| BET | TiO2-MgO | BET surface area of 36.3 m2∙g−1, pore volume 0.16 cm3∙g−1 and average pore diameter 16.1 nm | Increase of BET surface area (42.7 m2∙g−1), pore volume (0.21 cm3∙g−1), and average pore diameter (21.4 nm) | [31] |
| Li/CaO | BET surface area of 1.3 m2∙g−1 | Decrease of BET surface area (0.88 m2∙g−1) | [57] | |
| Calcined Mg-Al-Na and Mg-Al-K hydrotalcites | BET surface area of 189 m2∙g−1 for Mg-Al-Na and 174 m2∙g−1 for Mg-Al-K | Decrease of BET surface area (114 m2∙g−1 for Mg-Al-Na and 63 m2∙g−1 for Mg-Al-K) | [23] | |
| Palm oil mill fly ash supported CaO | BET surface area of 3.5 m2∙g−1 | Approximately the same surface area as the fresh (3.4 m2g−1 at the 5th cycle) | [58] | |
| Calcined Mg/Al hydrotalcite | BET surface area of 83 m2∙g−1, pore volume 0.48 cm3∙g−1 and average pore diameter 122.6 Å | Constant value of BET surface area (84 m2/g), decrease of pore volume (0.31 cm3/g) and increase of pore diameter (148.9 Å) | [59] | |
| SEM | Palm oil mill fly ash supported CaO | Uniform distribution of miniature agglomerates with irregular shapes to condensed mass | Physical change with more condensed mass | [58] |
| Calcined Mg/Al hydrotalcite | Uniform hexagonal platelet structure and sheet structure with smaller size of 372 nm width and 72 nm thickness | No uniform as initial one and platelet-like structure of 402 nm width and 64 nm thickness | [22] | |
| TG/DTA | TiO2-MgO | Loss of adsorbed water, decomposition of Ti(OH)4 (373 - 603 K) and Mg(NO3)2 (623 - 833 K); Combustion of organic derivatives with exothermic peak at 625 K | Weight loss of at 423 - 773 K with an exothermic peak at 603 K, corresponding to triglycerides and glycerol decomposition | [31] |
| Hammett indicator | Activated carbide slag | Basic strength of 9.8 < H_ < 15.0 | Constant basic strength of 9.8 < H_ < 15.0 at the 4th cycle | [55] |
| Li/CaO | High basic strength of 15 < H_ < 18.4 | Decrease of the basic strength (11.1 < H_ < 15.0) | [57] | |
| CO2-TPD | Calcined Mg/Al hydrotalcite | High total basicity (953 μmol CO2・g−1) and medium strength (432˚C) | Considerable decrease of the total basicity (441 μmol CO2・g−1) and medium strength (441˚C) at the 2nd cycle | [59] |
| Calcined Mg-Al-Na, Mg-Al-K hydrotalcites | Total desorbed amount of 355 μmol CO2 g−1 for Mg-Al-Na and 165 μmol CO2 g−1 for Mg-Al-K | Total desorbed amount of 351 μmol CO2 g−1 for Mg-Al-Na and 174 μmol CO2 g−1 for Mg-Al-K | [23] | |
| EDS | Supported CaO | High concentration of Ca (38 wt%) | Decrease of Ca concentration (15 wt% on the catalyst at the 4th cycle) | [58] |
| SrO/MgO | High Sr/Mg atomic ratio from 0.11 to 0.6 | Low Sr/Mg atomic ratio (<0.1 at the 3rd batch) | [9] | |
| ICP-AES | CaO-La2O3 | Concentration of 24.9 ppm for Ca and 65.3 ppm for La | Ca concentration from 22.8 ppm for 2nd to 15.2 ppm for 3rd use | [60] |