Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article The Fe-Co-Cu supported on MWCNT as catalyst for the tri-reforming of methane – Investigating the structure changes of the catalysts Camila Emilia Kozonoe a , Rodrigo de Paiva Floro Bonfim b , Rita M. Brito Alves a , Martin Schmal a,b, ⁎ a Department of Chemical Engineering, University of São Paulo, Brazil b Federal University of Rio de Janeiro – COPPE/PEQ/Nucat, Rio de Janeiro, Brazil ARTICLE INFO Keywords: Functionalized MWCNTs Copper Iron Cobalt Methane Tri-reforming ABSTRACT In this work we synthesized Fe-Co-Cu catalysts supported on MWCNT, using a selective mode of addition of metal on functionalized MWCNT as mono and bimetallic catalysts. The Fe was inserted in the MWCNT after functionalization and Cu impregnated selectively. Co was added in sequence. The (Fe@MWCNT/Metal, (Metal = Cu and/or Co)) catalysts were tested for methane tri-reforming at 800 °C and GSVH 60,000 h -1 , for 24 h. The Fe@MWCNT/Cu catalyst was more active and very stable compared to the Fe@MWCNT/CuCo. The influence of the feed composition CH 4 :CO 2 :O 2 :H 2 O and H 2 /CO ratio were tested, indicating prevailing steam and reverse WGSR reactions. Both catalysts were very stable for 24 h. However, TG results of the functionalized MWCNT indicated destruction of the carbon at higher temperature in the presence of oxygen. In view of the good stability and high activity of these catalysts during the tri-reforming at 800 °C we searched the causes, analyzing the structure and morphology of these materials, using different methods, before and after reaction. In fact, the functionalized MWCNT was destroyed for this reaction condition. However, TGA, MEV-FEG, Raman and XRD results showed the presence of very small amounts of carbon and the appearance of different species and phases before and after reaction. These results evidenced that the functionalized MWCNT is like a sacrificial support, dispersing very well the active and metal oxide species, and the formation of new phases as isolated active and stable nano particles, which inhibit carbon formation. 1. Introduction The tri-reforming process for syngas production aims to convert natural gas without CO 2 separation with relative low energy con- sumption [1] and at the same time to reduce the CO 2 emissions. The tri- reforming of natural gas occurs in one reactor, coupling steam re- forming (1), partial oxidation (2) and dry reforming of methane (3). According to Świrk et al. [2], energy saving in the tri-reforming has several advantages, due to the presence/addition of H 2 O and O 2 , which would inhibit the coke formation, and therefore increase the lifetime. Another very important feature of the tri-reforming is that it is not necessary to handle pure oxygen, producing directly synthesis gas with a desirable H 2 /CO ratio (e.g. H 2 /CO = 1.0–2). The tri-reforming has been first reviewed by Song et al. [1]. Complete reviews for different processes for methane conversion have been presented recently by Świrk et al. [2], Ghoneim et al. [3] and many other papers [4–25], including the thermodynamics of the process, the possible conversions of methane and carbon dioxide for the tri-reforming and the single processes (SMR, DMR and POM). The most popular catalysts for tri-reforming of methane are nickel supported by a wide range of different materials (Al 2 O 3 , ZrO 2 , CeO 2 , etc). There is a risk of re-oxidation of the catalyst by oxygen present in the feed. For catalysts resistant to coke formation, re-oxidation can be the main reason of deactivation [26]. Sonǵs group studied different Ni supported catalysts for tri-re- forming and showed decreasing activity for different supports [27]. They also varied feed compositions of CH 4 :CO 2 :O 2 :He:H 2 O and tem- peratures between 700 and 850 °C. Ma et al. [28] studied nickel na- noparticles loaded on CNTs and tested them for the dry methane re- forming. The literature has reported that the support plays an important role in the product distribution and CNT have been suggested because they have special electronic properties and accessibility to metallic active sites and great stability in aggressive materials or inert surface, and thus permit to obtain high metallic dispersions. Dongil et al. [29] have re- ported that the interaction of metal-support is different when the metal is located inside the nanotubes influencing the chemical properties deposited outside the CNT. Moreover, there are different steric and https://doi.org/10.1016/j.fuel.2019.115917 Received 10 April 2019; Received in revised form 25 July 2019; Accepted 26 July 2019 ⁎ Corresponding author at: Department of Chemical Engineering, University of São Paulo, Brazil. E-mail address: schmal@peq.coppe.ufrj.br (M. Schmal). Fuel 256 (2019) 115917 Available online 01 August 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved. T