Contentslistsavailableat ScienceDirect JournalofCO 2 Utilization journal homepage: www.elsevier.com/locate/jcou SynthesisandmorphologycontrolofnanoCuAl 2 O 4 hollowspheresandtheir applicationasanefcientandsustainablecatalyst forCO 2 fxation RezaKhalifeh a, *,MohammadKarimi a ,MaryamRajabzadeh a ,AliHafzi b , FarhadShahriariNogorani c a Department of Chemistry, Shiraz University of Technology, Shiraz, 71555-313, Iran b Department of Chemical Engineering, Shiraz University, Shiraz, 71345, Iran c Department of Materials Science and Engineering, Shiraz University of Technology, Shiraz, Iran ARTICLEINFO Keywords: Carbondioxidefxation Cyclic carbonates HollowCuAl 2 O 4 Heterogeneous catalysis Hydrothermal method ABSTRACT FourmorphologiesofthenanoCuAl 2 O 4 hollowmicrosphereweregeneratedviadiferentsynthesisconditions. The results revealed that the morphology, structure and number of the shells of the CuAl 2 O 4 product were stronglyassociatedwiththecarbontemplatesource,concentrationofmetalsaltsandhydrothermalprocessing time.Bychangingcarbontemplatesource,thehollowspheresofCuAl 2 O 4 transformedfromYolkshellstructure into triple shell hollow spheres. Further investigation also revealed that four types of the sample exhibited a varied catalysis performance for chemical fxation of carbon dioxide to produce cyclic carbonates with the efciency decreasing from the fower like triple-shelled CuAl 2 O 4 hollow spheres to the Yolk shelled CuAl 2 O 4 hollowspheres.Variousepoxideswereconvertedat85°C,0.3MPaCO 2 pressure,acatalystloadingof0.5mol% and a reaction time of 10h in a solventless reaction media with isolated yields up to 98 % of the respective carbonate. 1. Introduction Global warming and climate change due to greenhouse gases are amongthetopissuesofthecurrentera.Emissionofcarbondioxideinto theatmosphereasoneofthemostimportantgreenhousegasesmustbe controlled [1,2].Onewaytotacklethismajorglobalchallengeisthe storage and chemical utilization of CO 2 via converting it into value addedproducts[3].Recently,CO 2 isattractedmuchattentionasaC1 building block according to availability in large scale, cost efectivity, recycling to natural cycle, non-toxicity, nonfammability and high purityfrompointsources[4].Asteptowardorganictransformationsof CO 2 , would be the incorporation of CO 2 to epoxides due to simple operation,highyield,andtheharmlessnatureofthereagentsyielding fve-memberedcycliccarbonates[5–11]. Cyclic carbonates have diverse interesting applications such as green solvents [12], electrolytes in batteries [13], building blocks in organicsynthesis[14],rawmaterialforcosmetics[12], intermediates in the synthesis of ethylene glycol [15], acyclic carbonates [16] and polymers[17].Theyhavealsobeenfoundinnaturalproducts[18]and potential pharmaceuticals [19]. Therefore, development and fndinga new production technology for the synthesis of cyclic carbonates has becomeimportantforchemicalindustries.Numerouscatalyticsystems have been developed for synthesis of cyclic carbonates from CO 2 by cycloadditiontoepoxides.Recently,heterogeneouscatalystshavebeen developedandinvestigatedforCO 2 fxationastheycanreducethepost processing costs compared to the conventional homogenous catalysts. However,thesynthesisofaheterogeneouscatalystwithgoodactivity and high durability at mild conditions is challenging. Diferent het- erogeneouscatalystsincludingmetalorganicframeworks(MOF)[20], metalsaltsonoxides[21–25],supportedionicliquids[26],supported salen complex [27] and N-doped active carbon [28] have been em- ployedinCO 2 fxationreaction. Nanocrystalline aluminum-derived spinel structures are interesting class of metal oxides with high thermal stability, high mechanical re- sistance,hydrophobicityandlowsurfaceacidity[29–31].Theseprop- ertieshaveledtousethealumina-spinelsforpotentialstructuressuch ascatalystandcarrierforactivemetalsinhigh-temperatureprocesses [32]. Among the well-known aluminum-derived spinels, copper alu- minate(CuAl 2 O 4 )spinelsarerecognizedtobeactiveinthedegradation ofsomeorganiccompounds[33],reductionofNO 2 [34]andoxidation ofalcohols[35].Also,theyhavemanyapplicationsassensormaterials [36],andceramicpigments[37].Severalmethodshavebeenemployed for preparation of CuAl 2 O 4 . Solid-state reaction [38], co-precipitation [33], sol–gel method [35], micro- emulsion [39], sonochemical [40] https://doi.org/10.1016/j.jcou.2020.101233 Received29March2020;Receivedinrevisedform26June2020;Accepted27June2020 ⁎ Correspondingauthor. E-mail address: khalifeh@sutech.ac.ir (R.Khalifeh). Journal of CO₂ Utilization 41 (2020) 101233 2212-9820/ © 2020 Elsevier Ltd. All rights reserved. T