Adsorption and kinetics of dephosphorylation through P-OR ester bond scission, of phosphate monoesters on CeO2 surfaces are studied using DFT calculations, with relevance to the mitigation of environmental phosphorous contamination and recovery of phosphorous for recycle and reuse. The central P-atom of p-nitro phenyl phosphate (pNPP), methyl phosphate (MP), and phosphoric acid, binds strongly to lattice oxygen sites on CeO2(111) leading to the most stable adsorbed state (P/Olatt), as compared to binding of phosphoryl oxygen to lattice cerium atoms (P=O/Ce). The bonds between the central P and the adjacent oxygen atoms lengthen relative to the gas phase molecule in P/Olatt state, easing the P-OR ester bond scission. The reaction energies indicate that the adsorption of phosphates in their deprotonated states is favored with co-adsorption of dissociated hydrogen atoms. Distinct IR modes are identified to help distinguish between P=O/Ce and P/Olatt adsorption states. P-OR ester scission of phosphate monoesters leads to the formation of an alcohol along with HPO3, which is ultimately hydrated to form H3PO4. On CeO2(111), P-OR ester bond scission in the fully protonated p-NPP (H2-p-NPP) has a barrier of 0.13 eV, while hydration of HPO3 has a barrier of ~1.0 eV. The barrier for the ester bond scission increases with extent of deprotonation (H1-p-NPP- and H0-p-NPP2-), mirroring the kinetics of non-catalytic aqueous phase dephosphorylation. However, this is in contrast to the recently reported catalytic dephosphorylation on ceria, which is enhanced by increasing pH just like the activity of alkaline phosphatases, suggesting that the (111) facet may not be where the active site is located. A thorough investigation of the kinetics of dephosphorylation reaction on the three low index ceria facets is then performed to develop a comprehensive understanding of the reaction mechanism on low-index facets of ceria including (111), (110), and (100), which are variously exhibited by different shape-selected nanoparticles of ceria leading to markedly different dephosphorylation activities.

Theoretical investigation of the adsorption and dephosphorylation of phosphate monoesters on ceria surfaces

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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