The changes of chemical properties by treatment of sulfuric acid were examined by TPD analyzer (Autochem 2920 Analyzer, Micrometritic, America). About 100 mg of the dry sample was weighted accurately and put in a quartz tube.
The sample was pretreatment at 200 C under helium gas for 6 h for drying and degasing.
After degasing, evolved amounts of desorbed gas analyzed by thermal conductivity detector (TCD), while the temperature was increased up to 600 C at a rate of 10 C/min.