Chemistry of hydrocarbon compounds – Adding hydrogen to unsaturated bond of hydrocarbon – i.e.,... – Hydrocarbon is contaminant in desired hydrocarbon
Reexamination Certificate
1998-08-28
2001-09-11
Griffin, Steven P. (Department: 1754)
Chemistry of hydrocarbon compounds
Adding hydrogen to unsaturated bond of hydrocarbon, i.e.,...
Hydrocarbon is contaminant in desired hydrocarbon
C585S259000, C585S654000, C502S325000, C502S339000
Reexamination Certificate
active
06288295
ABSTRACT:
The present invention relates to a catalyst comprising at least one support and at least one metal from group VIII of the periodic table and characterized in that the metal particles deposited on the support are not isolated from each other.
BACKGROUND OF THE INVENTION
Supported metal catalysts are constituted by an active metal which can, for example, be a noble metal such as platinum or palladium deposited on a support in the form of particles.
The influence of particle size on catalyst activity has been widely debated in the literature for a large number of hydrocarbon transformation reactions.
For a certain number of reactions, such as hydrogenation of ethylene, propylene, cyclopentene, or benzene over supported metals such as platinum or palladium, particle size has little influence on the specific activity of the catalysts (J. C. Schlatter, M. Boudart, J. Catal. 24 (1972) 482; Y. Hadj Romdhane, B. Bellamy, V. De Gouveia, A. Masson, M. Che, Appl. Surf. Sci., 173 (1986), 383; M. Boudart, W. C. Cheng, J. Catal., 106 (1987), 134; J. M. Basset, G. Dalmai-Imelik, M. Primet, R. Martin, J. Catal., 37 (1975), 22).
The specific activity corresponds to the activity of the catalyst reduced to the number of metal atoms accessible to the molecules to be transformed. The number of accessible metal atoms can be determined by techniques involving chemisorption of probe molecules (oxygen, hydrogen, carbon monoxide) or from the particle size determined by electron microscopy. These different techniques are very well known to the skilled person.
The specific activity is also known as the turn over frequency (TOF). For such reactions and with the aim of increasing the overall activity of a catalyst for a given quantity of metal, it is important to disperse the metal on the support to the best extent, and thus to use a catalyst with the smallest possible particles.
The situation is substantially different for other reactions. As an example, for the hydrogenation of conjugated dioletins or alkynes, it has been shown that the specific activity of palladium based catalysts increases as the particle size increases. In that case, the optimum activity of the catalyst occurs when the particle size is about 4 nm (J. P. Boitiaux, J. Cosyns, S. Vasudevan, Appl. Catal., 6 (1983), 41).
SUMMARY OF THE INVENTION
The above examples show that particle size is a fundamental parameter which is a major factor in determining the activity of supported metal catalysts.
We have now discovered, and this forms the subject matter of the present invention, that when the metal particles are not deposited on the support in an isolated manner, the activity is higher than that of particles with the same size but deposited on the support in an isolated manner.
Particle aggregation is characterized by microscopic analysis of the catalyst after reducing the active phase at temperatures generally in the range 20° C. to 500° C. For the catalyst of the invention, microscopic analysis shows that at least 50% of the particles, preferably at least 70% of the particles present on the support have a point of contact with at least one other particle. The particles can equally be disposed in the form of clusters. agglomerates, strings or in any other configuration in which preferably at least 50% of the particles, and in more preferred way at least 70% of the particles have at least one point of contact with at least one other particle. In other words, the proportion of isolated particles is preferably less than 50%, in a more preferred way less than 30%.
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Didillon Blaise
Merlen Elisabeth
Pages Thierry
Uzio Denis
Griffin Steven P.
Ildebrando Christina
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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