Phthalocyanine catalytic behavior

The simple porphyrin category includes macrocycles that are accessible synthetically in one or few steps and are often available commercially. In such metallopor-phyrins, one or both axial coordinahon sites of the metal are occupied by ligands whose identity is often unknown and cannot be controlled, which complicates mechanistic interpretation of the electrocatalytic results. Metal complexes of simple porphyrins and porphyrinoids (phthalocyanines, corroles, etc.) have been studied extensively as electrocatalysts for the ORR since the inihal report by Jasinsky on catalysis of O2 reduction in 25% KOH by Co phthalocyanine [Jasinsky, 1964]. Complexes of all hrst-row transition metals and many from the second and third rows have been examined for ORR catalysis. Of aU simple metalloporphyrins, Ir(OEP) (OEP = octaethylporphyrin Fig. 18.9) appears to be the best catalyst, but it has been little studied and its catalytic behavior appears to be quite distinct from that other metaUoporphyrins [CoUman et al., 1994]. Among the first-row transition metals, Fe and Co porphyrins appear to be most active, followed by Mn [Deronzier and Moutet, 2003] and Cr. Because of the importance of hemes in aerobic metabolism, the mechanism of ORR catalysis by Fe porphyrins is probably understood best among all metalloporphyrin catalysts. 

Ship-in-Bottle Synthesis of Sterically Crowded Fe-Phthalocyanines in NaY Zeolite Hosts and Their Catalytic Behavior in Regioselective Oxidation of Alkanes... 

While much interest has been on the use of mononuclear Pcs as surface modifies, there has been a growing interest in the use of binuclear phthalocyanines (BiPcs) in the past decade as Table 1 shows [47-54], and hence, they deserve a separate section. In contrast to mononuclear Pcs, BiPcs have more redox processes and can have double the concentration of central atoms per single molecular unit. Hence, it is anticipated that they should demonstrate stronger catalytic behavior compared to mononuclear Pcs and show high thermal and photochemical stability properties. As a result, BiPcs have been used to functionalize ordered mesoporous carbon (OMC) [47] and SWCNT [48]. This section presents a summary of the use of... 

Similar behavior has been very recently observed in cobalt phthalocyanines bearing dendritic substituents [122], In 47, Co is oxidized in methanol in a mono-electronic reversible wave, whereas in 48 no clear oxidative wave is observed, suggesting that the electroactive core is encapsulated in the dendritic structure. The ability of the Co-phthalocyanine core of 47 and 48 to catalyze oxidation of 2-mer-captoethanol in the presence of oxygen was also investigated. The two compounds exhibit similar catalytic activity, indicating that the dendritic structure does not hinder penetration of small molecules 48 showed, however, an enhanced catalytic stability which was ascribed to the encapsulation of the core. 

The zeolite-encapsulated iron phthalocyanine catalyst exhibited a similar behavior. When the oxygen uptake in the first run had ceased, 1-decene was injected into the reactor (second run), and the oxygen uptake was measured again. A similar rate was measured in the second run as in the first one, i.e. the catalytic activity did not decrease during the oxidation reaction, in spite of the presence of the strong acid HCIO4 in the reaction mixture. 

Platinum group metal phthalocyanine monomers adsorbed on GCE auto-catalyze the oxidation of cysteine depending on the nature of axial ligands. Table 7.2. When DMSO or cyanide were employed as axial ligands, autocatalytic behavior was observed. Figure 7.2. These complexes also catalyzed the oxidation of methionine, hydroxylamin, and hydrazine. Ring based redox processes were implicated in the catalytic process shown by the following mechanism (Equations (7.8H7.10)) ... 

Most catalysts investigated usually have Fe and Co as metal centers. However, complexes of other metals have also been studied. For example, CrTSPc and MnTSPc exhibit catalytic activity for ORR [14] and they somehow resemble the behavior of Fe complexes, especially MnTSPc, in the sense that it shows a prewave where O2 reduction proceeds entirely via four electrons to give water. Peroxide is produced at higher polarizations. The lower activity of Cr and Mn phthalocyanines compared to Fe phthalocyanines can be attributed to their low redox potential, that is, they are easily oxidized [82, 105]. The activity of most macrocyclic metal complexes increases after heat treatment [145]. However, the opposite is observed for manganese complexes probably because the metal is lost from the N4 stmcture. So, most work dealing with heat-treated materials has focused on Fe and Co macrocycles. Complexes of Mo can only be used in alkaline solution since they are not stable in acid media. MoNPc is less activity than FeNPc as reported by Magner [146]. 

These inorganic systems have attracted much attention due to their potential applications in the design of electronic devices and catalytic process, among other fields [68-70]. Metal phthalocyanine (MPc) represents one of the most promising classes owing to its unique electronic properties and chemical stability. In the literature it is possible to find the MPc (M = Fe, Co and Cu) adsorption behavior on... 

Substitution at axial sites in metalloporphyrins and phthalocyanins is important in the context of their behavior as models for biological systems and for their potential catalytic properties. The reaction of imidazole (Him) with phthalocyaninatoiron(II) in DMSO has been reinvestigated and shows two distinct relaxation processes as shown in Eq. (2) and (3). Forward rate constants were kif=9.8 0.2x 10 s , k2f= 5.4 + 0.15 s ... 

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