Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Research Paper Vermiculites from Brazil and Palabora: Structural changes upon heat treatment and infuence on the depolymerization of polystyrene Marta Valášková a, ⁎ , Jana Madejová c ,AmerInayat a , Lenka Matějová a ,MichalRitz b , Alexandr Martaus a , Pavel Leštinský a a Institute of Environmental Technology, VŠB-Technical University of Ostrava, 17. listopadu 2172/15, Ostrava, Poruba 708 00, Czech Republic b Faculty of Material Science and Technology, VŠB-Technical University of Ostrava, 17. listopadu 2172/15, Ostrava, Poruba 708 00, Czech Republic c Institute of Inorganic Chemistry, SAS, Dúbravská cesta 9, 845 36 Bratislava, Slovakia ARTICLEINFO Keywords: Vermiculites Polystyrene Thermal changes X-ray difraction Infrared spectroscopy Raman spectroscopy ABSTRACT Although clay minerals have been widely used as catalysts and catalyst supports, the reports of natural clay minerals studied in their role as a catalyst are still rare. This work, therefore, for the frst time reports the possible catalytic efects of the two raw vermiculites from Brazil (VerS) and Palabora (VerP) on the depoly- merization of polystyrene (PS). The main experimental methods used to obtain a detailed structural char- acterization of vermiculites before and after the depolymerization experiment were X-ray powder difraction (XRD),thermogravimetricDTA/TGanalysis,infrared(FT-IR)andRamanspectroscopy.Thedetailedassignment ofthevibrationbandsofvermiculitesoccurringinthenear-IRandtheanalysisofcarboncoatingsonthesurface of vermiculite using Raman spectra are performed for the frst time. The thermal products of PS are styrene monomer(SM)about54.5mass%andpyrolyticvolatileoligomers(dimersandtrimers)about32.1mass%.The presence of VerS and VerP changes the relation between SM (about 50.7 and 53.6 mass%, respectively) and oligomers(about37and33.3mass%)duetothepyrolyticcarbonsdepositedontheVerSascokeandontheVerP asglassycarbon.Thevariableyieldsoftheproductscanbeattributedtothenaturalvermiculitepropertiessuch as are diferent negative layer charge emerging from the cation substitution in tetrahedra, number of water molecules released during thermal treatment, and textural properties (S BET and pores). 1. Introduction Clay-based and clay-supported catalysts as a suitable eco-friendly chemistrymaterialarestudiedforalongtime(e.g. Laszlo,1987; Brown and Rhodes, 1997; Theng, 2018). Among these catalysts, smectites (mostlymontmorillonites)showahighselectivityincatalyzingorganic reactions and syntheses (e.g. Adams and McCabe, 2006; Schoonheydt, 2016).Mostofthecatalyticprocessesmakeuseoftheacidicproperties of the montmorillonites, which derive from the dissociation of inter- layer water molecules coordinated to the exchangeable cations (MortlandandRaman,1968; Purnell,1990).Montmorillonitesoracid- treated montmorillonites have been used as solid acid-catalysts for numerous reactions, some on an industrial scale, e.g. the dimerization of unsaturated fatty acids to dicarboxylic acids and the alkylation of phenols, whereas others have been used at laboratory scale (Adams et al., 1983). Koster et al. (1998) found that the activity of montmor- illonite for any dimerization of oleic acid is dependent on the tetra- hedral substitution. The thermal conversion of heavy oils in the presenceofclaymineralsperformedbytheinsitucombustionmethod atthelow-temperatureoxidationconditionswasalsoreported(e,g. Kok and Gundogar, 2010; Zhengetal.,2019). Montmorillonitescanbeactivatedusingacidtreatment,heatingand microwave /ultrasound irradiation to promote catalytic activity (e.g. Steudeletal.,2009; Korichietal.,2012; Komadel,2016),regardlessof thefactthatsuchtreatedmontmorillonitesarebehindthecommercial modifedmontmorillonitecatalystsastheK10orKSF(Süd-Chemie)and theFe III -exchangedK10catalysts(e.g. LaszloandLucchetti,1984).The invention of thermally stable pillared clays in 1970 opened the ex- ploitationofclaysassolidacidcatalysts(e.g. Pinnavaia, 1983; Chitnis and Sharma, 1997). In addition to montmorillonites, vermiculites can also possess acid sites. Vermiculites are mixed-layer or interstratifed 2:1 phyllosilicates withthenegativelayerchargeof0.6–0.9eq/(Si,Al) 4 O 10 ,arisingmostly fromthesubstitutionofSi IV byAl III andFe III intetrahedraincontrastto montmorillonites with negative layer charge originated mainly in the octahedralsheets.Thesurfaceofboth,montmorilloniteandvermiculite https://doi.org/10.1016/j.clay.2020.105639 Received21February2020;Receivedinrevisedform21April2020;Accepted22April2020 ⁎ Corresponding author. E-mail address: marta.valaskova@vsb.cz (M. Valášková). Applied Clay Science 192 (2020) 105639 Available online 04 May 2020 0169-1317/ © 2020 Elsevier B.V. All rights reserved. T