The Effect Of ZSM-5 Loaded Catalyst Used In The Catalytic Oxidation Reaction Of Hexyl Alcohol

The hexanal, as one kind of organic intermediates, is an important raw material to compound spices and other organic matters, and among all the current methods of compound hexanal, the catalytic oxidation of hexyl alcohol draws widespread attention due to high efficiency and easy operation. This paper, with ZSM-5 as the carrier, adopted the incipient wetness impregnation method to prepare the catalysts of supported metal oxide, used it in the catalytic oxidation reactions from hexanol to hexanal alcohol, studied changes in the catalytic properties of catalysts after modification and analysis the microstructure as well as physical and chemical characteristics of catalysts through XRD, BET, SEM, FT-IR, TG, NH3-TPD and others to explain the catalytic properties. The main content of the paper is as follows:The ZSM-5 zeolite showed some catalytic activity due to its unique pore structure and the active center. And loading the oxide of metal such as Cr, Al, Bi, Mg and others could enhance the activity of the catalyst. The reason was that the load of metal oxide might increase the surface acidity of the catalyst, enhance the activity center and help with the reaction. The performance was best when loading Cr₂O₃.The difference in both the loading and calcinations temperature of Cr₂O₃ could affect the catalytic properties of Cr₂O₃/ZSM-5. Suitable loading and firing temperature was beneficial to maintain the quite large surface area, pore volume and pore size of the original catalyst, and more acidic catalyst surface to enhance the activity of the center, make Cr₂O₃ highly dispersed at the surface and the pores of ZSM-5 and provide a wealth of channels for the adsorption of hexyl alcohol and oxygen molecules to prompt the reaction and exhibit better catalytic activity. The catalytic effect would not be obvious if the loading amount was too small, while the excessive Cr₂O₃ may clump together to plug the catalyst pores and impede the exchange between the substances if the loading was too much. The too low firing temperature cannot achieve the desired effects, while too high temperature caused the metal oxide sintered with denatured inactivation. The catalytic effects of Cr₂O₃ effects of Cr₂O₃/ZSM-5 was best when the loading amount was 5% and the firing temperature was 500?.Attaching Bi₂O₃to the Cr₂O₃/ZSM-5 for the preparation of two-component metal oxide catalyst could effectively enhance the catalytic activity. This was because the loading of Bi₂O₃ could enhance the dispersion degree of Cr₂O₃ on ZSM-5 and provided the necessary active centers for catalyst to make the reactant better binding to the active site, promoting the reaction and exhibiting better catalytic" active. At this point, the 5% Cr₂O₃-2% Bi₂O₃/ ZSM-5's conversion rate to hexyl alcohol was 22.3% and the yield and selectivity of hexanal was 8.7% and 39.1%, respectively.The catalytic activity of 5% Cr₂O₃-2% Bi₂O₃/ZSM-5 could be enhanced by optimizing conditions of the hexyl alcohol to n-hexyl aldehyde oxidation reaction. The optimized conditions should be:reaction temperature was 140 ?, reaction time was 5h and catalyst dosage was 30ml hexyl alcohol corresponding to 1g catalyst. It was known from studies on the stability of the catalyst that the catalytic activity of 5% Cr₂O₃-2% Bi₂O₃/ZSM-5 reused three times still maintained a high value, although there was some decline. In this case, the conversion rate of hexyl alcohol was 23.3% and the yield and selectivity of n-hexanal was 7.1% and 30.5%, respectively.