Catalysts For Alkane Isomerization Framework Of Moo <sub> X </ Sub>-sio <sub> 2 </ Sub>

As one of the main routes to produce high-octane gasoline blending components in the crude oil refining industry, alkanes isomerization has drawn much attention throughout the world because it can greatly improve the gasoline quality. For n-alkane isomerization, one of the key issues is to develop catalysts with higher activity, high selectivity and higher stability, which has been widely pursued due to its importance both in academic research and in industrial utilization.n-Heptane isomerization on MoOx-based catalysts was carried out in a continuous fixed-bed reactor at 573 K under atmospheric pressure. According to the results of N2 adsorption-desorption characterization, the MoOx catalyst obtained from H2 reduction at 623 K was found to possess a mesoporous characteristic with its maximum pore volume at the diameter of 4.1 nm. The dynamics of n-heptane isomerization on the MoOx catalyst was investigated. In the reaction temperature ranged from 523 to 598 K, the apparent activation energy for the n-heptane isomerization and the cracking of n-heptane is about 49.3 kJ(mol-1 and 60.6 kJ(mol-1, respectively. At 573 K, the reaction order for H2 and n-heptane partial pressure on the MoOx catalyst for the n-heptane isomerization is 0.35 and 0.33, respectively. MoOx/(-Al2O3, MoOx/SiO2 and Ni-MoOx/SiO2 catalysts with a different loading of MoO3 and Ni were prepared by conventional incipient impregnation method. MoOx/SiO2 catalyst showed a better activity and isomerization selectivity than MoOx/(-Al2O3 catalyst, which could be a result that MoO3 has a weaker interaction with SiO2 than (-Al2O3 support. The MoOx/SiO2 catalyst with a 34.5wt% MoO3 loading exhibited an isomerization selectivity of 95% at n-heptane conversion of 26%, while its specific activity of per gram of MoO3 is only 1/2 of bulk MoOx catalyst. The adding of Ni promoted markedly the reduction of MoO3 phase to the active phase of MoOx. And the Ni-MoOx/SiO2 catalyst showed a higher activity but lower isomerization selectivity than MoOx/SiO2 catalyst. With the Ni loading increasing in Ni-MoOx/SiO2 catalyst, n-heptane conversion reached the maximum of ca. 31% and then kept almost at the level, which is accompanied by a decrease of isomerization selectivity. MoO3-SiO2 catalyst precursor was prepared by mixing the MoO3 powder with silica sol. The characterization of MoOx-SiO2 catalyst by means of SEM, N2 adsorption-desorption method, EDS and XRD showed that the SiO2 in MoOx-SiO2 (44.6 wt%) catalyst acts as a framework in which a large amount of bulk MoOx phase is enveloped to form typical mesoporous structure similar to that of bulk MoOx catalyst. And the 55.4wt%MoOx-SiO2 catalyst maintained the high catalytic activity and isomerization selectivity of bulk MoOx catalyst and exhibited a well-improved mechanical strength in comparison with bulk MoOx catalyst. A H2S pulse injection leads to a decrease firstly and then recovery of the catalytic activity of 55.4wt% MoOx-SiO2 catalyst, indicating the preferable sulfur resistance. Compared with bifunctional 0.5wt%Pt/H( catalyst, the 55.4wt%MoOx-SiO2 catalyst showed higher isomerization selectivity at the high n-heptane conversion level, and both the catalysts have a similar product distribution of n-heptane conversion.