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

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

Converting Waste Plastic to Liquid Organic Hydrogen Carriers.

The accumulation of waste plastics in landfills and the environment, as well as the contribution of plastics manufacturing to global warming, call for the development of new technologies that would enable circularity for synthetic polymers. Thus far, emerging approaches for chemical recycling of plastics have largely focused on producing fuels, lubricants, and/or monomers. In a recent study, Junde Wei and colleagues demonstrated a new catalytic system capable of converting oxygen-containing aromatic plastic waste into liquid organic hydrogen carriers (LOHCs), which can be used for hydrogen storage. The authors utilized Ru-ReOx /SiO2 materials with zeolite HZSM-5 as a co-catalyst for the direct hydrodeoxygenation (HDO) of oxygen-containing aromatic plastic wastes that yield cycloalkanes as LOHCs with a theoretical hydrogen capacity of ≈5.74 wt % under mild reaction conditions. Subsequent efficiency and stability tests of cycloalkane dehydrogenation over Pt/Al2 O3 validated that the HDO products can serve as LOHCs to generate H2 gas. Overall, their approach not only opens doors to alleviating the severe burden of plastic waste globally, but also offers a way to generate clean energy and ease the challenges associated with hydrogen storage and transportation.

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 H2. This catalyst significantly reduces the formation of undesired CH4 (≤5 wt %), a product which is favored when using bulk cobalt oxide or cobalt nanoparticles supported on other carriers (selectivity ≤95 wt %). The superior performance of Co/ZSM-5 is attributed to the stabilization of dispersed oxidic cobalt nanoparticles by the zeolite support, preventing further reduction to metallic species that appear to catalyze CH4 generation. While ZSM-5 is also active for propane formation at 523 K, the presence of Co promotes stability and selectivity. After optimizing the metal loading, it was demonstrated that 10 wt % Co/ZSM-5 can selectively catalyze the hydrogenolysis of low-density PE (LDPE), mixtures of LDPE and PP, as well as postconsumer PE, showcasing the effectiveness of this technology to upcycle realistic plastic waste. Cobalt supported on zeolites FAU, MOR, and BEA were also effective catalysts for C2-C4 hydrocarbon formation and revealed that the framework topology provides a handle to tune gas-phase selectivity.

The Critical Role of Process Analysis in Chemical Recycling and Upcycling of Waste Plastics.

There is an urgent need for new technologies to enable circularity for synthetic polymers, spurred by the accumulation of waste plastics in landfills and the environment and the contributions of plastics manufacturing to climate change. Chemical recycling is a promising means to convert waste plastics into molecular intermediates that can be remanufactured into new products. Given the growing interest in the development of new chemical recycling approaches, it is critical to evaluate the economics, energy use, greenhouse gas emissions, and other life cycle inventory metrics for emerging processes,relative to the incumbent, linear manufacturing practices employed today. Here we offer specific definitions for classes of chemical recycling and upcycling and describe general process concepts for the chemical recycling of mixed plastics waste. We present a framework for techno-economic analysis and life cycle assessment for both closed- and open-loop chemical recycling. Rigorous application of these process analysis tools will be required to enable impactful solutions for the plastics waste problem.

Conversion of Polyolefin Waste to Liquid Alkanes with Ru-Based Catalysts under Mild Conditions.

Chemical upcycling of waste polyolefins via hydrogenolysis offers unique opportunities for selective depolymerization compared to high temperature thermal deconstruction. Here, we demonstrate the hydrogenolysis of polyethylene into liquid alkanes under mild conditions using ruthenium nanoparticles supported on carbon (Ru/C). Reactivity studies on a model n-octadecane substrate showed that Ru/C catalysts are highly active and selective for the hydrogenolysis of C(sp3)-C(sp3) bonds at temperatures ranging from 200 to 250 °C. Under optimal conditions of 200 °C in 20 bar H2, polyethylene (average M w ∼ 4000 Da) was converted into liquid n-alkanes with yields of up to 45% by mass after 16 h using a 5 wt % Ru/C catalyst with the remaining products comprising light alkane gases (C1-C6). At 250 °C, nearly stoichiometric yields of CH4 were obtained from polyethylene over the catalyst. The hydrogenolysis of long chain, low-density polyethylene (LDPE) and a postconsumer LDPE plastic bottle to produce C7-C45 alkanes was also achieved over Ru/C, demonstrating the feasibility of this reaction for the valorization of realistic postconsumer plastic waste. By identifying Ru-based catalysts as a class of active materials for the hydrogenolysis of polyethylene, this study elucidates promising avenues for the valorization of plastic waste under mild conditions.

Shaping the Future of Higher Education: Practical, Community-Driven Initiatives to Improve Academic Climate.

Historically, efforts to improve academic climate have been siloed-many efforts involve the collection of data to understand issues affecting diversity at an institutional level, while others prioritize recruitment and retention of historically marginalized groups. Few initiatives, however, effectively combine the two in order to create concrete action plans to eliminate structural barriers that hinder the retention of minorities in STEM. In this Editorial, we present the history and details of a collaborative effort to improve the academic climate of the Department of Chemistry at University of California, Berkeley. This initiative began in 2016 as a graduate student-led, grassroots movement to develop a method to assess the department's academic climate. Over the past several years-and with support from stakeholders at all levels-it has grown into a department-wide effort to systematically collect data, exchange ideas, and implement goal-oriented interventions to make our academic community more inclusive. With the recent development of a five-year strategic plan and funding increase to provide financial support for student-led programs, we have institutionalized a method to maintain the initiative's momentum. Here, we share our approaches, insights, and perspectives from community members who have shaped this movement. We also provide advice to help other academic communities determine a practical path toward affecting positive cultural change.

Synthesis of Biomass-Derived Ethers for Use as Fuels and Lubricants.

Ethers synthesized from biomass-derived compounds have exceptional properties as fuels, lubricants, and specialty chemicals and can serve as replacements for petroleum-derived products. Recent efforts have identified heterogeneous catalysts for the selective synthesis of ethers from alcohols, aldehydes, ketones, furans, esters, olefins, carboxylic acids, and other molecules derived from biomass. This Review highlights the scope of etherification reactions and provides insights into the choice of catalysts and reaction conditions best suited for producing targeted ethers from the available starting materials. First, the properties of ethers for specific applications and the methods by which synthons for ether synthesis can be obtained from biomass are discussed. Then the progress that has been made on the synthesis of ethers via the following methods is summarized: direct etherification of alcohols; reductive etherification of alcohols with aldehydes or ketones; etherification of furanic compounds, esters, and carboxylic acids; and the addition of alcohols to olefins. Next, the mechanisms of these reactions and catalyst properties required to promote them are discussed, with the goal of understanding how reaction conditions can be tuned to optimize catalyst activity and selectivity towards desired ethers. The Review closes by examining the tradeoffs between catalyst selectivity, activity, stability, and reaction conditions required to achieve the most economically and environmentally favorable routes to biomass-derived ethers.