Heptamolybdate-intercalated CoMgAl hydrotalcites as precursors for HDS-selective hydrotreating catalysts
•Heptamolybdate-CoMgAl hydrotalcites prepared from terephthalate precursors.•Heptamolybdate-CoMgAl hydrotalcites prepared with Al atom fraction above 0.5.•CoMoMgAl mixed-oxides prepared from hydrotalcites with areas above 100 m2 g−1.•Sulfide catalysts from CoMoMgAl mixed-oxides more HDS selective than CoMo/Al2O3.
Two series of unsupported CoMgMoAl hydrotreating catalysts were prepared starting from CoMgAl-terephthalate layered double hydroxides (LDHs) with nominal aluminum molar fractions (Al/(Al + Ni + Mg) ratios) 0.3 (Al30 series) and 0.5 (Al50 series), and nominal cobalt atom fractions (Co/(Co + Mg)) in the 0.2–1.0 range in each series. The materials were prepared by ion exchange with ammonium heptamolybdate, followed by calcination at 723 K. Mixed oxides containing ca. 14–32 wt.% molybdenum and Ni/Mo atomic ratios in the 0.5–1.6 range were obtained. Despite the observed loss in long-range ordering and, in some cases, magnesium leaching during the ion-exchange, there was evidence that molybdenum-intercalated LHDs were indeed produced.The catalysts were sulfided in situ and subsequently tested in simultaneous thiophene HDS and cyclohexene hydrogenation (OHYD reaction) in a tubular flow micro-reactor at 573 and 623 K and 20 bar. In each series, both the HDS and the OHYD activities of the catalysts increased with increasing Mg content, possibly due to improved Co/Mo ratio. Although there was a trend of decreasing selectivity for the HDS reaction with increasing HDS activity, the HDS selectivity of the most active catalysts was higher than that of a commercial alumina-supported CoMo catalyst.
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Journal: Catalysis Today - Volume 250, 15 July 2015, Pages 38–46