Thermocatalytic Conversion Research Articles

Hydrogen peroxide mediated thermo-catalytic conversion of carbon dioxide to C1-C2 products over Cu (0)

The global challenge concerning CO2 conversion to valuable products is anticipated to execute an essential task towards net zero carbon emissions. Thermal CO2 reduction is advantageous in terms of higher conversion rates, selectivity, and already-established industrial thermal instruments for scalability. However, the method is energy-intensive, a hindrance to sustainably practical adoption. Herein, we present a comprehensive study of H2O2-mediated thermal CO2 conversion in the presence of dendritic zerovalent copper (d-ZCu) in a batch-type reactor, yielding C1 and C2 carbon products, with acetic acid (AcOH) as the major product (achieving an optimized yield of approximately 0.98 M and a selectivity of around 97 % at near ambient conditions of 25–150 °C and 1–15 bar), along with trace amounts of methanol and ethanol, and carbon monoxide (CO) as a gaseous product. The reaction parameters, including temperature, time, pressure, and concentrations, were optimized to gain better insight into the reaction. To further explore the feasibility of the process, experiments were conducted in a continuous flow-packed bed reactor using similar parameters as those in the batch reactor, where CO was identified as the primary product of CO2 reduction. For advanced real-life applicability, the as-emitted exhaust gases from diesel and petrol engines, as sources of anthropogenic CO2, were utilized to establish the practical applicability of the proposed method.

Dynamic Reconstruction of Yttrium Oxide-Stabilized Cobalt-Loaded Carbon-Based Catalysts During Thermal Ammonia Decomposition.

Hydrogen production from the decomposition of ammonia is considered an effective approach for addressing challenges associated with hydrogen storage and transportation. However, their relatively high energy consumption and low efficiency hinder practical multi-scenario applications. In this study, Y2O3-stabilized catalysts with Co-loaded onto porous nitrogen-doped carbon (Y2O3-Co/NC) are synthesized by pyrolysis of Y(NO3)3-modified ZIF-67 under an inert atmosphere, followed by annealing in a reducing environment. The introduction of Y2O3 enhanced the recombination and desorption of N atoms and facilitated the gradual dehydrogenation of NHx on the catalyst surface, resulting in improved catalytic activity for the thermal decomposition of ammonia. Benefitting from the electron-donating properties of Y2O3 and N-doped carbon, the optimized catalyst achieved a remarkable NH3 conversion efficiency of 92.3% at a high gas hourly space velocity of 20000 cm3· ·h-1 with an encouraging H2 production rate of 20.6 mmol· ·min-1 at 550°C. Moreover, the synthesized catalyst undergoes a fast-dynamic reconstruction process, resulting in exceptionally stable catalytic activity during the thermal decomposition of ammonia, rendering it a promising candidate for carbon-free energy thermocatalytic conversion technology.

Structure-activity relationship and deactivation behavior of iron oxide during CO2 hydrogenation

Identifying the dynamic structural evolution of iron during the thermocatalytic conversion of CO2 into liquid hydrocarbons is a promising approach for understanding the deactivation behavior and to design an efficient catalyst. Despite the understanding of the oxidation of χ-Fe5C2 to high-valent iron oxides (e.g., Fe3O4, Fe2O3) caused by water formed as the byproduct, the deactivation mechanism depending on the particle size during a long-term reaction remains unclear. Herein, the structural evolution and deactivation mechanism of Na-promoted Fe2O3 catalysts with varying particle sizes were investigated. The catalyst activity and deactivation behavior were highly dependent on the initial morphology of the calcined catalysts. The reduced iron catalyst with an average particle size (dave) of 0.52 μm maintained its domain integrity, whereas that with a dave value of 2.18 μm was severely pulverized during the CO2 hydrogenation. The pulverized particles exposed a new surface, making it highly susceptible to re-oxidation and catalyst deactivation. Conversely, maintenance of the iron integrity suppressed the re-oxidation, whereas the excess formation of graphitic carbon on the χ-Fe5C2 site was the main deactivation mechanism during long-term CO2 hydrogenation.

Comparison of thermo-catalytic and photo-assisted thermo-catalytic conversion of glucose to HMF with Cr-MOFs@ZrO2

Abstract Thermo-catalytic and photo-assisted thermo-catalytic are two effective pathways for conversion of glucose. Thermo-catalytic and photo-assisted thermo-catalytic conversion of glucose was studied with Cr-MOFs@ZrO2 as catalysts in nitrogen atmosphere at 150 °C. Cr-MOFs@ZrO2 possesses simultaneously Lewis acid sites as well as Brønsted acid sites, and also has strong Brønsted acidity, so it can exhibit good thermos-catalytic performanc. When the glucose was 3 g/L, the reaction was carried out at 150 °C for 2 h with DMF as solvent, the glucose conversion was 97.9% while the HMF yield was 38%. The yield of HMF can be increased to 51.1% by adding 500w xenon lamp irradiation on the basis of thermal catalytic reaction condition. A comparison of the two reactions revealed that light-assisted thermal catalysis was more favorable for the reaction.

Thermodynamic Reaction Study of Conversion of H2S and CO2 and the Promoting Effect of Light on the Reaction

H2S and CO2 are common coexisted gases widely existing in natural gas resources, and they need to be treated harmlessly. The traditional Claus treatment process only focuses on H2S treatment but ignores CO2. This article systematically conducted theoretical thermodynamic research on the thermocatalytic conversion of H2S and CO2. It was found that increasing the reaction temperature and H2S ratio would have a positive impact on the reaction, while increasing the pressure would lead to a decrease in the conversion rate of reactants and product yield, and introducing COS into the feed gas could have a promoting effect on the reaction. Furthermore, 5%Mo/Al2O3 catalyst was used to preliminarily explore the thermal and photothermal catalysis for H2S and CO2 conversion. The results showed that the photothermal catalysis significantly promoted the production of syngas (H2 and CO), and suppressed COS production in contrast to thermal catalysis. This indicates that the introduction of light could effectively convert H2S and CO2 into high‐value product syngas, providing important reference value for further research on the conversion of H2S and CO2.

Interfacial nanoarchitectonics for enhanced photo-assisted thermo-catalytic conversion of glucose to 5-hydroxymethylfurfural

Photo-assisted thermo-catalytic conversion of glucose to 5-hydroxymethylfurfural (HMF) is one of the most promising ways for channeling solar energy. Photo-assisted thermo-catalytic conversion of glucose and HMF yield were improved with SnO2/Cr-MOFs/Cr(OH)3 catalysts under visible light irradiation at 135 ℃-165 ℃ nitrogen atmosphere. SnO2/Cr-MOFs/Cr(OH)3 afforded relatively high Lewis acidity and Brønsted acidity, which was beneficial for thermo-catalytic conversion of glucose. The light and the interface between SnO2 and Cr-MOFs/Cr(OH)3 assistantly promoted the HMF formation. The photo-generated holes (h+) under light irradiation was the driving force for the formation of “free” protons from water and carboxylic acid in Cr-MOFs, which acted as Brønsted acid sites to promote HMF formation. With 576 mg glucose as the substrate and DMSO as the solvent, 92 % glucose conversion with 43.2 % HMF yield was achieved at 150 ℃ for 2 h under nitrogen atmosphere and 500 W Xe lamp irradiation. The results demonstrate the promise of photo-assisted thermo-catalytic conversion of glucose in the future.

Atomically Dispersed Metal Catalysts for the Conversion of CO2 into High-Value C2+ Chemicals.

The conversion of carbon dioxide (CO2) into value-added chemicals with two or more carbons (C2+) is a promising strategy that cannot only mitigate anthropogenic CO2 emissions but also reduce the excessive dependence on fossil feedstocks. In recent years, atomically dispersed metal catalysts (ADCs), including single-atom catalysts (SACs), dual-atom catalysts (DACs), and single-cluster catalysts (SCCs), emerged as attractive candidates for CO2 fixation reactions due to their unique properties, such as the maximum utilization of active sites, tunable electronic structure, the efficient elucidation of catalytic mechanism, etc. This review provides an overview of significant progress in the synthesis and characterization of ADCs utilized in photocatalytic, electrocatalytic, and thermocatalytic conversion of CO2 toward high-value C2+ compounds. To provide insights for designing efficient ADCs toward the C2+ chemical synthesis originating from CO2, the key factors that influence the catalytic activity and selectivity are highlighted. Finally, the relevant challenges and opportunities are discussed to inspire new ideas for the generation of CO2-based C2+ products over ADCs.

TiO2/SiC supported catalyst for efficient thermocatalytic conversion of SF6 waste gas

The harmless treatment of SF6 waste gas is currently a highly concerned focus in the power industry. This article used a new supported catalyst, TiO2/SiC, to study the thermocatalytic conversion of SF6 waste gas. Firstly, the catalytic activity of TiO2/SiC was tested, and it was found that the catalytic efficiency of TiO2/SiC was 3.73 times that of TiO2 at 700 °C; Subsequently, the optimal catalytic conditions for TiO2/SiC were figured out by experiments, which were conducted under different initial pressures and oxygen concentrations. It was found that the catalytic efficiency of TiO2/SiC was highest when the initial pressure was 0.16 MPa and the concentration rate of SF6 and O2 was 1:4. Under these conditions, the total conversion of SF6 by TiO2/SiC reached 288 ml in 6 h, and the average catalytic conversion efficiency reached 33 ml g−1 h−1. It was also found that when the conversion of SF6 reached 110–130 ml, the catalytic activity of TiO2/SiC decreased; the oxygen concentration has a significant influence on the products: the higher the oxygen concentration is, the higher the production of SO2F2 rate in the product, while the lower that of SO2 rate. Finally, in order to know the catalytic mechanism of TiO2/SiC, XPS tests were conducted on the catalysts before and after the experiment. According to the XPS spectrum, gaseous products would react with TiO2 and generate TiF4 and Ti(SO4)2. According to the test results, the catalytic mechanism of TiO2/SiC was summarized in this article. It explained the catalytic effect of TiO2/SiC from two aspects: promoting the defluorination of SF6 and consuming low-fluorinated sulfides. The empirical conclusions of this article provide a theoretical reference for the harmless treatment of SF6 waste gas.

Fenton-mediated thermocatalytic conversion of CO2 to acetic acid by industrial waste-derived magnetite nanoparticles.

Iron oxide dust, discarded as industrial waste, has been used here to fabricate magnetic iron oxide nanoparticles (Fe3O4-NPs). We have proposed the thermo-catalytic reduction of carbon dioxide (CO2) using Fe3O4-NPs in the presence of H2O2 to get acetic acid (AcOH) at near ambient conditions (100 °C, 10 bar) with a maximum yield of ∼0.4 M in a batch-reactor. The importance of H2O2 can be described as it facilitates the production of higher concentrations of OH˙ and H+/˙, which consequently supports the synthesis of AcOH.

Two-stage thermocatalytic conversion of waste XLPE to diesel-like fuel

Cross-linked polyethylenes (XLPE) are not preferred in industrial pyrolysis applications and mechanical recovery methods due to great thermochemical resistance to heat and deformation. The studies on pyrolysis of XLPE up to 600?C on obtaining fuel have generally yielded high levels of wax and have not been of interest to the energy sector. In this study, two-stage pyrolysis of XLPE was carried out catalytically and also without catalyst (thermal, T- -pyr) under 500?C with heating rates of 5 and 10?C min-1. In the pyrolysis experiments, three different catalytic studies were performed by adding MCM- -41 + HZSM-5 catalyst mixture to the polymer phase only (PPC-pyr), by filling Cu(I)-MAS + HZSM-5 catalyst mixture to the gas outlet column only (GPC- -Pyr) and adding catalyst mixtures in both polymer phase and gas phase (MPC- -pyr). The highest diesel-like fuel (91.40 wt. %) was obtained in multiphase catalytic pyrolysis experiments at 460?C with a heating rate of 5?C min-1. The calorific value, kinematic viscosity, density, flash point and cetane number of the fuel were found as 45.97 MJ kg-1, 2.72 cSt, 832.5 kg m-3, 57 and 59?C, respectively. The results of the two-stage catalytic cracking and the heating rate profile will be a guide for industrial pyrolysis applications. The simple feasibility for industrial applications showed that it would be a very profitable investment.

Accelerated design of nickel-cobalt based catalysts for CO2 hydrogenation with human-in-the-loop active machine learning.

Thermo-catalytic conversion of CO2 into more valuable compounds, such as methane, is an attractive strategy for energy storage in chemical bonds and creating a carbon-based circular economy. However, designing heterogeneous catalysts remains a challenging, time- and resource-consuming task. Herein, we present an interpretable, human-in-the-loop active machine learning framework to efficiently plan catalytic experiments, execute them in an automated set-up, and estimate the effect of experimental variables on the catalytic activity. A dataset with 48 catalytic activity tests was compiled from a design space of Ni-Co/Al2O3 catalysts with over 50 million potential combinations in only eight iterations. This small dataset was found sufficient to predict CO2 conversion, methane selectivity, and methane space-time yield with remarkable accuracy (R 2 > 0.9) for untested catalysts and reaction conditions. New experiments and catalysts were selected with this methodology, leading to experimental conditions that improved the methane space-time yield by nearly 50% in comparison to the previously obtained maximum in the dataset. Interpretation of the model predictions unveiled the effect of each catalyst descriptor and reaction condition on the outcome. Particularly, the strong predicted inverse trend between the calcination temperature and the catalytic activity was validated experimentally, and characterization implied an underlying structure-performance relationship. Finally, it is demonstrated that the deployed active learning model is excellently suited to predict and fit kinetic trends with a minimal amount of data. This data-driven framework is a first step to faster, model-based, and interpretable design of catalysts and holds promise for broader applications across catalytic processes.

Advancing C5+ hydrocarbons fuels production: An interpretable machine learning framework for Co-catalyzed syngas conversion

Thermocatalytic conversion of the renewable syngas into long chain hydrocarbons fuels was an attractive energy production technology, for combating climate change, energy crisis, and wastes disposal. However, this thermochemical process was very complicated, and target product also highly depended on the feedstock information, catalyst properties, and process condition. At present, it was still challenging to fully understand and optimize this process. To address this gap, we developed a machine learning framework to model Fischer-Tropsch synthesis process of syngas towards C5+ hydrocarbons fuels from experimental descriptors. A database of Cobalt-based catalyst with 406 datapoints was compiled from literature and subjected to data mining. Accurate ensemble-tree models (R2 > 0.82) were developed to predict the CO conversion and C5+ hydrocarbons fuels selectivity from 12 descriptors, where the significance of dispersion, pressure, temperature, and metal content was revealed. Casual analysis revealed that C5+ hydrocarbons fuels selectivity was positively correlated with lower temperature (<481 K) and higher dispersion (>7.72 %). Besides, some interesting findings were also observed, for example, smaller cobalt size, and lower pore size (<9.27 wt%) and cobalt loading (<22 wt%) were positively related to C5+hydrocarbons fuels selectivity. The framework was purely data-driven, interpretable, and highlighted the ability of this method to unearth relationships of target variables and descriptors in thermocatalytic conversion of syngas, by isolating effects of individual design parameters in a manner that would be difficult to achieve experimentally. These insights could help design and optimization of subsequent experiments.

Depolymerization of Pine Wood Organosolv Lignin in Ethanol Medium over NiCu/SiO2 and NiCuMo/SiO2 Catalysts: Impact of Temperature and Catalyst Composition.

The process of thermocatalytic conversion of pine ethanol lignin in supercritical ethanol was studied over NiCu/SiO2 and NiCuMo/SiO2 catalysts bearing 8.8 and 11.7 wt.% of Mo. The structure and composition of ethanol lignin and the products of its thermocatalytic conversion were characterized via 2D-HSQC NMR spectroscopy, GC-MC. The main aromatic monomers among the liquid products of ethanol lignin conversion were alkyl derivatives of guaiacol (propyl guaiacol, ethyl guaiacol and methyl guaiacol). The total of the monomers yield in this case was 12.1 wt.%. The temperature elevation up to 350 °C led to a slight decrease in the yield (to 11.8 wt.%) and a change in the composition of monomeric compounds. Alkyl derivatives of pyrocatechol, phenol and benzene were observed to form due to deoxygenation processes. The ratio of the yields of these compounds depended on the catalyst, namely, on the content of Mo in the catalyst composition. Thus, the distribution of monomeric compounds used in various industries can be controlled by varying the catalyst composition and the process conditions.

Improved bio-oil yield from thermo-catalytic pyrolysis of Citrus limetta waste over pumice: Determination of kinetic parameters using Kissinger method

The focus of this research is on thermo-catalytic conversion of Citrus limetta waste, with and without pumice, using thermo gravimetric analysis and a pyrolysis chamber. TG/DTG results demonstrated weight reduction occurring in four stages i.e., evaporation of water, degradation of hemicellulose, decomposition of cellulose and lignin. Activation energy (Ea) calculated using Kissinger method for non-catalytic decomposition of hemicellulose, cellulose, and lignin was found as 99.76, 157.96 and 174.59 kJ mol−1 and for catalyzed reactions as 83.14, 91.45 and 149.65 kJ mol−1respectively. Thermal degradation of Citrus limetta waste produced 30 % oil in the range of C2–C24, while catalytic pyrolysis produced more than 45 % pyrolysis oil with a wide range of components from C4 to C32 which shows, that pumice has not only decreased the activation energy of the pyrolysis reaction but improved the quality of bio-oil making it suitable for energy on upgradation.

Scalable Synthesis of Oxygen Vacancy-Rich Unsupported Iron Oxide for Efficient Thermocatalytic Conversion of Methane to Hydrogen and Carbon Nanomaterials.

Thermocatalytic methane decomposition (TCMD) involving metal oxides is a more environmentally friendly and cost-effective strategy for scalable hydrogen fuel production compared to traditional methane steam reforming (MSR), as it requires less energy and produces fewer CO/CO2 emissions. However, the unsupported metal oxide catalysts (such as α-Fe2O3) that would be suited for this purpose exhibit poor performance in TCMD. To overcome this issue, a novel strategy was developed as a part of this work, whereby oxygen vacancies (OVs) were introduced into unsupported α-Fe2O3 nanoparticles (NPs). Systematic characterization of the obtained materials through analytical techniques demonstrated that mesoporous nanostructured unsupported α-Fe2O3 with abundant oxygen vacancies (OV-rich α-Fe2O3 NPs) could be obtained by direct thermal decomposition of ferric nitrate at different calcination temperatures (500, 700, 900, and 1100 °C) under ambient conditions. The thermocatalytic activity of the resulting OV-rich α-Fe2O3 NPs was assessed by evaluating the methane conversion, hydrogen formation rate, and amount of carbon deposited. The TCMD results revealed that 900 °C was the most optimal calcination temperature, as it led to the highest methane conversion (22.5%) and hydrogen formation rate (47.0 × 10-5 mol H2 g-1 min-1) after 480 min. This outstanding thermocatalytic performance of OV-rich α-Fe2O3 NPs is attributed to the presence of abundant OVs on their surfaces, thus providing effective active sites for methane decomposition. Moreover, the proposed strategy can be cost-effectively scaled up for industrial applications, whereby unsupported metal oxide NPs can be employed for energy-efficient thermocatalytic CH4 decomposition into hydrogen fuel and carbon nanomaterials.

Direct Synthesis of Formamide from CO2 and H2O with Nickel-Iron Nitride Heterostructures under Mild Hydrothermal Conditions.

Formamide can serve as a key building block for the synthesis of organic molecules relevant to premetabolic processes. Natural pathways for its synthesis from CO2 under early earth conditions are lacking. Here, we report the thermocatalytic conversion of CO2 and H2O to formate and formamide over Ni-Fe nitride heterostructures in the absence of synthetic H2 and N2 under mild hydrothermal conditions. While water molecules act as both a solvent and hydrogen source, metal nitrides serve as nitrogen sources to produce formamide in the temperature range of 25-100 °C under 5-50 bar. Longer reaction times promote the C-C bond coupling and formation of acetate and acetamide as additional products. Besides liquid products, methane and ethane are also produced as gas-phase products. Postreaction characterization of Ni-Fe nitride particles reveals structural alteration and provides insights into the potential reaction mechanism. The findings indicate that gaseous CO2 can serve as a carbon source for the formation of C-N bonds in formamide and acetamide over the Ni-Fe nitride heterostructure under simulated hydrothermal vent conditions.

Selective Valorization of CO2 towards Valuable Hydrocarbons through Methanol‐mediated Tandem Catalysis

AbstractThe thermocatalytic conversion of carbon dioxide (CO2) into valuable hydrocarbons presents a promising solution for mitigating anthropogenic CO2 emissions while producing drop‐in replacements for fossil‐derived products. Among the two tandem mechanisms for the direct hydrogenation of CO2, the methanol synthesis coupled with the methanol to hydrocarbon (MTH) reaction offers an improvement over the reverse water‐gas shift coupled with Fischer‐Tropsch synthesis reaction (RWGS‐FTS), as it is not limited by Anderson‐Schulz‐Flory distribution and yields higher selectivity towards specific products (e. g., olefins, aromatics, higher hydrocarbons). Herein, we focus on the recent progress achieved through this pathway and outline the existing knowledge gaps. We discuss the challenges involved in the process and highlight the key descriptors in the selection of catalyst components. Finally, we present several potential solutions to circumvent the current challenges, aiming to expedite the advancement of this route toward an efficient CO2 hydrogenation process.

Evaluation of MgO as a promoter for the hydrogenation of CO2 to long-chain hydrocarbons over Fe-based catalysts

Thermocatalytic conversion of CO2 into liquid fuels and chemicals is a promising approach to mitigate global warming. Although, the CO2 conversion and long-chain hydrocarbon selectivity are highly dependent on the choice of metal-oxide promoter, but role of the promoter remains unclear. Herein, the role of MgO as a promoter for an Fe-based catalyst was investigated. Bimetallic Na-FeMgOx catalyst exhibited a high C5+ yield of 25.1% with a CO2 conversion of 49.1% at the early stage of the reaction. The presence of MgO facilitates the reduction of Fe oxides and formation of oxygen vacancies by transferring electrons to Fe-based phases. In addition, at the early stage of reaction, the decoration of the Mg oxide surface with nanosized χ-Fe5C2 enhances the C5+ yield. However, the progressive transformation of MgO to MgCO3 during CO2 conversion deactivates the Na-FeMgOx catalyst. A detailed deactivation mechanism is also discussed.

Noble Metals in Recent Developments of Heterogeneous Catalysts for CO2Conversion Processes

AbstractFollowing the advances in capture technologies, CO2utilization associated with low‐cost renewable H2in catalytic hydrogenation is a promising strategy for reducing the carbon footprint of industrial processes by providing valuable chemicals and fuels. However, the scalability and economic viability of these processes will depend on the development of efficient catalysts. Noble metal‐based catalysts have been extensively reported in the last few years as highly effective in promoting CO2hydrogenation to various products. Although promising, the scarcity, high cost, and environmental impact of mining make it challenging to scale up these materials from bench to plant. Developing advanced synthesis and characterization methods is essential to control and understand active sites’ behavior during the reaction, providing high activity and durability. This review carefully summarizes the recently reported noble metal‐based heterogeneous catalysts for thermocatalytic conversion of CO2into methane, carbon monoxide, methanol, formic acid, higher alcohols, C2+hydrocarbons, and syngas through dry reforming of CH4, to draw the state‐of‐the‐art development in the field. Finally, we critically discuss the impact of these elements on catalyst properties, the challenges related to their implementation, and future research opportunities.

Thermocatalytic Conversion of CO2 to Valuable Products Activated by Noble‐Metal‐Free Metal‐Organic Frameworks

AbstractThermocatalysis of CO2 into high valuable products is an efficient and green method for mitigating global warming and other environmental problems, of which Noble‐metal‐free metal–organic frameworks (MOFs) are one of the most promising heterogeneous catalysts for CO2 thermocatalysis, and many excellent researches have been published. Hence, this review focuses on the valuable products obtained from various CO2 conversion reactions catalyzed by noble‐metal‐free MOFs, such as cyclic carbonates, oxazolidinones, carboxylic acids, N‐phenylformamide, methanol, ethanol, and methane. We classified these published references according to the types of products, and analyzed the methods for improving the catalytic efficiency of MOFs in CO2 reaction. The advantages of using noble‐metal‐free MOF catalysts for CO2 conversion were also discussed along the text. This review concludes with future perspectives on the challenges to be addressed and potential research directions. We believe that this review will be helpful to readers and attract more scientists to join the topic of CO2 conversion.