Study On The Preparation Of Propylene Carbonate And Gamma-valerolactone

Chemical fixation of carbon dioxide?CO₂?has recently attracted much attention,owning to growing concerns about climate change and the need to exploit a user-friendly alternative C1 building block for our depleting and non-renewable fossil-based feedstock.From a sustainability point of view,CO₂ can be considered abundant,cheap,nontoxic,functional and renewable C1 resource,therefore much effort has been made for CO₂ conversion into valuable chemicals.One of the most attractive synthetic protocols is the atom-efficient cycloaddition of CO₂ with epoxides to afford five-membered cyclic carbonates,which are widely employed as polar aprotic solvents,electrolytes for lithium-ion batteries,the monomer units of polycarbonates,and the production of pharmaceuticals and fine chemicals.Biomass resource has been an important status in renewable energy field.Biomass resource can,not only provide energy,but also become important refined chemicals.The synthesis of gamma-valerolactone is one of the important routes of biomass conversion.The traditional reaction pathway is the hydrogenation levulinic acid wherein the presence of carboxylic acid groups may cause catalytic activity decline.But,the ethyl levulinate hydrogenation would not have these disadvantages.Titanate nanotubes?TNT?were found to be air-and water-tolerant,efficient,and recyclable Lewis acid catalysts towards the cycloaddition of carbon dioxide?CO₂?to propylene oxide?PO?for synthesis of cyclic propylene carbonate?PC?.Using TNT as the catalyst and potassium iodide,tetrabutylammonium bromide or tetraphenylphosphonium bromide as co-catalysts,PO was readily converted to PC with the yield up to >99.9% and PC selectivity of 100% under relatively mild conditions.An experimental research revealed that the TNT catalyst with the highest exposure of active sites,including surface hydroxyl groups and Lewis acid sites,proved to be the most active for the cycloaddition reaction.Our theoretical evaluation based on density functional theory calculation further indicated that the high Lewis acidity of TNT strongly reduces energy barrier for the ring-opening step through a polarization of C–O bond of PO,which allows a subsequent nucleophilic attack easily.Both experimental and computational studies demonstrated a synergetic effect between TNT and co-catalyst playing an important role in PC formation.TNT catalyst has richer insurface Lewis acid sites,shows large surface areas and mesoporous structures,and behaves as heterogeneous and recyclable nature,which makes TNT an excellent,interesting and ideal catalyst for chemical fixation of CO₂.For the synthesis of gamma-valerolactone,we prepared the Ru catalyst with the carbon nanotubes?CNT?as the carrier,and it has a very high catalytic activity,and the selectivity,yield of gamma-valerolactone is more than 99% in almost the room temperature.