Ruth L. Martins

Hydrogen–deuterium exchange between zeolite Y and 3-methylpentane

Zeolite Y undergoes hydrogen–deuterium exchange with 3-methylpentane at moderate temperatures (100 °C); the presence of non-framework aluminium species increases the reactivity of the zeolite.

Reactivity of zeolite hydroxy groups toward σ-donor bases. H–D exchange with 3-methylpentane

The H–D exchange of deuteriated Y zeolites, silica–alumina and γ-alumina with 3-methylpentane has been studied by IR spectroscopy. At 373 K exchange ocurred only in the zeolites. Silica–alumina required higher temperatures (523–623 K) and exchange did not occur in γ-alumina in the range of temperature studied. Ultrastable Y zeolite with non-framework alumina (NFA), showed a higher reactivity for H–D exchange and hexane cracking than Y zeolite dealuminated by (NH4)2SiF6. These findings were explained by the difference in acid strength between the zeolites, probably due to the presence of NFA as proposed in the literature, and stress the dependence of H–D exchange on acid strength. The IR study of H–D exchange between 3-methylpentane and Y zeolites having pyridine pre-adsorbed, neutralizing some of the hydroxy groups, showed that the high-frequency (hf) hydroxy group is responsible for the exchange. The low-frequency (If) and NFA hydroxy groups appear to exchange via hydrogen bridges with the hf hydroxy group, rather than by direct interaction with the hydrocarbon. The H–D exchange between solid acids and alkanes could be a qualitative test for acid strength, since only very strong acids would attack σ bonds.

Methane activation on alumina supported platinum, palladium, ruthenium and rhodium catalysts

Abstract Methane activation was conducted on Pt, Pd, Ru and Rh alumina supported catalysts. Simultaneously with the gas chemisorption, H 2 , CO 2 and CO were evolved from all the catalyst surfaces. The H2 evolution resulted from the association of hydrogen atoms provided from dissociative chemisorption of methane. CO and CO 2 evolution was explained by the partial migration of carbon adspecies, from metal surface to the metal-support interface, followed by their interaction with the alumina O 2− ions.

Activation of Methane on NiO Nanoparticles with Different Morphologies

Nanostructured surfaces can be defined as substrates in which the typical features have dimensions in the range of 1-100 nm. The recent focus of interest in these systems is based on the fact that interesting novel properties (catalytic, magnetic, ferroelectric, mechanical, optical and electronic) are developed as a result of the dimension reductions of these substrates. This paper describes the catalytic methane decomposition into hydrogen and carbon nanofilaments on unsupported Ni catalysts prepared from different methodologies, with controlled particle size and morphologies. Ni catalyst supported on zirconia was also used for performance comparison. For the unsupported catalysts, it was observed strong dependency of catalyst activities with particle size of nickel oxide precursors and their morphologies. Although all of them presented crystallite sizes with nanometric dimensions, only those prepared with ethylene glycol, NiEG, and by hydrothermal condition, NiHT, exhibited the same performance as the supported catalyst (activity and stability), 25NiZ. Catalyst synthesized in the presence of dimethylglyoxime, NiDMG, was less active and deactivated with time on stream.

FTIR evidences of the reactivity of spilt-over stored hydrogen: Transformation of Lewis acid sites into Brönsted sites on Pt/ZrO2 catalyst

The reactivity of hydrogen species resulted from backspillover of H atoms stored in the support when Pt/ZrO 2 catalyst is reduced was shown even in the absence of H 2 in the gas phase. These species were able to create acidic hydroxyls and move pyridine chemisorbed on Lewis acid sites to the new Bronsted sites just formed, when the sample was heated in a closed system. Also piperidine chemisorbed on Lewis acid sites was dehydrogenated to pyridine when the sample was heated in a closed system, and the IR spectrum showed bands which were assigned to pyridine chemisorbed on Lewis and Bronsted sites. The reactivity of hydrogen spillover species was also observed by CO chemisorption experiments using FTIR and TPD techniques.