Preparation and low temperature denitrification properties of ferric oxide red supported manganese oxide and manganese cerium co-oxide catalyst

Iron oxide red (IOR) is a kind of byproduct from spray pyrolysis treatment process of pickling waste liquid. In this project, manganese oxide and manganese cerium co-oxide were loaded onto the surface of IORto prepare IOR supported manganese oxide (Mn_x/IOR) and IOR supported manganese-cerium co-oxide (Mnx-Cey/IOR) catalysts by a simple combustion method. Low temperature NH3-selective catalytic reduction (NH3-SCR) denitrification properties of the synthetic catalysts were studied. XRD, SEM, EDS, TEM, BET, XPS, H₂-TPR and NH₃-TPD were used to characterize the physiochemical properties of the catalysts. The results show that during the combustion process for preparing Mnx/IOR catalyst, MnO_x, almost all in amorphous phase, can be well distributed on the surface of the IOR carrier. The NO_x conversions of Mn_x/IOR catalyst gradually increase with the increase of MnO_x loading amount within a specific working temperature range (<200 °C). When MnO_x loading amount x is 0.43, the NO_x conversion is up to 85% at most. The low temperature NH₃-SCR activity of Mn_x/IOR catalyst can be enhanced remarkably by introducing cerium. The NO_x conversions of Mn_0.43-Ce_y/IOR catalyst at the operating temperature range (<200 °C) increase steadily with the cerium adding amount increasing. All the Mn_0.43-Ce_y/IOR catalysts show excellent denitrification efficiency (more than 90%) at about 160 °C. Compared with Mn_0.43/IOR catalyst, Mn_0.43-Ce_0.1/IOR shows excellent denitrification performance and application prospect because of its higher manganese valence state, enhanced redox capacity, larger specific surface area, and significantly improved surface acidity and anti-SO₂ poisoning ability.     

NO reduction with H2 in the presence of excess O2 over Pd/MFI catalyst

The NO SCR (selective catalytic reduction) activity with H₂ in the presence of excess O₂ was investigated over Pd/MFI catalyst prepared by sublimation method. With GHSV=90?000 h⁻¹, a very high steady-state conversion of NO to N₂ (70%) is achieved at 100 °C. Significant reorganizations take place inside the catalyst upon its first contact with all reactants and products at the reaction temperature. Pd⁰, which has a significant role in the NO-H₂-O₂ reaction, is possibly the active site for NO reduction. The formation of Pd-β hydride deactivates the catalyst for NO reduction. Throughout the entire NO-H₂-O₂ reaction, no N₂O or NO₂ is formed; N₂ is the only N-containing product. The presence of O₂ inhibits the formation of undesirable NH₃. The rate of the NO+H₂ reaction is fast or comparable to that of the H₂+O₂ reaction. The oxidation of Pd⁰ and subsequent agglomeration of PdO are responsible for the decreased NO reduction activity at high temperature.     

Selective Catalytic Reduction of NO with NH3 over Fe-ZSM-5 Catalysts Prepared by Sublimation of FeCl3 at Different Temperatures

Fe-ZSM-5 catalysts were prepared by subliming FeCl₃ into H-ZSM-5. The method used allowed Fe-ZSM-5 catalyst preparation by FeCl₃ exchange at a desired sublimation temperature and was found to be more precise. The sublimation of FeCl₃ into H-ZSM-5 was carried out at 320 and 700 °C. Fe-ZSM-5 prepared by sublimation of FeCl₃ at 320 °C followed by rapid heating to 700 °C and the catalyst prepared by subliming FeCl₃ at 700 °C were found to be more active for NO reduction with NH₃ in the presence of simulated exhaust gases containing water vapor than catalysts prepared by subliming FeCl₃ at 320 °C. To determine the active sites, the catalysts were characterized by H₂-TPR, in situ DRIFTS of NO adsorption, NH₃-TPD, XRD and chemical analysis methods. The observed NO conversion differences in selective catalytic reduction using NH₃ could be correlated to the iron cation species present at different locations determined from diffuse reflectance infrared spectroscopy. Enhanced NO reduction activity was obtained when positions in Fe-ZSM-5, corresponding to Fe²⁺(NO) band at 1877 cm^-1 in DRIFTS, were preferentially occupied.     

Effect of Mn content on physical properties of CeOx–MnOy support and BaO–CeOx–MnOy catalysts for direct NO decomposition

A series of manganese–cerium mixed oxides were prepared by a glycothermal method, and the NO decomposition activities of the Ba-loaded Ce–Mn oxides were examined. Among the catalysts examined, the highest NO conversion was obtained on the BaO/Ce–Mn oxide catalyst with a Mn/(Ce+Mn) ratio of 0.25. The X-ray diffraction and Raman analyses indicated the formation of Ce–Mn oxide solid solutions with a cubic fluorite structure. The electron spin resonance analysis indicated the presence of paramagnetic Mn²⁺ species in the composite catalysts. Incorporation of Mn²⁺ in the fluorite structure of CeO₂ causes an increase in the concentration of oxygen vacancies, which play an important role in the NO decomposition activity of the catalysts. The catalysts were also characterized by X-ray photoelectron spectroscopy and temperature-programmed reduction techniques. Based on the results obtained, the relationship between the physical properties of the catalysts and their NO decomposition activities was discussed.     

Selective Reduction of NO with CO Over Titania Supported Transition Metal Oxide Catalysts

A series of transition metal oxides promoted titania catalysts (MO _x /TiO₂; M = Cr, Mn, Fe, Ni, Cu) were prepared by wet impregnation method using dilute solutions of metal nitrate precursors. The catalytic activity of these materials was evaluated for the selective catalytic reduction (SCR) of NO with CO as reductant in the presence of excess oxygen (2 vol.%). Among various promoted oxides, the MnO _x /TiO₂ system showed very promising catalytic activity for NO + CO reaction, giving higher than 90% NO conversion over a wide temperature window and at high space velocity (GHSV) of 50,000 h⁻¹. It is remarkable to note that the catalytic activity increased with oxygen, up to 4 vol.%, under these conditions leading primarily to nitrogen. Our TPR studies revealed the presence of mixed oxidation states of manganese on the catalyst surface. Characterization results indicated that the surface manganese oxide phase and the redox properties of the catalyst play an important role in final catalytic activity.     

The First Study of SCR of NO x by Acetylene in Excess Oxygen

Acetylene as a reducing agent for the selective catalytic reduction (C₂H₂-SCR) of NO in the presence of excess oxygen on various Ce-exchanged zeolites was investigated for the first time. Under the conditions of 1600 ppm NO, 800 ppm C₂H₂, and 9.95 % O₂ in He, the Ce-H-ZSM-5 (Si/Al=25) catalyst shows about 83% NO conversion to N₂ at the temperatures ranged from 300 to 350 °C. It is followed by the other zeolites in the activity order of Ce-H-Y (Si/Al=2.5), Ce-H-_ (Si/A1=20∼30), and Ce-H-SAPO (Si/Al=34), Ce-H-5A (Si/Al=12). Almost no NO conversion was obtained over Ce-Na-ZSM-5 (Si/Al=25) and Na-ZSM-5 (Si/Al=25) catalyst samples. The Conversion of NO to N₂ increased with O₂ concentration in the range of 0.1 ∼ 9.95% over the CeH-ZSM-5 (Si/Al=25) catalyst. It is suggested that O₂ plays an important role in the C₂H₂-SCR of NO reaction, by oxidizing NO to NO₂ on acid sites in assistant with cerium species of the catalyst. A large amount of CO, which seems to be in proportion with the NO conversion to N₂, was produced. Long-term experiments up to 56 h combined with a excursion of the reaction temperature up to 650 °C over the Ce-H-ZSM-5 (Si/A1=25) confirmed the catalyst’s durable performance under the reaction conditions. It is found that the de-NO_x activity of Ce-H-ZSM-5 catalyst can be enhanced by the presence of 50 ppm of sulfur dioxide in the dry-feed reaction conditions.     

Enhanced catalytic activity for selective catalytic reduction of NO over titanium nanotube-confined CeO2 catalyst

Titanium nanotubes (TNTs)-confined ceria were for the first time prepared in this paper and used for selective catalytic reduction (SCR) of NO with ammonia. In comparison with the catalysts supported by TiO₂ nanoparticles, the confined ceria showed a superiority in SCR of NO due to the improved redox potential and special adsorption of NH₃, where its NO conversion could exceed 95% at reaction temperature of 270–500 °C, which was much higher than that of TiO₂ nanoparticle supported catalysts.     

Microwave discharge-assisted NO reduction by CH4 over Co/HZSM-5 and Ni/HZSM-5 under O2 excess

Microwave discharge-assisted reduction of NO by CH₄ in the presence of excess O₂ over Co/HZSM-5 and Ni/HZSM-5 catalysts was studied. By comparing the activities of the catalysts in the microwave discharge mode with that in the conventional reaction mode, it is demonstrated that microwave discharge enhanced greatly the conversion of NO to N₂, and expanded the reaction temperature range of the catalysts. For the Co/HZSM-5 catalyst, the conversion of NO to N₂ increased by 30%, and the optimum temperature decreased by 200°C. With the Ni/HZSM-5 catalyst, the highest activity was close to 100%, and the optimum temperature decreased by 325°C. The conversion of CH₄ also increased in the microwave discharge mode over both of the catalysts.     

Reduction of NO by CH4 with Microwave Heating

The reduction of NO by CH₄ in the presence of excess O₂ over Co/HZSM-5, Ni/HZSM-5 and Mn/HZSM-5 catalysts with microwave heating was studied. By comparing the activities of the catalysts in the microwave heating mode with that in the conventional reaction mode, it was demonstrated that microwave heating could greatly reduce the reaction temperature, and could clearly expand the temperature window of the catalysts. Especially for the Co/HZSM-5 catalyst, the maximum conversion of NO to N₂ in the conventional reaction mode was consistent with that in the microwave heating mode. However, the temperature window for the maximum conversion in the microwave heating mode was from 260 to 360 °C instead of a temperature of 420 °C in the conventional reaction mode. The results suggest that microwave heating has a novel effect in the reduction of NO.     

Effect of Nickel as Dopant in Mn/TiO<Subscript>2</Subscript> Catalysts for the Low-Temperature Selective Reduction of NO with NH<Subscript>3</Subscript>

Nickel doped manganese oxide supported on titania materials were investigated for the low-temperature NH₃-SCR. For this purpose, a series of Ni modified Mn/TiO₂ catalysts were prepared and evaluated for the low-temperature SCR of NO with ammonia in the presence of excess oxygen. The catalytic performance of these materials was compared with respect to the nickel weight percentage in order to examine the correlation between physicochemical characteristics and reactivity of optimized materials. It was found that the 5% Mn–2% Ni/TiO₂ catalyst showed the highest activity and yielded 100% NO conversion at 200 °C. XRD results reveal highly dispersed manganese–nickel species on TiO₂ support for the Mn–Ni/TiO₂ catalysts. Our TPR data results suggested an increase in reducibility of manganese species in Mn–Ni/TiO₂ catalysts. The absence of the high-temperature (736 K) peak indicates that the dominant phase is MnO₂. This increase of reducibility and dominant MnO₂ phase seems to be the reason for the enhanced activity and time on stream patterns of nickel-promoted titania-supported manganese catalysts. BET results illustrate that the high NO conversion is strongly dependant on the specific surface area and pore volume of this catalyst. All the physicochemical techniques we used suggested that the composition of manganese and nickel oxides on the support surface is playing an important role for the enhancement of NO conversion and the prominent time on stream stability.     

Promotion effect and mechanism of MnOx doped CeO2 nano-catalyst for NH3-SCR

MnO_x-CeO₂ (denoted as Mn–Ce) nanorod and MnO_x-CeO₂ nanooctahedra catalysts were synthesized by the hydrothermal method and were used for selective catalytic reduction of NO with NH₃. The catalytic performance tests showed that the NO removal efficiency of CeO₂ catalysts was obviously improved after loading MnO_x. The structure and properties of catalysts had been characterized by SEM、TEM、XRD、BET、XPS、H₂-TPR、NH₃-TPD and in situ DRIFTS. It was found that Mn–Ce catalyst were of uniform core-shell structure, higher concentrations of Mn⁴⁺ and Ce³⁺, better reducibility, the increase of weak acid sites. The results of in situ DRIFTS indicated that the NH₃-SCR reaction should obey the E–R mechanism. Moreover, the promotion effect and mechanism of MnO_x doped CeO₂ was demonstrated, which improved the catalytic activity of Mn–Ce catalysts.     

Structural effects of WO3 incorporation on USY zeolite and application to free fatty acids esterification

Zeolites have occupied a distinguished position due to their unique properties as solid acids and catalytic results achieved in several industrial reactions. This work studied the influence of supported WO₃ on USY zeolite structure, acidity and activity towards an esterification reaction. High dispersion of WO₃ species on USY was achieved, but at higher loading (?11.4%), microcrystalites of WO₃ were detected below the theoretical monolayer coverage (∼32%). Tungsten species were deposited preferentially inside the zeolite structure and interacted with the Brønsted sites of USY as well as on silanol surface groups with the formation of small aggregates. In addition, dealumination took place, especially in the samples with high WO₃ loading. USY had the most and the strongest acidic sites (Brønsted type), but the incorporation of WO₃ decreased the amount and the strength of the new sites. However, all WO₃/USY catalysts were more active than USY in the esterification of oleic acid with ethanol (conversion above 74%, 2 h at 200 °C). The calculation of the TOF for a 1 h reaction demonstrated that 11.4% WO₃/USY was the most active catalyst. Furthermore, it had the lowest rate of deactivation of acid sites after the reaction (∼13% after four cycles). The better performance of the 11.4% WO₃/USY sample was also attributed to a better distribution of strength of the acidic sites and a more hydrophobic character of the synthesized material.     

Synthesis, characterization and performance of CuO/La2O3 composite catalyst for ammonia catalytic oxidation

This work considers the oxidation of ammonia (NH₃) by selective catalytic oxidation (SCO) over a CuO/La₂O₃ composite catalyst at temperatures between 150 and 400 °C. A CuO/La₂O₃ composite catalyst was prepared by co-precipitation of copper nitrate and lanthanum nitrate at various molar concentrations. This study also considers how the concentration of influent NH₃ (C₀ = 1000 ppm), the space velocity (GHSV = 92,000 l/h), the relative humidity (RH = 12%) and the concentration of oxygen (O₂ = 4%) affect the operational stability and the capacity for removing NH₃. The catalysts that were characterized using FTIR, XRD, UV-Vis, BET and PSA, have shown that the catalytic behavior is related to the copper (II) oxide, while lanthanum (III) oxide may serve only to provide active sites for the reaction during a catalyzed oxidation run. The experimental results show that the extent of conversion of ammonia by SCO in the presence of the CuO/La₂O₃ composite catalyst was a function of the molar ratio. The ammonia was removed by oxidation in the absence of CuO/La₂O₃ composite catalyst, and around 93.0% NH₃ reduction was achieved during catalytic oxidation over the CuO/La₂O₃ (8:2, molar/molar) catalyst at 400 °C with an oxygen content of 4.0%. Moreover, the effect of the reaction temperature on the removal of NH₃ in the gaseous phase was also monitored at a gas hourly space velocity of under 92,000 h^− 1.     

Noble Metal (Pt, Rh, Pd) Promoted Fe-ZSM-5 for Selective Catalytic Oxidation of Ammonia to N2 at Low Temperatures

We have reported previously the excellent performance of Fe-exchanged ZSM-5 for selective catalytic oxidation (SCO) of ammonia to nitrogen at high temperatures (e.g., 400-500 °C). The present work indicates that the reaction temperature can be decreased to 250-350 °C when a small amount of noble metal (Pt, Rh or Pd) is added (by both doping and ion exchange) to the Fe-ZSM-5. The SCO activity follows the order: Pt/Fe-ZSM-5 > Rh/Fe-ZSM-5 > Pd/Fe-ZSM-5. The noble metal promoted Fe-ZSM-5 catalysts also show higher activity for NH₃ oxidation than Ce-exchanged Fe-ZSM-5 at low temperatures. On the Pt promoted Fe-ZSM-5, near 100% of NH₃ conversion is obtained at 250 °C at a high space velocity (GHSV = 2.3 × 10⁵ h^-1) and nitrogen is the main product. The presence of H₂O and SO₂ decreases the SCO performance only slightly. This catalyst is a good candidate for solving the ammonia slip problem that plagues the selective catalytic reduction (SCR) of NO with ammonia in power plants.     

Iron oxide supported sulfated TiO2 nanotube catalysts for NO reduction with propane

Sulfated TiO₂ nanotubes and a series of iron oxide loaded sulfated TiO₂ nanotubes catalysts with different iron oxide loadings (1 wt%, 3 wt%, 5 wt% and 7 wt%) were prepared and calcined at 400 °C. The physico-chemical properties of the catalysts were studied by using XRD, N₂-physisorption, Raman spectroscopy, SEM-EDX, TEM, XPS, and pyridine adsorption using FTIR and H₂-TPR techniques. It was observed that iron oxide was highly dispersed on the sulfated TiO₂ nanotube support due to its strong interaction. The activity of these catalysts in the catalytic removal of NO with propane was also studied in the temperature range of 300–500 °C. Highest activity (90% NO conversion) was observed with 5 wt% iron oxide supported on sulfated TiO₂ catalyst at 450 °C. Selective catalytic reduction of NO activity of the catalysts was correlated with iron oxide loading, reducibility, and the Brönsted and Lewis acid sites of the catalysts. The catalyst also showed good stability under studied reaction conditions that no deactivation was observed during the 50 h of reaction.     

The positive effect of hydrogen on the reaction of nitric oxide with carbon monoxide over platinum and rhodium catalysts

The effect of adding 330–4930 ppm hydrogen to a reaction mixture of NO and CO (2000 ppm each) over platinum and rhodium catalysts has been investigated at temperatures around 200–250°C. Hydrogen causes large increases in the conversion of NO and, surprisingly, also of CO. Oxygen atoms from the additional NO converted are eventually combined with CO to give CO₂ rather than react with hydrogen to form water. This reaction is described by CO + NO +3/2H₂ CO₂ + NH₃ and accounts for 50–100% of the CO₂ formed with Pt/Al₂O₃ and 20–50% with Rh/Al₂O₃. With the latter catalyst a substantial amount of NO converted produces nitrous oxide. Comparison with a known study of unsupported noble metals suggests that isocyanic acid (HNCO) might be an important intermediate in a reaction system with NO, CO and H₂ present.     

Effect of SO2 on a cordierite honeycomb supported CuO catalyst for NO reduction by NH3

Supporting CuO on a Al₂O₃-coated cordierite honeycomb yields a good catalyst (CuO/HC–Al) for selective catalytic reduction (SCR) of NO with NH₃ at 350–500 °C. SO₂ has complex effects on the catalysts activity. It significantly promotes the SCR activity through conversion of CuO to CuSO₄, however, when a certain amount of CuO is converted, it slightly decreases the SCR activity through competitive adsorption with NH₃. This competitive adsorption reduces the amount of NH₃ adsorbed on the catalyst surface, especially on the sites highly active to the SCR. It also prevents transformation of CuO to CuSO₄ and as a result, the catalysts subjected to pre-sulfation and in situ sulfation show different SCR behaviors.     

Hydrogenation of Methyl Benzoate over Mn/Al Catalysts: Comparison among Catalyst Preparation Routes

Mn/Al catalysts for hydrogenation of methyl benzoate to benzaldehyde were prepared by different methods. The catalyst prepared from hydrotalcite-like precursor, the mesoporous MSU-γ supported Mn catalyst and the Mn-incorporated MSU-γ catalyst are more active than conventional Mn/γ-Al₂O₃ catalyst. The reaction temperature for the same yield level can be reduced by 20–60 °C. High specific surface area, high dispersion of manganese oxide species and strong interaction of manganese oxide species with γ-Al₂O₃ are of benefit to the reaction.     

Low Activation Energy Pathway for the Catalyzed Reduction of Nitrogen Oxides to N<Subscript>2</Subscript> by Ammonia

A low activation energy pathway for the catalytic reduction of nitrogen oxides to N₂, with reductants other than ammonia, consists of two sets of reaction steps. In the first set, part of the NO _x is reduced to NH₃; in the second set ammonium nitrite, NH₄NO₂ is formed from this NH₃ and NO + NO₂. The NH₄NO₂ thus formed decomposes at ~100 °C to N₂ + H₂O, even on an inert support, whereas ammonium nitrate, NH₄NO₃, which is also formed from NH₃ and NO₂ + O₂, (or HNO₃), decomposes only at 312 °C yielding mainly N₂O. Upon applying Redhead's equations for a first order desorption to the decomposition of ammonium nitrite, an activation energiy of 22.4 is calculated which is consistent with literature data. For the reaction path via ammonium nitrite a consumption ratio of 1/1 for NO and NO₂ is predicted and confirmed experimentally by injecting NO into a mixture of NH₃ + NO₂ flowing over a BaNa/Y catalyst. This leads to a yield increase of one N₂ molecule per added molecule of NO. Little N₂ is produced from NH₃ + NO in the absence of NO₂.     

Critical Influence of Mn on Low-Temperature Catalytic Activity of Mn/Na2WO4/SiO2 Catalyst for Oxidative Coupling of Methane

Oxidative coupling of methane (OCM) was investigated in the temperature range 370-775 °C over Mn/Na₂WO₄/SiO₂ catalysts with different loadings of manganese in integral-mode conditions. Na₂WO₄/SiO₂ shows no activity at low temperature (370 °C), whereas Mn-doped catalyst exhibits 14% C²⁺ yield under similar reaction conditions, indicating that manganese plays a critical role in low-temperature methane coupling reaction. Partial pressure of oxygen in the feed also influences the low-temperature OCM activity of the catalysts.