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The chemical reduction of carbon dioxide (CO2) has always drawn intensive attentions as it can not only remove CO2 which is the primary greenhouse gas but also produce useful fuels. Industrial synthesis of methanol utilizing copper-based catalysts is a commonly used process for CO2 hydrogenation. Despite extensive efforts on improving its reaction mechanism by identifying the active sites and optimizing the operating temperature and pressure, it is still remains completely unveiled. The selectivities of CO2 electroreduction at copper electrode could mainly be towards carbon monoxide (CO), formic acid (HCOOH), methane (CH4) or ethylene (C2H4), which depends on the chemical potentials of hydrogen controlled by the applied potential. Interestingly, methanol could hardly be produced electrochemically despite utilizing metallic copper as catalysts in both processes. Moreover, the mechanistic researches have also been performed aiming to achieve the higher selectivity towards more desirable higher hydrocarbons. In this work, we review the present proposals of reaction mechanisms of copper catalyzing CO2 reduction in industrial methanol synthesis and electrochemical environment in terms of density functional theory (DFT) calculations, respectively. In addition, the influences of the simulation methods of solvation and electrochemical model at liquid-solid interface on the selectivity are discussed and compared.

A novel, bioadsorbent material of polyethylenimine-modified magnetic chitosan microspheres enwrapping magnetic silica nanoparticles (Fe3O4-SiO2-CTS-PEI) was prepared under relatively mild conditions. The characterization results indicated that the adsorbent exhibited high acid resistance and magnetic responsiveness. The Fe3O4 loss of the adsorbent was measured as 0.09% after immersion in pH 2.0 water for 24 h, and the saturated magnetization was 11.7 emu/g. The introduction of PEI obviously improved the adsorption capacity of Cr(VI) onto the adsorbent by approximately 2.5 times. The adsorption isotherms and kinetics preferably fit the Langmuir model and the pseudo-second-order model. The maximum adsorption capacity was determined as 236.4 mg/g at 25 degrees C, which was much improved compared to other magnetic chitosan materials, and the equilibrium was reached within 60 to 120 min. The obtained thermodynamic parameters revealed the spontaneous and endothermic nature of the adsorption process. Furthermore, the Cr(VI)-adsorbed adsorbent could be effectively regenerated using a 0.1 mol/L NaOH solution, and the adsorbent showed a good reusability. Due to the properties of good acid resistance, strong magnetic responsiveness, high adsorption capacity, and relatively rapid adsorption rate, the Fe3O4-SiO2-CTS-PEI microspheres have a potential use in Cr(VI) removal from acidic wastewater. (C) 2015 Wiley Periodicals, Inc.