Transition metal nitrides relationship

Ti) solid solution and simple transition metal nitrides are classified using the radius ratio of nonmetal to metal atoms and the number of valence electrons. The relationship of the generalized number of valence electrons instead of the average number of valence electrons per atom to the thermal stability of transition metal nitride has been discussed. 

We need to develop methods to understand trends for complex reactions with many reaction steps. This should preferentially be done by developing models to understand trends, since it will be extremely difficult to perform experiments or DFT calculations for all systems of interest. Many catalysts are not metallic, and we need to develop the concepts that have allowed us to understand and develop models for trends in reactions on transition metal surfaces to other classes of surfaces oxides, carbides, nitrides, and sulfides. It would also be extremely interesting to develop the concepts that would allow us to understand the relationships between heterogeneous catalysis and homogeneous catalysis or enzyme catalysis. Finally, the theoretical methods need further development. The level of accuracy is now so that we can describe some trends in reactivity for transition metals, but a higher accuracy is needed to describe the finer details including possibly catalyst selectivity. The reliable description of some oxides and other insulators may also not be possible unless the theoretical methods to treat exchange and correlation effects are further improved. 

In earlier work, it was found for borides, silicides and nitrides that specific activity, expressed as total rate of methane consumption per unit surface area, plummeted with increasing surface area of the catalyst samples.1718 The same relationship was also found for transition metals carbides (Figure 16.4). It should be noted the dependence of specific activity on surface area rather than catalyst composition is unusual for heterogeneous catalytic reactions. In addition, it can be found that the reaction order in the oxidant is perceptibly in excess of 1 (Tables 16.8 and 16.9). Such an order is hard to explain in terms of common mechanism schemes for heterogeneous catalytic oxidative reactions. 

Fernandez E, Moses PG, Toftelund A, et al. Scaling Relationships for Adsorption Energies on Transition Metal Oxide, Sulfide and Nitride Surfaces. Angew Chem Int Ed. 2008 47 4683-6. 

Hoi] Holleck, H., Binary and Ternary Carbides and Nitrides of Transition Metals and Their Phase Relationships (in German), Report KfK 3087B, Kemforschungszentrum, Karlsruhe, 181-183 (1981) (Phase Diagram, Review, 41)... 

Fernandez EM, Moses PG, Toftelund A, Hansen HA, Martinez JI, Abild-Pedersen F, Kleis J, Hinnemann B, Rossmeisl J, Bligaard T, Nprskov JK. Scaling relationships for adsorption energies on transition metal oxide, sulfide, and nitride surfaces. Angew Chem Int Ed 2008 47 4683-f686. 

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