In Situ SAXS/WAXS of Zeolite Microwave Synthesis: NaY, NaA, and Beta Zeolites

Abstract

A custom waveguide apparatus is constructed to study the microwave synthesis of zeolites by in situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The WR-284 waveguide is used to heat precursor solutions using microwaves at a frequency of 2.45 GHz. The reaction vessels are designed to include sections of thin-walled glass, which permit X-rays to pass through the precursor solutions with minimal attenuation. Slots were machined into the waveguide to provide windows for X-ray energy to enter and scatter from solutions during microwave heating. The synthesis of zeolites with conventional heating is also studied using X-ray scattering in the same reactor. SAXS studies show that the crystallization of beta zeolite and NaY zeolite is preceded by a reorganization of nanosized particles in their precursor solutions or gels. The evolution of these particles during the nucleation and crystallization stages of zeolite formation depends on the properties of the precursor solution. The synthesis of NaA and NaX zeolites and sodalite from a single zeolite precursor is studied by microwave and conventional heating. Microwave heating shifts the selectivity of this synthesis in favor of NaA and NaX over sodalite; conventional heating leads to the formation of sodalite for synthesis from the same precursor. The use of microwave heating also led to a more rapid onset of NaA zeolite product crystallization compared to conventional heating. Pulsed and continuous microwave heating are compared for zeolite synthesis. The resulting rates of formation of the zeolite products, and the relative amounts of the products determined from the WAXS spectra, are similar when either pulsed or continuous microwave heating is applied in the reactor while maintaining the same synthesis temperature. The consequences of these results in terms of zeolite synthesis are discussed.

Synchrotron X-ray characterization of materials synthesized under microwave irradiation

“…A custom-built microwave reactor was used to monitor MWR-assisted silicate zeolite synthesis. 48,49 This reactor operated at 2.45 GHz and featured a rectangular waveguide, coaxial stub tuners, and a sliding short (Fig. 5).…”

“…This experimental setup was then used to study the role of precursor solution on silicate zeolite synthesis. 49 Panzarella et al found that MWR enhanced the rate of zeolite crystallization regardless of the precursor used. Despite the rate increase, certain precursor concentrations had no effect on the mechanisms of zeolite formation, as SAXS data indicated that the nanoparticle reorganization leading to crystallization is similar.…”

Application of Microwave Heating on the Facile Synthesis of Porous Molecular Sieve Membranes

“…The crystallization was found to be significantly accelerated by the exposure of synthesis gels to microwave radiation. Thereafter, microwave heating synthesis has been applied for the synthesis of a number of zeolites, including zeolite A (LTA) (Panzarella et al, 2007;Slangan et al, 1997 (a)), faujasite (FAU) (Panzarella et al, 2007;Srinivasan & Grutzeck, 1999), analcime (ANA) and Gobbinsite (GIS) (Sathupunya et al, 2002), beta (BEA) (Panzarella et al, 2007), ZSM-5 (MFI) (Phiriyawirut et al, 2003;Somani et al, 2003), silicalite-1 (MFI) (Hu et al, 2009), AlPO 4 -5 (AFI) , VPI-5 (VFI) (Carmona et al, 1997), and cloverite (CLO) (Park & Komarneni, 2006). The number of publications of microwave heating synthesis of zeolite increases year by year.…”

The First 20 Hours of Geopolymerization: An in Situ WAXS Study of Flyash-Based Geopolymers

“…Although in situ Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) has been applied to track zeolite formation by many authors [9,10,11,12,13], in situ SAXS and WAXS has only been applied in a limited way to the early kinetics studies of metakaolin geopolymers [14]. …”