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

Abstract

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 TiOOH 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 Oα–Oβ polarizations of TiOOH 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 TiOOH species was mainly responsible for low H2O2 utilization efficiencies. The stability of TiOOH 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 TiOOH species, adjusting the hydrogen-bonding interactions for the stability of TiOOH 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.