selective oxidation of alcohols, alkenes, amines, and sulfides are among the most challenging reactions in green chemis- try. [2] There is significant interest in the design of new, cost- effective, and environmentally friendly heterogeneous cata- lysts that use molecular oxygen (O 2 ) under mild conditions, to avoid the use of a large excess of toxic and expensive stoichiometric metal oxidants. [1, 3] Although a number of catalysts based on novel metals and transition-metal oxides have been introduced, [4] the precise design of catalysts with well-defined behaviors that depend on surface properties and electron features is still desired. Such catalysts are significant not only for use with multifunctional substrates, but also for insightful studies of catalytic mechanisms. These challenges are expected to be met through facet engineering and component control at the catalyst surface and in the active sites on the level of nanochemistry. [5] Crystal-facet engineering has been successfully intro- duced to exploit novel metal nanocatalysts with high-sur- face-energy planes. This approach has led to high activity and selectivity in oxidation catalysis. [5b, e, 6] However, it is difficult to control facet growth in metal-oxide catalysts with low- symmetry crystal structures owing to the complexity of their structures. [7] On the other hand, the ability to effectively vary the surface properties and electronic features of metal oxides by doping with other elements of different electronegativity, such as N, P, and S, enables new strategies for catalyst design. [8] For example, the introduction of N into metal oxides can increase the energy of the HOMO orbital and narrow the band gap to thus enhance the catalytic activity, [9] although controlled nitridation is difficult by current synthetic strat- egies. Recently, we proposed Ca 2+ - and SiO 2 -assisted urea methods for the controlled nitridation of transition metals. Remarkably, we discovered tunable oxidation ability associ- ated with tailored nitridation, [10] namely, improved activity and tunable selectivity for alkene epoxidation on TaON and Ta 3 N 5 nanoparticles (NPs) with H 2 O 2 . This discovery opens up opportunities to develop superior tantalum-based catalysts with well-defined properties, especially for reactions involv- ing cheap O 2 as the oxidant. Access to such catalysts is needed to enable the important factors for catalytic turnover and selectivity to be uncovered. However, the absence of O 2 activation in such (oxy)nitrides synthesized so far seriously limits further exploration. Biomimetic studies point to a new way to develop catalysts by learning from nature. In nature, the active center of nitrogenase enzymes contains metal atoms usually bound to sulfur, such as active Mo À S and Fe À S clusters. [11] In nitrogen fixation, Mo ÀS and Fe ÀS sites activate inert N 2 to react with H + , with the generation of NH 3 and H 2 . [11, 12] This process inspired the use of MoS x for electro- and photo- electrocatalytic H 2 evolution based on electron transfer from MoS 2 to H + . [12, 13] The close energy potentials of E 0 (H + /H 2 ) = 0 V and E 0 (O 2 /CO 2 ) = À0.16 V versus the normal hydrogen electrode [14] suggest that MoS x could be used as a biomimetic O 2 -activation reagent to exploit bifunctional tantalum-based nanocatalysts for aerobic oxidation reactions. Herein, we describe the development of a new MoS 2 / Ta 3 N 5 catalyst in which Ta 3 N 5 NPs are integrated with ultrathin MoS 2 layers on the nanoscale by a hydrothermal method. The MoS 2 nanolayers act as a biomimetic O 2 - activation reagent in the MoS 2 /Ta 3 N 5 NPs, which showed high activity and selectivity in the aerobic oxidation of alcohols as a result of the synergistic effect between MoS 2 and Ta 3 N 5 . The MoS 2 /Ta 3 N 5 NPs were also active in the aerobic oxidation of alkenes, amines, and sulfides. The different activities observed for these different substrates imply the potential use of this catalyst with multifunctional substrates. For example, high selectivity for hydroxy-group oxidation (> 90 %) was observed in the oxidation of unsaturated alcohols. Well-defined Ta 3 N 5 NPs of approximately 20 nm in diameter were prepared by our previously reported SiO 2 - assisted urea method (see Figure S1 in the Supporting Information). [10a] Hydrothermal treatment of the Ta 3 N 5 NPs with varying amounts of ammonium heptamolybdate (AHM) and thiourea at 180 8C for 20 h (see the Supporting Informa- tion) gave a series of MoS 2 /Ta 3 N 5 nanocomposites that varied in their MoS 2 content. The color of the composites changed from red to black as the MoS 2 content increased (Figure 1 a; see also Figure S2 in the Supporting Information). Inductively coupled plasma analysis and CHNS elemental analysis were used to determine the Mo and S content, respectively. The [*] Dr. Q. S. Gao, Dr. C. Giordano, Prof.Dr. M. Antonietti Department of Colloid Chemistry, Max Planck Institute of Colloids and Interfaces, Research Campus Golm 14424 Potsdam (Germany) E-mail: qingsheng.gao@mpikg.mpg.de Dr. Q. S. Gao Department of Chemistry, Jinan University 510632 Guangzhou (P.R. China) E-mail: tqsgao@jnu.edu.cn [**] We acknowledge financial support from the BMBF (Project No. 035F0353A-E), the Max Planck Society, and the NSFC (21203075). Q.S.G. thanks Dr. X. Liu and K. Otte of MPIKG for SEM, and Prof. C. Y. Liu and M. Meng of Jinan University for fruitful discussions. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201206542. . Angewandte Zuschriften 11910  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. 2012, 124, 11910 –11914