Adição de vanádio ao catalisador de níquel disperso em sílica aplicado na reação de reforma a seco do metano

Abstract

Methane dry reforming can be used as an alternative to methane and carbon dioxide mitigation. This process can reduce the environmental impact and is economically viable since it produces syngas. The drawback of this reaction is the carbon deposition (coke) on the catalyst surface, causing the deactivation process. To investigate the properties of coke and get high conversions of CH4 and CO2, it was studying the effect of addition of vanadium (V) to the catalyst NiSi in methane dry reforming reaction, varying the temperature (600°C, 700°C and 800°C) and reactive composition (CH4/CO2= 0.5, 1 and 2). The catalysts (NiSi and NiVSi) were synthesized by the polymeric precursor method and characterized by optical emission spectroscopy with inductively coupled plasma (ICP-OES), N2 adsorption/desorption isotherms, X-ray diffraction (XRD) and temperature-programmed reduction (TPR). The post-test catalysts characterization was done by temperature-programmed oxidation (TPO), thermogravimetric analysis (TG), Raman spectroscopy and scanning electron microscopy (SEM). After the catalytic test, the coked catalyst underwent acid treatment with hydrofluoric acid and acid chloride and was analyzed by XDR and TG. The N2 adsorption/desorption analysis showed that both catalysts are mesoporous with high surface area and pore volume. By XRD, it was observed that the addition of vanadium affects the sintering process of the nickel oxide and, the TPR shows the NiO reduction band shifting to a higher temperature. Such observations may be due to the formation of the Ni3V2O8 phase. The catalytic tests indicate that NiVSi catalyst exhibits higher conversions of CH4 and CO2 compared to NiSi, except for the condition of 800°C and CH4/CO2 ratio of 1.0. TPO analysis suggests the formation of multi-wall carbon nanotubes. The best experimental condition for the synthesis gas generation is the catalyst NiVSi provided 800°C and CH4/CO2 ratio equal to 1.0. However, for carbon nanotubes production, the catalyst NiVSi provides the best conditions at 800°C and CH4/CO2 ratio of 2.0. In such conditions, the H2/CO ratio was 1.2, with high coking (42%) and carbon nanotubes with smaller ratio ID/IG obtained via Raman spectroscopy.