Zhihua Lian

Significant Promotion Effect of Mo Additive on a Novel Ce–Zr Mixed Oxide Catalyst for the Selective Catalytic Reduction of NOx with NH3

A novel Mo-promoted Ce-Zr mixed oxide catalyst prepared by a homogeneous precipitation method was used for the selective catalytic reduction (SCR) of NO(x) with NH3. The optimal catalyst showed high NH3-SCR activity, SO2/H2O durability, and thermal stability under test conditions. The addition of Mo inhibited growth of the CeO2 particle size, improved the redox ability, and increased the amount of surface acidity, especially the Lewis acidity, all of which were favorable for the excellent NH3-SCR performance. It is believed that the catalyst is promising for the removal of NO(x) from diesel engine exhaust.

Novel MnWOx catalyst with remarkable performance for low temperature NH3-SCR of NOx

A novel W promoted MnOx catalyst (MnWOx) was used for the selective catalytic reduction (SCR) of NOx with NH3 at low temperatures, with high deNOx efficiency from 60 to 250 °C under relatively high space velocity. The MnWOx catalyst showed a unique core–shell structure with Mn3O4 covered by Mn5O8 while Mn4+ species at the outer surface served as a real active phase for NH3-SCR. The W doping resulted in the smaller particle size of MnOx active phase, increased the surface acidity and facilitated the NO/NH3 oxidation, thus enhancing low temperature deNOx efficiency by promoting both Langmuir–Hinshelwood and Eley–Rideal reaction pathways. This novel catalyst is promising to be used in the deNOx process for flue gas after dust removal and desulfurization.

Effect of preparation methods on the activity of VOx/CeO2 catalysts for the selective catalytic reduction of NOx with NH3

The effect of preparation methods on the activity of VOx/CeO2 catalysts for the selective catalytic reduction of NOx with NH3 was fully studied. VOx/CeO2 prepared by a simple homogeneous precipitation method showed higher NH3-SCR activity and higher SO2 and H2O resistance than catalysts prepared by other methods. Lower CeO2 crystallinity on the surface, better dispersion of vanadium species, and higher surface concentration of vanadium species together with more acid sites were all responsible for the higher SCR activity of VOx/CeO2 prepared by the homogeneous precipitation method. The NH3-SCR reaction over VOx/CeO2 catalysts mainly followed the Eley–Rideal mechanism, in which gaseous NO reacted with adsorbed NH3 species to finally form N2 and H2O.

Nb-doped VOx/CeO2 catalyst for NH3-SCR of NOx at low temperatures

The promotion effect of Nb addition to VOx/CeO2 catalysts for the selective catalytic reduction of NOx by NH3 was fully investigated. VOx/CeO2 and NbOx doped VOx/CeO2 catalysts were characterized by N2 physisorption, XRD, H2-TPR and NH3-TPD. The results showed that the addition of Nb could significantly promote the SCR activity of the VOx/CeO2 catalyst, especially in the low temperature range. VOx/CeO2 with 30 wt% NbOx catalyst showed the best catalytic performance and better SO2/H2O tolerance than VOx/CeO2 catalyst. 30Nb-1VOx/CeO2 also exhibited higher NH3-SCR activity than 3V2O5–WO3/TiO2. Lower crystallinity, stronger redox capability and more Bronsted acid sites of the Nb-VOx/CeO2 catalyst were all responsible for its more excellent NH3-SCR performance. Based on kinetic experiments and in situ DRIFTS results, it was concluded that the Langmuir–Hinshelwood mechanism existed for selective catalytic reduction of NO over Nb-VOx/CeO2, in which adsorbed NOx species reacted with adsorbed NH3 to finally form N2 and H2O.