Preparation of Pd-CuO@mSiO2 catalyst and its selective catalytic hydrogenation of substituted nitroaromatics to substituted aromatic amines
Selective catalytic hydrogenation of substituted nitroaromatic hydrocarbons is an effective method to prepare substituted aromatic amines.It is an urgent problem to precisely regulate the reaction site of precious metal catalyst and enhance its catalytic stability in this reaction.The SiO2 core-shell precursor containing PdCu alloy(PdCu@SiO2)was prepared by sol-gel method.Then the mesoporous core-shell SiO2 catalyst containing PdO-CuO(PdO-CuO@mSiO2),the mesoporous core-shell SiO2 catalyst containing Pd-CuO(Pd-CuO@mSiO2)and the mesoporous core-shell SiO2 catalyst containing PdCu alloy(PdCu@mSiO2)were prepared.The catalysts were characterized by TEM,XRD and TG,etc.,and their catalytic performances for selective catalytic hydrogenation of 4-nitrochlorobenzene to 4-aminochlorobenzene were studied.The results show that reaction under the optimal conditions(0.5 mmol 4-nitrochlorobenzene,12.0 mL ethanol,80℃and 1.0 MPa)for 4.0 h,Pd-CuO@mSiO2 has better catalytic performance than Pd@mSiO2 and PdCu@mSiO2,with 4-nitrochlorobenzene conversion rate of 96.5%and 4-amino-chlorobenzene selectivity of 99.6%.The good catalytic performance of Pd-CuO@mSiO2 is related to the strong interaction between Pd and CuO in the structure.Pd-CuO@mSiO2 also shows good catalytic performance for the catalytic hydrogenation of m-chloronitrobenzene,p-nitroacetophenone and 4-nitrobenzoate.In addition,cycling under the optimal reaction conditions for five times,the 4-nitrochlorobenzene conversion rate and 4-amino-chlorobenzene selectivity of Pd-CuO@mSiO2 maintain at 96.4%and 95.7%,respectively.
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