The deposition of VWOx on the CuCeOy microflower for the selective catalytic reduction of NOx with NH3 at low temperatures

Abstract

NO_x emissions are a major environmental problem, and the selective catalytic reduction (SCR) is the most effective method to convert NO_x in flue gas into harmless N₂ and H₂O. In this work, a new carrier, CuCeO_y microflower assembled from a large number of copper-cerium mixed oxide nanosheets, is firstly developed to load vanadium-tungsten mixed oxides (VWO_x) for the SCR of NO_x with NH₃. The resultant optimal VWO_x/CuCeO_y catalyst exhibits significantly enhanced low-temperature de-NO_x performance with the NO_x conversion of 60% at 180 °C, over 90% from 240 °C to 390 °C under the gas hourly space velocity (GHSV) of 36,000 h^-1. The reason can be mainly attributed the fact that the transfer of electrons among Ce, Cu and V ions is very easy to occur via the following equations Ce³⁺+Cu²⁺ ↔ Ce⁴⁺+Cu⁺, V⁵⁺ + Cu⁺ ↔ V⁴⁺ + Cu²⁺, V⁴⁺ + Ce⁴⁺ ↔ V⁵⁺ + Ce³⁺, which effectively decreases the apparent activation energy (E_a = 16.59 kJ/mol) of NH₃-SCR de-NO_x reaction. In addition, the enhanced reducibility and a large number of Brønsted acid sites also contribute the low-temperature de-NO_x performance. Both Eley-Rideal and Langmuir-Hinshelwood mechanisms are included in the NH₃-SCR de-NO_x reaction over the VWO_x/CuCeO_y catalyst.

Keywords: De-NO(x); Low temperature; Metal oxides; Reaction mechanism; Selective catalytic reduction.