Catalyst Species Research Articles

Active Ni and Fe species on catalysts Ni/Al2O3 and NiFe/Al2O3 for the oxidative dehydrogenation (ODH) of ethane to ethylene assisted by CO2

Ni/Al2O3 and NiFe/Al2O3 catalysts were synthesized by incipient wetness impregnation and tested for oxidative dehydrogenation (ODH) of ethane to ethylene. The effect of Ni loading and Fe as a promoter for bimetallic catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), scanning electron microscopy (SEM), and temperature-programmed reduction (H2-TPR). The catalyst with 10 wt% Ni and 6.6 wt% Fe (NiFe32) displayed the highest ODH activity. XRD results showed smaller crystalline NiO (˂ 7 nm) for bimetallic catalysts than the monometallic ones. Raman results depicted NiOx species in the monometallic catalysts. The bimetallic catalysts exhibited spinel-type structures as NiFe2O4 and FeAl2O4 related to more active species in ODH of ethane. DRS results revealed that the higher ODH activity for bimetallic catalysts is related to a predominance of Ni and Fe in tetrahedral symmetry (Td) than octahedral symmetry (Oh). These suggest that tetrahedral symmetry species were more effective than octahedral symmetry. TPR profiles showed that the iron addition increased the nickel species with strong interaction with the support. This rearrangement of Ni and Fe species in octahedral and tetrahedral sites of the NiO and alumina lattice could explain the shift reduction temperatures for Ni species and the formation of the spinel-type structure in the bimetallic catalysts. A relation between the metal-support interaction and the selectivity toward ethylene was found. A higher strong metal-support interaction favors a better catalytic activity.

N-doped carbon supported cobalt electrospun nanofibers activated peroxymonosulfate system for benzothiazole degradation: Multifunctional role of nitrogen species

Nitrogen doping is an effective way to enhance the activation performance in peroxymonosulfate (PMS) heterogeneous catalysis. However, the unique role of different nitrogen species was still controversial. Herein, N-doped carbon supported cobalt catalyst was synthesized by electrostatic spinning method and employed to activated PMS. Firstly, various nitrogen species in catalyst including graphitic N, pyridinic N, pyrrolic N and Co-Nx was identified. Subsequently, the specific role of various nitrogen species was revealed by a series of experiments (adsorption experiments, degradation experiments, quenching tests, characterization analysis.), that is: (1) graphitic N changes the electrical of surrounding C atoms for PMS adsorption; (2) pyrrolic N with special pentacyclic structure leaded to obvious defects in carbon structure, thus enhancing the PMS activation ability of carbon materials; (3) pyridinic N bind with metal Co to form Co-Nx, which acted as an efficient active site for PMS activation. In addition, the effects of pH, temperature, and coexisting ions were also studied. This study revealed the activation behavior of different N species on N-doped carbon supported transition metal base catalysts, which provides theoretical basis for further synthesis of N-containing catalysts with high activation efficiency and release the activation potential of N species.

Influence of Highly Stable Ni2+ Species in Ni Phyllosilicate Catalysts on Selective Hydrogenation of Furfural to Furfuryl Alcohol.

Enhancing the catalytic performance of non-noble Ni catalysts in the selective hydrogenation of furfural to furfuryl alcohol (FA) in terms of furfural conversion, selectivity, and good recyclability is challenging. Here, spherical nickel phyllosilicate catalysts (Ni_PS) with fibrous-like structures are prepared via a modified sol-gel method with Ni loadings of 2-30 wt %. Upon exposure to air, all the reduced Ni_PS catalysts exhibit more than 80% Ni0/Niphyllosilicate species on the surface, whereas a large portion of Ni oxide species (>55%) is presented on the impregnated catalyst. The Ni2+ species in nickel phyllosilicate catalysts are active and highly stable during reduction, reaction, and regeneration, yielding stable catalytic performance for multiple recycle tests in furfural hydrogenation to FA. Furfural conversion over the Ni_PS catalysts increased monotonically with increasing Ni loading without an FA selectivity drop. The presence of both metallic Ni0 and Niphyllosilicate also produces a synergistic promotional effect for FA formation.

Indium-based bimetallic clusters anchored onto silicon-doped graphene as efficient multifunctional electrocatalysts for ORR, OER, and HER

Exploring efficient, economical, and environmentally friendly multifunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) is a prerequisite for the development of renewable energy conversion and storage technologies. Herein, the catalytic performance of indium-based bimetallic clusters anchored onto silicon-doped graphene (In2M2/Si-G, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) as multifunctional electrocatalysts is investigated systematically by density functional theory methods. All the studied In2M2 bimetallic clusters can be stably anchored onto the Si-G substrate based on the calculated binding energy. Among these materials, In2V2/Si-G and In2Co2/Si-G are expected to be potential trifunctional (ORR/OER/HER) electrocatalysts with the low overpotentials of 0.51/0.76/−0.11 V and 0.56/0.36/−0.09 V, respectively. Emphatically, the electronic structure analysis reveals that such high catalytic activity can be attributed to the synergistic effect between indium and transition metal atoms, which could effectively promote electron transfer between catalyst and reaction species. This work would open a new perspective and provide guidance for designing promising multifunctional electrocatalysts to meet energy demand.

Tuning the olefin-VOCs epoxidation performance of ceria by mechanochemical loading of coinage metal

Under the background of carbon dioxide emission reduction, how to realize the treatment and the high value-added conversion of typical olefin volatile organic compounds (olefin-VOCs), such as styrene, is a big challenge. In this contribution, the ceria-supported coinage metal catalysts (M/CeO2, M = Au, Ag, and Cu) are successfully synthesized by a dry mechanochemical method, and their catalytic performance for styrene-VOC epoxidation with tert-butyl hydrogen peroxide (TBHP) as an oxidant to prepare high-value styrene oxide (SO) is investigated. The oxygen vacancies of ceria play a key role in the anchoring of metal nanoparticles. After ball milling, Au(III) is partially reduced and coexists on ceria in two valence states (Au3+ and Au0), and the reactive oxygen species of the as-prepared catalyst are enhanced. The catalytic behaviors, including solvents effect, substrate concentration, oxidant ratio, catalyst dosage, reaction time, and temperature, are systematically investigated. Au/CeO2 exhibits good styrene epoxidation performance with a total styrene conversion of 94% and a SO yield of 63%, along with good reusability and substrate scalability. Thermodynamics and kinetics show that Au/CeO2 was more favorable for styrene epoxidation and this reaction is dominated by the rate of intrinsic chemical reactions on the surface of the catalyst. Based on experimental discussions and a set of characterizations (XPS, XRD, in-situ FT-IR, ESR, ESI-HSMS, etc.), the mechanism is revealed as the synergistic catalysis between the reactive oxygen species of Au/CeO2 and the peroxide radicals generated by the homolysis of TBHP.

Effective Self-Support Growth of Spring-Like Carbon Nanotube Arrays with Ultra-Large Specific Surface Area

Carbon nanotube (CNT) long array with higher aspect ratio is an ideal electrode material for high performance supercapacitors due to its excellent conductivity and high specific surface area (SSA). How to quickly and concisely prepare high-quality CNT long-arrays is the key to achieving large-scale application. Herein, high-quality spring-like CNT (tube diameter 5–8[Formula: see text]nm) long arrays (100–400[Formula: see text][Formula: see text]m) with high purity (96.2% after purification) and ultrahigh graphitization ([Formula: see text]) were fabricated in a high yield (eight times) by a self-supporting catalyst chemical vapor deposition (CVD) method, and its formation process was first investigated under specific conditions of iron content in catalyst, growth temperature and carbon source species. The SSAs can reach 728[Formula: see text]m2/g, which is more than twice that of MWCNTs on the market. The high graphitization and ultra-large SSAs of this spring-like CNT arrays as electrodes exhibit potential electrochemical performance.

Highly reactive methyl group drives selective catalytic reduction of NOx by methanol on bismuth oxide nanoparticle implanted FER zeolite

Selective catalytic reduction by methanol (Methanol-SCR) is a promising technology for the deNOx treatment of the exhaust with high concentration of sulfur. Herein, nano-bismuth oxide implanted FER zeolites (Bi-FER) have been successfully synthesized as Methanol-SCR catalysts, on which the optimum reaction temperature shows a big shift from 450 down to 300 °C comparing with state of the art. The catalytic active species of Bi-FER catalyst have been investigated by multi-characterization methods combined by theoretical simulation. Methyl groups generated on Brønsted acid sites neighboring with nano-bismuth oxide were demonstrated to exhibit extraordinary reactivity towards NOx, resulting in a high deNOx performance at low temperature. A strategy by the activation of methanol to produce reactive methyl groups was put forward for the development of Methanol-SCR catalysts.

Tuning electron delocalization and surface area in COFs derived N, B co-doped carbon materials for efficient selective hydrogenation of nitroarenes

Metal-free carbon catalysts with excellent conduction performance have drawn much research attention in reduction reactions. Herein, a N, B co-doped carbon catalyst with high pyrrolic N proportion (35.75%) and excellent surface area (1409 m2/g) was successfully prepared via carbonizing covalent organic framework materials (COFs) containing N and B atoms assisted by ZnCl2 molten salt. The presence of ZnCl2 maintains the micropore structure of COFs to provide high specific surface areas and abundant lattice defects for carbon materials. In addition, electron-withdrawing B heteroatom further facilitates the formation of pyrrolic N at defect sites by modifying the electronic structure of carbon network. The tuning of surface areas and active N species in carbon catalysts successfully improve the selective hydrogenation of nitrobenzene to aniline. The optimized carbon material exhibits excellent nitrobenzene conversion (99.9%) and aniline selectivity (>99%) within 15 min, as well as excellent substrate suitability. This work provides a certain guiding for the design and application of metal-free catalysis.

Visible-light-assisted peroxydisulfate activation over Ag6Si2O7/Cu(II)-modified palygorskite composite for the effective degradation of organic pollutants by radical and nonradical pathways

Photoassisted persulfate activation (PPA) is highly efficient oxidation process, but the eligible catalysts are scarce. Herein, a visible-light-responsive Ag6Si2O7 was anchored on Cu(II)-exchanged attapulgite (Cu-Pal) via a facile precipitation-deposition method to construct a novel PDS activator. The synthesized catalyst was systemically analyzed by a series of characterization techniques. The results revealed that Ag6Si2O7 nanoparticles were evenly dispersed on Cu-Pal to form heterojunction. 16%-Ag6Si2O7/Cu-Pal, an optimal catalyst exhibited excellent catalytic performance and stability in the visible-light-assisted PDS activation for AR18 degradation. The influences of reaction parameters on this process were investigated. Under the optimal conditions ([catalyst] = 1.0 g L−1, [PDS] = 3.9 mM, pHi = 5.1), 50 mg L−1 of AR18 was completely degraded within 30 min. More importantly, quenching experiments and EPR tests revealed that besides the common SO4•− and •OH, 1O2 and O2•− were generated as main reactive oxygen species in the PPA by 16%-Ag6Si2O7/Cu-Pal. Moreover, it was found that surface hydroxyl groups of the catalyst and copper species incorporated in Pal could significantly influence PDS activation and ROS generation. Based on these results, together with PDS decomposition, fluorescent probe analysis, and XPS analysis of the used catalyst, the possible mechanisms of the PPA by 16%-Ag6Si2O7/Cu-Pal were proposed. Finally, the versatility and practicability of the established PPA process were verified by degrading other organic contaminants and testing effects of the coexisting anions and water matrices on AR18 degradation. This study may provide new insights for designing and developing the efficient heterogeneous catalysis for wastewater treatment via persulfate-based AOP.

Influence of nickel loading on the hydroisomerization of n-dodecane with nickel-tungsten oxide-alumina supported catalysts

Heterogeneous catalysts based on alumina-supported tungsten oxides (15 wt% W) with different loadings of nickel (0.5, 1, 2, 4, 6, 8 and 10 wt% Ni) were selected to study the influence of Ni loading on the hydroisomerization of n-dodecane. The catalysts were prepared by applying the wetness impregnation method on the supports to introduce W and Ni. The characterization techniques applied for determining physicochemical properties of the catalysts were N2 adsorption-desorption at 77 K (textural properties), X-ray diffraction (structure and crystalline phases), H2-TPR (redox properties), FTIR, NH3-TPD (acid sites analyses) and XPS (chemical surface analysis). The catalytic properties of such catalysts were found to be crucial in the n-dodecane conversion. The NH3-TPD profiles indicate that the medium acid sites are the main sites responsible for the reaction performance. The formation of bulky crystal structures of nickel species in the high nickel loading catalyst (10 wt% Ni) was confirmed by XRD and XPS results, resulting in the largest cracking activity. The conversion of n-dodecane and selectivity to i-C12+branched C12 tend to increase with Ni loading until the catalyst contains 6 wt% Ni (28% n-C12 conversion and 94% of branched C12 selectivity). The lower selectivity at high nickel loading is due to metal-based cracking reaction. An optimum balance between metal and acid centers is needed to achieve a compromise between conversion and selectivity, avoiding or minimizing cracking reactions.

(Keynote) Identification of Active Species and Mechanisms in Non-Precious Metal Oxygen Reduction Catalysts By Reductive Treatments and Magnetic Measurements

This talk addresses the Oxygen Reduction Reaction (ORR) utilizing Fe- and Co-based non precious metal (NPM) catalysts. There has long been uncertainty as to the active site for ORR in these materials due to the heterogeneity of the as-prepared catalyst. We report on two innovations directed at understanding the active sites in these materials. In the first, we interrogate the ORR activity in acid of a Fe porphyrin on different supports. While the activity is high when the Fe porphyrin is adsorbed on XC72 (a graphitic carbon), this activity is much lower when the porphyrin is adsorbed on either MoS2 or g-C3N4. Numerous physical characterization techniques show the electronic structure around the Fe center is the same for all three supports. Only the Fe porphyrin supported on XC72 exhibits a pH dependence in its ORR activity. This observation, coupled with the increased hydrophilicity of XC72 relative to the other supports, suggests that the support-electrolyte interaction controls the ORR activity. Modification of MoS2 to increase its hydrophilicity results in a more active ORR catalyst. In the second area, we use magnetometry and other techniques to examine the effect of two different reductive gas treatments on pyrolyzed ORR catalysts. We find that reductive gas treatments yield more superparamagnetic/ferromagnetic Fe species, with specific preparations yielding materials that consist almost entirely of reduced Fe (particularly Fe4N). Interestingly, catalysts exhibiting large percentages of superparamagnetic/ferromagnetic materials exhibit high activities for ORR catalysis as high as those reported in the literature.

CO2 methanation over γ-Al2O3 nanosheets-stabilized Ni catalysts: Effects of MnOx and MoOx additives on catalytic performance and reaction pathway

With 5 nm Ni nanoparticles anchored by the nanosheet-shaped γ-Al2O3 supports, a ~10 wt% Ni/Al2O3 catalyst displayed ca. 45% conversion and >98% CH4 selectivity in CO2 methanation reaction at 300 °C for 450 h. Benefited from stable interfaces between Ni sites and highly dispersed MnOx promoters on Al2O3, a modified Ni-Mn/Al2O3 catalyst exhibited 93–88% conversions, >99.9% selectivity and great stability in 1100 h reaction. As a contrast, a Mo-modified Ni-Mo/Al2O3 catalyst showed severe deactivation with declined conversions from >80 to 50% within initial 20 h. The high-dispersion MoOx species in the fresh catalyst occurred aggregation and reduction during the reaction, reconstructing the Ni-support interfaces. As clarified by in-situ DRIFT spectra, the COads-mediated hydrogenation reaction pathway was followed on these Ni catalysts via sequential steps, CO2 → bicarbonates → bidentate carbonates → bidentate formates → COads → CH4. Ni-Mn/Al2O3 catalyst exhibited significantly high and well-matched reaction rates in overall steps, whereas Ni/Al2O3 catalyst showed low activities in key steps of formate decomposition and COads methanation. Ni-Mo/Al2O3 catalyst displayed superior ability for CO2 dissociation into bicarbonates, and nonetheless, it could not steadily achieve the formation and hydrogenation of COads species, allowing the inactive surface species to be accumulated and to induce the catalyst structural change for deactivation.

Dual Ligand Enabled Nondirected C-H Chalcogenation of Arenes and Heteroarenes.

Chalcogenide motifs are present as principal moieties in a vast array of natural products and complex molecules. Till date, the construction of these chalcogen motifs has been restricted to either the use of directing groups or the employment of a large excess of electronically activated arenes, typically employed as a cosolvent. Despite being highly effective, these methods have their own limitations in the step economy and the deployment of an excess amount of arenes. Herein, we report the evolution of a catalytic system employing arene-limited, nondirected thioarylation of arenes and heteroarenes using a complimentary dual-ligand approach. The reaction is controlled by a combination of steric and electronic factors, and the utilization of a suitable ligand enables the generation of products on a complimentary spectrum to that generated by classical methods. The combination of ligands remains imperative in the reaction protocol with theoretical calculations pointing towards a monoprotected amino acid ligand being crucial in the concerted metalation deprotonation (CMD) mechanism by a characteristic [5,6]-palladacyclic transition state, while the pyridine moiety assists in the active catalyst species formation and product release. Combined experimental and computational mechanistic investigations point toward the C-H activation step being both regio- and rate-determining. Interestingly, oxidative addition of the diphenyl disulfide substrate is found to be unlikely, and an alternative transmetalation-like mechanism involving the Pd-Ag heterometallic complex is proposed to be operative.

High-purity syngas production by cascaded catalytic reforming of biomass pyrolysis vapors

A novel pyrolysis followed by in-line cascaded catalytic reforming process without additional steam was developed to produce high-purity syngas from woody biomass. The key to the proposed process is the construction of a cascaded biochar + NiAl2O4 catalytic reforming process in which biochar acts as a pre-reforming catalyst, and NiAl2O4 acts as a primary reforming catalyst. The large oxygenates in the pyro-vapors are deeply cracked in the biochar layer due to the increased residence time in the hot-biochar bed. The remaining small molecules are then reformed with the autogenerated steam from pyrolysis catalyzed by the reduced Ni0 species in the NiAl2O4 catalyst (NiAlO). The results showed that the yield of syngas for the optimized process was 71.28 wt% (including 44.44 mg-H2/g-biomass and 536.48 mg-CO/g-biomass), and the CO2 yield of the process was only 3 kg-CO2/kg-hydrogen. High-purity syngas with 89.47 vol% of (H2 + CO) was obtained, and the gas energy conversion efficiency (GECE) of the process reached 75.65%. The study shows that in the cascaded catalytic reforming process, cracking of the large oxygenates and reforming of the small molecules are promoted sequentially in separated biochar + NiAlO catalyst layers, which maximizes the syngas production and improves the activity and stability of the Ni-based catalyst.

Defect engineering over Co3O4 catalyst for surface lattice oxygen activation and boosted propane total oxidation

Developing efficient and stable catalyst is crucial for the catalytic removal of volatile organic compounds (VOCs). Herein, we report an effective and versatile surface defect engineering for regulation of surface lattice oxygen species in Co3O4 catalyst by alkaline-earth metal doping-etching strategy. The as-synthesized Ca-Co3O4-Ac exhibited remarkable catalytic activity and stability in propane oxidation, with high propane oxidation rate (5.65 × 10−7 mol g−1 s−1) and turnover frequency (TOF, 2.12 × 10−3 s−1) at 210 °C. Simultaneously, the doping-etching strategy could increase the specific surface area, low-temperature reducibility, and oxygen mobility of Co3O4 catalyst. In addition, in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), density function theory (DFT) calculation, and propane temperature-programmed desorption/surface reaction (C3H8-TPD/TPSR) further revealed that active lattice oxygen species induced by doping-etching strategy promoted the propane activation on the catalyst surface. This work offers a deeper understanding of the reactive oxygen species and provides a feasible strategy for the design of efficient catalysts for practical VOCs removal.

Effect of Liquid–Liquid Interfacial Area on Biphasic Catalysis Exemplified by Hydroformylation

Biphasic catalysis enables the effective recycling of homogeneous catalysts by their immobilization in an additional liquid phase immiscible with the products. The introduced liquid–liquid interfacial area implies mass transfer limitations that play an important role in understanding these catalytic systems, with many rate enhancement strategies revolving around optimizing said area. In this contribution, the relationship between liquid–liquid interfacial area and catalytic activity is elucidated by applying a methodology that utilizes an image-based in situ measurement of the transient droplet size distribution. When the industrially highly relevant aqueous biphasic hydroformylation of the long-chain olefin 1-octene is taken as the model reaction, it is found that the product nonanal and the addition of the ligand increases the interfacial area by a factor of up to 5. The rate of conversion is found to depend on the stirring speed. By variation of the catalyst concentration, it is shown that an accumulation of the catalyst species at the interface is unlikely. Using a mathematical model, it is highlighted that the effect of the aqueous–organic interfacial area on the catalytic activity is not linear as was previously assumed in the literature. Instead, a change in the interfacial composition is proposed that causes a shift in the dependence of catalytic activity on said area. Thus, the dynamic physical properties of a lean gas–liquid–liquid system were linked to the catalytic performance of the system.

Nature and role of Cu(II) species in doped C12A7 catalysts for soot oxidation

Two series of copper-doped mayenite catalysts (Cuₓ:C₁₂₋ₓA₇) were synthesized by one-pot-assisted solution combustion at different Cu loadings (0.06 ≤x ≤ 1) with the aim to correlate their performances in soot combustion and the nature and abundance of the different copper species present. The atmosphere composition influence, precisely of the presence of water, was also studied. It appears that Cu(II) interacted with the C12A7 matrix in three structurally different forms: isolated-Cu²⁺, clustered-Cu²⁺, and bulky CuO particles. Cu-C12A7 catalysts exhibited enhanced activity over bare-C12A7, both in terms of soot oxidation at low temperatures and CO₂ selectivity. The control over the dispersion of Cu, the texture, and superoxide concentration of the Cu-C12A7 catalysts achieved by adjusting the Cu loading and calcination temperature, appeared crucial in promoting the catalytic performance. We concluded that the well-dispersed clustered Cu²⁺ is the most likely active species responsible for the improved activity both under dry and wet conditions.

Coadsorption Interfered CO Oxidation over Atomically Dispersed Au on h-BN.

Similar to the metal centers in biocatalysis and homogeneous catalysis, the metal species in single atom catalysts (SACs) are charged, atomically dispersed and stabilized by support and substrate. The reaction condition dependent catalytic performance of SACs has long been realized, but seldom investigated before. We investigated CO oxidation pathways over SACs in reaction conditions using atomically dispersed Au on h-BN (AuBN) as a model with extensive first-principles-based calculations. We demonstrated that the adsorption of reactants, namely CO, O2 and CO2, and their coadsorption with reaction species on AuBN would be condition dependent, leading to various reaction species with different reactivity and impact the CO conversion. Specifically, the revised Langmuir–Hinshelwood pathway with the CO-mediated activation of O2 and dissociation of cyclic peroxide intermediate followed by the Eley–Rideal type reduction is dominant at high temperatures, while the coadsorbed CO-mediated dissociation of peroxide intermediate becomes plausible at low temperatures and high CO partial pressures. Carbonate species would also form in existence of CO2, react with coadsorbed CO and benefit the conversion. The findings highlight the origin of the condition-dependent CO oxidation performance of SACs in detailed conditions and may help to rationalize the current understanding of the superior catalytic performance of SACs.

Promoting Propane Dehydrogenation with CO2 over the PtFe Bimetallic Catalyst by Eliminating the Non-selective Fe(0) Phase

Fine tuning the structure of bimetallic nanoparticles is critical toward understanding structure–activity relationships and further improving the catalytic performance in propane dehydrogenation (PDH). Excessive Fe species in the PtFe bimetallic catalysts promote carbon deposition leading to low propylene selectivity, and it remains challenging to synthesize well-defined PtFe catalysts while selectively eliminating the excessive Fe. Herein, we show that the formation of coke can be significantly inhibited by introducing CO2 into the PDH over PtFe catalysts, where CO2 effectively eliminates the active Fe(0) coking sites without changing the catalytic surface structure of the PtFe alloy. With a CO2/C3H8 feeding ratio of 0.20, the Pt1Fe7/S-1 catalyst shows the highest propylene production rate and decreased amount of coke from 18.8 to 1.0 wt % compared with dehydrogenation without CO2. X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe Mössbauer results indicate that it is the oxidation of excessive unalloyed Fe species during the CO2-PDH reaction, instead of the reverse Boudouard reaction (CO2 + C = 2CO), that significantly inhibits the carbon deposition. This work provides a promising strategy for tuning the structure of PtFe bimetallic catalysts under reaction conditions and improving the performance of the PDH reaction.

Evidence and Governing Factors of the Radical-Ion Photoredox Catalysis

Photoinduced electron transfer of a radical species provides a promising strategy for expanding the scope of photoredox catalysis. However, the mechanism underlying the radical-ion photoredox catalysis has yet been fully established. In the present research, we investigated the generation and annihilation of the key catalytic intermediate in the borylation reaction of aryl halides. To disentangle the intricate catalysis cycle, we conducted experiments using electrochemical, transient absorption and photoluminescence spectroscopy and quantum chemical calculation techniques. Our mechanistic studies provided convincing evidence that the active catalyst species is the excited-state radical anion. We also found that the catalyst activation is retarded by multiple annihilative processes, among which the intrinsic relaxation of the excited-state radical anion of the catalyst is the most destructive. We expect these mechanistic findings will guide the future development of photoredox catalysis of radical species.