Development of Ni-Pd bimetallic catalysts for the utilization of carbon dioxide and methane by dry reforming

The present research deals with catalyst development for the utilization of CO₂ in dry reforming of methane with the aim of reaching highest yield of the main product synthesis gas (CO, H₂) at lowest possible temperatures. Therefore, Ni-Pd bimetallic supported catalysts were prepared by simple impregnation method using various carriers. The catalytic performance of the catalysts was investigated at 500, 600 and 700 °C under atmospheric pressure and a CH₄ to CO₂ feed ratio of 1. Fresh, spent and regenerated catalysts were characterized by N₂ adsorption for BET surface area determination, XRD, ICP, XPS and TEM. The catalytic activity of the studied Ni-Pd catalysts depends strongly on the support used and decreases in the following ranking: ZrO₂-La₂O₃, La₂O₃ > ZrO₂ > SiO₂ > Al₂O₃ > TiO₂. The bimetallic catalysts were more active than catalysts containing Ni or Pd alone. A Ni to Pd ratio = 4 at a metal loading of 7.5 wt% revealed the best results. Higher loading lead to increased formation of coke; partly in shape of carbon nanotubes (CNT) as identified by TEM. Furthermore, the effect of different calcination temperatures was studied; 600 °C was found to be most favorable. No effect on the catalytic activity was observed if a fresh catalyst was pre-reduced in H₂ prior to use or spent samples were regenerated by air treatment. Ni and Pd metal species are the active components under reaction conditions. Best conversions of CO₂ of 78% and CH₄ of 73% were obtained using a 7.5 wt% NiPd (80:20) ZrO₂-La₂O₃ supported catalyst at a reaction temperature of 700 °C. CO and H₂ yields of 57% and 59%, respectively, were obtained.