Demonstration of hydrogen spillover effects on Pd-Co/Al₂O₃ hydrocracking catalyst by temperature programmed studies

In recent years, the need for more efficient hydrocracking catalysts is growing due to increasing demand of lighter fuels and the escalation of crude oil prices. The key of developing an efficient catalyst is to obtain a proper balance between the cracking and the hydrogen transfer functionalities. In this study an attempt was made to enhance the hydrogenation activity of a Co/Al2O3 catalyst by a trace amount Pd. TPR studies show that the reducibility of the catalysts was significantly improved with Pd by shifting the reduction peak towards lower temperature as well as increased amount of Co reduction. Higher metal dispersion and H2-spillover effects were considered to be the main reasons for the increased reducibility, which was confirmed by the H2-pulse chemisorptions and NH3-desprotions. Pulse chemisorptions suggested that the metal dispersion was increased by almost 100 % and the metal surface area was significantly increased because of the smaller crystal size of the formed Co particles. From TPD, the heat of desorption was found 60 kJ/mol for Pd-Co/Al2O3, which is less than that for Co/Al2O3. Therefore, it is concluded that presence of Pd decreases the metal support interaction and the binding energies between the metals and the adsorbing molecules, with this playing a role to increase the generation of more reactive hydrogen species, i.e. spillover hydrogen. Further, the acidity, BET surface area and porosity of Pd-Co/Al2O3 was also unaffected due to the incorporation of Pd, which is also encouraging since higher hydrogenation activity of the catalyst can be achieved without compromising the cracking activity. Therefore, this study revealed that trace amount of Pd promoted Co/Al2O3 holds great promise for hydrocracking of heavy oil.