Surface groups basic

It has been suggested that the active sites for tiie ODE reaction over carbon catalysts are the basic surface groups [4]. As the air-treated composite possesses the greatest amount of CO-forming surface groups based on the sample wei t, while the HN03-treated composite... 

The silt fraction is particles 0.20-0.002 mm in diameter. This fraction or separate is produced by the same physical breakdown as described earlier for the formation of sand. Silt is more finely divided silica, but the surfaces are basically the same as those of sand (i.e., silicon and oxygen), and oxygen lone pairs of electrons and hydroxyl groups control its chemistry. Because the particles are smaller, they have more surface area per unit mass. This results in the availability of a greater number of bonds for chemical reactions [1],... 

The representation of the data for TiC in terms of the monoprotic surface group model of the oxide surface and the basic Stern model of the electric double layer is shown in Figure 5. It is seen that there is good agreement between the model and the adsorption data furthermore, the computed potential Vq (not shown in the figure) is almost Nernstian, as is observed experimentally. 

The reaction of Ru3(CO)i2 with MgO, independently of the degree of hydroxyl-ation, affords the surface anionic cluster [HRu3(CO)n], by nucleophilic attack of basic OH surface groups to a coordinated CO ... 

Adsorption of a specific probe molecule on a catalyst induces changes in the vibrational spectra of surface groups and the adsorbed molecules used to characterize the nature and strength of the basic sites. The analysis of IR spectra of surface species formed by adsorption of probe molecules (e.g., CO, CO2, SO2, pyrrole, chloroform, acetonitrile, alcohols, thiols, boric acid trimethyl ether, acetylenes, ammonia, and pyridine) was reviewed critically by Lavalley (50), who concluded that there is no universally suitable probe molecule for the characterization of basic sites. This limitation results because most of the probe molecules interact with surface sites to form strongly bound complexes, which can cause irreversible changes of the surface. In this section, we review work with some of the probe molecules that are commonly used for characterizing alkaline earth metal oxides. 

Aluminas are amphoteric, hence, they possess acidic and basic properties that are controlled by the surface groups or ions which terminate the microcrystallites [91]. The acidic and basic properties of these materials can be modified by the heat treatment conditions and by incorporating additives, such as halogen or alkali. 

The first chelate found to be electrocatalytic was cobalt phthalocyanine x>, which functions as an oxygen catalyst in alkaline electrolytes. Soon afterwards we were able to show 3,4,10,11) -that several phthalocyanines are also active in commercially important, sulfuric acid containing media. A comparison of various central atoms showed that activity increased in the order Cu Ni iron phthalocyanine, the nature of the carbon substrate plays a very important part FePc is more active on a carbon substrate with basic surface groups than on one with acid surface groups3). This property is however specific to phthalocyanines (Pc). 

The surface of the matrix side of cytochrome oxidase contains histidine and aspartate side chains close together. It has been suggested that they form a proton collecting antenna that contains groups basic enough to extract protons from the buffered matrix and guide them to a proton conduction pathway.154 Calcium ions also affect proton flow.153a b We will return to this topic in Section C,3 (p. 1040). 

Thus, the probable mechanism of catalytic redox transformation of the substrate within one catalytic domain is described in the framework of the BRC theory. It is implemented owing to two-proton transfer to the acidic-basic carrier (A1203) groups with electron transfer to active site perFTPhPFe(III)OH. In this context, of special attention are data on studies of qualitative and quantitative parameters of surface acidic-basic sites of inorganic matrices, including A1203 [8],... 

Alumina behaves as an amphoteric support due to acidity connected to OH surface groups (resulting from hydration of AI2O3) and basicity related to the available lone pairs on oxygen atoms. 

Furthermore, the increase in the scavenging rate of photoproduced electrons resulting from the presence of ozone should decrease the recombination rate of electrons and holes, and thereby augment the formation rate of hydroxyl radicals from basic OH surface groups and adsorbed water molecules (Fig. 1). 

The diverse types of oxygen functional groups determine the acidic and basic character of the carbon surfaces [175,182], The acidic character is typically linked with surface complexes like carboxyl, lactone, and phenol, while the basic nature is regularly assigned to surface groups, such as pyrone, ether, and carbonyl [173,178] (see Figure 2.32). 

In acidic medium the mechanisms are similar, althoguh the rate of is lower than at basic pH. Firstly, the density of surface states associated with 0HS surface groups, is smaller at acidic than at basic pH. Secondly, the overlapping between empty 02 levels and surface states considerably diminishes because of the shift towards positive nntentials of the semiconductor energy levels (including surface states) with respect to the pH independent °2 °2 redox potential (see Fig. 4). 

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