As-synthesized MCM-49 is a three-dimensional (3D) microporous
aluminosilicate zeolite with the MCM-22
framework topology. It is formed hydrothermally in a reaction gel
and is the first example of a zeolite with
this topology to be produced by direct synthesis, in contrast with the
conventional procedure in which a
precursor is formed first and is then calcined. When
hexamethyleneimine (HMI) is used as the directing
agent, a SiO2/Al2O3 ratio of the
framework as low as 17/1 can be achieved. X-ray powder diffraction
(XRD),
temperature programmed base desorption (TPBD) experiments, and
multinuclear NMR analyses of this zeolite
and others in this series (viz., calcined MCM-22 and its
precursor) provide new insights into the novelty of
this class of materials. TPBD and 13C NMR experiments,
for example, provide experimental evidence that
support the coexistence of different dual pore systems within both the
MCM-22 precursor and MCM-49.
The 27Al MAS NMR spectra of MCM-22 and calcined
MCM-49 exhibit three distinct Td resonances, a
feature
not previously observed for any other zeolite. And finally,
aluminum enrichment of the T1−O1−T1 bridge
in MCM-49 is postulated on the basis of the length of its unit cell
c-parameter.
The mixing conditions have a direct impact on the pore structure of alumina extrudates. We study the pore structure of samples prepared with two mixers: a standard Eirich mixer and a smaller yet more severe Fukae mixer, which operates at 1500 rpm. We present the development of a bimodal pore size distribution within the range of 25-150 Å produced by using the Fukae mixer. The pore structure consists of larger pores that grow at the expense of the smaller ones and can be tuned as a function of mixing time.
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