Jacques Saint-Just

Low temperature catalytic homologation of methane on platinum, ruthenium and cobalt

Abstract Adsorption of methane on metallic surfaces can proceed with hydrogen evolution if the temperature is sufficiently high (above approximately 100°C). Under flowing methane the desorbed hydrogen is continuously removed and the surface becomes increasingly covered with H- deficient CHx species. On Pt, Ru and Co, interruption of the methane flow followed by hydrogen flush causes the release of CH4 as well as higher hydrocarbons ranging from C2 to C7. On this basis a cyclic procedure is described for the selective homologation of methane at low temperature.

Influence of chlorine ions in Pt/A12O3 catalysts for methane total oxidation

Residual chlorine ions on a Pt/Al2O3 catalyst surface prepared from chlorine-containing precursors appear to inhibit the total oxidation of methane. At 450°C, as chlorine is eliminated with time on stream, the reaction rate increases despite the sintering of the platinum particles. The steady state reaction rate which is reached after 60 h is identical to that obtained with a catalyst prepared from a precursor containing no chlorine. Whether chlorine is present or not in the initial state of the catalyst does not appear to have an influence on the evolution of the platinum particle size.

Catalytic combustion of methane on aluminate-supported copper oxide

Abstract Copper oxide has been deposited onto high surface area magnesium aluminate spinel prepared from alumina and magnesium nitrate. The catalytic properties of such a solid have been investigated in methane combustion. At the laboratory scale a very good activity is observed (light-off of 530°C) and no CO is detected. Aging at 1000°C under water vapour has no influence on activity. The previous catalyst has been washcoated on monolith and tested on a rig either with methane or synthetic natural gas at very high GHSV under conditions close to those of a gas turbine. In that case also, a good activity was observed.

Catalytic combustion: from reaction mechanism to commercial applications

Abstract The present commercial applications of catalytic combustion are briefly reviewed. Difficulties still hinder the commercial development of this type of combustion as an NO x control technique. The problems are addressed by both academia and industry. The relevant activities of Gaz de France and GASTEC, both involved in several projects supported by the European Union, are described.

Homologation of methane under non-oxidative conditions

This review presents results obtained in recent years concerning the catalytic conversion of methane into higher hydrocarbons using metal catalysts under non-oxidative conditions at moderate temperature. Although only a limited amount of work has been carried out in this area, the non-oxidative homologation of methane has already proved itself to be a novel and interesting way of addressing the problem of methane upgrading. Chemisorption of methane on transition metal surfaces has been studied for long on either ill-defined surfaces or single crystals. These studies, reviewed here, concerned mainly the kinetics and dynamics of chemisorption. In contrast, little has been known concerning the nature and reactivity of the adspecies. The reactivity of C1 adspecies originating from precursors other than methane (carbon monoxide, diazomethane, ketene, etc.) is better understood, which can be useful in investigating the reactivity of the hydrocarbonaceous adspecies resulting from methane. Most of the work concerning homologation of methane under non-oxidative conditions has been done by the groups of Amariglio in France and van Santen in the Netherlands. Both use two-step procedures in which metal catalysts are exposed first to methane and then to hydrogen. However, the procedures differ markedly in essentially two points: (i) the temperature of the first step and (ii) the pressure of methane. The Dutch group always uses a two-temperature cycle, decomposing dilute methane on Ru and Co at a rather elevated temperature and then carrying out hydrogenation at a much lower temperature and at atmospheric pressure. The French group, in contrast, has shown that homologation can be performed isothermally and at a moderate temperature on Pt, Ru and Co, using methane and hydrogen at atmospheric pressure. Consequently, in the two procedures the nature and reactivity of the surface species formed at the end of the exposure step are different. When the exposure to methane has been carried out at a moderate temperature and at atmospheric pressure, Cγ, is not formed (therefore no irreversible poisoning) and the products do not obey the Anderson-Schultz-Flory distribution. Also, thermodynamic limitations are circumvented by both groups but for reasons specific to each procedure. Finally, this review outlines prospects for future research and attempts briefly to estimate the potential commercial interest of the concept.

Preparation and characterization of multiple ion-exchanged Pt/TiO2 catalysts

The amount of platinum introduced by ion exchange on TiO2 anatase (63 m2 g–1) can be increased by repeating the exchange procedure after reduction of the catalyst under hydrogen. From IR spectroscopy studies, two kinds of Lewis acid sites on the TiO2 support (α and β sites) have been found to participate in the ion-exchange mechanism. Only the strongest Lewis acid sites (α sites) are involved in anion exchange, whereas both kinds of sites participate in cation exchange. These adsorption sites are partly liberated by reduction under hydrogen allowing further ion-exchange procedures and thus increasing the amount of platinum. By modelling the quantity of platinum introduced by each exchange, a limit for the amount of platinum is expected to be reached after several exchange–reduction cycles: 1.3 wt.% for anion exchange and 3.1 wt.% for cation exchange.

Transportation fuels and chemicals directly from natural gas: how expensive?

Abstract Natural gas provides intermediates for both the chemical and the transportation fuel industries. Although these industries face very different market constraints, a common research objective is the design of efficient processes for direct conversion of methane. New routes have emerged, such as oxidative coupling, which could be used to liquefy and transport economically remote gas. Oxidative coupling is also seen as an alternative to steam cracking for ethylene production in industrialized countries. Recalling several recently published process evaluations, we review the merits of oxidative coupling for direct conversion of natural gas in comparison to proven indirect technologies via synthesis gas. Also, attention is given to new routes based on natural gas for the production of chemicals currently derived from ethylene, such as vinyl chloride.

The nature, role and fate of surface active sites in Li/MgO oxidative coupling catalysts

Abstract Drastic changes in nature and surface composition of lithium promoted magnesia are shown to occur in the course of the oxidative coupling of methane, together with changes in kinetics. Thus, the fresh material with a large and heterogeneous surface promotes the total oxidation of methane into CO, CO2 while the aged catalyst, sintered, partially decarbonated and coated by an alkali film leads preferentially to dimerization products. On the basis of the above features, the nature, role and fate of the active sites for methane conversion are discussed, aiming at possible catalyst improvements.

Methane coupling into acetylene in a two stage burner

Abstract An alternative route for methane direct conversion has been studied whereby methane is activated in a two stage burner by a hydrogen-oxygen flame. In an alumina reactor, acetylene is produced in significant yield (− 17 %) without coke formation. Simulation of the reaction with techniques used in combustion science confirms the interest of the concept.

Catalytic properties of palladium exchanged zeolites in the reduction of nitrogen oxide by methane in the presence of oxygen: Influence of hydrothermal ageing

Publisher Summary This chapter reports the catalytic properties of Pd loaded zeolites (ZSM-5, MOR and Y) in the catalytic reduction of NO with methane in oxidizing atmosphere. In order to evaluate their potential use in the treatment of exhaust gases on natural gas fueled vehicles, the influence of steam ageing on the physicochemical and catalytic properties of the most active catalysts is carefully examined and discussed in the chapter. Pd exchanged HZSM5 and HMOR catalysts were found highly active and selective in the catalytic reduction of NO by methane in the presence of oxygen at 773 K. Their specific catalytic behavior is ascribed to the presence of Pd ions dispersed in the zeolite channels. Both catalysts are totally deactivated after steam ageing at 1073 K. The migration and the reduction of Pd ions into large metal Pd particles, due to severe dealumination of zeolitic frameworks are thought to be responsible for the loss of activity.