It has been reported that the addition of citric acid on Co-Mo/B
2O
3/Al
2O
3 catalysts by a post-treatment considerably increases the HDS activity to the maximum potential activity compared with a simultaneous impregnation method. With the post-treatment, citric acid consumes already dispersed CoMoO
4 and polymolybdate species and thus increases the amount of Co-Mo-S after sulfidation. It seems that the effect of citric acid addition is greater for the calcined Co-Mo catalysts. In the present study, therefore, we investigated effect of calcination temperature of Co-Mo/B
2O
3/Al
2O
3 catalysts with the addition of citric acid by a post-treatment. Several characterizations were conducted in order to get the physicochemical properties of the prepared catalysts. It is shown that the HDS activity of the post-treatment Co-Mo/B
2O
3/Al
2O
3 is increased up to the calcination temperature of 500 deg. Celsius, the optimum temperature, suggesting that the large amount of well dispersed CoMoO
4 is formed while the sintering process occurs with a higher calcination temperature. Moreover, it is found that the HDS activity of Co-Mo/B
2O
3/Al
2O
3 catalysts is independent of the pH value on the citric acid addition. Co-Mo/Al
2O
3 catalysts were also investigated.
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