Ni-Ce-Zr dual functional materials were prepared by the sol-gel method and applied for ICCU-DRM. The addition of Ce enhanced the stability of the materials significantly (35 cycles of ICCU), as shown in the following figure. It is noted this stability test was done by TGA.
“TGA profiles of 35 carbonation/decarbonation cycles at 875 °C with 20% CO2 and 20% H2 using (a) SrNi and (b) SrCe0.5Ni0.5.” (https://doi.org/10.1039/D1TA09967A)
XRD analysis showed that the main components in the dual functional materials (DFMs) were SrCO3 and CeO2. The crystal phases could be changed at different stages of ICCU and affected by the content of Ce. For example, a higher content of Ce resulted in the formation of SrCeO3, and a lower concentration of Ce favoured the formation of SrO.
The TPR analysis (following figure) showed that a higher content of Ce shifted the reduction to a lower temperature. Therefore, the addition of Ce could reduce the conventional decomposition temperature of SrCO3 at the utilisation stage of ICCU. It was also suggested that Ce addition inhibited the sintering of catalysts, which was confirmed by TEM analysis related to Ni dispersion.
“ H2-TPR profile of the pre-carbonated SrCe1−xNix under 10% H2 at a heating rate of 10 °C min−1. Prior to H2-TPR, the sample underwent reduction (25% H2 for 4 h) to obtain metallic Ni and carbonation (25% CO2 for 2 h) at 800 °C.” (https://doi.org/10.1039/D1TA09967A)
For ICCU-DRM performance, the addition of Ce facilitated the conversion of CH4 and sorbent regeneration. However, the challenge of ICCU-DRM using ZrO2 as the sorbent is that too high temperature (>800 °C) is required. Personally, this type of DFMs based on ZrO2 are difficult to be deployed. In particular, CaO-based DFMs have excellent ICCU-DRM performance at lower temperatures.