Experimental and theoretical studies of surface nitrate species on Ag/Al2O3 using DRIFTS and DFT

Zhang, Xiuli; He, Hong; Gao, Hongwei; Yu, Yunbo

doi:10.1016/j.saa.2008.04.015

Cited by 41 publications

(31 citation statements)

References 22 publications

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“…7, -NH appeared at a lower temperature (80°C) after NH 3 activation, while the water-solvated surface nitrate ad-species were visible at a higher temperature (160°C) going with other nitrate ad-species; therefore, they should be assigned to different ad-species at different temperatures. The band at 1302 cm À1 was also close to that of bidentate nitrate on Ag/Al 2 O 3 [32,33]; thus we are inclined to assign this band to bidentate nitrate.…”

Section: Ftir Study Of No + O 2 Adsorptionmentioning

confidence: 83%

“…In addition, a weak band at 1750 cm À1 was also seen. Based on the previous studies of the NO + O 2 reaction on Al 2 O 3 or Ag/Al 2 O 3 catalysts, these peaks were tentatively assigned to adsorbed N 2 O 4 (1750 cm À1 ) and monodentate (1545 cm À1 ), bidentate (1579 cm À1 ), and bridging (1614 cm À1 ) nitrates [26,28,[31][32][33][34]. The bands at 1456 and 1302 cm À1 were close to the IR bands at 1411 and 1302 cm À1 for adsorbed water-solvated surface nitrates on Al 2 O 3 [31].…”

Section: Ftir Study Of No + O 2 Adsorptionmentioning

confidence: 99%

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Mechanism of selective catalytic oxidation of ammonia to nitrogen over Ag/Al2O3

Zhang

2009

Journal of Catalysis

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127

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Mechanism O 2 uptake In situ DRIFTS a b s t r a c tThe mechanism of selective catalytic oxidation (SCO) of NH 3 over Ag/Al 2 O 3 was studied by NH 3 temperature-programed oxidation, O 2 -pulse adsorption, and in situ DRIFTS of NH 3 adsorption and oxidation. The essence which affects the low temperature activity of Ag/Al 2 O 3 has been elucidated through the mechanism study. Different Ag species on Ag/Al 2 O 3 significantly influence O 2 uptake by catalysts; while different oxygen species affect the activity of NH 3 oxidation at low temperature. The activated -NH could react with the atomic oxygen (O) at low temperatures (<140°C); however, the -NH could also interact with the O 2 at temperatures above 140°C. At low temperatures (<140°C), NH 3 oxidation follows the -NH mechanism. However, at temperatures above 140°C, NH 3 oxidation follows an in situ selective catalytic reduction (iSCR) mechanism (two-step formation of N 2 via the reduction of an in situ-produced NO x species by a NH x species).

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Section: Ftir Study Of No + O 2 Adsorptionmentioning

confidence: 83%

Section: Ftir Study Of No + O 2 Adsorptionmentioning

confidence: 99%

Mechanism of selective catalytic oxidation of ammonia to nitrogen over Ag/Al2O3

Zhang

2009

Journal of Catalysis

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200

127

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“…13a), the bands between 1250 cm −1 and 1450 cm −1 became dominant on the spectrum and were difficult to assign due to the overlapping of nitrites and nitrates bands from both BaO and Al 2 O 3 . Tentatively, the bands at 1338 cm −1 and 1400 cm −1 may be attributed to the presence of monodentate nitrates over Ba sites [10], and the band centered at 1315 cm −1 may be a combination of bridged nitrites and bidentate nitrates associated on Al [10,34,47]. When the gas feed was switched to the rich conditions (Fig.…”

Section: Dynamic No X Storage and Reduction Performancesmentioning

confidence: 94%

Effect of Co addition to Pt/Ba/Al2O3 system for NOx storage and reduction

Wang

2010

Applied Catalysis B: Environmental

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a b s t r a c tA comparative study of Pt/Ba/Al 2 O 3 , Co/Ba/Al 2 O 3 , Pt/Co/Al 2 O 3 and Pt/Co/Ba/Al 2 O 3 was performed in regards to their NO x storage capacities and NO oxidation abilities as a function of temperature. The nitrate stability and dynamic behaviors of NO x storage reduction during lean/rich fuel cycles using hydrogen as a reductant were also investigated over these catalysts. It was found that Pt/Co/Ba/Al 2 O 3 possessed the largest NO x storage capacity within the temperature range of 200-350 • C. The existence of Co not only improved the oxidation of NO to NO 2 under lean conditions, but also enhanced the release and reduction of NO x during the rich phase. The Pt and Co co-supported catalysts showed better NO x storage reduction activity and higher N 2 selectivity than Pt supported Ba/Al 2 O 3 catalysts within the tested temperature range. As for Pt/Co/Ba/Al 2 O 3 , high conversion was obtained at either a low reductant concentration with long duration time or a high reductant concentration with short duration time during the rich phase. In situ FTIR studies showed that NO x adsorption over Co-containing catalysts takes "nitrite route" as an important pathway. The intimate contact of Co and Ba/Al could accelerate nitrite/nitrate formation and the synergistic effect of Pt and Co could accelerate NO x reduction.

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“…7a). These peaks are assigned to bridging, monodentate, bidentate, and isolated nitrate (Underwood et al, 1999;Zhang et al, 2008). The mechanism of nitrate species formation on mineral oxides surfaces were studied thoroughly (Miller and Grassian, 1998;Underwood et al, 1999).…”

Section: Water Adsorption On Nitrated Oxidesmentioning

confidence: 99%

In situ DRIFTS study of hygroscopic behavior of mineral aerosol

Liu

2010

Journal of Environmental Sciences

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107

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In situ diffusion reflectance infrared Fourier transform spectroscopy was used to study the water adsorption on mineral oxides (SiO 2 , α-Al 2 O 3 , MgO, Fe 2 O 3 , TiO 2 ). The results showed that all the water adsorption isotherms were well fitted with the Brunauer-EmmettTeller (BET)-III type equation, with the calculated monolayers occurring at 24%-30% relative humidity. It showed that about 1-5 layers of water adsorbed on oxides surfaces in ambient relative humidity (20%-90%). The measured deliquescence relative humidity of NaCl was (74 ± 1)%, which demonstrated that DRIFTS is a useful method for the study the hygroscopic behavior of mineral dust. In addition, the limits of DRIFTS were also discussed.

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Experimental and theoretical studies of surface nitrate species on Ag/Al2O3 using DRIFTS and DFT

Cited by 41 publications

References 22 publications

Mechanism of selective catalytic oxidation of ammonia to nitrogen over Ag/Al2O3

Mechanism of selective catalytic oxidation of ammonia to nitrogen over Ag/Al2O3

Effect of Co addition to Pt/Ba/Al2O3 system for NOx storage and reduction

In situ DRIFTS study of hygroscopic behavior of mineral aerosol

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