Each year millions of tonnes of 1,3-Butadiene (1,3-BDE) are used industrially. From the pool of potential precursors to obtain 1,3-BDE, 2,3-butanediol (2,3-BDO) stands as a promising option since it can be produced from renewable sources, instead of petrochemical steam cracking. The dehydration of 2,3-BDO is effectively catalyzed by silica-supported phosphate salts. However, mechanistic understanding of this process is currently limited, restricting our capacity to improve the efficiency of this process.<br/><br/>In this work, we analyze computationally all the possible reaction pathways that can take place during the SiO2/H3PO4-catalyzed dehydration of 2,3-BDO to obtain 1,3-BDE. This study results crucial to explain and improve critical aspects of the reaction such as product selectivity, reactivity, and catalyst inhibition. Energy profiles were calculated using a combination of density functional theory (DFT) and coupled-cluster theory (DLPNO-CCSD(T)/cc-pV(DT)Z//M06-2X-D3/6-31+G(d,p)) in order to obtain reliable outcomes. Interestingly, we found that the most favorable pathway leading to 1,3-BDE involves a multi-step mechanism enclosing an epoxidation and a 1,3-allylic substitution, two processes that had not been considered before as part of the dominant pathway.<br/><br/>Since in practice, these reactions take place on a SiO2 surface, mixed quantum/classical mechanics calculations were performed. Phosphate catalysts were embedded on the 111 face of the crystobalite form of solid silica. The inclusion of surface alkali metals was found to modulate Lewis basicity and Brønsted acidity of the active catalytic centers, which differs from previous proposals in which the metals act as a bulky blocking group.

Catalytic mechanisms of butanediol conversion by metal phosphates

2019 Fall National Meeting

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