Effect of water vapor on the deactivation of Pd-zeolite catalysts for selective catalytic reduction of nitrogen monoxide by methane

Ohtsuka, Hirofumi; Tabata, Takeshi

doi:10.1016/s0926-3373(99)00014-4

Cited by 74 publications

(55 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This fact indicates that the Brønsted acidity favors the oxidation of NO to NO 2 , which is in agreement with the results of other reports [8,10]. The intense band due to adsorbed NO + species reveals the occurrence of surface reaction (6). Another possibility for the formation of nitrosonium ion is the reaction of NO and NO 2 with the Brønsted acid sites of tungstated zirconia via process observed to take place on acidic zeolites [60]:…”

Section: Coadsorption Of No and Osupporting

confidence: 91%

“…3A) suggests that the nitrates species (bands in the 1650-1400 and 1300-1200 cm −1 regions) are produced mainly via reaction (6). The broad absorption with maximum at 2160 cm −1 is due to the ν(NO) stretching mode of the NO + species.…”

Section: Coadsorption Of No and Omentioning

confidence: 98%

“…Since the first report of Li and Armor [1] on Co-exchanged ZSM-5 catalysts, various zeolites containing transition and non-transition metals have been shown to be active in this reaction [2]. Palladiumexchanged H-ZSM5 and H-Mor catalysts are more attractive because they appear to be less sensitive to steam [3][4][5][6][7]. Nishizaka and Misono [8,9] first reported a high activity of Pd-exchanged H-ZSM-5 catalysts and indicated the direct involvement of protonic acid sites in both palladium dispersion and the mechanism of the CH 4 -SCR of NO.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Routes of formation and composition of NOx complexes adsorbed on palladium-promoted tungstated zirconia

Kantcheva

Çayırtepe

2006

Journal of Molecular Catalysis A: Chemical

View full text Add to dashboard Cite

Surface species obtained during the adsorption of NO and NO/O 2 coadsorption at room temperature on Pd-free (WZ) and Pd-promoted tungstated zirconia (Pd/WZ) are identified by means of in situ FT-IR spectroscopy. The WZ and Pd/WZ samples have a tetragonal structure and contain randomly distributed mesoporous phase. Dispersed palladium(II) species are present in two different environments: (i) Pd 2+ ions, which have only Zr 4+ ions in their second coordination sphere and (ii) Pd 2+ ions, which are linked to both zirconium and tungsten ions via oxygen bridges. On the Pd/WZ sample, NO undergoes oxidation to various NO x species depending on the temperature. The compounds formed at room-temperature oxidation are adsorbed N 2 O 3 and products of its self-ionization, NO + and NO 2 − . In this process W(VI) is involved, being reduced to W(IV). At high temperature N 2 O 3 decomposes, restoring the W O species. Under these conditions, NO undergoes oxidation to NO 2 by the Pd(II) ions, which are reduced to Pd(I). The nitrosyls of Pd(I) display high thermal stability and do not disappear upon evacuation at 623 K. During NO/O 2 coadsorption on the Pd/WZ catalyst at room temperature, the amounts of surface nitrates and NO 2 /N 2 O 4 formed in the gas phase are significantly lower than those observed under identical conditions in the presence of tungstated zirconia. It is concluded that promotion of tungstated zirconia with palladium(II) suppresses the oxidation of NO by molecular oxygen at room temperature due to the elimination of acidic protons involved in the process.

show abstract

Section: Coadsorption Of No and Osupporting

confidence: 91%

Section: Coadsorption Of No and Omentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Routes of formation and composition of NOx complexes adsorbed on palladium-promoted tungstated zirconia

Kantcheva

Çayırtepe

2006

Journal of Molecular Catalysis A: Chemical

View full text Add to dashboard Cite

show abstract

“…An important finding for these catalysts is that the presence of acid sites is necessary for achieving high CH 4 -SCR activity and selectivity [12,13]. Furthermore, low Si/Al ratios favor NO reduction activity even in the presence of steam [14]. On the other hand, it is recognized that the hydrocarbon type influences lean NO x reduction [15].…”

Section: Introductionmentioning

confidence: 99%

Lean NOx reduction with dodecane over cerium and palladium loaded mordenite

Córdoba

Flytzani‐Stephanopoulos

Correa

2001

Applied Catalysis B: Environmental

View full text Add to dashboard Cite

The selective catalytic reduction (SCR) of NO x by dodecane in excess oxygen-containing gas mixtures was studied on Ce and/or Pd-loaded HMOR. Under dry conditions the best fresh bimetallic catalyst, 6.2 wt.% Ce-0.08 wt.% Pd-HMOR, displayed a maximum of about 70% NO x conversion to N 2 at 350 • C and GHSV = 30,000 h −1 , while either Ce-HMOR or Pd-HMOR exhibited low activity for the SCR reaction. The presence of both Ce and Pd in the zeolite was crucial for high deNO x activity. The dodecane concentration is very important for the reaction. The catalyst is not active in the absence of the reducing agent and inhibition of NO x reduction is observed at dodecane concentrations higher than 440-500 ppm. The presence of 40 ppm SO 2 in the gas feed suppresses the reaction. However, the coexistence of 15% H 2 O and 40 ppm SO 2 has no appreciable effect on the catalyst activity. Enhanced activity and a broader temperature window was observed in the NO 2 + dodecane + O 2 reaction in the presence of 15% H 2 O and 100 ppm SO 2 . In this reaction mixture, the catalyst was capable of retaining a stable NO 2 conversion to N 2 for a period of ten days. Characterization by XPS and UV-VIS-diffuse reflectance spectra (UV-VIS-DRS) of selected fresh and aged catalyst samples indicates that Pd exists mainly as Pd 2+ cations in Ce-Pd-HMOR. Cerium is mostly present as CeO 2 on the surface of the zeolite particles. However, part of the cerium in 6Ce-Pd-HMOR, exists as stable Ce 3+ species.

show abstract

“…The selective reduction of NO x using CO [7], CH 4 [8] and C 3 H 6 [9] as reducting agents, and the direct NO decomposition reaction [10][11][12][13][14], represent a suitable alternative for the decomposition of these contaminant gases; in particular the direct NO decomposition since the process does not require a reducing agent. After the finding that a Cu-ZSM-5 catalyst was able to directly decompose NO, the study of different metals and supports has expanded with the ultimate goal of understanding and improving the catalytic performance [6,10].…”

Section: Introductionmentioning

confidence: 99%

Palladium and Molybdenum Mono and Bimetallic Catalysts on Modernite for Direct NO Decomposition Reaction

et al. 2009

View full text Add to dashboard Cite

show abstract

Effect of water vapor on the deactivation of Pd-zeolite catalysts for selective catalytic reduction of nitrogen monoxide by methane

Cited by 74 publications

References 25 publications

Routes of formation and composition of NOx complexes adsorbed on palladium-promoted tungstated zirconia

Routes of formation and composition of NOx complexes adsorbed on palladium-promoted tungstated zirconia

Lean NOx reduction with dodecane over cerium and palladium loaded mordenite

Palladium and Molybdenum Mono and Bimetallic Catalysts on Modernite for Direct NO Decomposition Reaction

Contact Info

Product

Resources

About