Enhancing the deN2O activity of the supported Co3O4|α-Al2O3 catalyst by glycerol-assisted shape engineering of the active phase at the nanoscale

Abstract

A series of supported Co3O4/α-Al2O3 catalyst synthesized by glycerol-assisted method was thoroughly characterized (X-ray micro-tomography, XRD, RS, FTIR, SEM/TEM/EDX, TG/DTA, TPR), and their reactivity was evaluated in N2O decomposition in 5% N2O/He and 1.5% N2O, 1% NOx, 1 vol.% H2O, 2.0 vol.% O2. Their superior catalytic activity in comparison to the benchmark Co3O4/α-Al2O3 catalyst, obtained via incipient wetness impregnation with the aqueous solution, was accounted for by differences in cobalt spinel dispersion on the alumina support, spinel nanoparticle size and faceting. Whereas for the samples prepared from the aqueous solution the spinel active phase exhibits a broad bimodal size distribution (with the maxima for 10–50nm crystallites and 300–600nm agglomerates) in the case of glycerol-assisted synthesis a monomodal distribution is featured by isolated spinel nanocrystallites of 10–30nm. At the same time, the presence of glycerol changes the spinel crystallites morphology from rhombicuboctahedron with abundant exposition of the less favorable (111) planes into the truncated cubic shape with the dominant more active (100) facets. It was shown that the beneficial effect of glycerol is sustained in typical gaseous residuals (H2O, NOx, O2) present in the tail gases of nitric acid plants. The observed effect of glycerol-assisted synthesis was accounted for by complexation of cobalt by glycerol, leading to the formation of an intrapore cobalt glycerolate, which upon calcination is transformed into well dispersed Co3O4 cubic nanocrystals.