졸-겔(sol-gel)법으로 Co-Mo/Al₂O₃ 촉매를 제조하여 XRD, FTIR, BET, TEM, thiophene 수첨탈황(HDS)반응성 등으로 촉매의 구조 및 반응성을 관찰하고 일반적인 함침법으로 제조한 촉매와 비교하였다. Co-Mo 졸-겔 촉매는 Al(OR)₃을 증류수와 질산으로 해교한 졸에 cobalt acetylacetonate(Co-acac) 와 molybdenum acetylaceto-nate(Mo-acac)를 혼합하거나, 건조 또는 소결한 겔에 Co-acac, Mo-acac를 함침하여 제조하였다. 반응성을 비교하기 위하여 γ-Al₂O₃에 Cobalt nitrate와 ammonium molybdate를 합침하여 촉매를 제조하였다. Co-, Mo-acac 전부를 한 번에 알루미나 졸에 혼합한 촉매는, 금속염으로부터 제조한 촉매보다 HDS 반응성은 떨어졌다. 그러나 알루미나 졸에 일부 Co-, Mo-acac를 혼합하고, 건조 또는 소결한 겔에 나머지 Co-, Mo-acac를 함침한 촉매의 반응성은 크게 증가하였다. 알루미나 졸에 먼저 Mo-acac를 혼합하고 소결한 겔에 Co-acac를 함침하여 제조한 촉매가, 알루미나 졸에 먼저 Co-acac를 혼합하고 소결한 겔에 Mo-acac를 함침하여 제조한 촉매보다 HDS 반응성이 컸다. 이러한 결과는 알루미나 졸에 혼합된 코발트가 알루미나 메트릭스 속에서 들어가 상승 효과가 없는 반면, 소결한 겔에 함침된 코발트는 몰리브덴 산화물 표면에 침적하여 상승효과를 나타냈기 때문이라고 보여진다. 그리고 졸-겔 촉매들이 γ-Al₂O₃에 금속염을 함침한 촉매보다 떨어진 것은, 졸-겔 촉매들의 경우 약 20Å의 micropore가 생기는데 이 micropore에 의해 thiophene이 활성점에 접근하는데 장애를 받기 때문이라고 보여진다.

Co-Mo/Al₂O₃ Sol-Gel Catalyst have been investigated by X-ray diffraction(XRD) FTIR BET and TEM, and thiophene hydrodesulfurization(HDS) and their activities were compared with that of impregnated catalyst. A series of sol-gel catalysts were prepared by mixing Co-, Mo-acetylacetonate(Co-, Mo-acac)with alumina sol, or by impregnating dried gel or calcined gel with these precursors. The alumina sol was obtained from hydrolysis of Al(OR)₃ with excess water and peptization of the resultant hydrate with HNO₃ . The reference catalyst was prepared by impregnating γ-Al₂O₃ with aqueous solution of cobalt nitrate and ammonium molybdate. For the sol-gel catalyst formed from mixing all Co-Mo-acac with alumina sol, the HDS activity was lower than that of reference catalyst. However, HDS activity was significantly increased to the activity of the reference catalyst, when the half of Co-, Mo-acac were mixed with alumina sol and the rest of them were impregnated into calcined gel. For the catalyst first formed from alumina sol mixed with only Co-acac, followed by impregnating a Mo-acac solution into the calcined gel, HDS activity was lower than that of catalyst prepared by reversing the order of adding Co-acac and Mo-acac. This reduction of activity results from the absence of synergic effect due to the migration of cobalt into the alumina matrix during sol-gel process. The impregnated cobalt are, however, deposited on the surface of the preoccupied MoO₃ fine crystallite, so that HDS activity is increased due to the synergic effect. The sol-gel catalysts have a micropore of about 2nm in radius which affects the access of thiophene reactants to active sites, thereby lowering the HDS activity of sol-gel catalysts than that of conventional cobalt-molybdenum on gamma alumina catalyst.

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