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CeTiO_x具有高的NH_3选择性催化还原(NH_3-SCR)活性和N_2选择性,被认为是具有应用前景的催化剂.但是,CeTiO_x不抗碱金属中毒,在含有大量K离子的生物质柴油的燃烧装置中中毒尤为严重,因而限制了CeTiO_x催化剂在生物质燃料装置上的进一步应用.本文通过在CeTiO_x催化剂中掺杂Zr元素来提升其抗K~+中毒的能力.采用共沉淀法制备了CeTiO_x(CT)和CeZrTiO_x(ZCT)两种NH_3-SCR催化剂.将不同含量的硝酸钾(K~+/Ce=0.1,0.2)负载在催化剂表面,焙烧处理后得到K~+中毒的催化剂(K0.1-CT,K0.2-CT,K0.1-ZCT和K0.2-ZCT).通过测定各催化剂的催化活性来研究Zr的添加对CT催化剂抗K~+中毒能力的影响.NH_3-SCR活性数据表明,CT和ZCT催化剂都达到了接近100%的NO_x转化率,且两种新鲜催化剂的催化性能基本无差别.浸渍不同含量的K~+之后,ZCT催化剂明显优于CT催化剂:K0.1-CT和K0.1-ZCT上的NO_x转化率分别为90%和62%;而K0.2-CT和K0.2-ZCT上分别为48%和13%.可见,随K~+添加,ZCT催化剂活性降低更缓慢,表明Zr的添加提高了CT催化剂抗K~+中毒能力.BET数据显示,在新鲜催化剂中,Zr的添加增加了催化剂比表面积和孔体积;K~+中毒之后,ZCT仍然表现出比CT更好的织构性能.X射线衍射和拉曼光谱结果显示,随着K~+负载量的增加,锐钛矿TiO_2的衍射峰逐渐变得尖锐,说明无定形TiO_2逐渐结晶并不断长大,从而导致催化剂比表面积下降.与CT相比,随着K~+负载量增加,催化剂晶型并没有明显变化.这说明Zr的添加可以抑制锐钛矿TiO_2的结晶及长大.由此可见Zr的添加可抑制因K~+中毒而引起的催化剂结构变化,所以仍能保持较高的NO_x转化率.透射电镜(TEM)结果表明,随着K~+负载量逐渐增加,催化剂的晶粒尺寸逐渐变大:CT,K0.1-CT和K0.2-CT的平均晶粒尺寸分别为7,13和15nm,而ZCT催化剂晶粒尺寸增大并不明显,分别为5,8和10nm.很明显,Zr的添加抑制了催化剂晶粒长大,从而提高了其结构稳定性能.综上可见,由负载KNO_3而引起的“熔盐效应”得到了有效抑制.X射线光电子能谱结果表明,随着K~+负载量增加,CeZrTiO+x催化剂的Ce~(3+)/Ce~(4+)值下降得比CeTiO_x更缓慢,说明加入Zr之后,催化剂具有更多的晶格缺陷和氧空缺,因而有利于NH_3-SCR活性的提高.另外,催化剂酸性也是影响NH_3-SCR活性的关键因素.NH_3程序升温脱附结果显示,Zr的添加可以使CeTiO_x催化剂在K~+中毒之后仍保持较高的酸性,即Zr的添加抑制了K~+对催化剂表面酸性的巨大破坏作用.综上可知,Zr的添加提升了CeTiO_x催化剂抗K~+中毒能力.
However, CeTiOx is not resistant to alkali metal poisoning. In the combustion of Biomass Diesel with a large amount of K ions, CeTiOx is considered as a catalyst with high NH3-selective catalytic reduction (NH3-SCR) activity and N2 selectivity. The poisoning of CeTiO_x catalyst is limited to the further application of CeTiO_x catalyst in biomass fuel plant.In this paper, CeTiO_x catalyst doped with Zr element to enhance its resistance to K ~ + poisoning.CeTiO_x (CT ) And CeZrTiO_x (ZCT) were prepared.The catalysts with different contents of potassium nitrate (K ~ + / Ce = 0.1,0.2) were loaded on the catalyst surface and calcined to obtain K ~ + poisoning catalyst (K0.1- CT, K0.2-CT, K0.1-ZCT and K0.2-ZCT) .Through the determination of the catalytic activity of each catalyst to study the effect of Zr addition on CT catalyst anti-K ~ + toxicity.NH3-SCR activity data The results show that both the CT and the ZCT catalysts achieve nearly 100% NO_x conversion, and the catalytic performance of the two fresh catalysts is basically the same. After impregnating K + with different contents, the ZCT catalyst is obviously superior to the CT catalyst K0.1- The NO_x conversion rates on CT and K0.1-ZCT were 90% and 62%, respectively; while K0.2-CT and K0.2-ZC T were 48% and 13%, respectively. It can be seen that with the addition of K ~ +, the activity of ZCT catalyst decreased more slowly, indicating that the addition of Zr increased the CT catalyst resistance to K ~ + poisoning.BET data showed that in the fresh catalyst, Zr ZCT still showed better texture properties than CT after K ~ + poisoning.X-ray diffraction and Raman spectroscopy showed that with the increase of K ~ + loading, The diffraction peak of anatase TiO 2 gradually becomes sharp, which indicates that the amorphous TiO 2 gradually crystallizes and grows, which leads to the decrease of the specific surface area of the catalyst. Compared with CT, the morphology of the catalyst is not obvious with the increase of K ~ + loading Which indicates that the addition of Zr can inhibit the crystallization and growth of anatase TiO 2 .Therefore, the addition of Zr can restrain the catalyst structure change caused by K ~ + poisoning, so the NO_x conversion rate can still be maintained. Transmission electron microscopy (TEM) results show that with the increasing of K ~ + loading, the grain size of the catalyst becomes larger: the average grain sizes of CT, K0.1-CT and K0.2-CT are 7, 13 And 15 nm, respectively, while the grain size of the ZCT catalyst did not increase significantly, at 5, 8 and 10 nm, respectively. Apparently, addition of Zr inhibited As a result, the grain size of the catalyst increased and its structural stability was improved. In conclusion, the “molten salt effect” caused by the KNO 3 loading was effectively suppressed. The X-ray photoelectron spectroscopy results showed that with the K ~ + load The Ce ~ (3 +) / Ce ~ (4 +) value of CeZrTiO + x catalyst decreased more slowly than that of CeTiOx, indicating that the catalyst possesses more lattice defects and oxygen vacancies after adding Zr, which is in favor of NH_3 -SCR activity.In addition, the catalyst acidity is also a key factor affecting the activity of NH_3-SCR.NH_3 temperature-programmed desorption results show that the addition of Zr CeTiO_x catalyst after K ~ + poisoning remained high acidity, namely Zr Of KT can inhibit the acidity of catalyst surface greatly.It is concluded that the addition of Zr enhances the resistance of KT to CeTiOx catalyst.