Preparation, Characterization And Catalytic Dechlorination Performance Of Pd-Ni/AC Bimetallic Nanocatalyst

In this paper,nano Pd-Ni bimetallic catalyst was synthesized and its preparation process and mechanism were studied.Nano Pd-Ni/AC bimetallic catalysts used were prepared by ultrasonic enhanced impregnation with lower energy consumption compared to traditional impregnation method.The chlorine content of bleached lac was used as the evaluation index of catalyst performance（activity and stability）.The effects of modification conditions of the support,ultrasonic time,ultrasonic intensity and Pd-Ni molar ratio on the hydrodechlorination performance of the catalysts were studied by single factor experiments to determine the optimum preparation conditions.The physical and chemical properties of the catalysts,such as composition,phase,particle size and structure,were analyzed with the present representative technologies such as X-ray diffraction,X-ray photoelectron spectroscopy,field emission scanning electron microscope,high resolution transmission electron microscope and H₂-Temperature programmed reduction.The results show that the activated carbon pre-treated with 20%HNO₃ and ultrasonic treatment for 10 minutes has the best performance,and the optimum preparation conditions of nano Pd-Ni/AC bimetallic catalyst are:ultrasonic time 30 minutes,ultrasonic intensity 720W（60%）and Pd-Ni molar ratio 1:1,Under the optimal preparation conditions,the nano Pd₁-Ni₁/AC bimetallic catalyst with the average diameter of 11.47 nm and the particle size distribution of 4?14 nm is uniform on the support without agglomeration.After the catalytic hydrodechlorination of bleached shellac using nano Pd₁-Ni₁/AC bimetallic catalyst,the chlorine content of the bleached shellac was reduced from 2.6312wt%to 0.1419wt%,and the chlorine content of the bleached shellac was reduced from 2.6312wt%to 0.2477 wt%in the fifth consecutive use of the nano Pd₁-Ni₁/AC bimetallic catalyst.Combined with the experimental and characterization results,the production of Pdⁿ⁺species in bimetallic structure promoted the catalytic performance of the catalyst.The nano Pd₁-Ni₁/AC bimetallic catalyst with the best preparation conditions was used to study the catalytic hydrodechlorination of the bleached shellac.The main factors affecting the hydrochlorination process were determined by single factor method:reaction time,reaction temperature and catalyst dosage.The effects of these factors on the hydrochlorination process were investigated.The experimental results show that the reaction conditions only have a positive effect on the catalytic efficiency within a certain range,the optimal reaction conditions for catalytic hydrodechlorination of the bleached shellac were determined by the design and optimization of response surface method,taking the residual chlorine content of the bleached shellac after hydrodechlorination as the only response variable,the optimal reaction conditions for the hydrochlorination of bleached shellac were finally determined as follows:reaction time 80 minutes,reaction temperature 83℃,and catalyst dosage 1.8g.The experimental results showed that the residual chlorine content of the bleached shellac is 0.1294wt%,and the hydrodechlorination efficiency was 95.08%.This chlorine content of 0.1294wt%was far lower than the standards of China for the chlorine content of the bleached shellac,which can completely meet the requirements of food,medicine and other industrial raw materials.In addition,the structure and composition of the bleached shellac before and after hydrodechlorination were analyzed by infrared spectroscopy.The results showed that the catalytic hydrodechlorination did not change the overall functional group structure of the bleached shellac,the only change was the C-Cl bond strength.The C-Cl bond before hydrodechlorination was very obvious,but the C-Cl bond strength after hydrodechlorination was greatly weakened,which proved that the reaction followed the catalytic hydrodechlorination reaction process:in the reaction system,the hydrogen induced is adsorbed and dissociated to H^*by bimetallic nanoparticles,which would react with the chlorine-containing shellac molecules on the surface of bimetallic catalyst under appropriate reaction conditions,and the hydrogen atom replaces the chlorine atom,the shellac with low chlorine is finally obtained.