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Unformatted text preview: ture XRD measurements was additionally performed. From the processes that are related to the intended partial oxidation of C3H8 it is known
that the basicity is an important factor in the coke resistance of the catalysts. For the
determination of the basicity of solids three methods are generally used: Hammett
measurements, temperature programmed desorption of probe molecules and test
reactions. Hammet measurements involve the adsorption of indicators from suitable
non-aqueous solutions, where the solvent does not interact with the catalyst acid or
basic sites, the acidity or basicity of the catalysts is determined from the colour change
of the indicator . As the studied catalysts change their own colour with the Ni/Mg
ratio, from white for pure Mg/Al catalyst to darkish green for the pure Ni/Al catalyst
Hammett indicators were regarded as not suitable for the measurement of the basicity. Basicity can also be determined by temperature programmed desorption (TPD) of
specific molecules adsorbed in a controlled manner prior to the desorption process. For
the measurement of the basicity CO2 has been repetitively employed [49, 89, 115, 116,
117]. CO2 can adsorbs on basic sides of oxide surfaces to form a superficial carbonate.
Various TPD of CO2 experiments were systematically performed in order to find optimal
test conditions. The basicity or acidity of solids can also be characterised by the certain reactions that
are either only catalysed by acidic or basic centres or that form different products over
basic centres than acidic centres. From several test reactions in the gas phase
reported in the literature two were chosen for the purpose of the scaling of the basicity
of the catalysts. The first test reaction is the transformation of isopropanol (2-propanol)
to propene and/or to acetone [48, 89, 116, 117, 118, 119, 120]. Generally speaking, 1. Introduction 49 ytrtrghrhrhhrhrhhffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
isopropanol is transformed to acetone by basic sites of t...
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