Copper phthalocyanine (CuPc) complexes immobilized on ''neat' ' and Ti 4? and Al 3? containing MCM-41 mimic the functionality of metalloenzymes. These novel materials catalyze the oxidation of benzyl alcohol to selectively benzaldehyde at moderate temperatures using peroxides and molecular oxygen as oxidant. Electron paramagnetic resonance and X-ray photoelectron spectroscopic studies revealed that the acidity of the support (MCM-41) influences the electronic structure of the immobilized CuPc. On acidic supports a part of copper in CuPc got reduced from a ''formal'' ?2 to ?1 oxidation state. This reduction of copper in its oxidation state on different supports decreased in the order: Al-MCM-41 (Brönsted and strong Lewis acid sites) [ MCM-41 (silanol sites) [ Ti-MCM-41 (weak Lewis acid sites). A linear variation in catalytic activity with the concentration of Cu 1? ions in different catalyst samples was observed. The study reveals that by suitably modifying the acidic properties of the support one can, in principle, fine-tune the electronic and catalytic properties of the active oxidation sites.

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Abstract:A novel non-precious multiwalled carbon nanotubes (CNTs)-supported metal oxide electrocatalyst was developed for methanol electrooxidation in alkaline medium. The catalyst was fabricated by simultaneous electrodeposition of copper-cobalt-nickel ternary nanostructures (CuCoNi) on a glassy carbon electrode (GCE) modified with CNTs. The proposed electrode was characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDX), and scanning electron microscopy (SEM). The electrochemical behavior and the electrocatalytic performance of the suggested electrode towards the oxidation of methanol were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) in alkaline medium. Several parameters were investigated, e.g., deposition time, potential scan rate, etc. Compared to Cu, Co, or Ni mono electrocatalysts, the electrode based on ternary-metals exhibited superior electrocatalytic activity and stability towards methanol electrooxidation. For instance, CuCoNi@CNTs/GCE has shown at least 2.5 times electrocatalytic activity and stability compared to the mono eletrocatalysts. Moreover, the present study found that the optimized loading level is 1500 s of simultaneous electrodeposition. At this loading level, it was found that the relation between the I p /ν 1/2 function and scan rate gives the characteristic features of a catalytic process. The enhanced activity and stability of CuCoNi@CNTs/GCE was attributed to (i) a synergism between three metal oxides coexisting in the same structure; (ii) the presence of CNTs as a support for the metal oxides, that offers high surface area for the deposited tertiary alloy and suppresses the aggregation and sintering of the metals oxide with time; as well as (iii) the increase of the conductivity of the deposited semiconducting metal oxides.

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