2,179 research outputs found
EXAFS studies on the reduction of palladium(II) in X zeolites
Palladium tetraammine ion exchange into zeolite, temperature treatments under
different atmospheres, and hydrogen reduction have been studied by EXAFS at
the Pd Κ edge. Complete autoreduction is found to take place between 473 and
623 Κ under vacuum.
Α bidisperse Pd metal phase is formed which agglomerates
at the expense of the small particles upon prolonged heating at 623 Κ. In
contrast, a similar treatment under oxygen suppresses autoreduction , and the
Pd cations remain in zeolite coordination sites. Additional small amounts of
palladium oxide are observed under these conditions. If hydrogen is admitted
to the dehydrated, ionic system at 295 K. the oxygen coordination of the Pd
disappears and evidence is obtained for the formation of Pd(0) dimers that
interact with the framework via a long Pd-0 bond
Reduction and cluster growth of palladium in zeolite Y containing transition metal ions. X-ray absorption studies
Surface chemistry of heterobimetallic Ge-M (M = Mo, W) complexes in zeolite Y.
The intrazeolite chemistry of the two germylene complexes Cl2CTHF)GeM(CO)5 (M = Mo,
W) was studied with x-ray absorption spectroscopy (Ge, Mo, W edge EXAFS) and in-situ
FTIR/TPD-MS techniques. The slightly decarbonylated GeMo complex interacts with the
framework of NaY zeolite at room temperature and retains the Ge-Mo bond up to about 100° C. In
proton-loaded HY zeolite, framework interactions increase at elevated temperature, and the attached
complex retains the Ge-Mo bond up to about 120° C. The Ge-Mo bond is cleaved at higher
temperatures. MoClx and Mo-Mo species are formed in NaY and HY zeolite, respectively, while
GeClx fragments are anchored to the zeolite framework.
The complex Cl2(THF)GeW(CO)5 retains all five CO ligands up to about 100° C in both
NaY and the proton form. Detectable anchoring occurs at room temperature in NaY and at about
80° C in the proton form. WC1X species are formed upon cleavage of the Ge-W bond at higher
temperatures
Reactivity of a trimethylstannyl molybdenum complex in mesoporous MCM-41
A highly thermostable tin–molybdenum complex is encapsulated into the hexagonal mesoporous channel host MCM-41 and thermally transformed into supported metal clusters
Encapsulation of Tetracarbonyl(trimethylstannyl)cobalt in NaY Zeolite. Reactivity and Alloy Cluster Formation
Organometallic fragments in microporous solids: intrazeolite chemistry of (cyclooctatetraene)iron tricarbonyl
The intrazeolite reactivity of (COT)Fe(CO)3 (COT = cyclooctatetraene) [ 11 in faujasites having different levels of Bronsted
acidity was examined with extended X-ray absorption fine structure, vibrational, and temperature programmed desorption/mass
spectrometric techniques. The data show that the precursor complex [l] associates with Na-Y zeolite, resulting in symmetry
changes of the Fe(C0)3 fragment while 1 remains chemically intact. If (COT)Fe(CO)3 is adsorbed into highly acidic H-Y
zeolite at room temperature, bicyclo[5.1 .O]octadienyliron tricarbonyl cation is formed in a clean reaction. This reaction
corresponds to the protonation of 1 with noncoordinating acids in homogeneous solution. At elevated temperatures, the carbonyl
ligands are cleaved off and the remaining organo-iron fragment is anchored to framework oxygens of the large zeolite supercages
Chemistry of cyclopentadienyliron dicarbonyl dimer and ferrocene in zeolite Y cavities. Anchoring organometallic fragments into microporous solids
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