Selective reduction of NO x by ethanol on catalysts composed of Ag/Al 2O 3 and Cu/TiO 2 without formation of harmful by-products

Abstract

An attempt was made to remove by-products such as NH 3, CH 3CN, HCN, CO and CH 3CHO which are produced from the reduction of lean NO x by ethanol over an alumina-supported silver catalyst. The efficiency of titania-supported noble metals, vanadium oxide, tungsten oxide, and copper sulfate for the removal of these compounds was examined. It was found that NH 3, CH 3CN, and HCN were easily oxidized to NO x and that the reduction of NO x to N 2 by these nitrogen-compounds did not occur effectively on noble metal catalysts. Among the tested catalysts, CuSO 4/TiO 2 was the most effective for simultaneously removing NH 3, CH 3CN, and HCN and reducing NO x to N 2 by using these nitrogen-compounds. Lean NO x were reduced to N 2 by ethanol effectively and the concentration of nitrogen-containing by-products was lowered over the composite catalyst, Ag/Al 2O 3+CuSO 4/TiO 2. However, in addition to CuSO 4/TiO 2, Pt/TiO 2 was required to remove harmful compounds completely. Consequently, a three-component composite catalyst, Ag/Al 2O 3+CuSO 4/TiO 2+Pt/TiO 2, has been employed in reducing lean NO x by ethanol. This composite catalyst has proved to be quite effective even in the presence of water vapor in that it can reduce lean NO x to N 2 by ethanol effectively and sufficiently lower the concentrations of all harmful by-products.