Regulating metal-acid double site balance on mesoporous SiO_(2)-Al_(2)O_(3) 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/Al_(2)O_(3)-SiO_(2) dual sites catalysts with different metal to acid active sites ratio(C_(M)/C_(SA))were constructed by ethanolassisted 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 C_(M)/C_(SA)and reached the balance at C_(M)/C_(SA)of 0.13.The proper ratio C_(M)/C_(SA)(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 only22.03 mg/cm^(2) at 750℃.Meanwhile,the few metal sites at low C_(M)/C_(SA)and the few strong acid sites at high C_(M)/C_(SA)are the main factors limiting the cracking activity.Low C_(M)/C_(SA)limit the activation of C-H bond and deep dehydrogenation of coking precursor,resulting in relative low cracking activity and carbon deposition,while high C_(M)/C_(SA)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.

Working state map of hydrocarbon fuels for regenerative cooling

Regenerative cooling by endothermic hydrocarbon fuel(EHF)is one of the most promising techniques for thermal management of supersonic or hypersonic aircraft.How to maintain the fuel working in proper states is an important issue to maximize the cooling potential of EHT.This work proposes a novel working state map,including risking zone(RZ),thermal cracking zone(TCZ),supercritical zone(SupZ)and subcritical zone(SubZ),to differentiate possible working states of an EHF during regenerative cooling.Using n-decane flowing in a circular tube as an example,the boundaries of four zones are determined by numerical simulation covering different heat fluxes(0.2-4.0 MW·m^(-2))and mass flow rates(0.5-10.5 g·s^(-1))under two operating pressures(3.45 and 5.00 MPa).Empirical correlations for three boundary lines are obtained and the maximum cooling capacity is identified,as well as the identification of the pressure effect.The revelation of such new perspective of regenerative cooling is of great implication to the design and optimization of cooling system for future thermal management.