• What is the main role of support material of the hydrotreater catalyst CoMo/NiMo? Does Support material participate in the hydrogenation reactions for HDS/HDN/HDA?

    Hydrotreater catalyst at times said to be acidic and at times to be neutral as per the documents, which is true? Acidic nature for the catalyst is due to catalyst material or due to support material? Kindly guide.



  • Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

    The catalyst carrier or support offers mechanical resistance, high supercial area aiming to ensure an adequate distribution of the active phase (metals), and it's responsible to control the acid function of the catalyst which is desired to be low in the hydrotreating units. The support normally don't have catalytic activity for hydrogenation reactions which is essentially carried out in the metal sites. Another function of the support in hydrotreating catalysts is to ensure an adequate pore distribution aiming to minimize the catalysts plugging due to coke or metals deposition which can lead to short operating lifecycle of the hydroprocessing units, this is a especial concern in residue hydrotreating units.

    The catalysts applied in most severe services normally present acid and hydrogenation characteristics especially those apllied in residue hydrotreating or hydrocracking processes. Catalysts applied in hydrocracking processes can be amorphous (alumina and silica-alumina) and crystallines (zeolites) and have bifunctional characteristics more pronunciated, once it's desired that the cracking reactions (in the acid sites) and hydrogenation (in the metals sites) occurs simultaneously. The active metals used to this process are normally Ni, Co, Mo and W in combination with noble metals like Pt and Pd.

    It’s necessary a synergic effect between the catalyst and the hydrogen because the cracking reactions are endothermic  and the hydrogenation reactions are exothermic, so the reaction is conducted under high partial hydrogen pressures and the temperature is controlled in the minimum necessary to achieve the desired convertion of the feed stream. Despite these characteristic, the hydrocracking global process is highly exothermic and the reaction temperature control is normally made through cold hydrogen injection between the catalytic beds.

    As described above, the acid function in hydrocracking catalysts is take place in the acidic support which can be amorphous silica-alumina (ASA) and/or a zeolitic material while the hydrogenation reactions are carried out in the metal sites.