Unusual low coordination numbers in ultradisperse MoS2

The local structure of high dispersive MoS2 with an average size of about 30 Å has been studied using EXAFS spectra measured at the MoK edge. The sample with the general formula MoS2+x was sintered by means of high temperature decomposition of MoS3. Coordination numbers for the first shell MoS (4.2) and the second shell MoMo (2.8) less than one could be expected for small size particles. However, interatomic distances and Debye-Waller factors are the same as for the MoS2 polycrystalline sample. It is commonly considered that a decreased of the coordination numbers is due to sulfur nonstoichiometry in MoS2Al2O3 catalysts. However, nonstoichiometry is absent in our sample. A possible reason for the decrease of the coordination numbers in this case may be the distortion of the outer layer of the particle, such that interatomic distances in this layer are not observed by EXAFS due to large Debye-Waller factors.