Switching on/off molybdenum nitride catalytic activity in ammonia synthesis through modulating metal-support interaction

Modulating the interaction between Mo nanoparticles and their support is an elegant approach to finely tune the structural, physico-chemical, redox and electronic properties of the active site. In this work, a series of molybdenum nitride catalysts supported on TiO2, and SBA-15 has been prepared and fully characterized. The results of characterization confirmed the high dispersion of Mo and the formation of small molybdenum nanoparticles in both the 10-Mo-N/SBA-15 and 10-Mo-N/TiO2 catalysts. In this context, we have shown that the catalytic activity of Mo species was strongly impacted by the nature of the catalytic support. Amongst the studied supports, SBA-15 was found to be the most appropriate for Mo dispersion. In comparison, when supported on a reducible oxide (TiO2), Mo species showed poor catalytic activity in both ammonia synthesis and decomposition and were prone to quick deactivation in the ammonia synthesis reaction. Evidence of charge transfer from the reducible support to the active phase, indicative of possible SMSI behaviour, has been observed by XPS and EPR. Differences in the oxidation states, redox behaviours, and electronic properties have been further studied by means of EPR, H-2-TPR and H-2-TPD.

Automated summary

Modulating the interaction between Mo nanoparticles and their support can finely tune the properties of the active site. In this study, molybdenum nitride catalysts supported on TiO2 and SBA-15 were prepared and characterized. The catalytic activity of Mo species was strongly influenced by the nature of the support, with SBA-15 being the most suitable for Mo dispersion. Mo species supported on a reducible oxide (TiO2) exhibited poor catalytic activity and quick deactivation in ammonia synthesis reaction due to charge transfer from the support. Differences in oxidation states, redox behaviors, and electronic properties were further studied.