A influência do estanho nas propriedades eletrônicas de catalisadores tipo Ni/Al2O3 na reforma a seco do metano (RSM) e uso do carbono depositado para a preparação de sensor químico

Abstract

Dry reforming of methane (RSM) is an important chemical process for producing synthesis gas with low H2/CO ratio. Ongoing research on the dry reforming methane (RSM) reaction points to the development of catalysts resistant to coke deposition. In this context, this work investigated the influence of tin on Ni/Al2O3 catalyst aiming at application in dry reforming reaction of methane. The xNiySn/Al type catalysts with different Ni/Sn mass ratios were synthesized by the Pechini method (polymeric precursors) and calcined in air and/or heat treated in N2 atmosphere. Characterization was done by means of XRD, FTIR, XPS, TPR, RAMAN, BET, SEM/EDS and TG/DTA techniques. The XRD results showed that larger amounts of the promoter metal (Sn) under the reduction conditions employed led to the formation of Ni-Sn bonds on the surface of the Ni particles (active metal) deactivating the catalyst. Conversely, low amounts of Sn improve the catalytic performance due to decreased coke production. Calculation of adsorption energies, via DFT, for the reactants: hydrogen, benzene, carbon dioxide and methane (dry reforming reactions of methane and hydrogenation of benzene), showed that the addition of Sn increases the electronic density on the Ni atom, decreasing the adsorption affinity of hydrogen and benzene. Thus, Sn becomes a good catalytic promoter favoring the performance of Ni/Al2O3 catalysts by decreasing the occurrence of parallel reactions that produce coke. The carbon deposited during the dry reforming of methane was used in the preparation of a chemical sensor for ammonia detection. The device containing only carbon did not show stability, but the compositions prepared with hematite (Fe2O3), or tin dioxide (SnO2) showed efficient detection of NH3, with detection limit of 2.4 ppm at 28 oC and relative humidity of 65%.