Recent NH₃-SCR Mechanism Research over Cu/SAPO-34 Catalyst

Abstract

The preliminary mechanism research of NH3-SCR and NH3 oxidation over Cu/SAPO-34 catalyst is explored. The XRD, SEM, in situ EPR, NH3-SCR, NH3 oxidation test, DRIFTs, and the kinetic tests were performed for the bulk characterization, catalytic activity measurement, and the mechanism estimation. The NH3-SCR result showed that Cu/SAPO-34 revealed excellent activity during 120–600 °C, while the NH3 oxidation appeared above 300 °C and caused the decline of NO conversion. The order of various reactants (NO, NH3, and O2 for NH3-SCR and NH3, O2, for NH3 oxidation) was estimated by the kinetic tests to explain their behaviors during the NH3-SCR process. The NH3-SCR presents strong dependence on adsorbed NH3 species on Cu/SAPO-34, but the NH3 oxidation does not. Furthermore, the EPR experiment proved that the isolated Cu2+ species are the active sites and the ammonia nitrites species are the intermediate for NH3-SCR over Cu/SAPO-34 catalysts. The different behavior of adsorbed NH3 species in NH3-SCR and NH3 oxidation was studied through DRIFTs to explain the competition between the two reactions for NH3 consumption at high temperature. Meanwhile, combining the results of previous research, the primary reaction mechanism over Cu/SAPO-34 during the NH3-SCR process was conducted.

Potassium poisoning on Cu-SAPO-34 catalyst for selective catalytic reduction of NOx with ammonia

“…NH 3 -SCR activities are reduced a lot only at a high content of potassium (2.5% of potassium). Some authors [20,38,49] reported that at high temperatures Brønsted acid sites existed as ammonia storage sites and offered activated ammonia for the active sites in the NH 3 -SCR on the Cu-SAPO-34 catalyst, since ammonia could no longer adsorb on the active sites. However, ammonia still can adsorb on the isolated Cu + on the Cu-SAPO-34 catalyst at high temperatures (>300 °C), which can be observed in Fig.…”

Effects of Alkali and Alkaline Earth Cocations on the Activity and Hydrothermal Stability of Cu/SSZ-13 NH3–SCR Catalysts

“…This is consistent with a consensus from a few recent studies that molecular NH 3 adsorbed on Cu ion sites is substantially more reactive than NH 4 + stored at Brønsted acidic sites. 20,27,37 It is further argued that molecular NH 3 adsorbed on other Lewis acid sites also contribute more than NH 4 + in the low-temperature regime. 20 Note specifically that fresh and HTA Cu,Ca/SSZ-13 samples show essentially no difference in SCR performance at low reaction temperatures.…”

In Situ DRIFTS Study of the Low Temperature Selective Catalytic Reduction of NO with NH3 over MnOx Supported on Multi-Walled Carbon Nanotubes Catalysts

“…The mechanism of the SCR reaction had been studied extensively elsewhere and different hypotheses had been proposed (Li et al, 2011;Zhou et al, 2011;Fu et al, 2014;Yu et al, 2014). Fig.…”