【作者】 张青蔚；

【导师】 王亚权；

【作者基本信息】 天津大学 ， 化学工艺， 2009， 博士

【摘要】 甲烷部分氧化制合成气（POM）方法因具有反应速率快、能耗低,可显著降低设备投资和生产成本,生成的合成气H₂/CO的比例为2,可直接用于甲醇及费-托合成等优点而成为国内外研究的热点。本文以甲烷部分氧化制合成气为模型反应,结合XRD、BET、TPR和分散度、TG-DTA、拉曼光谱、SEM、XPS等表征手段,研究了Ni、Pd系催化剂制备工艺、改性剂和改性效应、催化性能,并进行工业化初探,为POM催化剂设计提供基础数据。Ni系催化剂的研究表明,对于以α-Al₂O₃为载体的Ni基POM催化剂,Ni的最优负载量是10%;载体比表面有一个阈值,即4.042m²/g,当比表面大于阈值后,载体的孔容、孔径成为主要影响因素,因为孔容、孔径的增大可使反应物和产物扩散速度增大,从而提高催化剂的活性。在本实验中得出需要载体孔容Vt≥0.0160cm³/g,孔径Dp≥13.08nm。S_micro/S_BET能很好反映载体孔结构对催化剂的影响规律,当S_micro/S_BET≤37.79%时,催化剂的活性较好;助剂CeO₂-ZrO₂改性催化剂能有效提高催化活性和稳定性,在机械混合、分子混合和原子混合三种不同的载体混合方式中,机械混合载体催化剂的稳定性和抗积炭性能最好,主要是因为机械混合样品中Ni-Al₂O₃间具有较强的相互作用能够抑制活性组分的烧结和积炭,提高催化剂的稳定性。Pd系催化剂的研究表明,以CeO₂-ZrO₂为载体能减少活性组分Pd的负载量,并能提高POM催化剂的活性和稳定性,可归因于CeO₂-ZrO₂载体能提高活性组分分散度和CeO₂-ZrO₂中的晶格氧参与反应;还可以提高Pd催化剂的耐高温性能;以机械混合、分子混合和原子混合三种CeO₂-ZrO₂/Al₂O₃载体制备的催化剂中分子混合载体催化剂具有最佳的稳定性,这是因为分子混合样品中金属与CeO₂-ZrO₂接触的界面较大,CeO₂-ZrO₂中的晶格氧能及时消除金属上的积炭。对性能较好的Pd系模型催化剂开展工业化初探研究表明,将CeO₂-ZrO₂以助剂形式与Al₂O₃以摩尔比例1:1混合制得的催化剂,表面吸附的SO₂可形成具有一定氧化性的硫酸盐类,从而提高了催化剂的抗硫性能。采用金属蜂窝载体,可以有效降低催化剂床层飞温点温度为880℃,低于催化剂焙烧温度950℃,避免了活性中心团聚和载体烧结,延长了催化剂的使用寿命。更多还原

【Abstract】 Partial Oxidation of Methane （POM） has drawn great scientific interests due to high reaction rate, low energy consuming, limited operation cost, and producing the syngas with H₂/CO molar ratio of 2:1 that could be directly applied for methanol and Fischer-Tropsch Synthesis.The present works investigate Ni and Pd based POM catalysts concerning preparation methods, modifications, performances and initial industrial applications. The studies combine the analysis of model reactions, XRD, BET, TPR, dispersion measurement, TG-DTA, Raman, SEM and XPS to provide the fundamental references for POM catalysts design.Investigations over Ni based POM catalysts reveal the optimized 10% Ni loading onα-Al₂O₃. Surface areas’threshold is determined to be 4.042m²/g, and higher values induce larger pore volumes and diameters positive for mass transportation efficiency thus benefitting POM performances. Pore volume Vt≥0.0160cm³/g and pore diameter Dp≥13.08nm would be required accordingly. The parameter S_micro/S_BET well describes the correlation between supports’textures and catalytic performances, where the desired activities could be maintained at S_micro/S_BET≤37.79%. Catalytic activity and durability has been significantly improved by CeO₂-ZrO₂ promoters. Mechanical powder mixed POM catalyst shows the best comprehensive performance in comparison with precipitates or precursors mixed samples, which is contributed to the intense Ni-Al₂O₃ interaction resisting active sites sintering, carbon deposit.Investigations of Pd based POM catalysts confirm the advantages of CeO₂-ZrO₂ supports in reducing Pd amount for activity maintenance, promoting catalytic activity and durability. Better dispersion of active components with higher thermal stability on CeO₂-ZrO₂ and the reactive lattice oxygen of the latter are the main factors for those above advantages. Precipitates mixed catalyst performs the best activity in comparison with the mechanical powder or precursors mixed samples. Pd and CeO₂-ZrO₂ interaction is magnified in precipitates mixed catalysts, and the lattice oxygen of CeO₂-ZrO₂ is positive for carbon deposit removal on metal sites. Initial industrial application of the selected Pd catalysts, where CeO₂-ZrO₂ is mixed with Al₂O₃ as the promoter with molar ratio of 1:1, shows the improved sulfur resistance due to the formation of surface oxidative sulfate from SO₂ adsorption. Ignition temperature of the catalysts’bed is managed to be limited at 880℃in metal honeycomb supported materials, lower than 950℃for calcinations, avoiding active sites aggregation, supports sintering, and improving longevity of the catalysts.更多还原