Effects of support pre-calcination on the NOx storage and reduction performance of Pt-BaO/Al2O3 catalysts
Effects of support pre-calcination on the NOx storage and reduction performance of Pt-BaO/Al2O3 catalysts
复制标题
载体预焙烧对Pt-BaO/Al2O3催化剂NOx存储和还原性能的影响
DOI：
10.1039/c3cy00228d
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发表时间：
2013-01-01
影响因子：
5
通讯作者：
Xu, Bo-Qing
中科院分区：
文献类型：
--
作者：
Hu, Zhun;Li, Wei-Zhen;Xu, Bo-Qing
通过改变Al（OH）（3）水凝胶的煅烧温度（称为预煅烧温度，PCT），研究了Al 2 O3载体的晶体结构和表面性质对Pt-BaO/Al 2 O3催化剂的NOx储存和还原（NSR）性能的影响。采用N2吸附-脱附、XRD、NH3-TPD和吡啶吸附红外光谱等方法对Al 2 O3（PCT）载体的织构、晶体结构和表面酸性进行了表征。当PCT从450 ℃增加到800 ℃时，Al 2 O3（PCT）样品显示出γ-Al 2 O3相的逐渐有序化，并且当PCT进一步增加到1000 ℃时，从γ-Al 2 O3相到θ-Al 2 O3相的相变。Al 2 O3（PCT）样品的刘易斯酸中心的表面密度在PCT在800-900 ℃范围内表现出最大值。研究了由Al_2O_3（PCT）样品制备的Pt-BaO/Al_2O_3催化剂在循环贫/富条件下的NSR性能。在Pt-BaO/Al 2 O3（PCT）催化剂上储存和还原的NOx的数量显示出对PCT的类似的火山型依赖性，在PCT = 800 ℃时达到峰值。从Pt颗粒大小、BaO位的性质和Pt-BaO协同作用等方面讨论了载体PCT效应的来源。结果发现，γ-Al 2 O3相的结晶度和负载Al 2 O3样品的表面酸位密度的增加将导致Pt和BaO位点之间的邻近性和协同作用的改善，从而导致更有效的NSR Pt-BaO/Al 2 O3催化剂。
Effects of the crystalline structure and surface property of the Al2O3 support on the NOx storage and reduction (NSR) performance of Pt-BaO/Al2O3 catalysts were studied using catalysts prepared from a series of Al2O3 samples obtained by varying the calcination temperature of an Al(OH)(3) hydrogel in the range of 450-1000 degrees C (referred to as the pre-calcination temperature, PCT). The texture, crystalline structure and surface acidity of the Al2O3(PCT) supports were measured employing nitrogen adsorption-desorption, XRD, NH3-TPD and IR spectroscopy of adsorbed pyridine, respectively. The Al2O3(PCT) samples showed a gradual ordering of the gamma-Al2O3 phase when increasing the PCT from 450 to 800 degrees C, and a phase transition from the gamma- to theta-Al2O3 phase upon further increasing the PCT to 1000 degrees C. The surface density of Lewis acid sites of the Al2O3(PCT) samples exhibited a maximum at PCT in the range of 800-900 degrees C. The NSR performance of Pt-BaO/Al2O3 catalysts derived from the Al2O3(PCT) samples was studied under cyclic lean/rich conditions. The numbers of NOx stored and reduced on the Pt-BaO/Al2O3(PCT) catalysts showed similar volcano-type dependencies on PCT, peaking at PCT = 800 degrees C. The origins of the support PCT effect were discussed in the light of Pt particle size, the nature of BaO sites and Pt-BaO synergy. It was found that the increase in the crystallinity of the gamma-Al2O3 phase and the surface acid site density of the supporting Al2O3 samples would result in improved proximity and synergy between Pt and BaO sites, leading to much more efficient NSR Pt-BaO/Al2O3 catalysts.