(535e) Localizing Microwave Heat By Surface Polarization of Titanate Nanostructures for Enhanced Catalytic Reaction Efficiency

Titanate nanostructures (nanocube, nanotube and nanobelt) were successfully synthesized by using different alkalis in hydrothermal reaction. The titanate intermediates (protonated titanates, H₂Ti_nO_2n+1, n=3, 5) have been demonstrated critical in controlling the catalyst pore structure, surface area, crystal composition and the quantity of acid site. Especially, the open crystal structure of H₂Ti₃O₇ allows interlayer polarization of titanates, which is critical to enable a large number of Ti-O-SO₄^2- acid sites. The polarized titanate nanostructures can be used as microwave responsive catalysts for saccharide conversion reactions. The Ti-O-SO₄^2- not only serves as catalytic active site, but also the site for heat generation under microwave irradiation. Among the titanate nanostructures, titanate nanotube shows the best heat generation capability and gives the highest rate constant of 0.31 min^-1. The reaction equilibrium for HMF production can be reached within a few minutes at 140 ^oC. Benefited from the surface acidity and microwave heating ability, the energy efficiency of the reaction by titanate nanotube (5.6 mmol·(KJ·L)^-1) is 9 times higher than commercial TiO₂ solid acid (0.6 mmol·(KJ·L)^-1). The interlayer polarization is revealed as the major reason for the optimal microwave response and energy efficiency of the catalyst.