Improved Catalytic Performance toward Selective Oxidation of Benzyl Alcohols Originated from New Open-Framework...

A new organic-inorganic hybrid open-framework molybdovanadate with mixed-valences of vanadium (V⁴⁺ /V⁵⁺ =4/3) and molybdenum (Mo⁵⁺ /Mo⁶⁺ =8/2) cations has been synthesized. The complex possesses the unique V/Mo ratio (7/10), fascinating 8-C topological network and 1D 4-MR channels (7.793 Å×6.699 Å). Importantly, its catalytic activities for the selective oxidation of benzyl alcohol to benzaldehyde (oxidant: H₂ O₂ , 30 wt %) have been well evaluated. The results indicated that it exhibited improved catalytic activities (conv.: 96.8 %) compared with the catalyst (Cpyr)₅ PV₂ Mo₅ W₅ O₄₀ [conv.: 88.51 %, Cpyr=(C₁₆ H₃₂ C₅ H₄ N)⁺ )], high recyclability and structural stability. Moreover, the conversions and selectivities (conv.: 82.4-92.5 %; sele.: 91.5-95.7 %) of the substrates containing electron donating groups (-OH, -CH₃ , -OCH₃ and -Cl) were significantly higher than those of the substrate containing electron withdrawing group (-NO₂ ) (conv. 67.4 %; sele.: 80.8 %). This is due to the fact that the -NO₂ with a large Hammett substituent constant is not conducive to the generation of transition state products. The studies revealed the complex could act as a highly efficient heterogeneous catalyst in selective oxidation of benzyl alcohols.