2 diluted cf 4 and f 2 in addition h 2 and o 2 were supplied as decomposition assist gases with the amount of h 2 being such that the number of h atoms was at least equal to the total number of f atoms in cf 4 and f 2 and the amount of o 2 being at least equimolar to the amount of h 2 supplied these gases were flowed into the column at respective concentrations of 0 92 cf 4 1 1 f 2 5 0 h 2 and 6 0 o 2 as it turned out the removal of cf 4 dropped below 98 when passage of the cf 4 f 2 gas continued for 25 hours at this point in time throughput was 115 l l which was 1 51 times higher than the throughput for the case where only cf 4 gas was supplied throughout the experiment concentrations of co and f 2 were below tolerable levels 1 ppm for f 2 provided that f 2 had been decomposed into hf an experiment was conducted using the same equipment as in example 1 which was packed with the same u03b3 alumina in the same amount and heated to the same temperature as that of example 1 the total gas flow rate was 408 sccm.