Effect of local framework heterogeneity on NO adsorption in cobalt-ferrierite
Effect of local framework heterogeneity on NO adsorption in cobalt-ferrierite
复制标题
局部骨架异质性对钴镁碱沸石吸附 NO 的影响
DOI：
10.1016/s0021-9517(03)00196-9
复制
发表时间：
2003
影响因子：
7.3
通讯作者：
R. Snurr
中科院分区：
文献类型：
--
作者：
Scott A. McMillan;L. Broadbelt;R. Snurr
用量子化学方法计算了镁碱沸石骨架外环境中钴对NO的吸附。对于镁碱沸石的B和G钴位，考虑了两个邻近骨架铝原子的所有可能的排列。钴-亚硝基取向，即，弯曲与线性，取决于当地的沸石环境。吸附的势能和自由能也是局部沸石环境的函数。与G位点相比，在B位点中的钴上的NO吸附以约50 kJ/mol有利。这种巨大的差异可归因于两个因素：钴-沸石环境中NO诱导的应变的差异以及基于钴的配位不饱和度的固有差异。程序升温脱附曲线的模拟揭示了三种不同的钴环境吸附NO，显示依赖的宏观性质，这是相关的催化活性的局部沸石环境附近的金属阳离子。这一观察结果表明，在营业额的增加NO到N2每钴原子与增加钴负载在文献中报道的可能与相同的因素。还进行了钴-亚硝酰基键的详细分析。
Quantum chemical calculations have been performed to evaluate the adsorption of NO on cobalt in several extraframework environments within ferrierite zeolites. All possible arrangements of the two nearby framework aluminum atoms have been considered for the B and G ferrierite cobalt sites. The cobalt–nitrosyl orientation, i.e., bent versus linear, depends on the local zeolite environment. The enthalpies and free energies of adsorption are also functions of the local zeolite environment. NO adsorption is favored by about 50 kJ/mol on cobalt in the B site compared to the G site. This large difference is attributable to two factors: differences in NO-induced strain on the cobalt–zeolite environments as well as an intrinsic difference based on the coordinative unsaturation of cobalt. A simulation of the temperature-programmed desorption profile reveals three distinct cobalt environments for adsorbed NO, showing the dependence of a macroscopic property that is related to catalytic activity on the local zeolite environment near a metal cation. This observation suggests that the increase in the turnover of NO to N2per cobalt atom with increasing cobalt loading reported in the literature may be related to the same factors. A detailed analysis of the cobalt–nitrosyl bond was also performed.