Evaluation of Zr-based MOFs (UiO-66 and MOF-808) as Ru/NiO-CeO2 support for CO2 methanation

Ru/NiO-CeO 2 nanoparticles supported on Zr-MOFs (UiO-66 and MOF-808) have been prepared and studied for CO 2 hydrogenation to CH 4 , paying special attention to the MOFs stability under reaction conditions. Both supported catalysts were active and selective, and were characterised by means of XRD, N 2 physisorption isotherms at -196 ºC, TEM, XPS and DRIFTS before and after the reaction. The XRD characterization of the fresh and used supported catalysts evidences the gradual degradation of both MOF supports between 200 and 275 ºC under reaction conditions, which becomes very relevant at 300 ºC and higher temperatures. Despite this degradation, UiO-66 shows higher stability than MOF-808 under CO 2 methanation conditions, which can be attributed to the rigid structure of UiO-66 compared to MOF-808. The large pores and flexibility of MOF-808 seems to weaken the framework under reaction conditions. In situ DRFIT spectra showed that some characteristic bands of UiO-66 are still observed under reaction conditions until 300 ºC, suggesting that, despite the structural modifications, UiO-66 is not totally degraded but is transformed into a derived solid. This is also in agreement with the only partial decrease of the porosity deduced from N 2 adsorption characterization and with the TEM observations. On the contrary, Ru/NiCe/MOF-808 spectra evidence total degradation of this MOF-808 at 300 ºC. • Ru/NiO-CeO 2 /UiO-66 and Ru/NiO-CeO 2 /MOF-808 are active and selective for CO 2 hydrogenation to CH 4 • Both MOFs partially degrade between 200 and 275 ºC under reaction conditions • Total degradation of the XRD patterns occurs at 300 ºC • UiO-66 is more stable than MOF-808 under CO 2 methanation due to the rigid structure of UiO-66 compared to MOF-808. • The large pores and flexibility of MOF-808 weaken the framework under reaction conditions