【作者】 陈霄；

【导师】 梁长海；

【作者基本信息】 大连理工大学 ， 化学工艺， 2013， 博士

【摘要】 过渡金属硅化物是硅原子进入过渡金属晶格后而形成的一类化合物。由于其特殊的物理和化学性能,如高熔点、低电阻率、较好的传热性以及优异的耐高温、耐氧化、耐腐蚀和抗硫性等,过渡金属硅化物已被广泛应用于电热元件、集成电路和高温抗氧化涂层等领域。本文以开发高效过渡金属硅化物催化新材料为目的,通过程序升温硅化法制备了硅化镍修饰镍、硅化镍、镍钴双金属硅化物、负载型硅化镍催化剂,并将它们应用于苯乙炔、1,4-丁炔二醇、肉桂醛等不饱和化合物的选择加氢、二苯并噻吩的加氢脱硫、CO甲烷化等反应体系,表现出良好的催化性能。首先通过炭模板法制备氧化镍前驱体,并在SiH4/H2混合气中硅化处理,成功制备出了纳米尺度的硅化镍修饰镍。随着硅化温度的提高,硅化镍形成过程涉及如下相变过程：Ni2Si(斜方)→NiSi(斜方)→NiSi2(立方)。在苯乙炔选择加氢反应中,Si掺入Ni的晶格中,改变了金属Ni的晶体结构和电子结构,抑制了中间产物苯乙烯的反应吸附性能,从而提高其选择性。该新方法可以放大制备低成本、高催化活性和选择性的硅化物催化新材料,并为工业催化剂的设计提供了一个思路。此外,通过对工业用Raney Ni进行硅化处理,成功制备出Raney Ni-Si催化剂,从而提高了硅化镍修饰镍材料的比表面积。随着硅化温度的提高,表面壳层从Ni富集硅化镍转变成Si富集态。在1,4-丁炔二醇的选择加氢反应中,Si掺入Ni的晶格中,形成硅化镍降低了催化活性,但抑制了中间产物1,4-丁烯二醇的进一步加氢,显著提高了1,4-丁烯二醇的选择性。与传统的Lindlar催化剂相比较,所制备的Raney Ni-Si催化剂通过Si调变金属活性位点但避免了采用毒化助剂,具有良好的工业应用前景。为了消除催化剂中金属镍的影响,通过程序升温硅化法处理乙二醇沉淀法制备的高比表氧化镍(145m2g-1),成功合成出硅化镍纳米粒子。其在室温下呈铁磁性,且饱和磁场强度随着硅的量增加而发生显著变化。电化学性能测试表明硅化镍具有低电阻性和类贵金属性。对苯乙炔加氢,随着硅化温度的增加,所形成的硅化镍催化苯乙炔加氢的转化率先减小后增加；450-NiSiχ(主要成份：NiSi2)显示出高活性(反应时间3h,转化率接近100%,苯乙烯的选择性达90%以上)。对于肉桂醛加氢反应,不同相态的硅化镍催化剂都呈现出较高的活性,且硅原子的掺入抑制了C=O的加氢,促进了C=C的加氢,从而提高了中间产物苯丙醛的选择性。硅化镍作为新型催化材料在不饱和碳氢化合物的选择加氢中具有潜在应用。通过密度泛函理论计算对比了Ni2Si(111)和Ni(111)晶面的几何结构和电子态密度以及H2S在二者表面的解离吸附性能,发现硅化镍中Ni-Si相互作用,导致电子从Ni向Si转移,使其d态费米能级发生偏移,并且Si掺入Ni的晶格中导致Ni-Ni之间的间距发生变化,从而调变了其加氢脱硫活性和抗硫性能。因此,硅化镍是一种潜在的加氢脱硫催化剂,能有效的去除含硫化合物中的硫。其所具有的高抗硫性在工业应用上可替代镍催化剂。为了提高硅化镍加氢脱硫催化活性,通过直接硅化处理制备了不同镍钴比的双金属硅化物催化剂。随着Ni原子被Co原子均匀取代,其镍钴双金属硅化物结构和催化性能发生显著变化。富镍的Ni0.75Co0.25Si2催化剂表现出较单金属硅化物更高的加氢脱硫活性,且加氢性能显著提高,具有31.5%的加氢脱硫(HYD)选择性,硅化物中的Si的位点改变了金属的配位,弱化了金属与硫之间的结合,提高了其抗硫性能。基于硅化镍催化剂的选择加氢性能和抗硫性,通过Rochow逆反应以有机硅烷(CH3)nSiCl4-n为硅源,成功合成了单一相态的Ni2Si纳米粒子。其形成机理涉及到有机硅烷的反应沉积和Si原子的扩散。此外,通过直接硅化法成功制备了高分散性的Ni-Si/SiO2催化剂,并将其应用于CO甲烷化反应。结合原位CO化学吸附红外光谱和TPR-MS表征结果,Ni-Si/SiO2催化剂表现出高CO甲烷化催化活性,约在240℃就有CH4生成。硅化镍催化剂由于其电子结构和几何构型特殊性,显著提高了催化剂的抗烧结性能和抗积炭性能。更多还原

【Abstract】 Interstitial silicides of early transition metals have specific physical and chemical properties. Unfortunately, conventional preparation methods, such as molten salt method, co-reduction route, inherited from the microelectronic industry resulted in a low surface area and tough experimental conditions, which restricted their applications in catalysis. Based on this, we have reasonably designed silicide-modified nickel, nickel silicides, nickel-cobalt silicide solid solution, and Ni-Si/SiO2catalysts. Their catalytic activities have been detected by hydrogenation of alkyne and cinnamaldehyde, CO methanation, and hydrodesulfurization reaction.Nanoscale silicide-modified nickel catalysts with significant catalytic activity and high selectivity for phenylacetylene selective hydrogenation have been successfully synthesized by using the carbon template for oxides and further SiH4/H2silicification to silicides. Nickel silicide formation involves the following sequence as a function of increasing temperature:Ni (cubic)→Ni2Si (orthorhombic)→NiSi (orthorhombic)→NiSi2(cubic). The insertion of Si atoms into the interstitial sites between Ni atoms resulted in a significant change in the unit cell lattice of nickel. All of the silicide-modified nickel materials were ferromagnetic at room temperature, and saturation magnetization values drastically decreased when Si was present. The as-prepared bulk silicide-modified nickel showed above92%styrene selectivity in the hydrogenation of phenylacetylene under0.41MPa H2and at50℃for5h. In addition, only low conversions were obtained for styrene hydrogenation under the same hydrogen pressure and temperature for50min. These results indicated that these novel silicide-modified nickels are promising catalysts for the selective hydrogenation of unsaturated hydrocarbons.Raney Ni-Si catalysts were synthesized by treating Raney Ni with silane in fluidized bed reactor and tested in the selective hydrogenation of2-butyne-1.4-diol (BYD) in high concentration. Raney Ni-Si catalysts were composed of a Ni core surrounded by nickel silicide intermetallic compounds, which transformed form Ni-rich silicide (Ni2Si) to Si-rich silicide (NiSi2) with the increasing silicification temperature from250℃to450℃. The insertion of Si atoms into Raney Ni catalysts decreased the catalytic activity, but significantly improved the selectivity to2-butene-1,4-diol (BED). The beneficial effect of Si on the selective hydrogenation of BYD may be caused by the presence of Si at Ni-defect sites and the formation of nickel silicide surface intermetallic compounds, which suppress the hydrogenation of BED. Compared with the traditional Lindlar-type catalysts, such Raney Ni-Si materials can be used extensively in organic synthesis for selective hydrogenation of alkynes, avoiding the associated hazards of toxic additives.Nickel silicides with outstanding physical and chemical properties, were synthesized by the reaction of nickel oxide with silane at relatively low temperature and atmospheric pressure. Electrochemical measurements revealed that the nickel silicides exhibited remarkably like-platinum property and lower electric resistivity, indicating that the nickel silicides are potential and efficient materials for CMOS and electrocatalysis. Furthermore, nickel silicides particles presented much higher selectivity to the intermediate product (hydrocinnamaldehyde) than monometallic nickel catalyst, which may be attributed to the repulsive force between the electronegative silicon atoms in the nickel silicides and oxygen atoms in the C=O bond of cinnamaldehyde. In addition, nickel silicides showed excellent selectivity for the hydrogenation of phenylacetylene to styrene (ca.93%) due to the strong modification of the electronic structure derived from the interaction of nickel and silicon.Bulk nickel silicides (Ni2Si, NiSi, and NiSi2) have been designed as promising hydrodesulfurization catalysts with high activity toward hydrodesulfurization (HDS) and good sulfur tolerance, which is due to the formation of an electron-deficient Ni by the Ni-Si interaction in the nickel silicides. These compounds might also serve as highly sulfur tolerant substitutes for Ni catalysts in industrial applications. For improving the HDS activity, we report on the synthesis and characterization of ferromagnetic nickel-cobalt silicide (Ni1-x CoxSi2) solid solution catalysts having large surface area by the reaction of nickel cobalt oxide solid solutions with SiH4. The results showed that the saturation magnetization of the Ni1-x CoxSi2solid solutions with fluorite structure can be controlled by changing the molar ratio of Ni to Co. The nickel-rich Ni0.75Co0.25Si2catalyst was much more active than that of monometallic silicides (NiSi2and CoSi2) and significantly improved the hydrogenation property (31.5%HYD selectivity), proving the synergistic effect between the components. The valence electron concentration of the Ni increased with increasing the Co substitution, enhancing the metal-silicon and metal-metal interactions. In addition, the Si sites in the silicides alter the metal coordination, which engendered a high activity for the HDS of DBT and weakened the metal-sulfur bonds, improving the sulfur tolerance.Single phase Ni2Si nanoparticles (NPs) have been successfully synthesized by using the Rochow reverse reaction, in which organosilanes ((CH3)nSiCl4-n) were used as silicon source. The formation mechanism of Ni2Si NPs has been proposed, which involved reaction deposition and subsequently diffusion of Si atoms. Magnetism performance tests indicated that the saturation magnetization and coercive field of Ni2Si NPs depend greatly on the environmental temperature and particle size. The blocking temperature (TB) of the materials was found to strongly depend on selecting the organosilanes precursor:in the case of the Ni2Si-0(148K) and Ni2Si-2(336K). This novel methodology opened a route to prepare other metal silicides with single phase and stoichiometry.Silicon-nickel intermetallic compounds (IMCs) supported on silica (Ni-Si/SiO2), as a highly efficient catalyst for CO methanation, had been prepared by direct silicification of Ni/SiO2with silane at relatively low temperature in a fluidized bed reactor. The results indicate that uniform NiSix nanoparticles with about3-4nm were evenly dispersed on silica. The combined in situ FTIR and TPR-MS results suggest that the Ni-Si/SiO2catalysts afforded high activity in CO methanation, promoting the formation of CH4at ca.240℃.The catalytic hydrogenation of CO on the Ni-Si/SiO2was investigated in a fixed-bed reactor at GHSVs48,000mL·h-1·g-1under1atm in the temperature interval200-600℃. In the higher temperature reaction region (500-600℃), it is notable that the Ni-Si/SiO2catalysts present high activity for CO methanation as compared to the Ni/SiO2catalyst. More importantly, the Ni-Si/SiO2-350catalyst containing thermally stable Ni-Si IMCs shows significantly higher resistance to the sintering of Ni particles. Raman characterization of the spent materials qualitatively shows that carbon deposition observed on the conversional Ni/SiO2catalyst is much higher than that of the used Ni-Si/SiO2-350. It is proposed that small amounts of silicon interacting with Ni atoms selectively prevent the adsorption of resilient carbon species.更多还原