Firstly, there is no Bank of China set at the International Arrival Hall. However, the Travelex has set a money exchange center at the international baggage claim are of Beijing Airport. This center is in service 24 hours round the clock. But its exchange rate is not so nice compared to Bank of China. If possible, I think you could change some before leaving, and then find a Bank of China in downtown Beijing, which obeys to the current exchange rate.