基于能带理论研究非贵过渡金属对Pd基催化剂的影响

Influence of Non-noble Transition Metals on Pd-based Catalysts Based on Band Theory

采用乙二醇为溶剂和还原剂、谷氨酸为螯合剂、非贵过渡金属为助剂、 XC-72为载体的一步溶剂热法制备了3种Pd基催化剂:PdCr/XC-72, PdMn/XC-72和PdHg_(3.5)/XC-72.实验结果表明, Cr、 Mn、 Hg 3种非贵过渡金属元素的加入会影响催化剂中活性金属颗粒的粒径和分散度.其中, PdCr/XC-72催化剂具有金属粒径小、分散均匀的特点,其在无溶剂条件下对DL-sec-苯乙醇的转化率为91%,远远高于PdMn/XC-72(53%)和PdHg_(3.5)/XC-72(32%).同时,利用基于密度泛函理论的第一性原理,从能带理论和d带空穴的角度出发,进一步从理论上分析了PdCr/XC-72催化剂催化活性较好的原因.

Thre kinds of Pd-based catalysts: PdCr/XC-72, PdMn/XC-72 and PdHg3.5/XC-72 are synthesized by the one-pot solvothermal method, with ethylene glycol as solvent and reductant, glutamate as chelating agent, non-noble transition metals as additives and XC-72 as the carrier. The influence of Cr, Mn, Hg on the particle size and dispersion of Pd nanoparticles in the process of the catalysts preparation are investigated by utilizing XRD, TEM and EDS characterization methods. The results suggest that PdCr/XC-72 catalyst with small metal particle size and uniform dispersion has the highest catalytic oxidation reactivity for the solvent-free oxidation of DL-sec-phenethylalcohol. The test results of solvent-free oxidation of DL-sec-phenethylalcohol over PdCr/XC-72 catalyst showed that its alcohol conversion is 91% at 403 K, 3 h, which is much higher than that of PdMn/XC-72(53%) and PdHg3.5/XC-72(32%). Based on the band theory, the state density and d belt hole of PdCr, PdMn and PdHg were calculated by the first principles calculation based on density functional theory. The calculation results indicated the electronic state of Pd atom was optimized in the presence of Cr. Thus, the activity and selectivity of PdCr/XC-72 catalyst were improved.