Structure and surface reactivity of WO ₄ ^2-, SO ₄ ^2-, PO ₄ ^3- modified Ca-hydroxyapatite catalysts and their activity in ethanol conversion

In the current study, we have synthesized calcium hydroxyapatite (CaHAP) from different phosphorus sources namely, NH ₄H ₂PO ₄ and H ₃PO ₄. The structure of CaHAP was confirmed by XRD, FT-IR, and Raman characterization methods. The CaHAP was further modified with various anions such as WO ₄ ^2-, SO ₄ ^2-, and PO ₄ ^3- with fixed content of 10 wt %. To understand the textural and structural properties, these samples were thoroughly characterized by N ₂ physisorption, X-ray diffraction, Fourier transform infrared, Raman and thermogravimetry-differential thermal analysis methods. Ethanol adsorption at various temperatures was studied in detail using diffuse reflectance Fourier transform spectroscopic to unravel the formation and stability of surface species and the interaction of ethanol with CaHAP. The temperature programmed desorption of ethanol (ethanol-TPD) was performed to understand the stability, surface reactivity, and product distribution. The catalytic activity of the above catalysts was tested in ethanol conversion over a temperature range of 300-450 °C.