Synthesis of thermally stable metal substituted hydroxy apatites for the selective oxidation of light paraffins

Hydroxyapatite and a series of hydroxyapatite-type compounds containing Co, Fe or Sr were synthesized by co-precipitation and characterized by ICP-OES, BET, IR, Raman spectroscopy, powder and in-situ XRD, SEM, TEM, TPR, TPD and TGA. In-situ XRD and TGA studies indicate that the materials are able to maintain their structure at temperatures reaching 900 °C. The TPD data indicated that acidic sites of varying strengths were present in all the three hydroxyapatites. From SEM, the surface of the materials consisted of an agglomeration of irregular plate-like particles. The catalytic activity of the compounds was investigated in the oxidation of n-pentane and n-hexane. The conversion of the feed and composition of the products were largely influenced by changes in the temperature and flow rates. For n-pentane, the products consisted of lower hydrocarbons and oxygenated compounds, carbon oxides and very small amounts 1,3-pentadiene, furan and furfural. Low conversions of n-hexane were obtained for all the tested catalysts and selective products were the hexene isomers and some aromatics. KEY WORDS: Hydroxyapatite, Selective oxidation of n-pentane and n-hexane, Characterization, Oxygenates, Olefins Bull. Chem. Soc. Ethiop. 2013, 27(1), 57-68. DOI: http://dx.doi.org/10.4314/bcse.v27i1.6