Direct and easily prepared nanocomposite impurity-free hydroxyapatite derived from CKD as an effective catalyst for trans-2-butene production

This research is regarded as the first successful attempt at directly producing highly pure nanocomposite hydroxyapatite (HAPT) from cement kiln dust (CKD) using a cost-effective preparation method. The crystallite size of HAPT was 23.6 nm and showed a hierarchical mesoporous unit with a Ca-deficient structure according to SEM-EDX analyses. HAPT exhibits a high population of different acidic sites, i.e. weak, moderate and strong acidic sites, as determined by TG and DSC-TPD experiments using tetrahydrofuran as a probe molecule. The wide range of acidic sites over HAPT is clearly and positively enhanced its catalytic activity during the conversion of sec-butanol to trans-2-butene. In addition, our prepared HAPT demonstrated greater catalytic activity when sec-butanol was converted using air as a carrier rather than N₂-gas. A comparison between the catalytic activity of HAPT prepared from the waste CKD and pure Ca(NO₃)₂ was also conducted, showing HAPT derived from waste streams with higher catalytic activity.