Oxidative dehydrogenation of propane over Co, Ni and Mo mixed oxides/MCM-41 catalysts: Effects of intra- and extra-framework locations of metals on product distributions

A series of mesoporous MCM-41-based catalysts containing single and binary metal oxides (Mo, Co, Ni, NiMo and CoMo) has been prepared with binaries having one metal incorporated into MCM-41 structure while the other impregnated on the walls. A sample of the catalysts was characterized by temperature programmed reduction (TPR), X-ray diffraction (XRD) and BET surface area. The catalysts performances depended on the location of the active component - intra or extra - in MCM-41 framework. At similar level of propane conversions (14%), Mo- and Ni-incorporated MCM-41 exhibited selectivities to olefins (ethylene, propylene, 1-butylene, i-butylene and 1,3-butadiene) of 47.7% and 28.6% respectively. NiMCM-41, in addition exhibited selectivity to 1-pentylene of 12.2%. A catalyst produced by Mo incorporation followed by Ni impregnation (Ni-MoMCM-1) showed selectivity to propylene of 41.7% with no other olefins. When the sequence was reversed (Mo-NiMCM-41), the propylene selectivity was maintained and 10% ethylene and 14% C4-olefins were additionally produced, at similar propane of conversions. The highest olefins yield of 13.4% was obtained on Mo-NiMCM-41. The sequence of incorporation and impregnation of Mo- and Co- showed similar but less significant effects on the catalysts performance than in the case of Mo- and Ni-MCM-41. Thus, the location of the metals in the catalyst framework is a key parameter in determining the products distributions.