Investigating the Aluminum Chemistry of Individual Zeolite Domains in Single FCC Particles Using Scanning Transmission X-Ray Microscopy
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Type
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Conference
Paper
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Author
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Sam
Kalirai
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URL
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Date
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2015/06/16
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Conference
Name
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24th
North American Catalysis Society Meeting
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Abstract
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Fluid
Catalytic Cracking (FCC) particles are a major class of petrochemical
catalysts that account for 40-45% of global gasoline production. One of the
main components of FCC particles are acidic, polycrystalline zeolites, which
make up 20-50% of the particle. The rest of the particle consists of matrix,
binder and filler material, typically alumina, silica and clay. These
micro-porous aluminosilicate zeolites provide an advantageous shape and size
selectivity while acidic sites on the framework perform cracking leading to
favorable product distributions. Acidity in zeolites arises from the presence
of aluminum in the silicon oxide framework where the charge balance is made
up of Brønsted acidic protons. The acidity and thus the cracking capability
of zeolites are inextricably linked to the concentration, amount and
stability of aluminum in the zeolitic framework. The FCC process consists of
continual cracking and regeneration cycles during both of which FCC particles
are under severe physical and chemical stress. In regeneration, FCC particles
are subject to steam treatment under high temperature (> 700°C). These
harsh conditions promote the migration of aluminum from the lattice framework
into extra- and non-framework positions [1]. This process significantly
alters the chemical environment of the aluminum leading to a reduction in the
particles cracking capability. Furthermore, if the dealumination process
remains unchecked, zeolite domains may collapse thereby neutralizing their
beneficial shape and size selective properties [2].
In order to increase the stability of zeolites in FCC particles, Rare Earths such as Lanthanum or Cerium may be incorporated into the zeolite in order to stabilize framework aluminum. Due to the complex structure of FCC particles, zeolite dealumination has almost exclusively been studied in the context of model zeolites. However, to build an accurate description of aluminum migration from zeolites in FCC particles, where particle heterogeneities, the presence of metals and the active matrix structure may all play important roles in promoting or inhibiting dealumination, it is important to investigate particles that have experienced as close to in operando conditions as possible. Authors report a study of the silicon and aluminum chemistry of industrially deactivated FCC particles using synchrotron based soft X-ray Scanning Transmission X-ray Microscopy (STXM). |
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