Copper nitride

The sensitivity of chlorate-sulfur mixtures to initiation is increased by cobalt and its oxide, greatly so by copper nitride, copper sulfate, and extremely so by copper chlorate. Implications for manufacturing operations are discussed. 

Now the influence of water or ammonia on copper catalysts is being investigated. Previously A. BAIKER and coll, have shown that ammonia could modify the catalytic properties of copper catalysts used in the amination of alcohols (9). These authors noticed the formation of copper nitride after NH3 exposure at a temperature of about 300°C which is the reaction temperature of our study. The first results that we obtained in our study showed that both H2O and NH3 decrease significantly the copper dispersion in unpromoted catalysts and that this modification is less significant when Ca or Mn are added to the Cu-Cr catalyst. We are now studying what are the superfical modifications consecutive to the addition of promoters or/and water and ammonia. 

Cobalt(III) nitride, 4208 Copper nitride, 4283 Diseleniumdisulfur tetranitride, 4763 Disulfur dinitride, 4749 Gold nitride—ammonia, 0117... 

The extensive surface reconstruction in the presence of N has implications for our discussion of the recombination process, since we must consider whether N2 forms from recombination on the unreconstructed Cu(l 1 1) surface or is formed by decomposition of copper nitride islands. In the latter case N recombination may either leave the local Cu atoms in a metastable (100) arrangement or else recombination might be associated with substantial motion of the Cu atoms as they relax from the nitride adsorption geometry. If N recombination occurs at nitride islands then the dynamics of recombinative desorption will sample a phase space which is completely different to that for dissociation on clean flat Cu terraces, making it impossible to relate these two processes by detailed balance. This is the behaviour of H recombination on Si where the large change in the Si equilibrium geometry induced by H adsorption ensures that the adsorption and desorption processes sample very different channels [13]. 

The two phase model describes all the principle features of the desorption kinetics, suggesting that recombinative desorption under conditions where the coverage is less than saturation occurs by the recombination of N atoms from a dilute phase on the Cu(l 11) surface. This behaviour is the same as that observed for H recombinative desorption on many surfaces [63]. Desorption from the dilute phase is preferred over direct decomposition of the nitride islands because this leaves the copper surface in its equilibrium (111) orientation, rather than as an unstable Cu(l 00) overlayer [99]. As a result we expect that detailed balance can be used to relate measurements of recombination from the N covered Cu(l 1 1) surface with nitrogen dissociation on bare Cu(l 1 1) terraces. In contrast, if desorption occurred via decomposition of reconstructed copper nitride islands then detailed balance arguments would not reveal anything about the energetics or dynamics of N2 dissociation on a Cu(l 1 1) surface. 

The reaction of copper metal with ammonia [42] between 540 and 570 K gave copper nitride, CujN. A reactant containing a high proportion of CujN (92%) was more stable than that containing more copper metal (70% CujN). Decomposition occurred at 700 K and above in nitrogen. Reaction (- NHj) commenced at about 380 K in Hj and above 650 K in NH,. Nickel metal reacted with ammonia to give NijN at 623 K and the main decomposition occurred at 723 K. NijN was stable only... 

Previous works have shown that copper catalysts are selective in the dehydrogenation of esters (5-7), in the hydrolysis of nitrile (8), in the selective hydrogenation of nitrile or in alcohol amination (10). The catalyst systems such as copper chromite are often used for the preparation of substituted amines. These solids, however, are very sensitive to the presence of water and ammonia (formation of copper nitrides... 

In order to corroborate the main steps of the synthesis of dimethylethylamine and of the main by-products, we studied the reactivity of some intermediates and products with or without reagents (MEA, MeOH) under the same experimental conditions i) In the absence of methanol (replaced by n-heptane), monoethylamine is transformed mainly into diethylamine (DEA), the deactivation of the catalyst being very fast due to an increase of the formation of ammonia (15). Baiker and Kijenski showed, for instance, that part of the copper was transformed into copper nitride during the amination of alcohols (12). In the presence of methanol, the monoethylamine surface coverage is lower and a decrease cf the DEA formation can be observed. Methanol acts as an inhibitor in the synthesis of DEA and as a promotor of the catalyst duration. 

A similar chemisorption can take place on other metals which do not form a nitride from N2. The much lower ability of other metals to chemisorb N2 seems to come primarily from the difficulty in activating the N2 molecule. Even a copper surface can chemisorb N2 when the copper surface is activated by ion bombardment [34], even though copper nitride, CU3N, is unstable. Chemisorption of N2 was found on reduced cobalt oxide with a potassium oxide promoter at room temperature [35, 36] and even on noble metals (Ru, Rh,... 

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