Silver-alumina catalysts for selective reduction of NO by higher hydrocarbons: structure of active sites and reaction mechanism

Shimizu, Ken‐ichi; Shibata, Junji; Yoshida, Hisao; Satsuma, Atsushi; Hattori, Tadashi

doi:10.1016/s0926-3373(00)00229-0

Cited by 293 publications

(312 citation statements)

References 31 publications

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“…This effect may be due to the presence of larger particles, which favor oxygen and propylene adsorption on the same active particle; hence, the propylene oxidation is more effective than the NO reduction. These results are in accord to other authors, 10,[22][23][24][25] that found a relationship between particle size, oxidation state and catalytic activities.…”

Section: Resultssupporting

confidence: 93%

Selective reduction of NOx by propylene over silver catalyst under oxidative conditions

Cónsul

Thiele

Baibich

et al. 2004

J. Braz. Chem. Soc.

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Neste trabalho foram estudados catalisadores Ag/Al 2 O 3 e Ag/Al 2 O 3 /Corderita, preparados por um método de impregnação convencional, na reação de redução de NO utilizando propeno como agente redutor. Os catalisadores foram caracterizados por redução a temperatura programada (RTP), quimissorção de oxigênio e área superficial, pelo método BET. A atividade catalítica foi determinada utilizando uma mistura reacional contendo 100 ppm de NO, 250 ppm de C 3 H 6 e 2% de oxigênio e uma velocidade espacial de 100000 h -1 . Os produtos da reação foram estudados por FTIR. Os resultados dos testes catalíticos mostraram 56% de conversão de NO para o catalisador 2,22%Ag/ Al 2 O 3 a 723 K. Os catalisadores de cordierita apresentaram um comportamento semelhante, mas a temperatura de máxima conversão de NO deslocou-se para temperaturas menores.In this study, a Ag/Al 2 O 3 and Ag/Al 2 O 3 /Cordierite catalyst was prepared by a conventional impregnation method and NOx reduction investigated using propylene as a reducing agent. The catalysts were characterized by Temperature Programmed Reduction (TPR), oxygen chemisorption and surface area, using the standard BET method. The catalytic activities were measured under the same reaction conditions, i.e., 100 ppm NO, 250 ppm C 3 H 6 , 2% of oxygen and 100000 h -1 space velocity. The reaction products were analyzed by FTIR. The results of the catalytic activity obtained for the 2.22%Ag/Al 2 O 3 catalyst showed 56% NO conversion at 723 K. The catalysts based on Cordierite presented an analogous behavior, but the temperature of maximum NO conversion was lower (620 K).Keywords: NOx reduction, silver/alumina catalyst, propylene, Cordierite IntroductionThe generation of NOx effluents from stationary and mobile sources poses an important environmental problem. [1][2][3][4] Gas effluent control in internal combustion engines, whose air/gasoline ratio is stoichiometric, can be achieved by using the so-called "three way catalysts" (TWC) typically containing Pt and Rh as the active metals. On the other hand, lean-burn engines, such as diesel engines and stationary sources for industrial use, operate with excess oxygen to ensure complete combustion. In these cases, TWCs are ineffective for NO elimination, for which reason selective catalytic reduction (SCR) is used. A typical commercial SCR catalyst uses V 2 O 5 -WO 3 -TiO 2 as the metal system and NH 3 as the reducing agent. This catalyst involves problems relating to the transport and storage of NH 3 and to vanadium toxicity. 5 In their studies of several catalysts prepared from zeolites substituted with H + , Na + , K + , Mg 2+ , Ca 2+ , Cr 3+ , Fe 3+ , Co 3+ , Ni 2+ , Cu 2+ , Zn 2+ and Ag, Iwamoto et al. 6,7 found that Cu-ZSM5 provided better NO reduction activity when hydrocarbons were used as reductants. However, this catalyst has a low thermal stability 6 and deactivates in the presence of water vapor and SO 2 . Moreover, large amounts of water vapor inhibit the catalyst's action, promoting the migration of Al +3 out of the zeolite struct...

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Section: Resultssupporting

confidence: 93%

Selective reduction of NOx by propylene over silver catalyst under oxidative conditions

Cónsul

Thiele

Baibich

et al. 2004

J. Braz. Chem. Soc.

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“…The enolic species has a crucial role in the -NCO formation during the SCR of NO x [7,9,10,23]. In addition, the strong peaks around 1,572-1,579 cm -1 and 1,464-1,468 cm -1 are assigned to the acetate species, and the peaks around 1,585-1,589 cm -1 and 1,300-1,304 cm -1 are due to the nitrates adsorbed on Ag/Al 2 O 3 [7,9,10,[29][30][31]. The peaks around 1,591-1,595 cm -1 , 1,379 cm -1 and 1,390-1,392 cm -1 are assigned to the surface formate species formed from the partial oxidation of C1 reductants over Ag/Al 2 O 3 ( Fig.…”

Section: Introductionmentioning

confidence: 99%

Review of Ag/Al2O3-Reductant System in the Selective Catalytic Reduction of NO x

Zhang

et al. 2008

Catal Surv Asia

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Ag/Al 2 O 3 is a promising catalyst for the selective catalytic reduction (SCR) by hydrocarbons (HC) of NO x in both laboratory and diesel engine bench tests. New developments of the HC-SCR of NO x over a Ag/ Al 2 O 3 catalyst are reviewed, including the efficiencies and sulfur tolerances of different Ag/Al 2 O 3 -reductant systems for the SCR of NO x ; the low-temperature activity improvement of H 2 -assisted HC-SCR of NO x over Ag/ Al 2 O 3 ; and the application of a Ag/Al 2 O 3 -ethanol SCR system with a heavy-duty diesel engine. The discussions are focused on the reaction mechanisms of different Ag/ Al 2 O 3 -reductant systems and H 2 -assisted HC-SCR of NO x over Ag/Al 2 O 3 . A SO 2 -resistant surface structure in situ synthesized on Ag/Al 2 O 3 by using ethanol as a reductant is proposed based on the study of the sulfate formation. These results provide new insight into the design of a high-efficiency NO x reduction system. The diesel engine bench test results showed that a Ag/Al 2 O 3 -ethanol system is promising for catalytic cleaning of NO x in diesel exhaust.

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“…Another new band at 2158 cm −1 can be assigned to -CN surface species [12,24]. Similar peak at 1630 cm −1 was also observed on Ag/Al 2 O 3 in the flow of n-hexane + NO + O 2 and assigned to carbonate species [20]. Turek et al [25] reported that when CO 2 chemisorbed on the surface of ␥-Al 2 O 3 , main adsorbed species was carbonate.…”

Section: In Situ Diffuse Reflectance Infrared Fourier Transform Spectmentioning

confidence: 58%

“…2, many IR peaks appeared in the region between 1700 and 1300 cm −1 . According to the previous literatures [12,18,19], the strong bands at 1651, 1591, and 1392 cm −1 were attributed to (-ONO), (-NO 2 ) and ␦(-CH 3 ), respectively, which suggested that the organic compounds C x H y NO z (R-ONO and R-NO 2 ) were largely formed on the catalyst surface at 200 • C. The peaks at 1300 and 1580 cm −1 were assigned to the bidentate nitrates and monodentate nitrates, respectively [7,12,20]. The peaks at 1562 and 1454 cm −1 are assigned to as (COO) and s (COO) of the adsorbed acetate [20][21][22][23].…”

Section: In Situ Diffuse Reflectance Infrared Fourier Transform Spectmentioning

confidence: 97%

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Novel Pd promoted Ag/Al2O3 catalyst for the selective reduction of NOx

Wang

Feng

et al. 2003

Applied Catalysis B: Environmental

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A novel palladium promoted Ag/Al 2 O 3 catalyst (denoted Ag-Pd/Al 2 O 3 ) has been developed for the selective catalytic reduction of NO by C 3 H 6 . The Ag-Pd/Al 2 O 3 shows a higher NO x conversion than Ag/Al 2 O 3 , especially at the temperatures ranging from 300 to 450 • C. The addition of a small amount of Pd (0.01 wt.%) to Ag/Al 2 O 3 is considered to be favorable for the partial oxidation of C 3 H 6 . In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) suggest that the presence of Pd catalyzes the formation of enolic species which is converted from C 3 H 6 . The enolic species is very active towards NO 2 and NO 3 − , resulting in the formation of -NCO species which is the key reaction intermediate in the selective catalytic reduction of NO.

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Silver-alumina catalysts for selective reduction of NO by higher hydrocarbons: structure of active sites and reaction mechanism

Cited by 293 publications

References 31 publications

Selective reduction of NOx by propylene over silver catalyst under oxidative conditions

Selective reduction of NOx by propylene over silver catalyst under oxidative conditions

Review of Ag/Al2O3-Reductant System in the Selective Catalytic Reduction of NO x

Novel Pd promoted Ag/Al2O3 catalyst for the selective reduction of NOx

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