<action method="addColumnCountLayoutDepend"><layout>empty</layout><count>6</count></action>
  <action method="addColumnCountLayoutDepend"><layout>one_column</layout><count>3</count></action>
  <action method="addColumnCountLayoutDepend"><layout>two_columns_left</layout><count>3</count></action>
  <action method="addColumnCountLayoutDepend"><layout>two_columns_right</layout><count>3</count></action>
  <action method="addColumnCountLayoutDepend"><layout>three_columns</layout><count>2</count></action>
  <action method="setToolbarBlockName"><name>product_list_toolbar</name></action>

You need to look for these references they could be in the catalo.xml files a few times for different scenarios such as if the category is an anchor or layered navigation is used.

Once you have found this code you adjust the<count>number</count> according to your layout / number of columns required.