Investigation of the robust hydrothermal stability of Cu/LTA for NH3-SCR reaction

Wang, Aiyong; Arora, Prakhar; Bernin, Diana; Kumar, Ashok; Kamasamudram, Krishna; Olsson, Louise

doi:10.1016/j.apcatb.2019.01.039

Cited by 73 publications

(44 citation statements)

References 59 publications

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“…The data in Table 1 show that the hydrothermal aging at 900 • C resulted in about 7% decrease in BET surface area of PdLTA, whereas the corresponding value was about 27% for PdAl. The BET results are in line with earlier measurements on similar samples, for example we observed 542 m 2 /g for Cu/LTA treated at 750 • C and 495 m 2 /g when it was aged at 900 • C [17]. Moreover, the aging only caused minor changes in pore volume for PdLTA and PdAl (Table 1).…”

Section: Characterizationsupporting

confidence: 92%

“…For PdAl, small changes in diffraction peaks corresponding to the support material can be noted, however it can be concluded that support material mainly consisted of γ-Al 2 O 3 also after the hydrothermal aging [23]. The N 2 physisorption and XRD results indicate that the LTA zeolite is extraordinarily resistant towards structural changes upon hydrothermal aging, which agrees well with our previous report [17]. However, Al 2 O 3 expressed also high thermal stability.…”

Section: Characterizationsupporting

confidence: 90%

“…Two catalyst samples were prepared, Pd/H-LTA (PdLTA) and Pd/γ-Al 2 O 3 (PdAl). The Si/Al-ratio of the H-LTA zeolite was 44 (measured by ICP-SFMS performed by ALS Scandinavia AB) and it was synthesized according to the procedure described in our previous publication [17]. For the γ-Al 2 O 3 support, Puralox SBa 200 calcined at 700 • C for 2 h was used.…”

Section: Catalyst Preparationmentioning

confidence: 99%

“…However, hydrothermal aging of SSZ-13 at high temperatures (typically > 850 • C) causes structural damage expressed by decreased surface area, pore volume, and changes in X-ray diffraction (XRD) patterns [16]. By contrast, it has recently been demonstrated that the small pore LTA zeolite has extraordinarily good stability with only minor changes in N 2 physisorption and XRD pattern after hydrothermal aging at 900 • C [17,18]. This makes LTA a promising future candidate as a thermally stable zeolite support for heterogenous catalysts.…”

Section: Introductionmentioning

confidence: 99%

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Hydrothermal Aging of Pd/LTA Monolithic Catalyst for Complete CH4 Oxidation

2020

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Palladium-based catalysts are known to provide high CH4 oxidation activity. One drawback for these materials is that they often lose activity in the presence of water vapor due to the formation of surface hydroxyls. It is however possible to improve the water vapor tolerance by using zeolites as support material. In this study, we have investigated Pd supported on thermally stable LTA zeolite with high framework Si/Al ratio (Si/Al = ~44) for CH4 oxidation and the effect of hydrothermal aging at temperatures up to 900 °C. High and stable CH4 oxidation activity in the presence of water vapor was observed for Pd/LTA after hydrothermal aging at temperatures ≤ 700 °C. However, aging at temperatures of 800–900 °C resulted in catalyst deactivation. This deactivation was not a result of structural collapse of the LTA zeolite as the LTA zeolite only showed minor changes in surface area, pore volume, and X-ray diffraction pattern after 900 °C aging. We suggest that the deactivation was caused by extensive formation of ion-exchanged Pd2+ together with Pd sintering. These two types of Pd species appear to have lower CH4 oxidation activity and to be more sensitive to water deactivation compared to the well dispersed Pd particles observed on the LTA support prior to the hydrothermal aging. By contrast, Pd/Al2O3 was generally sensitive to water vapor no matter of the aging temperature. Although the aging caused extensive Pd sintering in Pd/Al2O3, only minor deterioration of the CH4 oxidation activity was seen. The results herein presented show that Pd/LTA is a promising CH4 oxidation catalyst, however Pd rearrangement at high temperatures (≥800 °C) is one remaining challenge.

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Section: Characterizationsupporting

confidence: 92%

Section: Characterizationsupporting

confidence: 90%

Section: Catalyst Preparationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Hydrothermal Aging of Pd/LTA Monolithic Catalyst for Complete CH4 Oxidation

2020

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“…Limited by the narrow temperature window (320-450 • C), insufficient hydrothermal stability and biotoxicity, conventional vanadia catalysts have gradually been replaced by nontoxic metal-based zeolite catalysts, especially Cu-based zeolites with a wide temperature window (200-500 • C) and high hydrothermal stability in NH 3 -SCR [4,5], owing to their unique properties such as high surface areas, considerable acidity and well-defined pore systems with stable structure which can sustain up to 800 • C [6,7]. In addition, due to the high redox activity of Cu species, Cu-based zeolites such as Cu/SSZ-13 [7,8], Cu/SAPO-34 [9,10], Cu/LTA [8,11] and Cu/SSZ-39 [12,13] have become the most used catalysts in NH 3 -SCR, especially in the low temperature range (200-350 • C) [13,14]. Currently, Cu/SSZ-13-based catalysts have been commercially applied in the treatment of diesel engine exhausts in the USA and Europe [5,14,15].…”

Section: Introductionmentioning

confidence: 99%

Catalytic Performances of Cu/MCM-22 Zeolites with Different Cu Loadings in NH3-SCR

et al. 2020

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The NH3-SCR activities and hydrothermal stabilities of five xCu/MCM-22 zeolites with different Cu loadings (x = 2–10 wt%) prepared by incipient wetness impregnation method were systematically investigated. The physicochemical properties of xCu/MCM-22 zeolites were analyzed by XRD, nitrogen physisorption, ICP-AES, SEM, NH3-TPD, UV-vis, H2-TPR and XPS experiments. The Cu species existing in xCu/MCM-22 are mainly isolated Cu2+, CuOx and unreducible copper species. The concentrations of both isolated Cu2+ and CuOx species in xCu/MCM-22 increase with Cu contents, but the increment of CuOx species is more distinct, especially in high Cu loadings (>4 wt%). NH3-SCR experimental results demonstrated that the activity of xCu/MCM-22 is sensitive to Cu content at low Cu loadings (≤4 wt%). When the Cu loading exceeds 4 wt%, the NH3-SCR activity of xCu/MCM-22 is irrelevant to Cu content due to the severe pore blockage effects caused by aggregated CuOx species. Among the five xCu/MCM-22 zeolites, 4Cu/MCM-22 with moderate Cu content has the best NH3-SCR performance, which displays higher than 80% NOx conversions in a wide temperature window (160–430 °C). Furthermore, the hydrothermal aging experiments (xCu/MCM-22 was treated at 750 °C for 10 h under 10% water vapor atmosphere) illustrated that all the xCu/MCM-22 zeolites exhibit high hydrothermal stability in NH3-SCR reactions.

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