Co(II)-substituted α-Keggin-type 12-tungstenphosphate [(n-C(4)H(9))(4)N](4)H[PW(11)Co(H(2)O)O(39)]-(PW(11)Co) is synthesized and used as a single-component, solvent-free catalyst in the cycloaddition reaction of CO(2) and epoxides to form cyclic carbonates. The mechanism of the cycloaddition reaction is investigated using DFT calculations, which provides the first computational study of the catalytic cycle of polyoxometalate-catalyzed CO(2) coupling reactions. The reaction occurs through a single-electron transfer from the doublet Co(II) catalyst to the epoxide and forms a doublet Co(III)-carbon radical intermediate. Subsequent CO(2) addition forms the cyclic carbonate product. The existence of radical intermediates is supported by free-radical termination experiments. Finally, it is exhilarating to observe that the calculated overall reaction barrier (30.5 kcal mol(-1)) is in good agreement with the real reaction rate (83 h(-1)) determined in the present experiments (at 15 °C).
Recovering
phosphorus (P) from sewage sludge has been proposed
as a promising substitute for phosphate ores, while hydrothermal carbonization
(HTC) has emerged as an energy-efficient method for sewage sludge
treatment with substantial merits. Migration and transformation of
phosphorus in the sludge during HTC is vital for subsequent P recovery.
In this study, the role of pH and calcium additive (CaCl2) in the partitioning and transformation of phosphorus species as
well as the associated transformation mechanism was investigated via
Standards, Measurements, and Testing Program analysis, X-ray diffraction
analysis, and the aid of thermochemical equilibrium approach. The
results indicated that higher feedwater pH and dosage of CaCl2 favored the enrichment of phosphorus in the hydorchars with R
P > 80%, which was mainly presented as inorganic
phosphorus. The obvious transformation from nonapatite inorganic phosphorus
to apatite phosphorus was observed, promoting by higher feedwater
pH or dosage of CaCl2. Unlike the addition of CaO, Ca3(PO4)2, and Ca2P2O7 have been calculated as the main Ca-associated phosphorus
compounds at equilibrium state while less hydroxyapatite (Ca5(PO4)3OH) was reported. These findings were
confirmed by XRD analyses well. The work described here can provide
new insights into the phosphorus recovery from sewage sludge.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.