In Situ DRIFTS Studies of NH3-SCR Mechanism over V2O5-CeO2/TiO2-ZrO2 Catalysts for Selective Catalytic Reduction of NOx

Abstract

TiO2-ZrO2 (Ti-Zr) carrier was prepared by a co-precipitation method and 1 wt. % V2O5 and 0.2 CeO2 (the Mole ratio of Ce to Ti-Zr) was impregnated to obtain the V2O5-CeO2/TiO2-ZrO2 catalyst for the selective catalytic reduction of NOx by NH3. The transient activity tests and the in situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) analyses were employed to explore the NH3-SCR (selective catalytic reduction) mechanism systematically, and by designing various conditions of single or mixing feeding gas and pre-treatment ways, a possible pathway of NOx reduction was proposed. It was found that NH3 exhibited a competitive advantage over NO in its adsorption on the catalyst surface, and could form an active intermediate substance of -NH2. More acid sites and intermediate reaction species (-NH2), at lower temperatures, significantly promoted the SCR activity of the V2O5-0.2CeO2/TiO2-ZrO2 catalyst. The presence of O2 could promote the conversion of NO to NO2, while NO2 was easier to reduce. The co-existence of NH3 and O2 resulted in the NH3 adsorption strength being lower, as compared to tests without O2, since O2 could occupy a part of the active site. Due to CeO2’s excellent oxygen storage-release capacity, NH3 adsorption was weakened, in comparison to the 1 wt. % V2O5-0.2CeO2/TiO2-ZrO2 catalyst. If NOx were to be pre-adsorbed in the catalyst, the formation of nitrate and nitro species would be difficult to desorb, which would greatly hinder the SCR reaction. All the findings concluded that NH3-SCR worked mainly through the Eley-Rideal (E-R) mechanism.

Effect of Hydrothermal Aging Treatment on Decomposition of NO by Cu-ZSM-5 and Modified Mechanism of Doping Ce against This Influence

“…In addition to affecting the natural environment, NO also causes respiratory, cardiovascular, and cerebrovascular diseases [1,2]. Although most coal-fired power station boilers are equipped with a Selective Catalytic Reduction (SCR) denitration system [3], ammonia escapes, the narrow temperature window, the highly toxic of V 2 O 5 catalyst, and the blocked downstream air preheater caused by side reactions seriously affects the stability and reliability of SCR [4,5].…”

Calcium Poisoning Mechanism of Cu‐SAPO‐18 for Selective Catalytic Reduction of NOx with Ammonia

“…Adsorption peaks of bridging nitrate (1611 cm –1 ), [43] bidentate nitrate (1580 cm –1 ), and monodentate nitrate (1560 cm –1 ) were recorded in the fresh and Ca‐poisoned samples [36,44] . The intensity of bridging nitrate on the Ca‐poisoned sample was significantly lower than that on the fresh Cu‐SAPO‐18 sample, and the characteristic peak of N 2 O 2 2– (1371 cm –1 ) [45] was only observed on the fresh Cu‐SAPO‐18 sample. When NH 3 was introduced, bridging nitrate and N 2 O 2 2– in the fresh Cu‐SAPO‐18 sample disappeared rapidly and the NH 3 species at the Lewis acidic sites (1462 cm –1 ) and Brönsted acidic sites (1632 and 1280 cm –1 ) were detected.…”

“…(1371 cm -1 ) [45] was only observed on the fresh Cu-SAPO-18 sample. When NH 3 was introduced, bridging nitrate and N 2 O 2…”

In Situ DRIFTS Investigation on CeOx Catalyst Supported by Fly-Ash-Made Porous Cordierite Ceramics for Low-Temperature NH3-SCR of NOX

“…Bands at 3332, 3274 and 1166 cm −1 were mainly related to NH3 adsorbed on Lewis acid sites [32]. The band centered at 1583 cm −1 indicated the existence of amide species after NH3 treatment [35]. Two bands located at 965 and 929 cm −1 could also be observed, which was mainly due to the weakly adsorbed or gas phase NH3 [34].…”

“…Among these bands, the ones located at 3368 and 3271 cm −1 could be linked to the adsorbed NH3 on Lewis acid sites, while the band centered at 1384 cm −1 could be ascribed to the NH4 + on Brønsted acid sites [34]. The two bands located at 1580 and 1295 cm −1 were associated to the -NH2 species [35,36]. Based on the above analysis, both 0.6Ce/CPCC and 0.6Ce/SPCC have Lewis and Brønsted acid sites on the surface.…”