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ZnCl2-modified activated carbon supported nanoscale zero-valent iron material (nZVI/BC600) was synthesized by green carbothermal reduction and liquid phase reduction to explore the removal efficiency of U(VI) under different conditions. The results showed that under the optimal conditions (C0 = 10 mg/L, C/Fe = 5:1, pH = 5.5, t = 30 min), the removal rate of U(VI) by nZVI/BC600 was 99.68%, which was 9.18% higher than that of ZnCl2-modified activated carbon and conformed to the pseudo-second-order kinetic model. SEM and XPS analysis showed that nZVI was uniformly distributed on activated carbon, and U(VI) was reduced to U(IV) or U(V). The removal mechanism of U(VI) by nZVI/BC600 is chemical adsorption, redox and co-precipitation. [ABSTRACT FROM AUTHOR]

Ceria catalysts have attracted considerable interest in the NH3-SCR reaction. The modification of SO42− into CeO2 promotes the NH3-SCR reaction. NH3 adsorption property and four possible reaction paths are further design over CeO2 (111) and SO42−–CeO2 (111) surface. The results reveal that NH3 adsorption of the Lewis acid site is stronger than the Brønsted acid site, and the adsorption energies of the Lewis acid site range from − 0.397 to − 0.963 eV with the modification of SO42−. Thus, the introduction of SO42− into CeO2 increases the adsorption site stability of NH3. NH3 adsorption is the first step in NH3-SCR reaction, and then, the key intermediates such as NH2, NH2NO, NNOH, NH3NO2 species are found. Standard SCR reaction and fast SCR reaction constitute a catalytic cycle in CeO2 catalyst. The different paths of NH3NO2 and NH2NO formation are different, and it led to NNOH only emerge in the fast SCR reaction. Lewis acid site is main reaction site for the standard SCR reaction. Energy barriers of Lewis acid site range from 15.82 to 15.68 kcal/mol by the introduction of SO42−, which makes the NH3-SCR reaction easily occur. [ABSTRACT FROM AUTHOR]

HCN catalytic hydrolysis mechanism over Cu-ZSM-5 was investigated based on the density functional theory (DFT) with 6-31++g (d, p) basis set. Five paths (A, B, C, D, and E) were designed. For path A and path B, the first step is the nucleophilic attack of water molecule. Next, the hydrogen atom of H2O is transferred to the nitrogen atom first for path A, while in path B, the hydrogen atom of the HCN is first transferred to the nitrogen atom. In path C, HCN isomerizes to HNC initially, and the remaining steps are similar to that of path A. The H atom of HCN shifts to Cu-ZSM-5 initially in path D, and the H atom is transferred to N atom subsequently. The last step is the attack on water molecule. The first step for path E is similar to that of path D. The next step is the attack on water molecule, in which the H atom of water molecule shifts to N atom, and the H on Cu-ZSM-5 shifts to the N atom. Meanwhile, the H atom of oxygen atom is transferred to the N atom. The results show that path C is the most favorable path, with the lowest free energy barrier (35.45 kcal/mol). The results indicate that the Cu-ZSM-5 strongly reduces the energy barrier of HCN and isomerizes to HNC, making it an effective catalyst for HCN hydrolysis. [ABSTRACT FROM AUTHOR]