载体晶型对被负载金属氧化物分散性能的影响

发布时间：2018-05-22 09:21

本文选题：相似相分散 + SnO_2/TiO_2　；参考：《南昌大学》2017年硕士论文

【摘要】：单层分散理论认为,盐类和金属氧化物等可在载体表面自发分散形成亚单层或单层结构,具有单层分散阈值。这一理论已被普遍接受,并为有效设计高性能催化剂提供了重要依据。本文基于单层分散理论,探究了同一金属氧化物负载在化学组成相同、晶体结构不同的金红石型(r-TiO_2)和锐钛矿型(a-TiO_2)TiO_2上的分散性能及催化性能差异。SnO_2为金红石型结构,与金红石型TiO_2晶型相同。采用物理混合法制备了一系列不同SnO_2负载量的n%SnO_2/r-TiO_2、n%SnO_2/a-TiO_2和n%SnO_2/P25催化剂,通过XRD外推法测定了SnO_2在r-TiO_2、a-TiO_2和P25上的单层分散阈值分别为0.559 mmol/(100 m~2 r-TiO_2)、0.229 mmol/(100 m~2 a-TiO_2)和0.305 mmol/(100m~2 P25)。这表明被负载的金属氧化物与载体金属氧化物晶体结构相同时更有利于被负载组分的分散。类似于“相似相溶”原理,我们首次发现了“相似相分散”现象。为验证“相似相分散”现象,采用沉积沉淀法制备一系列不同SnO_2负载量的n%SnO_2/r-TiO_2和n%SnO_2/a-TiO_2催化剂,利用XRD外推法测定了SnO_2在r-TiO_2和a-TiO_2上的单层分散阈值分别为0.610 mmol/(100 m~2 r-Ti O_2)和0.232mmol/(100 m~2 a-TiO_2)。显然,通过不同制备方法所测得的分散阈值在误差范围内一致,进一步验证了“相似相分散”现象的存在。由H_2-TPR结果可知SnO_2在两种晶型载体上还原性能不同,SnO_2负载在r-TiO_2上一步还原,在a-TiO_2上却分两步还原;且SnO_2负载在r-TiO_2上时具有更高的CO催化氧化活性。表明TiO_2载体晶型不同,与被负载的SnO_2相互作用不同,可影响所得催化剂的结构和催化活性。为了进一步探究相似相分散的普遍性,考察了金红石型结构的RuO_2在r-TiO_2和a-TiO_2载体上的分散性能。采用浸渍法制备出一系列不同RuO_2负载量的n%RuO_2/a-TiO_2和n%RuO_2/r-TiO_2催化剂,分别通过XRD和Raman测定了RuO_2在a-TiO_2和r-Ti O_2上的单层分散阈值,为0.112 mmol/(100 m~2 a-TiO_2)和0.557 mmol/(100 m~2 r-TiO_2)。这一结果进一步表明被负载的金属氧化物与载体金属氧化物具有相同晶型时更有利于其分散,证实了“相似相分散”现象存在的普遍性。这一现象的发现对有效设计高性能催化剂提供了新的思路。基于相似相分散原理,设计制备了2 wt%Ru含量的RuO_2/a-TiO_2和RuO_2/r-TiO_2催化剂。发现RuO_2负载在相同晶型的r-TiO_2载体上所得催化剂其CO活性远远高于RuO_2/a-TiO_2催化剂。H_2-TPD、H_2-TPR、XPS和Raman等表征结果表明,因金红石型RuO_2与载体r-TiO_2晶型相同,RuO_2/r-TiO_2催化剂中RuO_2有更高的分散度,二者间相互作用更强,且表面存在更多活泼氧物种,导致其活性远远高于RuO_2/a-TiO_2催化剂。
[Abstract]:Monolayer dispersion theory suggests that salts and metal oxides can spontaneously disperse into submonolayer or monolayer structure on the surface of the carrier and have monolayer dispersion threshold. This theory has been widely accepted and provides an important basis for the effective design of high performance catalysts. Based on the monolayer dispersion theory, the dispersion and catalytic properties of the same metal oxide loaded on the same metal oxide in the same rutile type r-TiO2 with the same chemical composition, different crystal structure and anatase type a-TiO2TiO2 have been investigated. It is the same as rutile TiO_2 crystal. A series of nSnOs with different SnO_2 loads were prepared by physical mixing method. A series of nSnOs / s / 2r-TiOs / 2nSnOs / 2nTiO2and n%SnO_2/P25 catalysts were prepared. By XRD extrapolation, the monolayer dispersion thresholds of SnO_2 on r-TiO2tia-TiO2 and P25 were determined to be 0.559 mmol/(100 m2r-TiO2o0.229 mmol/(100 m2a-TiO2 and 0.305 mmol/(100m~2 P25O2, respectively. The results show that the supported metal oxide is more favorable to the dispersion of the loaded component when the crystal structure of the supported metal oxide is the same as that of the carrier metal oxide. Similar to the principle of "similar phase dissolving", we have discovered the phenomenon of "similar phase dispersion" for the first time. In order to verify the phenomenon of "similar phase dispersion", a series of n%SnO_2/r-TiO_2 and n%SnO_2/a-TiO_2 catalysts with different SnO_2 loading amounts were prepared by means of deposition precipitation method. The monolayer dispersion thresholds of SnO_2 on r-TiO_2 and a-TiO_2 were determined to be 0.610 mmol/(100 mt2r-Ti O 2 and 0.232mmol/(100 mc2a-TiO2T respectively by XRD extrapolation. It is obvious that the dispersion threshold measured by different preparation methods is consistent within the error range, which further verifies the existence of the phenomenon of "similar phase dispersion". The results of H_2-TPR show that the reduction performance of SnO_2 on two kinds of crystal supports is different. Sno _ 2 supports are reduced in one step on r-TiO_2, but they are reduced in two steps on a-TiO_2, and SnO_2 supports on r-TiO_2 have higher catalytic activity for CO oxidation. The results showed that the structure and catalytic activity of the catalyst were affected by the different crystal type of TiO_2 support and the interaction with the supported SnO_2. In order to further explore the universality of similar phase dispersion, the dispersion properties of rutile RuO_2 on r-TiO_2 and a-TiO_2 carriers were investigated. A series of n%RuO_2/a-TiO_2 and n%RuO_2/r-TiO_2 catalysts with different RuO_2 loading amounts were prepared by impregnation method. The monolayer dispersion thresholds of RuO_2 on a-TiO_2 and r-Ti O _ 2 were determined by XRD and Raman, respectively. The thresholds of RuO_2 dispersion on a-TiO_2 and r-Ti O _ (2) were 0.112 mmol/(100 mf2a-TiO2) and 0.557 mmol/(100 mr-TiO2 respectively. The results further show that the supported metal oxides have the same crystal form as the carrier metal oxides are more favorable for their dispersion, which confirms the universality of the phenomenon of "similar phase dispersion". The discovery of this phenomenon provides a new idea for the effective design of high performance catalysts. Based on the principle of similar phase dispersion, RuO_2/a-TiO_2 and RuO_2/r-TiO_2 catalysts with 2 wt%Ru content were designed and prepared. It was found that the CO activity of the catalyst supported on the same crystal type of r-TiO_2 was much higher than that of RuO_2/a-TiO_2 catalyst. H2-TPD-H2-TPRO and Raman. The results showed that the dispersion of RuO_2 in the rutile RuO_2 was higher than that in the support r-TiO_2, because the rutile RuO_2 had the same crystal form as r-TiO_2. The interaction between them is stronger and there are more active oxygen species on the surface, which leads to their activity being much higher than that of RuO_2/a-TiO_2 catalyst.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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