A computational study of the heterogeneous synthesis of hydrazine on Co3Mo3N

Periodic and molecular density functional theory calculations have been applied to elucidate the associative mechanism for hydrazine and ammonia synthesis in the gas phase and hydrazine formation on Co3Mo3N. We find that there are two activation barriers for the associative gas phase mechanism with barriers of 730 and 658 kJ/mol, corresponding to a hydrogenation step from N2 to NNH2 and H2NNH2 to H3NNH3, respectively. The second step of the mechanism is barrierless and an important intermediate, NNH2, can also readily form on Co3Mo3N surfaces via the Eley–Rideal chemisorption of H2 on a pre-adsorbed N2 at nitrogen vacancies. Based on this intermediate a new heterogeneous mechanism for hydrazine synthesis is studied. The highest relative barrier for this heterogeneous catalysed process is 213 kJ/mol for Co3Mo3N containing nitrogen vacancies, clearly pointing towards a low-energy process for the synthesis of hydrazine via a heterogeneous catalysis route

Metal-Substituted Microporous Aluminophosphates

This chapter aims to present the zeotypes aluminophosphates (AlPOs) as a complementary alternative to zeolites in the isomorphic incorporation of metal ions within all-inorganic microporous frameworks as well as to discuss didactically the catalytic consequences derived from the distinctive features of both frameworks. It does not intend to be a compilation of either all or the most significant publications involving metal-substituted microporous aluminophosphates. Families of AlPOs and zeolites, which include metal ion-substituted variants, are the dominant microporous materials. Both these systems are widely used as catalysts, in particular through aliovalent metal ions substitution. Here, some general description of the synthesis procedures and characterization techniques of the MeAPOs (metal-contained aluminophosphates) is given along with catalytic properties. Next, some illustrative examples of the catalytic possibilities of MeAPOs as catalysts in the transformation of the organic molecules are given. The oxidation of the hardly activated hydrocarbons has probably been the most successful use of AlPOs doped with the divalent transition metal ions Co2+, Mn2+, and Fe2+, whose incorporation in zeolites is disfavoured. The catalytic role of these MeAPOs is rationalized based on the knowledge acquired from a combination of the most advanced characterization techniques. Finally, the importance of the high specificity of the structure-directing agents employed in the preparation of MeAPOs is discussed taking N,N-methyldicyclohexylamine in the synthesis of AFI-structured materials as a driving force. It is shown how such a high specificity could be predicted and how it can open great possibilities in the control of parameters as critical in catalysis as crystal size, inter-and intracrystalline mesoporosity, acidity, redox properties, incorporation of a great variety of heteroatom ions or final environment of the metal site (surrounding it by either P or Al)

20-Year Risks of Breast-Cancer Recurrence after Stopping Endocrine Therapy at 5 Years

The administration of endocrine therapy for 5 years substantially reduces recurrence rates during and after treatment in women with early-stage, estrogen-receptor (ER)-positive breast cancer. Extending such therapy beyond 5 years offers further protection but has additional side effects. Obtaining data on the absolute risk of subsequent distant recurrence if therapy stops at 5 years could help determine whether to extend treatment