The mono and bimetallic catalysts for hydrogenation of PAO lubricants

Using halloysite as a natural support and palladium and rhodium salts, one bimetallic and two monometallic catalysts were prepared through wet-impregnation method. The catalysts were characterized via TGA, XRD, FTIR, EDS and elemental mapping analyses and their activity for hydrogenation of poly-alpha-olefin oil was examined and compared. The results indicated that among the three catalysts, halloysite supported Pd nanoparticles and bimetallic halloysite supported Pd-Rh catalyst exhibited the highest and lowest activity, respectively. To clarify the origin of the observed difference in the activity of the catalyst, they have been further characterized via ICP and TEM analyses. The result indicated that the nature of the metallic species affected the loading and dispersion of the formed metallic nanoparticles. In the case of halloysite supported Pd nanoparticles, while metal loading was the highest, the formed particles were fine and well-dispersed. It is whilst that in the case of bimetallic catalyst aggregation of particles was observed which was correlated to its lower efficiency. Optimization of the reaction variables via response surface methodology was also conducted using Pd/HNT catalyst. It was shown that using 5 wt.% catalyst at 130 degrees C under H-2 gas with pressure of 8 bar, hydrogenation led to 97 % yield in 7 h. The catalyst was also reusable for 6 consecutive runs with negligible loss of activity.