4. Results and discussions
4.1. Characterization
4.1.1. XRD analysis
Powder X-ray diffraction patterns for CaO (inset) and 1–5% Li loaded CaO are presented in Fig. 1. It was observed that the XRD patterns of CaO were altered with increasing Li loading. Initially the XRD peaks that were observed for 1% and 2% of Li loading on CaO consists of CaO (JCPDS 21-0155) peaks and Li2O (JCPDS 09-0355) peaks along with new peaks at 2θ ~18.48°, 34.28°, 47.37°, 51.07° and 72.22° which correspond to crystalline Li–Ca phase (JCPDS 65-0763). The peaks of Li2O are observed for Li-2% onwards. The fact that Li2O appears in the XRD pattern of the catalyst is probably due to the reason that Li+ attract electrons of O2− strongly since it has a high electronegativity (Pauling scale 0.98 kJ•mol−1) [19]. In addition the small radius of Li+ (90 pm) allows its incorporation into the lattice structure of CaO easily. The new phases might also have formed during the interaction between Li with the support (CaO). However the peak for CaO is replaced by new peaks as the Li % loading is increased indicating that the crystal structure of CaO is compressed by Li incorporation. It was observed that in the XRD pattern for 5% Li loading diffraction peaks of Li–Ca were the dominant one suggesting that CaO could not retain its structure with increasing Li loading resulting in the formation of Li containing phase.
4.1.2. FT-IR analysis
The Fourier transform infrared (FTIR) spectra of different Li loadings on CaO are presented in Fig. 2. The spectra clearly shows that the CaO structure was altered after the introduction of Li as new peaks were observed in the FTIR spectra of Li loaded CaO catalysts. In the low energy region of egg shell derived CaO, weak bands corresponding to CO