Catalytic functionalities of supported sulfides I. Effect of support and additives on the CoMo catalyst

Abstract

C---S hydrogenolysis (HDS) of thiophene, hydrogenation (HYD) of 1-hexene, and hydrocracking (HCG) of 2,4,4-trimethyl-1-pentene, were used as separate model test reactions to differentiate and assess the catalytic functionalities of sulfided CoMo catalysts, and their dependence on the nature of the support and incorporation of additives. Rate constants and relative catalyst activities for these three reaction types were determined. HDS and HYD activities of CoMo supported on different types of Al2O3 were higher, while the HCG activity was lower compared with CoMo supported on SiO2---Al2O3, SiO2---MgO, or TiO2. For SiO2---Al2O3 supports both HDS and HYD activities decreased with increase in SiO2 content from 10 to 75%, while HCG activity showed the opposite trend. Additives to a finished CoMo catalyst at 0.5% level caused variations in HDS and HCG activities, while HYD was essentially unaffected. HDS was promoted by NH4HF2 and NH4Cl, but depressed by NaNO3, Ca(NO3)2, and H3BO3. HCG was promoted by NH4HF2, NH4Cl, and H3BO3. Additives at 5% level, prior to or after CoMo impregnation, showed a strong depressing effect on HDS and a lesser effect on HYD, while HCG was strongly promoted by NH4HF2, Ti isopropoxide, and H3BO3. The changes in catalytic functionalities are rationalized in terms of different interactions between CoMo phase, support, and additives.