Ca Doping Effect on the Competition of NH₃–SCR and NH₃ Oxidation Reactions over Vanadium-Based Catalysts

Abstract

The Ca poisoning effect constrains vanadium-based catalysts from further application in high-calcium content flue gas, and the deactivation effect of CaO on V2O5–WO3/TiO2 (VWT) and V2O5/TiO2 (VT) catalysts has been investigated from a new perspective. As the NH3 selective catalytic reduction (NH3–SCR) results showed, the NO conversion at 400 °C declined by 71.7% for VT and by 34.8% for VWT after CaO doping, and the decrease in NO conversion for NH3–SCR at temperatures greater than 300 °C was mainly caused by the competition of the NH3 oxidation reaction. The characterization of catalysts by NH3–SCR, XRD, Raman spectroscopy, H2-TPR, NH3-TPD, and TEM showed that the number of surface acid sites decreased and that the oxidation and reduction properties of the catalysts all deteriorated after CaO doping, which is the primary reason for the decrease in NO conversion. CaO also affected NH3 oxidation, and the L-NH3 adsorbed on CaO favored the NH3 oxidation reaction, as DRIFTS showed. NH3 reaction pathways changed by CaO doping because NH3 oxidation becomes more competitive at temperatures greater than 300 °C. Density functional theory (DFT) calculations confirmed the NO formation pathway on CaO, and the competition mechanism of NH3–SCR and NH3 oxidation reactions has been described, which has hardly been reported.

Effects of Catalyst Physicochemical Properties on the Catalytic Activity of Cu Zeolite Selective Catalytic Reduction at Different Inlet Gas Conditions

“…When the temperature was higher than 400 °C, the oxidation rate of NH 3 accelerated with the increase in temperature. From the point of the distribution of products in NH 3 oxidation, the main product was N 2 , and the competition between NH 3 oxidation and the NH 3 –SCR reaction was affected by CaO, which could increase the NO selectivity . In the high-temperature range (400–550 °C), the two-stage SCR system could also complement each other in the NH 3 oxidation reaction, causing the NH 3 oxidation rate to increase by 46.9–88.7%.…”

“…The decrease in the NOx conversion at temperatures greater than 300 °C was mainly caused by the competition of the NH 3 oxidation reaction (eqs 8910). 49 At the same time, the conversion rate of the back-SCR increased accordingly, which caused the total SCR conversion rate to maintain a high level.…”

Poisoning Process of the V2O5–CeO2/TiO2 Catalyst by the Cumulative Effect of CaO

“…The V 2 O 5 −CeO 2 /TiO 2 catalyst with 0.5 wt % V 2 O 5 and 20 wt % CeO 2 loading (denoted by V 0.5 Ce 20 Ti) and the Ca-poisoned catalysts were prepared using a typical wet impregnation method, as reported previously. 7 Additional experimental details can be found in the Supporting Information. The poisoned samples were denoted by xCa, where x represents the molar ratio of Ca/V.…”

“…The poisoning effect of K, Na, or Ca on catalysts has been extensively studied in the laboratory; the doping ratio of toxic elements is generally as high as 1–3 wt %. − However, according to the actual operating conditions, the poisoning process is gradual and dynamic, , which has not been sufficiently investigated. It is worth noting that the cumulative rate of poisoning affects the degree of deactivation, which is essential for catalyst lifetime that affects its application.…”

High-Dispersed V2O5-CuOX Nanoparticles on h-BN in NH3-SCR and NH3-SCO Performance

“…Among the existing control techniques of NO X , the selective catalyst reduction of NO X with NH 3 (NH 3 -SCR), which entails the use of ammonia as a reductant, is one of the most commonly applied techniques in stationary likes coal-fired power plant owing to its convenient operation and maintenance and effective NO X conversion performance [ 6 ]. The commercial performance of NH 3 -SCR can reach 90% when using V 2 O 5 -WO 3 /TiO 2 as the catalyst at 300–450 °C [ 7 , 8 , 9 ]. The corresponding working principle can be expressed as follows: …”