Retraction of "Hydrogenolysis of Polyethylene and Polypropylene into Propane over Cobalt-Based Catalysts".

[This retracts the article DOI: 10.1021/jacsau.2c00402.

Economic and Environmental Competitiveness of Ethane-Based Technologies for Vinyl Chloride Synthesis.

The synthesis of the vinyl chloride monomer (VCM), employed to manufacture poly(vinyl chloride) (PVC) plastic, primarily relies on oil-derived ethylene, resulting in high costs and carbon footprint. Natural gas-derived ethane in VCM synthesis has long been considered a transformative feedstock to lower emissions and expenses. In this work, we evaluate the environmental potential and economics of recently developed catalytic ethane chlorination technologies for VCM synthesis.

Hydrogenolysis of Polyethylene and Polypropylene into Propane over Cobalt-Based Catalysts.

The development of technologies to recycle polyethylene (PE) and polypropylene (PP), globally the two most produced polymers, is critical to increase plastic circularity. Here, we show that 5 wt % cobalt supported on ZSM-5 zeolite catalyzes the solvent-free hydrogenolysis of PE and PP into propane with weight-based selectivity in the gas phase over 80 wt % after 20 h at 523 K and 40 bar H. This catalyst significantly reduces the formation of undesired CH (≤5 wt %), a product which is favored when using bulk cobalt oxide or cobalt nanoparticles supported on other carriers (selectivity ≤95 wt %).

Elucidation of radical- and oxygenate-driven paths in zeolite-catalysed conversion of methanol and methyl chloride to hydrocarbons.

Understanding hydrocarbon generation in the zeolite-catalysed conversions of methanol and methyl chloride requires advanced spectroscopic approaches to distinguish the complex mechanisms governing C-C bond formation, chain growth and the deposition of carbonaceous species. Here operando photoelectron photoion coincidence (PEPICO) spectroscopy enables the isomer-selective identification of pathways to hydrocarbons of up to C in size, providing direct experimental evidence of methyl radicals in both reactions and ketene in the methanol-to-hydrocarbons reaction. Both routes converge to C molecules that transform into aromatics.

Ethane-Based Catalytic Process for Vinyl Chloride Manufacture.

The use of ethane as a platform molecule for the manufacture of polyvinyl chloride (PVC) is a longstanding challenge, which would allow to reduce the raw material costs and CO emissions to produce this plastic. Herein, we discover that rare earth oxychlorides catalyze in a selective (up to 90 %) and stable (>50 h on stream) manner the reaction of ethane and molecular chlorine into 1,2-dichloroethane, which, upon established cracking, will translate into an order of magnitude higher vinyl chloride productivity compared to ethane oxychlorination technologies. In addition, representative europium oxychloride was supported on suitable carriers and was demonstrated to be selective (up to 90 %) and stable (>40 h on stream) in extrudate form.

Status and prospects of the decentralised valorisation of natural gas into energy and energy carriers.

Natural gas is widely considered as the key feedstock to enable the transition from the oil to the renewables era. Despite its vast reserves, the use of this resource to produce energy and chemicals does not match its full potential. The main reason lies in the nature of its wells, which are often found in remote locations around the globe, rendering access and transportation challenging.

Key role of chemistry versus bias in electrocatalytic oxygen evolution.

The oxygen evolution reaction has an important role in many alternative-energy schemes because it supplies the protons and electrons required for converting renewable electricity into chemical fuels. Electrocatalysts accelerate the reaction by facilitating the required electron transfer, as well as the formation and rupture of chemical bonds. This involvement in fundamentally different processes results in complex electrochemical kinetics that can be challenging to understand and control, and that typically depends exponentially on overpotential.

Quantification of Redox Sites during Catalytic Propane Oxychlorination by Operando EPR Spectroscopy.

Identification and quantification of redox-active centers at relevant conditions for catalysis is pivotal to understand reaction mechanisms and requires development of advanced operando methods. Herein, we demonstrate operando EPR spectroscopy as an important technique to quantify the oxidation state of representative CrPO and EuOCl catalysts during propane oxychlorination, an attractive route for propylene production. In particular, we show that the space-time-yield of C H correlates with the amount of Cr and Eu ions generated over the catalysts during reaction.

Operando Photoelectron Photoion Coincidence Spectroscopy Unravels Mechanistic Fingerprints of Propane Activation by Catalytic Oxyhalogenation.

Herein, we demonstrate photoelectron photoion coincidence (PEPICO) spectroscopy as a pivotal technique for evidencing unprecedented mechanistic insights by isomer-selective radical detection within complex hydrocarbon-functionalization reaction networks, such as those of catalyzed propane oxychlorination and oxybromination. In particular, while the oxychlorination is surface-confined, we show that in oxybromination alkane activation follows a gas-phase reaction mechanism with evolved bromine and bromine radicals, favoring 2-propyl over 1-propyl radical formation, as evidenced by isomer-selective threshold photoelectron analysis. Furthermore, we provide new mechanistic insights into the cracking and coking pathways that are observed in oxybromination.

Mechanistic Understanding of Halogen-mediated Catalytic Processes for Selective Natural Gas Functionalization.

Development of catalytic technologies enabling the direct functionalization of light alkanes, main components of abundant natural gas, into value-added chemicals and liquid fuels is quite possibly the key strategy to transit from the oil to the renewables era. A cornerstone to meet this great challenge comprises the in-depth understanding of complex reaction mechanisms over dynamic surfaces, allowing to elucidate catalyst design criteria for selective alkane functionalization processes. Prominent examples are the oxybromination of methane into bromomethanes (CH₃Br+CH₂Br₂) and the oxychlorination of ethane into ethylene, which are the two highly selective routes (selectivity ≤98.

Halogen-Dependent Surface Confinement Governs Selective Alkane Functionalization to Olefins.

The product distribution in direct alkane functionalization by oxyhalogenation strongly depends on the halogen of choice. We demonstrate that the superior selectivity to olefins over an iron phosphate catalyst in oxychlorination is the consequence of a surface-confined reaction. By contrast, in oxybromination alkane activation follows a gas-phase radical-chain mechanism and yields a mixture of alkyl bromide, cracking, and combustion products.

Olefins from Natural Gas by Oxychlorination.

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.

Selective Production of Carbon Monoxide via Methane Oxychlorination over Vanadyl Pyrophosphate.

A catalytic process is demonstrated for the selective conversion of methane into carbon monoxide via oxychlorination chemistry. The process involves addition of HCl to a CH -O feed to facilitate C-H bond activation under mild conditions, leading to the formation of chloromethanes, CH Cl and CH Cl . The latter are oxidized in situ over the same catalyst, yielding CO and recycling HCl.

Catalyst design for natural-gas upgrading through oxybromination chemistry.

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.