Catalysts For Hydrodeoxygenation Research Articles

Revealing the Potential of Bimetallic Carbide Catalysts for Upgrading Biomass‐Derived Bio‐Oil: A First Principles‐Based Investigation Using Representative Bio‐Oil Constituents

AbstractBimetallic carbides, especially based on molybdenum carbide, proved to be a promising hydrodeoxygenation (HDO) catalyst, with enhanced selectivity towards C─O bonds cleavage. However, catalysts are generally investigated using limited model components derived from only one of the biopolymers in biomass (either lignin or carbohydrates), therefore, HDO of raw biomass‐derived bio‐oil still remains a challenge, as it contains molecules of different functionalities. This paper presents a systematic comparison of the monometallic carbide, Mo2C, with the novel bimetallic carbide incorporating W using representative bio‐oil components of different functionalities and derived from different bio‐polymers components of biomass. We employed quantum mechanical investigation to reveal that the W‐doped Mo2C carbide (MoWC) catalyst with increased oxophilicity, owing to tungsten incorporation, can perform HDO of real bio‐oil more effectively in comparison to its monometallic counterpart (Mo2C) using six substrates representing different components of bio‐oil. We showed MoWC can selectively cleave both single/double (C─O/C═O) bonds with similar barriers in comparison to Mo2C which can only selectively cleave single C─O bonds. This observation was consistent for 5‐HMF, Acetic acid, and Methyl Glyoxal. We also showed that MoWC outperforms its metallic counterpart Mo2C in the HDO for aromatic and carbohydrates components.

Efficient Hydrodeoxygenation of Lignin-Derived Phenolic Compounds Over Ru-Based Catalyst with Biochar and Al2O3 as Composite Support.

Hydrodeoxygenation (HDO) is a common strategy for upgrading lignin-derived phenolic compounds into high-quality liquid fuels, and the support rational design of HDO catalysts is critical to achieve a good reaction performance. This work proposed a novel Ru-based catalyst with biochar and Al2O3 as composite support. The addition of biochar can enlarge the porous structure, and the addition of Al2O3 can enhance the acid property of the support. By regulating the content of biochar and Al2O3 components, Ru/CA-2 catalyst achieved the best HDO performance of lignin-derived phenolic compounds, with the optimal component balance of 50 %C and 50 %Al2O3. This catalyst possesses the high Ru metal dispersion (1.38 nm particle size) to activate the hydrogen source, the moderate acid property to suppress carbon deposition and the abundant oxygen vacancy to promote substrate adsorption at the same time. 99.9 % conversion of guaiacol is obtained at 230 °C, with 99.9 % selectivity towards cyclohexane. Ru/CA-2 catalyst also has a good recyclability, with no obvious activity loss after five runs. Furthermore, in the application of catalytic lignin-oil HDO, the content of hydrocarbons increase from 10.7 % to 95.7 %, showing great potential on the industrial usage.

Efficient C–O Bond Hydrogenolysis Over Polyoxometalate Catalysts in Mild Hydrodeoxygenation of Lignin-Derived Phenols to Cycloalkanes

Efficient C–O Bond Hydrogenolysis Over Polyoxometalate Catalysts in Mild Hydrodeoxygenation of Lignin-Derived Phenols to Cycloalkanes

Effect of rhenium on the activity of ZrO2-supported copper catalysts for hydrodeoxygenation of m-cresol

This work studies the effect of adding different loadings of Re on the performance of ZrO2-supported Cu catalysts for hydrodeoxygenation (HDO) of m-cresol. H2-TPR and XPS show a synergistic effect between Cu and Re, decreasing the reduction temperature of both metals and promoting the reduction of Re oxide. Moreover, the addition of Re changes Cu dispersion and acid properties of all catalysts. High Re contents results in a coverage of Cu surface. Catalytic tests reveal that HDO reaction rate and product distribution vary considerably depending on the Re loading. Cu catalyst was inactive for HDO reaction, forming only hydrogenation products. In contrast, Re catalyst stood out for its high capacity to promote HDO reaction, with significant production of toluene. For the bimetallic catalysts, the addition of Re increases HDO reaction rate from 0 to 0.39 mmol gmetal−1 min−1 and the selectivity towards toluene (0–82.6 %), whereas the formation of hydrogenation and dehydration products decreases.

Electrospun Pt-TiO2 nanofibers Doped with HPA for Catalytic Hydrodeoxygenation

Electrospinning is utilized to fabricate catalytic nanofiber scaffold for biocrude upgrading in hydrodeoxygenation (HDO) following computational studies suggesting the need for nano-catalysts for efficient HDO conversion and selectivity. Here, Pt-TiO2 nanofibers are fabricated through electrospinning, followed by wet impregnation with a heteropoly acid (HPA), tungstosilicic acid. Intensive heat treatments were incorporated during and after processes to obtain a HPA doped Pt-TiO2 nano-catalyst. Catalytic HDO was performed in a batch reactor with phenol as the raw biocrude dissolved in hexadecane. The HPA doped Pt-TiO2 catalyst demonstrated promising HDO performance of 37.2% conversion and a 78.9% selectivity to oxygen free benzene and the remainder 21.1% as diphenyl ester as a result of esterification by acidic components of the catalyst. Additionally, BET surface area characterization show a low surface area 16.9 m2 g−1 significantly lower than existing commercial catalysts and a mesoporous nature suitable for selectivity. The presence of HPA on the anatase nanofiber compensated for low platinum nanoparticles crystallinity on the nanofibers. This work might create needed alternatives for preparing HDO catalysts for efficient aromatics production.

SBA-15 supported Ni-Cu catalysts for hydrodeoxygenation of m-cresol to toluene.

Amidst concerns over fossil fuel dependency and environmental sustainability, the utilization of biomass-derived aromatic compounds emerges as a viable solution across diverse industries. In this scheme, the conversion of biomass involves pyrolysis, followed by a hydrodeoxygenation (HDO) step to reduce the oxygen content of pyrolysis oils and stabilize the end products including aromatics. In this study, we explored the properties of size controlled NiCu bimetallic catalysts supported on ordered mesoporous silica (SBA-15) for the catalytic gas-phase HDO of m-cresol, a lignin model compound. We compared their performances with monometallic Ni and Cu catalysts. The prepared catalysts contained varying Ni to Cu ratios and featured an average particle size of approximately 2 nm. The catalytic tests revealed that the introduction of Cu alongside Ni enhanced the selectivity for the direct deoxygenation (DDO) pathway, yielding toluene as the primary product. Optimal performance was observed with a catalyst composition comprising 5wt.% Ni and 5wr.% Cu, achieving 85% selectivity to toluene. Further increasing the Cu content improved turnover frequency (TOF) values, but reduced DDO selectivity. These findings underscore the importance of catalyst design in facilitating biomass-derived compound transformations and offer insights into optimizing catalyst composition for more selective HDO reactions.

Effect of Acid Properties of Fluorinated Beta and ZSM-5 Zeolites Used as Supports of Ni Catalysts for the Catalytic Hydrodeoxygenation of Guaiacol

Commercial NH4-Beta and Na-ZSM-5 zeolites were fluorinated with different amounts of NH4F and using different procedures (room temperature, conventional refluxing, microwave refluxing). Samples were characterized by XRD, N2 physisorption, FTIR, 1H NMR, SEM-EDS, and TGA of adsorbed cyclohexylamine. An increase in the concentration of NH4F led to fluorinated zeolites with higher surface areas and slightly lower amounts of Brønsted acid sites due to some dealumination. Fluorination by conventional or microwave refluxing at shorter times did not dealuminate ZSM-5, resulting in the formation of higher particle sizes. Ni/fluorinated beta catalysts were more active than Ni/fluorinated ZSM-5 catalysts for the hydrodeoxygenation of guaiacol at 180 °C and 15 bar of H2 for 1 h due to their higher amount of acid sites. The appropriate proportion of metallic and Brønsted acid centers allowed for the selective obtention of cyclohexane (58%) for the Ni supported on beta fluorinated with NH4F 0.1 M catalyst. The combination of this fluorinated beta to a Ni/ordered mesoporous carbon catalyst significantly boosted its selectivity to cyclohexane from 0 to 65%. Fluorinated ZSM-5 samples, although having stronger Brønsted acid sites, as observed by 1H NMR, they had lower amounts, leading to higher selectivity to cyclohexanol when used as catalytic supports.

Efficient hydrodeoxygenation of cresol by hierarchical porous FLRC-TiO2 nanoflower

The construction of highly efficient and selective hydrodeoxygenation (HDO) catalysts is of great significance for upgrading pyrolysis oil. In this work, nickel and iron-based NiFe(x)/FLRC-TiO2 catalysts with a flower-like radial channel structure were successfully fabricated with a facile strategy. The effects of Ni/Fe molar ratios and operation conditions on the structure, morphology and HDO performance were investigated using p-cresol as model compound. Impressively, the NiFe(x)/FLRC-TiO2 catalysts exhibit a well-defined radial channel structure with an average pore diameter of 27.4 nm and the NiFe(5)/FLRC-TiO2 with appropriate Ni/Fe ratio of 5 exhibits the best HDO performance. Under the conditions of T=275 °C, p=3 MPa, and t=2.5, the conversion rate of p-cresol and the selectivity to the target product MCH reaches 100 % and 97.8 %, respectively, which supresses most of the reported Ni based catalysts. Combining with the structure and morphology charateriazation results, this excellent HDO performance could be ascribed to: (a) the unique flower-like radial channel structure of the catalysts stemmed from FLRC-TiO2 provides more exposed active sites for HDO and fast mass transfer; (b) an appropriate Ni/Fe ratio contributes to the increase of specific surface area and pore volume of the catalyst, which boots the higher catalytic HDO activity; (c) the addition of Fe enhances acidity of catalyst and promotes the hydrodehydration of C–OH to target product MCH, together with the synergistic effect of FeNi metal sites, favoring the higher catalytic HDO activity. The proposed strategy for the preparation of radial channel structure FLRC-TiO2 support can be extended to various other reactions.

Phyllosilicate-derived Ni/SiO2 catalyst for liquid-phase hydrodeoxygenation of phenol: Synergy of Lewis acid sites and Ni0

Designing effective catalysts using non-noble metals for bio-oil hydrodeoxygenation (HDO) into liquid fuels is greatly sought after, yet it remains a great challenge. Contrary to the prevailing belief that monometallic nickel lacked activity in the HDO of oxygen-containing compounds, this study demonstrates a remarkable catalytic performance over monometallic Ni catalyst. Herein, a Ni/SiO2 catalyst having both nickel phyllosilicate and Ni0 was synthesized by the ammonia evaporation (AE) method. The Ni-PS-400 catalyst reduced at 400 ℃ achieves a significant high activity and yields 97 % cyclohexane at a low reaction temperature of 190 ℃, surpassing both Ni-IMP-400 prepared by impregnation method and most of the reported other non-noble metal catalysts which are generally used at high temperature of above 240 ℃. It was found that the reduction temperature of Ni-PS-X influences the catalytic activity, as more dispersed Ni nanoparticles and acidic sites can be produced on the surface of the support at an appropriate temperature. The outstanding catalytic performance can be ascribed to the collaborative effect of well-scattered Ni nanoparticles and the significant presence of Lewis acidic sites, which result from coordinatively unsaturated Ni2+ sites situated within the remaining nickel phyllosilicate.

Atmosphere toward regulation of MoO3 microstructure for lactic acid hydrodeoxygenation to propionic acid

Regulation of MoO3 microstructure was explored at different atmospheres, which was further evaluated for catalytic performance on lactic acid hydrodeoxygenation. Catalyst structure was characterized by XRD, FT-IR, HRTEM, and oxygen vacancies were measured by EPR and XPS spectra. It was found that the direct H2-Ar treatment generated an obvious change in MoO3 microstructure to form rich oxygen vacancies in MoO3-H, and the succedent H2-Ar treatment had negligible influence in MoO3-A-H, indicating that the non-crystallizing MoO3 is effortless to generate oxygen vacancy with H2-Ar atmosphere treatment. Correspondingly, MoO3-H achieved 58.6 % of lactic acid conversion and 64.7 % of propionic acid selectivity much higher than MoO3-A-H with 41.7 % of lactic acid conversion and 56.9 % of propionic acid selectivity, which also outperformed most of the LA hydrodeoxygenation catalysts in propionic acid selectivity. This work demonstrates that the calcined atmospheres can efficiently regulate MoO3 microstructure to form rich oxygen vacancies for lactic acid hydrodeoxygenation to propionic acid.

Encapsulated metal-based MOF nanoparticles as efficient catalysts for catalytic transfer hydrodeoxygenation of lignin-derived vanillin to 2-methoxy-4-methylphenol

A range of carbon-encapsulated non-precious metal catalysts (Ni@C, Ce@C, Mo@C, and Zn@C) were prepared using the hydrothermal approach for the catalytic transfer hydrodeoxygenation of vanillin compound derived from lignin. The catalytic efficacy was affected by the level of acid sites, catalyst durability, and the cooperation with H-donor solvents. Analysis indicated that the thin carbon layer enclosing the active sites notably improved catalytic effectiveness and thermodynamic stability compared to alternative catalysts. Notably, Ni@C demonstrated superior catalytic performance, achieving a vanillin conversion rate of 98.72 % and an 87.12 % yield of the major product 2-methoxy-4-methylphenol under specific conditions (240 ℃, 2.0 MPa N2, ethanol as a solvent, 4-hour reaction time). These findings underscore the significant potential of carbon-wrapped MOF catalysts in advancing the sustainable utilization of lignin and fostering the growth of a more eco-friendly bioeconomy.

Insights into reverse oxygen spillover effect induced via CeO2 modulation to enhance the stability of CuCoOx catalysts in hydrodeoxygenation of biomass derivatives

In hydrodeoxygenation (HDO) reactions, the evolution of the chemical states of active species in the catalyst caused by the spillover effects greatly influences their catalyst performance. Herein, the HDO of guaiacol (GUA) over CuCoOx and CuCoCeOx catalysts synthesized by co-precipitation method was systematically investigated. During the HDO reaction of GUA, acid sites (Co(II)) facilitated the C-O bond (demethylation via -OCH3) cleavage, which was the rate-determining step. A series of characterizations and experimental results revealed that introducing CeO2 into the CuCoOx catalyst could enable the catalyst to undergo reverse oxygen spillover in the hydrogenation environment, promoting the regeneration of CoO in the catalyst. Therefore, the deactivation of the CuCoOx catalyst due to hydrogen spillover and CoO reduction could be avoided, and the catalyst stability improved. The present study methodically investigated the spillover effects induced by Cu and CeO2 and provided the theoretical basis for the structural design of heterogeneous catalysts.

Lignin-incorporated Co-MOFs-derived catalysts for selective hydrodeoxygenation of lignin-derived phenols into cyclohexanols

Lignin accounted for the second largest amount in biomass, and was regarded as an important carbon source and important renewable source for value-added chemicals. Herein, a series of lignin-derived carbon-based heterogeneous catalyst was synthesized through a simple hydrothermal method, using Co-MOFs as template. Lignin was introduced as a carbon material into MOF catalysts. Through some characterizations, it has been proven that lignin has been successfully introduced into MOF materials and significantly improved the catalyst performance. Then, lignin-MOF derived catalysts (Co/C-EL-X) were successfully introduced into the catalytic hydrodeoxygenation of lignin-derived phenols. The addition of enzymatic hydrolysis lignin (EL) in catalysts, calcination temperature and some other factors were investigated in detail, considering the catalytic performance during the HDO of vanillin and other typical lignin-derived phenols. Co/C-EL-0.5(500) exhibited the best catalytic performance for the conversion of different kinds of lignin-derived phenols to either 2-methoxy-4-methylphenol (MMP) or cyclohexanol. Under the optimal conditions of 240 °C, 0 MPa N2, and 2 h, the conversion rate of vanillin reached 100 %, and the yield of 4-methyl-2-methoxyphenol (MMP) was up to 92 %. Furthermore, vanillin could also be converted into 4-methylcyclohexanol (MCYL) by changing the initial nitrogen pressure. Also, Co/C-EL-0.5 (500) exhibited high activity for the conversion of other lignin-derived phenols into cyclohexanol (COL). This work provided a novel strategy for the catalytic valorization of lignin sources.

Synthesis of ultrafine Mo2N particles supported on N doped carbon material for guaiacol hydrodeoxygenation

A series of Mo2N particles supported on nitrogen-doped carbon (Mo2N@NC) catalysts for guaiacol hydrodeoxygenation were synthesized in situ through a one-step method employing dopamine as C and N resources and ammonium molybdate as Mo resource, respectively. During synthesis, molybdate ions are adsorbed on dopamine because of a complexation between them; then dopamine/molybdate ions/TMB/F127 nanoemulsions are formed. After polymerization, growth, drying, and carbonization, Mo2N particles supported on nitrogen-doped carbon catalysts are obtained. Because of the interaction between Mo and N, Mo2N particles are anchored onto the support, preventing the aggregation of Mo2N during carbonization. As a result, ultrafine Mo2N particles with a size of 1.0–1.3 nm are highly dispersed on Mo2N@NC catalysts. The guaiacol hydrodeoxygenation for these Mo2N@NC catalysts was performed at 280–380 °C, a H2 flow rate of 80 mL/min and different pressures and weight hourly space velocities. Among them, Mo2N@NC with a Mo2N loading of 40 % presents the highest guaiacol conversion (99.9 %) and aromatic hydrocarbon selectivity (80.2 %), which is also better than Mo2N/C with a Mo2N loading of 40 % prepared by the wet impregnation method.

The promoting role of framework Ti(IV) in enhancing the hydrodeoxygenation performance of palmitic acid over a mesoporous TS-1 supported Ni catalyst

Developing a highly efficient Ni-based hydrodeoxygenation catalyst is crucial for the production of renewable biodiesel. Herein, a mesoporous TS-1 zeolite supported Ni catalyst (Ni/TS-1-M) exhibited exceptional hydrodeoxygenation (HDO) activity and achieved 100 % yield of deoxygenated hydrocarbons (97.3 % pentadecane vs 2.7 % hexadecane), outperforming other catalysts such as Ni on mesoporous ZSM-5 (Ni/ZSM-5-M), mesoporous Silicalite-1 (Ni/Silicalite-1-M) and TiO2 (Ni/TiO2). The Ti(IV) atoms in the form of TiO4 and TiO6 can transfer its electron to nearby metal Ni, leading to the increase in electron density of metal Ni, which enhanced the hydrogenation activity and facilitated the C–C bond cleavage of the hexadecanal to produce pentadecane. Furthermore, the framework Ti(IV) species accelerated the esterification process to generate palmityl palmitate, which was easily hydrogenolyzed to the main intermediate of hexadecanol under the synergistic effect of metal Ni and Ti(IV) on Ni/TS-1-M catalyst. The formed hexadecanol mainly underwent successive dehydrogenation/decarbonylation process to transform into pentadecane.

Highly selective hydrodeoxygenation catalyst for sustainable aviation fuel production from used cooking oil

The production of Sustainable Aviation Fuel (SAF) utilizing used cooking oil (UCO) as a renewable bio-waste resource holds immense potential for promoting sustainability in the aviation sector. In this study, SAF synthesis via hydrodeoxygenation of pretreated UCO over Ni-Mo/alumina-silica catalysts followed up hydroisomerization of deoxygenated oil has been investigated in a fixed-bed reactor. The effect of Al2O3/SiO2 ratio on the physico-chemical properties of Al2O3-SiO2 support and on the overall hydrodeoxygenation performance of the Ni-Mo catalyst supported on Al2O3-SiO2 has been investigated. NiMo catalyst supported on Al2O3-SiO2 in a 70:30 ratio achieved 86.69 % UCO conversion during the hydrodeoxygenation step and exhibited 74.79 % jet range hydrocarbon fuel selectivity under mild conditions (350°C, 1.1 h⁻¹ WHSV, 6 MPa, H2/oil (v/v): 400). The catalyst activity remained stable for >100 hours highlighting its good stability under the experimental conditions investigated. This work demonstrates the potential of tailor-made supported catalysts for highly selective single-step conversion of UCO into jet-range hydrocarbons, offering a significant step towards the production of sustainable aviation fuels.

Tuning of the acid sites in the zeolite-alumina composite Ni catalysts and their impact on the palm oil hydrodeoxygenation reaction

The hydrodeoxygenation (HDO) of bio-oil is one of the potential approaches to produce green diesel. However, HDO catalyst requires the development of bifunctionality which translates to the simultaneous presence of acidic and metal sites for desired catalytic activity and selectivity. Zeolites and their composites are attractive candidates for the conversion of biomass to fuels. In the present work, a series of Ni-incorporated Al2O3-zeolite beta bifunctional composite catalysts with distinct Al2O3 (25–75 wt%) and Ni contents (5–15 wt%) were synthesized via a facile one-pot method directly from nickel acetate, nano-boehmite (γ-AlO(OH)) and the NH4+ form of beta zeolite (NH4+-BZ). The nano-boehmite particles, due to the positive charges on their surface, electrostatically attract negatively charged beta zeolite crystals, which leads to the assembly of a hierarchical pore structure upon calcination. Interestingly, the composite catalysts synthesized were quite homogeneous with uniform dispersion of Ni particles. All composite catalysts were thoroughly characterized using XRD, SEM-EDX, SEM-mapping, HR-TEM, H2-TPR, H2-TPD, NH3-TPD, XPS, 31P MAS NMR, 27Al MAS NMR and N2 sorption analysis. The synthesized composite catalysts with distinct Al2O3 contents showed diverse textural properties, distinct nature of acid sites and improved performance in hydrodeoxygenation of palm oil. Particularly, the Ni/BZ-Al50 (with BZ:Al2O3 = 50:50) composite catalyst significantly enhanced the conversion of palm oil (up to 90%) and yield of n-C15-C18 hydrocarbons (up to 69%) at moderate temperature of 375 °C as compared to 10Ni/BZ catalyst (Conv. = 75%, yield of n-C15-C18 = 52%). The higher catalytic performance realized with composite catalysts can be ascribed to its hierarchical pore structure, moderate acidity (chemisorption studies), tuned acid sites nature (solid state NMR) and homogeneous distribution of active Ni sites (H2 chemisorption) which helps to improve product selectivity by minimizing side reactions. The time-on-stream (TOS) experiments were carried out up to 20 h which clearly showed that composite catalysts are more stable suggesting the lower amount of coke deposition (TPO studies) and suppression of metal sintering.

Ce-Doped Co-ZIF as an efficient catalyst for hydrodeoxygenation of lignin-derived phenols: From guaiacol to cyclohexanol

Through the utilization of diverse technological processes, lignin could be transformed into a multitude of valuable chemicals and fuels. This transformation not only reduces our dependence on fossil energy but also fosters the promotion of environmental sustainability. In this study, Ce metal was incorporated into the zeolite imidazolium framework-67 (ZIF-67) using the impregnation method to prepare a series of bimetallic catalysts. Using isopropanol solvent as the hydrogen source, guaiacol was effectively converted to cyclohexanol with over 80.0% selectivity over the optimum catalyst at 240 °C, 1.5 MPa N2, for 4 hours. The prepared catalysts were subjected to characterization methods such as BET, SEM, XPS, TEM, XRD, H2-TPR and NH3-TPD. The results of the characterization show that the addition of Ce changed the zeolitic imidazolium ester backbone structure of ZIF-67 and encouraged the emergence of more oxygen vacancies, which strengthened the catalyst hydrodeoxygenation activity and reducibility. Based on the findings of the catalytic performance tests and a retesting, the reaction pathway of the guaiacol hydrodeoxygenation process was suggested.

Efficient hydrodeoxygenation of methyl palmitate over NiMo/ZrO2 catalyst with electron transfer between Ni and Mo

The hydrodeoxygenation of biomass into high quality fuels is one of the effective technologies to produce green diesel and solve the environmental pollution of fossil fuels at source. In this work, the catalytic performances of NixMoy/ZrO2 catalysts for methyl palmitate hydrodeoxygenation were evaluated, and the characterization results were combined to understand their role of physicochemical and structural properties in modulating the specific selectivity of alkanes. Under mild reaction condition (270 °C, 3 MPa), the Ni1Mo1/ZrO2 catalyst showed the best hydrodeoxygenation reactivity (conversion: 99.4%) and alkane selectivity (95.0%, hexadecane: 73.6%) of methyl palmitate. It was found that the electron transfer from Mo to Ni in Ni1Mo1/ZrO2 catalyst promoted the active site Ni anchoring and H2 molecules activation, which were associated with the better hydrodeoxygenation activity. In addition, the highest oxygen vacancies and Mo5+ content in Ni1Mo1/ZrO2 catalyst benefited the adsorption and breaking capacity of CO/C-O bonds and hexadecane yield. The Ni1Mo1/ZrO2 catalyst maintained excellent catalytic performance and structural stability after a long-term test of 60 h, which could be efficiently applied for hydrodeoxygenation of methyl palmitate.

Hydrodeoxygenation of Oxygen-Containing Aromatic Plastic Wastes into Cycloalkanes and Aromatics.

Chemical recycling and upcycling offer promising approaches for the management of plastic wastes. Hydrodeoxygenation (HDO) is one of the appealing ways for conversion of oxygen-containing plastic wastes, including polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), polyphenyl ether (PPO), and polyether ether ketone (PEEK), into cyclic alkanes and aromatics in high yields under mild reaction conditions. The challenge lies in achieving C-O activation while preserving C-C bonds. In this review, we highlight the recent advancements in catalytic strategies and catalysts for the conversion of these oxygen-containing plastic wastes into cycloalkanes and aromatics. The reaction systems, including multi-step routes, direct HDO and transfer HDO methods, are exemplified. The design and performance of HDO catalysts are systematically summarized and compared. We comprehensively discuss the functions of the catalysts' components, reaction pathway and mechanism to gain insights into the HDO process for efficient valorization of oxygen-containing plastic wastes. Finally, we provide perspectives for this field, with specific emphasis on the non-noble metal catalyst design, selectivity control, reaction network and mechanism studies, mixed plastic wastes management and product functionalization. We anticipate that this review will inspire innovations on the catalytic process development and rational catalyst design for the HDO of oxygen-containing aromatic plastics to establish a low-emission circular economy.