Study of the “Fast SCR”-like mechanism of H2-assisted SCR of NOx with ammonia over Ag/Al2O3

It is shown that Ag/Al2O3 is a unique catalytic system for H2-assisted selective catalytic reduction of NOx by NH3 (NH3-SCR) with both Ag and alumina being necessary components of the catalyst. The ability of Ag/Al2O3 and pure Al2O3 to catalyse SCR of mixtures of NO and NO2 by ammonia is demonstrated, the surface species occurring discussed, and a “Fast SCR”-like mechanism of the process is proposed. The possibility of catalyst surface blocking by adsorbed NOx and the influence of hydrogen on desorption of NOx were evaluated by FTIR and DFT calculations.

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► Presence of both Ag and Al2O3 is vital for high activity of Ag/Al2O3 in NOx SCR.
► The primary role of Ag is the H2-assisted oxidative activation of NO.
► The second role of hydrogen is the removal of nitrates blocking the Al2O3 surface.
► NO, NO2 and NH3 can react over pure alumina according to “Fast SCR” mechanism.
► The results are obtained using transient experiments, FTIR and DFT calculations.