金属掺杂对Mn基与Cr基催化剂氧化NO性能的影响
发布时间：2018-08-17 17:17
【摘要】：在稀燃汽车尾气的催化净化技术中,NO氧化催化剂具有十分重要的作用。它不仅可以提高稀燃汽车尾气中NO2的比例,还有助于提高选择性催化还原(SCR)催化剂低温活性以及存储还原(NSR)催化剂吸附性能,同时促进颗粒物捕集(DPF)和颗粒氧化催化剂(POC)的连续再生。本文研究的主要内容:1)考察Al2O3-TiO2复合载体制备中,不同Ti/Al摩尔比、钛溶胶pH值和复合载体包覆次数对Al2O3-TiO2复合载体结构以及性能的影响;2)考察不同金属掺杂对Mn/Al2O3-TiO2催化剂性能的影响,筛选出最佳掺杂金属,考察催化剂活性组分的掺杂比、浸渍顺序等因素对催化剂活性的影响,并对催化剂的抗硫性能展开初步的研究;3)考察不同金属掺杂对Cr/Al2O3-TiO2催化剂性能的影响,筛选出最优掺杂金属,同时考察Cr的负载量及焙烧温度对催化剂活性的影响,并对催化剂的抗硫性能进行初步研究。实验的主要结果如下:1)采用溶胶凝胶法制备的Al2O3-TiO2复合载体包覆比为1/16、pH=3时NO转化率较高,在300℃时达到63%,此条件下TiO2包覆在Al2O3表面形成较薄的包覆层,使载体的热稳定性提高,而且较薄包覆层的形成对NO的催化氧化反应有利;包覆次数为两次时载体的比表面积增大,由一次包覆的197.97 m2·g-1增加到237.41 m2·g-1,分析原因可能是两次包覆的载体制备过程中添加了两倍的分散剂PEG,使TiO2在氧化铝表面的分散性增强,并且有助于载体颗粒之间堆积形成新的孔,使催化剂的活性位增多,从而提高复合载体催化剂的催化活性。2)以Ce、Co、Cu、Fe金属对Mn/Al2O3-TiO2进行掺杂,结果发现Co掺杂的催化剂活性较好,使催化剂的低温活性有所提高。Mn、Co掺杂摩尔比为2:1时,催化剂在低温区的活性最好,XRD显示Co掺杂后的催化剂活性组分MnOx在催化剂表面的分散性增强,其H2-TPR还原峰温度较低。XPS结果表明Mn在Mn/Al2O3-TiO2催化剂表面主要是以Mn3+形式存在的。而经Co掺杂后Mn3+比例下降,Mn4+比例上升。共浸渍法制备的催化剂活性相对较好,活性组分主要以Mn4+形式存在,催化剂表面氧主要是以化学吸附氧的形式存在。硫化后的催化剂活性出现了一定程度的下降,并且催化剂的活性顺序也与催化剂表面化学吸附氧及Mn4+比例呈正相关。因此说明MnO2可能是Co-Mn/Al2O3-TiO2催化剂催化氧化NO反应中起主要作用的活性Mn物种,而表面化学吸附氧则是主要的活性氧物种。3)考察Cr负载量对Cr/Al2O3-TiO2催化剂的活性的影响,催化剂按活性顺序对应为10%15%20%5%。以Mn、Ce、Co元素掺杂Cr/Al2O3-TiO2催化剂活性结果显示,在整个反应温度区间内,催化剂活性顺序对应为Co-CrCrCe-CrMn-Cr,Co添加的催化剂活性有了显著的提高。对Co-Cr/Al2O3-TiO2催化剂考察焙烧温度,结果发现催化剂的活性随着焙烧温度的升高而先增后减。XPS结果表明在450~550℃的温度范围内,随着焙烧温度的升高,催化剂的活性组分Cr可能更多是以高价态Cr6+形式存在,催化剂预硫化后活性下降,Cr6+含量也随着之下降。因此说明高价Cr6+可能是Co-Cr/Al2O3-TiO2催化剂催化氧化NO反应中起主要作用的活性Cr物种。
[Abstract]:NO oxidation catalyst plays an important role in catalytic purification of lean-burn automobile exhaust. It can not only increase the proportion of NO2 in lean-burn automobile exhaust, but also improve the low-temperature activity of selective catalytic reduction (SCR) catalyst and the adsorption performance of storage-reduction (NSR) catalyst, and promote particle trapping (DPF) and particles. The main contents of this paper are as follows: 1) The effects of Ti/Al molar ratio, pH value of titanium sol and coating times on the structure and properties of Al_2O_3-TiO_2 composite support in the preparation of Al_2O_3-TiO_2 composite support were investigated; 2) The effects of different metal doping on the properties of Mn/Al_2O_3-TiO_2 catalyst were investigated, and the best one was selected. The influence of doping ratio of active components and impregnation sequence on the activity of the catalyst was investigated, and the sulfur resistance of the catalyst was studied preliminarily. 3) The effect of different metal doping on the performance of Cr/Al2O3-TiO2 catalyst was investigated, and the optimum doping metal was selected. The effects of Cr loading and calcination temperature on the catalytic activity were also investigated. The main results are as follows: 1) The coating ratio of Al_2O_3-TiO_2 composite carrier prepared by sol-gel method is 1/16, and the NO conversion rate is higher when pH=3, reaching 63% at 300 C. Under this condition, a thin coating layer is formed on the surface of Al_2O_3, which makes the carrier thermal stable. The specific surface area of the carrier increased from 197.97 m2.g-1 to 237.41 m2.g-1 when the number of coatings was twice, which was probably due to the addition of twice dispersant PEG during the preparation of the carrier. The dispersion of Mn/Al2O3-TiO2 was enhanced, and the new pore was formed between the carrier particles, which increased the active sites of the catalyst. 2) Mn/Al2O3-TiO2 was doped with Ce, Co, Cu and Fe. The results showed that the Catalyst Doped with Co had better activity and the low temperature activity of the catalyst was improved. XRD showed that MnOx, the active component of Co-doped catalyst, was more dispersed on the surface of the catalyst, and the reduction peak temperature of H2-TPR was lower. XPS results showed that Mn existed mainly in the form of Mn3+ on the surface of Mn/Al2O3-TiO2 catalyst. However, the Mn3+ ratio decreased and Mn4+ ratio decreased after Co-doping. The activity of the catalyst prepared by co-impregnation method is relatively good. The active component mainly exists in the form of Mn4+ and the surface oxygen of the catalyst mainly exists in the form of chemisorbed oxygen. Therefore, MnO2 may be an active Mn species that plays a major role in the catalytic oxidation of NO over Co-Mn/Al2O3-TiO2 catalysts, and surface chemisorbed oxygen is the main active oxygen species.3) The effect of Cr loading on the activity of Cr/Al2O3-TiO2 catalysts was investigated. The catalysts were doped with Mn, Ce and Co elements in the order of 10% 15% 20% 5%. The activity of Al2O3-TiO2 catalyst showed that the order of catalyst activity corresponded to Co-CrCrCe-CrMn-Cr in the whole range of reaction temperature. The activity of Co-Cr/Al2O3-TiO2 catalyst increased markedly. The calcination temperature of Co-Cr/Al2O3-TiO2 catalyst was investigated. The results showed that the activity of the catalyst increased first and then decreased with the increase of calcination temperature. The results show that the active component Cr may be more in the form of high valence Cr6+ with the increase of calcination temperature in the range of 450~550 C. The activity of the catalyst decreases after pre-vulcanization and the content of Cr6+ decreases with the increase of calcination temperature. Cr species.
【学位授予单位】：广州大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36
本文编号：2188343
[Abstract]:NO oxidation catalyst plays an important role in catalytic purification of lean-burn automobile exhaust. It can not only increase the proportion of NO2 in lean-burn automobile exhaust, but also improve the low-temperature activity of selective catalytic reduction (SCR) catalyst and the adsorption performance of storage-reduction (NSR) catalyst, and promote particle trapping (DPF) and particles. The main contents of this paper are as follows: 1) The effects of Ti/Al molar ratio, pH value of titanium sol and coating times on the structure and properties of Al_2O_3-TiO_2 composite support in the preparation of Al_2O_3-TiO_2 composite support were investigated; 2) The effects of different metal doping on the properties of Mn/Al_2O_3-TiO_2 catalyst were investigated, and the best one was selected. The influence of doping ratio of active components and impregnation sequence on the activity of the catalyst was investigated, and the sulfur resistance of the catalyst was studied preliminarily. 3) The effect of different metal doping on the performance of Cr/Al2O3-TiO2 catalyst was investigated, and the optimum doping metal was selected. The effects of Cr loading and calcination temperature on the catalytic activity were also investigated. The main results are as follows: 1) The coating ratio of Al_2O_3-TiO_2 composite carrier prepared by sol-gel method is 1/16, and the NO conversion rate is higher when pH=3, reaching 63% at 300 C. Under this condition, a thin coating layer is formed on the surface of Al_2O_3, which makes the carrier thermal stable. The specific surface area of the carrier increased from 197.97 m2.g-1 to 237.41 m2.g-1 when the number of coatings was twice, which was probably due to the addition of twice dispersant PEG during the preparation of the carrier. The dispersion of Mn/Al2O3-TiO2 was enhanced, and the new pore was formed between the carrier particles, which increased the active sites of the catalyst. 2) Mn/Al2O3-TiO2 was doped with Ce, Co, Cu and Fe. The results showed that the Catalyst Doped with Co had better activity and the low temperature activity of the catalyst was improved. XRD showed that MnOx, the active component of Co-doped catalyst, was more dispersed on the surface of the catalyst, and the reduction peak temperature of H2-TPR was lower. XPS results showed that Mn existed mainly in the form of Mn3+ on the surface of Mn/Al2O3-TiO2 catalyst. However, the Mn3+ ratio decreased and Mn4+ ratio decreased after Co-doping. The activity of the catalyst prepared by co-impregnation method is relatively good. The active component mainly exists in the form of Mn4+ and the surface oxygen of the catalyst mainly exists in the form of chemisorbed oxygen. Therefore, MnO2 may be an active Mn species that plays a major role in the catalytic oxidation of NO over Co-Mn/Al2O3-TiO2 catalysts, and surface chemisorbed oxygen is the main active oxygen species.3) The effect of Cr loading on the activity of Cr/Al2O3-TiO2 catalysts was investigated. The catalysts were doped with Mn, Ce and Co elements in the order of 10% 15% 20% 5%. The activity of Al2O3-TiO2 catalyst showed that the order of catalyst activity corresponded to Co-CrCrCe-CrMn-Cr in the whole range of reaction temperature. The activity of Co-Cr/Al2O3-TiO2 catalyst increased markedly. The calcination temperature of Co-Cr/Al2O3-TiO2 catalyst was investigated. The results showed that the activity of the catalyst increased first and then decreased with the increase of calcination temperature. The results show that the active component Cr may be more in the form of high valence Cr6+ with the increase of calcination temperature in the range of 450~550 C. The activity of the catalyst decreases after pre-vulcanization and the content of Cr6+ decreases with the increase of calcination temperature. Cr species.
【学位授予单位】：广州大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O643.36
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