Surface covering promoters

For time scales shorter than that of a catalytic turnover (typically 10 2 to 102s) the three phenomena are indistinguishable. Looking at the Na-promoted Pt surface on the cover of this book and imagining that CO oxidation is taking place on that surface, there is no way to distinguish if this is a classically promoted surface where Na has been added from the gas phase,... 

However, an interpretation of this experiment is not straightforward in view of the experimental conditions, which imply a monolayer on the substrate surface covered by the solution of molecules. Cis-trans isomerization for an observed molecule is supposed to promote desorption, so that a pattern change includes absorption-desorption equilibria. It would be important therefore, to observe a light induced change of a 2D pattern only for adsorbed molecules. This is, indeed, possible for C9(DIA)C8ISA... 

The amount adsorbed is thus greater, the smaller vjkp, High rates of condensation, and low rates of evaporation, promote complete covering of the surface. 

From the results of both pulse reaction and adsorption experiments, it could be confirmed that Ni has a strong affinity with methane, while alkali promoters with carbon dioxide. The retardation of coke deposition on KNiCa/ZSI catalyst must be ascribed to the abundantly adsorbed CO2 species. This explanation is similar to the suggestion of Horiuchi et al. [5], showing that the surface of the Ni cat2ilyst with basic metal oxides was labile to CO2 adsorption, while the surface without them was labile to CH4 adsorption. Since coke deposition was mainly caused by methane decomposition, the catalyst surface covered with adsorbed CO2 or reactive oxygen species from the dissociation of CO2 would suppress coke deposition. The addition of alkaline promoters also seemed to greatly suppress the activity of supported Ni catalyst for the direct decomposition of methane. 

Fig. 5. Surface image of non-promoted CuCb/Sitedi after 3 h reaction, and EDX analysis 1) non-attacked surface, 0.5 wt.% Cu, 98 wt.% Si 2) reacted surface covered by an overlayer, 77 wt.% Cu, 20 wt.% Si.

Further work on modified Fe single crystals explored the role of promoters such as aluminium oxide and potassium [49, 50 and 51]. It was found that the simple addition of aluminium oxide to Fe single crystal surfaces decreased the ammonia synthesis rate proportionally to the amount of Fe surface covered, indicating no favourable interaction between Fe and aluminium oxide under those conditions. However, by exposing an aluminium-oxide-modified Fe surface to water vapour, the surface was oxidized, inducing a favourable interaction between Fe and the Al O. This interaction resulted in a 400-fold increase in ammonia synthesis activity for A1 0yFe( 110) as compared to Fe( 110) and an activity for A1 0 e( 110) comparable to that of Fe... 

Effects of Aluminum Oxide in Restructuring Iron Single-Crystal Surfaces for Ammonia Synthesis The initial rate of ammonia synthesis has been determined over the clean Fe(l 11), Fe(lOO), and Fe(l 10) surfaces with and without aluminum oxide. The addition of aluminum oxide to the (110), (100), and (111) faces of iron decreases the rate of ammonia synthesis in direct proportion to the amount of surface covered [47]. This suggests that the promoter effect of aluminum oxide involves reaction with iron which cannot be achieved by simply depositing aluminum oxide on an iron catalyst. 

Well-compacted, fine-grained soils should be used for the final cover to promote surface water runoff by minimizing infiltration. 

The inhibition effect of promoters on the methanation. R is commonly believed that for fused iron catalyst, AI2O3 increases iron surface area (structural effect), while K2O donates electrons to iron atom, and increases electron density and enhances the activity of ammonia synthesis reaction (electronic effect). For the supported ruthenium catalysts, the effect of promoters on performances becomes more complex due to the existence of support. ARhough there are a lot of studies on the role of promoter for ammonia synthesis reaction, the chemical state, the distribution and the mechanism are still unclear. The role of promoters include covering chemisorption s site, donating electron to active metal, direct interacting with the adsorption intermediate and electrostatic field and so For supported... 

The oxidation products are almost insoluble and lead to the formation of protective films. They promote aeration cells if these products do not cover the metal surface uniformly. Ions of soluble salts play an important role in these cells. In the schematic diagram in Fig. 4-1 it is assumed that from the start the two corrosion partial reactions are taking place at two entirely separate locations. This process must quickly come to a complete standstill if soluble salts are absent, because otherwise the ions produced according to Eqs. (2-21) and (2-17) would form a local space charge. Corrosion in salt-free water is only possible if the two partial reactions are not spatially separated, but occur at the same place with equivalent current densities. The reaction products then react according to Eq. (4-2) and in the subsequent reactions (4-3a) and (4-3b) to form protective films. Similar behavior occurs in salt-free sandy soils. 

Plaic-and-frame exchangers are an arrangement of gasketed, pressed metal plates aligned on carrying bars and secured between two covers by comptession bolts. The pressed metal plates are corrugated in patterns to provide increased surface area, to direct the flow in specific directions, and to promote turbulence. The plates are gasketed such that each of the... 

There is a wide variety of solid electrolytes and, depending on their composition, these anionic, cationic or mixed conducting materials exhibit substantial ionic conductivity at temperatures between 25 and 1000°C. Within this very broad temperature range, which covers practically all heterogeneous catalytic reactions, solid electrolytes can be used to induce the NEMCA effect and thus activate heterogeneous catalytic reactions. As will become apparent throughout this book they behave, under the influence of the applied potential, as active catalyst supports by becoming reversible in situ promoter donors or poison acceptors for the catalytically active metal surface. 

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