Controllable Fabrication And Performance Of HZSM-5 Nanosheet Catalytic Thin-films For Active Cooling Technology With Hydrocarbon Fuel

Catalytic cracking of hydrocarbons over HZSM-5 zeolite under supercritical condition is an effective way to overcome thermal barrier form hypersonic flight.However,the diffusion of hydrocarbons in micropores of HZSM-5 zeolite was reduced under supercritical condition,leding to seriously decreased activity and stability.In this paper,HZSM-5 nanosheet zeolites were prepared by various methods.Examination of their catalytic performance using model reaction of catalytic cracking and combustion of hydrocarbons were performed to study the effects of micro-mesopore structure of zeolites.Two HZSM-5 zeolite nanosheets with Si/Al molar ratios of 25 and 50(NS-25 and NS-50)and thicknesses of about 2.0nm were synthesized using C_22-6-6 as structure directing agent.The catalytic cracking of JP-10 over NS-25 gave a conversion of45.33%,which is 77%higher than that obtained over a conventional HZSM-5 catalyst.The better catalytic performance may be attributed to more Br?nsted acid sites on the external surface,and higher accessibility of acid sites.The enhanced diffusion of JP-10over HZSM-5 nanosheets also leads to high olefin yields,and better coking tolerance.To solve the mesopores sacrifice by interlayer condensation after calcination during preparation in nanosheet zeolite,two pillared nanosheet HZSM-5 zeolites were synthesized,by dual-template(C_22-6-6 and TPAOH)method and Si-precursor(TEOS)intercalation.Dual-template strategy(DZN-2)was demonstrated preserving more mesopores between individual nanosheet with better channel connections than Si-intercalation method(PZN-2).The uniquely pillar-designed structure facilitated diffusion of product and restricted the secondary reaction such as hydride transfer or aromatization which consumed light olefins.DZN-2 catalyst gave 100%higher light olefins selectivity than CZ-500 at 500?.Moreover,DZN-2 displayed an outstanding anti-coking stability,ascribing to the facilitated diffusion of coke precursors.HZSM-5 nanosheet film vertically grown on the surface of support was synthesized by seed-assisted secondary growth method.Owing to the enhanced mass transfer along ultra thin b-axis pathway and hierarchical structure,the prepared nanosheet zeolite films showed reaction rate enhancement up to 300%in catalytic cracking of n-dodecane.The introduction of silicalite-1 crystals effectively enhanced the adhesive strength,zeolite loading as well as the continuity of films.Pillared HZSM-5 nanosheet films on the surface of support were synthesized by dual-tempalted method.The introduction of TPAOH in the synthetic solution can form a pillared structure between the nanosheet layers,avoiding the collapse of the interlayer structure.Owing to the highly connected mesopores,DZN-4(n(C_22-6-6)/n(TPAOH)=10/4)film gave the highest heat sink as 2.99MJ·kg^-1,which is 32%higher than that of conventional ZSM-5.DZN-4 zeolite film also showed the best catalytic stability.A sandwich-structured Pt@ZSM-5 nanosheets(Pt@PZN-2)was fabricated by controllable intercalating Pt nanoparticles between ZSM-5 single-layer sheets.Pt clusters(ca.4.4nm)confined between nanosheet layers exhibits better dispersion and higher thermal stability even after high-temperature treatment,while the Pt clusters also served as pillars which well protected the inter-layers mesopores.Catalytic combustion of toluene shows catalytic activity of Pt@PZN-2 is significant higher than that of Pt-loaded nanosheet ZSM-5 zeolite prepared by conventional impregnation(Pt/ZN-2).For example,the temperature at 5%toluene conversion of Pt@PZN-2 is only 146?.TOF value of Pt@PZN-2 is 4 times that of bulky ZSM-5 supported Pt by impregnation(Pt/CZ-500)and Ea is 17%lower than Pt/CZ-500,which was attributed to the high accessibility and enhanced diffusion of the bulky reactant to active site confined in the stable inter-layer mesopores resulting from the pillar of Pt nanoparticles.