Metal phosphonates as heterogeneous catalysts for highly efficient chemical fixation of CO2 under mild conditions

In this study, two novel metal phosphonate networks based on zoledronic acid ((1-hydroxy-2-(1H-imidazol-1-yl)ethane-1,1-diyl)bis(phosphonic acid), abbreviated as EIBPA), with chemical formulas [Co-3(HEIBPA)(2)(H3PO4)(2)(H2O)(2)] and [Cd-3(HEIBPA)(2)(H2O)(4)]center dot 2H(2)O, namely, compounds 1 and 2, were successfully prepared under hydrothermal conditions. The obtained samples were fully characterized using PXRD, FT-IR, TGA and elemental analysis. The cobalt-phosphonate network has been introduced as an efficient catalyst to transform CO2 gas to cyclic carbonates with almost complete conversion and 100% selectivity under 1 atm pressure and free of solvent. The active centers of the catalyst are inferred to be Lewis acid sites and Bronsted acid sites in the structure of the compound. In addition, the catalyst can be recycled at least eight times without a significant decrease of the activity in the CO2 cycloaddition reaction.

Automated summary

Two novel metal phosphonate networks based on zoledronic acid were successfully prepared and used as efficient catalysts for the conversion of CO2 gas to cyclic carbonates. The active centers of the catalyst were identified as Lewis acid sites and Bronsted acid sites in the compound structure. Furthermore, the catalyst exhibited good recyclability.