Spherical Al-MCM-41 Doped with Copper by Modified TIE Method as Effective Catalyst for Low-Temperature NH3-SCR

Abstract

Aluminum containing silica spherical MCM-41 was synthesized and modified with copper by the template ion-exchange method (TIE) and its modified version, including treatment of the samples with ammonia solution directly after template ion-exchange (TIE-NH3). The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low temperature N2 sorption), morphology (SEM-EDS), form and aggregation of deposited copper species (UV-vis DRS), reducibility of copper species (H2-TPR), and surface acidity (NH3-TPD). The deposition of copper by the TIE-NH3 method resulted in much better dispersion of this metal on the MCM-41 surface comparing to copper introduced by TIE method. It was shown that such highly dispersed copper species, mainly monomeric Cu2+ cations, deposited on aluminum containing silica spheres of MCM-41, are significantly more catalytically effective in the NH3-SCR process than analogous catalysts containing aggregated copper oxide species. The catalysts obtained by the TIE-NH3 method effectively operated in much broader temperature and were less active in the side process of direct ammonia oxidation by oxygen.

Studies of NO Reduction with Ammonia Over Copper Species Deposited on MCM‐41 Nanospheres ‐ Experimental Evidence of Reaction Mechanism

“…[40] High selectivity of ammonia oxidation to nitrogen over copper modified mesoporous silica was reported in our previous paper. [23] These scientific hypotheses need confirmation by the future studies.…”

“…A detailed description of the experimental procedures used for the catalyst preparation can be found in our previous papers. [22,23,24] Three series of Cu-modified MCM-41 nanospheres were prepared using template ion-exchange method (T), its modified version including post-treatment with ammonia solution (TA) and cocondensation approach (C).…”

“…Experimental systems and procedures used for these measurements as well as characterization results have been presented in detail in our previous papers. [22,23,24] The main goal of the presented studies is recognition of the NH 3 -SCR reaction mechanism depending on the methods used for the catalyst's synthesis. Thus, in this work only selected examples of the samples characterization are presented but of course the results shown in this work are discussed in relation to the results of the sample characterization presented in our previous papers.…”

“…[21] Recently, a very promising catalytic performance in the lowtemperature NH 3 -SCR process has been reported for copper modified mesoporous silicas obtained by template ion-exchange (TIE) method. [22,23,24] In general, mesoporous silica materials, due to their high surface area, uniform mesoporous structure are relatively high thermal and hydrothermal stability, are assumed to be very good catalytic supports. Because pure silica mesoporous materials do not exhibit ion-exchange properties, deposition of catalytically active metal species in controlled, highly dispersed, and uniform forms, is difficult and sometimes very expensive.…”

“…[27] Catalysts obtained by this method presented very good performance in the low-temperature NH 3 -SCR process. [22,23,24,27] The cost of the TIE method used for copper deposition could be in the future decreased by recovering and reusing surfactants. The recovery of organic templates from freshly synthesized silica sieves by extraction under mild conditions, without surfactant degradation, was already reported by M. Benjelloun et al, [28] who used a methanol solution of mineral acid for surfactant extraction and then recovered surfactants from such mixture by distillation.…”