コード

import pandas as pd

list1 = [1, 2, 3, 4, 5, 6, 7, 8]
list2 = [1,3,5,7,9,11]
list3 = list1 + list2

pd.Series(list3).drop_duplicates().tolist()

結果

[1, 2, 3, 4, 5, 6, 7, 8, 9, 11]