【摘要】 甲烷部分氧化制合成气反应(POM)是天然气、页岩气资源利用的重要途径之一,常用的Ni/SiO2催化剂在反应中易发生表面积炭而失活。为了解决这一问题,我们采用尿素沉淀法制备W修饰的Ni基催化剂,并考察其在POM反应中的稳定性和W的作用。结果表明,催化剂中适量W的存在可显著改善其POM反应稳定性。其原因为Ni-W作用修饰了Ni的化学态或其亲氧能力,从而改善了其表面抗积炭能力。此外,反应中催化剂表面形成的α-WC具有一定的抑制表面积炭形成的能力,且该α-WC具有良好的稳定性。更多还原

【Abstract】 With the discovery and large-scale exploitation of natural gas resources such as shale gas and combustible ice, which are mainly composed of methane, their effective utilization has become a national strategic interest. Partial oxidation of methane（POM） to synthesis gas is one of the important methods for the utilization of natural gas and shale gas resources. The commonly used Ni/SiO2 catalyst for POM easily deactivates due to carbon deposition on the surface. To solve this problem, a urea precipitation method was employed in this work to prepare Ni-based catalysts modified with different amounts of tungsten（at W/Ni molar ratios of 0, 0.01,0.03, 0.05, 0.07, and 0.10）, and the catalyst stability in POM as well as the role of W were investigated. From characterizations such as X-ray diffraction （XRD）, transmission electron microscopy（TEM）, temperature-programmed reduction（H2-TPR）, and X-ray photoelectron spectroscopy（XPS）, we obtained the following results. The amount of W added to the Ni-based catalysts has a significant influence on their catalytic performances in POM and their physicochemical properties. The particle size of Ni in the catalysts decreases with W addition, and the Ni particle distribution on the support surfaces becomes more uniformed; however, the catalytic activity for POM is not significantly influenced. However, W-modified Ni-based catalysts show an increasing improvement in their stability in POM with increasing W/Ni molar ratio, with an optimum at the W/Ni molar ratio of 0.07; at the W/Ni molar ratio of 0.10, they exhibit a rapid deactivation in POM in a short time. Although interactions between Ni and SiO₂ in the as-prepared catalysts are weak, the presence of adequate tungsten（W/Ni molar ratio of 0.05 and above） in the Ni-based catalysts can reduce the Ni particle size to some extent, and lead to the formation of strong interactions between Ni and W, which leads to an improvement in the dispersion of Ni on the support surface and imparts resistance for Ni particle growth in the POM reaction. The increased interaction between Ni and W changes the chemical state or oxygen affinity of Ni particles on the catalyst surfaces, and some of the partially oxidized Ni species（Niδ+） on the catalyst surfaces coexist with reduced Ni species（Ni0） during POM. Using an adequate amount of W-modified Ni catalysts results in almost no carbon deposition on the surfaces during POM, but using only a moderate amount results in good catalytic behavior and stability in POM. This finding suggests that the presence of W can not only enhance the anti-coking ability of the Ni-based catalysts and sustain their good stability in POM if the W content is low（i.e., W/Ni molar ratio of 0.07 and below）, but also lead to the deactivation of W-modified catalysts in POM if the W content is high（i.e., W/Ni molar ratio of 0.10 and above）, due to high oxygen affinity or the presence of more Ni species in oxidized form. In addition, α-WC（tungsten carbide） was identified using XRD to be formed on the surface of the moderate-amount W-modified Ni catalysts after POM, and it could inhibit or eliminate carbon deposition on the Ni-based catalyst surfaces. The catalytic performance evaluation of the catalysts in POM under a long time period confirmed that α-WC is stable.更多还原