Wulin Wang

New insight into the promotion effect of Cu doped V2O5/WO3–TiO2 for low temperature NH3-SCR performance

The promotion effect of Cu on the V/WTi catalyst for the selective catalytic reduction of NOx by NH3 was investigated in the temperature range of 150–400 °C. The Cu addition shows a superior NH3-SCR performance in comparison with the V/WTi sample. The catalysts were characterized by XRD, Raman, EPR, H2-TPR, XPS, and in situ DRIFTS techniques. The obtained results reveal that the Cu oxides in close proximity to V oxides on the surface facilitate the formation of double redox couples of V5+/V4+ and Cu2+/Cu+, which may play a critical role in the superior NH3-SCR performance. The electronic interactions caused by the redox cycle of Cu2+ + V4+ ↔ V5+ + Cu+ could significantly improve the redox properties of the vanadium species, which is beneficial for the activation of NH3 species bound to the vanadium species. Moreover, the redox cycle of Cu2+ + V4+ ↔ V5+ + Cu+ induces the formation of high-activity nitrate species adsorbed on Cu species. The kinetic analysis reveals that the Cu doping induces the decrease of the activation energy (Ea) of NH3-SCR.

Steam effects over Pd/Ce0.67Zr0.33O2 three-way catalyst

Abstract In the purification process of automobile exhaust, existing water plays an important role as an oxidant, which converts CO and hydrocarbons (HCs) by the water-gas shift (WGS) and the steam reforming (SR) reactions, respectively, especially at high temperatures. Meanwhile it is major component of the exhaust which can affect significantly the thermal stability of the three-way catalyst. Activity experiments were carried out close to the real operation conditions (GHSV, concentration, etc.) with a Pd/Ce0.67Zr0.33O2 catalyst supplying information on the CO and C3H8 oxidation reactions in feedstream formed by different reactant combinations. The obtained results showed that the activity of the CO and C3H8 oxidation was promoted by the addition of steam due to the WGS and SR reactions. The WGS and SR reaction were competitive under oxygen-lean conditions. The kinetic analysis was considered for WGS and SR reactions.

Effect of synthesis methods on activity of V2O5/CeO2/WO3-TiO2 catalyst for selective catalytic reduction of NOx with NH3

Abstract The effect of synthesis methods on the activity of V/Ce/WTi catalysts was investigated for the selective catalytic reduction (SCR) of NO x by NH 3 . V/Ce/WTi-DP (deposition precipitation) catalyst showed excellent NH 3 -SCR performance, especially the better medium-temperature activity and the less N 2 O formation than V/Ce/WTi-IMP (impregnation). These catalysts were characterized by X-ray diffraction (XRD), Brumauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H 2 -TPR), and in situ DRIFTS techniques. The XPS and H 2 -TPR results revealed that V/Ce/WTi-DP exhibited more surface Ce species, higher level of O α and higher reducibility of Ce species. Reflected by in situ DRIFTS results, the deposition precipitation method (DP) contributed to a greater amount of weakly adsorbed NO 2 , monodentate nitrate and NH 3 species with better reactive activity. Meanwhile, the cis-N 2 O 2 2– species, an intermediate for N 2 O formation, was very limited. As a result, these advantages brought about the superior SCR activity and N 2 selectivity for V/Ce/WTi-DP.

Effects of Pd doping on N 2 O formation over Pt/BaO/Al 2 O 3 during NO x storage and reduction process

AbstractN2O is a powerful greenhouse gas and plays an important role in destructing the ozone layer. This present work investigated the effects of Pd doping on N2O formation over Pt/BaO/Al2O3 catalyst. Three types of catalysts, Pt/BaO/Al2O3, Pt/Pd mechanical mixing catalyst (Pt/BaO/Al2O3 + Pd/Al2O3) and Pt-Pd co-impregnation catalyst (Pt-Pd/BaO/Al2O3) were prepared by incipient wetness impregnation method. These catalysts were first evaluated in NSR activity tests using H2/CO as reductants and then carefully characterized by BET, CO chemisorption, CO-DRIFTs and H2-TPR techniques. In addition, temperature programmed reactions of NO with H2/CO were conducted to obtain further information about N2O formation mechanism. Compared with Pt/BaO/Al2O3, (Pt/BaO/ Al2O3 + Pd/Al2O3) produced less N2O and more NH3 during NOx storage and reduction process, while an opposite trend was found over (Pt-Pd/BaO/Al2O3 + Al2O3). Temperature programmed reactions of NO with H2/CO results showed that Pd/Al2O3 component in (Pt/BaO/Al2O3 + Pd/Al2O3) played an important role in NO reduction to NH3, and the formed NH3 could reduce NOx to N2 leading to a decrease in N2O formation. Most of N2O formed over (Pt-Pd/BaO/Al2O3 + Al2O3) was originated from Pd/BaO/Al2O3 component. H2-TPR results indicated Pd-Ba interaction resulted in more difficultto- reduce PdOx species over Pd/BaO/Al2O3, which inhibits the NO dissociation and thus drives the selectivity to N2O in NO reduction.