Pt And Pt-Sn Catalyst Supported On Hierarchical Porous ZSM-5 For Selective Hydrogenation Of Cinnamaldehyde

Selective hydrogenation of a,β-unsaturated aldehydes to corresponding unsaturated alcohols has been studied deeply because of its great importance both in product applications and in academic research. Due to its specific role in producing fine chemical such as perfume, spice and pharmaceutical, cinnamyl alcohol, which is synthesized via selective hydrogenation of cinnamaldehyde, has been one of the focus of heterogeneous catalysis. However, both thermodynamic calculations and reaction kinetics indicated that hydrogenation of C=C is more favorable than that of C=O bond, which makes selective hydrogenation of C=O greatly challengeable. Although metal hydride works well, the high cost of metal hydride hinders its industrial application. Among the researches reported, metal oxides such as SiO2, TiO2 and Al2O3 and carbon materials such as graphene and carbon nanotube were the most frequently used supports. However, Pt catalyst supported on these materials is usually not selective mainly due to difficult modulation of electronic properties of Pt particles by interaction with support. In this thesis, we applied hierarchically porous ZSM-5 (HZSM-5) obtained by partly alkaline desilication as support for loading platinum nanoparticles for the selective hydrogenation of cinnamaldehyde (CAL). In order to modulate the surface property of Pt nanoparticles, trace amount of tin was added as a promoter to prepare Pt-Sn/HZSM-5 catalyst for the tested reaction.Hierarchicaly porous ZSM-5 was prepared by simple alkaline desilication of original ZSM-5. Characterizations show that the structure of ZSM-5 remained after desilication treatment and the morphology didn’t change obviously. Mesopore appeared as expected indicating the existence of hierarchical pores, which is centered at 4 nm.The Pt/HZSM-5 catalyst was prepared by general impregnation to catalyze selective hydrogenation of CAL. As a result, the Pt/HZSM-5 catalyst showed better performance than those supported on β zeolite or original ZSM-5. It can be attributed to the increased mass transportation in mesopores of HZSM-5, larger Pt particle size and more Lewis acid sites, which prefer the adsorption of C=O to C=C.Minimal Sn was added as promoter to prepare Pt-Sn/HZSM-5 by impregnation and the Pt-Sn/HZSM-5 catalyst furnished high conversion and high selectivity (96% in conversion over 80% in selectivity). A series of characterizations are employed to investigate the structure and composition of the support and catalyst. It was found that the addition of trace amount of Sn didn’t affect the structure and surface property evidently except that the diameter of Pt particles was a little larger. The trace amount of tin in the Pt-Sn/HZSM-5 catalyst plays a crucial role in getting higher conversion with relatively high selectivity to desirable cinnamyl alcohol.