Sulfur resistance and activity of Pd-Ni bimetallic catalysts for Styrene Hydrogenation

CAROLINA BETTI; JUAN M. BADANO; M. JULIANA MACCARRONE; CECILIA R. LEDERHOS; NICOLÁS CARRARA; MARIANA BUSTO; CARLOS VERA; M. QUIROGA

Conferencia; 16th International Congress on Catalysis (ICC 16); 2016

Pyrolisis gasoline (PYGAS) is an intermediate boiling product of naphtha steam cracking with a high octane number and high aromatic/unsaturated contents. PYGAS must be purified in order to minimize the concentration of diolefins, responsible for the formation of gums. The widespread method of purification is the selective hydrogenation of vinyllic bonds, keeping the aromatic rings unaltered. These streams can have up to 1000 ppm of sulfur compounds. Among these compounds thiophenes are the most common ones and they are the main cause of the activity loss of metal catalysts in several refinery processes. The objective of this work is to evaluate the activity and sulfur resistance of bimetallic Pd-Ni catalysts during the partial hydrogenation of styren.Bimetallic PdNiN and NiNPd catalysts were the most active during the poison-free selective hydrogenation of styrene. A higher concentration of Pdδ- species would be responsible for the higher activity of these catalysts. The PdNiCl and NiClPd catalysts had the highest values of the superficial Cl/Pd atomic ratio and were also the most sulfur resistant. Pd oxychlorinated species (Pdδ+) probably prevented the adsorption of thiophene both by a steric hindrance effect (big size of oxychlorinated species) and an electronic one (high electronegativity of Cl). The NiClPd catalyst was more sulfur resistant than the PdNiCl one. This is likely due to a higher amount of exposed Pdδ+ species and the absence of Ni0 on NiClPd. Both effects would promote a weak adsorption of thiophene and an increase of the concentration of the most active sites.