Characterization and activity of novel copper-containing catalysts for selective catalytic reduction of NO with NH3 (original) (raw)
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Catalysis Today, 2002
The influence of ammonia and nitric oxide oxidation on the selective catalytic reduction (SCR) of NO by ammonia with copper/nickel and vanadium oxide catalysts, supported on titania or alumina have been investigated, paying special attention to N 2 O formation. In the SCR reaction, the VTi catalyst had a higher activity than VAl at low temperatures, while the CuNiAl catalyst had a higher activity than CuNiTi. A linear relationship between the reaction rate of ammonia oxidation and the initial reduction temperature of the catalysts obtained by H 2 -TPR showed that the formation rate of NH species in copper/nickel catalysts would be higher than in vanadia catalysts. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that copper/nickel catalysts presented ammonia coordinated on Lewis acid sites, whereas ammonium ion adsorbed on Brønsted acid sites dominated on vanadia catalysts. The NO oxidation experiments revealed that copper/nickel catalysts had an increase of the NO 2 and N 2 O concentrations with the temperature. NO could be adsorbed on copper/nickel catalysts and the NO 2 intermediate species could play an important role in the reaction mechanism. It was suggested that the presence of adsorbed NO 2 species could be related to the N 2 O formation.
Journal of Catalysis, 2005
The formation of nitrous oxide in the selective catalytic reduction of NO x with ammonia was studied in nitric acid plant exhaust gas under low-temperature conditions. The important role played by the support in this process was evidenced by a comparison of CuO/γ -Al 2 O 3 and CuO/TiO 2 monolithic catalysts. Textural properties and CuO crystal phases were analysed. Temperature-programmed desorption of NH 3 , NO, and NO 2 and X-ray photoelectron spectroscopy (XPS) after in situ adsorption of NO and NO 2 experiments were carried out. Even at low temperature, N 2 O generation takes place at a greater rate for the catalysts supported on titania than for those on alumina. In the case of alumina, the N 2 O concentration detected was independent of the CuO content. For the CuO/TiO 2 system it was associated with the active phase configuration. After in situ adsorption of NO and NO 2 , a band associated with nitrate species was identified in the XPS spectra. Adsorbed NO 3 − species seem to be responsible for the NO 2 , NO, and O 2 desorbed products detected in the NO x -TPD. The results suggests that NO − 3(ads) along with NH x(ads) species, were involved in N 2 O formation at low temperature. (S. Suárez).
Reaction Kinetics, Mechanisms and Catalysis, 2017
Hydrotalcite originated mixed metal Cu-Mg-Al oxide system was doped with various amounts of cerium (0.5 or 3.0 wt%) and tested in the role of catalysts for the selective catalytic oxidation of ammonia to dinitrogen (NH 3-SCO) and the selective catalytic reduction of NO with ammonia (NH 3-SCR). The activating effect of cerium was observed in both studied processes. However, the CeO 2 loading is a very important parameter determining catalytic performance of the studied samples. It was shown that an introduction of cerium into Cu-Mg-Al mixed oxide resulted in its significant activation in the low-temperature NH 3-SCR process, independently of the CeO 2 loading and a decrease in the efficiency of the NO reduction at higher temperatures, which was more significant for the catalyst with the lower cerium content. In the case of the NH 3-SCO process, the introduction of cerium into Cu-Mg-Al mixed oxide resulted in the activation of the low temperature reaction, which was more intensive for the catalyst with lower cerium content. These effects were related to the presence of cerium in the form of crystallites of various size and therefore their different reducibility.
Journal of Catalysis, 2004
Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, Fe, Co, Ni, and Cu supported on anatase TiO 2 has been studied. Among the catalysts tested, Mn/TiO 2 supported on Hombikat TiO 2 provided the best performance with 100% N 2 selectivity and complete NO conversion at temperatures as low as 393 K under numerous conditions. The catalytic performance for various transition metal oxides supported on TiO 2 decreased in the following order: Mn > Cu Cr Co > Fe V ≫ Ni. For Mn-based catalysts the activity increases with an increase in Mn loading and the reaction temperature. TiO 2 alone did not give any NO conversion at 573 K, and calcination at low temperature ( 673 K) is preferable. XRD coupled with XPS confirmed the presence of MnO 2 as a major phase (peak at 642.2 eV) with Mn 2 O 3 , and partially undecomposed Mn-nitrate as the minor phases for supported manganese catalysts. It is proposed that MnO 2 contributes to the high activity of Mn/TiO 2 . XPS results also confirmed a higher concentration of active metal oxides on the surface of Mn/TiO 2 compared to the other catalysts. The NH 3 FT-IR study showed the presence of Lewis acid sites for the most active catalysts, while the peak corresponding to Brönsted acid sites was weak or absent. This strongly suggests that Brönsted acid sites are not necessary for the reaction to occur at low temperatures. The H 2 TPR study indicated the difficulty of reducing Mn oxide when the metal loading is low and/or the catalysts are calcined at temperatures higher than 773 K. It is concluded that lower catalyst calcination temperatures, Lewis acidity, the redox properties of metal oxides and their higher surface concentration are important for very high SCR activity at low temperatures. Mn/TiO 2 provided the best performance at 50,000 h −1 when the catalysts were tested in the presence of 11 vol% H 2 O. Under these conditions, the catalytic activity of the transition metal oxides decreases in the following order: Mn > V Co > Cu > Cr > Fe Ni.
Journal of Catalysis, 2004
Low-temperature SCR of NO with NH 3 in the presence of excess oxygen on the oxides of V, Cr, Mn, Fe, Co, Ni, and Cu supported on anatase TiO 2 has been studied. Among the catalysts tested, Mn/TiO 2 supported on Hombikat TiO 2 provided the best performance with 100% N 2 selectivity and complete NO conversion at temperatures as low as 393 K under numerous conditions. The catalytic performance for various transition metal oxides supported on TiO 2 decreased in the following order: Mn > Cu Cr Co > Fe V ≫ Ni. For Mn-based catalysts the activity increases with an increase in Mn loading and the reaction temperature. TiO 2 alone did not give any NO conversion at 573 K, and calcination at low temperature ( 673 K) is preferable. XRD coupled with XPS confirmed the presence of MnO 2 as a major phase (peak at 642.2 eV) with Mn 2 O 3 , and partially undecomposed Mn-nitrate as the minor phases for supported manganese catalysts. It is proposed that MnO 2 contributes to the high activity of Mn/TiO 2 . XPS results also confirmed a higher concentration of active metal oxides on the surface of Mn/TiO 2 compared to the other catalysts. The NH 3 FT-IR study showed the presence of Lewis acid sites for the most active catalysts, while the peak corresponding to Brönsted acid sites was weak or absent. This strongly suggests that Brönsted acid sites are not necessary for the reaction to occur at low temperatures. The H 2 TPR study indicated the difficulty of reducing Mn oxide when the metal loading is low and/or the catalysts are calcined at temperatures higher than 773 K. It is concluded that lower catalyst calcination temperatures, Lewis acidity, the redox properties of metal oxides and their higher surface concentration are important for very high SCR activity at low temperatures. Mn/TiO 2 provided the best performance at 50,000 h −1 when the catalysts were tested in the presence of 11 vol% H 2 O. Under these conditions, the catalytic activity of the transition metal oxides decreases in the following order: Mn > V Co > Cu > Cr > Fe Ni.
Catalysis Letters, 2011
Mg-Cu-Fe oxide systems, obtained from hydrotalcite-like precursors, were tested as catalysts for the selective catalytic oxidation (SCO) of ammonia. Copper containing catalysts were active in low-temperature SCO processes; however, their selectivity to nitrogen significantly decreased at higher temperatures. The optimum composition of the catalyst to guarantee high activity and selectivity to N 2 was proposed. Temperature-programmed experiments, SCO catalytic tests performed with various contact times and additional tests on the samples in the selective catalytic reduction of NO with ammonia showed that the SCO process over the studied calcined hydrotalcites proceeds according to the internal SCR mechanism and oxidation of ammonia to NO is a rate-determining step in the low-temperature range.
Catalysis Today, 1996
The formation of nitrate and NO 2 adspecies over Cu/MFI and copper-on-alumina catalysts and their role in the mechanism of reaction is discussed on the basis of FF-IR results and catalytic tests in unsteady-state conditions. Three specific cases are discussed: (i) reduction of NO by propane/O 2 over Cu/MFI, (ii) conversion of NO by NH3/O 2 over copper-on-alumina catalysts and (iii) oxygen-promoted reduction of NO in the absence of reductants over Cu/MFI. The formation of nitrate species leads to self-deactivation, but Cu2+-NO2 like adspecies are suggested to be a key intermediate in the reduction of NO to N 2 in all three cases examined.
Kinetics of the selective catalytic reduction of NO by NH 3 on a Cu-faujasite catalyst
Applied Catalysis B-environmental, 2004
The kinetics of the selective catalytic reduction (SCR) of NO by NH3 in the presence of O2 has been studied on a 5.5% Cu-faujasite (Cu-FAU) catalyst. Cu-FAU was composed of cationic and oxocationic Cu species. The SCR was studied in a gas phase-flowing reactor operating at atmospheric pressure. The reaction conditions explored were: 458<TR<513K, 250<NO (ppm) < 3000, 1000<NH3 (ppm)
Reaction Kinetics, Mechanisms and Catalysis, 2014
The influence of the increase of the specific surface area of the support Ca-HAp on the dispersion of copper species and their activity in the NO-SCR by NH3 has been studied. The copper ion exchange does not alter the Ca-HAp structure whatever the copper concentration. The increase of the specific surface area of the support changed the dispersion and the reducibility of copper species. The high NO conversion in the whole temperature range for the catalyst with the lowest specific surface area (35 m2/g) was related to the highly dispersed CuO particles that are easily reduced. Nevertheless, the increase of the specific surface area of the support (76 m2/g), induces an increase of the size of CuO particles that become less active in NO-SCR by NH3. The addition of 2.5 % of H2O to the reaction gas feed strongly affects the NO conversion in the whole temperature range. This deactivation can be related to the change of the nature of copper species rather than to the destruction of the Ca...