NiMo/Al2O3 promoted hybrid catalysts of nanosized alumina and beta zeolite for hydrocracking with isomerization

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 Al 2O3-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/ Al 2O3 molar ratio of beta zeolite on the performance of three-component catalysts and found that beta zeolite with a SiO 2/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/Al2O 3 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 SiO 2 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.