An Al K-edge EXAFS study of MoO3/H-ZSM-5 catalyst precursors

Nitridation of MoO3/HZSM-5 and Fe-MoO3/HZSM-5

“…This demonstrates a surface enrichment of N. It emphasised that, in order to remove any potential artefacts associated with the adsorption of NH 3 upon cooling, samples were cooled under N 2 . In this respect it is notable that, on related MoO 3 /HZSM-5 samples, desorption of NH 3 from the strong acid sites of the framework has been reported to occur below 550°C, which is lower than that for the corresponding HZSM-5 sample [26] and well below the temperature at which the flow is switched to N 2 in the present study, which suggests that the contribution of N entities adsorbed on the framework should be minor.…”

Methane dehydroaromatisation and methanol activation over zeolite catalysts: an overview

“…It is known that excessive heat treatment can have deleterious effects upon catalytic performance through dealumination of the zeolite framework and the formation of aluminium molybdate which can be identified in 27 Al MAS NMR studies as evidenced by bands at -14 and/or ?14 ppm (corresponding to anhydrous and hydrated aluminium molybdate, respectively [14]). Indeed, the molybdenum species perturb the local environment of the Al in the framework as has been demonstrated by the application of Al EXAFS [15]. Table 1 presents the results of Al XAS studies upon activated MoO 3 /H-ZSM-5 for which 27 Al MAS NMR shows the presence of only a small amount of extraframework Al.…”

“…2, where a ca. 50°C reduction of the temperature maximum of the high temperature desorption feature corresponding to the interaction of NH 3 with the Bronsted acid sites is evident (the two lower temperature features corresponding to weakly adsorbed NH 3 and that interacting with silanol groups) [15]. Figure 3 presents the difference FTIR spectrum of the adsorbed NH 3 over the activated MoO 3 /H-ZSM-5, where the loss of the ca 3600 cm -1 feature and the growth of the 1460 cm -1 feature corresponds to the consumption of bridging OHs and the formation of NH 4 ?…”