Preparation Of Nano-SiO₂ Spherical Hydrogenation Catalystand Its Application Study On The Hydrogenation Of α-pinene

α-Pinene mainly exists in turpentine.As a major producer of turpentine in China,a large amount of turpentine is directly used without further processing,which has led to a serious imbalance between the production capacity and output value of China’s pine industry.α-Pinene can be hydrogenated to produce downstream products.As one of the hydrogenation products ofα-pinene,cis-pinane is an important chemical intermediate.Due to its unique spatial structure,it has been widely used in the fields of spices,medicine,and other fields.Therefore,further research on the hydrogenation of pinene in turpentine oil is of great significance to improve the high value utilization of the pine forest industry in China.The application of traditional catalysts is limited due to their low activity,poor life and unfriendly environment,so it is particularly important to prepare a high-efficiency,structurally stable and green catalyst for the hydrogenation ofα-pinene.SiO₂has many advantages,such as small particle size,many micropores,large specific surface area,strong surface adsorption and easy surface modification,which has attracted much attention in the field of catalysis.In this paper,nano-SiO₂is used as the carrier,and loaded metal was used for hydrogenation ofα-pinene modified by-NH₂.The catalyst were analyzed by FT-IR,TEM,XRD,XPS,H₂-TPR and N₂adsorption-desorption.The main contents are as follows:（1）Spherical SiO₂with an average size of 170 nm was prepared by the sol-gel method,and was modified by 3-aminopropyltriethoxysilane（APTS）.The surface of modified SiO₂is rich in nitrogen containing functional groups-NH₂.The presence of-NH₂can anchor and disperse active metals.The modified SiO₂was named SiO₂-NH₂.With SiO₂-NH₂as catalyst carrier and Pd as active component,Pd/SiO₂-NH₂with different Pd sources was prepared by impregnation method.Pd/SiO₂-NH₂was used for the hydrogenation ofα-pinene.The results showed that the catalytic performance of Pd/SiO₂-NH₂prepared with K₂Pd Cl₄as Pd source was the best.The optimum reaction conditions were determined:0.1 g Pd/SiO₂-NH₂,2.0 gα-pinene,Pd loading 2 wt%,initial pressure 3MPa,reaction temperature 120℃,reaction time 1.5 h,the conversion ofα-pinene reached99.3%,and the selectivity of cis-pinane reached 75.2%.The activity of the catalyst decreased after 4 times of repeated use,and the loss of active metals is the main reason for the decrease in catalytic activity.In addition Kinetic analysis ofα-pinene hydrogenation reaction shows that Pd/SiO₂-NH₂can effectively reduce the good performance ofα-pinene hydrogenation reaction activation energy is attributed to smaller Pd particles and higher dispersion.The smaller the particle size,the greater the effective surface area,and the more favorable the adsorption of reaction molecules.（2）In order to increase the service life of the catalyst and the selectivity of cis-pinane,Based on the previous chapter,we introduced the second metal Ni and wrapped the outer layer with a mesoporous shell to prepare a Pd-Ni bimetallic SiO₂@Pd-Ni@mSiO₂core-shell catalyst,the morphology of the catalyst was optimized by changing the amount of NH₃·H₂O added,and the morphology of the synthesized catalyst was optimal when the amount of NH₃·H₂O added was 1 m L.The effects of reduction temperature,shell thickness,and shell pore size on the catalytic reaction were investigated.The optimal reduction temperature was 300℃,the optimal shell thickness was below 25 nm,and the optimal shell pore size was 2.37 nm;The optimum ratio of Pd-Ni was determined,2Pd-10Ni is the best,In addition,the presence of Ni in the oxidized state can promote the conversion of the reaction product to cis-pinane.The reaction conditions were optimized:under the conditions of catalyst dosage 0.1 g,α-pinene 3.0 g,reaction temperature 80℃,initial pressure 3 MPa,reaction time 1.5 h,the conversion ofα-pinene can reach 99.4%,and the selectivity of cis-pinane can reach 93.3%.The reason for the high activity is due to the electronic effect between Pd-Ni bimetals.In addition,the cycle service life of the catalyst was investigated.The activity of the catalyst remained unchanged after 6 cycles and only decreased by 7.9%after 8 cycles.After a series of characterization,it was found that the decrease in catalytic activity may be due to the aggregation of metal particles caused by high temperatures during multiple regeneration processes.（3）In order to further improve the selectivity of cis-pinane,we introduced the third metal（Al,Co,Cu）on the basis of the third chapter.Through screening,we determined that the performance of the SiO₂@Pd-Ni-Cu@mSiO₂three-metal core-shell catalyst prepared by Cu as modified Pd-Ni was the best.The introduction of Cu could significantly improve the selectivity of cis-pinane,and determined the optimal Cu content.On the basis of the optimal Cu content,we optimized the reaction conditions:catalyst dosage 0.1 g,α-pinene 3.0 g,reaction temperature 100℃,Under the conditions of initial pressure of 3 MPa and reaction time of 2 h,the conversion ofα-pinene is 99.1%,and the selectivity of cis-pinane can reach 97.5%.The reason for high selectivity is mainly due to the synergy between Pd-Ni-Cu,and the resulting electronic structure is more conducive to the formation of cis-pinane adsorption.In addition,the cycle life of the catalyst was investigated,and the activity of the catalyst remained high after 5 cycles.In conclusion,we have prepared three kinds of catalysts Pd/SiO₂-NH₂,SiO₂@Pd-Ni@mSiO₂,SiO₂@Pd-Ni-Cu@mSiO₂and used in the hydrogenation ofα-pinene in this paper.The results showed that the synergism between various metals and the core-shell structure not only achieved the high selectivity of the target product,but also improved the cycle life of the catalyst.Therefore,the hydrogenation catalyst with high activity and stability designed in this study provides a new strategy for the hydrogenation ofα-pinene.