Abstract
Spherical MCM-41 with various copper and iron loadings was prepared by surfactant directed co-condensation method. The obtained samples were characterized with respect to their structure (X-ray diffraction, XRD), texture (N2 sorption), morphology (scanning electron microscopy, SEM), chemical composition (inductively coupled plasma optical emission spectrometry, ICP-OES), surface acidity (temperature programmed desorption of ammonia, NH3-TPD), form, and aggregation of iron and copper species (diffuse reflectance UV-Vis spectroscopy, UV-Vis DRS) as well as their reducibility (temperature programmed reduction with hydrogen, H2-TPR). The spherical MCM-41 samples modified with transition metals were tested as catalysts of selective catalytic reduction of NO with ammonia (NH3-SCR). Copper containing catalysts presented high catalytic activity at low-temperature NH3-SCR with a very high selectivity to nitrogen, which is desired reaction products. Similar results were obtained for iron containing catalysts, however in this case the loadings and forms of iron incorporated into silica samples very strongly influenced catalytic performance of the studied samples. The efficiency of the NH3-SCR process at higher temperatures was significantly limited by the side reaction of direct ammonia oxidation. The reactivity of ammonia molecules chemisorbed on the catalysts surface in NO reduction (NH3-SCR) and their selective oxidation (NH3-SCO) was verified by temperature-programmed surface reactions.
Highlights
Development of mesoporous silica materials in 1990s [1,2] was undoubtedly one of the most specular challenges in materials sciences
The spherical MCM-41 samples containing various content of copper or iron incorporated into the silica walls were obtained by surfactant directed co-condensation method
Similar effect was observed for spherical MCM-41 containing iron incorporated into silica walls (Figure 1B)
Summary
Development of mesoporous silica materials in 1990s [1,2] was undoubtedly one of the most specular challenges in materials sciences. An interesting option is the introduction of catalytically-active metal species by co-condensation method during mesoporous silica formation [13] This relatively simple and cheap method, depending on the synthesis conditions, may result in quite uniform distribution of metal species in silica matrix. The presented studies include the synthesis of spherical MCM-41 with copper and iron species incorporated into amorphous silica matrix and verification their catalytic performance in the selective catalytic reduction of NO with ammonia (NH3 -SCR). The efficiency of this process at higher temperatures is limited by the side reaction of direct ammonia oxidation by oxygen present in flue gases. The activity of the catalysts in the reaction of selective ammonia oxidation (NH3 -SCO) was studied and compared with their catalytic activity in the process of NO reduction with ammonia
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