The next frontier in clean flight? Jet fuel from city waste

Research explores sustainable aviation fuel from municipal solid waste

Harvard John A. Paulson School of Engineering and Applied Sciences

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 Municipal solid waste-based sustainable aviation fuel potential and its contribution to jet fuel demand across regions and scenarios. 

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Credit: McElroy group / Harvard SEAS

 

Key Takeaways

• A new study finds that sustainable aviation fuel made from municipal solid waste could reduce greenhouse gas emissions by 80-90% compared with traditional jet fuel.

• Municipal solid waste-derived sustainable aviation fuels are less costly than other sustainable fuel pathways but still require policy support.

Aviation currently contributes about 2.5% of total global carbon emissions, and with air travel demand expected to double by 2040, cutting those emissions has become a pressing priority. One path forward is sustainable aviation fuel, a low-carbon alternative made from feedstocks such as used cooking oil and crops. But despite its potential, sustainable aviation fuel makes up less than 1% of global jet fuel use, mainly due to high production costs and limited supply.

A new study in Nature Sustainability points to a promising breakthrough: using municipal solid waste as a reliable, low-emission, cost-effective feedstock for sustainable aviation fuel.

Researchers from Tsinghua University and the Harvard-China Project on Energy, Economy, and Environment evaluated municipal solid waste-based jet fuel produced through industrial-scale gasification and Fischer-Tropsch synthesis. A life cycle analysis found that jet fuel made from municipal waste could reduce greenhouse gas emissions by 80-90% compared with conventional jet fuel. The main technical hurdle lies in scaling up gasification systems for widespread use.

“Unlike road transport, which is quickly shifting toward electrification, there’s no silver-bullet solution for achieving carbon-neutral aviation,” said Jingran Zhang, the study’s first author and a postdoctoral fellow at the Harvard-China Project who is supported by the Salata Institute for Climate and Sustainability at Harvard. “Turning everyday trash into jet fuel could be an innovative but major near-term step toward cleaner aviation. By converting municipal waste into low-carbon jet fuel that already works in today’s engines, we can start cutting emissions immediately, without waiting for future technology.”

Municipal solid waste as a feedstock

Municipal solid waste includes organic matter like food scraps and paper as well as plastics and metals. Traditionally, much of this waste has been landfilled or incinerated, which consumes land or can contribute to air pollution. As landfill space shrinks and waste generation rises, converting municipal solid waste into liquid fuels could conserve land, cut emissions, and produce cleaner energy to help cities move toward zero-waste goals.

The Harvard study explores the largely under-researched potential of municipal solid waste-based jet fuel using real-world data on Fischer-Tropsch gasification technology. The researchers analyzed key emission sources, calculated greenhouse gas impacts, and identified ways to boost efficiency. They found that while the process significantly lowers emissions, only about 33% of input carbon is converted into fuel due to gas composition mismatches. Efficiency could be improved by capturing carbon dioxide or adding green hydrogen, produced with renewable power, during processing.

Global implications

Many countries are ramping up efforts to make aviation more sustainable by adopting cleaner fuels. In the United States, the government aims to produce up to 35 billion gallons of sustainable aviation fuels annually by 2050, supported by strong financial incentives. In the European Union, new regulations will require all departing flights to gradually increase their share of sustainable aviation fuels, catapulting from 2% in 2025 to 70% by 2050. On a global scale, the International Civil Aviation Organization’s CORSIA program requires operators to offset emissions growth, which they can do by buying eligible offsets or by using sustainable fuels.

The study examined how municipal solid waste could be converted into sustainable aviation fuel under several scenarios. In the most practical case, global municipal solid waste could yield around 50 million tons (62 billion liters) of jet fuel globally, cutting aviation’s greenhouse gas emissions by roughly 16%. If waste management and conversion systems are inefficient, the benefits drop substantially. However, if green hydrogen is integrated into the process, production could reach 80 million tons per year, which is enough to supply up to 28% of global jet fuel demand and reduce emissions by as much as 270 million tons of carbon dioxide annually.

In Europe, the projected output would already exceed the European Union’s jet fuel-blending targets while remaining compliant with sustainability standards. Economically, the study suggests that adopting municipal solid waste-based jet fuels could save airlines money under carbon pricing systems like CORSIA, particularly when government incentives and subsidies are factored in.

Ultimately, sustainable aviation fuel currently makes up less than 1% of global jet fuel use, mainly because of its high production costs. This underscores the urgent need for strong policy action and financial incentives to scale up supply.

“This study presents a blueprint for converting urban waste into sustainable aviation fuel, offering future environmental and economic benefits,” said lead author Michael B. McElroy, the Gilbert Butler Professor of Environmental Studies at Harvard and chair of the Harvard-China Project on Energy, Economy, and Environment. “Moving forward, broad collaboration among governments, fuel producers, airlines, and aircraft manufacturers will be essential to increase production, lower costs, and accelerate aviation’s path to net-zero emissions.”

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Journal

Nature Sustainability

DOI

10.1038/s41893-025-01644-3 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

Powering air travel with jet fuel derived from municipal solid waste

Article Publication Date

13-Nov-2025

 

Advances in iron-based Fischer-Tropsch synthesis with high carbon efficiency

Dalian Institute of Chemical Physics, Chinese Academy Sciences

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Simultaneously suppressing primary CO2 formation through the stabilization of phase-pure iron carbides and secondary CO2 generation via hydrophobic surface engineering and graphene confinement has emerged as a promising strategy in iron-based Fischer-Tropsch synthesis. These approaches effectively mitigate side reactions such as the water-gas shift and CO disproportionation, enhance active phase stability, and ultimately improve carbon efficiency, reduce CO2 emissions, and promote selective formation of long-chain hydrocarbons under realistic FTS conditions.

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Credit: Chinese Journal of Catalysis

Fischer-Tropsch synthesis (FTS) is an important technology for converting carbon-rich resources such as coal, natural gas, and biomass into clean fuels and high-value chemicals through synthesis gas. Iron-based catalysts are widely used in industrial applications due to their low cost and strong adaptability, especially for syngas derived from coal or biomass with low H2/CO ratios. However, the catalytic process is complicated by frequent phase transformations among metallic iron, iron oxides, and iron carbides, which hinder mechanistic understanding and stability. Additionally, side reactions, such as CO disproportionation and the water-gas shift reactions, lead to excessive CO2 formation, significantly reducing carbon utilization efficiency.

 

Iron-based catalysts exhibit complex and dynamic phase behavior during FTS, with iron carbides generally recognized as the primary active phases. Different iron carbide phases (e.g., ε-Fe2C, χ-Fe5C2, and θ-Fe3C) demonstrate distinct catalytic performances and readily interconvert under reaction conditions, critically influencing activity and product selectivity. In situ characterization has revealed the coexistence and transformation of multiple phases during operation, underscoring the importance of precise regulation to stabilize the most catalytically favorable phase.

 

To address high CO₂ selectivity and improve carbon efficiency, three key strategies have emerged:

ⅰ. Stabilization of phase-pure iron carbides, which prevents their oxidation into less active species like Fe₃O₄ and mitigates primary CO₂ formation; ⅱ. Hydrophobic surface modification, which reduces H₂O adsorption and thereby suppresses secondary CO₂ formation from the WGS reaction; ⅲ. Graphene confinement and 2D material encapsulation, which enhances the thermal and structural stability of active phases, tunes the electronic environment, and further inhibits CO₂-generating pathways. Together, these approaches offer a comprehensive framework for enhancing the stability and catalytic performance of iron-based FTS catalysts, enabling more efficient and sustainable FTS processes with reduced CO2 emissions.

 

This review summarizes recent advances aimed at enhancing carbon efficiency in iron-based FTS catalysts. It highlights the critical role of constructing and stabilizing iron carbide active phases which critically influence catalytic activity, product selectivity, and phase dynamics under reaction conditions. Various strategies to suppress CO2 formation including promoter addition, hydrophobic surface modification, and active phase stabilization, are critically examined for their effectiveness in improving carbon utilization. Particular attention is given to the application of two-dimensional materials, such as graphene, which enhance the thermal stability, sintering resistance, and electronic structure of iron carbides, thereby reducing CO₂ emissions and promoting selective formation of desired hydrocarbon products. This innovative approach offers new opportunities for developing catalysts with high activity, low CO2 selectivity, and enhanced stability, which are key factors for enhancing both the efficiency and sustainability for FTS. Such advancements are crucial for advancing more efficient and sustainable FTS technologies, supporting the global push for net-zero emissions goals, and contributing to carbon reduction efforts worldwide.

The results were published in Chinese Journal of Catalysis (DOI: 10.1016/S1872-2067(25)64738-3)

About the Journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top one journals in Applied Chemistry with a current SCI impact factor of 17.7. The Editors-in-Chief are Profs. Can Li and Tao Zhang.

At Elsevier http://www.journals.elsevier.com/chinese-journal-of-catalysis

Manuscript submission https://mc03.manuscriptcentral.com/cjcatal

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Journal

Chinese Journal of Catalysis

DOI

10.1016/S1872-2067(25)64738-3 

Article Title

Advances in iron-based Fischer-Tropsch synthesis with high carbon efficiency

 

From coal to chemicals: Breakthrough syngas catalysis powers green industrial future

Dalian Institute of Chemical Physics, Chinese Academy Sciences

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Researchers from the Dalian Institute of Chemical Physics have advanced syngas conversion by integrating Fischer–Tropsch synthesis with heterogeneous hydroformylation. By designing Co–Co₂C and Rh single-atom catalysts, the team achieved efficient, selective, and scalable production of alcohols and α-olefins. Their technologies have already entered industrial use and continue to evolve toward high-value product chains, laying the foundation for greener chemical manufacturing to realize China’s carbon neutrality goals.

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Credit: Chinese Journal of Catalysis

Two decades-long catalytic journey has borne industrial fruit—greener, cleaner, and smarter. Fischer–Tropsch synthesis (FTS) and heterogeneous hydroformylation are two cornerstone processes in modern chemical manufacturing. They convert syngas (a mixture of CO and H₂, typically derived from coal or biomass) into hydrocarbons and oxygenates that underpin fuel, plastics, and pharmaceutical industries. Yet for over a century, challenges in selectivity, catalyst longevity, and process integration have limited their broader industrial deployment—until now.

In a newly published account in Chinese Journal of Catalysis (DOI: 10.1016/S1872-2067(25)64701-2), a team led by Prof. Yunjie Ding and Prof. Li Yan at the Dalian Institute of Chemical Physics (DICP), in collaboration with Dr. Ronghe Lin (Zhejiang Normal University) and Dr. Shenfeng Yuan (Zhejiang University), presents a comprehensive roadmap of scientific breakthroughs that move these legacy reactions into a modern era of green chemistry.

A New Generation of Co–Co₂C Catalysts for FTS. The team developed a series of carbon-supported cobalt–cobalt carbide (Co–Co₂C) catalysts that fundamentally reshape FTS performance. By tuning the interface between metallic cobalt and its carbide phase, they achieved dual-active sites that guide syngas molecules through controlled C–C coupling and CO insertion steps—enabling selective formation of long-chain α-alcohols and olefins. These insights, backed by DFT calculations and operando spectroscopy, translated into real-world application. A 150 kt/a industrial slurry-phase reactor based on the Co–Co₂C system has been in full operation since 2020 in Yulin, China—the first such carbon-supported Co catalyst in global use.

Single-Atom Rh Catalysts Transform Hydroformylation. To overcome the well-known separation and precious metal leaching issues of homogeneous Rh-based hydroformylation, the researchers pioneered a porous organic polymer (POP)-anchored single-atom Rh catalyst: Rh₁/POPs-PPh₃. The catalyst features robust multi-dentate Rh–P bonds, delivering exceptional activity, transient sulfur poisoning and self-recovery, and structural integrity under harsh industrial conditions. In 2020, this innovation was scaled up to the world’s first commercial heterogeneous hydroformylation plant in Zhenhai, China, producing 50 kt/a of n-propanol from ethylene with unprecedented catalyst efficiency and longevity. The losses of Rh and ligand are negligible, and the reactor operates continuously, marking a transformative step in green olefin functionalization.

Extending the Value Chain to High-Value Products. Based on these catalytic platforms, they also developed integrated separation schemes and extraction processes to isolate alcohols and paraffins from complex FTS product mixtures with high purity. They further advanced value-chain by converting the FTS-derived α-alcohols into high-value commodities such as, α-olefins, lubricants, and fatty acids, which are not commonly synthesized from coal.

From bench-scale insights to commercial milestones, this research illustrates how a “mechanism-insight-to-green-manufacture” approach—grounded in catalyst design and process coupling—can unlock new industrial opportunities for syngas utilization, especially in coal-rich economies transitioning toward low-carbon futures.

 

About the journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top six journals in Applied Chemistry with a current SCI impact factor of 17.7.

At Elsevier http://www.journals.elsevier.com/chinese-journal-of-catalysis

Manuscript submission https://mc03.manuscriptcentral.com/cjcatal

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Journal

Chinese Journal of Catalysis

DOI

10.1016/S1872-2067(25)64701-2 

Article Title

Integrated Fischer-Tropsch synthesis and heterogeneous hydroformylation technologies toward high-value commodities from syngas

Article Publication Date

27-Jul-2025

 

Spanish and Italian scientists design sustainable and more resistant asphalt using cigarette butts

University of Granada

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alternative for recycling cigarette butts (from any type of cigarette, but especially electronic cigarettes, as they contain a higher amount of usable fibre) as an additive in road construction.

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Credit: University Of Granada

Researchers from the Building Engineering Laboratory (LabIC.UGR) are collaborating with the University of Bologna (Italy) on the design and evaluation of the resistance of asphalt made from pellets of this waste, in a project co-funded by the Chinese government

Since the advent of filter cigarettes, cigarette butts have become a predominant form of waste, with projections indicating that around 9 trillion will be generated worldwide in 2025. This poses a serious environmental problem, as many of them are improperly disposed of in natural environments, beaches, forests, waterways, etc.

Since the advent of filter cigarettes, cigarette butts have become a predominant form of waste, with projections indicating that around 9 trillion will be generated annually by 2025. In addition, since the emergence of low-nicotine e-cigarettes, the consumption and production of this waste has been on the rise (especially among young people aged 14 to 30). Much of this waste poses a serious environmental problem, as it is improperly disposed of in natural environments, beaches, forests, aquatic environments, etc., and has an extremely slow degradation rate.

An innovative collaborative research project between the University of Granada (UGR) and the University of Bologna (Italy), co-funded by the Chinese government, proposes an alternative for recycling cigarette butts (from any type of cigarette, but especially electronic cigarettes, as they contain a higher amount of usable fibre) as an additive in road construction. The research carried out has demonstrated the feasibility of incorporating this waste to improve the crack resistance of road pavements and the reuse of higher rates of recycled material.

The Department of Civil, Chemical, Environmental and Materials Engineering at the University of Bologna designed and manufactured different types of pellets from cigarette butts. To do this, the end of the cigarette butt (composed of organic ash) was discarded, while the rest (almost all of the weight, consisting of cellulose fibres and PLA plastic) was crushed and mixed with a Fischer-Tropsch-type wax (which acts as a binder) and subjected to a process of pressing, heating and cold cutting to produce the pellets.

Subsequently, the Building Engineering Laboratory (LabIC.UGR) was responsible for evaluating the resistance of asphalts manufactured with 40% of their weight coming from recycled material from deteriorated roads and pellets from electronic cigarette butts. LabIC.UGR, directed by professors Mª Carmen Rubio Gámez and Fernando Moreno Navarro, is one of the university’s unique laboratories and a world leader in the development of sustainable asphalt materials.

During the manufacture of asphalt, when the pellets come into contact with the hot bitumen, the wax melts and releases the recycled cellulose and plastic fibres from the cigarette butts. These fibres act as a reinforcement within the asphalt matrix, increasing its resistance to cracking, but also as a binder, allowing its content to be increased, making the material more ductile and flexible. In addition, the presence of waxes would make it possible to modify the viscosity of the bitumen and reduce the manufacturing temperature of the mixture, thereby reducing energy consumption and pollutant emissions.

The results of the tests carried out at LabIC.UGR have shown that the use of these pellets would allow the manufacture of asphalts with high recycled material content that offer better resistance to cracking under traffic loads and thermal shrinkage than conventional asphalts. Among the tests carried out, the UGR-FACT® method for the structural and durability study of the material, patented by the University of Granada, stands out.

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Journal

Construction and Building Materials

DOI

10.1016/j.conbuildmat.2025.141832 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Use of Engineered Pellets Containing E-Cigarette Butts and a Recycling Agent for Stone Mastic Asphalt Mixtures Incorporating Recycled Asphalt

Article Publication Date

21-Jul-2025