Structure/function relationships for basic zeolite catalysts containing occluded alkali species

The basicity and reactivity of alkali-modified zeolites were investigated in order to elucidate the role of occluded species on catalytic activity. To synthesize intrazeolite oxide or metal species, cesium acetate or cesium azide was impregnated into the pores of zeolites and decomposed in situ. To characterize the basicity of the samples, we used adsorption of iodine and carbon dioxide. The blue shift in the UV–visible spectrum of adsorbed iodine was found to increase with increasing electropositivity of the exchangeable cation, indicating greater donor strength of the zeolite framework. Cesium-exchanged zeolite X was an active catalyst for the reaction of ethylene oxide and carbon dioxide to form ethylene carbonate. For a series of faujasite-type zeolites with different loadings of occluded cesium oxide, the CO2 uptake increased linearly with the amount of occluded Cs. The catalytic activities of the CsOx/CsX samples for the isomerization of 1-butene and dehydrogenation of 2-propanol increased linearly with the amount of excess cesium, consistent with results from the adsorption of CO2. A majority of the base sites on these materials exhibited a heat of CO2 adsorption around 85 kJ mol−1, which is much lower than the 270 kJ mol−1 seen on bulk cesium oxide. After thermal pretreatment, Na(azide) and Cs(azide) modified X zeolites catalyzed the side-chain alkylation of toluene with ethylene and the side-chain alkenylation of o-xylene with butadiene, whereas occluded cesium oxide was inactive in the reactions.