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Lead (Pb) is a heavy metal commonly found in industrial exhaust gases, which can reduce catalytic activity of a catalyst for the NH3‐SCR reaction. In this study, 4.0 wt% Mn‐loaded Fe‐pillared interlayer clay (4Mn/Fe‐PILC) and its Co‐modified catalyst (2Co‐4Mn/Fe‐PILC) were prepared, in the meanwhile the 4Mn/Fe‐PILC‐Pb and 2Co‐4Mn/Fe‐PILC‐Pb samples were also obtained using the impregnation method with a Pb(CH3COO)2 aqueous solution. It was found that the addition of 2.0 wt% cobalt could significantly enhance Pb resistance of the 4Mn/Fe‐PILC catalyst. The characterization results revealed that the doping of Co to Mn/Fe‐PILC increased the surface Mn4+ species concentration, reducibility, and acid site amount, thereby improving Pb resistance of the catalyst. Furthermore, the in situ DRIFTS results demonstrated that Co modification enhanced the adsorption capacity of NH3 or NO, especially influenced formation of the NH3 intermediates and bridging nitrate species, which were also conducive to the improvement in Pb resistance of the catalyst. [ABSTRACT FROM AUTHOR]

This present study investigated the catalytic effect of Na 2 CO 3 on the reduction of ferromanganese spinel (MnFe 2 O 4) using biochar as reducing agent. The reduction of the MnFe 2 O 4 -biochar composite briquettes at 1050 °C for 30 min showed that the iron metallization degree of the reduced briquettes increased from 61.1% to 84.2%, with significant decrease of initial reduction temperature due to the addition of 5 wt% Na 2 CO 3. There also existed higher CO and CO 2 concentrations in the off-gas in the presence of Na 2 CO 3. According to the first-principles calculations, these differences were attributed to the reaction between Na 2 CO 3 and carbon which produced oxygen vacancies on the Na 2 CO 3 surface. These vacancies were then filled by the oxygen atoms of CO 2 , forming CO which was desorbed from the surface of Na 2 CO 3 before it participated in the reduction. By creating oxygen vacancies through its reaction with carbon, Na 2 CO 3 played a catalytic role in the reduction process. Unlabelled Image • The MnFe 2 O 4 -biochar composite briquettes were reduced in the presence of Na 2 CO 3. • The reduction of the briquettes was enhanced by addition of Na 2 CO 3. • The reaction between Na 2 CO 3 and carbon produced oxygen vacancies for reduction. • Na 2 CO 3 played an obvious catalytic role in the reduction process. [ABSTRACT FROM AUTHOR]

To investigate the effect of Ca poisoning on Cu‐SAPO‐18, a series of samples with different Ca amounts were prepared by the impregnation method, and their NH3‐SCR activities were evaluated. When the Ca amount was 0.8 mmol/gcat, NO conversion at 350 °C was 40.6% (lower than that over the fresh Cu‐SAPO‐18 sample), which shows that the catalytic deNOx performance was significantly decreased after Ca poisoning. Ca poisoning did not have a great influence on the structure of Cu‐SAPO‐18, but the formed CaO blocked part of the micropores, which reduced surface area and micropore volume, and further reduced accessibility of the active sites and surface acidity of the sample. The total amount of the isolated Cu2+ species decreased from 62.83 μmol/gCu‐SAPO‐18 to 23.45 μmol/g0.8Ca‐Cu‐SAPO‐18, which resulted in conversion of the isolated Cu2+ species to Cu2O in the sample after the addition of Ca. In addition, the substitution of Ca2+ with H or Cu2+ in Si–O(H)–Al or Si–O(Cu2+)–Al to form the Si–O(Ca2+)–Al species decreased amounts of the Lewis and Brönsted acid sites, which might be the important reasons for the drop in catalytic activity. Both the Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) reaction mechanisms existed over the samples in the NH3‐SCR reaction, but the L–H reaction mechanism was dominant. The catalytic mechanism over the sample did not change, but the reaction was slower after Ca poisoning. [ABSTRACT FROM AUTHOR]

The Ce-Cu-SAPO-18 samples were prepared by the ion exchange method. Physicochemical properties of the samples were systematically characterized by a number of analytical techniques, and Ce doping and hydrothermal temperature effects on NH3-SCR activity of Cu-SAPO-18 were also investigated. The results show that doping of Ce increased NH3-SCR activity and hydrothermal stability of the Cu-SAPO-18 sample. After Ce doping, a more amount of the isolated Cu2+ ions entered the D6R and the catalyst structure was more stable. The structure and catalytic activity of Ce-Cu-SAPO-18 remained almost intact after hydrothermal aging at 650 °C. After hydrothermal aging at 850 °C, however, the structure of Ce-Cu-SAPO-18 was greatly destroyed, and its catalytic activity declined remarkably. The high-temperature hydrothermal aging treatment led to decreases in amount of the isolated Cu2+ ions and acidic sites, destroying in the zeolitic structure, and drop in NH3-SCR activity. [ABSTRACT FROM AUTHOR]

The yCe/Al‐Mn‐pillared interlayered clay (PILC, y [Ce content] = 8–9 wt%) catalysts were prepared using the impregnation method. Catalytic activities of the materials for the selective catalytic reduction (SCR) of NO with NH3 at low temperatures were evaluated, and physicochemical properties of the samples were characterized by X‐ray diffraction, N2 adsorption–desorption, temperature‐programmed reduction, ammonia temperature‐programmed desorption, X‐ray photoelectron spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy techniques. It is found that introduction of cerium enhanced NO conversions at low temperatures, and the 8Ce/Al‐Mn‐pillared sample showed the highest NO conversion (92% at 300°C). The superior catalytic activity of 8Ce/Al‐Mn‐PILC was associated with the change in active component and increases in amounts of the surface chemisorbed oxygen species and the acid sites after ceria loading. Additionally, the SCR reaction mechanism over 8Ce/Al‐Mn‐PILC followed both Langmuir–Hinshelwood and Eley–Rideal mechanisms, with the former being dominant. [ABSTRACT FROM AUTHOR]

The Cu/SAPO-18 samples with different Cu/Al mass ratios were prepared, their catalytic activities for the NH3-SCR of NO in simulated diesel exhaust were evaluated, and effects of Cu/Al mass ratio and hydrothermal aging temperature on catalytic performance of Cu/SAPO-18 was examined. Physicochemical properties of the samples were characterized by means of various techniques. It is found that the activity of the sample changed with a rise in Cu/Al mass ratio, with the highest overall activity being achieved over the sample with a Cu/Al mass ratio of 0.045. The H2-TPR results indicate that the Cu/Al mass ratio could affect the distribution of Cu species, and the Cu/SAPO-18-0.045 sample possessed the highest amount of the isolated Cu2+ species. BET and XRD results reveal that the Cu/Al mass ratio exerted little effect on the structure of the sample. Low-temperature hydrothermal treatment had the least influence on the sample, and the effect of high-temperature hydrothermal treatment on the sample became increasingly obvious with a rise in hydrothermal treatment temperature. It is concluded that the hydrothermal aging treatment mainly affected the sample by destroying the structure, blocking the pores, migration and transformation of the Cu species, and changing the acidic sites of the sample. [ABSTRACT FROM AUTHOR]

yCeO2/Zr-PILC (y = 2.5–7.4 wt%) catalysts were prepared using an impregnation method. The physiochemical properties of the materials were investigated by means of XRD, BET, XPS, H2-TPR, NH3-TPD, and in situ DRIFT techniques, and their catalytic activities were evaluated for the selective catalytic reduction of NO with ammonia (NH3-SCR). The 5CeO2/Zr-PILC sample showed a high NH3-SCR activity, with the NO conversion being more than 80% in the temperature range (350–450 °C). The Zr-incorporated support was beneficial for the dispersion of ceria. There was a strong interaction between ceria and Zr-PILC, which led to increased H2 consumption and high-temperature reduction. An appropriate CeO2 loading could generate the 5CeO2/Zr-PILC catalyst that contained higher amounts of Ce3+ and the chemisorbed oxygen species favoring the NH3-SCR reaction. Moreover, the high acidity and strong NH3 adsorption ability of 5CeO2/Zr-PILC were responsible for good NH3-SCR performance in a wide temperature range. The NH3-SCR reaction occurred according to both the Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanisms, with the former being dominant. [ABSTRACT FROM AUTHOR]

yCeO2/Zr-PILC (y = 2.5–7.4 wt%) catalysts were prepared using an impregnation method. The physiochemical properties of the materials were investigated by means of XRD, BET, XPS, H2-TPR, NH3-TPD, and in situ DRIFT techniques, and their catalytic activities were evaluated for the selective catalytic reduction of NO with ammonia (NH3-SCR). The 5CeO2/Zr-PILC sample showed a high NH3-SCR activity, with the NO conversion being more than 80% in the temperature range (350–450 °C). The Zr-incorporated support was beneficial for the dispersion of ceria. There was a strong interaction between ceria and Zr-PILC, which led to increased H2 consumption and high-temperature reduction. An appropriate CeO2 loading could generate the 5CeO2/Zr-PILC catalyst that contained higher amounts of Ce3+ and the chemisorbed oxygen species favoring the NH3-SCR reaction. Moreover, the high acidity and strong NH3 adsorption ability of 5CeO2/Zr-PILC were responsible for good NH3-SCR performance in a wide temperature range. The NH3-SCR reaction occurred according to both the Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanisms, with the former being dominant. [ABSTRACT FROM AUTHOR]

Effects of hydrothermal aging at 80 and 850 °C on catalytic performance and stability of Cu/SAPO-34 catalysts with different Cu loadings were examined, and their catalytic activities were investigated for the selective catalytic reduction (SCR) of NOx with ammonia. Over the fresh catalysts, the NH3-SCR activity increased with the loading of copper in the low-temperature range and decreased in the high-temperature range. Both of the isolated Cu2+ ions and CuO synergistically influenced the SCR behavior of the Cu/SAPO-34 catalysts, which gave rise to the distinct trends of catalytic activity in the two temperature ranges. Structural damage and dealumination, however, were observed in the aged samples, leading to a severely decreased amount in acid site and a loss in crystallinity. After hydrothermal aging at 850 °C, there was some aggregation in Cu species and the redox capacity of the 0.8Cu/SAPO-34-850 catalyst was improved. It is found that the isolated Cu2+ ions were transformed into the Cu-AlOx species after hydrothermal aging at 80 °C. These results clearly demonstrate that the change in the state of copper species and the damage in structure led to different catalytic activity of the sample. [ABSTRACT FROM AUTHOR]

Abstract: The undoped and rare earth oxide (REO x , RE=La, Ce, Pr, Sm)-doped acid-treated sepiolite (H-Sep)-supported copper oxide catalysts (Cu/H-Sep and RE-Cu/H-Sep; Cu and RE loading=15 and 4wt%, respectively) were prepared using the incipient wetness impregnation method. The catalysts were characterized by means of the XRD, BET, XPS, H2-TPR and NH3-TPD techniques, and their catalytic activities were evaluated for the selective catalytic reduction (SCR) of NO with propylene. It is shown that the doping of REO x led to an enhancement in catalytic performance of Cu/H-Sep in the SCR of NO with C3H6. Among the RE-Cu/H-Sep catalysts, Ce-Cu/H-Sep performed the best, with 62% NO conversion being achieved at 350°C in the (NO+C3H6 +O2) reaction. We believe that the high catalytic performance of Ce-Cu/H-Sep for the SCR of NO with C3H6 was associated with the good low-temperature reducibility, high copper oxide dispersion, and strong metal–support interaction. [Copyright &y& Elsevier]

Abstract: Copper, iron, and mixed copper/iron exchanged zeolites containing ZSM-5 and chabazite-like zeolites (SSZ-13, SAPO-18 and SAPO-34) were studied for selective catalytic reduction (SCR) of NO with NH3 with or without propene. Cu/ZSM-5, Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 exhibited high NO conversions without propene. However, as compared to Cu/ZSM-5, NO conversions over Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 were more stable with propene, due to coke formation over Cu/ZSM-5. The results of N2-adsorption/desorption and XPS showed that the surface area, Cu+/Cu2+ ratio and the surface amount of Cu content of Cu/ZSM-5 catalysts changed from 324m2/g, 0.03 and 11.5wt% for the fresh Cu/ZSM-5 catalyst to 68m2/g, 0.34 and 5.3wt% for the used sample. However, there were little changes between fresh and used Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 catalysts. Moreover, Cu/ZSM-5 catalyst showed a larger decline in NO conversion with time on stream and a higher adsorption amount of propene compared to Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 catalysts. The resistance to hydrocarbon poisoning depended on the pore geometry of the zeolites. During NH3-SCR, the presence of medium-pore sizes in Cu/ZSM-5 led to hydrocarbon deposition, which blocked the active sites and also decreased the active intermediates needed for NO conversion. Cu/SSZ-13, Cu/SAPO-18 and Cu/SAPO-34 catalysts, on the other hand, with small pores and cage diameters and with one-dimensional channel structures, showed higher hydrocarbon poison resistance. Moreover, these copper exchanged small-pore zeolites showed much higher hydrothermal stability than the medium-pore Cu/ZSM-5. [Copyright &y& Elsevier]

As a heavy metal, Pb is one component in coal-fired flue gas and is widely considered to have a strong negative effect on catalyst activity in the selective catalytic reduction of NOx by NH3 (NH3-SCR). In this paper, we investigated the deactivation mechanism of the Mo-Ce/Zr-PILC catalyst induced by Pb in detail. We found that NO conversion over the 3Mo4Ce/Zr-PILC catalyst decreased greatly after the addition of Pb. The more severe deactivation induced by Pb was attributed to low surface area, lower amounts of chemisorbed oxygen species and surface Ce3+, and lower redox ability and surface acidity (especially a low number of Brønsted acid sites). Furthermore, the addition of Pb inhibited the formation of highly active intermediate nitrate species generated on the surface of the catalyst, hence decreasing the NH3-SCR activity. [ABSTRACT FROM AUTHOR]

The poisoning effects of alkali metals (K and Na) and alkaline earth metals (Ca and Mg) on catalytic performance of the 2Nb4Ce/Zr-PILC catalyst for the selective catalytic reduction of NOx with NH3 (NH3-SCR) were investigated, and physicochemical properties of the catalysts were characterized by means of the X-ray diffraction XRD (XRD), Brunner−Emmet−Teller (BET), hydrogen temperature-programmed reduction (H2-TPR), X-ray Photoelectron Spectroscopy (XPS), ammonia temperature-programmed desorption (NH3-TPD), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) techniques. Doping of M (M = K, Na, Ca, and Mg) deactivated the 2Nb4Ce/Zr-PILC catalyst according to the sequence of 0.8 K > 0.8 Na > 0.8 Ca > 0.8 Mg (M/Ce molar ratio = 0.8). The characterization results showed that the decreases in redox ability, NH3 adsorption, Ce3+/Ce4+ atomic ratio, and amount of the chemisorbed oxygen (Oβ) were the important factors influencing catalytic activities of the alkali metal-and alkaline earth metal-doped samples. Consequently, compared with the Mg- and Ca-doped samples, doping of K caused the 2Nb4Ce/Zr-PILC sample to possess the lowest redox ability, NH3 adsorption, and amount of the Oβ species, which resulted in an obvious deactivation effect. [ABSTRACT FROM AUTHOR]

The Ce-Cu-SAPO-18 catalysts were prepared using the ion exchange method. The impact of sulfur dioxide on catalytic performance of Ce-Cu-SAPO-18 for the selective catalytic reduction (SCR) of NO with NH3 was examined. Detailed characterization of the fresh and sulfur-poisoning Cu-SAPO-18 and Ce-Cu-SAPO-18 samples was conducted. XRD and BET results show that SO2 treatment of the Ce-doped Cu-SAPO-18 (Ce-Cu-SAPO-18-S) sample did not induce a remarkable change in structure, as compared with that of the fresh counterpart. According to in situ DRIFT, H2-TPR, SEM, and EDS results, it is found that the sulfation species attached preferentially to the cerium species, rather than the isolated Cu2+ species. In particular, the TG/DSC results confirm that the sulfate species on the Ce-Cu-SAPO-18-S sample was easier to decompose than that on the Cu-SAPO-18-S sample. The catalytic active sites of Ce-Cu-SAPO-18 were less influenced after SO2 treatment, as demonstrated by the TPR and XPS results. All of the above results show that the Ce-Cu-SAPO-18 sample exhibited better sulfur-resistant performance than the Cu-SAPO-18 sample. [ABSTRACT FROM AUTHOR]

The proposed NH 3 -SCR reaction mechanism over V-Ce/Ti-PILC sample. [Display omitted] • The Ti-pillared support is suitable for dispersing the V-Ce composite oxides. • The strong interaction between V and Ce lead to increased H 2 consumption and reduction. • Ce4+/Ce3+ and V5+/V4+ redox cycle account for the excellent catalytic activity of 1V4Ce/Ti-PILC. • NH 3 -SCR over y V4Ce/Ti-PILC obey L–H and E–R mechanisms, with the former being dominant. The Ti-pillared clay-supported vanadia − ceria (y V4Ce/Ti-PILC, y was the V weight percentage (wt%), Ce weight percentage = 4 wt%) samples were prepared using the impregnation method. The catalytic activity for the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) decreased in the order of 1V4Ce/Ti-PILC > 4Ce/Ti-PILC > 2V4Ce/Ti-PILC > 1 V/Ti-PILC > 1V4Ce/Clay > Ti-PILC > Clay, with the 1V4Ce/Ti-PILC sample exhibiting the best activity (NO x conversion >90% at 280–450 °C). Physiochemical properties of the samples were investigated by means of XRD, N 2 absorption-desorption, SEM, H 2 -TPR, NH 3 -TPD, XPS, and in situ DRIFT techniques. The vanadia was uniformly dispersed on the Ti-PILC support, while the ceria were mainly present in CeO 2. The Ti-pillared support was suitable for dispersing the V-Ce composite oxides. The strong interaction between vanadia and ceria led to increased H 2 consumption and high-temperature reduction. The Ce4+/Ce3+ and V5+/V4+ redox cycle (V4+ + Ce4+ ↔ V5+ + Ce3+) accounted for the excellent NH 3 -SCR catalytic performance of the 1V4Ce/Ti-PILC sample. The doping of a proper amount of vanadia could promote formation of Ce3+ on the surface of 1V4Ce/Ti-PILC, and the formed Ce3+ could generate a more amount of the chemisorbed oxygen species that favored the NH 3 -SCR reaction. Furthermore, the 1V4Ce/Ti-PILC sample possessed high catalytic acidity and strong NH 3 adsorption ability, which were responsible for high NO conversion in a wide range of temperatures. The NH 3 -SCR reaction on the 4Ce/Ti-PILC and 1V4Ce/Ti-PILC samples obeyed the Langmuir–Hinshelwood (L–H) and Eley-Rideal (E–R) mechanisms, with the former being dominant. [ABSTRACT FROM AUTHOR]

The x CN/Ce-OMS-2 (x is the nominal weight percentages of g-C 3 N 4 , x = 5.0, 10.0, and 15.0 wt%) catalysts were prepared via an in-situ synthesis method. Physicochemical properties of the as-prepared materials were measured by means of the XRD, TEM, SEM, BET, XPS, H 2 -TPR, NH 3 -TPD, and in-situ DRIFTS techniques, and their catalytic activities for the selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) at low temperatures were evaluated. Among all the catalysts, the 10CN/Ce-OMS-2 catalyst showed the widest temperature span for NH 3 -SCR reaction and the best resistance to SO 2 poisoning. This may result from that the modification of g-C 3 N 4 promoted the electron transfer in catalyst, not only increased the concentration of active Mn4+ species and chemisorbed oxygen species, but also improved the surface acidity of the catalyst. In-situ DRIFTS results further showed that the modification of g-C 3 N 4 increased the amount of acid sites and enhanced the formation of NH 3 or NO intermediates (i.e., monodentate and bidentate nitrate), which enhanced the reaction activity of the catalyst. [Display omitted] • A g–C 3 N 4 –modified catalyst was developed basing on Ce-doping manganese oxide octahedral molecular sieves (Ce-OMS-2). • The catalyst exhibits superior NO x degradation activity, broader temperature range, and enhanced resistance to SO 2. • The g-C 3 N 4 promoting electron transfer and improving the redox ability of the catalyst. • In-situ DRIFTS analysis provided further evidence for the mechanism behind the improved activity. [ABSTRACT FROM AUTHOR]

The hydrothermal stability of the CuSSZ-13 samples with various Si/Al ratios was examined. The NO conversions in the NH 3 -SCR and NH 3 oxidation were measured. Physicochemical properties of the samples were characterized by means of a number of analytical techniques. It is shown that the NH 3 -SCR activity and hydrothermal stability of the CuSSZ-13 samples decreased with the rise in Si/Al ratio. Such decreases were attributed to the drop in the amount of the isolated Cu 2+ in the D6R and CHA cage of the CuSSZ-13 samples. Part of the isolated Cu 2+ ions were transformed to CuO after hydrothermal aging treatment, especially in the high-Si/Al-ratio samples. A large amount of the aggregated CuO destroyed the skeleton structure of SSZ-13, leading to the deactivation of the samples. [ABSTRACT FROM AUTHOR]