TPD and TPR Studies of Molybdenum Nitride

The surface species of passivated and nonpassivated molybdenum nitride samples and their stability at elevated temperatures have been investigated by temperature-programmed decomposition and temperature-programmed reduction with H2. Large differences between fresh and passivated Mo2N were found. (i) Two types of NHxadsorbed species remain on the freshly prepared Mo2N. The first type, weakly adsorbed, desorbed at 200–300°C. Another type is strongly bonded NHxon the surface of Mo2N, which decomposed to H2and N2at 560°C. For passivated Mo2N samples, only weakly adsorbed NHxspecies are present. (ii) An obvious change in the crystalline phase of fresh Mo2N occurred when it was heated at 850°C in He, while for the passivated Mo2N sample no change was observed. When Mo2N was heated to 1000°C, the resulting solid consisted of β-Mo2N and metallic Mo. Mo2N is completely reduced to metallic Mo at 880°C in H2. (iii) The H2consumption peak around 470°C for passivated Mo2N samples is attributed to the reduction of the passivating oxygen. It is suggested that the main effect of passivation on fresh Mo nitride is to eliminate most of the NHxand H species strongly bonded on nitride and then forming a protective oxide layer. The oxygen incorporated during passivation can be removed by H2at a moderate temperature.