Carbonate deposition, factors affecting

Another important factor affecting carbon deposition is the catalyst surface basicity. In particular, it was demonstrated that carbon formation can be diminished or even suppressed when the metal is supported on a metal oxide carrier with a strong Lewis basicity [47]. This effect can be attributed to the fact that high Lewis basicity of the support enhances the C02 chemisorption on the catalyst surface resulting in the removal of carbon (by surface gasification reactions). According to Rostrup-Nielsen and Hansen [12], the amount of carbon deposited on the metal catalysts decreases in the following order ... 

The comparison of deposition chemistry variables was made with other possible factors, which might affect the interaction of biogeochemical cycles of C, N, S, and P, like the climate patterns (annual precipitation and mean temperature). There was no correlation between these climate parameters and decomposition rates. This examination shows that atmospheric deposition chemistry is the most important factor affecting litter decomposition rates and carbon-to-element ratios at study sites along the gradient. 

Now let us take a look at some of the results of the analysis. Figure 4.32 shows the reactant composition and carbon deposition profiles computed from equations (4-147) and (4-148). Note that these are nonlinear and time-variant in shape as well as magnitude. Note also that the coke profiles show a decrease in content from bed inlet to bed outlet. This is directly the result of the fact that the reactant is the coke precursor so that, all other factors being the same, the maximum rate of coke deposition (and deactivation) will occur where the precursor is present in the greatest concentration, that is, at the bed inlet. Changing the nature of the C, versus s relationship, for example from exponential to linear, does not affect the general form of these trends. 

As it was discussed above, the carbon with small mesopores used as support produce high dispersion of the PtRu nanoparticles. However, in the fuel cell test they can show a poorer performance than the catalysts supported on Vulcan. Catalyst nanoparticles deposited in a tight pore might be tmconnected to the perfluorosulfonate ionomer and inaccessible to the methanol. However, other factors affect the triple phase boundary and in consequence the performance of the cell using small mesopores carbon supports. For example, the method of catalyst layer formation, including ink formation and dispersion of the catalyst... 

Measurements of friction factors and heat exchange efficiencies can indicate fouling. While all sorts of deposits can affect flow and heat transfer in an operating industrial system, biofilms are especially effective. A 165-pm thick biofilm shows 100 times the relative roughness of a calcite scale and a thermal conductivity close to that of water, that is, almost 100 times less than carbon steel [9]. 

A question must be raised as to why the tap water and the calcium bicarbonate washing treatments give such different results. The alkaline pH of the tap water suggests that calcium carbonate or bicarbonate is present and that the final product deposited in the fiber should be similar to that obtained with the pure bicarbonate solution. However, the chemical makeup of any city tap water is very complex and must contain a number of components that could affect the stability of cellulose. For example, the municipal treatment plant in Ottawa adds large amounts of alum (aluminum sulfate) to the water to settle particulate matter. Because alum makes the water very acidic, lime is then added to raise the pH. The result is that a large amount of calcium sulfate is present in the tap water and must affect the overall chemistry of the salts deposited in the fibers. One may further speculate that the anions present can influence the stability of cellulose as much as the cations. Any comprehensive understanding of the factors involved must include aH parameters. 

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