稀土金属氧化物对Pd/Al_2O_3催化剂上Pd的分布和蒽醌氢化活性影响

Effect of rare earth metal oxides on the distributing of palladium and catalytic activity of Pd/Al_2O_3 catalyst for anthraquinone hydrogenation

分别以稀土金属硝酸盐和Na2PdCl4水溶液浸渍条形Al2O3,制备了系列用于蒽醌法生产过氧化氢的Pd-RE·Al2O3催化剂.考察了稀土金属氧化物(La2O3,Pr2O3,Nd2O3,Sm2O3)对催化剂上Pd的分布和活性的影响.使用电子探针显微分析(EPMA),H2-O2滴定,N2物理吸附等方法对催化剂进行表征.结果表明,加入适量稀土氧化物,能增加催化剂BET表面积,减小催化剂的Pd层厚度,增加催化剂表面Pd浓度,提高Pd金属分散度,因而提高了催化剂的氢化活性,其影响顺序是:La2O3>Nd2O3>Pr2O3>Sm2O3.

Pd?/Al_2O_3 catalysts modified with rare earth metal oxides (La_2O_3, Pr_2O_3, Nd_2O_3, Sm_2O_3) for anthraquinone hydrogenation to H_2O_2 were prepared by impregnating Al_2O_3 columns with aqueous solutions of rare earth nitrates and Na_2PdCl_4, respectively. The effects of rare earth metal oxides on palladium disperses and catalytic activity of the catalysts were studied by means of electro-probe microanalysis (EPMA), N_2 physisorption and H_2-O_2 titration. It was concluded that rare earth metal oxides are good promoters for Pd- Al_2O_3 in the reaction. The rare earth metal oxides promoters can enhance the BET surface area of the catalysts, increase Pd concentration on the outskirts of the catalyst and decrease Pd thickness in the catalysts, promote the dispersion of Pd on the surface of the support and enhance the catalytic activity of the catalysts. Effect of rare earth metal oxides on the both of anthraquinone hydrogenation activity and distributing of Pd is in the order of La_2O_3>Nd_2O_3>Pr_2O_3>Sm_2O_3.