Catalyst particles, schematic representation

Fig. 9. Schematic representation of a catalyst for ethylene oxide synthesis (not to scale). The porous support particle consists of microparticles held together...

Fig. 14. Schematic representation of a (5.5) tubule growing on the corresponding catalyst particle. The decomposition of acetylene on the same catalyst particle is also represented. The catalyst contains many active sites but only those symbolized by grey circles are directly involved in the (5,5) tubule growth.

Fig. 2. Schematic representation of electrodes, (a) Content of Nafion too low not enough catalysts with ionic connection to membrane, (b) Optimal Nafion content electronic and ionic connections well balanced, (c) Content of Nafion too high catalyst particles electronically isolated from diflusion layer. Reproduced from [9].

Figure 3.3. Schematic representation of the adsorption, surface diffusion, and surface reaction steps identified by surface-science experiments on model supported-palladium catalysts [28]. Important conclusions from this work include the preferential dissociation of NO at the edges and defects of the Pd particles, the limited mobility of the resulting Nads and Oads species at low temperatures, and the enhancement in NO dissociation promoted by strongly-bonded nitrogen atoms in the vicinity of edge and defect sites at high adsorbate coverages. (Figure provided by Professor Libuda and reproduced with permission from the American Chemical Society, Copyright 2004).

Figure 2.1 Schematic representation of a random model catalyst surface (a) and an idealized model catalyst (b). The black dots correspond to metal particles, dotted circles to their capture...

Because of the inadequacies of the aforementioned models, a number of papers in the 1950s and 1960s developed alternative mathematical descriptions of fluidized beds that explicitly divided the reactor contents into two phases, a bubble phase and an emulsion or dense phase. The bubble or lean phase is presumed to be essentially free of solids so that little, if any, reaction occurs in this portion of the bed. Reaction takes place within the dense phase, where virtually all of the solid catalyst particles are found. This phase may also be referred to as a particulate phase, an interstitial phase, or an emulsion phase by various authors. Figure 12.19 is a schematic representation of two phase models of fluidized beds. Some models also define a cloud phase as the region of space surrounding the bubble that acts as a source and a sink for gas exchange with the bubble. 

Figure 3.12 Schematic representation of the dispersion of Zr02 particles and the extent to which the silica support is covered in three Zr02/Si02 catalysts prepared by impregnation with an aqueous zirconium nitrate solution, and one prepared via an exchange reaction of the support with zirconium ethoxide. The rectangles represent 100 nm2 of silica support area, and the circles represent a half-spherical particle of Zr02 seen from above. See Table 3.3 for corresponding numbers (adapted from Meijers et al. [33]).

Figure 6. Schematic representation of the catalysts particles for explaining synergy effect for mixtures of Bi2Mo30j2 and 67 0 33 4 ...

Bead-string reactors represent the limit of parallel-passage reactors They contain single-catalyst-particle subunits. Figure 10 gives a schematic representation (25). 

Fig. 3.13 Schematic representation of the dispersion of Zr02 particles and the extent to which the silica support is covered in three Zr02/Si02 catalysts prepared by impregnation with an aqueous zirconium nitrate solution, and one prepared via an...

Figure 9.5 Carbon nucleus on the surface of the metal catalyst particle (a) schematic two-dimensional representation (b-e) TEM images, [(a) From ref. 60, with permission. Copyright 2001 American Physical Society, (b-e) From ref. 62, with permission. Copyright 2007 American Chemical Society.]...

Figure 1.12. Schematic representation of composite particles consisting of thermosensitive core-shell particles in which metallic nanoparticles are embedded. The composite particles are suspended in water, which swells the thermosensitive network attached to the surface of the core particles. In this state the reagents can diffuse freely to the nanoparticles, which act as catalysts. At higher temperatures (T> 32 °C) the network shrinks and the catalytic activity of the nanoparticles is strongly diminished.

Figure 3.1. Schematic representation of a PEM fuel cell single membrane electrode assembly (MEA) with electrochemical reactions occurring at catalyst particles (dark circles).

The spontaneous deposition of noble metals onto less noble metal particles or metal surfaces is emerging as a viable technic ne for creating new catalyst architectures as well as allowing one to introduce single noble metal sites over the surface of a non-noble metal phase. A schematic representation of the spontaneons deposition of a high-valent metal via redox transmetalation is shown in Fig. 6 for a hypothetical non-noble metal phase supported on a condnctive material. 

FIGURE 8.13 Schematic representation of the texture and morphology of a cogeUed xerogel catalyst divided in three levels (i = 1, 2, 3) pellet (i = 1), aggregate of elementary Si02 particles (i = 2), and elementary sUica particle (i = 3) (reprinted from [34] with permission from AIChE-Wiley). = characteristic diameter , = characteristic pore width /O = bulk... 

FIGURE 8.14 Schematic representation of a metal nanoparticle caged inside a microporous silica particle in sol-gel catalysts prepared by cogelation. 

Figure 22.9. Schematic planar representation of the cataljhic layer [81] (A) at low Nafion content, not all the catalyst particles are connected to the membrane hy a Nafion bridge (C) when there is too much Nafion not all the catalyst particles are electronically connected to the diffusion layer (B) at the optimal Nafion content all the catalyst particles have good connections for ionic and electronic conduction. (Reprinted from Electrochimica Acta, 46(6), Passalacqua E, Lufrano F, Squadrito G, Patti A, Giorgi L. Nafion content in the catalyst layer of polymer electrol)de fuel cells effects on structure and performance, 799-805, 2001, with permission from Elsevier.)...

Figure 6.9.9 Schematic representation of coke burn-off during regeneration of a coked fixed bed catalyst on the level of a fixed bed reactor (a) and a single particle (b).

Fig. 16.3 (a) Schematic representation of the spherical catalyst agglomerate model, (b) Modified agglomerate model with distribution of discrete Pt particles. Reproduced from [82] with permission of The Electrochemical Society... 

FIGURE 13.15 Schematic illustrations of a standard NSTF cathode (a) and various approaches (b, c, and d) demonstrated in Ref. [122] to improve the fuel cell operational robustness of NSTF. (b) NSTF cathode was coated with 4-nm-thick ionomer. (c) NSTF cathode was decorated with lOnm silica particles, (d) A few-micron-thick dispersed-catalyst layer was located adjacent to NSTF cathode. Reprinted with permission from Ref. [122]. ECS. (See insert for color representation of the figure.)... 

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