Tungstated zirconia catalysts with a porous support for heptane isomerization

Abstract

The advanced WO3-ZrO2 catalysts with palladium as the active metal and porous alumina supports of different phase composition have been synthesized. Aluminum oxides purchased from Sasol, which were formed as extrudates (E), and spherical aluminum oxides (S), in which the phase composition is represented by alumina modifications θ-Al2O3, δ-Al2O3 and α-Al2O3, served as the supports . The phase composition of the support was shown to strongly affect the activity of supported Pd/WO3-ZrO2 catalysts. When passing from the set of Al2O3 θ- and δ-phases to the phase composition θ- and α-Al2O3, an increase in activity of the catalysts is observed, which is indicated by a 10–30 °С shift of the temperature dependences of heptane conversion toward lower temperatures. The appearance of the α-Al2O3 phase is accompanied by a decrease in specific surface area of the catalysts, thus increasing the density of acid sites and hence changing the activity. Pd/WZ catalysts with supports S have a higher acidity (3.7–6.3 μmol/m2) compared to the samples with supports E (2.8–3.6 μmol/m2). The increased acidity of Pd/WZ/S catalysts amplifies side reactions of heptane cracking with the formation of gaseous С1–С4 hydrocarbons. In its turn, moderate acidity of Pd/WZ/E catalysts increases the formation selectivity of heptane isomers (89.2–89.3 % at a heptane conversion of 81.5–83.2 %) in comparison with the catalysts with supports S (the isomerization selectivity 84.9–85.6 % at a heptane conversion 80.4–81.4 %).