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Methanol Conversions
Published in Saeed Sahebdelfar, Maryam Takht Ravanchi, Ashok Kumar Nadda, 1 Chemistry, 2022
Saeed Sahebdelfar, Maryam Takht Ravanchi, Ashok Kumar Nadda
The production of acetic acid by iridium catalytic system was commercialized as Cativa process by BP Amaco in 1996 (Sunley and Watson, 2000). Although to achieve similar activity level as Rh, more Ir is required, the catalyst is capable of operating at reduced levels of water (lower than 8 wt% for Cativa compared to 14–15 wt% for traditional Monsanto). Therefore, byproduct formation is reduced, carbon monoxide-based yield improves and steam consumption decreases. One of the main advantages of Ir-based processes is high stability of catalytic species of iridium. Tolerating low water concentrations (0.5 wt%) of the catalyst is especially important and is ideal for optimizing methanol carbonylation process. It has been found that iridium catalyst is active in wide range of conditions in which the rhodium counterparts are decomposed to completely inactive and to large extent nonregenerable salts. In addition to higher stability, iridium catalysts are much more soluble than rhodium catalysts; therefore, higher solution concentrations are achieved which provide much higher reaction rates available.
Steam Reforming
Published in Martyn V. Twigg, Catalyst Handbook, 2018
For many years nickel has been recognized as the most suitable metal for steam reforming of hydrocarbons. Other metals can be used; for example cobalt, platinum, palladium, iridium, ruthenium and rhodium. Although some precious metals are considerably more active per unit weight than nickel, nickel is much cheaper and sufficiently active to enable suitable catalysts to be produced economically. The reforming reaction takes place on the nickel surface, so the catalyst must be manufactured in a form which produces the maximum stable nickel surface area available to the reactants. This is done by dispersing the nickel as small crystallites on a refractory support which must be sufficiently porous to allow access by the gas to the nickel surface. This is usually achieved by precipitating nickel as an insoluble compound, from a soluble salt, in the presence of a refractory support such as mixtures of aluminium oxide, magnesium oxide, calcium oxide and calcium aluminate cement. Alternatively, the nickel can be incorporated by impregnating a preformed catalyst support, such as alumina or an aluminate, with a solution of a nickel salt which is subsequently decomposed by heating to the oxide. In either case the nickel oxide is reduced to the metal by hydrogen supplied from another plant, or by cracking a suitable reactant gas (e.g. ammonia) over the catalyst as the reformer is being started up (see Section 5.8.7.1). In some instances process gas itself is used to reduce the nickel oxide to metal as the reformer is gradually brought on-line.
Ir, 77]
Published in Alina Kabata-Pendias, Barbara Szteke, Trace Elements in Abiotic and Biotic Environments, 2015
Alina Kabata-Pendias, Barbara Szteke
Iridium (Ir), a noble metal of the group 9 in the periodic table of elements, is one of the rarest elements in the Earth’s crust, present in the range of 0.02–0.05 µg/kg in the upper and bulk continental zones, respectively. Due to the tendency of Ir to bind with Fe, its content in the Earth’s crust is lower than in deeper layers. It is concentrated mainly in the Fe–Ni core and in some meteorites. Its geochemical behavior is close to that of Co and Ni. Like other platinum group metals, it is very hard, brittle, silver-white, and the second densest metal (22.4 g/cm3). Iridium contents of some coals may be up to 200 µg/kg.
Mechanical and thermophysical properties of high-temperature IrxRe1−x alloys
Published in Phase Transitions, 2020
Navneet Yadav, Shakti Pratap Singh, A. K. Maddheshiya, P. K. Yadawa, R. R. Yadav
The compelling demand of materials’ sustained use at temperature greater than about 1500 °C, there are challenging tasks for material-scientists and engineers to develop high-temperature materials [1,2]. The high-temperature alloys paved the way to overcome this difficulty. Such types of alloys have very high melting point and exhibit improved resistance to oxidation at higher temperature regime [3]. These alloys are used to manufacture flight-type rockets, turbine blades and other components of jet engine. Unfortunately, the materials that have higher melting points are rapidly oxidized in the environments. Iridium (Ir) has very high melting point (2454 °C), so it is the most promising material for applications in high-temperature environments [4]. Iridium is a quite expensive element compared with other elements used in high-temperature applications. The incorporation of rhenium (Re) into iridium-containing alloys overcomes this difficulty because Re has also a higher melting point like Ir, but generally Re is less expensive than Ir. Iridium-rhenium (IrRe) alloys are very economical and used to make thruster chamber in an on-orbit communication satellite. These alloys demonstrate the excellent reliability and compatibility in a high-temperature oxidizing environment [4–10].