Tungsta supported on zirconia and alumina catalysts: temperature-programmed desorption/reaction of methanol and pyridine DRIFTS studies

Larsen, Gustavo; Raghavan, Srinivasanallur; Márquez, María del Mar Simón; Lotero, Edgar

doi:10.1007/bf00813520

Cited by 21 publications

(13 citation statements)

References 14 publications

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“…Therefore, a detailed study of the nature and abundance of the W species in the oxidic catalysts is important in order to develop more efficient and selective catalysts. Towards this objective, oxides such as Al 2 O 3 , TiO 2 , SiO 2 , and ZrO 2 have been tested as supports [10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48]. WO 3 /ZrO 2 catalysts have received increasing interest due to their strongly acidic properties when obtained by impregnation of Zr(OH) 4 or by coprecipitation of appropriate Zr and W precursors [20,21,22,23,24,25,26,…”

Section: Introductionmentioning

confidence: 99%

Surface characterization of WO3/ZrO2 catalysts

2002

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A series of WO(3)/ZrO(2) catalysts with tungsten (W) loadings ranging from 0.5 to 11.4 wt% was prepared by incipient wetness impregnation on a preformed ZrO(2) support. The oxidic catalysts were characterized using XRD, Raman spectroscopy, XPS, ISS, and IR spectroscopy. XRD and Raman results showed that the ZrO(2) support was predominantly present in the monoclinic form. XPS and Raman measurements indicated the formation of increasing amounts of W interaction species for catalysts with W loadings up to 8.8 wt% WO(3). In addition to the W interaction species, bulk WO(3) was also observed for catalysts with W loadings > or = 3.0 wt% WO(3). Comparison of the XPS results with coverage measurements by ISS and CO adsorption suggests that the W surface phase is in the form of two-dimensional polymeric patches for catalysts with W loadings 3.0 < or = wt% WO(3) < or = 4.5. For catalysts with W loadings >4.5 wt% WO(3), the results indicated an additional build-up of a bilayer (or multilayer) polymeric W species. Analysis of the hydroxyl region of ZrO(2) by IR spectroscopy showed that initial additions of W occur on the high frequency hydroxyl group. A schematic for the structure of the catalysts has been proposed based on the above observations.

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Section: Introductionmentioning

confidence: 99%

Surface characterization of WO3/ZrO2 catalysts

2002

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“…The presence of this peak can be related to the re-adsorption of desorbed pyridine species. Other modes of ring-stretching vibrations (v8b, v19a, and v19b) corresponding to physisorbed pyridine were not observed [39,40]. It is possible that due to domination by strong overlapping peaks, the peaks corresponding to v8b, v19a, and v19b may be hidden.…”

Section: Diffuse Reflectance Infrared Fourier Transform Spectroscopy mentioning

confidence: 95%

“…The 1605 cm -1 , 1487 cm -1 , and 1448 cm -1 bands corresponding to Lewis acid sites become more dominant for the binder-incorporated samples. In addition to the Lewis acid sites, several negative bands were observed at 1635 cm -1 , 1558 cm -1 , 1533 cm -1 , and 1483 cm -1 which have been reported to be a result of pyridinium cation interaction with Brønsted acid sites [39,40,[42][43][44][45]. Billingham et al also observed such a behavior and the decrease in intensity of the peaks was related to hydrogen bond formation of pyridine to the pyridinium cation [43].…”

Section: Diffuse Reflectance Infrared Fourier Transform Spectroscopy mentioning

confidence: 95%

“…It is possible that due to domination by strong overlapping peaks, the peaks corresponding to v8b, v19a, and v19b may be hidden. The peaks at 1605 cm -1 , 1572 cm -1 , 1487 cm -1 , and 1448 cm -1 in Figure 4 (a) correspond to Lewis acid sites [39][40][41]. Presence of 1532 cm -1 IR band can be attributed to pyridinium cations [39,40,42,43].…”

Section: Diffuse Reflectance Infrared Fourier Transform Spectroscopy mentioning

confidence: 95%

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In-situ incorporation of binder during sol-gel preparation of Pd-based sulfated zirconia for reduction of nitrogen oxides under lean-burn conditions: Effect on activity and wash-coating characteristics

Majumdar

Çelik

Alexander

et al. 2017

Applied Catalysis B: Environmental

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We have developed a dual-catalyst aftertreatment system for reducing nitrogen oxides (NOx) in the exhaust stream of natural-gas fired lean-burn engines by utilizing the unburned hydrocarbons present in the engine exhaust. The dual-catalyst bed consists of a physical mixture of a reduction catalyst (Pd/SZ) and an oxidation catalyst (Co/CeO2). In order to make this dualcatalyst system viable for practical use in the real aftertreatment units, it is necessary to develop a catalytically active washcoat for loading it onto cordierite monolith cores. To be able to handle large throughputs of gases typical of aftertreatment units, irreversible loss of activity due to separation of the wash-coat from the monolith walls can be reduced by adding binders to improve the adhesive properties of the wash-coat. However, addition of such binders may affect the catalytic activity of the resulting dual-catalyst bed. In our study, we have incorporated binders such as alumina, boehmite, bentonite or silica to the Pd/SZ catalyst using a novel technique in which the binders were added in situ during the sol-gel synthesis rather than the conventional method of adding binders (ex-situ) in catalyst slurry. Surface area analysis, X-ray diffraction (XRD) and diffuse reflectance Fourier transform spectroscopy (DRIFTS) with pyridine show that in-situ addition of binder affects the textural properties, crystal phase of zirconia and the acidic properties of the resulting Pd/SZ catalyst respectively. Electron Paramagnetic Resonance (EPR) indicated the presence of Pd + , Pd 3+ and Zr 3+ species in the binder-free and in situ alumina-incorporated Pd/SZ catalysts. Furthermore, steady-state activity tests on the modified dual-catalyst bed with the alumina-incorporated Pd/SZ exhibit the best performance amongst the other binder-incorporated catalysts in the dual-catalyst bed. In-situ incorporation of binder during sol-gel synthesis yielded catalysts with far superior catalytic activity for NOx reduction than conventional ex-situ binder addition to the catalyst slurry for wash-coating. Time-on-stream experiments show that the alumina-incorporated Pd/SZ catalyst maintains the hydrothermal stability of the binder-free Pd/SZ in the mixed bed. Several parameters such as pH of the binder-incorporated catalyst slurry and calcination temperature of the wash-coat have also been optimized to develop a catalytically active wash-coat and its adhesivity and uniformity were tested using ultrasonication, cyclic thermal shock and SEM imaging.

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“…Two further signals appear at 1593 and 1392 cm −1 , which are thought to be related to the weakly bound species due to their disappearance at 373-473 K. The spectra after pyridine adsorption exhibit strong signals at 1591 and 1442 cm −1 resulting from hydrogen bridged pyridine. 36,37 This type of adsorbed species is found on Brønsted acidic hydroxyl groups. The signal at 1442 cm −1 masks the signal at about 1445 cm −1 , becoming visible only at elevated temperatures due to the desorption of hydrogen bridged pyridine, and thus the disappearance of the corresponding signal.…”

Section: View Article Onlinementioning

confidence: 99%