Non-thermal plasma assisted synthesis and physicochemical characterizations of Co and Cu doped Ni/Al2O3 nanocatalysts used for dry reforming of methane

Abstract

Ni/Al2O3 nanocatalysts doped with Co and Cu were prepared by co-impregnation and modified by non-thermal plasma. The nanocatalysts were characterized by XRD, FESEM, TEM, EDX dot-mapping, BET, FTIR, TGA-DTG, and XPS analysis. According to XRD and XPS results, good interaction between active phase and support can be observed in both Ni–Co/Al2O3 and Ni–Cu/Al2O3 nanocatalysts. A uniform morphology, high surface area, and well dispersed particles of active sites in Ni–Co/Al2O3 nanocatalyst were observed that shows the effect of cobalt in controlling Ni ensemble size. In contrast Ni–Cu/Al2O3 nanocatalyst had no homogenous dispersion of active phase due to sintering of copper particles. The activity measurements illustrated better Ni–Co/Al2O3 nanocatalyst activity in comparison to Ni/Al2O3 and Ni–Cu/Al2O3 in terms of CH4 and CO2 conversion. H2 and CO yield were higher for Ni–Co/Al2O3 and higher H2/Co ratio was obtained as well. Whereas Ni/Al2O3 and Ni–Co/Al2O3 did not experience deactivation, Ni–Cu/Al2O3 suffered from activity loss by ca. 22% and 16% for CH4 and CO2 conversion, respectively. Sintering most likely happened in Ni–Cu/Al2O3 nanocatalyst due to high temperature of calcination while cobalt by controlling the size of Ni particles, alternated the size of active sites to a size range in which carbon formation was suppressed. Ni/Al ratio from XPS analysis which signifies Ni dispersion on alumina support was 5.15, 9.16, and 6.35 for Ni/Al2O3, Ni–Co/Al2O3, and Ni–Cu/Al2O3 nanocatalysts respectively. The highest ratio of Ni/Al was for Ni–Co/Al2O3 nanocatalyst that shows the best coverage of support by Ni active phase in this nanocatalyst.