Insitu DRIFTs study of Ni/CeO2-CaO for ICCU-methanation

https://doi.org/10.1016/j.cej.2022.135394

“The in-situ DRIFTS study was used to investigate the interaction between highly dispersed Ni clusters and oxygen vacancies over Ni/CeO₂ sub-nanometer catalysts. After introducing CO₂ (1^st stage of ICCU), the IR bands centered at 2326, 2360, 3597, 3631, 3698 and 3734 cm⁻¹ come out immediately as shown in Fig. 5a, indicating the adsorption of gas-phase CO₂ [60], [61]. In addition, the IR features developed at 877, 1070, 1450 and 1540 cm⁻¹ represent different vibrational modes of bicarbonates [14], and the peak centered at 1780 cm⁻¹ is the C = O vibration mode of calcite carbonate [62]. The peaks centered at 2500, 2850 and 2950 cm⁻¹ are assigned to the formate species, which was derived from the hydrogenation of bicarbonate assisted by the hydrogen on Ni particles in reduced catalysts as previously reported [63]. These results indicate the formation of formate, calcite carbonate and bicarbonate species after CO₂ capture stage during the ICCU process caused by the chemical reaction between CaO sites and the introduced CO₂ gas phase. The IR bands centred at 2114 and 2176 cm⁻¹ are attributed to the CO species due to the oxygen vacancies in CeO₂ will direct cleavage CO₂. After switching the feed gas to H₂, the intensities of the above-mentioned calcite carbonate and formate species remain almost unchanged. However, the peak intensity of CO species are gradually decreased, while the IR band at 3016 cm⁻¹ attributed to CH₄ species can be detected as shown in Fig. 5b, implying that CO is probably intermediate and conveted to CH₄ during the 2^nd stage of ICCU. This is because the formed CO species react with dissociated hydrogen on Ni metallic particles to release CH₄ in the presence of hydrogen [64]. An in-situ DRIFTS experiment included CO adsorption and subsequent H₂ conversion is conducted to verify the reaction schemes and the results are diaplayed in Fig. 5c. It is found that after introducing CO into the cell, IR bands at 2114 and 2176 cm⁻¹ come out immediately. After swithcing the feed gas to H₂, a peak centered at 3016 cm⁻¹ assigned to the CH₄ species can be detected. This further confirms that CO is converted to CH₄ over the 1%Ni/CeO₂-CaO.”

“Fig. 5. In-situ DRIFTS spectra of the species formed over 1%Ni/CeO₂-CaO: (a, b) CO₂ capture stage and H₂ conversion stage during the ICCU process, respectively, (c) CO adsorption and subsequent H₂ conversion.”