Preparation, Characterization and Catalytic Activity in 2-Propanol Conversion of Potassium and Antimony Mixed Oxides

Abstract

Potassium and antimony mixed oxides were obtained by calcination of the commercial potassium-antimony tartrate trihydrate K(SbO)C4H4O6.3H2O at temperatures ranging from 300 to 800 °C. The structure varied with temperature as revealed by XRD characterization. The modifications occurring during the calcination process were also studied by FT-IR and DRS spectroscopies, along with by thermal analysis (TG/DTG). The solids were tested in 2-propanol decomposition at 200 °C, used as probe reaction for the investigation of acid-basic and redox properties. The catalytic activity was function of the calcination temperature and the best 2-propanol conversion was achieved with the tartrate precursor calcined at 500 °C that crystallizes forming KSbO3 as main phase along with K0.51Sb2.67O6.26 as secondary phase. Under N2 the activity reached the maximum after 10 min, 80% of 2-propanol conversion was the highest value, over the sample calcined at 500 °C, but rapidly decreased with time on stream and almost declined after 1 h. In the presence of air in the reaction mixture, 85% of 2-propanol conversion was achieved at 200 °C, after 20 min under stream, with the most active sample. By increasing the calcination temperature above 500 °C, the conversion decreased, especially for the sample calcined at 800 °C showing the worse conversion, although the stability over time increased, likely due to the achievement of stable crystalline phases and crystallite sizes. In all cases, the 2-propanone selectivity was close to 100%. This behaviour confirmed the occurrence of a dehydrogenation reaction involving the basic sites typical of KSbxOy oxides along with the redox couple Sb(V)/Sb(III).