Selective Catalysts Research Articles

Electrochemical CO2Reduction Reaction: Comprehensive Strategic Approaches to Catalyst Design for Selective Liquid Products Formation.

The escalating concern regarding the release of CO2 into the atmosphere poses a significant threat to the contemporary efforts in mitigating climate change. Amidst a multitude of strategies for curtailing CO2 emissions, the electrochemical CO2 reduction presents a promising avenue for transforming CO2 molecules into a diverse array of valuable gaseous and liquid products, such as CO, CH3OH, CH4, HCO2H, C2H4, C2H5OH, CH3CO2H, 1-C3H7OH and others. The mechanistic investigations of gaseous products (e.g. CO, CH4, C2H4, C2H6 and others) broadly covered in the literature. There is a noticeable gap in the literature when it comes to a comprehensive summary exclusively dedicated to coherent roadmap for the designing principles for a selective catalyst all possible liquid products (such as CH3OH, C2H5OH, 1-C3H7OH, 2-C3H7OH, 1-C4H9OH, as well as other C3-C4 products like methylglyoxal and 2,3-furandiol, in addition to HCO2H, AcOH, oxalic acid and others), selectively converted by CO2 reduction. This entails a meticulous analysis to justify these approaches and a thorough exploration of the correlation between materials and their electrocatalytic properties. Furthermore, these insightful discussions illuminate the future prospects for practical applications, a facet not exhaustively examined in prior reviews.

VO Supported on Functionalized CNTs for Oxidative Conversion of Furfural to Maleic Anhydride

Commercial non-functionalized (CNTs) and functionalized carbon nanotubes (CNT-COOH and CNT-NH2) were used as supports to synthesize vanadium-supported catalysts to be used in the gas phase partial oxidation of furfural towards maleic anhydride (MA). The CNTs and the VO2-V2O5/CNTs, so-called VO/CNT catalysts, were characterized by AAS, TGA, XRD, N2 adsorption isotherms at −196 °C, Raman, NH3-TPD and XPS. The surface area values, TGA and XRD results indicate that the larger thermal stability and larger dispersion of vanadium species is reached for the VO/CNT-NH2 catalyst. XPS indicates presence of surface VO2 and V2O5 species for the non-functionalized (CNT) and functionalized (CNT-COOH and CNT-NH2) catalysts, with a large interaction of the functional group with the surface vanadium species only for the VO/CNT-NH2 catalyst. The catalytic activity, evaluated in the range 305 °C to 350 °C, indicates that CO, CO2 and MA yield (%) and MA productivity are associated to the redox properties of the vanadium species, the oxygen exchange ability of the support and the vanadium–support interaction. For the reaction temperatures between 320 °C and 335 °C, the maximum MA yield (%) is found in the functionalized VO/CNT-COOH and VO/CNT-NH2 catalysts. This behavior is attributed to a decreased oxidation capability of the CNT with the functionalization. In addition, VO/CNT-NH2 is the more active and selective catalyst for MA productivity at 305 °C and 320 °C, which is related to the greater interaction of the surface vanadium species with the -NH2 group, which enhances the redox properties and stabilization of the VO2 and V2O5 surface active sites. Recycling at 350 °C resulted in 100% furfural conversion for all catalysts and a similar MA yield (%) compared to the fresh catalyst, indicating no loss of surface active sites.

Nitrogen-Tungsten Oxide Nanostructures on Nickel Foam as High Efficient Electrocatalysts for Benzyl Alcohol Oxidation.

Electrocatalytic alcohol oxidation (EAO) is an attractive alternative to the sluggish oxygen evolution reaction in electrochemical hydrogen evolution cells. However, the development of high-performance bifunctional electrocatalysts is a major challenge. Herein, we developed a nitrogen-doped bimetallic oxide electrocatalyst (WO-N/NF) by a one-step hydrothermal method for the selective electrooxidation of benzyl alcohol to benzoic acid in alkaline electrolytes. The WO-N/NF electrode features block-shaped particles on a rough, inhomogeneous surface with cracks and lumpy nodules, increasing active sites and enhancing electrolyte diffusion. The electrode demonstrates exceptional activity, stability, and selectivity, achieving efficient benzoic acid production while reducing the electrolysis voltage. A low onset potential of 1.38 V (vs. RHE) is achieved to reach a current density of 100 mA cm-2 in 1.0 M KOH electrolyte with only 0.2 mmol of metal precursors, which is 396 mV lower than that of water oxidation. The analysis reveals a yield, conversion, and selectivity of 98.41%, 99.66%, and 99.74%, respectively, with a Faradaic efficiency of 98.77%. This work provides insight into the rational design of a highly active and selective catalyst for electrocatalytic alcohol oxidation.

Eley−Rideal path enhanced NH3-SCR: Central Fe atoms activation for electron transfer promotion

Manganese modified Fe2O3 catalyst is a promising candidate to replace the commercial NH3-SCR catalyst for controlling NOx emission due to its superior performance and N2 selectivity at low temperature. In order to elucidate the effects of different modification methods of Mn on physicochemical properties and reaction mechanism in Fe-Mn binary catalysts, two kinds of Mn modified Fe2O3 are prepared by co-precipitation and impregnation method, respectively. Compared with MnO2 loaded Fe2O3, Mn doped Fe2O3 achieves above 85 % of NOx conversion with 20 % increase in N2 selectivity within 100–200°C. Transient reaction experiments and DFT calculation results prove that doping Mn effectively increases the reaction rate of the main reaction and reduces the formation of N2O through Eley−Rideal path. The formation of multiple Fe-O-Mn structures after Mn doping facilities the formation of coordination bond between the central Fe atoms and NH3 via modulating local charge density of Fe atoms, effectively improving the adsorption of NH3 and preventing its excessive oxidation, which leads to high activity and N2 selectivity at low temperature. This mechanism provides theoretical support for increasing the activity and N2 selectivity of NH3-SCR catalysts at low temperature and gains clear insight on the interaction between binary metal oxides.

Enhancing Localized Electron Density over Pd1.4Cu Decorated Oxygen Defective TiO2-x Nanoarray for Electrocatalytic Nitrite Reduction to Ammonia.

Electrocatalytic nitrite (NO2 -) reduction to ammonia (NH3) is a promising method for reducing pollution and aiding industrial production. However, progress is limited by the lack of efficient selective catalysts and ambiguous catalytic mechanisms. This study explores the loading of PdCu alloy onto oxygen defective TiO2-x, resulting in a significant increase in NH3 yield (from 70.6 to 366.4µmolcm-2h-1 at -0.6V vs reversible hydrogen electrode) by modulating localized electron density. In situ and operando studies illustrate that the reduction of NO2 - to NH3 involves gradual deoxygenation and hydrogenation. The process also demonstrated excellent selectivity and stability, with long-term durability in cycling and 50h stability tests. Density functional theory (DFT) calculations elucidate that the introduction of PdCu alloys further amplified electron density at oxygen vacancies (Ovs). Additionally, the Ti─O bond is strengthened as the d-band center of the Ti 3d rising after PdCu loading, facilitating the adsorption and activation of *NO2. Moreover, the presence of Ovs and PdCu alloy lowers the energy barriers for deoxygenation and hydrogenation, leading to high yield and selectivity of NH3. This insight of controlling localized electron density offers valuable insights for advancing sustainable NH3 synthesis methods.

Highly Selective O-Phenylene Bisurea Catalysts for ROP: Stabilization of Oxyanion Transition State by a Semiflexible Hydrogen Bond Pocket.

Organocatalyzed ring-opening polymerization (ROP) is a versatile technique for synthesizing biodegradable polymers, including polyesters and polycarbonates. We introduce o-phenylene bisurea (OPBU) (di)anions as a novel class of organocatalysts that are fast, easily tunable, mildly basic, and exceptionally selective. These catalysts surpass previous generations, such as thiourea, urea, and TBD, in selectivity (kp/ktr) by 8 to 120 times. OPBU catalysts facilitate the ROP of various monomers, achieving high conversions (>95%) in seconds to minutes, producing polymers with precise molecular weights and very low dispersities (Đ ≈ 1.01). This performance nearly matches the ideal distribution expected from living polymerization (Poisson distribution). Density functional theory (DFT) calculations reveal that the catalysts stabilize the oxyanion transition state via a hydrogen bond pocket similar to the "oxyanion hole" in enzymatic catalysis. Both experimental and theoretical analyses highlight the critical role of the semirigid o-phenylene linker in creating a hydrogen bond pocket that is tight yet flexible enough to accommodate the oxyanion transition state effectively. These new insights have provided a new class of organic catalysts whose accessibility, moderate basicity, excellent solubility, and unparalleled selectivity and tunability open up new opportunities for controlled polymer synthesis.

Machine Learning Big Data Set Analysis Reveals C-C Electro-Coupling Mechanism.

Carbon-carbon (C-C) coupling is essential in the electrocatalytic reduction of CO2 for the production of green chemicals. However, due to the complexity of the reaction network, there remains controversy regarding the underlying reaction mechanisms and the optimal direction for catalyst material design. Here, we present a global perspective to establish a comprehensive data set encompassing all C-C coupling precursors and catalytic active site compositions to explore the reaction mechanisms and screen catalysts via big data set analysis. The 2D-3D ensemble machine learning strategy, developed to target a variety of adsorption configurations, can quickly and accurately expand quantum chemical calculation data, enabling the rapid acquisition of this extensive big data set. Analyses of the big data set establish that (1) asymmetric coupling mechanisms exhibit greater potential efficiency compared to symmetric coupling, with the optimal path involving the coupling CHO with CH or CH2, and (2) C-C coupling selectivity of Cu-based catalysts can be enhanced through bimetallic doping including CuAgNb sites. Importantly, we experimentally substantiate the CuAgNb catalyst to demonstrate actual boosted performance in C-C coupling. Our finding evidence the practicality of our big data set generated from machine learning-accelerated quantum chemical computations. We conclude that combining big data with complex catalytic reaction mechanisms and catalyst compositions will set a new paradigm for accelerating optimal catalyst design.

MOFs-derived CuCeOx supported on H-zeolite socony mobile-5 for catalytic oxidation of 1,2-dichlorobenzene

The catalytic elimination of chlorinated aromatic hydrocarbons is the frontier of catalytic oxidation of organic pollutants, and the screen of efficient catalysts (low cost, high activity, durability and selectivity) remains challenging. In this work, the CuCeOx derived from metal-organic frameworks supported on H-zeolite socony mobile-5 (HZSM-5) complex catalyst (CuCeOx-H-C) was prepared through impregnation combined with pyrolysis and applied in the catalytic oxidation of 1,2-dichlorobenzene. The results indicate that the introduction of carboxyl groups on the surface of HZSM-5 is crucial for the formation of Ce-MOF/HZSM-COOH core–shell structure. This introduction facilitates the uniform deposition of CuCeOx on HZSM-5 and significantly enhances the overall acidity. Furthermore, the synergistic effect of Cu-Ce significantly enhanced the catalyst’s activity at low temperatures. Therefore, CuCeOx-H-C exhibited the highest activity, with a T90 of 236 °C. Additionally, the CuCeOx-H-C catalyst showed high selectivity for HCl and suppressed the generation of chlorinated by-products. The differences in catalyst activity among various catalysts arise from multiple factors, including specific surface area, dispersion of active species, oxygen mobility, oxygen storage capacity, redox properties, and others. Under the synergetic effects of above-mentioned factors, the activity of CuCeOx-H-C is remarkably enhanced and would be promising for potential industrial application.

Accelerated thioanisole oxidation using partially β-brominated Cobalt(II) porphyrin heterogenized within UiO-66 scaffold

Heterogenization of a partially β-brominated cobalt (II) tetraphenylporphyrin complex (CoIITPPBr4) within the cavities of an UiO-66 (UiO stands for Universitetet i Oslo) metal-organic framework (MOF) using bottle-around-ship (BAS) strategy resulted in the formation of highly selective recoverable biomimetic catalyst (CoIITPPBr4@UiO-66). Integrating partial β-bromination with entrapment within the MOF host improved the porphyrin complex's stability and efficiency while preventing its deactivation owing to self-destruction. Under the influence of a heterogenized catalyst with a low active component loading, the selective oxidation of thioanisole (PhSMe) to methyl phenyl sulfoxide (PhSOMe) by hydrogen peroxide (H2O2) in acetonitrile (MeCN) solvent in the presence of imidazole (ImH) co-catalyst and acetic anhydride (Ac2O) activator was expedited significantly with an outstanding conversion (96.01 %) and selectivity (100 %). Also, the utilization of diverse analysis techniques verified the efficacious fabrication, as well as the stability and recyclability of the catalyst after four catalytic cycles.

Bimetallic NiSn supported on mesoporous carbon as an efficient catalyst for selective methanol synthesis from CO2

Global warming and climate change represent the most significant environmental challenges of the 21st century, primarily attributed to the rise in CO2 emission in the atmosphere. Efforts to mitigate this increase involve exploring various methods to reduce CO2 levels, with chemical reactions, such as hydrogenation, being a prominent approach. However, the stable and inert nature of CO2 necessitates the use of catalysts to facilitate its conversion. In this research, NiSn nanoparticles with varying atomic ratios were deposited onto a mesoporous carbon support and subsequently utilized as catalysts for CO2 conversion through hydrogenation reactions at ambient pressure. The diffraction patterns of NiSn/MC reveal peaks indicating the presence of a graphitic carbon structure and the existence of a nickel-tin alloy. SEM-EDX mapping and TEM characterization demonstrate the uniform dispersion of NiSn particles on the mesoporous carbon surface, without the formation of agglomerated particles. Catalytic hydrogenation reactions indicate that the atomic ratio of Ni:Sn significantly influences the catalyst activity and selectivity for methanol formation. Among the NixSny/MC catalysts and monometallic Ni/MC, Sn/MC, and NiSn NPs without support, Ni5Sn1/MC demonstrated the highest CO2 conversion of 39.9 %. Additionally, at a reaction temperature of 175 °C and a CO2:H2 gas ratio of 1:7, Ni5Sn1/MC exhibited a methanol yield of 86.31 mmol/gcat, outperforming other catalysts in the study.

ZSM-5-Based Catalyst Structure Design and Selectivity Control for Liquid Hydrocarbon Formation: A Mini Review

The selectivity limitation has long posed a significant challenge in the conversion of CO or CO2 into liquid hydrocarbon-based sustainable fuels via Fischer–Tropsch synthesis (FTS) and other related processing pathways due to the Anderson–Schulz–Flory (ASF) distribution. The unique pore structure, thermal stability, and acidic sites of ZSM-5 have enabled its widespread applications in various catalytic processes of value-added chemicals and sustainable fuels. In the reaction pathways from CO/CO2 to liquid HCs of interest, incorporating ZSM-5 into metal catalysts provides new opportunities to enhance product selectivity and catalytic activity, and even lower the reaction energetics. This review highlights recent advancements over the past five years in the structural design of ZSM-5-based catalysts aimed at improving the conversion selectivity of advanced liquid biofuels such as renewable diesel and sustainable aviation fuel. It explores innovative strategies for optimizing catalyst composition, the acidity, mesoporosity, and structures of ZSM-5 to design more efficient, selective, and robust catalysts. Additionally, the review addresses the direct hydrogenation of CO and CO2 into C5+ liquid hydrocarbons, focusing on catalyst selection, acidic site optimization, and the structural configuration of ZSM-5. The mechanisms involved in these processes are also surveyed.

Error Awareness in the Volcano Plots of Oxygen Electroreduction to Hydrogen Peroxide.

Electrocatalysis holds the key to the decentralized production of hydrogen peroxide via the two-electron oxygen reduction reaction (ORR, O2g+2H++e-→H2O2aq). However, cost-effective, active, and selective catalysts are still sought after. While density functional theory (DFT) has already led to the discovery of various enhanced catalysts, it has a severe yet often unnoticed drawback: the ill description of O2 and H2O2. Here, we analyze the impact of the errors in those two species on the most widespread activity plots in the literature, namely free-energy diagrams and Sabatier-type volcano plots. Uncorrected or partially corrected gas-phase energies lead to appreciably different activity plots that may provide inaccurate predictions. Indeed, we show for a variety of electrocatalysts that only when the errors in O2 and H2O2 are corrected can DFT mimic the experiments. In sum, this work provides concrete guidelines to avoid a common pitfall of computational models for electrocatalytic hydrogen peroxide production.

Enhancing Water Tolerance and N2 Selectivity in NH3-SCR Catalysts by Protecting Mn Oxide Nanoparticles in a Silicalite-1 Layer.

Mn-based catalysts are promising candidates for eliminating harmful nitrogen oxides (NOx) via selective catalytic reduction with ammonia (NH3-SCR) due to their inherent strong redox abilities. However, poor water tolerance and low N2 selectivity are still the main limitations for practical applications. Herein, we succeeded in preparing an active catalyst for NH3-SCR with improved water tolerance and N2 selectivity based on protecting MnOx with a secondary growth of a hydrophobic silicalite-1. This protection suppressed catalyst deactivation by water adsorption. Interestingly, impregnating MnOx on MesoTS-1 followed by silicalite-1 protection allowed for a higher dispersion of MnOx species, thus increasing the concentration of acid sites. Consequently, the level of N2O formation is decreased. These improvements resulted in a broader operating temperature of NOx conversion and a modification of the NH3-SCR mechanism. Diffuse reflectance infrared Fourier transform spectroscopy analysis revealed that unprotected Mn/MesoTS-1 mainly followed the Eley-Rideal mechanism, while Mn/MesoTS-1@S1 followed both Langmuir-Hinshelwood and Eley-Rideal mechanisms.

Electrons redistribution of palladium-copper nanoclusters boosting the direct oxidation of methane to methanol

The direct oxidation of methane to methanol (DOMM) at mild conditions is an enormous attractive yet highly challenging, which is known as the “Holy Grail” reaction. In this work, we prepare the PdxCuy NCs supported on mesoporous sulfur-carbon materials and investigate their catalytic DOMM performance. The Pd14Cu1 NCs exhibits the excellent DOMM performance with the productivity of 34.3 mmol g−1 h−1 and the selectivity of 92.3 % at 150 °C when H2/O2 as active oxygen species, which was obviously superior to other PdCu catalysts. The enhanced performance of Pd14Cu1 NCs in DOMM is attributed to the non-crystalline atomic arrangement of tiny cluster structures and the synergistic electronic effect between Pd and Cu atoms, which can reduce the desorption temperature for methane, improve the in-situ generation of H2O2, and provide more active oxygen. The time-resolved in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrated that a radical-involved reaction pathway on Pd14Cu1 NC. This work provides the understanding for synergistic effect dual metallic and helps to design highly efficient and selective catalysts for the direct oxidation of CH4.

Trends in the hydricities of iron, cobalt, and nickel complexes and the metal-hydride reactivities with CO2

Catalytic CO2 hydrogenation is considered one of the most efficient strategies for CO2 reduction, provided that we have efficient and selective catalysts. This paper explores a mass-spectrometric approach to rapidly compare the reactivities of 21 metal complexes (iron, cobalt, and nickel complexes with three bidentate N,N′-ligands and four bidentate P,P′-ligands) by energy-resolved MS/MS experiments. The experiments show relative hydricities of these complexes, singling out iron complexes with N,N′-ligands and cobalt complexes with P,P′-ligands as particularly reactive for hydride-donor reactions. Comparing these results with relative affinities of metal hydrides for CO2 led to the conclusion that iron hydrides should be particularly suited for CO2 hydrogenation reactions. The results, however, cannot account for the effects of the polar reaction environment in the condensed phase.

Reduced Graphene Oxide-Magnetite for the Development of Highly Active, Selective and Methanol-Tolerant Pt Catalyst

Reduced Graphene Oxide-Magnetite for the Development of Highly Active, Selective and Methanol-Tolerant Pt Catalyst

Boosting and stabilizing the electrocatalytic reduction of carbon dioxide on Bi2O2CO3 via surface modification with p-aminobenzoic acid

In the realm of electrocatalytic CO2 reduction (ECR) reactions, the challenges of instability and self-reducibility present significant obstacles to the practical application of bismuth oxide-based catalysts. Herein, Bi2O3 pre-catalyst was synthesized and surface-modified with 4-aminobenzoic acid (PABA). Theoretical studies confirmed that PABA was effectively grafted through oxygen vacancies on the Bi2O3 surface, leading to electronic rearrangement. PABA efficiently prevented surface Bi3+ on Bi2O3 from self-reducing to Bi0 during the ECR reaction. The Bi2O3PABA pre-catalyst transformed into the active Bi2O2CO3PABA ECR catalyst via electrolyte mediation. A Faraday efficiency of 98.6 % for formate was achieved at −1.1 V vs. RHE, with a wide potential window of 800 mV. The current density reached 210 mA cm–2 in a 2×2 cm2 flow cell system. Theoretical calculations illustrate that PABA facilitates stabilizing the *OCHO intermediate, diminishing the adsorption barrier. These results may provide valuable insights for designing highly selective ECR catalysts through interface engineering.

Direct CO2 Hydrogenation over Bifunctional Catalysts to Produce Dimethyl Ether—A Review

Hydrogenation of CO2 represents a promising pathway for converting it into valuable hydrocarbons and clean fuels like dimethyl ether (DME). Despite significant research, several challenges persist, including a limited understanding of reaction mechanisms, thermodynamics, the necessity for catalyst design to enhance DME selectivity, and issues related to catalyst deactivation. The paper provides a comprehensive overview of recent studies from 2012 to 2023, covering various aspects of CO2 hydrogenation to methanol and DME. This review primarily focuses on advancing the development of efficient, selective, and stable innovative catalysts for this purpose. Recent investigations that have extensively explored heterogeneous catalysts for CO2 hydrogenation were summarized. A notable focus is on Cu-based catalysts modified with promoters such as Zn, Zr, Fe, etc. Additionally, this context delves into thermodynamic considerations, the impact of reaction variables, reaction mechanisms, reactor configurations, and recent technological advancements, such as 3D-printed catalysts. Furthermore, the paper examines the influence of different parameters on catalyst deactivation. The review offers insights into direct CO2 hydrogenation to DME and proposes paths for future investigation, aiming to address current challenges and advance the field.

A mini‐review of intensified synthesis of 1st and 2nd generation biofuels in the presence of perovskite catalysts

AbstractEnhancement of a sustainable environment through the choice of a selective catalyst with high activity, regeneration nature, and high stability is an important aspect to be focused on to achieve a high yield and maximum conversion of feedstock to biodiesel (1st generation biofuel), and also in the biomass valorization/pyrolysis (2nd generation biofuel synthesis). Depending on the nature of the catalyst and synthesis method adopted for biofuel production and biomass valorization, the variations in the process conditions, final yield, and conversion are varied accordingly. A prospective development and application of perovskite catalysts in the synthesis of 1st and 2nd generation biofuels using various process intensification strategies for the development of a clean and green environment is reviewed in this study. The synthesis of types of perovskite catalysts polycrystalline, nano‐sized, and powdered oxide are also discussed in this review. It is also concluded that, apart from other process parameters, molar ratio is one of the most influencing sensitive factors in the case of 1st generation biofuel synthesis, whereas during the production of 2nd generation biofuels, catalyst concentration and liquid–solid ratio are more significant process parameters that change based on the nature of the catalyst selected for the reaction.

SCR + ASC systems control by backward induction with adaptive grid and different disturbance scenarios

The purpose of this study is to enhance control strategies for selective catalytic reduction (SCR) and ammonia slip catalyst (ASC) systems, aiming to effectively reduce NOx emissions from automotive engines during realistic driving cycles. Despite the effectiveness of these after-treatment systems (ATS), their dynamic and non-linear characteristics present significant challenges in achieving precise control. Therefore, this research proposes a hybrid approach that combines backward induction (BI) as the primary optimization technique with model predictive control (MPC) framework for real-time application. The article introduces a reduced-state control-oriented model of the SCR + ASC system, which is embedded into the BI algorithm to calculate optimal control actions within a finite horizon. Additionally, it is proposed an alternative approach for adapting the grid of model states within the BI algorithm, effectively reducing the computational cost. This adjustment enables the algorithm to operate in real-time with near-optimal results, as confirmed by experimental validation. Lastly, the study explores how different degrees of knowledge regarding system disturbances impact the strategy’s performance, examining three distinct scenarios: constant prediction horizon, probabilistic description, and full knowledge of the prediction horizon.