Base catalysis by alkali modified zeolites

Abstract

The development, characterization, and catalytic application of a novel zeolite with solid base properties has been completed. From isopropanol decomposition to acetone and propylene, the acid/base properties of various alkali exchanged, faujasite-type zeolites are explored. It is found that upon impregnation of CsNaY with cesium hydroxide or cesium acetate, acetone production (normally attributed to base sites) is promoted by an order of magnitude above the untreated (not impregnated) CsNaY zeolite. Furthermore, selectivity to acetone is above 97% and on a surface area basis, acetone activity is found to be comparable to MgO. Impregnation of CsNaX shows little promotion in acetone activity resulting in acetone activity comparable to the untreated CsNaY zeolite and acetone selectivity at 62%. From numerous characterization studies of the impregnated CsNaY zeolite (many in situ) it appears that a highly dispersed intracrystalline cesium oxide is formed from the decomposition of the occluded salt and is believed to be the active site for acetone formation. Evidence is provided also to indicate the presence of an isopropoxide intermediate which is responsible for the acetone and the minor amounts of propylene formed by the acetate impregnated CsNaY zeolite.

The cesium acetate impregnated CsNaY catalyst was tested for activity by the base catalyzed alkylation of toluene, acetone, ethane, and methane with methanol. For toluene alkylation, it is determined that little improvement is gained over previous faujasite-type catalysts. This appears to be a result of the rapid decomposition of formaldehyde, i.e., the alkylating agent derived from the dehydrogenation of methanol. MgO is demonstrated to possess base properties similar to the acetate impregnated CsNaY zeolite, yet MgO is found to be inactive in toluene alkylation. Neither ethane or methane is alkylated at 425°C or 465°C by the acetate impregnated zeolites. Acetone is alkylated slightly to methylvinylketone and methylethylketone at 425°C but the majority of the reacted acetone appears to form aldol condensation products.