Density Functional Theroy Study On The Thiophene Cracking Mechanism Over Br(?)nsted Acidic Zeolites

This thesis includes the following two parts.Part1: A Density Functional Theroy Study on the Thiophene Cracking Mechanism over Bronsted Acidic ZeolitesA new mechanism of thiophene cracking over Bronsted acidic zeolite, in which an additional thiophene molecule is introduced near the active site, has been investigated by using cluster models and density functional methods. A 5T cluster is used to locate all stationary points along the reaction pathway at B3LYP/6-311G (d, p) level. The reaction path involves two important steps, which are polymerization of the two thiophene molecules and cracking of the C-S bond. With the assistant of an additional thiophene, the calculated barrier for C-S bond cracking is only 103.2 kJ/mol after refined by single point energies and zero point energies, remarkably lower than the previous theoretical studies (222-318 kJ/mol) of single thiophene cracking mechanism, and even lower than the polymerization step of 143.2 kJ/mol, which is the rate-determining step of this reaction. This is in agreement with the experimental fact that this reaction can occur at ambient temperatures. The activation energies obtained from 5T cluster calculations can be improved by considering the long-range electrostatic interaction and using larger 34T and 56T clusters. It is shown that the barriers are especially sensitive to long-range electrostatic effect, which could be reduced by 42.4 kJ/mol for the rate-determining step and 37.0 kJ/mol for C-S bond cracking from 5T to 56T cluster.Part2: The Free Software R and Its Application in ChemistryThe importance of spreading free software in academic area is stressed. As a free software, R has a wide range of application. In this article, three different types of usage of R in chemistry are listed in detail, which are statistics system, graphical techniques and developing platform.