Preparation Of Cerium Modified Aluminosilicate Supported Platinum Catalysts Toward Glycerol Oxidation

With the mass production of biodiesel,the output of by-product glycerin has increased dramatically,and whether glycerin can be developed and utilized reasonably and effectively has become an important factor restricting the development of the biodiesel industry.Therefore,the preparation of a variety of high value-added products through the oxidation reaction of glycerol has become a research hotspot for the efficient use of glycerol.According to reports in the literature,Pt catalysts have problems such as oxygen poisoning,loss and sintering,and deactivation caused by the adsorption of acidic products.This thesis aims to prepare a highly active glycerol oxidation catalyst.The research is carried out around the pore structure of the carrier,the method of cerium modification of the carrier,and the relationship between the ratio of CeO₂ and the carrier and the catalytic performance.Function to solve the problem of catalyst deactivation.The main research contents and conclusions are as follow:First,three different methods were used to prepare the cerium-modified NaY molecular sieve carrier.The nano-platinum catalyst was loaded by NaBH₄ reduction method.Comparing the catalytic data,it was found that the catalyst obtained by loading CeO₂ with the impregnation method had higher catalytic activity than the ion exchange method.In order to further determine the optimal loading of CeO₂,a series of CeO₂/NaY supports with different loadings of cerium oxide were synthesized by the impregnation method to investigate their catalytic performance.When the loading of CeO₂ was 2 wt%,its catalytic performance reached its best.The experiment found that the loading of CeO₂ through the impregnation method affected the electronic structure of Pt,further changed the adsorption of the reaction substrate and oxidation products to the active center,and suppressed the deactivation of the catalyst to a certain extent.In order to explore the effect of the pore structure and pore size distribution of the support on the catalyst activity and product selectivity.The multi-hole NaY molecular sieve was prepared by desilication and dealuminization of the molecular sieve framework.The molecular sieve treated with acid and alkali not only changed the pore properties of the molecular sieve,but also changed the acid site of the molecular sieve.The experiment found that the Pt/NaY-DeAl catalyst obtained by citrate dealumination modification showed higher activity.After 12 hours of reaction,its conversion rate reached 53%,which was about 15%higher than that of Pt/NaY.The appearance of multi-stage molecular sieve not only maintains the screening effect of microporous molecular sieve,but also improves the diffusion rate of the reaction substrate inside the catalyst and further improves the catalyst activity.In order to further increase the diffusion rate of glycerol in the catalyst and improve the conversion efficiency of the catalyst,HNTs with a larger pore size than the NaY zeolite molecular sieve were selected as the catalyst carrier.The experiment found that by controlling the thermal activation temperature to adjust the hydroxyl content on the surface of the HNTs carrier and different preparation methods of Pt/HNTs,the dispersion of Pt nanoparticles on the carrier can be affected,and the catalyst activity can be further improved.The advantages of the tubular structure in the oxidation reaction of glycerol are brought into play,and the reaction substrate can be continuously and gradually catalyzed when it diffuses in the lumen of the catalyst,which provides a new idea for the design of an efficient catalyst for glycerol oxidation.Four different methods were used to prepare the CeO₂/HNTs carrier,and the nano-platinum catalyst was supported by ethylene glycol hydrothermal reduction method.Comparing the catalytic data,it was found that the catalyst obtained by impregnation method loading CeO₂ had higher catalytic activity.By further controlling the roasting temperature of the dipping method,the loading conditions of CeO₂ were optimized and the optimal loading of CeO₂ was explored.The experiment found that the 2 wt%CeO₂/HNTs carrier was prepared by the impregnation method.The platinum catalyst supported by the ethylene glycol hydrothermal reduction method had the best performance.The conversion rate of glycerol reached 80%at the end of the reaction,which was increased by about 25%compared with Pt/NaY.The addition of CeO₂ affects the electronic structure of Pt,and further changes the adsorption of the reaction substrate and oxidation products to the active center,to a certain extent,alleviates the problem of Pt-based catalyst deactivation.