中文摘要：

采用量子力学中的密度泛函理论（DFT）研究了Y分子筛Br？nsted酸中心Al—OH周围NNN（Next nearest neighbor）和NNNN（Next next nearest neighbor）位置上的Al原子对分子筛Br？nsted酸强度的影响,并分析了Al原子对酸强度影响的化学细节。结果表明,当Al原子分布在酸中心Al—OH周围的NNN位置时,Al原子会明显降低酸中心的酸强度;酸中心NNN位置分布的Al原子数目越多,酸强度降低越明显。因此当Al原子以NNN方式分布于酸中心Al—OH周围时,酸强度随着Si/Al摩尔比的降低而显著降低。当Al原子分布在酸中心Al—OH周围NNNN位置时,Al原子对酸中心强度的影响较小;酸中心NNNN位置上分布多个Al原子时,酸强度也无明显变化。因此当Al以NNNN方式分布于酸中心周围时,酸强度基本不随Si/Al摩尔比的变化而明显改变。由此可见,不同位置的Al原子对酸强度的影响不同,不能仅从Y分子筛Si/Al摩尔比大小判断分子筛酸强度,还需考虑Al原子的分布方式。

英文摘要：

With the density functional theory（DFT）quantum chemical method,the effects of Al atoms in the NNN（Next nearest neighbor）and NNNN（Next next nearest neighbor）positions of the Br？nsted acid Al—OH of Y zeolite on Br？nsted acid strength were studied.The results showed that the effects of Al atoms in different positions on the acid strength were different.Al atoms in the NNN positions of the Br？nsted acid decreased the acid strength of the acid center significantly.The more the Al atoms in the NNN positions of the acid center,the more obvious the decrease of acid strength.So when the Al atoms distributed in the NNN positions of the Al—OH,the acid strength decreased with the decrease of Si/Al molar ratio.Al atoms in the NNNN positions of the Br？nsted acid had little effect on the acid strength.No appreciable change was found in the acid strength when there were more than one Al atoms in the NNNN positions of the Br？nsted acid Al—OH.So when the Al atoms distributed in the NNNN positions of the Al—OH,the acid strength had little change with the decrease of Si/Al molar ratio.The Br？nsted acid strength is determined not only by Si/Al molar ratio,but also by the distribution of Al atoms in Y zeolite.