On the synergic effect of various anti-coke materials (Ca–K–W) and glow discharge plasma on Ni-based spinel nanocatalyst design for syngas production via hybrid CO2/O2 reforming of methane

Abstract

Ni-based spinel nanocatalysts (NiAl₂O₄) with various anti-coke materials (Ca, K and W) were fabricated with sol-gel technique followed by plasma treatment and evaluated in hybrid CO₂/O₂ reforming of methane (CRPOM). To scrutinize the physiochemical properties of nanocatalysts, XRD, FESEM, EDX, TEM, BET, FTIR and TG-DTG analyses were used. XRD patterns revealed that, the lowest peaks intensity was obtained for W promoted NiAl₂O₄ (NW5A (SGP)). Also, nickel was dispersed more uniformly in NW5A (SGP) compared to K and Ca promoted ones (NK5A (SGP) and NCa5A (SGP)). Owning to the FESEM and EDX analysis all samples illustrated the acceptable dispersion which was resulted from the synergistic effect of sol-gel method and plasma treatment. However, NW5A (SGP) presented the slightly better dispersion and finer particles size compared the other ones. Also, highest surface area was found for the tungsten promoted one. Owing to the nature of sol-gel method, lower basicity of the synthesis media for NW5A (SGP) compared to that of NK5A (SGP) and NCa5A (SGP) resulted in better surface and adsorption properties. A superior interaction between metallic particles can be concluded from the TEM images of NW5A (SGP). Results of activity testes proved better catalytic activity of NW5A (SGP). It was ascribed to its superior characterization. Although throughout the time of stream test (TOS) at 750 °C and for 48 h, NW5A (SGP) presented the greater performance, but all of the fabricated nanocatalysts approximately exhibited the stable performance. TG-DTG analysis (after 48 h TOS) revealed that the lowest amount of coke deposition (4.6%) was obtained for the NW5A (SGP). Regarding to the EDX and FESEM images of spent nanocatalysts, well-maintained structure and excellent dispersion was gained for NW5A (SGP) after 48 h TOS. Accordingly, it is expected that tungsten modifier causes higher coke resistance compared to potassium and calcium at longer times on stream.