Obtenção de Nanotubos de Carbono a partir do CH4 usando catalisadores a base de Ni suportados em MgAl2O4 substituídos com Fe ou Mn

Abstract

This work aims to develop nickel catalysts supported on magnesium aluminate substituted with Fe or Mn, using chitosan as a chelating agent. For this, the materials were synthesized via microwave-assisted combustion, partially replacing the spinel B site with Fe or Mn, and the impregnation of the active phase was due to incipient moisture. The supports were subjected to X-ray diffraction analysis (XRD) in order to identify the formed phases and had their specific area and pore distribution evaluated by N2 adsorption using the BET and BJH methods, respectively. The catalysts were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), field emission scanning electron microscopy (FEG-MEV) and temperature programmed reduction (RTP). The synthesized catalysts were submitted to a catalytic bed reaction for CH4 decomposition and synthesis of carbon nanotubes (CNT). After the decomposition reaction, the CNT formed were evaluated by SEM-FEG and Raman spectroscopy. In XRD, peaks in 2θ of 18.7°; 31.2°; 36.8°; 44.6°; 55.6°; 59.2° and 65.8° confirm the obtaining of MgAl2O4 (ICSD31375). For the replaced samples there was the formation of different phases, Mg1Al1,9Fe0,1O4 (ICSD26847) and Mg0,7Fe0,23Al1,97O4 (ICSD89056) for MAF01Q; Mg0.5Fe0.5Al2O4 (ICSD 40314) and Mg0.7Fe0.23Al1.97O4 (ICSD89056) for MAF05Q and the Mg0.74Mn0.26Al2O4 phase (ICSD 180738) for samples MAM01Q and MAM05Q. In FTIR, the bands at 472 and 682 cm-1 confirm the formation of MgAl2O4, reinforcing the result obtained in XRD. The peaks at 44° and 63º in the XRD were attributed to NiO. The N2 physisorption analysis showed that the supports had a specific area between 19-39 m2/g, being classified as mesoporous and pore volume of a maximum of 0.06 cm3/g. The RTP allowed to evaluate the reduction profile of the catalysts in which strong Ni/support interactions were observed for Ni/MAQ, Ni/MAF01Q and Ni/MAF05Q samples. Reduction events in the range of 250-500°C were attributed to NiO reduction. Raman spectroscopy together with SEM confirmed, by the presence of RBM bands (radial breathing mode), D, G, 2D and characteristic morphology, the obtainment of carbon nanotubes.