States of transition metal ions in modified mesoporous MCM-41 and in microporous ZSM-5 studied by ESR spectroscopy

Hydrogen absorption in palladized MCM-41

Hydrogen absorption by palladium (Pd) in Pd/MCM-41 was studied at 298.2 ± 0.1 K and between 0.5 and 1.0 atm [Formula: see text]. Mass percent Pd loadings of 0.81%, 1.10%, 1.16%, and 2.30% of total Pd/MCM-41 were used. Absorption was measured in gas-tight stainless steel cells equipped with computer-logged pressure transducers. The average maximum hydrogen absorption for all samples was 0.85 ± 0.18 H/Pd. An apparent trend of increasing hydrogen absorption as the mass percent loading of Pd increased was determined to be non-significant. Similar experiments using Pd black showed a lower absorption of 0.79 ± 0.09 H/Pd.

Photodecomposition of chloroform catalyzed by unmodified MCM-41 mesoporous silica

Unactivated MCM-41 mesoporous silica catalyzes the photodecomposition of chloroform to phosgene and hydrogen chloride under near-UV (λ > 360 nm) irradiation. The rate of photodecomposition increases toward an asymptotic limit as the O(2) partial pressure is increased. Deuterochloroform does not decompose under the same experimental conditions. Low concentrations of both cyclohexane and ethanol quench the photodecomposition, whereas water, up to its solubility limit, does not. Dissolved tetraalkylammonium salts suppress photodecomposition. The data are consistent with a mechanism in which light absorption by an SiO(2) defect yields an electron-deficient oxygen atom, which then abstracts hydrogen from chloroform. The resulting CCl(3) radicals react with oxygen to form a peroxy radical that decomposes, eventually yielding phosgene and hydrogen chloride.