Direct addition of the precursor salts of Mo, Co or Ni oxides during the sol formation of γ-Al2O3 and ZrO2 - The effect on metal dispersion
Introduction
Due to the increase of the SOx emissions, the environmental regulations have strongly diminished the limits of the sulfur content in fuels. Catalytic hydrodesulfurization of petroleum feedstocks has been a strategic process to produce clean fuels [1] and the requirement to improve the catalyst performance becomes the most important issue. In this sense, the researches are devoted to study the nature of the support and the active species [1], [2], [3], [4]. Traditional HDS catalysts are Al2O3 supported Mo or W sulfides promoted by Co or Ni sulfides. Supports like ZrO2[1], [2], [3], TiO2[1], [3] or mesoporous molecular sieves [4] or ZrO2-Al2O3 mixed oxides have also been proposed [5]. In the present work, Mo-, CoMo- and NiMo-oxides were prepared introducing the precursor metallic salts directly during the sol preparation (in situ addition) of γ-Al2O3 and ZrO2 supports under controlled pH conditions.
Section snippets
Preparation of γ-Al2O3 and ZrO2 and in situ Mo-, CoMo- and NiMosupported oxides via the sol-gel procedure
The supports and the metallic supported oxides were prepared using the procedure described by Lebihan et al. (1994) [6]. Firstly, aluminum tri-sec-butoxide (ATSB, Aldrich 97%) or zirconium propoxide (PZr, Aldrich 70%) and 2-butanol (Aldrich, ≥ 99%) were mixed at 85 °C under stirring for 30 min. Then, an appropriate amount of 1,3-butanediol (Aldrich, 99+%) was added to the solution and left under stirring for 1 h. Subsequently, the hydrolysis step was done by mixing deionized water and maintaining
Thermogravimetric Analysis (TGA)
The TGA curves (not shown) of the zirconia and alumina supports show between 25 and 200 °C a weight loss attributed to dehydration and other two events at higher temperatures mainly due to decomposition and combustion of organic compounds [6], [7]. The TGA for samples containing the precursor of the metallic salt of Mo, Co and Ni incorporated in situ no significant in weight loss profile was observed.
X-ray diffraction
The XRD patterns of the Mo, CoMo and NiMo oxides supported on ZrO2 or γ-Al2O3 are shown in
Conclusions
Mo, CoMo and NiMo supported oxides were successful prepared by in situ addition during the sol-gel preparation of γ-Al2O3 and ZrO2 with the simultaneous adjusting of pH during the hydrolysis step. High specific surface area mesoporous γ-Al2O3 and ZrO2 were obtained with the metallic Mo, Co and Ni species highly distributed. As expected Co and Ni species promoted the reduction of Mo at lower temperatures. Nevertheless, the Co and Ni promoting effect in the reduction of Mo was more pronounced