Transformation from NaA to MCM-49 Zeolite and Its Catalytic Alkylation Performance

Abstract

The transformation from NaA (LTA) to MCM-49 (MWW) zeolite was achieved in the synergism of hexamethyleneimine (HMI), NaOH, and SiO2, in spite of no common composite build units between LTA (lta, sod, and d4r) and MWW (mel and d6r) structure. NaA (SiO2/Al2O3 = 2.0) was employed as the parent zeolite. The samples prepared at different crystallization stages were characterized by XRD, SEM, 29Si/27Al/13C MAS NMR, and STEM-EDS to investigate the intermediates during the transformation from NaA to MCM-49. As shown in SEM and STEM-EDS images, MCM-49 was proposed to be transformed gradually from the exterior to the interior of NaA, which was clearly observed by the core (LTA, low SiO2/Al2O3)–shell (MWW, high SiO2/Al2O3) coexisting zeolites as intermediates. With high relative crystallinity and the uniform sizes of crystals, the final MCM-49 was featured by Si enrichment on the external surface, which was proved by the shell (SiO2/Al2O3 = 45.4) wrapping around the core (SiO2/Al2O3 = 22.0). For transformed H-MCM-49 zeolite, the uniform sizes of crystals and the increase of total acid sites contributed to better accessibility of active centers, which achieved simultaneous improvement in ethylene conversion and ethylbenzene selectivity in the liquid-phase alkylation of benzene with ethylene.

Catalytic Performances of Cu/MCM-22 Zeolites with Different Cu Loadings in NH3-SCR

“…The X-ray powder diffraction (XRD) patterns collected on a PANalytical X'pert Pro MPD X-ray diffractometer (Philips, Eindhoven, Netherlands) was adjusted to a Cu Kα radiation of 154.06 pm in the range of 2θ from 3 • to 50 • with a scan speed of 4 • /min. Using a paper by Xing and co-workers [40], the relative crystallinity (RC) of metal modified zeolites was obtained by dividing the sums of their diffraction peak intensities at 2θ of 14. The practical atomic composition of catalysts was measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES, Autoscan16, TJA, Seymour Fisher Corporation, USA).…”

“…Cu a (wt%) [40]. c Surface area and pore volume of each of the zeolites were determined by nitrogen physisorption experiments.…”

Recent advances of pore system construction in zeolite-catalyzed chemical industry processes

“…It was found that the main reaction occurred in the pockets at the surface while coke deposition and oligomerization of ethylene were more favorably produced in the large space of the supercages and 10-R pores. Shu et al [122][123][124] obtained MCM-49 zeolite via the transformation from NaA (LTA) zeolite in the synergism of hexamethyleneimine (HMI), NaOH, and SiO 2 (Fig. 12A).…”

Efficient and Sustainable Hydrogenation of Levulinic Acid to γ-Valerolactone in Aqueous Phase over Ru/MCM-49 Catalysts

“…MWW zeolites are attractive materials in several important industrial applications, such as catalytic cracking, hydrocracking, alkylation, oxidation, and isomerization. − MWW zeolites possess a layered structure with an abundance of 12MR surface pockets on the surface, which supply places for the reaction of large molecules. MCM-49 is a type of MWW zeolite with a relatively large pore size that exhibits promising properties in liquid-phase alkylation of benzene with ethylene to produce ethylbenzene .…”