Heterogeneous Catalysis of Lanthanoid Ions for the Hydrolysis of p-Nitrophenyl Phosphate Enhanced by Incorporation to Cyano-Bridged Heterometallic Coordination Polymers

Abstract

Solid materials containing lanthanoid ions (LnIII = TbIII or EuIII), i.e., lanthanoid oxide (LnIII 2O3), lanthanoid ions immobilized on silica–alumina by cation exchange (LnIII/Al-SiO2), and lanthanoid ions incorporated into cyano-bridged heterometallic coordination polymers ([LnIII(H2O) x ] y ­[MC(CN)6], LnIII = TbIII or EuIII; MC = FeIII or RuII; x ≥ 2), were examined as heterogeneous catalysts for hydrolysis of p-nitrophenyl phosphate (p-NPP). LnIII 2O3 and LnIII/Al-SiO2 exhibit lower catalytic activity (∼50% and ∼55% for 72 h, respectively) than LnIII ions used as homogeneous catalysts (∼65%) for the hydrolysis of p-NPP. Ex situ IR measurements after the hydrolysis of p-NPP indicated that active sites of the heterogeneous catalysts were inhibited by a product of dihydrogen phosphate. On the other hand, [LnIII(H2O) x ] y [MC(CN)6] exhibited higher activity (≥81%) for the hydrolysis of p-NPP compared with not only the homogeneous LnIII-ion catalysts but also cyano-bridged heterometallic coordination polymers containing 3d-metal ions such as FeIII ions (38%) previously reported as active catalysts. The high activity of [LnIII(H2O) x ] y [MC(CN)6] resulted from suitable interaction among LnIII ions in the coordination polymers, p-NPP, and water as evidenced by the ex situ IR measurements.

Synergistic Effect of FeII and MnII Ions in Cyano-Bridged Heterometallic Coordination Polymers on Catalytic Selectivity of Benzene Oxygenation to Phenol

“…Catalysts for selective oxidation or reduction with high robustness and recyclability have been prepared using coordination polymers, because the electronic properties and coordination environment of metal ions can be tuned using appropriate bridging ligands. − Several coordination polymers have been developed for benzene oxygenation. − Recently, cyano-bridged heterometallic coordination polymers composed of CN – ions as the bridging ligands have been utilized as heterogeneous catalysts for various acid–base and redox reactions including benzene oxygenation. − The cyano-bridged heterometallic coordination polymers composed of Fe II and Ru II ions ([Fe II (H 2 O) 3 ] 2 [Ru II (CN) 6 ]) incorporated in mesoporous silica–alumina have been reported to act as a photocatalyst for benzene oxygenation to phenol using molecular oxygen as an oxygen source (Figure a) . However, the conversion of benzene to phenol was as low as 0.6% for 24 h at the optimum conditions due to limited diffusion of benzene in the interior space of the mesoporous silica–alumina.…”