Microwave assisted growth of SAPO-34 on β-SiC foams for methanol dehydration to dimethyl ether

Abstract

SAPO-34 layers were successfully grown on β-SiC foam with medium specific surface-area, using microwave-assisted hydrothermal synthesis method (MAHyS) for applications as a structured catalyst. Preliminary investigations on SAPO-34 phase purity were conducted to select the appropriate concentrations and protocol to grow pure SAPO-34 on SiC foams. SAPO-34/SiC foam composite was obtained via microwave-assisted synthesis route. X-ray diffraction (XRD) was used to confirm the formation of the composite. Microwave irradiation time, number of coating cycles and pretreatment of the SiC support with zeolite precursor and the template solution were studied to optimize the growth and coverage of SAPO-34 crystals on the SiC foam surface. SAPO-34 crystals with cubic morphologies having 7μm average size were obtained after 6h microwave irradiation at 180°C. However, multi coating steps were required to obtain full coverage of SAPO-34 crystals. Template pretreatments of the host material (SiC foams) significantly improved the loading of crystals on the support surface. Full coverage of SAPO-34 on SiC foams was obtained after 3 times of coatings, which is mostly attributed to the template layer formed on the foam surface that induced the heterogeneous nucleation on the support. The SAPO-34/SiC foam structured catalyst exhibited excellent selectivity and stability in methanol dehydration to dimethyl ether, which was carried out in a fixed bed reactor.