Mesoporous silica supported Rh catalysts for high concentration N2O decomposition

• Rh1+ species acting as Lewis acidic sites.
• Key role of the 3-D mesoporosity to favour the Rh active sites dispersion.
• The most promising catalyst (Rh-MCF) showed the highest amount of Rh1+ species.
• Dispersion-sensitivity of N2O decomposition over RhOx nanoparticles.

A set of Rh-containing catalysts (Rh-MCM-41, Rh-SBA-15, Rh-KIT-6 and Rh-MCF, nominal Rh content = 1 wt.%) has been prepared by wet impregnation of mesoporous silicas and tested for high concentration N2O abatement. The physico-chemical properties of the materials have been investigated by means of complementary techniques.The best performances, in terms of N2O decomposition, have been achieved for the Rh-MCF catalyst, due to the better textural properties of the MCF silica. In fact, the MCF-type support exhibits three-dimensional mesoporosity with ultra-large cells (up to 40 nm), which allow a uniform distribution of small RhOx particles (≈1 nm) over the high (internal) surface area of the MCF. Moreover, the Rh active sites are also readily accessible to N2O molecules.The most promising catalyst has shown the highest amount of Rh1+ species, the easiest rhodium reducibility and the greatest abundance of Rh surface sites. These important features reflect the different Rh particle sizes and play a role in catalytic activity.A remarkable relationship between the catalytic activity and the dimension of the RhOx particles has been observed in the 1–2.5 nm size domain, thus confirming the dispersion-sensitivity of N2O decomposition over RhOx nanoparticles.

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