Buying a ticket at the trainstation (Beijing West)

Hello everyone,

I will arrive at Beijing airport on Sunday the 8th of July at 09:50 and I would like to take trainnumber D133 (leaving at 14:20 and arriving at 20:01) to Zhengzhou. Do you know if it is possible if I can buy the ticket as soon as I arrive at the trainstation? And where should I be? After I retrieved my luggage I will go to Beijing West by taxi (directly), so I will arrive around 3 hour prior to departure. Hopefully someone can answer this question for me!

Thanks in advance,

Mark