Mechanism of dichloromethane disproportionation over mesoporous TiO2 under low temperature

Mesoporous TiO2 was synthesized via nonhydrolytic template-mediated sol-gel route.Catalytic degradation performance upon dichloromethane over as-prepared mesoporous TiO2,pure anatase and rutile were investigated respectively.Disproportionation took place over as-made mesoporous TiO2 and pure anatase under the presence of water.The mechanism of disproportionation was studied by in situ FTIR.The interaction between chloromethoxy species and bridge coordinated methylenes was the key step of disproportionation.Formate species and methoxy groups would be formed and further turned into carbon monoxide and methyl chloride.Anatase(001)played an important role for disproportionation in that water could be dissociated into surface hydroxyl groups on such structure.As a result,the consumed hydroxyl groups would be replenished.In addition,there was another competitive oxidation route governed by free hydroxyl radicals.In this route,chloromethoxy groups would be oxidized into formate species by hydroxyl radicals transfering from the surface of TiO2.The latter route would be more favorable at higher temperature.

Research progress in green synthesis of ammonia as hydrogen-storage carrier under‘hydrogen 2.0 economy’

Hydrogen energy is characterized by its environmental friendliness,high efficiency,lack of carbon emissions and wide range of applications.However,its transportation and storage are challenges that limit further development of the hydrogen-energy industry.Ammonia is a carbon-free hydrogen-rich carrier.The storage of hydrogen in ammonia has unique advantages of high energy density,easy storage and transportation,reliable safety,a mature industrial foundation and no tail-end carbon emissions.However,industrial ammonia synthesis still heavily relies on the Haber-Bosch process,which accounts for significant energy consumption and greenhouse gas emissions.Therefore,the development of green and sustainable ammonia-synthesis methods is extremely important and urgent.Recently,ammonia-synthesis technologies such as electrocatalysis,photocatalysis,photoelectrocatalysis and biocatalysis have successfully produced ammonia from nitrogen and water,resulting in lower costs.The nitrogen-reduction-reaction conditions of these methods are mild and can be carried out under ambient temperatures and atmospheric pressure with low energy consumptions.Meanwhile,these methods bypass the traditional hydrogen-production section and their routes are simpler.Therefore,these technologies can be used to flexibly integrate renewable energy,including intermittent renewable energy,to achieve distributed ammonia synthesis.These benefits contribute to both global energy and environmental sustainability goals.In this study,the mechanisms of ammonia synthesis under ambient conditions are reviewed and the technical difficulties of various catalysts for ammonia synthesis are summarized.Based on the optimization strategies reported for various catalysts,the high-performing catalysts reported for ammonia synthesis are reviewed and the developmental trend of this field has been forecasted.