Carbon dioxide reduction in tandem with light-alkane dehydrogenation

New Dynamic Fingerprint in Derivative-Based Phase Space: Rapid Gas Sensing in Seconds

Many studies have focused on smart electronic noses combining machine learning and gas sensor arrays, but feature extraction for training has generally relied on dimensionality reduction techniques based on raw time-series data. These methods do not reflect the principles of sensor responses, limiting their applicability in diverse gas environments. In this study, we propose a new phase space, expressed through the first and second derivatives of dynamic response signals, to effectively characterize the nonlinear responses between gas sensors and gases. Sensing data transformed into a phase space showed unique patterns depending on the type and concentration of gases, and these were investigated for alkanes with various chain lengths (CH4, C3H8, C4H10). By applying these patterns as a preprocessing method, CNN-based gas identification machine learning achieved a high classification accuracy of 99.1% and a low concentration prediction error of 2.23 ppm using only a single sensor. Additionally, the algorithm was trained and validated across various regions of the phase space, identifying the minimum time and region required for simultaneous gas classification and concentration prediction. This study presents a novel strategy for the fast and accurate identification of gases within seconds and is expected to have significant scalability in diverse gas environments.

Molten-Salt-Mediated Chemical Looping Oxidative Dehydrogenation of Ethane with In-Situ Carbon Capture and Utilization

The molten-salt-mediated oxidative dehydrogenation (MM-ODH) of ethane (C2H6) via a chemical looping scheme represents an effective carbon capture and utilization (CCU) method for the valorization of ethane-rich shale gas and concurrent mitigation of carbon dioxide (CO2) emissions. Here, stepwise experimentation with Li2CO3-Na2CO3-K2CO3 (LNK) ternary salts (i) assessed how each component of the LNK mixture impacted ethane MM-ODH performance and (ii) explored physicochemical and thermodynamic mechanisms behind melt-induced changes to ethylene (C2H4) and carbon monoxide (CO) yields. Of fifteen screened LNK compositions, nine exhibited ethylene yields greater than 50 % at 800 °C while maintaining C2H4 selectivities of 85 % or higher. LNK salts rich in Li2CO3 content yielded more ethylene and CO on average than their counterparts, and net CO2 capture per cycle reached a maximum of ~75 %. Extended MM-ODH cycling also demonstrated long-term stability of a high-performing LNK medium. Density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations suggested that the molten salt does not directly activate C2H6. Meanwhile, an empirical model informed by experimental data and reaction thermodynamics adequately predicted overall MM-ODH performance from LNK composition and provided insights into the system's primary drivers.

Co-Feeding CO2 for Methylfuran Aromatization over Bifunctional Zeolite-Supported ZnMoO4

Aromatization of biofuran offers promising approaches for sustainable biochemical production. However, this process is often hampered by low yields and severe coking on traditional zeolite catalysts. Herein, we report co-feeding CO2 for 2-methylfuran (MF) aromatization (CCMA) over bifunctional ZSM-5 supported ZnMoO4. This bifunctional catalyst can achieve both MF and CO2 conversions of >97 %, generating >85 % carbon yield of target arenes and CO with negligible alkenes (0.05 %). Meanwhile, coke formation is remarkably suppressed from 22.3 % to 8.6 %. ZnMoO4/ZSM-5 is capable of selectively manipulating the reaction intermediates and pathways of the CCMA reactions, favoring the cyclopentenones- and alkenes-based dehydro-aromatization rather than the benzofurans-based pathway. This finding challenges the prevailing understanding that MF aromatization follows a hydrocarbon pool mechanism. Moreover, the abundant surface oxygen vacancies of ZnMoO4 facilitate the adsorption of CO2 and its subsequent reaction with coke. These insights into reaction mechanism and catalyst design for co-conversion of CO2 and biofuran can offer guidelines for process intensification in biomass utilization with a carbon-negative manner.

Strong Electron-Withdrawing Effect Activates Metal-Free Carboxylate Anion into Efficient Active Sites for Electrocatalytic Acetylene Semihydrogenation

The exploration of novel and high-performance organo-electrocatalysts with well-defined active sites is vital for understanding catalytic mechanisms and replacing metal-based catalysts, but remains a formidable challenge. Here, we report metal-free trifluoroacetate as a new organo-electrocatalyst, where the strong electron-withdrawing trifluoromethyl (-CF3) group intrinsically transforms the neighboring carboxylate anions (-COO-) into highly efficient active sites for electrocatalytic acetylene semihydrogenation. The electrophilic acetylene molecule bonds to the negatively charged O- sites of the carboxylate anion via the σ-configuration. Benefiting from precise molecular engineering of electron-withdrawing groups, the ethylene partial current density presents a volcano relationship with the total natural charge of the -COO- anions. In 1 M KOH aqueous solution, trifluoroacetate delivers an ethylene partial current density of 260 mA/cm2 with an ethylene Faradaic efficiency of 96.8% at -0.9 V versus the reversible hydrogen electrode (RHE) under a pure acetylene atmosphere, outperforming metal-based electrocatalysts. This work presents a new type of high-activity organo-electrocatalysts with -COO- anions as active center and promises its application in electrocatalysis.

Synergistic effect of scattered rare metals on Pt/CeO2 for propane oxidative dehydrogenation with CO2

The oxidative dehydrogenation of propane with CO2 (CO2-ODP) is a green industrial process for producing propene. Cerium oxide-supported platinum-based (Pt/CeO2) catalysts exhibit remarkable reactivity toward propane and CO2 due to the unique delicate balance of C-H and C[double bond, length as m-dash]O bond activation. However, the simultaneous activation and cleavage of C-H, C-C, and C-O bonds on Pt/CeO2-based catalysts may substantially impede the selective activation of C-H bonds during the CO2-ODP process. Here, we report that the scattered rare metal oxide (SRO x , SR = Ga, In) overlayer on Pt/CeO2 exhibits extraordinary activity and selectivity for the CO2-ODP reaction. With the assistance of Pt, the SRO x -Pt/CeO2 could achieve a propane conversion of 38.13% and a CO2 conversion of 67.72%. More importantly, the selectivity of the product propene has increased from 33.28% to 88.24%, a level that is even comparable to the outstanding performance of currently reported PtSn/CeO2 catalysts. A mechanistic study reveals that the strong affinity of the overlayer SRO x to the propane reduces the barrier of C-H bond activation and balances the C-H cleavage rates and the C-O bond groups, accounting for the excellent selective CO2-ODP performance of SRO x -Pt/CeO2 catalysts. The SRO x -modified Pt/CeO2 strategy offers a novel approach to modulating CO2-ODP, thereby facilitating the highly selective preparation of propene.

Merger of Single-Atom Catalysis and Photothermal Catalysis for Future Chemical Production

Photothermal catalysis is an emerging field with significant potential for sustainable chemical production processes. The merger of single-atom catalysts (SACs) and photothermal catalysis has garnered widespread attention for its ability to achieve precise bond activation and superior catalytic performance. This review provides a comprehensive overview of the recent progress of SACs in photothermal catalysis, focusing on their underlying mechanisms and applications. The dynamic structural evolution of SACs during photothermal processes is highlighted, and the current advancements and future perspectives in the design, screening, and scaling up of SACs for photothermal processes are discussed. This review aims to provide insights into their continued development in this rapidly evolving field.

Ultrafine Pt Nanoparticles on Defective Tungsten Oxide for Photocatalytic Ethylene Synthesis

The selective conversion of ethane (C2H6) to ethylene (C2H4) under mild conditions is highly wanted, yet very challenging. Herein, it is demonstrated that a Pt/WO3-x catalyst, constructed by supporting ultrafine Pt nanoparticles on the surface of oxygen-deficient tungsten oxide (WO3-x) nanoplates, is efficient and reusable for photocatalytic C2H6 dehydrogenation to produce C2H4 with high selectivity. Specifically, under pure light irradiation, the optimized Pt/WO3-x photocatalyst exhibits C2H4 and H2 yield rates of 291.8 and 373.4 µmol g-1 h-1, respectively, coupled with a small formation of CO (85.2 µmol g-1 h-1) and CH4 (19.0 µmol g-1 h-1), corresponding to a high C2H4 selectivity of 84.9%. Experimental and theoretical studies reveal that the vacancy-rich WO3-x catalyst enables broad optical harvesting to generate charge carriers by light for working the redox reactions. Meanwhile, the Pt cocatalyst reinforces adsorption of C2H6, desorption of key reaction species, and separation and migration of light-induced charges to promote the dehydrogenation reaction with high productivity and selectivity. In situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculation expose the key intermediates formed on the Pt/WO3-x catalyst during the reaction, which permits the construction of the possible C2H6 dehydrogenation mechanism.

Catalyst development for O2-assisted oxidative dehydrogenation of propane to propylene

O2-Assisted oxidative dehydrogenation of propane (O2-ODHP) could convert abundant shale gas into propylene as an important chemical raw material, meaning O2-ODHP has practical significance. Thermodynamically, high temperature is beneficial for O2-ODHP; however, high reaction temperature always causes the overoxidation of propylene, leading to a decline in its selectivity. In this regard, it is crucial to achieve low temperatures while maintaining high efficiency and selectivity during O2-ODHP. The use of catalytic technology provides more opportunities for achieving high-efficiency O2-ODHP under mild conditions. Up to now, many kinds of catalytic systems have been elaborately designed, including transition metal oxide catalysts (such as vanadium-based catalysts, molybdenum-based catalysts, etc.), transition metal-based catalysts (such as Pt nanoclusters), rare earth metal oxide catalysts (especially CeO2 related catalysts), and non-metallic catalysts (BN, other B-containing catalysts, and C-based catalysts). In this review, we have summarized the development progress of mainstream catalysts in O2-ODHP, aiming at providing a clear picture to the catalysis community and advancing this research field further.

Ethylene electrosynthesis from low-concentrated acetylene via concave-surface enriched reactant and improved mass transfer

Electrocatalytic semihydrogenation of acetylene (C2H2) provides a facile and petroleum-independent strategy for ethylene (C2H4) production. However, the reliance on the preseparation and concentration of raw coal-derived C2H2 hinders its economic potential. Here, a concave surface is predicted to be beneficial for enriching C2H2 and optimizing its mass transfer kinetics, thus leading to a high partial pressure of C2H2 around active sites for the direct conversion of raw coal-derived C2H2. Then, a porous concave carbon-supported Cu nanoparticle (Cu-PCC) electrode is designed to enrich the C2H2 gas around the Cu sites. As a result, the as-prepared electrode enables a 91.7% C2H4 Faradaic efficiency and a 56.31% C2H2 single-pass conversion under a simulated raw coal-derived C2H2 atmosphere (~15%) at a partial current density of 0.42 A cm-2, greatly outperforming its counterpart without concave surface supports. The strengthened intermolecular π conjugation caused by the increased C2H2 coverage is revealed to result in the delocalization of π electrons in C2H2, consequently promoting C2H2 activation, suppressing hydrogen evolution competition and enhancing C2H4 selectivity.

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

Elevated levels of carbon dioxide (CO2) in the atmosphere and the diminishing reserves of fossil fuels have raised profound concerns regarding the resulting consequences of global climate change and the future supply of energy. Hence, the reduction and transformation of CO2 not only mitigates environmental pollution but also generates value-added chemicals, providing a dual remedy to address both energy and environmental challenges. Despite notable advancements, the low conversion efficiency of CO2 remains a major obstacle, largely attributed to its inert chemical nature. It is imperative to engineer catalysts/materials that exhibit high conversion efficiency, selectivity, and stability for CO2 transformation. With unparalleled precision at the atomic level, atomic layer deposition (ALD) and molecular layer deposition (MLD) methods utilize various strategies, including ultrathin modification, overcoating, interlayer coating, area-selective deposition, template-assisted deposition, and sacrificial-layer-assisted deposition, to synthesize numerous novel metal-based materials with diverse structures. These materials, functioning as active materials, passive materials or modifiers, have contributed to the enhancement of catalytic activity, selectivity, and stability, effectively addressing the challenges linked to CO2 transformation. Herein, this review focuses on ALD and MLD's role in fabricating materials for electro-, photo-, photoelectro-, and thermal catalytic CO2 reduction, CO2 capture and separation, and electrochemical CO2 sensing. Significant emphasis is dedicated to the ALD and MLD designed materials, their crucial role in enhancing performance, and exploring the relationship between their structures and catalytic activities for CO2 transformation. Finally, this comprehensive review presents the summary, challenges and prospects for ALD and MLD-designed materials for CO2 transformation.

Soil processes modify the composition of volatile organic compounds (VOCs) from CO2- and CH4-dominated geogenic and landfill gases: A comprehensive study

Degradation mechanisms affecting non-methane volatile organic compounds (VOCs) during gas uprising from different hypogenic sources to the surface were investigated through extensive sampling surveys in areas encompassing a high enthalpy hydrothermal system associated with active volcanism, a CH4-rich sedimentary basin and a municipal waste landfill. For a comprehensive framework, published data from medium-to-high enthalpy hydrothermal systems were also included. The investigated systems were characterised by peculiar VOC suites that reflected the conditions of the genetic environments in which temperature, contents of organic matter, and gas fugacity had a major role. Differences in VOC patterns between source (gas vents and landfill gas) and soil gases indicated VOC transformations in soil. Processes acting in soil preferentially degraded high-molecular weight alkanes with respect to the low-molecular weight ones. Alkenes and cyclics roughly behaved like alkanes. Thiophenes were degraded to a larger extent with respect to alkylated benzenes, which were more reactive than benzene. Furan appeared less degraded than its alkylated homologues. Dimethylsulfoxide was generally favoured with respect to dimethylsulfide. Limonene and camphene were relatively unstable under aerobic conditions, while α-pinene was recalcitrant. O-bearing organic compounds (i.e., aldehydes, esters, ketones, alcohols, organic acids and phenol) acted as intermediate products of the ongoing VOC degradations in soil. No evidence for the degradation of halogenated compounds and benzothiazole was observed. This study pointed out how soil degradation processes reduce hypogenic VOC emissions and the important role played by physicochemical and biological parameters on the effective VOC attenuation capacity of the soil.

Cobalt catalyzed ethane dehydrogenation to ethylene with CO2: Relationships between cobalt species and reaction pathways

TiO2, ZrO2 and a series of TiO2-ZrO2 (TxZ1, x means the atomic ratio of Ti/Zr = 10, 5, 1, 0.2 and 0.1) composite oxide supports were prepared through co-precipitation, and then 3 wt% Co was loaded through wetness impregnation methods. The obtained 3 wt% Co/TiO2 (3CT), 3 wt% Co/ZrO2 (3CZ) and 3 wt% Co/TxZ1 (3CTxZ1) catalysts were evaluated for the oxidative ethane dehydrogenation reaction with CO2 (CO2-ODHE) as a soft oxidant. 3CT1Z1 catalyst exhibits excellent catalytic properties, with C2H4 yield, C2H6 conversion and CO2 conversion about 24.5 %, 33.8 % and 18.0 % at 650 °C, respectively. X-Ray Diffraction (XRD), in-situ Raman, UV-vis diffuse reflectance spectra (UV-vis DRS), H2 temperature-programmed reduction (H2-TPR), Electron paramagnetic resonance (EPR) and quasi in-situ X-ray Photoelectron Spectroscopy (XPS) have been utilized to thoroughly characterize the investigated catalysts. The results revealed that 3CT1Z1 produced TiZrO4 solid solution with more metal defect sites and oxygen vacancies (Ov), promoting the formation of Co2+-TiZrO4 structure. Furthermore, the presence of Ov and Ti3+can facilitate the high dispersion and stabilization of Co2+, as well as suppressing the severe reduction of Co2+, leading to superior ethane oxidative dehydrogenation activity. Besides, less Co0 is beneficial to ODHE reaction, because of its promotion effects for reverse water gas shift reaction; however, more Co0 results in dry reforming reaction (DRE). This work will shed new lights for the design and preparation of highly efficient catalysts for ethylene production.

Reduction of Cofed Carbon Dioxide Modifies the Local Coordination Environment of Zeolite-Supported, Atomically Dispersed Chromium to Promote Ethane Dehydrogenation

The reduction of CO2 is known to promote increased alkene yields from alkane dehydrogenations when the reactions are cocatalyzed. The mechanism of this promotion is not understood in the context of catalyst active-site environments because CO2 is amphoteric, and even general aspects of the chemistry, including the significance of competing side reactions, differ significantly across catalysts. Atomically dispersed chromium cations stabilized in highly siliceous MFI zeolite are shown here to enable the study of the role of parallel CO2 reduction during ethylene-selective ethane dehydrogenation. Based on infrared spectroscopy and X-ray absorption spectroscopy data interpreted through calculations using density functional theory (DFT), the synthesized catalyst contains atomically dispersed Cr cations stabilized by silanol nests in micropores. Reactor studies show that cofeeding CO2 increases stable ethylene-selective ethane dehydrogenation rates over a wide range of partial pressures. Operando X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectra indicate that during reaction at 650 °C the Cr cations maintain a nominal 2+ charge and a total Cr-O coordination number of approximately 2. However, CO2 reduction induces a change, correlated with the CO2 partial pressure, in the population of two distinct Cr-O scattering paths. This indicates that the promotional effect of parallel CO2 reduction can be attributed to a subtle change in Cr-O bond lengths in the local coordination environment of the active site. These insights are made possible by simultaneously fitting multiple EXAFS spectra recorded in different reaction conditions; this novel procedure is expected to be generally applicable for interpreting operando catalysis EXAFS data.

Explainable machine-learning predictions for catalysts in CO2-assisted propane oxidative dehydrogenation

Propylene is an important raw material in the chemical industry that needs new routes for its production to meet the demand. The CO2-assisted oxidative dehydrogenation of propane (CO2-ODHP) represents an ideal way to produce propylene and uses the greenhouse gas CO2. The design of catalysts with high efficiency is crucial in CO2-ODHP research. Data-driven machine learning is currently of great interest and gaining popularity in the heterogeneous catalysis field for guiding catalyst development. In this study, the reaction results of CO2-ODHP reported in the literature are combined and analyzed with varied machine learning algorithms such as artificial neural network (ANN), k-nearest neighbors (KNN), support vector regression (SVR) and random forest regression (RF)and were used to predict the propylene space-time yield. Specifically, the RF method serves as a superior performing algorithm for propane conversion and propylene selectivity prediction, and SHapley Additive exPlanations (SHAP) based on the Shapley value performs fine model interpretation. Reaction conditions and chemical components show different impacts on catalytic performance. The work provides a valuable perspective for the machine learning in light alkane conversion, and helps us to design catalyst by catalytic performance hidden in the data of literatures.

Hydrogen Spillover Accelerates Electrocatalytic Semi-hydrogenation of Acetylene in Membrane Electrode Assembly Reactor

Electrocatalytic acetylene semi-hydrogenation (EASH) offers a promising and environmentally friendly pathway for the production of C2H4, a widely used petrochemical feedstock. While the economic feasibility of this route has been demonstrated in three-electrode systems, its viability in practical device remains unverified. In this study, we designed a highly efficient electrocatalyst based on a PdCu alloy system utilizing the hydrogen spillover mechanism. The catalyst achieved an operational current density of 600 mA cm-2 in a zero-gap membrane electrode assembly (MEA) reactor, with the C2H4 selectivity exceeding 85%. This data confirms the economic feasibility of EASH in real-world applications. Furthermore, through in situ Raman spectroscopy and theoretical calculations, we elucidated the catalytic mechanism involving interfacial hydrogen spillover. Our findings underscore the economic viability and potential of EASH as a greener and scalable approach for C2H4 production, thus advancing the field of electrocatalysis in sustainable chemical synthesis.

Atomically synergistic Zn-Cr catalyst for iso-stoichiometric co-conversion of ethane and CO2 to ethylene and CO

Developing atomically synergistic bifunctional catalysts relies on the creation of colocalized active atoms to facilitate distinct elementary steps in catalytic cycles. Herein, we show that the atomically-synergistic binuclear-site catalyst (ABC) consisting of [Formula: see text]-O-Cr6+ on zeolite SSZ-13 displays unique catalytic properties for iso-stoichiometric co-conversion of ethane and CO2. Ethylene selectivity and utilization of converted CO2 can reach 100 % and 99.0% under 500  °C at ethane conversion of 9.6%, respectively. In-situ/ex-situ spectroscopic studies and DFT calculations reveal atomic synergies between acidic Zn and redox Cr sites. [Formula: see text] ([Formula: see text]) sites facilitate β-C-H bond cleavage in ethane and the formation of Zn-Hδ- hydride, thereby the enhanced basicity promotes CO2 adsorption/activation and prevents ethane C-C bond scission. The redox Cr site accelerates CO2 dissociation by replenishing lattice oxygen and facilitates H2O formation/desorption. This study presents the advantages of the ABC concept, paving the way for the rational design of novel advanced catalysts.

Photocatalytic ethane conversion on rutile TiO2(110): identifying the role of the ethyl radical

Oxidative dehydrogenation of ethane (C2H6, ODHE) is a promising approach to producing ethene (C2H4) in the chemical industry. However, the ODHE needs to be operated at a high temperature, and realizing the ODHE under mild conditions is still a big challenge. Herein, using photocatalytic ODHE to obtain C2H4 has been achieved successfully on a model rutile(R)-TiO2(110) surface with high selectivity. Initially, the C2H6 reacts with hole trapped OTi- centers to produce ethyl radicals , which can be precisely detected by a sensitive TOF method, and then the majority of the radicals spontaneously dehydrogenate into C2H4 without another photo-generated hole. In addition, parts of the radicals rebound with diversified surface sites to produce C2 products via migration along the surface. The mechanistic model built in this work not only advances our knowledge of the C-H bond activation and low temperature C2H6 conversion, but also provides new opportunities for realizing the ODHE with high C2H4 efficiency under mild conditions.

Site Diversity and Mechanism of Metal-Exchanged Zeolite Catalyzed Non-Oxidative Propane Dehydrogenation

Metal-exchanged zeolites are well-known propane dehydrogenation (PDH) catalysts; however, the structure of the active species remains unresolved. In this review, existing PDH catalysts are first surveyed, and then the current understanding of metal-exchanged zeolite catalysts is described in detail. The case of Ga/H-ZSM-5 is employed to showcase that advances in the understanding of structure-activity relations are often accompanied by technological or conceptional breakthroughs. The understanding of Ga speciation at PDH conditions has evolved owing to the advent of in situ/operando characterizations and to the realization that the local coordination environment of Ga species afforded by the zeolite support has a decisive impact on the active site structure. In situ/operando quantitative characterization of catalysts, rigorous determination of intrinsic reaction rates, and predictive computational modeling are all significant in identifying the most active structure in these complex systems. The reaction mechanism could be both intricately related to and nearly independent of the details of the assumed active structure, as in the two main proposed PDH mechanisms on Ga/H-ZSM-5, that is, the carbenium mechanism and the alkyl mechanism. Perspectives on potential approaches to further elucidate the active structure of metal-exchanged zeolite catalysts and reaction mechanisms are discussed in the final section.

CO2-Assisted Dehydrogenation of Propane to Propene over Zn-BEA Zeolites: Impact of Acid–Base Characteristics on Catalytic Performance

Research results about the influence of BEA zeolite preliminary dealumination on the acid–base characteristics and catalytic performance of 1% Zn-BEA compositions in propane dehydrogenation with CO2 are presented. The catalyst samples, prepared through a two-step post-synthesis procedure involving partial or complete dealumination of the BEA specimen followed by the introduction of Zn2+ cations into the T-positions of the zeolite framework, were characterized using XRD, XPS, MAS NMR, SEM/EDS, low-temperature N2 ad/desorption, C3H8/C3H6 (CO2, NH3)-TPD, TPO-O2, and FTIR-Py techniques. Full dealumination resulted in the development of a mesoporous structure and specific surface area (BET) with a twofold decrease in the total acidity and basicity of Zn-BEA, and the formation of Lewis acid sites and basic sites of predominantly medium strength, as well as the removal of Brønsted acid sites from the surface. In the presence of the ZnSiBEA catalyst, which had the lowest total acidity and basicity, the obtained selectivity of 86–94% and yield of 30–33% for propene (at 923 K) exceeded the values for ZnAlSiBEA and ZnAlBEA. The results of propane dehydrogenation with/without carbon dioxide showed the advantages of producing the target olefin in the presence of CO2 using Zn-BEA catalysts.

Metallic Catalysts for Oxidative Dehydrogenation of Propane Using CO2

The oxidative dehydrogenation of propane using CO₂ (CO₂ -ODP) is a promising technique for realizing high-yield propylene production and CO₂ usage. Developing a highly efficient catalyst for CO₂ -ODP is essential and beneficial to the chemical industry and for realizing net-zero emissions. Many studies have investigated metal oxide-based catalysts, revealing that rapid deactivation and low selectivity remain limiting factors for their industrial applications. In recent years, metallic nanoparticle catalysts have become increasingly attractive due to their unique properties. Therefore, we summarize the performance of metal-based catalysts in CO₂ -ODP reactions by considering catalyst design concepts, different mechanisms in the reaction process, and the role of CO₂ .

Light olefin synthesis from a diversity of renewable and fossil feedstocks: state-of the-art and outlook

Light olefins are important feedstocks and platform molecules for the chemical industry. Their synthesis has been a research priority in both academia and industry. There are many different approaches to the synthesis of these compounds, which differ by the choice of raw materials, catalysts and reaction conditions. The goals of this review are to highlight the most recent trends in light olefin synthesis and to perform a comparative analysis of different synthetic routes using several quantitative characteristics: selectivity, productivity, severity of operating conditions, stability, technological maturity and sustainability. Traditionally, on an industrial scale, the cracking of oil fractions has been used to produce light olefins. Methanol-to-olefins, alkane direct or oxidative dehydrogenation technologies have great potential in the short term and have already reached scientific and technological maturities. Major progress should be made in the field of methanol-mediated CO and CO₂ direct hydrogenation to light olefins. The electrocatalytic reduction of CO₂ to light olefins is a very attractive process in the long run due to the low reaction temperature and possible use of sustainable electricity. The application of modern concepts such as electricity-driven process intensification, looping, CO₂ management and nanoscale catalyst design should lead in the near future to more environmentally friendly, energy efficient and selective large-scale technologies for light olefin synthesis.

Bimetallic Exsolved Heterostructures of Controlled Composition with Tunable Catalytic Properties

In this paper, we show how the composition of bimetallic Fe-Ni exsolution can be controlled by the nature and concentration of oxygen vacancies in the parental matrix and how this is used to modify the performance of CO₂-assisted ethane conversion. Mesoporous A-site-deficient La_0.4Sr_0.6-αTi_0.6Fe_0.35Ni_0.05O_3±δ (0 ≤ α ≤ 0.2) perovskites with substantial specific surface area (>40 m²/g) enabled fast exsolution kinetics (T < 500 °C, t < 1 h) of bimetallic Fe-Ni nanoparticles of increasing size (3-10 nm). Through the application of a multitechnique approach we found that the A-site deficiency determined the concentration of oxygen vacancies associated with iron, which controlled the Fe reduction. Instead of homogeneous bimetallic nanoparticles, the increasing Fe fraction from 37 to 57% led to the emergence of bimodal Fe/Ni₃Fe systems. Catalytic tests showed superior stability of our catalysts with respect to commercial Ni/Al₂O₃. Ethane reforming was found to be the favored pathway, but an increase in selectivity toward ethane dehydrogenation occurred for the systems with a low metallic Fe fraction. The chance to control the reduction and growth processes of bimetallic exsolution offers interesting prospects for the design of advanced catalysts based on bimodal nanoparticle heterostructures.

Research progress of CO2 oxidative dehydrogenation of propane to propylene over Cr-free metal catalysts

CO₂-assisted oxidative dehydrogenation of propane (CO₂-ODHP) is an attractive strategy to offset the demand gap of propylene due to its potentiality of reducing CO₂ emissions, especially under the demands of peaking CO₂ emissions and carbon neutrality. The introduction of CO₂ as a soft oxidant into the reaction not only averts the over-oxidation of products, but also maintains the high oxidation state of the redox-active sites. Furthermore, the presence of CO₂ increases the conversion of propane by coupling the dehydrogenation of propane (DHP) with the reverse water gas reaction (RWGS) and inhibits the coking formation to prolong the lifetime of catalysts via the reverse Boudouard reaction. An effective catalyst should selectively activate the C-H bond but suppress the C-C cleavage. However, to prepare such a catalyst remains challenging. Chromium-based catalysts are always applied in industrial application of DHP; however, their toxic properties are harmful to the environment. In this aspect, exploring environment-friendly and sustainable catalytic systems with Cr-free is an important issue. In this review, we outline the development of the CO₂-ODHP especially in the last ten years, including the structural information, catalytic performances, and mechanisms of chromium-free metal-based catalyst systems, and the role of CO₂ in the reaction. We also present perspectives for future progress in the CO₂-ODHP.

Ethane oxidative dehydrogenation with CO2 on thiogallates

The CO2-assisted oxidative dehydrogenation of ethane (ODH-CO2) attracts a lot of research interest since it combines greenhouse gas utilization with the production of valuable chemicals.

Screening of Adsorbent/Catalyst Composite Monoliths for Carbon Capture-Utilization and Ethylene Production

Combining CO₂ adsorption and utilization in oxidative dehydrogenation of ethane (ODHE) into a single bed is an exciting way of converting a harmful greenhouse gas into marketable commodity chemicals while reducing energy requirements from two-bed processes. However, novel materials should be developed for this purpose because most adsorbents are incapable of capturing CO₂ at the temperatures required for ODHE reactions. Some progress has been made in this area; however, previously reported dual-functional materials (DFMs) have always been powdered-state composites and no efforts have been made toward forming these materials into practical contactors. In this study, we report the first-generation of structured DFM adsorbent/catalyst monoliths for combined CO₂ capture and ODHE utilization. Specifically, we formulated M-CaO/ZSM-5 monoliths (M = In, Ce, Cr, or Mo oxides) by 3D-printing inks with CaCO₃ (CaO precursor), insoluble metal oxides, and ZSM-5. The physiochemical properties of the monoliths were vigorously characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N₂ physisorption, elemental mapping, pyridine Fourier transform infrared spectroscopy (Py-FTIR), H₂-temperature-programmed reduction (H₂-TPR), and NH₃-temperature-programmed desorption (NH₃-TPD). Their performances for combined CO₂ adsorption at 600 °C and ODHE reaction at 700 °C under 25 mL/min of 7% C₂H₆ were then investigated. The combined adsorption/catalysis experiments revealed the best performance in Cr-CaO/ZSM-5, which achieved 56% CO₂ conversion, 91.2% C₂H₄ selectivity, and 33.8% C₂H₄ yield. This exceptional performance, which was improved from powdered-state DFMs, was attributed to the high acidity and numerous oxidation states of the Cr₂O₃ dopant which were verified by NH₃-TPD and H₂-TPR. Overall, this study reports the first-ever proof-of-concept for 3D-printed DFM adsorbent/catalyst materials and furthers the area of CO₂ capture and ODHE utilization by providing a simple pathway to structure these composites.

Waste to energy conversion for a sustainable future

Air pollution, climate change, and plastic waste are three contemporary global concerns. Air pollutants affect the lungs, green gases trap heat radiation, and plastic waste contaminates the marine food chain. Two-thirds of climate change and air pollution drivers are emitted in the process of burning fossil fuels. Pollutants settle in months, green gases take centuries, and plastics take thousands of years. The most polluted regions on the planet are also the ones that are greatly affected by climate change. Air pollutants grow in most climate-change affected areas, contributing to the greenhouse effect. Smog affects local and regional transboundary countries. The biggest greenhouse gas (GHG) emitters may not be the worst-hit victims because wind and water flow distribute green gases and plastic waste worldwide. The major polluters are often rich and developed countries, and the worst affected countries are the underdeveloped poor communities. Technologically advanced countries may help the developing countries in research into removing particulate matter, green gases, and plastic waste. Intergovernmental Panel on Climate Change (IPCC) and Paris Accord have emphasized on immeasurable efforts to encourage the conversion of pollution, green gases, and plastic waste into energy. Conversion of CO₂ into petrol, GHG gases into chemicals, biowaste into biofuels, plastic waste into building bricks, and concrete waste into construction materials fosters a circular economy. This work reviews existing waste to power, energy, and value-added product conversion technologies.

Conversion of CO2 and small alkanes to platform chemicals over Mo2C-based catalysts

The performance of Mo2C-based catalysts in CO2 assisted oxidative dehydrogenation (CO2-ODH) of ethane was evaluated. Mo2C on SiO2 was synthesized via three different techniques: wet impregnation (WI), hybrid nanocrystal technique (HNC) and sol-gel method (SG) and exposed to the same carburization conditions. In terms of characteristic properties, the allotrope composition was the most affected, with the SG sample containing MoOxCy and the WI and HNC samples containing β-Mo2C. The two different allotropes were suggested to follow different reaction pathways, leading to small differences in the catalytic performance. However, overall, all three catalysts showed a decrease in activity (below 6%) and an increase in C2H4 selectivity (from 60 to 80 C%) with time on stream (TOS). The deactivation mechanism was suggested to be mainly due to oxidation of the carbide to MoOx and carbon deposition. Mo2C was also supported on various metal oxide materials via the wet impregnation technique. Mo2C supported on Al2O3 and ZrO2 increased initial activity (about 8% C2H6 conversion) but a faster deactivation with TOS was observed. Mo2C/Ga2O3 favoured the direct dehydrogenation reaction achieving high C2H4 selectivities (above 80 C%), but deactivation with TOS due to carbon deposition was significant. Mo2C supported on CeO2 and TiO2 had lower activity (about 3% C2H6 conversion). Oxidation to MoO2 and carbon deposition is again suggested to be the main deactivation mechanism. H2 co-feeding, on Mo2C/SiO2 and Mo2C/ZrO2, increased the stability of the catalysts but C2H4 yield was affected (from 5 to 2%). At 17 vol% H2 co-feeding, Mo2C/ZrO2 showed promising catalyst stability over a 20 h period, paralleled by a stable C2H4 yield.