Role of Na in the stability enhancement of CeO2 catalysts for ketonization of propionic acid

Abstract

A series of CeO2 catalysts with varying Na content were tested for vapor-phase ketonization of propionic acid at 350 °C. Na+ diffuses into the CeO2 lattice and excess NaOx accumulates on the surface, which dilutes surface contiguous and partially covers Ce-O acid-base pairs. The intrinsic reaction rate in terms of surface area always decreased with increasing Na, likely originated from the altered acid-base property and the increased distance and steric hindrance between enolate and carboxylate for C-C coupling. On the other hand, the stability was significantly improved, with almost no deactivation being observed for Na0.1Ce0.9Ox. This improvement is resulted from the dilution and/or coverage effects of NaOx, which significantly reduces accumulation of inactive bidentate propionate. This work demonstrates a strategy of dilution and/or coverage of surface acid-base pairs by alkaline metal oxides to reduce bidentate carboxylate and therefore to enhance the stability of metal oxide catalysts toward ketonization of carboxylic acids.