Study On The Preparation And Application Of Pd/AC Catalyst For Decomposition Of Formic Acid Solution

Pd/Active Carbon (Pd/AC) catalysts were prepared by dipping– reducing methods, and the effect of the modification of the activated carbon on the decomposition of formic acid solution was studied. The preparation condition of the catalysts and reaction conditions for formic acid decomposition was optimized, and the decomposition reaction kinetics and mechanism of formic acid solution were investigated.Based on the experiment data the essential investigation results were summarized as follows. The effect of the modifier (acid, alkali, salt) on the carrier was investigated. It is found that among these modifiers, alkali is the best modifier, and the order of the performance of the catalysts is as follows from greater to lower, Alkali, salt, acid. The catalyst which is modified by weak base was more active than that modified by strong base in alkali catalyst modification. The catalyst which is modified by Na2CO3 shows the best catalytic activity, and the decomposition rate of formic acid solution can reach to 86.4%.The preparation conditions of Pd/AC catalyst were optimized. And the optimum conditions are as follows, the carrier AC was pretreated in 1 % Na2CO3 solution, then impregnated in PdCl2 solution for 5 minutes, and formic acid solution was put into the solution to reduce Pd2+ at 70℃, the mole ratio of methanal/Pd was controlled at 1: 0.8, the catalyst then was dried at 80℃and calcined at 400℃in Nitrogen for 3 h.The optimum reaction conditions were investigated and listed as follows, the internal and external effect can be eliminated under the conditions that the hunting speed is at 200 RPM and the particle size is 80-100 meshes. Under those conditions, it was studied that with the increasing of reaction temperature; with the increasing of catalyst usage and the reaction time, the decomposition rate of formic acid solution was increased linearly; and after reacting for 110 min, the concentration of HCOOH was kept unchanged.Empirical rate equation of the decomposition of formic acid solution on Pd/AC catalyst at 80℃was calculated, and the apparent activation energy is 39.2 kJ·mol-1 within the range of 50-90℃. Thermodynamic calculation shows that, under the reaction conditions, the decomposition of formic acid is a spontaneous process. The mole ratio of CO2 / CO was kept unchanged in first 20 minutes, and it was kept similar when the reaction at 90℃and 70℃, which indicates that the activation energy of two reactions are basically similar. When the reaction time is more than 20 minutes, the molar ratio of CO2 / CO was increased constantly, and it is favorable for the reaction to produce CO2 under the low concentrations of formic acid solution.