Theoretical Investigation Of Transition Metal Catalytic Activity For The Reaction Of CO₂ Hydrogenation In Gas Phase

The sharp increase of Global CO₂ caused by a series of environmental problems such as the "greenhouse effect", and it is paid attention extensively. Therefore to CO₂ as a carbon source, it can be recycled by means of chemistry and chemical engineering, which is not only important for improving the environment the practical significance, but also for the shortage of petrochemicals can also play a role in mitigation. As we all know, two stable ? delocalized bond of CO₂ molecule lowest energy so that it is in a steady state that difficult to be activated in theory. In recent years, carbon dioxide as a carbon source, especially interest in catalysis has become a hot research.For transition metal or transition metal oxides, the existence of empty or half full of d orbitals in the chemical reaction can interact with the frontier orbital of substrate molecule and formed intermediate formation,?e.g., electronic grantedaccepted?. the process reduces the reaction energy barrier, which is most chemists with transition metals and their complexes as catalyst. the triplet possible reaction mechanism of CO₂ hydrogenation catalyzed by TiO has been studied by Der- Yan Hwang et al. puts forward the optimal orders in triplet potential energy surface reaction path; density functional theory to discuss mechanism of carbon dioxide and the transition metal ruthenium reaction has been used by Xian- Yang Chen et al.Found by experiment, the transition metals or transition metal oxides as catalysts can actually reduce the reaction energy barrier. However, when the participation of a transition metal reacts, electronic under the action of the spin- orbit coupling spin flip easily occur because of it has several unpaired electrons, so that not to comply with "spin conservation law", that reaction is referred to as spin-forbidden reaction.Transition metals in the catalytic process may cause a change in spin states, so that the two reaction potential energy surface crossing may occur, namely the "two-state reaction?TSR?", therefore, the reaction of the transition metal participation in the need for reaction mechanism of spin-forbidden in-depth analysis, which has important theoretical significance for the activation of small molecules of carbon dioxide.To illustrate the two-state reaction would affect the reaction rate or even determine the selectivity of the reaction. Based on the density functional theory, in this paper, the mechanisms of CO₂ hydrogenation Catalyzed by TiO in the singlet and triplet two a potential energy surface and Ru catalytic CO₂ in a single, triplet and quintet potential energy surfaces have been studied. The intersystem crossing probabilities were calculated and finally obtain the minimum energy reaction path.This paper reviews the catalytic system of TiO's single, triplet for CO₂ hydrogenation by formic acid reaction, in addition, the reaction mechanism is also discussed. There exist four cross points?CPS? and MECPS in this process on the PES of single, triplet. The reaction conducts in twain and four situation potential energy surfaces alternately. according to the intersection of configuration computing spin-orbit coupling constant?SOC?, finally the use of Landau-Zener nonadiabatic transition probability formula to calculate the MECPS of transition probability. The results showed that strong spin- orbit coupling effects and higher energy transition probabilities in MECPS. And the electron spin flip had occurred in separate d orbitals of Ti atoms. Finally, ensure the lowest energy reaction path. Finally, the turnover frequency?TOF? and XTOF at 298 K has been obtained by citing the energetic span model proposed by Kozuch, Determine the fast mode in the process of reaction.Gas–phase CO₂ catalyzed activation hydrogenation by Ru atoms was studied at the density functional theory. Based on the structure optimization of the different potential energy surface, there are two crossing points between singlet and triplet potential energy surfaces and there is a crossing point between quintet and triplet potential energy surfaces in the dehydration process. Spin transition probabilities in the vicinity of the intersections have been calculated by the Landau–Zener model theory. The results showed that 3 MECPs have strong spin–orbit coupling effect and higher spin transition probability, and all spin inversion occurred in s orbit and different d orbits of ruthenium,indicate this is a typical two–state reactivity?TSR?reaction. During the formation of formaldehyde and methanol is an endothermic reaction are all go against to reaction. Among them, the formaldehyde of heat absorption capacity is higher than methanol, so in the course of the reaction, hardlyproduce formaldehyde. The reaction of these two parts are in the triplet state reaction,are single-state reaction?SSR?.