DFT study of phenol alkylation with propylene on H-BEA in the absence and presence of water

We employ ab initio density functional theory calculations to investigate the mechanisms of phenol (a model compound for lignin-derived bio-oil) alkylation with propylene to 2-isopropylphenol, in the presence and absence of water on H-BEA. We also compute the reaction pathways for phenol alkylation in the uncatalyzed gas phase to understand H-BEA catalysis. In the uncatalyzed gas phase, phenol acts as a self-catalyst, activating propylene by transferring a proton from phenolic oxygen and facilitating the carbon-carbon bond formation reaction. We find that the lowest barrier process proceeds via an intermediate both in the uncatalyzed gas phase and on dry H-BEA. On H-BEA, the intermediate is stabilized by the transfer of a zeolitic proton. Our calculations show that, in comparison to the uncatalyzed gas phase, H-BEA reduces the barrier for converting the reactant complex to the intermediate by similar to 40 kJ mol(-1), which translates to a four order-of-magnitude increase in the transition-state theory rate coefficient at 350 degrees C. However, we find that the rate coefficient for the next step, which is also the rate-limiting step, remains unchanged on H-BEA. We further find that the presence of water reduces the activation barrier for this step-i.e., the rate-limiting step-by similar to 30 kJ mol(-1), which leads to a two order-of-magnitude increase in the transition-state theory rate coefficient at 350 degrees C.