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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 [114]. 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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