Research For New Type Catalysts Of N-heptane Isomerization

With the increasing demand for high-octane gasoline and the more importantenvironmental protection, the isomerization of alkanes is supposed to be of greater and greaterimportance. For alkanes isomerization, one of the key issues is to develop catalysts withhigher activity and higher stability, which has been given great concern in oil and chemicalfield. There is great actual significance for producing superior quality gasoline and decreasingenvironment pollution.The objective of our work is to investigate the isomerization of n-heptane overmolybdenum oxide based catalysts. The effects of the preparation and reaction conditions onthe conversion and isomerization selectivity of n-heptane were studied carefully. The maincontents of the thesis were discussed as follows:(1) It has been found that the MoOx catalyst obtained by H2 reduction at 623K in a periodof 6 hours termed as [MoOx(6h)] exhibites a maximum catalytic activity in the reductiontemperature ranging from 573K to 673K;and the catalytic activity of the catalyst reaches themaximum value with the conversion of n-heptane being 9.8% at 623K in the reactiontemperature range of 548K to 623K. XRD studies show that the active phase of MoOx catalystfor n-heptane isomerization is MoOxHy and MoO2. It is also found from the result of pore-sizedistribution that the MoOx catalyst obtained from H2 reduction has a microporouscharacteristics, with its maximum pore diameter being at 17.9?. In the reaction temperatureranged from 548K to 598K, the apparent activation energy for the n-heptane isomerizationand the cracking of n-heptane is 86.3kJ/mol and 137.8kJ/mol, respectively.(2) It is indicated that catalytic activity of MoOx catalyst for n-heptane isomerization ismarkedly enhanced by incorporation of Ni in the catalyst. On the MoOx(6h) catalyst obtainedby H2 reduction at 623K, the conversion of n-heptane is 3.92%;and the conversion ofn-heptane reaches to 19.63% on the 2wt.%Ni-MoOx(6h) catalyst at the same reactionconditions. The action of Ni might be attributed to the promoted H2 activation, thus in favorof the reduction of MoOx catalyst. XRD studies show that the active phase of MoOx catalystfor n-heptane isomerization was strongly affected by the nickel content. Comparing withMoOx catalysts, the 2wt.%Ni-MoOx(6h) catalysts have a lower specific surface area and porediameter, and also maintain its microporous characteristics.(3) N-Heptane isomerization on the MoOx/SiO2 catalyst was studied. The MoOx/SiO2catalyst shows lower catalytic activity than bulk MoOx catalyst, which can be explained by theinteraction between the support and MoO3 in MoOx/SiO2 catalyst.