Cerium promoted and silica-alumina supported molybdenum oxide in the zeolite-containing hybrid catalyst for the selective deep catalytic cracking of petroleum naphthas

The high performance of hybrid catalysts in the selective deep catalytic cracking of n-hexane and n-heptane – used herein as model molecules for petroleum naphthas – is due to the pore continuum effect created by the close connection between the micropores of the acidified silicalite crystallites and the mesopores of the cocatalyst particles, located in fixed positions within a rigid matrix. The resulting enhanced conversion over the “micro–meso” hybrid catalyst is obtained regardless of the surface composition of the mesoporous cocatalyst or the molecular nature of the feed. However, it disappears when the two catalyst components are both mesoporous materials, i.e. in the case of a “meso–meso” hybrid catalyst. The main active component of the mesoporous cocatalyst, molybdenum oxide supported on silica–alumina, shows surface acidity of both nature (Bronsted and Lewis). Cerium oxide incorporated as dopant, has as main catalytic effect to increase the selectivity to light olefins, while the production of aromatics significantly decreases. However, when the ratio of [Ce]/[Mo] molar concentrations is higher than 0.8, the␣yield of product BTX aromatics rapidly increase at the expenses of that of light olefins. On the other hand, Ce loading onto the microporous silicalite or ZSM5 zeolite results in the same catalytic behavior as with the cerium-doped cocatalyst.