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运用近似分子轨道理论MINDO/2方法,对甲醛和异丁烯在酸碱固体催化剂表面上的缩合反应进行了量子化学计算,按照SIMPLEX方法实现各种酸碱吸附态以及反应过程中各状态能量的几何构型最优化。根据本所甲醛和异丁烯气相一步合成异戊二烯的实验和量子化学一般原理,设计了由八个状态组成的反应途径,较详细地讨论了它们的反应机理。 计算结果指出:反应中甲醛均以酸吸附为主。体系中适量的碱性物质产生的酸碱协同效应,对于降低反应的初始排斥能是重要的,并且有利于提高反应选择性,防止异丁烯甲基的热分解。计算还指出:本反应的中间过渡态主要是形成一种“类烯醇互变”的状态,该脱水过程是由甲醛上的氧和碱性中心分别夺取异丁烯的甲基上两个氢。计算得到的势能位垒比较满意。 相似文献
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SiO2 monoliths with double-pore structure were synthesized with tetraethyl orthosilicate, polyethylene glycol, starch, ethanol and ammonia as the main raw materials via a sol-gel route. The effect of different content of starch of the samples was studied on the mesopore structure, macropore appearance, hydrothermal stability and enzyme activity to immobilize gluczyme. The results indicate that porous blocks with mesopores of 10~12 nm and macropores of 10~30 μm can be formed by the removal of polyethylene glycol and starch after heating at 600 ℃. The minimal density of the obtained samples was 0.34 g·cm-3 and the maximal porosity was 76%. After being immersed in water at 80 ℃ for 7 d, the density, porosity and shape of N2 adsorption-desorption curves of the samples were almost unchanged, showing that the sample has a good hydrothermal stability. The initial enzyme activity of sample P2KD30 was 11 190 U, and definite enzyme activity could be maintained after five cycles. 相似文献
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本工作采用近似分子轨道理论MINDO/2方法对甲醛和异丁烯在固体酸碱催化剂表面上的缩合反 应进行了量子化学计算,较详细地研究和讨论了它们的脱水机理。按照SIMPLEX方法(即单纯形法)实现各种酸碱吸附态以及反应过程中各种状态的能量的几何构型最优化。 相似文献
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