F.H. Cao

Synthesis, characterization and catalytic performances of Cu- and Mn-containing ordered mesoporous carbons for the selective catalytic reduction of NO with NH3

A series of copper- and manganese-containing ordered mesoporous carbons (OMCs) were synthesized for the low-temperature selective catalytic reduction (SCR) of NO with NH3. The results demonstrated that NO conversion can be greatly improved by the addition of Cu or Mn. In addition, Cu and Mn had a synergetic effect and the optimal catalytic performance was obtained over the bimetallic catalyst Cu5Mn5-OMC. N2 sorption, small-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to confirm the ordered mesoporous structures. Wide-angle XRD results showed that in the bimetallic catalysts some Cu ions were substituted by Mn ions, resulting in lattice contraction by the formation of a solid solution. X-ray photoelectron spectroscopy (XPS) results indicated that the O–CO groups and chemisorbed oxygen species increased with the addition of Cu or Mn. Temperature-programmed desorption of CO/CO2 and NH3 (CO/CO2-TPD and NH3-TPD) results verified that the acidity of the catalyst was enhanced by the addition of Cu and Mn and the bimetallic catalyst Cu5Mn5-OMC had the strongest acidity. Temperature-programmed reduction of H2 (H2-TPR) results showed that Cu5Mn5-OMC had the strongest oxidizing capacity. Based on the above analysis, a possible synergetic catalytic effect was proposed through the electron transfer between Cu and Mn ions.

Adsorption of NO on ordered mesoporous carbon and its improvement by cerium

Ordered mesoporous carbon (OMC) was synthesized through a solvent evaporation-induced self-assembly method and used for NO adsorption. The structural properties, surface chemistry, and adsorption mechanism were investigated using nitrogen sorption, X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and temperature programmed desorption of CO and CO2. Results showed that the ordered mesoporous structure was synthesized and remained stable after exposure to NO and O2. The NO adsorption capacity of OMC was 16.35 mg gcat−1, which was 7.5 times that of activated carbon. This finding may be due to the large surface area of OMC and the full use of its mesopores. Characterization results showed that monodentate nitrito (–O–NO) was the adsorbed species, and it originated from the adsorption of NO on the oxidized C(O) sites formed by the oxidation of active free Cf sites. In addition, cerium was introduced into OMC to further improve its NO adsorption capacity to 18.61 mg gcat−1. The redox cycle between Ce4+ and Ce3+, which can provide excess adsorbed oxygen atoms to react with Cf sites and generate C(O) sites, may be responsible for the improved adsorption capacity.

Corrosion behavior of magnesium and its alloy in NaCl solution

The electrochemical behavior of cast Mg, AZ91, and cast AZ91 in 0.1 M NaCl solution is investigated by measuring open-circuit potential (OCP), steady-state current-potential, and electrochemical impedance spectra (EIS). The similar electrochemical impedance behavior is found of three corrosion electrodes. There are two capacitances in high-and medium-frequency domains and one inductive loop or component in low-frequency domain. From equivalent circuit simulation, cast AZ91 has the worst corrosion resistance. The EIS results are in good agreement with those obtained by OCP and polarization curves. Based on the Cao theory, a simple corrosion mechanism is put forward, supplying a possible explanation for low-frequency inductive behavior for Mg and its alloy in NaCl solution at OCP.