The influence of water on the activity of nitridated zeolites in base-catalyzed reactions

The ammonia treatment of zeolites with FAU-topology at 700 degreesC leads to materials in which Si-NH2, si-NH-Si and Si-NH2-Al groups are present, i.e. NaXN, NaYN and DAYN (n(Si)/n(Al) = 30). These catalysts are active in base-catalyzed reactions, such as Knoevenagel condensations. It could be shown that the catalytic activity increases with increasing n(Si)/n(Al)-ratio. Furthermore, TG-MS experiments revealed that the uptake of water leads to slow hydrolysis with concomitant release of ammonia. The sensitivity to water increases with increasing hydrophilicity of the catalyst, viz. increasing aluminum content of the parent zeolite. It is, however, possible to preserve the catalytic activity by keeping the freshly nitridated material in a dry nitrogen atmosphere.