Mechanism for Catalytic Stability Enhancement of FeIII[CoIII(CN)6] by Doping Divalent Ions for Organophosphate Hydrolysis

• Published in: Journal of physical chemistry. C Vol. 126; no. 12; pp. 5564 - 5574
• Main Authors: Seki, Yusuke, Tabe, Hiroyasu, Yamada, Yusuke
• Format: Journal Article
• Language: English
• Published: American Chemical Society 31.03.2022
• Subjects: C: Chemical and Catalytic Reactivity at Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.2c00772

Catalytic activity and stability of iron hexacyanocobaltate (FeIII[CoIII(CN)6], Fe–Co) for organophosphate hydrolysis are improved by doping of divalent metal ions (M II = MnII, NiII, or CuII). The catalytic activity of a series of (FeIII 0.8MII 0.3)­[CoIII(CN)6] (FeM–Co compounds) was examined in a mixed solution of water and ethanol [9:1 (v/v)] containing disodium p-nitrophenyl phosphate (p-NPP) at 60 °C. FeM–Co compounds exhibited high conversions (≥60%, 25 h), which are about four times that of Fe–Co (16%). Repetitive catalytic examinations indicated that the conversion at the second runs in the systems using FeM–Co compounds maintained over 90% of those at the first runs. The low catalytic activity of Fe–Co in the mixed solution resulted from decomposition due to leaching of FeIII ions by ligand exchange from the CN ligand to p-NPP as evidenced by IR and XPS measurements for recovered precipitates after catalytic examination. Thus, the catalytic stability enhancement observed in FeM–Co compounds resulted from weaker interaction between p-NPP and FeIII ions, which can be evidenced by reduced surface acidity evaluated from temperature-programmed desorption of pyridine on the surfaces. The heats of pyridine adsorption on FeM–Co compound surfaces were around 60–80 kJ mol–1, which were less than half that of Fe–Co (160 kJ mol–1). Based on these results, a mechanism is proposed for securing Fe–NC bonds and enhancing the catalytic stability by doping of divalent metal ions to Fe–Co.