The selective catalytic reduction of NOx over Ag/Al2O3 with isobutanol as the reductant

• Isobutanol as NO reductant achieves 90% NOx conversion over Ag/Al2O3 between 300–400 °C.
• Isobutanol SCR activity is comparable to that of ethanol and appears to follow a similar mechanism.
• Isobutyraldehyde and NO2 are key intermediates during SCR with isobutanol.
• COH group in alcohols governs the SCR reaction over Ag/Al2O3.

This study investigates the potential of isobutanol (iBuOH) as a reductant for the selective catalytic reduction (SCR) of NOx over 2 wt% Ag/Al2O3 between 150 and 550 °C and gas hourly space velocities (GHSV) between 10,000 and 35,000 h−1. The feed gas consists of 500 ppm NO, 5% H2O, 10% O2, and 375–1500 ppm iBuOH (C1:N ratios of 3–12); additionally, blends of 24 and 48% v/v iBuOH in gasoline are evaluated. Over 90% NOx conversion is achieved between 300 and 400 °C using pure iBuOH, including a 40% peak selectivity toward NH3 that could be utilized in a dual HC/NH3-SCR configuration. The iBuOH/gasoline blends are only able to achieve greater than 90% NOx conversion when operated at a GHSV of 10,000 h−1 and employing a C1:N ratio of 12. Iso-butyraldehyde and NO2 appear to function as intermediates in the iBuOH-SCR mechanism, which mirrors the mechanism observed for EtOH-SCR. In general, the performance of iBuOH in the SCR of NOx over a Ag/Al2O3 catalyst is comparable with that of EtOH, although EtOH/gasoline blends display higher NOx reduction than iBuOH/gasoline blends. The key parameter in employing alcohols in SCR appears to be the COH:N ratio rather than the C1:N ratio.

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