PNNL

Abstract

Zeolite BEA, a promising catalyst for organic reactions in water, was stabilized against hydrolytic degeneration. This was achieved by reducing the local hydrophilicity, i.e., the concentration of water molecules in presence of the reacting substrate. Lower intraporous water concentrations directly correlated with a longer lifetime and a higher turnover number for cyclohexanol dehydration. The Brønsted acid site concentration rather than the concentration of defects determines the concentration of water in the zeolite pores. The concentration of intraporous water was inversely related to the rate of hydrolysis of Si4+ from the zeolite lattice. The state of the lattice atoms during modification and the gradual degradation were followed by cross-polarization enhanced 29Si MAS NMR, 27Al MAS NMR as well as IR spectroscopy. The intraporous water content was determined by liquid phase adsorption of cyclohexanol. While being fairly irrelevant during the catalytic reaction, defects of the zeolite lattice determined the rate of framework degradation in pure hot liquid water.