Three different mesoporous materials were investigated to understand the role of different pore structures in their catalytic performance. MCM-41 was chosen as mesoporous material with unidimensional pore channels, while MCM-48 and KIT-1 were chosen as mesoporous materials with three dimensional pore channels. The post-salt treatment was applied to increase the hydrothermal stability of M41S materials, while KIT-1 was used without the post-salt treatment. Molybdenum catalysts supported on MCM-41, MCM-48 and KIT-1 were prepared using incipient wetness impregnation method and they were characterized with X-ray diffraction(XRD), $N_2$-adsorption, NH3-TPD, TEM and TGA. The effect of different connectivity of the mesopore materials was investigated in view of the catalytic activities and coke deposit in thiophene hydrodesulfurization(HDS) over the mesoporous material supported molybdenum catalysts. The thiophene HDS reaction was carried out in a micro-flow reactor at 400℃ and 20 atm with space time of 5.71 gr·min/cc and the $H_2$/thiophene mole ratio of 15.
The characteristic XRD peaks of mesoporous materials were identified even up to 10 wt% loading of molybdenum. As the metal loading increased, the BET surface area , the pore volume and the average pore diameter of the catalysts decreased. However, the mesoporosity and rather high surface area of the catalysts were retained in all cases. The mesostructure and physical properties of supported molybdenum catalysts were not affected significantly via post salt treatment during the impregnation.
Mo/MCM-41, Mo/MCM-48 and Mo/KIT-1 catalysts showed a similar activity change from the start of HDS reaction to 5hr. The Mo/MCM-41 catalysts showed rapid deactivation after 5hr. The rapid deactivation of Mo/MCM-41 catalysts is believed due to the blocking of their unidimensional pore channels with coke deposits. On the other hand, the Mo/MCM-48 and Mo/KIT-1 catalysts showed a stable activity up to 8hr. The three dimensional pore structure of these catalysts should have reduced the risk of channel blockage by coke and facilitated the transport of reactant and product molecules. The amount of coke deposit during thiophene HDS was measured by TGA and their effects on the pore structure and surface area were observed with XRD and $N_2$-adsorption, respectively.
The aluminosilicate mesopore material(Al-MCM-41, Al-MCM-48 and Al-KIT-1) were prepared through post impregnation of AlCl3 into the siliceous mepore materials, MCM-41, MCM-48 and KIT-1, respectively. The aluminosilicate supported molybdenum catalysts showed higher activity than their siliceous counterparts. The acidity of the aluminosilicate supports as measured by NH3-TPD might help to crack the thiophene so as to improve the HDS activity. The rapid deactivation of Al-MCM-41 supported molybdenum catalysts would be also due to the blocking of the unidimensional pore channels with coke deposits and metal oxide crystallites. The Mo(10)/Al-MCM-48 and Mo(10)/Al-KIT-1 catalysts with three dimensional pore channels showed stable activities up to 5hr for a given Si/Al ratio.
It is expected that the molybdenum catalysts having three- dimensional mesopore structure would be useful for HDS process in view of their resistance to coke depositions.
post-salt treatment를 거친 메조포어 분자체에 몰리브데늄 금속을 담지하여 탈황촉매를 제조하였다. 담지 과정과 탈황반응을 거친 후에도 각 담체 고유의 XRD pattern과 우수한 물리적 성질을 유지하고 있었다. 이는 post-salt treatment를 통해 메조포어 분자체의 수열안정성과 기계적 강도가 크게 향상되어 촉매의 구조 붕괴가 거의 일어나지 않았음을 의미한다.
MCM-48과 KIT-1에 몰리브데늄을 담지한 촉매의 경우가 MCM-41에 몰리브데늄을 담지한 촉매보다 티오핀 탈황반응에서 높은 안정성을 보였다. MCM-41을 담체로 사용한 촉매상에서 반응 개시 후 5시간부터 나타나는 급격한 비활성화 현상은 MCM-41 담체의 일차원적 세공구조가 탄소침적에 의해 막혀 반응물의 유입 및 확산이 어려워졌기 때문이며 MCM-48, KIT-1 담체에서는 탄소침적에 의해 세공이 막히더라도 담체의 삼차원적 세공구조로 인하여 지속적인 반응물의 유입 및 확산이 용이해져 반응개시 후 8시간까지 높은 탈황 활성이 유지되었다.
세가지 담체 (MCM-41, MCM-48, KIT-1)에 알루미늄을 첨가하여 촉매를 제조한 후에 티오핀 탈황반응의 촉매활성을 측정하였다. 모든 촉매상에서 증가된 산도(acidity)에 의해 탈황활성이 증가했으나 Al-MCM-41을 담체로 사용한 경우는 반응시작과 동시에 활성저하가 관찰되었다. Al-MCM-48과 Al-KIT-1을 담체로 사용한 경우, 반응개시 후 5시간까지 담체의 삼차원적 세공구조로 인하여 높은 탈황활성을 유지하고 있었으나 시간이 지남에 따라 Mo(10)/Al-KIT-1(5) 촉매에서도 서서히 활성이 저하되는 현상을 관찰할 수 있었으며 이는 KIT-1 담체의 경우 MCM-48 담체와 달리 short-range 메조포어를 가지고 있어 탄소침적에 영향을 받았기 때문이라 사료된다. Mo(10)/Al-MCM-48 촉매의 경우는 5, 20의 Si/Al 몰비에서 모두 높고 안정적인 탈황활성을 보였다.
