Zeolites monoliths

Gas Selective oxidation in H2-rich mixture Fuel cells CO oxidation Stable catalyst Pt/zeolite/monolith (170)... 

Figure 9 Examples of novel materials with potential catalytic applications. From left to right and top to bottom, these pictures represent (a) Ag nanowires. (Reprinted with permission from Ref 63. 2002 American Chemical Society) (h)Ag nanoparticles. (Reprinted with permission from Y. Sim and Y. Xia, Science, 2002, 298, 2176. 2002 AAAS (www.sciencemag.org)) (c) zeolite monolith. (Ref. 67. Reproduced hy permission of Kluwer Academic/Plenum Publishers) (d) zeolite coatings on stainless steel grids. (Ref 68. Reproducedby permission of Wiley-VCH) (e) arrays of Pt nano lithography-made particles on Si02. (Ref. 70. Reproduced by permission of Kluwer Academic/Plenum Publishers) and (f) Ag nanoparticles vapor deposited on an AI2O3 thin film ...

Zeolite monoliths have been useful for such apphcations as rotatory adsorbers for use as dehumidifiers and desiccant cooling processes [253] or in VOC treatment systems [269]. Alumina-coated sUicon carbide monoliths have also been employed as supports for B-ZSM-5 membranes [270] providing a larger surface area per unit volume, compared to traditional membrane supports. With these membranes, these authors have reported n/f-butane and H2/f-butane separation selectivities of 35 and 77, respectively [85]. Also, silicalite-1 membranes supported on stainless steel grids (Figure 10.29) have shown a good performance in the separation of n/f-butane mixtures, with separation factors as high as 53 at 63°C [255]. 

The two promising candidates are adsorbent monoliths and adsorbent sheets. The fabrication of activated carbon and zeolite monoliths are reported in the literature. Zeolite monoliths have also been tested for air separation application by PSA.50 51 However, the use of monoliths for use in H2 PSA is not known to the authors. Monoliths having very high cell density (several hundred to thousand cells per square inch) will be necessary in order to have fast adsorption kinetics as well as reasonable bulk density for a PSA application. Manufacture of such monoliths is complex, and they are not yet commercially available. Gas channeling through the monoliths can also be a problem.52 Adsorbent sheets have been used for air separation by RPSA.53 54 The thickness of the adsorbent sheets and the space between the... 

Li, Y.Y., Perera, S.P., and Crittenden, B.D. Zeolite monoliths for air separation. Part 2 oxygen enrichment, pressure drop and pressurization. Chemical Engineering Research Design, 1998, 76, 931. 

Zeolite monlith with macropores can be considered as a micro-macroporous material. Mechanically stable zeolite monoliths[177] containing 3-D, ordered, closed macropores have been fabricated by hydrothermal treatment of nano-zeolite seeded mesoporous silica spheres. The easy speed of sedimentation and digestion renders the whole process suitable for large-scale production of macroporous zeolite materials. 

A.A. Dong, Y.J. Wang, Y. Tang, Y.H. Zhang, N. Ren, and Z. Gao, Mechanically Stable Zeolite Monoliths with Three-dimensional Ordered Macropores by the Transformation of Mesoporous Silica Spheres. Adv. Mater., 2002, 14, 1506-1510. 

Li YY, Perera SP, Crittenden BD, Bridgwater J (2001) The effect of binder on the manufacture of a 5A zeolite monolithe. J Powder Technology 116 85-96... 

The Metkar et al. [76] model was also used to predict the performance of combined Fe- and Cu-zeolite monolithic catalysts in the form of either sequential bricks or dual layers. Without any adjustment of the kinetic parameters from the tuning of the single component catalysts, the model predicted all of the main trends in the combined system data. An example result is shown in Fig. 11.22. The model predicts the wide expansion in the temperature window giving a high conversion... 

Zampieri, A., Kulhnann, S., Selvam, T., Bauer, J., Schwieger, W., Sieber, H., Pey, T., and Greil, P. (2006) Bioinspired rattan-derived SiSiC/zeolite monoliths Preparation and Characterisation, Microporous Mesoporous Mater. 90, 162. 

Dong, A., Ren, N., Yang, W., Wang, Y Zhang, Y., Wang, D., Hu, J., Gao, Z., and Tang, Y. (2003) Prqtaration of hollow zeolite spheres and three-dimensionally ordered macroporous zeolite monoliths with functionalized interiors. Adv. Funct. Mater., 13, 943-948. 

Figure 4.6 Variation of Various Characteristic Times in the Temperature Range of 200-575 C for the Standard SCR Reaction on Fe-Zeolite Monolithic Catalysts.

Figure 4.7 Variation of the Dimensionless Numbers P (Transverse Peclet Number) and C (Weisz-Prater Modulus) in the Temperature Range of 200-575 C for the Standard SCR Reaction on Fe-Zeolite Monolithic Catalysts. Extracted from Metkaretal. [129], with permission...

Catalysts can be metals, oxides, sulfides, carbides, nitrides, acids, salts, virtually any type of material. Solid catalysts also come in a multitude of forms and can be loose particles, or small particles on a support. The support can be a porous powder, such as aluminium oxide particles, or a large monolithic structure, such as the ceramics used in the exhaust systems of cars. Clays and zeolites can also be solid catalysts. 

The catalytically active material on the monolith also comes in many forms. Formulations based on iron, chromium, and vanadium as the active components supported on Ti02, AI2O3, Si02, and zeolites have been reported see the review by Bosch and Janssen [H. Bosch and F.J.J.G. Janssen, Catal. Today 2 (1988) 369]. 

In addition to the particulate adsorbents listed in Table 16-5, some adsorbents are available in structured form for specific applications. Monoliths, papers, and paint formulations have been developed for zeolites, with these driven by the development of wheels (Fig. 16-60), adsorptive refrigeration, etc. Carbon monoliths are also available as are activated carbon fibers, created from polymeric materials, and sold in the forms of fabrics, mats, felts, and papers for use in various applications including in pleated form in filters. Zeolitic and carbon membranes are also available, with the latter developed for separation by selective surface flow [Rao and Sircar, J. Membrane Sci., 85, 253 (1993)]. 

Zeolite catalysts and adsorbents have also been incorporated into monolithic contactors by several routes, including extruded zeoHte/binder composites [70], wash-coated ceramic monoliths [71] and corrugated thin-sheet monoliths [72]. 

Marques, P., Remy, C., and Sorensen, C.M. (2005) Monolithic zeolite coated structures and a method of manufacture. US Patent 6,935,551. 

Since 1981, three-way catalytic systems have been standard in new cars sold in North America.6,280 These systems consist of platinum, palladium, and rhodium catalysts dispersed on an activated alumina layer ( wash-coat ) on a ceramic honeycomb monolith the Pt and Pd serve primarily to catalyze oxidation of the CO and hydrocarbons, and the Rh to catalyze reduction of the NO. These converters operate with a near-stoichiometric air-fuel mix at 400-600 °C higher temperatures may cause the Rh to react with the washcoat. In some designs, the catalyst bed is electrically heated at start-up to avoid the problem of temporarily excessive CO emissions from a cold catalyst. Zeolite-type catalysts containing bound metal atoms or ions (e.g., Cu/ZSM-5) have been proposed as alternatives to systems based on precious metals. 

In this section the methods described in Sections III and IV are applied to derive a dynamic numerical model of the SCR of NO-N02 with NH3 over a commercial V205/W03/Ti02 extruded monolith catalyst. The extension of the same dynamic model to a zeolite-based catalyst is currently in progress (Chatterjee et al., 2007). 

Figure 24 Schematic representation of the operation of a monolith channel, washcoated with a zeolite catalyst, under Taylor-flow conditions.

The potential of structured packings as catalyst carriers for reactive stripping, film-flow-monoliths, Sulzer DX -packings, both coated with zeolite BEA, and katapak-S , filled with BEA-particles, was explored in cold-flow experiments and under reactive stripping conditions in a pilot-scale plant. 

In diagnostic tests crushing of the particles will not always be conclusive. Egg-shell catalysts or other types, zeolites and washcoated monoliths are exceptions. In washcoated monoliths the layer thickness is generally already quite low (<50 (im) and crushing will not yield smaller sizes. Cracking catalysts consist often of zeo-litic crystals of /im dimensions and a binder yielding particles of about 30 /im. If diffusion limitations exist in the zeolitic crystals, crushing will not eliminate these. 

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