I am using VSTO Deveopment | Excel 2007 | C#. Is there any event to identify that the tab selection in excel ribbon has changed ?
No.
In VSTO2010, the ability to programmatically switch the selected tab was added. Norm Estabrook blogged about it.
this.RibbonUI.ActivateTabMso("TabAddIns");
So while there isn't an event that can be latched onto, at least you can switch the selected tab. For instance, I'm going to use the sheet selection event; when users switch between different sheets of my workbook, I am going to change their selected tab. Each sheet will correspond to a different ribbon tab.