Unprecedented propane–SCR-NOx activity over template-free synthesized Al-rich Co-BEA∗ zeolite

• Al-rich compared to Si-rich Co-BEA∗ provides extraordinarily high SCR activity.
• The most active site is [Co(III)O]+ attached to one AlO4− of AlSiAl sequence.
• High density of [Co(III)O]+ causes synergism in SCR-NOx.
• 12 times increased reaction rate and 5 times higher TOFCo for Al-rich Co-BEA∗.
• The Al-rich Co-BEA∗ exceeds previously reported catalysts for C3H8–SCR-NOx.

An Al-rich Co-BEA∗ zeolite (Si/Al 4.2, Co/Al 0.5) was prepared by organotemplate-free hydrothermal synthesis and [Co(II)(H2O)6]2+ ion exchange. The structure of the Co species and their activity in C3H8–SCR-NOx were compared to that of Si-rich Co-BEA∗ (Si/Al 11.3). The high population of AlSiAl sequences in Al-rich BEA∗ with AlO4− facing different channels, contrary to their absence in Si-rich BEA∗, results in dehydrated Co-BEA∗ in easily reducible counter-ion [Co(III)O]+ species attached to one AlO4−. The high concentration and density of these Co-oxo species in Al-rich Co-BEA∗ facilitates extra-ordinarily high SCR-NOx rate even under water vapor up to 10 vol.%, twelve-times outperforming Si-rich Co-BEA∗. The five-to-six times increased TOF and easier reducibility suggest a synergetic redox effect of water-resistant Co-oxo species. The Al-rich Co-BEA∗ provides the highest reaction rate at conditions of wet NOx streams, exceeding that previously reported for metal ion/oxo zeolite catalysts, with a high selectivity to molecular nitrogen and efficient utilization of propane.

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