For a more direct assessment of PTM and POM siting, we turned to difference envelope density (DED) analysis of synchrotron-based X-ray scattering data. The analysis shows that the disk-like clusters are centered in the c-pore of NU1K, but extend into the triangular micropores; see Figures and. SEM images show that the size and morphology of NU1K crystallites are well maintained after H2S annealing (Figure ) with no obvious presence of nanoparticles or clusters on exterior surfaces. EDS mapping suggests that Co, Mo and S are evenly distributed throughout the MOF. Co, Mo and S spatial distributions match well with that of Zr (Figure ), suggesting uniform dispersion of isolated CoMo6S24 cluster throughout the crystal, rather than their accumulation at regions near the crystal surface. CoMo6O24 clusters are also uniformly distributed within NU1K; see Figure .