Chemical recycling of polycarbonate waste into advanced aviation fuel candidates via nickel–oxygen vacancy dual sites

Abstract

Transforming polycarbonate (PC) waste to C15 dicycloalkane offers a green pathway for plastic recycling and advanced aviation fuel production. Conventional metal–zeolite catalysts rely on noble metals and suffer from diffusion limitations and coke deposition. Herein, we report cost-effective Ni/CeO₂ catalysts featuring nickel–oxygen vacancy dual sites that convert PC waste into advanced aviation fuel-range hydrocarbons with 96.5% total alkane yield, including 84.4% C15 dicycloalkane. The catalyst demonstrates excellent stability, maintaining activity over four consecutive cycles with strong resistance to coke formation. It also demonstrates comparable performance when applied to real waste PC plastics. Mechanistic insights reveal a conversion pathway driven by dual active sites: (1) chain scission through C–O bond hydrogenolysis on metallic Ni, (2) stepwise hydrogenation of the resulting monomers on Ni to form C15 alcohols, and (3) deoxygenation on oxygen vacancies to yield C15 dicycloalkane. Fuel property evaluations further confirm that C15 dicycloalkane and its blends with commercial RP-3 fuel meet key specifications for advanced aviation fuel. This work positions PC waste as a promising feedstock for advanced aviation fuels and establishes an efficient conversion pathway enabled by nickel–oxygen vacancy dual sites.

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Green foundation

1 Upcycling polycarbonate waste into advanced aviation fuels over a recyclable catalyst addresses both plastic pollution and sustainable energy demands. It demonstrates a circular approach that converts an environmental burden into a renewable energy resource.

2 This work develops a novel cost-effective Ni/CeO₂ catalyst system featuring nickel–oxygen vacancy dual sites for upcycling polycarbonate waste. It achieves a 96.4% total alkane yield, including 84.4% high-energy-density C15 dicycloalkane, while maintaining activity over four consecutive cycles with strong resistance to coke formation.

3 Future research could integrate this system into continuous-flow processes to further improve the conversion efficiency.

1. Introduction

Global plastic production has increased exponentially over the past few decades, as is the build-up of plastic waste.¹ From 1950 to 2021, an estimated 11 billion ton of plastic were produced, with the vast majority either discarded in landfills or incinerated.² Conventional waste management strategies not only squander valuable carbon resources, but also contribute to severe environmental challenges, including greenhouse gas emissions, microplastic pollution, and threats to ecosystems.³ Therefore, developing innovative approaches for plastic waste upcycling has become an urgent priority. Recently, much attention has been directed toward transforming plastics into liquid fuels within the gasoline- and diesel-range.^4–14 Yet these fuels are dominated by linear paraffins, which often exhibit low energy content and limited economic competitiveness. By contrast, polycyclic hydrocarbons, as essential components of advanced aviation fuels (loaded on missiles and aircrafts), exhibit higher energy density that enables extended flight range and enhanced payload capacity.¹⁵ A representative example is JP-10 fuel, a classical polycyclic hydrocarbon fuel with a volumetric energy density of 39.6 MJ L⁻¹ and a market price of approximately USD 12 500 per ton, which is widely employed in military aviation.¹⁶

Polycarbonate (PC), widely used in food packaging, automotive components, medical devices, and aviation, possesses a unique polycyclic aromatic structure that provides strong potential for conversion into polycyclic hydrocarbons.^17,18 Hydrodeoxygenation of PC yields propane-2,2-diyldicyclohexane (hereinafter referred to as C15 dicycloalkane), a polycyclic hydrocarbon with an energy density of 39.1 MJ L⁻¹, comparable to that of JP-10 and RJ-4 fuels.^19,20 This transformation positions PC as a promising feedstock for high-energy-density aviation fuels, offering both significant economic value and a sustainable pathway for both plastic upcycling and advanced fuel production. Catalytic hydrodeoxygenation with recyclable heterogeneous catalysts represents an attractive strategy for upcycling PC into cycloalkanes. Metal–zeolite catalysts have been investigated for the hydrodeoxygenation of PC wastes, including Rh/C + H-USY,¹⁹ Pt/C + Hβ,²¹ Ru–Ni/Hβ,²² Ru-ReO_x/SiO₂ + HZSM-5,^23,24etc. However, their confined micropores impose severe diffusion limitations, while restricted accessibility of active sites and susceptibility to coke deposition compromise long-term stability.²⁵ Furthermore, reliance on noble metals has constrained the practical application of these systems.

To address these challenges, it is essential to design nonporous, non-acidic, and noble-metal-free catalytic systems and to clarify their upcycling process and mechanism. The hydrodeoxygenation (HDO) of PC to cycloalkanes proceeds via hydrogenation and C–O bond cleavage.^26–28 Nickel, a cost-effective transition metal with intrinsic hydrogenation activity, offers a practical alternative to noble metals.²⁹ Unlike C–O bond cleavage facilitated by acid sites, oxygen vacancies in defect-rich metal oxides (such as CeO₂) exhibit strong oxygen affinity, enabling efficient adsorption and activation of C–O bonds.³⁰ Moreover, their electron-deficient structure stabilizes the active hydrogen generated by Ni, leading to the formation of Ce-H and O–H species.³¹ Inspired by these insights, we report a bifunctional Ni/CeO₂ catalyst that efficiently converts PC waste into advanced aviation fuel-range hydrocarbons, achieving a total alkane yield of 96.5% and a C15 dicycloalkane yield of 84.4% (Fig. 1). This system delivers promising activity comparable to other noble-metal-based systems (Table S1).^19,22,24,32 Controlled reactions with PC and probe molecules, combined with comprehensive catalyst characterization, elucidate the reaction pathway and highlight the role of nickel and oxygen-vacancy dual sites in Ni/CeO₂. The catalyst can be reused for at least four consecutive cycles without loss of activity, demonstrating excellent stability and strong resistance to coke deposition. Furthermore, evaluation of the fuel properties of the C15 dicycloalkane and its blend with commercial RP-3 fuel confirms its potential as advanced aviation fuel (component).

Fig. 1 Recycling PC waste into advanced aviation fuel over nickel–oxygen vacancy dual sites.

2. Experimental

2.1. Materials

Polycarbonate (PC) powder was purchased from Dongguan Ruixiang Plastic Co., Ltd, and its physicochemical properties and elemental composition are summarized in Table S2. Cyclopentane, cyclohexanol, diphenyl carbonate, and bisphenol A were obtained from Shanghai Adamas Reagent Co., Ltd. Nickel(II) nitrate hexahydrate was bought from Chengdu Cologne Chemicals Co., Ltd. Anhydrous magnesium sulfate was purchased from Shanghai Titan Scientific Co., Ltd. CeO₂ (20 nm) and SiO₂ (20 nm) nanoparticles were obtained from Shanghai Macklin Biochemical Technology Co., Ltd. The real waste PC plastics used in this study included DVDs, safety goggles, and syringes. Prior to activity testing, these plastics were cut into small pieces and washed three times with ethanol and deionized water, respectively. For the DVDs, the metallic coating on the surface was first removed by sanding with sandpaper before cutting.

2.2 Catalyst preparation

Ni/CeO₂ catalysts with different Ni loadings were synthesized via the conventional impregnation method and denoted as xNi/CeO₂ (where x represents the Ni loading in wt%).³³ Typically, 0.5 g of nickel(II) nitrate hexahydrate was dissolved in 20 mL of deionized water under stirring, followed by the addition of 1.9 g of CeO₂. The suspension was stirred at room temperature for 3 h to ensure sufficient impregnation. After impregnation, excess water was removed by rotary evaporation, and the resulting solid was dried in an oven at 80 °C for 12 h. The dried sample was then calcined in a muffle furnace at 500 °C for 4 h with a heating rate of 5 °C min⁻¹. After cooling to room temperature, the sample was transferred to a tubular furnace and reduced under a H₂ atmosphere at 300 °C for 4 h (5 °C min⁻¹ heating rate). The reduced catalyst was naturally cooled to room temperature and subsequently passivated under a 1% O₂/99% N₂ flow for 1 h, yielding the 5Ni/CeO₂ catalyst. Catalysts with different Ni loadings and Ni/SiO₂ were prepared following the same procedure.

2.3 Catalyst characterization

The crystal structures of the catalysts were analysed by X-ray diffraction (XRD) using a Rigaku Smart Lab diffractometer (Japan) with Cu Kα radiation. The diffraction patterns were recorded over a 2θ range of 10°–80° at a scanning rate of 5° min⁻¹. The Ni content of the samples was quantified by inductively coupled plasma optical emission spectroscopy (ICP-OES, Agilent 5110). The specific surface area and average pore diameter were determined using a fully automated surface area analyzer (ASAP 2460, Micromeritics, USA). Prior to measurement, the samples were degassed at 300 °C for 8 h. The Brunauer–Emmett–Teller (BET) method was applied to calculate the specific surface area. H₂ chemisorption measurements were conducted on a quartz-tube reactor using an automated catalyst characterization system (AutoChem1 II 2920, Micromeritics, USA). The samples were reduced in H₂ at 300 °C for 1 h, cooled to 50 °C, and subsequently purged with high-purity He until a stable baseline was obtained. The surface morphology of the catalysts was examined by scanning electron microscopy (SEM, Hitachi Regulus 8230, Japan). High-resolution transmission electron microscopy (TEM, JEOL JEM-2100F, Japan) was employed to investigate the lattice fringes of the catalysts, while energy-dispersive X-ray spectroscopy (EDS) was used to analyse the elemental distribution.

The surface chemical states of the catalysts were determined by X-ray photoelectron spectroscopy (XPS, Thermo Fisher K-Alpha, USA) with Al Kα radiation (hν = 1486.8 eV). The X-ray beam spot size was set to 400 μm, and the analysis chamber pressure was maintained at 2 × 10⁻⁹ mbar. Survey spectra were acquired at a pass energy of 150 eV with a step size of 1.0 eV, while high-resolution spectra were collected at a pass energy of 50 eV with a step size of 0.1 eV. Each spectrum was accumulated over at least five scans (depending on the element), and the binding energies were calibrated against the C 1s peak at 284.8 eV. The concentration of oxygen vacancies on the catalyst surface was quantified by electron paramagnetic resonance analysis (EPR, Bruker A300, Germany).

Thermogravimetric analysis (TGA, Mettler TGA/DSC1, Switzerland) was performed in air with a heating rate of 5 °C min⁻¹ to evaluate the carbon deposition on the catalysts before and after the reaction. Prior to TGA measurements, the spent catalyst was washed with cyclopentane to remove weakly adsorbed reactants and then dried at 80 °C for 12 h.

2.4 Activity tests

The conversion of PC was carried out in a 50 mL high-pressure stainless-steel autoclave. Typically, 0.3 g of PC (including commercial PC powder and real waste PC plastics), 0.06 g of catalyst, and 30 mL of cyclopentane were charged into the reactor. The reactor was purged three times with N₂ and H₂ to remove residual air, followed by pressurization with H₂ to 4 MPa. The reaction was conducted at 523 K for 16 h with continuous stirring at 400 rpm. When the reaction was completed, the autoclave was cooled in an ice-water bath to room temperature, after which the gaseous products were collected using a gas bag, and the liquid products together with the spent catalyst were recovered. The collected products were filtered and dried over anhydrous magnesium sulfate, followed by rotary evaporation at 30 °C to recycle the solvent cyclopentane. The temperature was then increased to 75 °C to remove the monocyclic components, and the remaining C15 products were used for fuel performance testing. The gaseous products were analysed using a gas chromatograph (GC2600, Ruimin, Shanghai) equipped with a thermal conductivity detector (TCD). The liquid products were analysed on a gas chromatograph (GC-9860, Shimadzu, Japan) equipped with an HP-5 capillary column (30 m × 0.25 mm × 0.25 μm) and a flame ionization detector (FID). In addition, qualitative analysis of molecular ion peaks and molecular weights was performed using a gas chromatography-mass spectrometry (GC-MS, Shimadzu GCMS-QP2020) system equipped with an Rtx-5MS capillary column (50 m × 0.25 mm × 0.25 μm). The reactions using diphenyl carbonate (DPC) and bisphenol A (BPA) as model compounds were conducted at 453 K and 523 K, respectively.

In the catalyst recycling experiments, the used catalyst was recovered by filtration, followed by ultrasonic washing with 30 mL of cyclopentane three times. The sample was then dried at 80 °C for 12 h before being used for the next activity test.

3. Results and discussion

3.1 PC conversion pathway over Ni/CeO₂

Unlike metal-acid catalysis, the reaction process and mechanism of PC conversion over Ni/CeO₂ remain unclear. A Ni/CeO₂ catalyst was prepared and applied in the conversion of PC, with product samples collected (Fig. 2). At the initial stage, the products consisted of bicyclic oxygenated compounds, C15 dicycloalkane, monocyclic oxygenated compounds, C7–C10 monocyclic alkanes, and aromatic compounds, with bicyclic oxygenated compounds dominating. As the reaction proceeded, the yields of bicyclic oxygenated compounds and aromatics reached their peaks at approximately 1 h, with values of 76.6% and 1.5%, respectively, and then gradually declined. In contrast, the yield of C15 dicycloalkane steadily increased, indicating that bicyclic oxygenated and aromatic compounds serve as intermediates, with the bicyclic oxygenated species being the primary intermediates in C15 dicycloalkane formation. After 8 h, the yield of C15 dicycloalkane reached its maximum value of 84.4%. Upon extending the reaction to 16 h, unsaturated compounds were completely converted.

Fig. 2 Overall reaction profile of PC conversion over the Ni/CeO₂ catalyst. Reaction conditions: 523 K, 4 MPa H₂, 0.3 g PC, 0.06 g Ni/CeO₂ and 30 mL cyclopentane.

The detailed reaction pathway and the role of nickel–oxygen vacancy dual sites in Ni/CeO₂ were investigated using probe molecules (diphenyl carbonate and bisphenol A). Conversion of PC to cycloalkanes proceeds via two sequential steps: depolymerization to smaller intermediates, followed by hydrodeoxygenation.²⁴ Diphenyl carbonate (DPC), which shares an ester linkage (C_aryl–O bond) with PC, was selected as a model substrate to examine the depolymerization step. Two possible routes were considered for DPC conversion over Ni/CeO₂ (Fig. 3): (1) hydrogenation to a saturated DPC species prior to hydrodeoxygenation; (2) direct hydrogenolysis of the C_aryl–O bond to form reactive intermediates that subsequently undergo hydrodeoxygenation.

Fig. 3 Product distribution for the catalytic conversion of diphenyl carbonate over (a) Ni/CeO₂ and (b) Ni/SiO₂; (c) proposed depolymerization pathway.

Time-resolved sampling revealed benzene, phenol, cyclohexanone, cyclohexanol, and cyclohexane as the main products. The absence of saturated DPC excludes Route 1 and confirms Route 2 as the mechanism, indicating that depolymerization is initiated by direct C_aryl–O bond hydrogenolysis. DPC conversion was further examined over Ni/SiO₂ (without oxygen vacancies), yielding a product distribution similar to that with Ni/CeO₂. This confirms that metallic Ni sites, rather than CeO₂ oxygen vacancies, trigger C_aryl–O bond cleavage during PC depolymerization. Furthermore, to obtain deeper insight into the deoxygenation pathway of alcohols, we conducted additional experiments using cyclohexanol as the feedstock under N₂ and H₂ atmospheres, as shown in Fig. S4. Under a N₂ atmosphere, cyclohexanol remained unconverted, with no formation of cyclohexene or cyclohexane. In contrast, under a H₂ atmosphere, cyclohexanol was completely converted to cyclohexane. These results suggest that the deoxygenation of cyclohexanol proceeds via direct hydrogenolysis rather than through a dehydration/hydrogenation process.

Bisphenol A (BPA) was selected as a representative intermediate to further elucidate the hydrodeoxygenation pathway of PC-derived species. Product distribution profiles reveal a sequential transformation: BPA is initially hydrogenated to C15 phenolic species, followed by hydrogenation to C15 alcohols and subsequent deoxygenation to C15 dicycloalkane (Fig. 4). The formation of monocyclic saturated alkanes was also observed, resulting from C–C bond cleavage of unsaturated BPA intermediates during hydrogenolysis. A comparison between Ni/CeO₂ and Ni/SiO₂ demonstrated that the CeO₂-supported catalyst exhibited significantly higher activity for converting bicyclic oxygenates into C15 dicycloalkane. Over Ni/CeO₂, complete transformation of bicyclic oxygenates into saturated hydrocarbons was achieved within 6 h. These results highlight the critical role of oxygen vacancies on CeO₂ in converting C15 alcohols into C15 dicycloalkane. Therefore, an overall conversion pathway of PC could be proposed (Fig. 5): (1) chain scission via direct C–O bond hydrogenolysis on metallic Ni, (2) stepwise hydrogenation of the resulting monomers on Ni to yield C15 alcohols, and (3) deoxygenation on oxygen vacancies to form C15 dicycloalkane.

Fig. 4 Product distribution for the conversion of bisphenol A over (a) Ni/CeO₂ and (b) Ni/SiO₂; (c) proposed hydrodeoxygenation pathway.

Fig. 5 Overall reaction pathway for PC conversion over Ni/CeO₂.

3.2 Effect of Ni/CeO₂ structure on product distribution

The relationship between Ni/CeO₂ structure and overall catalytic performance in PC conversion is still indistinct. The high-resolution transmission electron microscopy (HRTEM) image of the Ni/CeO₂ catalyst reveals that the fringes at positions 1 and 2 correspond to the CeO₂ (111) plane and the Ni (111) plane, respectively (Fig. 6a). The XRD profiles demonstrate the characteristic face-centered cubic (FCC) structure of CeO₂ (Fig. 6b).³⁴ And the diffraction peaks corresponding to metallic Ni are clearly visible at 2θ = 44.5° and 51.8° as the Ni loading increases,³⁵ showing the existence of metallic Ni on the surface of CeO₂, and the varying loading of Ni does not alter the crystal structure of CeO₂. Furthermore, the Ni 2p_3/2 spectra (Fig. 6c) reveal four peaks at 852.6 eV, 853.8 eV, 855.8 eV, and 861.1 eV, which correspond to Ni⁰, Ni²⁺, and two satellite peaks, respectively.³⁶ A comparison of the peak areas for Ni⁰/(Ni⁰ + Ni²⁺) shows that the proportion of Ni⁰ gradually rises as the Ni loading increases. Meanwhile, as shown in Fig. 6d, the O 1s spectra of the Ni/CeO₂ samples exhibit two distinct peaks at approximately 529.4 eV and 531.3 eV, corresponding to lattice oxygen (O_L) and surface oxygen vacancies (O_V), respectively.³⁶ And the signal at g = 2.003 in electron paramagnetic resonance (EPR) spectra corresponds to oxygen vacancies (Fig. 6e).³⁷ Both XPS and EPR results demonstrate that the metal Ni content is proportional to the oxygen vacancy concentration.

Fig. 6 (a) TEM image, (b) XRD spectra, (c) Ni 2p_3/2 XPS spectra, (d) O 1s XPS spectra, and (e) EPR spectra of Ni/CeO₂ catalysts; (f) product distribution.

As shown in Fig. 6f, at a low Ni loading (5 wt%), the catalyst lacks sufficient oxygen vacancies and Ni⁰ sites, leading to poor hydrodeoxygenation activity. As a result, unsaturated products dominate and the saturated hydrocarbon yield drops sharply (14.1% + 4.4%). Raising the Ni content to 20 wt% enables complete conversion of oxygenates into alkanes, but monocyclic saturated alkanes become predominant (72.0%), while the yield of the desired C15 bicyclic fraction decreases markedly (23.7%). These results indicate that higher oxygen vacancy density enhances deoxygenation activity, whereas excessive Ni⁰ favors C–C bond cleavage. Given that high C15 dicycloalkane selectivity is crucial for improving the fuel energy density, an optimum was achieved at 15 wt% Ni, presenting a 96.5% total alkane yield, with 84.4% corresponding to C15 dicycloalkane.

3.3 Recycling of real-world PC plastic wastes over Ni/CeO₂

Common waste PC plastics from daily life, including DVDs, safety goggles, and syringes, were selected as representative samples to evaluate the applicability of the Ni/CeO₂ catalyst for real waste PC plastics (Fig. 7). The Ni/CeO₂ catalyst exhibited comparable catalytic performance for the real waste PC plastics and the commercial PC powder, with yields of C15 dicycloalkanes reaching 82.2%, 79.7%, and 79.8%, respectively. It demonstrates that the Ni/CeO₂ catalyst is effective for the practical conversion of waste PC plastics into advanced aviation fuels.

Fig. 7 Recycling of real PC wastes over the Ni/CeO₂ catalyst. Reaction conditions: 523 K, 4 MPa H₂, 0.3 g PC wastes, 0.06 g Ni/CeO₂ and 30 mL cyclopentane.

3.4 Catalyst stability

Conventional metal–zeolite catalysts rely on noble metals and suffer from diffusion limitations and coke deposition, restricting practical application.^19,21–25 Therefore, we conducted Ni/CeO₂ catalyst stability evaluation, as presented in Fig. 8a. It can be observed that, after four consecutive cycles, the yield of saturated alkanes remained almost unchanged. Thermogravimetric (TG) analysis revealed that the mass loss profiles of the catalyst before and after recycling were nearly identical (Fig. 8b), indicating that the catalyst exhibited negligible coke formation. Furthermore, XRD analysis confirmed that the crystalline structure of the catalyst remained unchanged after the recycling tests (Fig. 8c). Overall, the catalyst exhibited excellent resistance to carbon deposition and outstanding cyclic stability. In addition, the solvent cyclopentane could be effectively recycled. The recycled cyclopentane was then reused in the subsequent reaction, and the yield of C15 dicyclic saturated alkanes remained nearly unchanged (Fig. S7).

Fig. 8 (a) Ni/CeO₂ catalyst stability; (b) TG profiles and (c) XRD spectra of fresh and recycled Ni/CeO₂ catalysts. Reaction conditions: 523 K, 4 MPa H₂, 0.3 g PC, 0.06 g Ni/CeO₂ and 30 mL cyclopentane.

3.5 Fuel properties of PC-derived dicycloalkane and its blends

The properties of fuel are critical in determining its practical applicability. Among them, density is one of the most important specifications, as it directly influences fuel energy characteristics. In addition, excellent low-temperature properties (freezing point and viscosity) are crucial to ensure easy flow under high-altitude conditions.

The density of the obtained C15 dicycloalkane was measured at 0.911 g mL⁻¹, with a volumetric heating value of 39.1 MJ L⁻¹ and a freezing point as low as −27 °C, meeting the basic requirements for advanced aviation fuels (Table 1). Owing to these favorable properties, PC-derived C15 dicycloalkane represents a promising green additive to commercial jet fuel (such as RP-3) for enhancing the energy density and other properties. Blending tests were therefore conducted with RP-3 fuel, and the results are summarized in Table 1. The two fuels were fully miscible, and a linear increase in density was observed with increasing C15 dicycloalkane content. Specifically, densities of 20, 40, and 60 wt% blends increased from 0.773 g mL⁻¹ to 0.855 g mL⁻¹. The freezing point of pure C15 dicycloalkane (−27 °C) was further improved by blending with RP-3, reaching as low as −60 °C at 20 wt%, thereby ensuring excellent fluidity under extreme conditions. Viscosity measurements showed a decline with increasing RP-3 content, with the low-temperature viscosity decreasing from 15.50 mm² s⁻¹ to 2.58 mm² s⁻¹ at −20 °C.

Table 1 The properties of the fuel mixtures of C15 dicycloalkane and commercial RP-3

Fuel composition	C15	60 wt% C15 + 40 wt% RP-3	40 wt% C15 + 60 wt% RP-3	20 wt% C15 + 80 wt% RP-3	RP-3
Density at 15 °C (g mL^−1)	0.911	0.855	0.826	0.800	0.773
Freezing point (°C)	−27	<−60	<−60	<−60	<−60
Minimum ignition temperature (°C)	301	300	339	399	394
Viscosity (mm^2 s^−1)	4.10 (20 °C)	3.46 (20 °C)	1.98 (20 °C)	1.38 (20 °C)	1.30 (20 °C)
	8.12 (0 °C)	5.50 (0 °C)	2.85 (0 °C)	1.82 (0 °C)	1.78 (0 °C)
	15.50 (−20 °C)	10.14 (−20 °C)	4.43 (−20 °C)	2.58 (−20 °C)	2.46 (−20 °C)
	—	25.44 (−40 °C)	8.97 (−40 °C)	4.23 (−40 °C)	4.08 (−40 °C)
Heating value (MJ L^−1)	39.1	36.7	35.4	34.3	33.1

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In addition, advanced propulsion demands fuels that ignite rapidly and burn efficiently to maximize energy release in the combustion chamber. Generally, a low minimum ignition temperature and a short ignition delay time (The ignition delay time is defined as the time interval between the moment when the droplet contacts the plate and the moment when the flame first appears.³⁸) indicate superior ignition and combustion performance. These parameters were determined using high-speed imaging, and the results are presented in Fig. 9. C15 dicycloalkane exhibited an attractive minimum ignition temperature of 301 °C, significantly lower than that of RP-3 fuel (394 °C, Table 1). The ignition delay time was also much shorter for C15 dicycloalkane (227 ms) compared with RP-3 (822 ms). Furthermore, blending C15 dicycloalkane with RP-3 reduced both the minimum ignition temperature and ignition delay time, demonstrating improved ignition and combustion behavior. These mixtures provide a tunable balance of energy density, low-temperature properties, and ignition performance, presenting strong potential for application in advanced propulsion systems.

Fig. 9 Images of the ignition and combustion process of fuel mixtures at 420 °C.

4. Conclusions

In summary, this work presents an efficient strategy for transforming polycarbonate waste into advanced aviation fuel-range hydrocarbons using a bifunctional Ni/CeO₂ catalyst. Mechanistic investigations revealed that the conversion proceeds via nickel–oxygen vacancy dual active sites: PC first undergoes chain scission through C–O bond hydrogenolysis over metallic Ni; the resulting intermediates are then stepwise hydrogenated to C15 alcohols on Ni, followed by deoxygenation on oxygen vacancies to yield C15 dicycloalkanes. The optimized catalyst containing 15 wt% Ni achieves a total alkane yield of 96.5%, including 84.4% C15 dicycloalkanes. The Ni/CeO₂ catalyst also exhibits excellent cyclic stability and strong resistance to carbon deposition and demonstrates comparable performance when applied to real waste PC plastics, affording total alkane yields of up to 96.0%. Fuel property evaluations further confirmed that the produced C15 dicycloalkanes possess high energy density, superior ignition quality, and favorable low-temperature properties. Blending tests with commercial RP-3 fuel highlighted their practical applicability. These findings establish PC waste as a promising feedstock for sustainable advanced aviation fuels and showcase a cost-effective catalytic pathway enabled by nickel–oxygen vacancy dual sites.

Author contributions

Y. Huang: writing – original draft, conceptualization, investigation, and data curation; J. Xie: writing – review & editing, funding acquisition, and supervision; Y. Zhou: software, validation, and visualization; Q. Song: investigation; Y. Lei: resources; C.-a. Zhou: supervision; C. Wang: visualization; K. Ma: visualization; L. Song: data curation; H. Yue: writing – review & editing; J.-J. Zou: writing – review & editing.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included as part of the supplementary information (SI). Supplementary information is available. See DOI: https://doi.org/10.1039/d5gc04561d.

Acknowledgements

This work was supported by the Sichuan Science and Technology Program (2025YFHZ0334), the Postdoctoral Fellowship Program of CPSF (GZB20240477), the China Postdoctoral Science Foundation (2025M771178), the Project of State Key Laboratory of Polymer Materials Engineering (Sichuan University) (sklpme2024-2-13), and the Sichuan University Postdoctoral Interdisciplinary Innovation Fund.

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