Steam stability of MCM-22 and its all siliceous analogue, ITQ-1, with MWW structure was investigated in a mixture of water vapor and nitrogen (95 mol% H2O, 5 mol% N2) at 10 barg pressure and two different temperatures of 600 °C and 350 °C for a period of 84 days. Further, the effect of calcination temperature and silicon tetrachloride (SiCl4) treatment on the steam stability of ITQ-1 was studied. Behavior of these zeolites was monitored in 21-day intervals using XRD, SEM, TEM, 29Si solid-state NMR, nitrogen and argon adsorption analyses. It was found that structural defects adversely affected the steam stability of the zeolites but SiCl4 treatment was effective to enhance the zeolite resistance to water vapor attack. It was observed that long-term steaming can generate holes in the crystals along with some amorphization; however, it also generated highly homogeneous short range order in the crystals.
Bibliographical noteFunding Information:
We would like to thank Dr. Miguel A. Camblor for providing the SDA recipe for synthesis of ITQ-1. We would like to thank Dr. Son-Jong Hwang for performing NMR analysis. We gratefully acknowledge financial support from the U.S. Department of Energy (DOE) (Grant DE-09FE0001322 ) for this work. Parts of this work were carried out in the Characterization Facility, University of Minnesota, a member of the NSF-funded Materials Research Facilities Network ( www.mrfn.org ) via the MRSEC program.
- MWW structure zeolites
- Steam stability