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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Bonding of supported chromium during thermal activation of the CrO_x/SiO_2(phillips) ethylene polymerization catalyst
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Bonding of supported chromium during thermal activation of the CrO_x/SiO_2(phillips) ethylene polymerization catalyst

机译：CrO_x / SiO_2（phillips）乙烯聚合催化剂热活化过程中负载铬的键合

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摘要

An active surface science model for the Phillips ethylene polymerization catalyst has been prepared by impregnating aqueous Cr0_3 on a flat silicium( 100) substrate covered by amorphous silica. Using a combination of X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and Rutherford backscattering spectrometry, we studied the effect of calcination on the state of the supported chromium. Depending on the calcination temperature and the initial Cr loading of the catalyst, two processes are observed. The impregnated chromate anchors to the silica surface in an esterification reaction with the surface silanol groups of the support. The saturation coverage of these surface chromates is 2.4 Crm~2 for a calcination temperature of 450 deg C. Superficial, not anchored, chromate slowly desorbs from the flat silica surface. Under crowded conditions a portion of the surface chromates also desorb if the calcination temperature is increased, while low Cr loadings (>1 Crm~2) are stable up to the highest calcination temperature in our experiments (730 deg C). The silica-bound surface chromates are monocliromates exclusivly, independent of the initial loading or calcination temperature.
机译：Phillips乙烯聚合催化剂的活性表面科学模型已通过将Cr0_3水溶液浸渍在覆盖有无定形二氧化硅的平坦硅（100）基底上而制备。通过结合使用X射线光电子能谱，二次离子质谱和Rutherford背散射光谱，我们研究了煅烧对负载铬状态的影响。取决于煅烧温度和催化剂的初始Cr负载量，观察到两个过程。浸渍的铬酸盐在与载体的表面硅烷醇基团进行酯化反应的过程中锚定在二氧化硅表面。在450摄氏度的煅烧温度下，这些表面铬酸盐的饱和覆盖度为2.4 Cr / nm〜2。表面的铬酸盐（不是固定的）铬酸盐从平坦的二氧化硅表面缓慢脱附。在拥挤的条件下，如果提高煅烧温度，一部分表面铬酸盐也会解吸，而低铬含量（> 1 Cr / nm〜2）在我们的实验中最高煅烧温度（730℃）下是稳定的。与二氧化硅结合的表面铬酸盐排他地为单斜酸盐，与初始装载或煅烧温度无关。

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