http://blogs.msdn.com/b/krishnab/archive/2008/10/04/disable-all-default-ribbons-in-excel-application.aspx
Excel.Style style;
style = Globals.ThisWorkbook.Styles.Add("Style1", Type.Missing);
style.Font.Name = "Calibri";
style.Font.Size = 11;
style.NumberFormat = "General";
style.Borders[(Excel.XlBordersIndex)Excel.Constants.xlTop].LineStyle = Excel.XlLineStyle.xlContinuous;
style.Borders[(Excel.XlBordersIndex)Excel.Constants.xlBottom].LineStyle = Excel.XlLineStyle.xlContinuous;
style.Borders[(Excel.XlBordersIndex)Excel.Constants.xlLeft].LineStyle = Excel.XlLineStyle.xlContinuous;
style.Borders[(Excel.XlBordersIndex)Excel.Constants.xlRight].LineStyle = Excel.XlLineStyle.xlContinuous;
style.HorizontalAlignment = Excel.XlHAlign.xlHAlignCenter;
style.VerticalAlignment = Excel.XlVAlign.xlVAlignCenter;
Set this style object to Excel Range instance
excelRange.Style = style;