Shape-controlled synthesis of Pt particles and their catalytic performances in the n-hexadecane hydroconversion

Abstract

The platinum nanocrystals with truncated octahedral, spherical and cubic morphologies were synthesized and well dispersed onto the ZSM-22 support, in order to investigate the shape effect of Pt crystals on n-hexadecane hydroconversion. It is found that the crystal facets of Pt nanoparticles play more profound roles in determining the catalytic properties. The reaction test shows that both the conversion of n-hexadecane and selectivity of iso-hydrocarbons are higher for the catalysts with octahedron nanoparticles of Pt that are predominantly enclosed by Pt {111} crystal facets than those with spherical and cubic morphologies of Pt, whose surfaces consist of more Pt {100} facets. Combined with the results of CO-IR and TPHD, it is suggested that the activity and selectivity of the reaction are well correlated to the fractions of exposed Pt {111} crystal facets, which possess more activated surface defect sites and higher amounts of activated hydrogens either on the Pt surface or in the Pt phase. Meanwhile, the catalyst activity and selectivity are found to be highly sensitive to the Pt particle size. Smaller Pt particles have higher activity and lower isomerization selectivity.