The promotion effects of TiO₂ on the selective catalytic reduction of NO_x with NH₃ over ceo₂‐WO₃/ZrO₂: The catalytic performance and reaction route

Abstract

ZrO 2 -TiO 2 mixed oxides with different contents of TiO 2 were prepared by a co-precipitation method, which were used as the carrier material of CeO 2 -WO 3 /ZrO 2 -TiO 2 catalysts. The influence of doping TiO 2 on NH 3 -SCR activity and reaction path of CeO 2 -WO 3 /ZrO 2 was systematically investigated by several techniques, including N 2 -physisorption, XRD, H 2 -TPR, XPS, NO x -TPD, NH 3 -TPD, and in situ DRIFTS. The activity result suggested that the CeO 2 -WO 3 /ZrO 2 -TiO 2 with 0.20 g/g TiO 2 exhibited the optimal NH 3 -SCR performance, its operational temperature window was broadened about 55 8C from 254-445 8C of CeO 2 -WO 3 /ZrO 2 to 221-467 8C of CeO 2 -WO 3 /ZrO 2 -TiO 2 . The characterization results indicated that the reducibility of CeO 2 -WO 3 /ZrO 2 was obviously improved by adding TiO 2 into ZrO 2 , which could improve the low-temperature NH 3 -SCR activity. Besides, TiO 2 -doping enhanced the adsorption and activation of NH 3 , which played a positive role in NH 3 -SCR reaction. Finally, the results of in situ DRIFTS demonstrated that the NH 3 -SCR reaction route could be transferred from the Eley-Rideal mechanism over CeO 2 -WO 3 /ZrO 2 to the Langmuir-Hinshelwood mechanism over CeO 2 -WO 3 /ZrO 2 -TiO 2 at 250 8C.

Preparation and Performance of Cerium-Based Catalysts for Selective Catalytic Reduction of Nitrogen Oxides: A Critical Review

“…Up to now, CeO 2 as the main active component and promoter of NH 3 -SCR catalysts has been widely studied [12][13][14]. In general, CeO 2 is an acid-based substance, which has a large number of Lewis acid sites and a few Brönsted acid sites.…”