Combustion of propane over novel zinc aluminate-supported ruthenium catalysts

Nanocrystalline ZnAl2O4 spinel, with high specific surface area, was synthesized by the improved co-precipitation method and used to prepare novel Ru/ZnAl2O4 catalysts. The catalysts were prepared by impregnation method using Ru(NO)(NO3)3 and their performance in propane combustion was investigated. The structure of the catalysts was characterized by FTIR, BET, XRD, TEM, H2 chemisorption and O2 uptake in order to correlate their performance with physicochemical properties. Dispersion (H/Ru) of the Ru/ZnAl2O4 catalysts was high and decreased from 71 to 56% with the rise of ruthenium content from 0.5 to 4.5 wt.%. Dispersion data were consistent with TEM and XRD studies. The O2 uptake results showed that ruthenium in the 0.5–1% Ru/ZnAl2O4 catalysts was oxidized already at 150 °C (O/Ru = 2), while in the 4.5% catalyst at 400 °C. The Ru/ZnAl2O4 catalysts exhibited good activity in propane combustion under oxygen-rich conditions and 100% conversion was reached at about 230 °C. The catalyst activities correlate well with a high dispersion and low Ru particle sizes. It was found that specific reaction rate (TOF) does not depend on the Ru loading or the mean Ru particle size. Moreover, only insignificant aggregation of the highly dispersed ruthenium species occurs under the reaction conditions and samples especially at low metal loadings, form a very stable catalyst for propane combustion. The effect of the regeneration treatment in H2 on the activity of the 4.5% Ru/ZnAl2O4 catalyst was also studied. The catalytic performance of Ru slightly declined in the regenerated samples. The large structural changes in the high-loaded Ru/ZnAl2O4 catalyst observed after regeneration treatment, are probably the best explanation for the lower activity of this system.

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► Zinc aluminate with high surface area is a promising support for Ru catalysts.
► Novel Ru/ZnAl2O4 catalysts exhibit good activity for propane combustion.
► High activity is attributed to high ruthenium dispersion.