Optimizing the Synthesis of Nitrogen-Substituted Zeolites

We examine the effect of synthesis conditions on the degree of substitution and retention of crystallinity and microporosity during ammonia treatment of Y zeolite. Our objective is to find a reproducibly optimal synthesis protocol to make nitrogen substituted (nitrided) zeolites. We find that a temperature of approximately 750 degrees C at a mean ammonia flow rate of 600 cm(3)/min produces substitution without loss of crystallinity or microporosity. We have investigated the effects of several synthesis parameters using fifteen different synthesis protocols. The most important parameter in the synthesis is the ammonia now rate; we recommend keeping the flow rate as high as possible. Calculations of the NMR and vibrational spectra of substituted zeolites are used to investigate the overall utility of these techniques for confirming the presence of nitrogen in the zeolite. Infrared and Raman spectroscopy were not found to be diagnostic, but they can corroborate the presence of nitrogen in the framework. We recommend a combination of Si-29 MAS NMR spectroscopy, X-ray diffraction, and high-resolution adsorption to test any new reactor design; these techniques can establish nitrogen Substitution in the framework, as well as crystallinity and microporosity in the product.