Periodic Reporting for period 1 - LAUREL (Challenging catalytic routes of hydrogen production from waste plastics)
Berichtszeitraum: 2022-10-01 bis 2024-09-30
Plastic pollution is a global issue with significant environmental and health risks. This problem is exacerbated by the lack of effective recovery and recycling systems, leading to uncontrolled disposal and landfill use for both recyclable and non-recyclable plastics. Recyclable plastics like polyethylene terephthalate (PET) face recycling challenges due to inadequate infrastructure and high costs; compostable plastics helps to some extent, but composting results in a loss of material resources, which contradicts the principles of a circular economy; and their valorization has revealed high significant production of CO2 emissions. There is a clear need for eco-friendly methods to remove plastics and reduce landfill waste.
In this context, the LAUREL project proposed exploring aqueous phase reforming (APR) of plastics as an alternative method to eliminate and valorize to H2 under mild conditions. However, applying APR to plastic waste is challenging because plastics typically have low oxygen content, and the optimal C/O ratio for APR is around 1. Therefore, a pretreatment of soft photooxidation (PhOx) of the plastics was planned, using layered double hydroxides (LDH), and achieving degradation products that could be easily reformed. Thus, the objectives were design and developing LDH materials to use in both catalytic reactions, to identify the most active and understanding the catalytic mechanism.
LDH and related materials were synthetized, used in PhOx/APR and studying their effects in the subsequent APR stage, which required catalysts based on precious metals. New LDH-based heterostructures were developed to create dual catalysts capable of catalyzing PhOx/APR. The study found that some plastics could be reformed directly in APR without pretreatment. Additionally, the role of LDH in the process was studied in depth, including the mechanism. PLA and PET were directly reformed. Differences in the products (yield and selectivity) were achieved after the PhOX/APR instead of direct APR. PP, PC and PS were still refractory to the PhOX/APR proccess.
In this context, the LAUREL project proposed exploring aqueous phase reforming (APR) of plastics as an alternative method to eliminate and valorize to H2 under mild conditions. However, applying APR to plastic waste is challenging because plastics typically have low oxygen content, and the optimal C/O ratio for APR is around 1. Therefore, a pretreatment of soft photooxidation (PhOx) of the plastics was planned, using layered double hydroxides (LDH), and achieving degradation products that could be easily reformed. Thus, the objectives were design and developing LDH materials to use in both catalytic reactions, to identify the most active and understanding the catalytic mechanism.
LDH and related materials were synthetized, used in PhOx/APR and studying their effects in the subsequent APR stage, which required catalysts based on precious metals. New LDH-based heterostructures were developed to create dual catalysts capable of catalyzing PhOx/APR. The study found that some plastics could be reformed directly in APR without pretreatment. Additionally, the role of LDH in the process was studied in depth, including the mechanism. PLA and PET were directly reformed. Differences in the products (yield and selectivity) were achieved after the PhOX/APR instead of direct APR. PP, PC and PS were still refractory to the PhOX/APR proccess.
A library of LDH and related materials were prepared mainly through co-precipitation with different metal cations and exchange anions. Interesting heterostructures were prepared by growing Pt nanoparticles on LDH. There were characterized using various characterization techniques such as X-ray diffraction, electronic microscopies, thermogravimetric analysis, etc.
Thus, initially plastics (PET, PLA, PP, PC, and PS) were micronized using cryogenic milling. Direct APR tests showed promising results for PET and PLA. Various conditions such as temperature (190–235 °C), pH (3–12), reaction time (2-16 h), metal catalysts (Pt, Pd, Rh, Ru, and their combinations), and supports (carbon black variants) were studied. For PET, Pt catalysts produced up to 10 mmol H2/g PET in 8 hours. PLA showed similar results with PtRu and PtRh catalysts. The PhOx as pretreatment improved the APR results: PET showed an increase of H2 yield (13 mmol H2/g PET) in 4 h of reaction time. Pt/LDH heterostructures, employed as dual catalysts showed similar behavior. LDH based on ZnCr and NiFe were identified as the most effective LDH materials. This strategy demonstrates potential for converting plastic waste, especially PET into H2.
Thus, initially plastics (PET, PLA, PP, PC, and PS) were micronized using cryogenic milling. Direct APR tests showed promising results for PET and PLA. Various conditions such as temperature (190–235 °C), pH (3–12), reaction time (2-16 h), metal catalysts (Pt, Pd, Rh, Ru, and their combinations), and supports (carbon black variants) were studied. For PET, Pt catalysts produced up to 10 mmol H2/g PET in 8 hours. PLA showed similar results with PtRu and PtRh catalysts. The PhOx as pretreatment improved the APR results: PET showed an increase of H2 yield (13 mmol H2/g PET) in 4 h of reaction time. Pt/LDH heterostructures, employed as dual catalysts showed similar behavior. LDH based on ZnCr and NiFe were identified as the most effective LDH materials. This strategy demonstrates potential for converting plastic waste, especially PET into H2.
The LAUREL project aimed to develop LDH heterostructures to serve as catalysts in PhOx and APR processes, targeting the valorization of plastic waste into H2. The project successfully developed a protocol achieving high selectivity for H2, with the primary gas products being H2 and CO2. This separation process is feasible for large-scale implementation. Although the goal was broad, the project's impact could extend across various sectors:
The synthesized heterostructure materials, which included LDH combined with carbon materials and Pt nanoparticles, have potential applications in other scientific fields as sorbents or catalysts for different reactions.
While APR has traditionally been used for biomass conversion and wastewater treatment, this project explored its application to plastics. Furthermore, the tandem PhOx/APR reaction and the understanding of the catalytic degradation pathway, have laid the groundwork for applying this method to other waste types (e.g. pollutants resistant to APR, textile waste) to generate energy.
The topics related to reducing plastic waste and new methods for H2 production are gaining attention. Environmental preservation is a priority for both science and society, and this project offers an alternative method to eliminate and valorize plastics, producing H2, a green energy vector. Although still in its early stages and requiring further research, this work aligns with the circular economy concept, recovering resources from waste and preventing landfill or uncontrolled disposal, in line with the European Green Deal. The LAUREL project significantly contributes to the current knowledge, given the limited literature on APR of plastics. The published and forthcoming articles will enhance its impact.
The synthesized heterostructure materials, which included LDH combined with carbon materials and Pt nanoparticles, have potential applications in other scientific fields as sorbents or catalysts for different reactions.
While APR has traditionally been used for biomass conversion and wastewater treatment, this project explored its application to plastics. Furthermore, the tandem PhOx/APR reaction and the understanding of the catalytic degradation pathway, have laid the groundwork for applying this method to other waste types (e.g. pollutants resistant to APR, textile waste) to generate energy.
The topics related to reducing plastic waste and new methods for H2 production are gaining attention. Environmental preservation is a priority for both science and society, and this project offers an alternative method to eliminate and valorize plastics, producing H2, a green energy vector. Although still in its early stages and requiring further research, this work aligns with the circular economy concept, recovering resources from waste and preventing landfill or uncontrolled disposal, in line with the European Green Deal. The LAUREL project significantly contributes to the current knowledge, given the limited literature on APR of plastics. The published and forthcoming articles will enhance its impact.