Selective Catalysts Research Articles

Divergent Synthesis of Di‐ and Mono‐Alkylated Indoles via Tunable Iron‐Catalyzed Hydroarylation of Styrenes

AbstractWe report an iron‐catalyzed divergent synthesis of alkylated indoles based on precise control of the activation sites on indoles through the selection of catalysts. Using indoles and styrenes as starting materials, 3,5‐di‐alkylated indoles could be prepared selectively and directly for the first time by treating with a catalytic amount of Fe(OTf)3 and 3‐alkylated indoles were achieved exclusively by adding a catalytic amount of γ‐cyclodextrin as the cocatalyst with Fe(OTf)3. This simple method was demonstrated with 52 examples with high yields and broad functional group compatibilities.

Density functional theory-based screening of Ti4C3O2-loaded single atoms for efficient selective catalytic oxidation of formaldehyde

Indoor formaldehyde (HCHO) pollution poses a major risk to human health. Low-temperature catalytic oxidation is an effective method for HCHO removal. The high activity and selectivity of single atomic catalysts provide a possibility for the development of efficient non-precious metal catalysts. In this study, the most stable single-atom catalyst Ti–Ti4C3O2 was screened by density functional theory among many single atomic catalysts with two-dimensional (2D) monolayer Ti4C3O2 as the support. The computational results show that Ti–Ti4C3O2 is highly selective to HCHO and O2 in complex environments. The HCHO oxidation reaction pathways are proposed based on the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. According to the reaction energy and energy span models, the E-R mechanism has a lower maximum energy barrier and higher catalytic efficiency than the L-H mechanism. In addition, the stability of the Ti–Ti4C3O2 structure and active center was verified by diffusion energy barrier and ab initio molecular dynamics simulations. The above results indicate that Ti–Ti4C3O2 is a promising non-precious metal catalyst. The present study provides detailed theoretical insights into the catalytic oxidation of HCHO by Ti–Ti4C3O2, as well as an idea for the development of efficient non-precious metal catalysts based on 2D materials.

Promotional effects of Nb2O5 on ceria doped Ni catalysts for selective hydrogenation of 1,3-butadiene to butenes: Combined experimental and DFT approach

Developing low cost, active and selective catalysts that would replace the more deployed noble metals is desirable for hydrogenation of 1,3-butadiene. Herein, we prepared Ni catalysts supported on niobium-cerium oxides and characterization was carried out with TGA, XRD, H2-TPR, H2-TPD, HR-TEM, XPS, FTIR, N2 adsorption–desorption, and EDS mapping. Density functional theory (DFT) computes the reaction energies controlling the 1,3-butadiene hydrogenation. H2-TPR revealed that the inclusion of niobium oxide in the catalysts confer stronger metal support interaction that promotes the surface and bulk reduction of cerium oxide and leads to the improvement in the formation of surface Ce3+ as confirmed from the XPS analysis. 1,3-butadiene conversion was tested between 100 °C-350 °C and the catalysts exhibit high conversion at lower Ni loading. We found that the niobium inclusion directed the selectivity towards near complete butene formation even at higher temperature. The onset of decline in activity was observed at temperatures above 250 °C with the simultaneous formation of propene and propane and the disappearance of butane. Guided by the reaction results and the temperature programmed oxidation analysis (TPO), we proposed the reaction mechanism leading to the deactivation, and this entails butane decomposition to propene and surface carbene, while propane is formed from propene, the surface carbene occasioned in the formation of harmful carbon as evident from TPO results. Carbonaceous species formed on the catalysts were minimized on the niobium containing catalysts.

Multi-criteria decision framework for catalyst selection: Production of formic acid as a circular liquid organic hydrogen carrier in the hydrogen economy

This study aims to use the multi-criteria decision analysis (MCDA) for the selection of suitable catalysts for the production of formic acid (FA), which serves as a circular liquid H2 carrier for the H2-carbon cycle. TOPSIS, VIKOR, ARAS, COPRAS, and PROMETHEE analytical decision-making methods were used to establish priority rankings for each method. With the exception of the top two ranks, the rankings differed across the methods. Therefore, we proposed an alternative ranking for the catalyst selection in the FA production, where all the methods’ results were given equal priority. By aggregating the outcomes from the decision methods and sorting them in ascending order, a final prioritized ranking was established. Our results showed that the proposed MCDA method was effective in identifying the most suitable catalyst for the FA production as a circular LOHC in the H2-carbon cycle. The model determined that Pd nanoparticle-based activated carbon-supported catalyst exhibited high activity, selectivity, and stability, while also being cost-effective. The findings of this study might contribute to the development of more efficient H2 storage systems based on FA.

Advances and Challenges in Oxygen Carriers for Chemical Looping Partial Oxidation of Methane

To cope with global warming and increasing carbon emissions, the chemical looping process has attracted attention due to its excellent ability to convert fossil fuel and capture CO2. In this case, chemical looping partial oxidation technology has become the focus of attention due to its advantages in the production of syngas and hydrogen, especially with respect to the design and selection of oxygen carriers, which directly affect the efficiency of the production of syngas and hydrogen. In particular, the conversion of methane can reach 95% in the chemical looping partial oxidation of methane, and the selectivity of syngas, in the range of 700 °C to 900 °C at atmospheric pressure, can reach 99% for twenty or more cycles. In this review, from the perspective of metal oxide selection and structure regarding the chemical looping partial oxidation process, we discuss the role of oxygen carriers in the chemical looping partial oxidation cycle, in which the specific surface area, the lattice oxygen mobility, and the thermal stability are understood as the important factors affecting reactivity. We hope to summarize the design and development of efficient oxygen carriers with high oxygen-carrying capacity and syngas selectivity, as well as contribute to the selection, design, optimization, and redox reaction mechanism of redox catalysts.

Heterogeneous Rhodium Single-Atom-Site Catalyst Enables Chemoselective Carbene N-H Bond Insertion.

Transition-metal-catalyzed carbene insertion reactions of a nitrogen-hydrogen bond have emerged as robust and versatile methods for the construction of C-N bonds. While significant progress of homogeneous catalytic metal carbene N-H insertions has been achieved, the control of chemoselectivity in the field remains challenging due to the high electrophilicity of the metal carbene intermediates. Herein, we present an efficient strategy for the synthesis of a rhodium single-atom-site catalyst (Rh-SA) that incorporates a Rh atom surrounded by three nitrogen atoms and one phosphorus atom doped in a carbon support. This Rh-SA catalyst, with a catalyst loading of only 0.15 mol %, exhibited exceptional catalytic performance for heterogeneous carbene insertion with various anilines and heteroaryl amines in combination with diazo esters. Importantly, the heterogeneous catalyst selectively transformed aniline derivatives bearing multiple nucleophilic moieties into single N-H insertion isomers, while the popular homogeneous Rh2(OAc)4 catalyst produced a mixture of overfunctionalized side products. Additionally, similar selectivities for N-H bond insertion with a set of stereoelectronically diverse diazo esters were obtained, highlighting the general applicability of this heterogeneous catalysis approach. On the basis of density functional theory calculations, the observed selectivity of the Rh-SA catalyst was attributed to the insertion barriers and the accelerated proton transfer assisted by the phosphorus atom in the support. Overall, this investigation of heterogeneous metal-catalyzed carbene insertion underscores the potential of single-atom-site catalysis as a powerful and complementary tool in organic synthesis.

Tuning CO2 electroreduction by facet-dependent metal-support interaction

Electrochemical carbon dioxide reduction reaction (CO2RR) helps to build a sustainable carbon cycle system. The selectivity and stability of CO2RR catalysts can be tuned by manipulating Metal-Support Interaction (MSI). Here, we conducted a theoretical and experimental research on the interaction between Ag nanoparticles and diverse crystal faces of Cu2O. It was found the strong electron transfer from Ag to (100) facet of hexahedral Cu2O enabled the formation of charge-redistributed interface with positively charged Ag and negatively charged Cu2O, which was more favorable to the stability of integrated structure and CO2-to-CO catalytic process compared to Ag-decorated octahedral and dodecahedral Cu2O with exposed (111) and (110) facets, respectively. Consequently, the composite of Ag on hexahedral Cu2O exhibited an impressive CO Faradaic efficiency of 93%, surpassing Ag on octahedral and dodecahedral Cu2O as well as individual Ag and Cu2O nanoparticles. This work provides an effective avenue to tune CO2RR process by interface engineering.

Tuning the strong metal support interaction of the Fischer-Tropsch synthesis silica-coated cobalt-based nano-catalyst

The catalyst is crucial in enhancing productivity within the Fischer-Tropsch synthesis (FTS). The metal support interaction (MSI) plays a pivotal role in the FTS catalyst performance, impacting activity, stability, and selectivity. he configuration and composition of the catalyst dramatically impact MSI, with a strong MSI (SMSI) specified for the core-shell structure. In this study, two methods consisting of chemical treatment of etching and adding a promoter (Ru) for tuning the SMSI of the FTS catalyst are presented, and their footprints on the catalysts’ performance are screened by utilizing various characterization tests, molecular dynamic simulation, and catalytic tests. It is recognized that the silica interfacial perimeter acts as a barrier that restricts the charge transfer and boosts the SMSI in the silica-coated catalyst. Conversely, the etched catalyst exhibits a moderate MSI, contributing to increased reducibility, stability, and activity. Furthermore, the Ru-doped etched catalyst represents the optimum MSI, resulting in the highest overall performance.

P-d hybridized In-Co dual sites promote nitrite electroreduction to ammonia at high current density

Electrochemical reduction of NO2- to NH3 (NO2RR) represents an attractive route to simultaneously mitigate hazardous nitrite and produce value-added NH3. Herein, main-group In atomically doped into CoS2 (In-CoS2) is firstly developed as an active and selective NO2RR catalyst. Atomic-level characterizations of In-CoS2 reveal that In dopant coordinates with its neighboring Co atom to form p-d hybridized In-Co dual active sites. In situ spectroscopic measurements combined with theoretical computations reveal that In-Co dual active sites can synergistically promote NO2- activation and hydrogenation to NH3, while concurrently inhibiting the competing hydrogen evolution, consequently resulting in a high NO2--to-toNH3 conversion efficiency. Impressively, a flow cell with In-CoS2 presents an unprecedented NH3 yield rate of 1834.6 µmol h−1 cm−2 with a corresponding NH3-Faradaic efficiency of 95.1% at a current density of 310.5 mA cm−2, as well as an exceptional durability for 100 h electrolysis.

Enhancing Low-Temperature HCHO Oxidation: Investigation selectivity and Catalytic Activity of Ag, Co, Mo, and Cr Catalysts Supported on γ-Al2O3

Enhancing Low-Temperature HCHO Oxidation: Investigation selectivity and Catalytic Activity of Ag, Co, Mo, and Cr Catalysts Supported on γ-Al2O3

Advanced Functionalized Nanoclusters (Cu, Ag, and Au) as Effective Catalyst for Organic Transformation Reactions.

A considerable amount of research has been carried out in recent years on synthesizing metal nanoclusters (NCs), which have wide applications in the field of optical materials with non-linear properties, bio-sensing, and catalysis. Aside from being structurally accurate, the atomically precise NCs possess well-defined compositions due to significant tailoring, both at the surface and the core, for certain functionalities. To illustrate the importance of atomically precise metal NCs for catalytic processes, this review emphasizes 1) the recent work on Cu, Ag, and Au NCs with their synthesis, 2) the parameters affecting the activity and selectivity of NCs catalysis, and 3) the discussion on the catalytic potential of these metal NCs. Additionally, metal NCs will facilitate the design of extremely active and selective catalysts for significant reactions by elucidating catalytic mechanisms at the atomic and molecular levels. Future advancements in the science of catalysis are expected to come from the potential to design NCs catalysts at the atomic level.

Dry reforming of ethane over titania-based catalysts for higher selectivity and conversion to syngas

Ethane, one of the key components of shale gas, is a valuable feedstock for the production of syngas (CO + H2) via the CC bond cleavage during dry reforming of ethane (DRE) reaction. Selective catalysts are needed to direct this reaction pathway against the competing CH bond cleavage for ethylene formation. In this study, Fe, V and Rh oxides supported on TiO2 catalysts were prepared by impregnation method. The catalysts were tested for DRE with the main target of enhancing selectivity to syngas (CO and H2) and reducing byproducts (methane and ethylene) formation. The catalysts were characterized using X-ray diffraction, scanning electron microscopy, NH3/CO2 temperature programmed desorption and H2-temperature programmed reduction. Temperature programmed oxidation was utilized to characterize the coke contents of the spent catalysts. The catalysts were evaluated for DRE reaction in a fixed-bed reactor at the temperature range from 500 °C to 650 °C and CO2/ethane ratio from 2:1 to 10:1 (mol/mol). It was found that ethane conversion over the three catalysts increased in the order Rh/TiO2 > Fe/TiO2 > V/TiO2. Rh/TiO2 catalyst exhibited > 99 % ethane conversion, 36 % and 61 % yields of H2 and CO, respectively, at 650 °C and CO2/ethane ratio of 5.0. The high conversion of ethane was mainly attributed to the enhanced dispersion of Rh oxides on the TiO2 support coupled with the balanced surface acidic and basic sites. The Rh catalyst facilitated CC bond dissociation of ethane thereby forming methyl intermediates which then reacted with adsorbed CO2, thereby enhancing higher syngas production during DRE reaction.

Review and Outlook on Regulation of Catalyst Activity, Selectivity, and Stability for Biomass Hydrodeoxygenation Reaction in an Aqueous Environment

Review and Outlook on Regulation of Catalyst Activity, Selectivity, and Stability for Biomass Hydrodeoxygenation Reaction in an Aqueous Environment

Performance evaluation of low heat rejection diesel engine operated with biofuels under-selective catalytic reduction

Vehicle emissions are responsible for about 30% of all air pollution in the world. Vehicle emissions can be significantly reduced through the use of selective catalyst reduction (SCR). The present work emphasizes the impact of thermal barrier-coated pistons on diesel engine performance as well as emission qualities. A Ni–Cr–Al–Y bond coat was applied to the tested engine piston that was 50 microns thick and a top coat that was 250 microns thick. These coatings were applied using the plasma spray technique to a combination of 2 mol. % of Gadolinium oxide (Gd2O3), 2 mol. % of Neodymium oxide (Nd2O3), 3 mol. % of Yttria (Y2O3), and continuing 93 mol. % of Zirconia (ZrO2). In a 4-stroke, 1-cylinder diesel engine, the testing was carried out utilizing diesel, Mahua, and Jatropha fuels with and without coating. The selective catalytic reduction technique was employed in the current test to reduce NOx emissions. The findings of this analysis indicate that the brake thermal efficiency of an insulated piston engine improved by 3.9%, and when JB 100 was chosen as the fuel, the insulated piston reduced brake-specific fuel consumption by 3.5% in comparison to the normal piston. In engines coated with SCR, hydrocarbon emissions were lowered by 20.1%, while carbon monoxide emissions were dropped by 13.4%. In comparison to the baseline engine, the oxide of nitrogen emissions were reduced by 39.1%.

Total hydrogenation of furfural on Pd/COFs under mild conditions

Total hydrogenation of furfural (FAL) is an efficient way to produce the industrially important tetrahydrofurfuryl alcohol (THFOL). However, it is a challenge to obtain highly selective catalysts for this transformation especially under mild reaction conditions. Herein, we report that the β-ketoenamine-linked covalent organic framework (TpBD COF) supported ultrafine Pd nanoparticles exhibit significantly enhanced selectivity for THFOL compared to Pd/C (95% vs. 82 %) at almost full FAL conversion. This heightened selectivity is attributed to the increased electronic density on the Pd surface, resulting from the electron-donating effect of pendant groups in the TpBD COF. Moreover, kinetic investigations reveal that the activity of total FAL hydrogenation on Pd surface is linked to the rate-determining step in its first C = O hydrogenation process. Additionally, Pd/TpBD COF could catalyse various other bio-based furanic compounds to the corresponding furan ring saturated products in high yields. This work provides guidance for the rational design catalysts to improve its tandem hydrogenation efficiency.

Investigation on Catalytic Cracking Performance of Metal Catalysts for 1,1,2‐TCE

AbstractPVDC played an irreplaceable role in the field of sealed packaging, and its polymer monomer, VDC, was in short supply. At present, the saponification of 1,1,2‐TCE and sodium hydroxide was used to generate VDC in industry, which was a process with great environmental pollution. Catalytic dehydrochlorination of 1,1,2‐TCE to produce VDC was a green process route, but the selection of catalysts had always been controversial. This study aimed to screen catalysts suitable for industrial applications. The cesium based catalysts with good catalytic performance were systematically characterized and evaluated, and the overall reaction process was calculated using DFT calculation. The experimental results indicated that the cesium chloride catalyst with a 3 % molar fraction had the best catalytic performance, achieving 55.27 % conversion of 1,1,2‐TCE and 76.85 % selectivity for VDC, respectively. The reaction paths and transition state of several catalysts were calculated by DFT method. It was revealed that the activation energy required for the reaction of CsCl catalyst was the lowest, at 130.61 kcal/mol, and the energy of the product VDC was the lowest, at −63.25 kcal/mol, making it the most stable. The calculation results were consistent with the experimental data, indicating that cesium chloride catalyst had the best reaction performance. Therefore, the subsequent research could focus on the method of improving the supported dispersity of cesium chloride catalyst and the development of core‐shell catalyst to lay the foundation for further industrialization.

Cu@SiO2 catalyst with high copper dispersion for chemoselective hydrogenation of p-chloronitrobenzene

Selective hydrogenation of p-chloronitrobenzene (p-CNB) is not only of significant industrial importance, but also an important model reaction for selectivity investigation. Despite non-precious metal Cu has been proven to be an effective promoter in bimetallic catalysts, Cu as a single active metal achieving both high conversion and high selectivity are rare reported. In this work, Cu@SiO2 catalysts with high specific surface area (509.8–694.3 m2/g), high Cu dispersion (58.4–69.6 %), and small particle size (2.0–3.0 nm) has been prepared by a simple sol–gel method. The catalysts completely suppress the dechlorination reaction, achieving complete conversion of p-CNB with 99.9 % selectivity for p-chloroaniline (p-CAN). Its microstructure, composition, chemical state, adsorption and reaction behavior have been identified by various conventional ex-situ characterizations of catalysts and in-situ DRIFTs of hydrogenation of p-CNB. Interestingly, even at high loadings, Cu in the catalyst could be highly dispersed, thus exhibiting good catalytic activity. In addition, the Cu catalyst exhibits unique adsorption performance towards p-CNB, which perhaps one of the factors for its good performance. This work not only provides a selective hydrogenation catalyst with high Cu dispersion even at high loading amount by a simple method and but also reveals the importance of the adsorption mode of p-CNB, providing guidance for the development of more efficient catalysts in the future.

Surface Ligand Evolution: Sulfur-Directed Covalent Bonding of PPh3 on Pd4S with Improved Semi-hydrogenation of Terminal Alkynes.

Surface modification of metallic nanocatalysts with organic ligands has emerged as an effective strategy to enhance catalytic selectivity, although often at the expense of catalytic activity. In this study, we demonstrate a compelling approach by surface modifying Pd4S nanocrystals with PPh3 ligands, resulting in a catalyst with excellent catalytic activity and durable selectivity for the semi-hydrogenation of terminal alkynes. Experimental and theoretical investigations reveal that the presence of S sites on the Pd surface directs PPh3 ligands to preferentially form covalent bonds with S, creating distinctive surface S=PPh3 motifs. This configuration induces a partial positive charge on Pd, facilitating hydrogen transfer and thus promoting catalytic activity. Furthermore, the covalent bond between the ligand and catalyst surface forms a robust network, ensuring ligand stability and increasing the hydrogenation energy barrier of olefins. Consequently, the Pd4S@PPh3 catalyst exhibits an improved catalytic selectivity with durability in terminal alkyne semi-hydrogenation. This study introduces an effective strategy for designing selective hydrogenation catalysts with an enhanced performance.

Understanding Advanced Transition Metal-Based Two Electron Oxygen Reduction Electrocatalysts from the Perspective of Phase Engineering.

Non-noble transition metal (TM)-based compounds have recently become a focal point of extensive research interest as electrocatalysts for the two electron oxygen reduction (2e- ORR) process. To efficiently drive this reaction, these TM-based electrocatalysts must bear unique physiochemical properties, which are strongly dependent on their phase structures. Consequently, adopting engineering strategies toward the phase structure has emerged as a cutting-edge scientific pursuit, crucial for achieving high activity, selectivity, and stability in the electrocatalytic process. This comprehensive review addresses the intricate field of phase engineering applied to non-noble TM-based compounds for 2e- ORR. First, the connotation of phase engineering and fundamental concepts related to oxygen reduction kinetics and thermodynamics are succinctly elucidated. Subsequently, the focus shifts to a detailed discussion of various phase engineering approaches, including elemental doping, defect creation, heterostructure construction, coordination tuning, crystalline design, and polymorphic transformation to boost or revive the 2e- ORR performance (selectivity, activity, and stability) of TM-based catalysts, accompanied by an insightful exploration of the phase-performance correlation. Finally, the review proposes fresh perspectives on the current challenges and opportunities in this burgeoning field, together with several critical research directions for the future development of non-noble TM-based electrocatalysts.

CO2 Electrolyzers.

CO2 electrolyzers have progressed rapidly in energy efficiency and catalyst selectivity toward valuable chemical feedstocks and fuels, such as syngas, ethylene, ethanol, and methane. However, each component within these complex systems influences the overall performance, and the further advances needed to realize commercialization will require an approach that considers the whole process, with the electrochemical cell at the center. Beyond the cell boundaries, the electrolyzer must integrate with upstream CO2 feeds and downstream separation processes in a way that minimizes overall product energy intensity and presents viable use cases. Here we begin by describing upstream CO2 sources, their energy intensities, and impurities. We then focus on the cell, the most common CO2 electrolyzer system architectures, and each component within these systems. We evaluate the energy savings and the feasibility of alternative approaches including integration with CO2 capture, direct conversion of flue gas and two-step conversion via carbon monoxide. We evaluate pathways that minimize downstream separations and produce concentrated streams compatible with existing sectors. Applying this comprehensive upstream-to-downstream approach, we highlight the most promising routes, and outlook, for electrochemical CO2 reduction.