Effect of Rhenium on Ruthenium Dispersion in the Ru-Re/γ-Al2O3 Catalysts

Ru-Re/gamma-Al2O3 catalysts were prepared by the incipient wet co-impregnation method and characterized by ICP-AES, BET, H-2-TPR, XRD, SEM, TEM and H-2 chemisorption. Structure and chemisorption properties of these catalysts were compared with monometallic (Ru, Re) catalysts synthesized by using the same Ru(NO)(NO3)(3) or RuCl3 and NH4ReO4 precursors. Results showed that Ru-Re/gamma-Al2O3 catalysts consist primary of bimetallic nanoparticles with small sizes (< 3 nm), while the larger particles were monometallic Re, especially for the bimetallic catalyst at the Ru/Re atomic ratio of 50:50. Chemisorption data revealed that Re modifies the interaction of hydrogen with ruthenium surface sites. In the chlorine-free Ru-Re catalysts, dispersion of ruthenium increased with the rise of the Re loading. The mean particle size decrease from 1.3 to 0.9 nm by change of the Ru/Re ratio from 90:10 to 50:50. Ruthenium particle size calculated from H-2 uptake agreed well with XRD and TEM data. Ruthenium dispersion of the chlorine-containing bimetallic Ru-Re catalyst (Ru/Re = 75:25) was significantly lower and comparable with the Ru(Cl) catalyst. Also, the large discrepancies between the mean particle size obtained from H-2 chemisorption (3.9 nm) and TEM (1.1 nm) were observed what is explained by the contamination of Ru surface by the Cl- ions.