Importance of amine in carbon dioxide conversion to methanol catalyzed by Ru-PNP complex

The theoretical insight with DFT calculations was carried out to explore the mechanism of CO2 conversion to methanol. The tandem catalysis with the Ru-Macho-BH complex and ethylenediamine (EDA) was investigated. Three possible routes, Route A, B, and C, were realized for the process. Route A (delta E > 60 kcal mol-1) consists of three steps, formic acid formation, formamide formation, and methanol formation (from alkanolamine). Route B (delta E = 35.07 kcal mol-1) contains four steps, formic acid formation, formamide formation, formaldehyde syn-thesis, and methanol formation (from formaldehyde). Route C (delta E = 39.14 kcal mol-1), a non-amine route, involves three steps, formic acid formation, formaldehyde dehydration, and methanol formation. Route B has the lowest energetic span and, thus, we propose it as a favorite route for CO2 conversion to methanol. Although Route C has a lower activation barrier, it has a larger delta E. The exogenic reaction of the formamide formation step in Route B can affect lower energy requirements in further methanol formation. In the absence of EDA, CO2 hydrogenation to formic acid cannot produce, because the formate form is trapped by the catalyst. Thus, it can explain why CO2 conversion to methanol is impossible without the presence of amines.

Automated summary

In this study, DFT calculations were used to gain theoretical insight into the mechanism of CO2 conversion to methanol. The tandem catalysis of the Ru-Macho-BH complex and ethylenediamine (EDA) was found to play a crucial role in the process. Among the three possible routes explored, Route B was proposed as the most favorable route for CO2 conversion to methanol due to its lowest energetic span.