Low-temperature oxidative chlorination of methane over supported platinum chloride catalyst

Data on the kinetics, kinetic isotope effects, substrate selectivity, and activation parameters for the first step of oxidation of alkylbenzenes by permanganate in acidic aqueous solutions are surveyed. The MnO4-. HMnO.~. and lVlnO3" species serve as oxidants at different acidities. The increase in the positive charge in this series enhances the electrophilicity of the reagent, which manifests itself as an increase in the reaction rate and a change in the site of attack on the atkylbenzene molecule (either the aromatic ring or C-H bond in the alkyl group). The oxidation of the alkyl C--H bonds in alkylbenzenes and in alkanes follows similar mechanisms, while the attack on the aromatic ring proceeds via the electrophilic aromatic substitution mechanism with a transition state intermediate between the charge transfer complex and r

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“…43 The syringe reactor method 6 implies that the reaction is carried out in the absence of a gas phase (~. = Ol.…”

Section: Approaches To the Study Of The First Step Of Oxidation And Ementioning

confidence: 99%

The first step of oxidation of alkylbenzenes by permanganates in acidic aqueous solutions

Rudakov

Lobachev

2000

Russ Chem Bull

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“…Why was it that the alkane activation reactions of sections IIIF and IIIG took so long to be discovered, given the long-standing interest in the area? It certainly was not the existence of any large intrinsic kinetic barrier to the reaction L"M + C-H -L"VU (51) This is demonstrated most dramatically by the remarkable observation of photoactivation of methane by Cp*Ir(CO)2 at 12 K86 and by the relatively small kinetic selectivity between different types of C-H bonds that is usually observed in the successful alkane activation systems.84 Even before these recent discoveries it was clear that alkyl hydride complexes tend to decompose rapidly to alkane, suggesting the reverse reaction (alkane activation) would have no very great kinetic barrier. 35 As we saw in section IIIA the problem had consistently been that the metal tended to activate C-H bonds in its own ligands by cyclometalation.8 This is presumably due to the entropic advantage to be gained in an intramolecular reaction (the chelate effect) and also the high thermodynamic stability of the cycloadduct.…”

Section: Kinetic Considerationsmentioning

confidence: 99%

The organometallic chemistry of alkanes

Crabtree¹

1985

Chem. Rev.

1,225

466

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“…54 CH 3 Cl, obtained from the direct chlorination of CH 4 at moderate reaction conditions, is converted into olefins without the additional energy penalty of O 2removal. 55 The development of the methyl chloride-to-olefins (MCTO) on one hand, and the Montreal protocol & toxicology reports on the other hand, shifted the focus of the research from polychlorinated C 1 in the 1970's and early 1980's 40,[56][57][58][59][60] to the selective production of CH 3 Cl in the late 1980's 61,62 . However, the Cu-based catalyst system still suffered from leaching and overoxidation of the feedstock.…”

Section: -2002 Safety Oil Crisis and Regulationsmentioning

confidence: 99%

New Insights in the Working Principles of Europium-Based Methane Oxychlorination Catalysts

Terlingen¹

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The aim of this PhD thesis is to design new catalytic materials for the CH4 oxychlorination (MOC) reaction and to study these solid catalysts under real working conditions by applying light, i.e., operando spectroscopy. In this way, the activity and spectroscopic information can be coupled, yielding crucial mechanistic insights to improve the design of the catalytic materials. The presented work reveals that redox properties, bulk and synergistic effects play a crucial role in the working mechanism of bulk MOC catalysts. In chapter 2, a set of lanthanide oxychloride catalysts were synthesized, characterized and tested. EuOCl came out as the most promising candidate as it possessed the highest MOC activity, the best activity/selectivity relation and was proven to be stable. Moreover, the catalytic performance of EuOCl could be tuned by increasing the HCl concentration in the feed, thereby mitigating the unwanted catalytic destruction of chloromethanes to COx. Operando Raman spectroscopy revealed that the chlorination of the catalyst was rate limiting as an increase in the HCl concentration in the feed resulted in enhancement of activity, but did not cause bulk chlorination of the catalyst. While EuOCl appeared promising as a MOC catalyst, its catalytic performance was limited by the rate of chlorination. The catalyst design was improved in chapter 3 by adding a chlorinating agent for Eu3+. The activity of all La3+-Eu3+ bimetallic catalysts was significantly higher than anticipated for the linear combination of LaOCl and EuOCl. More important was that a higher CH3Cl selectivity could be achieved without giving in on the excellent CO selectivity obtained for monometallic EuOCl. Operando luminescence spectroscopy revealed that La3+ acted as a chlorinating agent for Eu3+, even when the phases were completely segregated as in the case for the physical mixture. By applying operando catalyst thermometry in chapter 4, the observed catalytic performance of EuOCl could be linked to the actual catalyst temperature, gaining more insights in arguably one of the most important reaction parameters. A catalyst temperature of maximum 16 °C higher compared to the oven temperature was recorded, due to the exothermic nature of the MOC reaction. Heat dissipation by means of radiation was identified as the main heat loss mechanism, resulting in a uniform catalyst bed temperature. The concept that irreducible elements can make up a very active catalyst for the MOC reaction is proven by the design of irreducible Mg2+-Al3+ mixed-metal oxide (MMO) catalysts. The Mg4Al MMO possessed one of the highest reported activities under the tested reaction conditions, which was all the more surprising considering that MgO and -Al2O3 did not show any significant activity. Operando Raman spectroscopy revealed that Mg2+ acted as a Cl- buffer and as a chlorinating agent for Al3+, which was the active metal in the CH4 activation step. Adding 2 atom-% of the redox active Eu3+ in the material doubled the activity, made the activity/selectivity relation tuneable and preserved the activity under high HCl concentrations. These results indicate that both redox activity as well as synergistic effects are required to obtaining benchmark performance.

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Low-temperature oxidative chlorination of methane over supported platinum chloride catalyst

Cited by 11 publications

References 1 publication

The first step of oxidation of alkylbenzenes by permanganates in acidic aqueous solutions

The first step of oxidation of alkylbenzenes by permanganates in acidic aqueous solutions

The organometallic chemistry of alkanes

New Insights in the Working Principles of Europium-Based Methane Oxychlorination Catalysts

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