A Rhombus-Like Tetrameric Vanadoniobate Containing Pseudo-Sandwich-Type {Li ⊂ V<sub>2</sub>O<sub>8</sub>(Nb<sub>5</sub>O<sub>14</sub>)<sub>2</sub>} and Its Electrocatalytic Activity for the Selective Oxidation of Benzyl Alcohol
Ni Zhen, Jing Dong, Zhengguo Lin, Wei Lü, Jie Li, Yingnan Chi, Changwen Hu
Abstract
Ongoing research on V-containing polyoxoniobates (PONbs) is driven by their diverse structures and potential applications. Although Lindqvist-type {Nb 6 O 19 } is a widely used building block in PONbs, vanadoniobates based on {Nb 6 O 19 } and/or its derivatives are still very limited. Herein, a discrete vanadoniobate, LiNa 14 K 11 [Li 2 ⊂ V IV 8 Nb 32 O 110 ]·45H 2 O ( 1 ), has been synthesized by a hydrothermal method, which shows a rhombus-like tetrameric structure composed of two {V 2 O 6 (Nb 6 O 19 )} and two {Li ⊂ V 2 O 8 (Nb 5 O 14 ) 2 } subunits derived from {Nb 6 O 19 }. Notably, the {Li ⊂ V 2 O 8 (Nb 5 O 14 ) 2 } subunit has an interesting pseudo-sandwich-type structure, where a {LiV 2 O 8 } belt is coordinated by two monolacunary {Nb 5 O 14 } molecules and the central site of the cluster is occupied by Li + . Considering that 1 has both basic hexaniobates and redox active V centers, 1 was used as a noble metal-free electrocatalyst for the selective oxidation of benzyl alcohol to benzaldehyde, achieving complete conversion of benzyl alcohol with 94% selectivity for benzaldehyde in 3 h under ambient conditions without using any alkaline additives. Moreover, the catalytic performance of 1 remained largely unchanged after four cycles.