甲醇转化制丙烯反应机理研究

以杂化轨道理论和关于含Si、Al元素催化剂酸中心的认识为理论依据和研究方法，从反应物与催化剂B酸中心相互作用为切入点，分析相互作用过程中甲醇与B酸中心分子结构变化，揭示甲醇制烯烃反应机理本质。研究结果表明甲醇转化制丙烯反应过程可分为3步：(1)B酸中心释放H+攻击甲醇分子中C-O键，C-O键断裂生成甲基碳正离子(CH+3)和H2O，CH+3中C原子外层有个空轨道，释放了H+后的B酸中心失去活性。(2)失活B酸中心从CH+3中获得H+，反应生成了一种新中间体H-form，H-form中C原子外层有1对孤对电子(e-)和1个空轨道，结构式为C↑↓〇H2；失活的B酸中心获得H+后恢复活性。第3步，有3个H-form结构的C原子，第1个C原子上的孤对e－占据第2个C原子上空轨道，第2个C原子上的孤对e－占据第1个C原子上空轨道，彼此共用2对e-，形成C=C键；第3个C原子上的空轨道与第1个C原子上C、H原子重叠轨道再次重叠，形成C、H和C三原子共用1对e－结构，结果是第1个C原子与第2个C原子形成C=C键，第1个C原子与第3个C原子形成C-C键，3个C原子形成C=C-C结构，即生成丙烯。

Reaction Mechanism of Methanol to Propylene

Based on the hybrid orbital theory, knowledge of acid center of Silicon and Aluminum-containing catalysts and the mutual interaction between the reactant and the catalyst B-acid center, the molecular structure of methanol and B acid center in the interaction process are investigated. Through the above studies, the nature of reaction mechanisms of methanol to olefins are understood. It was found that the methanol-to-propylene (MTP) reaction process could be divided into three steps: At the first step, the B-acid center provides hydrogen proton (H+) to attack the C- bond in the methanol molecule, and the C-O bond breaks to form methyl carbocation (CH+3) and H2O. The outer layer of the carbon atom of the CH+3 has an empty orbit, but the B-acid center after the release of the hydrogen proton (H+) loses its activity. At the second step, the inactivated B-acid center obtains hydrogen proton (H+) from CH+3, and the reaction produces a new intermediate H-form. H-form has a pair of lone pairs of electrons (e-) and an empty orbit. The structural formula is C↑↓〇H2, where the double arrow represents the lone pair e-, and the circle represents the empty orbit. Thus, the inactive B-acid center recovers the activity after obtaining hydrogen proton (H+). At the third step, there are three carbon atoms of H form structure, the lone pair e- on the first carbon atom occupies the an empty of the second carbon atom, and the lone pair e- on the second carbon atom occupies an empty orbit of first carbon atom, then first carbon and second carbon atoms share two pairs e- to form a C=C double bond；the empty orbit on the third carbon atom overlaps with the overlapping orbit of the carbon and hydrogen atoms on the first carbon atom, forming a pair e- structure which carbon, hydrogen and carbon atoms share with each other. As a result, the first carbon atom forms a C=C bond with the second carbon atom, and the first carbon atom forms a C-C bond with the third carbon atom. Then the three carbon atoms of H-form structure lead to a C=C-C structure, which is propylene.