Comparative study on the performance of n-dodecane isomerization reaction on molecular sieve catalysts with different topological structures

The catalysts were prepared by loading about 0.5% Pt noble metal on Y molecular sieves, ZSM-5 molecular sieves and β molecular sieves with similar Si/Al ratios. The crystal structures of the molecular sieves with different topologies, elemental compositions, pore structures, activities, and Al distributions were investigated by means of XRD, XRF, TEM, N₂ physical adsorption and desorption, NH₃-TPD, Py-FTIR, and ²⁷Al NMR. And then the effect of topology on the catalytic performance of n-dodecane isomerization reaction was investigated. The results showed that when the Si/Al ratios were close to each other, the ZSM-5 molecular sieve had the highest total acid and skeleton Al ratio and the smallest average pore size, the Y molecular sieve had the lowest total acid and skeleton Al ratio and the largest average pore size, and the β molecular sieve's total acid, skeleton Al ratio, and average pore size were between the two others, which indicated that different topologies of the molecular sieves with different combinations of Si/Al atoms affected not only the structure of the pores and the size of the pore but also the number of acidity. In the n-dodecane isomerization reaction, the Pt/ZSM-5 catalyst had the highest activity and the main reaction occurred on the outer surface without selectivity, the Pt/Y catalyst had the lowest activity and the isomerization reaction mainly occurred inside the pores, while the Pt/β catalyst had the activity between the other two catalysts and the isomerization reaction occurred dominantly at the pore opening as the key-locking reaction.