Insights into the efficiency of hydrogen peroxide utilization over titanosilicate/H₂O₂ systems

The key to high efficiency of utilization of hydrogen peroxide (H₂O₂) over titanosilicate/H₂O₂ systems was discovered thanks to a comprehensive catalytic investigation. The H₂O₂ utilization efficiency depended chiefly on the competition between the epoxidation and decomposition pathways of the H₂O₂ reaction. In terms of the epoxidation pathway, the formation of Ti[sbnd]OOH species could be promoted by enhancing the intrinsic catalytic activity of titanosilicates by improvement of Lewis acid strength. Meanwhile, the ability of active “O” to transfer to reactants could be enhanced by improving the nucleophilicity of alkene (reactant), the surface hydrophobicity of zeolites, and the O_α–O_β polarizations of Ti[sbnd]OOH species. These were beneficial for the increase of H₂O₂ utilization efficiency. In the ineffective decomposition pathway, the self-decomposition of H₂O₂ hardly occurred within a short period of time and at a low temperature, while the oxidative decomposition of H₂O₂ (OD) with Ti[sbnd]OOH species was mainly responsible for low H₂O₂ utilization efficiencies. The stability of Ti[sbnd]OOH species could be improved by enhancing the hydrogen-bonding interactions with the addition of hydrogen-bond acceptors and the proper solvent, which was helpful for suppressing OD. Thus, the synergistic effect of regulating the intrinsic catalytic activity of titanosilicates for the formation of Ti[sbnd]OOH species, adjusting the hydrogen-bonding interactions for the stability of Ti[sbnd]OOH species, and enhancing the ability of active “O” to transfer to reactants was the key to achieving high utilization efficiency of H₂O₂ over titanosilicates/H₂O₂ systems. These discoveries could provide beneficial ideas for designing a highly efficient titanosilicates-catalyzed epoxidation system.