Low-Temperature Selective Catalytic Reduction of NO with NH3 over Manganese Oxides Supported on Fly Ash-Palygorskite

Xianlong Zhang, Shuangshuan

Abstract

A catalyst of manganese oxides (MnOx) supported on fly ash-palygorskite (MnOx/FA-PG) was prepared for low temperature selective catalytic reduction (SCR) of nitric oxides (NOx) by ammonia (NH3). The influences of the preparation method, active species precursors, calcination temperature, calcination time and particle size on the SCR performance of the MnOx/FA-PG catalyst were studied. Catalysts were characterized by Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescent spectrometry (XRF), and NH3 adsorption and temperature programmed desorption (TPD) to illustrate the physic-chemical properties of catalysts. Results showed that a negligible difference in SCR activity is observed on the MnOx/FA-PG catalyst prepared by heterogeneous deposition and wetness impregnation. Activity of the MnOx/FA-PG catalyst prepared by wetness impregnation with Mn(NO3)2 as precursor was significantly superior to that of prepared with Mn(CH3COO)2 as precursor. Moreover, calcination temperature significantly influenced catalytic activity. Over 70% NO conversion could be achieved at 100°C for Mn8/FA-PG catalysts calcined at 400°C for 3 h. The active component of the catalysts mainly existed in Mn4+. According to the results of NH3 adsorption and temperature programmed desorption (TPD), adsorption capacity of NH3 was not the decisive factor of catalytic activity and the key was the activation of adsorbed NH3.