The simple method for the preparation of dual functional materials (or combined functional materials) is to mix adsorbent (e.g. CaO) and catalysts (e.g. Ni/Al2O3) together. The method has been commonly used. It is noted that preparation methods such as one-pot sol gel and physical mixing has significant influence on ICCU performance. This is related to the dispersion of catalytic sites, and the interaction between adsorption and catalysis. However, our work had indicated that pure CaO could act as both adsorbent and catalysts for ICCU-DRM (https://doi.org/10.1016/j.ccst.2021.100001). This could have great impacts, as it can change the perspective of RWGS without any transition metals in catalysts.
Nevertheless, the following methods demonstrated the simple mixing of catalysts and adsorbents for DMFs development.
1) Preparation of different Ni-based catalysts (https://doi.org/10.1016/j.seppur.2022.121604):
“ZrO2 (Sigma-Aldrich, 99%), TiO2 (Sigma-Aldrich, 99.5%) and Al2O3 (Sigma-Aldrich, 99.5%) were dried at 120 °C before the impregnation process. CeO2 was prepared by a hydrothermal method as reported in previous work [17], [19]. Briefly, 5.21 g Ce(NO3)3·6H2O (Sigma-Aldrich, 99%) was dissolved in deionised water (30 ml) to prepare a Ce source solution, followed by the dissolution of 57.6 g NaOH (Sigma-Aldrich, 99%) in deionised water (210 ml) to prepare the precipitant. The Ce source was mixed with the precipitant dropwise for 30 mins at room temperature to obtain a slurry. The slurry was transferred into a stainless-steel autoclave and kept at 100 °C for 24 h. The precipitate was washed and separated by vacuum filtration using distilled water and ethanol to neutrality and dried at 120 °C overnight, to produce a yellow powder, labeled as CeO2. Ni-based catalysts were prepared by the wet impregnation method, using Ni(NO3)2·6H2O (Sigma-Aldrich, 97%) as the metal precursor. Typically, 3.0 g support material was added into 30 ml Ni(NO3)2 (0.15 mol L-1) aqueous solution, stirred at room temperature for 2 h and evaporated under stirring to produce a sample paste. The sample paste was dried at 120 °C overnight, and calcined at 800 °C for 5 h with a heating rate of 5 °C min−1, to produce NiO/ZrO2, NiO/TiO2, NiO/CeO2 and NiO/Al2O3, respectively. The NiO/supports were reduced at 550 °C for 2 h with a heating rate of 5 °C min−1 in 5% H2/N2, and labeled as Ni/ZrO2, Ni/TiO2, Ni/CeO2 and Ni/Al2O3, respectively.”
2) Preparation of CaO sorbent
“The sol–gel derived CaO was prepared as reported in previous work [20], [32]. Briefly, 23.6 g Ca(NO3)2·4H2O (Sigma-Aldrich, 99%) and 19.2 g citric acid monohydrate (Sigma-Aldrich, 99.5%) were dissolved into 72 ml distilled water, stirred at room temperature at 80 °C, and dried at 120 °C overnight. The sample was ground and calcined at 850 °C for 5 h with a heating rate of 5 °C min−1, labeled as sol–gel CaO. The bifunctional combined materials were prepared by physically mixing the Ni/support catalysts and the sol–gel CaO with a mass ratio of 1:2, labeled as Ni/ZrO2-CaO, Ni/TiO2-CaO, Ni/CeO2-CaO and Ni/Al2O3-CaO, respectively.”