2. Experimental
2.1. Catalyst preparation
Catalysts with different Ca/La atomic ratios (0.5e10.0 atomic%)
were prepared using co-precipitation method. In a typical catalyst
preparation procedure, the required amount of Ca(NO3)2$4H2O and
La(NO3)3$6H2O was dissolved in deionized water. The two precursor
solutions were mixed homogeneously and allowed to precipitate
using a NaOH and Na2CO3 basic solutions at a constant pH of 10
and controlled by slow addition in metal salt mixture. The sample
was stirred for 24 h at 60 C. Finally, the precipitate formed was
then filtered, washed until the pH of the filtrate was 7 and dried at