Formation of Base Sites on Calcined Mg−Ga Hydrotalcite-like [Mg1 - x Ga x (OH)2](CO3) x /2·mH2O

• Published in: The journal of physical chemistry. B 1997-06, Vol.101 (26), p.5112-5117
• Main Authors: López-Salinas, Esteban, García-Sánchez, Mayela, Llanos-Serrano, Ma. Elena, Navarrete-Bolañoz, Juán
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp9702558

A series of Ga-substituted hydrotalcite-like materials (GaHTs), [Mg1 - x Ga x (OH)2](CO3) x /2·mH2O where x = 0.12−0.36, were prepared in order to examine their textural and basic properties upon different Mg/Ga contents and calcination temperature. Specific surface area increases from 46 to 156 m2 g-1 (Mg/Ga = 7.7) when calcining from 523 to 673 K as a consequence of dehydroxylation and decarbonation of the material. The total number of base sites increases upon higher calcination temperatures until reaching a maximum at 873 K and then decreases. CO2 thermal programmed desorption indicates that different Mg/Ga relative contents have a considerable effect on the amount of base sites. For instance, a GaHT with Mg/Ga = 7.7 exhibits 2.4 times more total base sites than that of Mg/Ga = 2.9. Additionally, in the former, the generation of medium and strong base sites is considerably higher than in the latter. By means of CDCl3 adsorption and FTIR, several types of base sites were identified. The base sites strength (pK a = −1 to +19) and proton affinity (815−987 kJ mol-1) values were estimated considering the νCD shift of adsorbed CDCl3 and correlating it with the pK a of bases that form hydrogen-bonded complexes.