Abstract
Ni-containing Calcium Hydroxyapatite (NiCaHAp; 3.31 wt.% Ni) was synthesized by coprecipitation and used as catalyst support. Molybdenum was supported on NiCaHAp by impregnation using ammonium heptamolybdate. The prepared catalysts Mo(x)/NiCaHAp (x: 2 to 8 wt % in Mo) were characterized by elemental analysis, XRD, FT-IR, N2 adsorption-desorption and TEM-EDX. The catalysts were sulfided in-situ at 673 K under flowing H2S/H2 (15 Vol.% H2S) and tested in hydrodesulfurization (HDS) of thiophene at 673 K. The main XRD peaks of hydroxyapatite CaHAp phase were observed in all samples and a peak due probably to crystalline MoO3 phase was also identified from the results. However, no crystalline phase of NiO was found for the catalysts, which showed its Ni species were highly dispersed. The sulfided catalysts Mo(x)/NiCaHAp presented are active in HDS of thiophene, despite the presence of some large MoO3 crystallites and incomplete sulfidation. This activity may be due to interaction of NiO and MoO3 on CaHAp resulting in the formation of Ni-Mo-S phase under flowing H2S/H2. When the molybdenum content increased the HDS activity increasead slightly, which was caused by the agglomeration of MoO3. The Mo(8)/NiCaHAp catalyst is about two times less active for thiophene HDS than the commercial NiMoP/Al2O3.
Highlights
It is currently known that a great part of natural phosphates adopts a crystalline structure similar to that of synthetic hydroxyapatite Ca10(PO4)6(OH)2 [1]
Calcium hydroxyapatite containing transition metals were found to be very active in the methane dry reforming [2], the hydrogenolyse of S-containing substrates [3], the propane oxidative dehydrogenation [4] and the epoxidation of olefin [5]
We studied the use of nickelcontaining calcium deficient hydroxyapatite Ni-CaHAp (3.31 wt% Ni) prepared by coprecipitation at pH basic and calcined at 773 K, as a support for molybdenum catalysts during the hydrodesulfurization of thiophene
Summary
It is currently known that a great part of natural phosphates adopts a crystalline structure similar to that of synthetic hydroxyapatite Ca10(PO4)6(OH)2 [1]. The apatitic lattice allows various anionic and cationic substitutions Despite their low cost and their availability in the market, the use and application of apatite in catalysis is still a subject of relatively scarce investigations. We have been looking for some new catalytic applications for apatitic compounds with a special interest for hydroxyapatite. Most of these studies are focused on the hydrodesulfurization (HDS) of petroleum distillate fractions for the reduction of atmospheric pollution due to the emission of hazardous compounds such as SO2. We studied the use of nickelcontaining calcium deficient hydroxyapatite Ni-CaHAp (3.31 wt% Ni) prepared by coprecipitation at pH basic and calcined at 773 K, as a support for molybdenum catalysts during the hydrodesulfurization of thiophene. The hydrodesulfurization catalytic activity was assessed at atmospheric pressure using thiophene as a probe molecule
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