Catalytically active sites carbon dioxide addition

Transition metal catalysts, specifically those composed of iron nanoparticles, are widely employed in industrial chemical production and pollution abatement applications [67], Iron also plays a cracial role in many important biological processes. Iron oxides are economical alternatives to more costly catalysts and show activity for the oxidation of methane [68], conversion of carbon monoxide to carbon dioxide [58], and the transformation of various hydrocarbons [69,70]. In addition, iron oxides have good catalytic lifetimes and are resistant to high concentrations of moisture and CO which often poison other catalysts [71]. Li et al. have observed that nanosized iron oxides are highly active for CO oxidation at low tanperatures [58]. Iron is unique and more active than other catalyst and support materials because it is easily reduced and provides a large number of potential active sites because of its highly disordered and defect rich structure [72, 73]. Previous gas-phase smdies of cationic iron clusters have included determination of the thermochemistry and bond energies of iron cluster oxides and iron carbonyl complexes by Armentrout and co-workers [74, 75], and a classification of the dissociation patterns of small iron oxide cluster cations by Schwarz et al. [76]. 

Addition of certain metal cations to MgO increased the catalytic activity. In the case of Cr and Zr ion addition, the catalytic activity reaches maximum at the amount of metal cation of 0.5 —1.0%. The increases in activity were attributed to the increase in the strength of base sites caused by the addition of proper amounts of the metal cations. The increase in base strength on addition of proper amounts of metal cations was confirmed by TPD experiments for adsorbed carbon dioxide on the catalysts. 

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