Method

Catalyst

Fresh catalyst propertiesa

Used catalyst propertiesb

Reference

XRD

Calcium oxide

Crystalline phases of calcium oxide with 2θ values of 32˚ and 37˚

Major crystalline phase of calcium diglyceroxide with 2θ values of 8˚,10˚, 21˚, 24˚ and 26˚

[47]

Calcined waste carbide slag

Dominant composition of cubic CaO with 2θ values of 32.2˚, 37.4˚, 53.8˚, 64.1˚ and 67.4˚

Appearance of news peaks of calcium diglyceroxide with 2θ values of 8˚, 10˚, 21˚, 24˚, and 26˚

[56]

Activated carbide slag

Crystalline phases of calcium oxide

News peaks of calcium diglyceroxide units with 2θ values of 10˚, 21˚, 24˚ and 26˚

[55]

Palm oil mill fly ash supported CaO

Crystalline CaO phase with high concentration of 83 wt.% (2θ = 32.32˚, 37.48˚, 53.95˚, 64.31˚ and 67.47˚)

Crystalline CaO phase with concentration of 56% at 5th cycle

[58]

Li/CaO

Major phase of cubic CaO, hexagonal Ca(OH)2 (2θ = 20.94, 37.25˚, 48.99˚, 53.70˚, 64.40˚ and 72.2˚) and minor hexagonal calcium carbonate phase (2θ = 21.46˚, 36.3˚, 43.3˚, 48.8˚) with Li/CaO crystallite size of 60 nm

Structural changes with appearance of new peaks of hexagonal calcium carbonate as major phase (2θ = 32.3 and 67.6) and decrease of Li/CaO crystallite size of 52 nm

[57]

SrO/MgO

Diffraction lines of SrO, Sr and Mg carbonates and hydroxides

Roughly disappear of diffraction lines of the Sr phase (oxide, hydroxides and carbonates).

[9]

Calcined Mg/Al hydrotalcite

Highly crystalline layered double hydroxide structure (2θ = 11.7˚, 23.2˚, 34.7˚, 38.8˚, 46.0˚, 60.6˚ and 61.8˚), with crystallite size of 11.2 nm

Major modification in the structure of the catalyst, with both hydrotalcite and MgO phases

[59]

Calcined

Mg/Al hydrotalcite

Mg-Al complex oxides (MgO-like or magnesia-alumina solid) phases with 2θ values of 43 and 63˚, and small peaks of Al cations

Disappear of active sites due the structure collapsed

[22]

Calcined clam shells

Prominent phase of CaO (2θ = 32.1, 37. 4, and 53.8˚) and minor phase of Ca(OH)2 (2θ = 8.1 and 34.2˚)

Prominent phase of calcium glyceroxide with 2θ values of 8.2 and 10.1˚

[53]

FTIR

Calcined waste carbide slag

Major bands of (1416 and 874 cm−1), and minor bands of H2O (3645 and 1648 cm−1) adsorbed on the surface of the solid sample

Apparition of new bands similar to glyceroxide units : stretching vibration of C-H (2920, 2879, and 2849 cm−1), bending modes of C-H bonds (1470, 1448, 1425, 1265, 1231, 947, and 916 cm−1), C-O-H bending modes (1379 and 1311 cm−1), and the stretching mode of C-O bonds (1132 and 1076 cm−1)

[56]

Activated carbide slag

Absence of carbonate and hydroxide bands

New bands similar to calcium diglyceroxide with stretching vibration of C-O bonds (1022 - 1083 cm−1 and 1120 - 1147 cm−1), vibration of H-C-H bonds (705 - 1022 cm−1 and 1209 - 1346 cm−1), and weak band of O-H bonds (3643 cm−1) corresponding to water

[55]

SrO/MgO

Bands similar to Sr (1450 and 1250 cm−1) and Mg carbonates and hydroxides

Disappearance of Sr hydroxide and carbonate bands

[9]

Calcined Mg/Al hydrotalcite

Non determined

Viscous liquid adsorbed on the surface of the catalyst similar to glycerol bands (3415, 2934, 1654, 1047, 923, 851 cm−1)

[22]