Regulating metal-acid double site balance on mesoporous SiO2–Al2O3 composite oxide for supercritical n-decane cracking

The balance between metal and acid sites directly affects the preparation of high-performance cracking catalysts with high heat sink and low coking. Nevertheless, how to control acid-metal sites balance and its relationship with cracking performance are reported scarcely. In this work, a series of Pt/Al2O3–SiO2 dual sites catalysts with different metal to acid active sites ratio (CM/CSA) were constructed by ethanol-assisted impregnation method and the impact on n-decane cracking under supercritical conditions was systematically and deeply investigated. The results showed that the conversion and carbon deposition increased gradually with varied CM/CSA and reached the balance at CM/CSA of 0.13. The proper ratio CM/CSA (0.13) can balance the deep dehydrogenation coking over metal active sites and high heat sink of cracking over acid active sites, the chemical heat sink reaches amazing 1.75 MJ/kg and carbon deposition is only 22.03 mg/cm2 at 750 °C. Meanwhile, the few metal sites at low CM/CSA and the few strong acid sites at high CM/CSA are the main factors limiting the cracking activity. Low CM/CSA limit the activation of C–H bond and deep dehydrogenation of coking precursor, resulting in relative low cracking activity and carbon deposition, while high CM/CSA limit the activation of C–C bond and increase the deep dehydrogenation. In this contribution, design and construction of metal-acid dual sites can not only provide the technical solution for the preparation of high heat sink and low coking cracking catalyst, but also deepen the understanding of the cracking path of hydrocarbon fuel.