meta-Stannic acid as an effective support for the preparation of sulfated and tungstated stannias Original Research Article

Sulfated stannia (SO4/SnO2) obtained by drying meta-stannic acids (supplied by Koujundo Kagaku and Yamanaka) at 200 °C, followed by exposing to 3 M H2SO4 and calcining at 300 °C showed catalytic activities higher than those of the materials obtained from conventional gels (preparation of stannia gels from SnCl4 and calcination at 500 °C) for the dehydration of methanol and the isomerization of butane. The catalytic activities were much higher than those of sulfated zirconias. The high activity for the reaction of methanol was kept beyond 8 h of time on stream under flow conditions. The highest activity for the reactions of methanol and butane was brought out by the sulfation with 3–9 M H2SO4. The thermal analysis determined the sulfur value in the catalyst to be 1.7, 2.6, 5.7, and 5.6 wt.% S for the materials prepared by sulfation with 0.5, 1.5, 3, and 6 M concentrations of H2SO4, followed by calcination at 300 °C, respectively. Those quantities of S were coincident with their catalytic activities for the reactions of methanol and butane. Tungstated stannia (WO3/SnO2) was obtained by impregnating meta-stannic acid (Koujundo Kagaku Ltd.) with aqueous ammonium metatungstate (1–80 wt.% W) followed by calcining in air; the materials were examined in the dehydrations of methanol and ethanol and the isomerization of cycloheptane to methylcyclohexane. The materials with small quantities of W gave their highest activities in the high temperature range of calcination, indicating the following tendency; the lower the quantity, the higher was the temperature showing the highest activity: 900, 1000, 1100, 1150, and 1250 °C for the materials with 20, 10, 5, 2, and 1 wt.% W, respectively. The results led to the synthesis of a ceramic acid, calcined at temperatures above 1000 °C, by impregnating with 5 and 10% W followed by calcining at 1000 or 1100 °C in air. The surface acidity determined by the adsorption heat of Ar and the catalytic activity for decompositions of toluene and ethylbenzene were intermediate between the values for mordenite and for silica–alumina, and the stability to water was high.