金屬摻雜對Mn基與Cr基催化劑氧化NO性能的影響
發(fā)布時間：2018-08-17 17:17
【摘要】：在稀燃汽車尾氣的催化凈化技術(shù)中,NO氧化催化劑具有十分重要的作用。它不僅可以提高稀燃汽車尾氣中NO2的比例,還有助于提高選擇性催化還原(SCR)催化劑低溫活性以及存儲還原(NSR)催化劑吸附性能,同時促進顆粒物捕集(DPF)和顆粒氧化催化劑(POC)的連續(xù)再生。本文研究的主要內(nèi)容:1)考察Al2O3-TiO2復合載體制備中,不同Ti/Al摩爾比、鈦溶膠pH值和復合載體包覆次數(shù)對Al2O3-TiO2復合載體結(jié)構(gòu)以及性能的影響;2)考察不同金屬摻雜對Mn/Al2O3-TiO2催化劑性能的影響,篩選出最佳摻雜金屬,考察催化劑活性組分的摻雜比、浸漬順序等因素對催化劑活性的影響,并對催化劑的抗硫性能展開初步的研究;3)考察不同金屬摻雜對Cr/Al2O3-TiO2催化劑性能的影響,篩選出最優(yōu)摻雜金屬,同時考察Cr的負載量及焙燒溫度對催化劑活性的影響,并對催化劑的抗硫性能進行初步研究。實驗的主要結(jié)果如下:1)采用溶膠凝膠法制備的Al2O3-TiO2復合載體包覆比為1/16、pH=3時NO轉(zhuǎn)化率較高,在300℃時達到63%,此條件下TiO2包覆在Al2O3表面形成較薄的包覆層,使載體的熱穩(wěn)定性提高,而且較薄包覆層的形成對NO的催化氧化反應有利;包覆次數(shù)為兩次時載體的比表面積增大,由一次包覆的197.97 m2·g-1增加到237.41 m2·g-1,分析原因可能是兩次包覆的載體制備過程中添加了兩倍的分散劑PEG,使TiO2在氧化鋁表面的分散性增強,并且有助于載體顆粒之間堆積形成新的孔,使催化劑的活性位增多,從而提高復合載體催化劑的催化活性。2)以Ce、Co、Cu、Fe金屬對Mn/Al2O3-TiO2進行摻雜,結(jié)果發(fā)現(xiàn)Co摻雜的催化劑活性較好,使催化劑的低溫活性有所提高。Mn、Co摻雜摩爾比為2:1時,催化劑在低溫區(qū)的活性最好,XRD顯示Co摻雜后的催化劑活性組分MnOx在催化劑表面的分散性增強,其H2-TPR還原峰溫度較低。XPS結(jié)果表明Mn在Mn/Al2O3-TiO2催化劑表面主要是以Mn3+形式存在的。而經(jīng)Co摻雜后Mn3+比例下降,Mn4+比例上升。共浸漬法制備的催化劑活性相對較好,活性組分主要以Mn4+形式存在,催化劑表面氧主要是以化學吸附氧的形式存在。硫化后的催化劑活性出現(xiàn)了一定程度的下降,并且催化劑的活性順序也與催化劑表面化學吸附氧及Mn4+比例呈正相關(guān)。因此說明MnO2可能是Co-Mn/Al2O3-TiO2催化劑催化氧化NO反應中起主要作用的活性Mn物種,而表面化學吸附氧則是主要的活性氧物種。3)考察Cr負載量對Cr/Al2O3-TiO2催化劑的活性的影響,催化劑按活性順序?qū)獮?0%15%20%5%。以Mn、Ce、Co元素摻雜Cr/Al2O3-TiO2催化劑活性結(jié)果顯示,在整個反應溫度區(qū)間內(nèi),催化劑活性順序?qū)獮镃o-CrCrCe-CrMn-Cr,Co添加的催化劑活性有了顯著的提高。對Co-Cr/Al2O3-TiO2催化劑考察焙燒溫度,結(jié)果發(fā)現(xiàn)催化劑的活性隨著焙燒溫度的升高而先增后減。XPS結(jié)果表明在450~550℃的溫度范圍內(nèi),隨著焙燒溫度的升高,催化劑的活性組分Cr可能更多是以高價態(tài)Cr6+形式存在,催化劑預硫化后活性下降,Cr6+含量也隨著之下降。因此說明高價Cr6+可能是Co-Cr/Al2O3-TiO2催化劑催化氧化NO反應中起主要作用的活性Cr物種。
[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.
【學位授予單位】：廣州大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：O643.36
本文編號：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.
【學位授予單位】：廣州大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：O643.36
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