Search

Chlorine species, widely presented in industrial flue gas such as the waste incineration plants, can poison the catalysts and affect the selective catalytic reduction (SCR) performance. In this work, effects of Cl on the SCR performance of V2O5–WO3/TiO2 (VW/Ti) catalysts were investigated by NH4Cl deposition. The results showed that the NOx conversion efficiency at low reaction temperature (< 300 °C) decreased with the loading of NH4Cl after calcination. It was found that instead of causing the chlorination of VW/Ti catalyst the NH4Cl decomposed into volatile Cl species due to the weak V–Cl bonding. Such decomposition reduced significantly the surface non-lattice oxygen species to inhibit NO adsorption and activation, but hardly affected the redox ability and acidity of VW/Ti catalyst. Time–resolved in situ DRIFTs results indicated that NH3 activation and the SCR process predominated by Eley–Rideal mechanism were not influenced with NH4Cl impregnation, while the SCR at low temperature following a Langmuir–Hinshelwood path was limited by the decreased and weaker binding sites for NO activation. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction of NOx by ammonia (NH3‐SCR) was affected by HCl, which was widely present in industrial flue gas. In this study, the SCR performances over MOx‐WO3/TiO2 (MW/Ti, M=Mn, Ce and V) catalysts after HCl treatment were investigated. It was found that HCl poisoning showed inhibition and promotion in NOx conversion over MnW/Ti and CeW/Ti catalysts, respectively. While the SCR activity over VW/Ti catalyst was hardly affected by HCl. Over MnW/Ti catalyst, the rupture of the Mn−O bond by the strong Mn−Cl binding induced the formation of amorphous MnCl2 species. This Cl‐containing species with Mn in a low oxidation state exhibited poorer redox ability and NO activation, resulting in a decrease in low‐temperature SCR activity. However, instead of directly affecting the CeOx and VOx sites, gaseous HCl reacted with NH3 to form NH4Cl species on the surface of CeW/Ti and VW/Ti catalysts. As a result, the SCR activity of VW/Ti catalyst was scarcely influenced by HCl, taking the unchanged redox ability and NH3 adsorption. With a further accumulation of NH4Cl on CeW/Ti catalyst, the NOx conversion at low temperature was evidently enhanced due to the promotion in NO‐to‐NO2 conversion (Fast‐SCR). [ABSTRACT FROM AUTHOR]

Selective catalytic reduction of NOx by ammonia (NH3‐SCR) was affected by HCl, which was widely present in industrial flue gas. In this study, the SCR performances over MOx‐WO3/TiO2 (MW/Ti, M=Mn, Ce and V) catalysts after HCl treatment were investigated. It was found that HCl poisoning showed inhibition and promotion in NOx conversion over MnW/Ti and CeW/Ti catalysts, respectively. While the SCR activity over VW/Ti catalyst was hardly affected by HCl. Over MnW/Ti catalyst, the rupture of the Mn−O bond by the strong Mn−Cl binding induced the formation of amorphous MnCl2 species. This Cl‐containing species with Mn in a low oxidation state exhibited poorer redox ability and NO activation, resulting in a decrease in low‐temperature SCR activity. However, instead of directly affecting the CeOx and VOx sites, gaseous HCl reacted with NH3 to form NH4Cl species on the surface of CeW/Ti and VW/Ti catalysts. As a result, the SCR activity of VW/Ti catalyst was scarcely influenced by HCl, taking the unchanged redox ability and NH3 adsorption. With a further accumulation of NH4Cl on CeW/Ti catalyst, the NOx conversion at low temperature was evidently enhanced due to the promotion in NO‐to‐NO2 conversion (Fast‐SCR). [ABSTRACT FROM AUTHOR]

Selective catalytic reduction of nitrogen oxides (NOx) with C3H6 (C3H6‐SCR) was investigated over NiO catalysts supported on different metal‐oxides. A NiAlOx mixed oxide phase was formed over NiO/γ‐Al2O3 catalyst, inducing an immediate interaction between NiOx and AlOx species. Such interaction resulted in a charge transfer from Ni to Al site and the formation of Ni species in high oxidation state. In comparison to other NiO‐loaded catalysts, NiO/γ‐Al2O3 catalyst exhibited the highest NOx conversion at temperature higher than 450 °C, but a poor C3H6 oxidation activity due to the decreased nucleophilicity for surface oxygen species. By temperature‐programed NO oxidation, it is indicated that nitrate species were rapidly formed and stably maintained at high temperature over NiO/γ‐Al2O3 catalyst. In situ transient reactions further verified the Langmuir–Hinshelwood mechanism for C3H6‐SCR, where both gaseous NO and C3H6 were adsorbed and activated on catalyst surface and reacted to generate N2. Due to the strong metal‐support interaction over NiO/γ‐Al2O3 catalyst, both nitrate and CxHyOz intermediates were well preserved to attain high C3H6‐SCR activity. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction of nitrogen oxides (NOx) with C3H6 (C3H6‐SCR) was investigated over NiO catalysts supported on different metal‐oxides. A NiAlOx mixed oxide phase was formed over NiO/γ‐Al2O3 catalyst, inducing an immediate interaction between NiOx and AlOx species. Such interaction resulted in a charge transfer from Ni to Al site and the formation of Ni species in high oxidation state. In comparison to other NiO‐loaded catalysts, NiO/γ‐Al2O3 catalyst exhibited the highest NOx conversion at temperature higher than 450 °C, but a poor C3H6 oxidation activity due to the decreased nucleophilicity for surface oxygen species. By temperature‐programed NO oxidation, it is indicated that nitrate species were rapidly formed and stably maintained at high temperature over NiO/γ‐Al2O3 catalyst. In situ transient reactions further verified the Langmuir–Hinshelwood mechanism for C3H6‐SCR, where both gaseous NO and C3H6 were adsorbed and activated on catalyst surface and reacted to generate N2. Due to the strong metal‐support interaction over NiO/γ‐Al2O3 catalyst, both nitrate and CxHyOz intermediates were well preserved to attain high C3H6‐SCR activity. [ABSTRACT FROM AUTHOR]

Abstract: Copper‐exchanged H‐SAPO‐47 zeolites were synthesized by an aqueous solution ion exchange method and applied in the selective catalytic reduction of NO with NH3 (SCR). The microporous chabazite (CHA) structure of the catalysts was characterized and confirmed using synchrotron X‐ray diffraction and nitrogen adsorption–desorption experiments. The synthesized Cux‐SAPO‐47 catalysts exhibited excellent SCR activity and nearly 100 % N2 selectivity in a wide temperature range. The Cu0.1‐SAPO‐47 sample exhibited higher activity than the other samples below 250 °C. The weak Lewis acid sites originating from the introduction of Cu2+ were more active than the Brønsted acid sites of the zeolites framework at low temperature. Two types of isolated Cu2+ species with different coordination surroundings were found, namely, Cu2+ cations bonded with the six‐membered rings and those bonded in the CHA cages. The former species exhibited good stability and activity at high temperature, whereas the latter ones were more active at low temperature. The Cu0.1‐SAPO‐47 catalyst provided a considerable amount of isolated Cu2+ bonded in the CHA cages. These results indicated that active Lewis acid sites and isolated Cu2+ species are responsible for their excellent SCR activity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mn, Co, Ni and Zn are doped into the structure of iron spinel oxides. [•] Surface acidity and redox properties are related to iron spinel structures. [•] Competition of NH3-CR and NH3-CO exists over metal-doped iron spinel catalysts. [•] SCR performance is affected by the redox cycle of Fe3+/Fe2+ in octahedral sites. [Copyright &y& Elsevier]

Highlights: [•] Presence of bulk WO3 on titania surface leads to deficiency of Brønsted acid sites. [•] Two-dimension VO x has a tendency to anchor onto titania surface in vicinity of WO x . [•] WO x shows compressing effects on monolayer VO x species at high vanadium loadings. [•] NH3-SCR performance is mainly dependent on vanadium contents of V W/TiO2 catalysts. [ABSTRACT FROM AUTHOR]

Chlorine species, widely presented in industrial flue gas such as the waste incineration plants, can poison the catalysts and affect the selective catalytic reduction (SCR) performance. In this work, effects of Cl on the SCR performance of V2O5–WO3/TiO2 (VW/Ti) catalysts were investigated by NH4Cl deposition. The results showed that the NOx conversion efficiency at low reaction temperature (< 300 °C) decreased with the loading of NH4Cl after calcination. It was found that instead of causing the chlorination of VW/Ti catalyst the NH4Cl decomposed into volatile Cl species due to the weak V–Cl bonding. Such decomposition reduced significantly the surface non-lattice oxygen species to inhibit NO adsorption and activation, but hardly affected the redox ability and acidity of VW/Ti catalyst. Time–resolved in situ DRIFTs results indicated that NH3 activation and the SCR process predominated by Eley–Rideal mechanism were not influenced with NH4Cl impregnation, while the SCR at low temperature following a Langmuir–Hinshelwood path was limited by the decreased and weaker binding sites for NO activation. [ABSTRACT FROM AUTHOR]

Abstract: A series of non-stoichiometric Fe–Ti spinel (Fe3−x Ti x )1−δ O4 were synthesized using a co-precipitation method and then developed as environmental-friendly and low cost catalysts for the selective catalytic reduction (SCR) of NO with NH3. As Ti was incorporated into γ-Fe2O3, the SCR reaction over (Fe3−x Ti x )1−δ O4 through the Langmuir–Hinshelwood mechanism was restrained. Therefore, the SCR activity of (Fe3−x Ti x )1−δ O4 (x ≠0) was less than that of γ-Fe2O3 at 150–250°C. However, the SCR reaction over (Fe3−x Ti x )1−δ O4 through the Eley–Rideal mechanism was promoted due to the incorporation of Ti. The SCR activity of (Fe3−x Ti x )1−δ O4 (x ≠0) was mainly related to the oxidative ability of Fe3+ cation on the surface, the concentration of NH3 adsorbed on the surface and the concentration of reducible Fe3+ cation on the surface. Although the oxidative ability of Fe3+ cation on the surface decreased due to the incorporation of Ti into γ-Fe2O3, the concentration of NH3 adsorbed on the surface and the concentration of reducible Fe3+ cation on the surface both increased. As a result, (Fe2Ti)0.8O4 showed excellent activity, selectivity, and H2O/SO2 durability for the SCR reaction at 300–400°C. [Copyright &y& Elsevier]

Lignite is widelyused as the fuel for coal-fired power plants, and its flue gas temperatureis about 50–100 °C higher than others. V2O5–WO3/TiO2is extremely restrictedin the selective catalytic reduction (SCR) of NO from the coal-firedpower plants burning lignite due to the drop of NOxconversion, low N2selectivity, and volatilityof vanadium pentoxide at high temperatures. Therefore, a more environmental-friendlySCR catalyst with excellent SCR activity and better N2selectivityat 350–450 °C should be developed for this application.In this work, sulfated Fe–Ti spinel catalyst was developedfor the SCR of NO from the coal-fired power plants burning lignite.The drop of NOxconversion at high temperatureswas mainly related to the simultaneous occurrence of the catalyticoxidization of NH3to NO during the SCR reaction. Ti wasincorporated into γ-Fe2O3to decease theoxidization ability of Fe3+on the surface, and the sitesfor −NH2adsorption and the active components for−NH2oxidization were separated after the sulfationto decrease the probability of the collision between −NH2adsorbed and Fe3+on the surface. They both inhibitedthe catalytic oxidization of NH3to NO over γ-Fe2O3. However, the SCR reaction over γ-Fe2O3was simultaneously restrained after the incorporationTi and the sulfation. Therefore, NOxconversionover γ-Fe2O3at high temperatures dependedon the ratio of NH3conversion through the catalytic oxidizationof NH3to NO to that through the SCR reaction. This ratiodecreased after the incorporation of Ti, and it further decreasedafter the sulfation, resulting in an obvious promotion of NOxconversion at high temperatures. Therefore, sulfatedFe–Ti spinel showed excellent SCR activity, N2selectivity,and H2O+SO2durability at 300–450 °C,which was suitable for the application in the coal-fired power plantsburning lignite. [ABSTRACT FROM AUTHOR]