You have 2 options - either freeze panes "Windows" then "Freeze Panes" or on the right hand scroll bar theres a very small horizontal line above the up arrow. If you place the cursor over that line cursor should change to 2 horizontal lines with an up and down arrow.
If you drag that down, you will split the current window you are in. Stop where you need to and you can scroll the lower window as much as you need, and the upper window which will have your categories will always remain visible.