A kinetic insight into the activation of n-octane with alkaline-earth metal hydroxyapatites

Abstract

Alkaline-earth metal hydroxyapatites are prepared by the co-precipitation method and characterized using XRD, ICP, NH 3 -TPD, SEM-EDX, TEM and N 2 physisorption analysis. The metal present in the hydroxyapatite influences the acidity of the catalyst. Oxidative dehydrogenation reactions carried out in a continuous flow fixed bed reactor showed that the selectivity towards desired products was dependent on the alkaline-earth metal in the hydroxyapatite. All hydroxyapatite catalysts showed high selectivity towards carbon oxides, followed by cracked products, octenes and aromatics. The highest selectivity and turnover numbers towards C8 products and a high specific rate was shown by Sr-HAp. The activation of n-octane over these catalysts followed the Eley-Rideal mechanism.

Gas-Phase Oxidative Dehydrogenation of n-Octane over Metal Oxide Catalysts: A Review

“…A variety of classes of catalysts have been employed for the ODH of n-octane. These include unsupported metal oxides [43][44][45][46], supported metal oxides [47][48][49][50][51][52], mixed metal oxides, zeolites [53,54] and hydroxyapatites [24,[55][56][57]. This review focuses on unsupported and supported metal oxides.…”

“…The combined acidity of the phosphate groups and the alkali earth metal create active sites which are capable of activating oxygen, resulting in oxygen species that are able to abstract hydrogen in alkanes [64]. Dasireddy et al [56] reported the use of alkali earth metal hydroxyapatites in the oxidation of n-octane. The conversion increased with an increase in temperature, which was reported to be due to the surface oxygen species chemisorbed on the catalyst (Figure 10).…”

“…[64]. Dasireddy et al [56] reported the use of alkali earth metal hydroxyapatites in the oxidation of n-octane. The conversion increased with an increase in temperature, which was reported to be due to the surface oxygen species chemisorbed on the catalyst (Figure 10).…”

“…The effect of temperature on n-octane conversion over alkaline earth metal hydroxyapatites (GHSV = 4000 h −1 , n-octane-to-oxygen molar ratio of 1:1). Reproduced from [56].…”

“…hydroxyapatite catalysts at an iso-conversion of 8% (GHSV = 3700-4250 h , n-octane-to-oxygen mo lar ratio of 1:1, temperature = 500 °C). Reproduced from [56].…”