【作者】 于伟鹏；

【导师】 郑瑛；

【作者基本信息】 福建师范大学 ， 物理化学， 2009， 硕士

【摘要】 本研究以淀粉为碳源,正硅酸乙酯（TEOS）为硅源,草酸或硝酸为TEOS水解的催化剂,以不同的金属盐为碳热还原催化剂,采用溶胶凝胶法制备淀粉-SiO₂混合凝胶,通过惰性气氛和动态真空的碳热还原方法合成了不同结构的SiC及C/SiC复合材料。用XRD、IR、SEM、TEM和低温N₂吸附-脱附等手段对合成的样品进行表征,优化合成条件。筛选出适合于氨合成反应的高比表面积SiC及C/SiC复合材料作为催化剂载体,制备一系列钌催化剂,在一定的温度和压力条件下,考察了催化剂在氨合成反应中的活性。取得了以下研究结果:1.用溶胶凝胶法制备的淀粉-SiO₂混合凝胶,在惰性气氛中1500℃下进行碳热还原,能制备出比表面积达130 m²/g,孔径大约分别在2和16 nm的高比表面积的SiC。凝胶中添加铁催化剂后生成SiC的还原温度降低,但所合成的SiC比表面积随着硝酸铁含量的增加而减小,孔径分布趋于宽化。2.以淀粉为碳源,正硅酸乙酯为硅源,硝酸铈为碳热还原催化剂,通过溶胶-凝胶和碳热还原反应制备了具有核壳异质结构的β-SiC纳米线。3.利用动态真空碳热还原合成碳化硅的研究中,发现在动态真空条件下淀粉-SO₂混合凝胶转化生成SiC的温度比在惰性气氛中合成碳化硅降低550℃,在950℃动态真空条件下即可合成出晶粒尺寸约为50 nm,结晶度较高的β-SiC。4.将合成的SiC应用于氨合成反应研究中发现,以比表面积为130 m²/g的SiC为载体制备的钌催化剂中,钌负载量为4 wt%（相对载体100%计算）,助剂钾和钡的添加量分别为10 wt%和4 wt%时,在450℃,10.0 Mpa和10 000 h^-1,N₂:H₂=1:3的条件下,出口氨浓度为9.89%（体积分数）。5.以比表面积422 m²/g的C/SiC复合材料为载体制备的Ru4%/Ba4%/K10%/C/SiC催化剂,在450℃,10 Mpa及10000 h^-1的条件下,出口氨浓度达12.6%,催化剂具有较高的氨合的活性。进一步的研究发现:经CA处理后的C/SiC载体制备的催化剂中Ru的分散度显著提高,当载体中CA的吸附量为4%时,处理的载体制备的Ru4%/Ba4%/K10%/C/SiC催化剂,在450℃,10Mpa及10000h^-1的条件下出口氨浓度达14.4%,进一步提高了催化剂的活性,且催化剂稳定性较高。本研究制备的C/SiC可望成为氨合成反应的新载体。更多还原

【Abstract】 Tetraethoxysilane（TEOS） was used as silicon source and starch was used as carbon source for preparing the carbonaceous starch-SiO₂ hybrids gel containing nitrate cerium or ferric nitrate.Then the starch-SiO₂ hybrids gel was treated by the carbothermal reaction at high temperature under inert gas or vacuum condition.XRD,IR,SEM,TEM and N₂ physisorption were carried out to characterize the obtain samples.A kind of high surface specific area SiC,C/SiC suit for ammonia synthesis was choosed,and it was used as support to prepare ruthenium catalyst.The ammonia synthesis activities for a series of ruthenium catalyst were measured at a high temperature and under a high pressure.The results were showed as follows:1.When the dried starch-SiO₂ hybrids gel were treated under inert gas,the carbothermal reduction temperature for preparing silicon carbide from the precursors without Fe need to be 1500℃.High surface areas about 130m²/g and pore size distribution at 2 or 16 nm were obtained;the cabothermal reduction temperature would be decreased when the Fe was employed to the precursors,but the surface specific area of the obtained sample was decreased at the same time,and the pore size distributions go to diversification.2.The silicon carbide nanowires were synthesized by the carbothermal reduction of the carbonaceous starch-SiO₂ hybrids gel containing cerium nitrate.The results indicated that the product wasβ-SiC/SiO₂ core-shell nanowires.3.When the starch-SiO₂ hybrids gel were treated under vacuum,we discovered that the carbothermal reduction temperature for preparing SiC under dynamic vacuum condition was lower than that under inert gases for 550℃and high crystallineβ-SiC with average crystalline size of 50 nm could be synthesized at 950℃under dynamic vacuum condition.4.The high surface specific area SiC was used as catalyst support for ammonia synthesis.The prepared SiC-supported ruthenium catalyst has a relative high active（9.89 %）.5.The prepared C/SiC-supported（422 m²/g） ruthenium catalyst has a relative high active（12.60%） under Ru=4%,Ba=4%,K=10%,450℃,10.0Mpa and 10 000h^-1.A suitable amount of citric acid acid is advantageous to improve the Ru dispersion by further research,when the amount of citric acid in support is 4 wt%,Catalytic activity of the prepared C/SiC-supported ruthenium catalyst reaches 14.4%under Ru=4%,Ba=4%, K=10%,450℃,10.0Mpa and 10 000h^-1,and the active would maintain when the catalyst was tested for the heat resistance at this temperature for 20 h,which showed the stability performance of the prepared C/SiC-supported catalyst.It indicated that the prepared high surface area C/SiC would be a new support for ammonia synthesis.更多还原