Ni/SiO2 fiber catalyst for syngas production from steam reforming of ethanol and acetic acid

Abstract

In this research, synthesis of Ni/silica fiber (NiSF) catalyst for hydrogen production in ethanol steam reforming was successfully synthesized by electrospinning technique following by conventional impregnation method. The effects of reaction temperature, steam to carbon ratio (S/C), weight to flow rate ratio (W/F) and Ni loading of the NiSF catalyst on the reaction activity and H2 production as well as CNTs characteristics (as a by-product) were investigated. The NiSF catalyst exhibited high activity to the simultaneous production of hydrogen and CNTs. The optimized conditions of ethanol steam reforming in terms of ethanol conversion and H2 yield were achieved at 600 °C, S/C of 9:1 and W/F of 18 gcath/mol with a maximum hydrogen yield of 55%. Whereas, the quality and the quantity of CNTs formation along with a H2 yield of 29% were obtained at Ni loading of 30 wt%, S/C of 1:1 and W/F of 9 gcath/mol. The novel carbon nanotubes-silica fiber composite (CNTs-SF-E) obtained from ethanol steam reforming exhibited relatively high surface area and easy accessibility, which can be applied as a support catalyst. Therefore, in the second part of this study, the CNTs-SF-E composite was applied as a support catalyst for Ni in ethanol steam reforming for hydrogen production by Ni loading at 5 and 10 wt%. The reaction performance of 10NiCNTs-SF-E catalyst was investigated and compared with that of Ni/silica fiber catalyst (10NiSF), and Ni/silica porous catalyst (10NiSP). The effect of temperature on ethanol conversion and products distribution was studied at low-temperature in the range of 300 and 500 °C. The 10NiCNTs-SF-E catalyst exhibited the best performance in term of stability and high activity at lower reaction temperature. The outstanding performance of 10NiCNTs-SF-E catalyst could be associated with high metallic dispersion and easy accessibility of ethanol to the active site. In the third part of this study investigated CNTs characteristics produced from steam reforming of different carbon sources: acetic acid and ethanol. Under the similar reaction conditions, ethanol was found to favor the growth of CNTs, while acetic acid was capable of the formation of both CNTs and curled shape filament carbon. Furthermore, CNTs obtained from acetic acid had larger outer diameters and a shorter length as compared to CNTs obtained from ethanol. The difference in the carbon formation could be attributed to the different number of oxygen atoms of both feed. The carbon nanotubes-silica fiber composite (CNTs-SF-A) produce from acetic acid was used as a support catalyst in acetic acid steam reforming, using 10NiCNTs-SF-E, 10NiSF and 10NiSP as comparative support. 10NiCNTs-SF-A and 10NiCNTs-SF-E catalysts exhibited high dispersion and smaller metal nanoparticles. Catalytic performances demonstrated that 10NiCNTs-SF-E exhibited significantly higher acetic acid conversion as compared with the other catalysts. The results of catalysts after 4 h of the reaction indicated that most of the carbon species over fibrous composite and fiber catalysts were relatively reactive carbon species which could be easily removed by oxidation, while carbon formation on 10NiSP was difficult to be removed and estimated the exact amount because 10NiSP surface was covered by a large amount of polymerized carbon.