Abstract
An efficient catalyst is desired to produce lighter isoparaffins from heavy n-paraffins by isomerization and hydrocracking, which are environmentally friendly processes for producing high-octane fuel. This paper assesses the suitability of a catalyst consisting of beta zeolite and nanosized (i.e., 5-50 nm; hereafter ns) alumina particles for isomerization and hydrocracking of large n-paraffins. The catalytic performances of three catalysts, namely an alumina-supported metal catalyst (NiMo/γ-Al2O3), a two-component catalyst (ns Al2O3–beta zeolite), and a three-component catalyst (NiMo/γ-Al2O3–ns Al2O3–beta zeolite) for an isothermal reaction with n-hexadecane were evaluated. The results reveal that the conversion and selectivity are improved by increasing the number of components in a catalyst. Specifically, the three-component catalyst exhibits superior catalytic performance between 225 and 350 °C due to concerted effect of the three components. We investigated the effect of the SiO2/Al2O3 molar ratio of beta zeolite on the performance of three-component catalysts and found that beta zeolite with a SiO2/Al2O3 molar ratio of 25 has a higher activity and cracking selectivity with high isoparaffin selectivity of the cracked products (hereafter iso-selectivity) than three-component catalysts with SiO2/Al2O3 molar ratios of 16, 50, and 150; this indicates that there is an optimum SiO2/Al2O3 molar ratio of zeolite in the three-component catalyst.The three-component catalyst composed of NiMo/γ-Al2O3, ns Al2O3, and dealuminated beta zeolite had a high conversion and iso-selectivity. Its catalytic performance is more suitable for producing isoparaffins of gasoline fraction than these of three three-component catalysts composed of ns Al2O3 and non-dealuminated beta zeolite, ns SiO2 and non-dealuminated beta zeolite, or ns SiO2 and dealuminated beta zeolite. Acid treating was found to remove extra-framework aluminum and amorphous alumina from the beta zeolite surface to make Si–OH. It produced reformed acid sites between the Si–OH of the external zeolite surface and ns Al2O3 surfaces, which consequently improved the isomerization and cracking activities due to the acid sites existing at nanopores.
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