Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay Research Paper Catalytic activity of porphyrin-catalyts immobilized on kaolinite Thais E. Cintra a , Michelle Saltarelli a ,RosangelaM.deF.Salmazo a ,TiagoHonoratodaSilva a , Eduardo J. Nassar a, ⁎ , Raquel Trujillano b , Vicente Rives b ,MiguelA.Vicente b , EmersonH.deFaria a ,KatiaJ.Ciuf a, ⁎ a Universidade de Franca, Av. Dr. Armando Salles Oliveira, 201 - Pq. Universitário, 14404-600 Franca, SP, Brazil b GIR-QUESCAT, Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad de Salamanca, 37008 Salamanca, Spain ARTICLEINFO Keywords: Ironporphyrin Kaolinite Oxidation reactions Degradation of dyes ABSTRACT Two new biomimetic iron-porphyrin heterogeneous catalysts prepared by grafting of iron(III)-5,10,15,20-tet- rakis(4-hydroxyphenyl)porphyrin (FeTHPP) on 3-chloropropyltrimethoxysilane (ClPTMS) functionalized kaoli- niteandonasilicapreparedthroughhydrolysisandcondensationoftetraethylorthosilicate(TEOS)andClPTMS, arereported.Thecatalystswerecharacterizedandtestedfortheepoxidationof(Z)-cycloocteneandoxidationof cyclohexaneusingiodosylbenzeneasoxygendonor.ThepositionoftheSoretbandconfrmedthatthestructure ofFeTHPPwaspreservedinthe fnalsolids.Allcatalystsshowedahighconversionofthesubstrates,withtotal selectivitytotheepoxideintheoxidationofcyclooctene,andhighselectivitytotheketoneintheoxidationof cyclohexane.Thecatalystswerealsousedfordegradationofdyesinaqueoussolutions.Theferroporphyrin-silica catalystshowedthebestbehaviorfor(Z)-cyclooctene(48%epoxide)andcyclohexane(48%conversion,sumof alcoholandketoneasproducts)andalsoforthedegradationofthedyes(97%formethyleneblue,althoughwith simultaneous adsorption, close to 85% for Orange II and Brilliant Green), while the ferroporphyrin-kaolinite system showed the best behavior for cyclohexane oxidation (48%, with total selectivity to the ketone). 1. Introduction Heterogeneous catalysts have numerous applications in vital areas such as food production and the pharmaceutical and chemical in- dustries. An estimated 90% of all the chemical processes use hetero- geneouscatalysts,whicharealsousedinemergingfeldslike fuelcells, green chemistry, nanotechnology, biotechnology, and biorefneries (Boudartetal.,2008; Zaera, 2013). Considerableeforthasbeendevoted for improving the technology involved in the production of chemicals through oxidation reactions. Methods to accomplish the selective oxidation of organic substrates with atom economy (i.e., methods that use fewer atoms along the oxidation reaction) have become the largest research feld in today chemistry both in the academic and in the industrial felds (Sheldon, 2007; SheldonandWoodley,2018).Onestrategyhasbeentomovefrom harmful reagents and oxidants to more environmentally friendly sub- stances. Another strategy has been to reduce the amount of energy consumed throughout the oxidation process (Sheldon, 2007; Sheldon et al., 2007; Boudart et al., 2008; Cavani, 2010; Dichiarante et al., 2010). To achieve a higher efciency in the chemical industry and to ensure the development of greener and more selective catalytic oxidationreactions,moredetailedresearchinvolvingtransformationof certain types of molecules is mandatory. Investigations into new het- erogeneous catalysts and/or alternative oxidants that will help to en- hance reaction selectivity toward the target products still remain a challenge in the area of catalysis (Rothenberg, 2008; Deutschmann etal.,2009; Cavani, 2010; Vidaletal.,2018). The development of new active, selective, and recyclable catalysts withinthecontextofgreenchemistryisanurgentmatter.Theinterest in the search for new multifunctional hybrid materials that meet the requirements of Green Chemistry has grown recently. This is because hybrid materials combine maximum usability with environmental compatibility, mimicking Nature. To attain this goal, a selective heterogeneous catalyst should con- taining an isolated and well-defned active center resembling the prosthetic group of biological enzymes like the cytochrome P450 monooxygenases P450 (Thomas and Raja, 2006; Goti and Cardona, 2008; Stair, 2008; Jung, 2011), where a protein, globin, isolates the active site of P450, an iron protoporphyrin IX (Groves, 1995; Suslick, 1999; Costasetal.,2000; Meunieretal.,2004; Mansuy,2007).Among itsmanyfeatures,the“isolatedsiteprinciple”controlstheaccessofthe substrate to the active site and the oxidation reaction selectivity. The https://doi.org/10.1016/j.clay.2018.12.012 Received 21 June 2018; Received in revised form 3 December 2018; Accepted 11 December 2018 ⁎ Corresponding author. E-mail addresses: eduardo.nassar@unifran.edu.br (E.J. Nassar), katia.ciuf@unifran.edu.br (K.J. Ciuf). Applied Clay Science 168 (2019) 469–477 0169-1317/ © 2018 Elsevier B.V. All rights reserved. T