COx co-methanation over coal combustion fly ash supported Ni-Re bimetallic catalyst: Transformation from hazardous to high value-added products.

The hazardous industrial waste, coal combustion fly ash (CCFA), was creatively applied as Ni-Re bimetallic catalyst support. The expected catalyst was facilely prepared by co-impregnation method and further tested for COx co-methanation in a continuous fixed-bed reactor. The physico-chemical properties of the catalyst were examined by a series of techniques including XRF, ICP, XRD, N2 isothermal adsorption, H2-TPR, SEM and TEM. The results showed that compared to non-promoted monometallic Ni catalyst, the addition of Re promoter forming Ni-Re bimetallic catalyst was able to facilitate NiO reduction and increase Ni dispersion as well as inhibit carbon deposition and Ni sintering during reaction. The performance tests revealed that Ni15Re1.0 presented superior COx co-methanation activity over Ni15Re0, Ni15Re0.5 and Ni15Re1.5 due to its better anti-coking and anti-sintering ability. Based on in-situ DRIFTS analysis, a possible cycle reaction mechanism of COx co-methanation was reasonably proposed in the end. The reaction pathway for CO and CO2 methanation differed from each other, where CO was linearly adsorbed on Ni metals followed by stepwise hydrogenation while CO2 was first immobilized by the surface hydroxyl group and then gradually reacted with H2 to form CH4.