Thiophene HDS on La-Modified CoMo/Al2O3 Sulfided Catalysts. Effect of Rare-Earth Content

Abstract

Alumina-lantana (2.5, 5, 7.5 and 10 wt% La) mixed oxides of suitable texture to be applied as supports of catalysts for hydrodesulfurization of FCC naphtha-range oil-derived distillates were prepared by rare-earth pore-filling impregnation through corresponding nitrate. Co, Mo and P were deposited on binary carriers by one-pot simultaneous impregnation method used during commercial hydrotreating catalysts preparation. Materials were characterized by N2 physisorption, XRD, SEM–EDS, adsorbed CO2 FTIR (basicity measurements), Raman and UV–vis spectroscopies. Sulfided catalysts were studied by chemical composition (EDAX) and HR-TEM. In general, amount and strength of surface basic sites increased with rare-earth content in binary carriers at 5 wt% and higher. Deposited molybdates dispersion augmented with lanthanum content in carriers. However, progressively increasing rare-earth loading on supports was detrimental on gas-phase thiophene HDS (523–563 K, steady-state fixed-bed plug-flow reactor operating at atmospheric pressure). Hardly sulfidable tetrahedral Mo species could be originated by decomposition of heteropolymolybdates originally present in one-pot acidic (pH ~ 1.9) Co–Mo–P solutions by impregnating at basic conditions in pores of La-modified carriers. At isoconversion (~ 10%) rare-earth containing sulfided CoMo catalysts had decreased yield to fully saturated n-butane as to the material supported on pristine alumina.