Natural gas contains large volumes of light alkanes, and its abundant reserves make it an appealing feedstock for value-added chemicals and fuels. However, selectively activating the C-H bonds in these useful hydrocarbons is one of the greatest challenges in catalysis. Here we report an attractive oxybromination method for the one-step functionalization of methane under mild conditions that integrates gas-phase alkane bromination with heterogeneously catalysed HBr oxidation, a step that is usually executed separately. Catalyst-design strategies to provide optimal synergy between these two processes are discussed. Among many investigated material families, vanadium phosphate (VPO) is identified as the best oxybromination catalyst, as it provides selectivity for CH3Br up to 95% and stable operation for over 100 hours on stream. The outstanding performance of VPO is rationalized by its high activity in HBr oxidation and low propensity for methane and bromomethane oxidation. Data on the oxybromination of ethane and propane over VPO suggest that the reaction network for higher alkanes is more complex.

The catalytic oxyhalogenation is an attractive route for the functionalization of methane in a single step. This study investigates methane oxychlorination (MOC) and oxybromination (MOB) in a wide range of conditions over various materials having different oxidation properties to assess the impact of hydrogen halide (HX, X = Cl, Br) on the catalyst performance. The oxyhalogenation activity of the catalysts, ranked as RuO2 > Cu-K-La-X > CeO2 > VPO > TiO2 > FePO4, is correlated with their ability to oxidize the hydrogen halide and the gas-phase reactivity of the halogen with methane. The product distribution is found to be strongly dependent on the nature of the catalyst and the type of the halogen. The least reducible FePO4 exhibits a marked propensity to halomethanes (CH3X, CH2X2) and the strongly oxidizing RuO2 favors combustion in both reactions, while other systems reveal stark selectivity differences between MOC and MOB. VPO and TiO2 lead to a selective CH3Br production in MOB, and pronounced CO formation in MOC, whereby product distribution was only slightly affected by the variation of the HX concentration. On contrary, CeO2 and Cu-based catalyst provide a high selectivity to CH3Cl, but give rise to a marked CO2 formation when HBr is used as a halogen source. The behavior of the latter systems is explained by the higher energy of the metal-Cl bond compared to the metal-Br, enabling more suppression of the unwanted CO and CO2 formation when HCl is used, as also inferred from the more pronounced performance dependence on the HX content in the feed. Extrapolating this result, the highest reported yields of chloromethanes (28% at > 82% selectivity) and bromomethanes (20% at > 98% selectivity) are attained over CeO2, by adjusting the feed HX content to curb the CO2 generation. A vis-à-vis comparison of MOC and MOB presented for the first time in this study deepens the understanding of halogen-mediated methane functionalization as a key step towards the design of an oxyhalogenation process.

Ethylene and propylene are the key building blocks of the chemical industry, but current processes are unable to close the growing gap between demand and manufacture. Reported herein is an exceptional europium oxychloride (EuOCl) catalyst for the selective (≥95 %) production of light olefins from ethane and propane by oxychlorination chemistry, thus achieving yields of ethylene (90 %) and propylene (40 %) unparalleled by any existing olefin production technology. Moreover, EuOCl is able to process mixtures of methane, ethane, and propane to produce the olefins, thereby reducing separation costs of the alkanes in natural gas. Finally, the EuOCl catalyst was supported on suitable carriers and evaluated in extrudate form, and preserves performance for >150 h under realistic process conditions.

This article investigates SiO2-supported Ru-, Pt-, Ir-, Rh-, and Pd-based catalysts (1 wt % metal loading) as new catalytic systems for the oxychlorination and oxybromination of methane, both pivotal steps in the halogen-mediated production of commodities from natural gas. Furthermore, this article provides insights into the structure–performance relationships and mechanism of these reactions as a function of the metal and the hydrogen halide. In-depth characterization of the equilibrated catalysts by X-ray diffraction, electron microscopy, Raman, and X-ray photoelectron spectroscopies demonstrate a fast restructuring of the starting oxide nanoparticles into metallic, metal silicide, or metal halide phases. The oxychlorination activity, which decreases in the order: Ru/SiO2 > Pt/SiO2 > Ir/SiO2 > Rh/SiO2 ≈ Pd/SiO2, is enhanced in the presence of metal oxides, while the activity order in oxybromination: Ru/SiO2 ≈ Ir/SiO2 ≈ Pd/SiO2 > Pt/SiO2 > Rh/SiO2 is less dependent on the phase composition. The highest selectivity to chloromethanes (78–83%) and bromomethanes (92–98.5%) at moderate methane conversion (20%), rivaling the performance of the best oxyhalogenation catalysts, is attained over Ir/SiO2, Rh/SiO2, and Pd/SiO2, and correlates with their ability to reduce and form metal halides. Catalyst propensity toward halogenation depends on the halide type, although it is less pronounced at higher loadings (up to 5 wt %), while supporting over other inert carriers has a marginal impact on the restructuring patterns. Finally, kinetic analysis coupled with detection of radical intermediates by operando photoelectron photoion coincidence spectroscopy indicates a significant role of gas-phase halogenation in methane activation via oxyhalogenation. In oxychlorination, the latter pathway has a similar contribution as surface activation for Pd/SiO2, Rh/SiO2, and Pt/SiO2, and major contribution for Ir/SiO2 and Ru/SiO2 catalysts, while in oxybromination, it dominates for all the systems, limiting the potential to enhance the selectivity to mono- over dihalomethanes.

+ + ]T hese authors contributed equally to this work.Supportinginformation, includingc atalyst preparation,c haracterization, and evaluation, descriptions of the operando PGAA and PEPICO techniques, DFT calculations, and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

The industrialization of bromine-mediated natural gas upgrading is contingent on the ability to fully recycle hydrogen bromide (HBr), which is the end form of the halogen after the activation and coupling of the alkanes. Europium oxybromide (EuOBr) is introduced as a unique catalytic material to close the bromine loop via HBr oxidation, permitting low-temperature operation and long lifetimes with a stoichiometric feed (O :HBr=0.25)-conditions at which any catalyst reported to date severely deactivates because of excessive bromination. Besides, EuOBr exhibits unparalleled selectivity to methyl bromide in methane oxybromination, which is an alternative route for bromine looping. This novel active phase is finely dispersed on appropriate carriers and scaled up to technical extrudates, enhancing the utilization of the europium phase while preserving the performance. This catalytic system paves the way for sustainable valorization of stranded natural gas via bromine chemistry.

Methane halogenation over solid materials is dominated by radical intermediates, the stabilization of which through confinement effects enhances the activity.

The catalyzed semihydrogenation of dibromomethane (CH 2 Br 2 ) to methyl bromide (CH 3 Br) is a key step in the bromine-mediated upgradation of methane. This study presents a cutting-edge strategy combining density functional theory (DFT), catalytic tests complemented with the extensive characterization of a wide range of metal catalysts (Fe, Co, Ni, Cu, Ru, Rh, Ag, Ir, and Pt), and statistical tools for a computer-assisted investigation of this reaction. The steady-state catalytic tests identified four classes of materials comprising (i) poorly active (<8%) Fe/SiO 2 , Co/SiO 2 , Cu/SiO 2 , and Ag/SiO 2 ; (ii) Rh/SiO 2 and Ni/SiO 2 , which exhibit intermediate CH 3 Br selectivity (<60%); (iii) Ir/SiO 2 and Pt/SiO 2 , which display great propensity to CH 4 (>50%); and (iv) Ru/SiO 2 , which exhibits the highest selectivity to CH 3 Br (up to 96%). In-depth characterization of representative catalysts in fresh and used forms was done by X-ray diffraction, inductively coupled plasma optical emission spectroscopy, N 2 sorption, temperature-programmed reduction, Raman spectroscopy, electron microscopy, and X-ray photoelectron spectroscopy. The dimensionality reduction performed on the 272 DFT intermediate adsorption energies using principal component analysis identified two descriptors that, when employed together with the experimental data in a random forest regressor, enabled the understanding of activity and selectivity trends by connecting them to the energy intervals of the descriptors. In addition, a representative analytic model was found using the Bayesian inference. These findings illustrate the exciting opportunities presented by integrated experimental/computational screening and set the fundamental basis for the accelerated discovery of superior hydrodebromination catalysts and beyond.