【作者】 邹吉军；

【导师】 刘昌俊；

【作者基本信息】 天津大学 ， 化学工艺， 2005， 博士

【摘要】 负载型金属催化剂应用广泛,制备高效催化剂是提高效率、降低成本的关键。发展新的催化剂制备方法具有重要的现实和理论意义。本文对等离子体处理制备高效催化剂进行了系统研究,分析了制备方法与催化剂的物理化学性质和活性之间的关系,探讨了等离子体制备催化剂的共性特征,力图建立等离子体制备高效催化剂的方法体系。同时,鉴于能源和环境问题日益严峻,太阳能和生物质等可再生能源的利用受到越来越多的重视,本文分别选取用于光催化制氢和葡萄糖氧化的催化剂作为研究对象。利用等离子体增强的浸渍法制备了Pt/TiO₂催化剂,制备步骤包括:浸渍、等离子体处理、焙烧和还原。对于醇/水混合物制氢反应,等离子体制备的催化剂具有比常规催化剂更高的活性,当负载0.5wt%金属时,其活性是常规催化剂的2.3倍。金属负载量对等离子体制备的催化剂活性影响不大,而对常规催化剂影响极大。催化剂表征证明,等离子体处理将负载的氯铂酸还原为特殊金属团簇,焙烧后金属被氧化,同时与载体形成扭曲的金属-载体界面,导致增强的金属-半导体相互作用,使得催化剂的物理化学性质得到改善。等离子体制备的催化剂具有较高的金属分散性和稳定性,以及较强的近紫外区域吸光能力。同时,特殊的金属-载体界面有力地促进了电子从半导体到金属的传递速率,从而极大地提高催化效率。为了使氧化镍与载体之间生成一个金属夹层,提高负载NiO的半导体催化剂的效率,对金属-载体界面进行了设计和控制。常规方法包括:浸渍、焙烧分解、500℃还原和200℃氧化。在热分解过程中,镍原子由于热扩散进入载体体相,形成扩散的界面区域,没有获得理想的金属-载体界面。等离子体方法利用等离子体处理代替焙烧,在常温下使Ni（NO₃）₂迅速分解,红外照相测量等离子体的温度低于40℃,有效地避免了镍原子的热扩散,经过后续的还原-氧化过程,形成了界线分明的平整的金属-载体界面。等离子体处理还提高了金属-载体界面面积和金属分散性。在光催化中,扩散的界面会妨碍光生电荷的分离和传递,而平整金属-载体界面具有更高的电荷分离和传递效率。对于水分解反应,具有平整金属-载体界面的NiO/Ta₂O₅和NiO/ZrO₂的活性分别是常规催化剂的1.7倍和1.5倍。建立了等离子体还原负载型金属催化剂的方法。等离子体可以使H₂PtCl₆快速地还原为金属单质,获得高分散的非晶态金属团簇。对于光催化制氢,等离子体还原的Pt/TiO₂活性与氢还原催化剂相当,比化学还原和光沉积的催化剂高。在更多还原

【Abstract】 Metal-loaded catalysts have been extensively used in chemical industry. Theoperating efficiency and cost depend on the activity of catalysts. The presentstate-of-art status of technologies for catalyst preparation is far from perfect and theexploring of new preparation method is necessary. In this dissertation, the plasmamethod was systematically investigated with the aim of establishing a new andeffective technique for the preparation of highly efficient catalysts. With regard to theincreasing interest in utilization of solar energy and biomass, the catalysts forphotocatalytic hydrogen generation and glucose oxidation were chose as the modelcatalysts.Pt/TiO₂ was prepared by a plasma-enhanced impregnation method includingimpregnation, glow discharge plasma treatment, calcination and reduction. For thephotocatalytic H2 from water/methanol mixture, such catalysts show significantlyhigh activity. Especially, the plasma-prepared 0.5wt%Pt/TiO₂ exhibits a 2.3 timeshigher activity when compared with the conventional one. The activity ofplasma-prepared catalysts does not change much with the amount of Pt loaded, whilethat of conventional catalysts is greatly dependent on the loading-amount. Catalystcharacterizations show that the plasma treatment produces novel metal clusters. Theseclusters are oxidized with calcinations in air. And a largely distorted metal-supportinterface is produced, inducing an enhanced metal-semiconductor interaction. Thisinteraction improves several properties of the catalysts such as metal dispersion andstability, and optical absorption in near UV region. Moreover, the novel metal-supportinterface greatly facilitates the electron transfer from the semiconductor to metalparticles, leads to remarkably high efficiency.The metal-support interface was designed and controlled to improve the activityof NiO-loaded semiconductor catalysts. In conventional method, semiconductors wereimpregnated with Ni（NO₃）₂, calcined, reduced at 500℃ and re-oxidized at 300℃.The nickel atoms migrate into the crystal of support during the thermal decomposition,and a diffused interfacial region is produced for the resulted catalysts. This is differentfrom the previously designed interface. A plasma treatment was used to replace thethermal calcination to decompose Ni（NO₃）₂. IR image shows that the temperature ofplasma is less than 40℃. Thus the thermal diffusion of nickel atoms is avoided. Withthe sequent reduction-oxidation treatment, a clean metal-support interface is producedwhich is identical to the designed one. In addition, the size and shape of nickelparticles are modified towards larger metal-support interface and larger metal surfacearea. In photocatalysis, the clean metal-support interface is favorable for theseparation of photoinduced charges and transfer of electron from the semiconductor toNiO. The activity for water splitting over NiO/Ta2O5 and NiO/ZrO2 with the cleanmetal-support interface is 1.7 and 1.5 times higher than those with the diffusedinterfacial region, respectively.A novel plasma reduction of metal-loaded catalysts was established. H2PtCl6 isquickly reduced into highly dispersed amorphous metals. For photocatalytic H2generation reaction, such plasma-reduced Pt/TiO2 shows an activity slightly higherthan the hydrogen-reduced sample, much higher than the chemical-reduced andphoto-deposited samples. The metal clusters are crystallized with calcinations in inertatmosphere, with the activity being improved.Pd/Al2O3 was reduced by the plasma method. PdCl2 is reduced into amorphousclusters. For glucose oxidation, this Pd/Al2O3 is as efficient as the hydrogen-reducedone. Thermal calcinations transfer the metal clusters into crystals but decrease theactivity, indicating that amorphous catalysts are more efficient for this reaction.The characteristics of the preparation of highly efficient catalysts using plasmatreatment were studied from the point view of plasma physics and cluster physics. Theplasma behaves similar to dusty plasma in the presence of catalyst powders. Thechemical and physical states of loaded metal are greatly modified by the plasmatreatment. The chemical bonds are elongated and distorted by coulomb repulsions,and then they are quickly split when collided with the energetic species in plasma.Furthermore, they can be reduced by the electrons produced in plasma. A criterion issuggested to determine whether the metal salts can be reduced or not. The ions pair（Mn+/M） with positive standard electrode potential can be reduced and vice verse.Novel amorphous metal （oxide） clusters with lattice defects and vacancies areproduced with the plasma treatment, which may be highly active in catalysis. Whencalcined in air, the defects and vacancies are occupied by oxygen atoms, and novelmetal-support interface is produced. Meanwhile, the clusters are crystallized intocrystals when calcined in inert atmosphere, and the lattice distortion may be healed.更多还原