Insights into Nickel-Based Dual Function Materials for CO2 Sorption and Methanation: Effect of Reduction Temperature

Ni-MgO dual function materials (DFMs) show promise for integrated CO2 sorption and methanation. To improve CO2 sorption capacity, Ni-MgO DFMs are promoted with alkali metal nitrates. However, the high catalyst reduction temperature will result in high energy consumption, huge temperature gap between reduction (∼650 °C) and CO2 sorption and methanation (∼300 °C), and the loss of alkali metal nitrates. In this work, we prepared a Ni/CeO2 catalyst and investigated the effect of reduction temperature on its structure–property relationships in CO2 methanation, aiming to lower the reduction temperature to an isothermal level that matches CO2 methanation. Results indicated that the reduction temperature fell from over 650 to 300 °C, and Ni/CeO2 reduced at 300 °C featured high CO2 conversion (72.7%) and CH4 selectivity (98.9%). The CO2 methanation activity of Ni/CeO2 declined significantly when the reduction temperature exceeded 400 °C. The formation of more oxygen vacancy defects due to the interaction between NiO and CeO2 promoted the reduction of NiO species at lower temperatures. The declined CO2 methanation activity at high reduction temperatures was ascribed to the consumption of oxygen vacancies in catalyst reduction, and less defects were available for CO2 activation and methanation. An alkali metal nitrate promoted MgO adsorbent was physically mixed with Ni/CeO2 to construct (Li-Na-K)NO3-MgO-Ni/CeO2-phy DFMs for integrated CO2 sorption and methanation. The DFMs could be facilely reduced at 300 °C, and this has made it possible to realize the isothermal operation of catalyst reduction and CO2 sorption and methanation in integrated CO2 capture and utilization (ICCU). The (Li-Na-K)NO3-MgO-Ni/CeO2-phy DFMs reduced at 300 °C exhibited an impressive CO2 uptake of 2.74 mmol CO2/g DFMs and a great CH4 yield of 1.10 mmol CH4/g DFMs, and they could be a promising alternative to Ru-based DFMs with respect to their comparable CO2 sorption capacity and methanation activity and minimized cost of raw materials.