The intramolecular radical cation [2+2] cycloadditions of a series of bis(styrenes) have been explored by DFT (U)B3LYP method in conjunction with the 6-31G(d,p) and 6-311G(d,p) basis sets. According to our calculations, the pathway of the cycloaddition is stepwise via the formation of a 5-membered ring intermediate. The final cyclobutane products are formed by electron transfer between the long-bond radical cation product and the neutral reactant. The understanding of the mechanism gives a new insight into the stereoconvergency of the cycloaddition.
Computational methodsAll calculations were performed using the Gaussian 09 Programs. The geometries in the gas-phase were fully optimized with the DFT (U)B3LYP (Becke, 3-parameter, Lee-Yang-Parr) method. 28 Each structure of the stationary points along the reaction paths was classified as a minimum (no imaginary
Electrochemical hydrodesulfurization technology is a promising approach to remove sulfur compounds from fossil fuels, having the advantages of moderate operating condition, low energy consumption, and high automation. This method is still in the research and development stage, and the desulfurization efficiency needs to be improved. Here, we report an attempt to improve the desulfurization efficiency by increasing the active sites of catalysts. The amorphous MoS x are chosen as the catalysts and synthesized by the electrodeposition method at diffusionlimited conditions, which is regulated by either increasing the deposition potential or by adding glycerol into the electrolyte. With the decrease of chemical diffusion, the morphology of MoS x catalysts changes from continuous lamellae to dispersed nanoparticles on the surface of carbon cloth. Owing to the extensive exposure of the bridging sulfur groups S 2 2− and undercoordinated Mo(V) regions, the MoS x particles exhibit a more than two times increase of the desulfurization efficiency, reaching 22.5% in the electrochemical hydrodesulfurization. This study shows that structure optimization of catalysts by diffusion control is a facile and general strategy to improve reaction efficiency, which may be applied to various catalysts.
The antibiotic mycelial residue (AMR) generated from cephalosporin C production is a hazardous organic waste, which is usually disposed of by landfilling that causes potential secondary environmental pollution. AMR combustion can be an effective method to treat AMR. In order to develop clean combustion technologies for safe disposal and energy recovery from various AMRs, the emission characteristics of NOx and SO2 from AMR combustion were studied experimentally in this work. It was found that the fuel-N is constituted by 85% protein nitrogen and 15% inorganic nitrogen, and the fuel-S by 78% inorganic sulfur and 22% organic sulfur. Nitrogen oxide emissions mainly occur at the volatile combustion stage when the temperature rises to 400 °C, while the primary sulfur oxide emission appears at the char combustion stage above 400 °C. Increasing the combustion temperature and airflow cause higher NOx emissions. High moisture content in AMR can significantly reduce the NOx emission by lowering the combustion temperature and generating more reducing gases such as CO. For the SO2 emission, the combustion temperature (700 to 900 °C), airflow and AMR water content do not seem to exhibit obvious effects. The presence of CaO significantly inhibits SO2 emission, especially for the SO2 produced during the AMR char combustion because of the good control effect on the direct emission of inorganic SO2. Employing air/fuel staging technologies in combination with in-situ desulfurization by calcium oxide/salts added in the combustor with operation temperatures lower than 900 °C should be a potential technology for the clean disposal of AMRs.
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