Modulating the Activity and SO2 Resistance of α-Fe2O3 Catalysts for NH3-SCR of NOx via Crystal Facet Engineering.

The development of Fe-based catalysts for the selective catalytic reduction of NOx by NH3 (NH3-SCR of NOx) has garnered significant attention due to their exceptional SO2 resistance. However, the influence of different sulfur-containing species (e.g., ferric sulfates and ammonium sulfates) on the NH3-SCR activity of Fe-based catalysts as well as its dependence on exposed crystal facets of Fe2O3 has not been revealed. This work disclosed that nanorod-like α-Fe2O3 (Fe2O3-NR) predominantly exposing (110) facet performed better than nanosheet-like α-Fe2O3 (Fe2O3-NS) predominantly exposing (001) facet in NH3-SCR reaction, due to the advantages of Fe2O3-NR in redox properties and surface acidity. Furthermore, the results of the SO2/H2O resistance test at a critical temperature of 250 °C, catalytic performance evaluations on Fe2O3-NR and Fe2O3-NS sulfated by SO2 + O2 or deposited with NH4HSO4 (ABS), and systematic characterization revealed that the reactivity of ammonium sulfates on Fe2O3 catalysts to NO(+O2) contributed to their improved catalytic performance, while ferric sulfates showed enhancing and inhibiting effects on NH3-SCR activity on Fe2O3-NR and Fe2O3-NS, respectively; despite this, Fe2O3-NR showed higher affinity for SO2 + O2. This work set a milestone in understanding the NH3-SCR reaction on Fe2O3 catalysts in the presence of SO2 from the aspect of crystal facet engineering.

3D Shape Measurement of Aeroengine Blade Based on Fringe Projection Profilometer Improved by Multi-Layer Concentric Ring Calibration.

The precision requirements for aeroengine blade machining are exceedingly stringent. This study aims to improve the accuracy of existing aeroengine blade measurement methods while achieving comprehensive measurement. Therefore, this study proposes a new concentric ring calibration method and designs a multi-layer concentric ring calibration plate. The effectiveness of this calibration method was verified through actual testing of standard ball gauges. Compared with the checkerboard-grid calibration method, the average deviation of the multilayer concentric ring calibration method for measuring the center distance of the standard sphere is 0.02352, which improves the measurement accuracy by 3-4 times. On the basis of multi-layer concentric ring calibration, this study builds a fringe projection profiler based on the three-frequency twelve-step phase shift method. Compared with the CMM, the average deviation of the blade chord length measured by this solution is 0.064, which meets the measurement index requirements of aeroengine fan blades.

Regulation of d-Band Centers in Localized CdS Homojunctions through Facet Control for Improved Photocatalytic Water Splitting.

The accelerated kinetic behaviour of charge carrier transfer and its unhindered surface reaction dynamic process involving oxygenated-intermediate activation and conversion are urgently required in photocatalytic water (H2 O) overall splitting, which has not been nevertheless resolved yet. Herein, localized CdS homojunctions with optimal collocation of high and low index facets to regulate d-band center for chemically adsorbing and activating key intermediates (*-OH and *-O) have been achieved in H2 O overall splitting into hydrogen. Density functional theory, hall effect, and in situ diffuse reflectance infrared Fourier transform spectroscopy confirm that, electrons and holes are kinetically transferred to reductive high index facet (002) and oxidative low index facet (110) of the localized CdS homojunction induced by facet Fermi level difference to dehydrogenate *-OH and couple *-O for hydrogen and oxygen evolution, respectively, along with a solar conversion into hydrogen (STH) of 2.20 % by Air Mass 1.5 Global filter irradiation. These findings contribute to solving the kinetic bottleneck issues of photocatalytic H2 O splitting, which will further enhance STH.

Cation Bridge Mediating Homo- and Cross-Coupling in Copper-Catalyzed Reductive Coupling of Benzaldehyde and Benzophenone.

A novel mechanism of organobase-mediated Brook rearrangement and C-C coupling in the copper-catalyzed reductive coupling of benzaldehyde and benzophenone is proposed. The results demonstrate that this reaction proceeds mainly through five sequential elementary steps: transmetalation, carbonyl addition, σ-bond metathesis, Brook rearrangement, and C-C coupling. The organobases played a significant role not only in forming the active catalyst but also in mediating the Brook rearrangement and chemoselectivity in homo- and cross-coupling. Brook rearrangement mediated by organobases is more favored than that without organobases. In the C-C coupling step, the cation bridge combines two O atoms with the same electronegativity to form a pre-reaction complex. Moreover, a significant charge difference is a major factor in the selectivity of carbonyl addition and C-C coupling.

Strong Electronic Orbit Coupling between Cobalt and Single-Atom Praseodymium for Boosted Nitrous Oxide Decomposition on Co3O4 Catalyst.

Nitrous oxide (N2O) has gained increasing attention as an important noncarbon dioxide greenhouse gas, and catalytic decomposition is an effective method of reducing its emissions. Here, Co3O4 was synthesized by the sol-gel method and single-atom Pr was confined in its matrix to improve the N2O decomposition performance. It was observed that the reaction rate varied in a volcano-like pattern with the amount of doped Pr. A N2O decomposition reaction rate 5-7.5 times greater than that of pure Co3O4 is achieved on the catalyst with a Pr/Co molar ratio of 0.06:1, and further Pr doping reduced the activity due to PrOx cluster formation. Combined with X-ray photoelectron spectroscopy, X-ray absorption fine structure, density functional theory and in situ near-ambient pressure X-ray photoelectron spectroscopy, it was demonstrated that the single-atom doped Pr in Co3O4 generates the "Pr 4f-O 2p-Co 3d" network, which redistributes the electrons in Co3O4 lattice and increases the t2g electrons at the tetracoordinated Co2+ sites. This coupling between the Pr 4f orbit and Co2+ 3d orbit triggers the formation of a 4f-3d electronic ladder, which accelerates the electron transfer from Co2+ to the 3π* antibonding orbital of N2O, thus contributing to the N-O bond cleavage. Moreover, the energy barrier for each elementary reaction in the decomposition process of N2O is reduced, especially for O2 desorption. Our work provides a theoretical grounding and reference for designing atomically modified catalysts for N2O decomposition.

Single-Atom Ce-Modified α-Fe2O3 for Selective Catalytic Reduction of NO with NH3.

A single-atom Ce-modified α-Fe2O3 catalyst (Fe0.93Ce0.07Ox catalyst with 7% atomic percentage of Ce) was synthesized by a citric acid-assisted sol-gel method, which exhibited excellent performance for selective catalytic reduction of NOx with NH3 (NH3-SCR) over a wide operating temperature window. Remarkably, it maintained ∼93% NO conversion efficiency for 168 h in the presence of 200 ppm SO2 and 5 vol % H2O at 250 °C. The structural characterizations suggested that the introduction of Ce leads to the generation of local Fe-O-Ce sites in the FeOx matrix. Furthermore, it is critical to maintain the atomic dispersion of the Ce species to maximize the amounts of Fe-O-Ce sites in the Ce-doped FeOx catalyst. The formation of CeO2 nanoparticles due to a high doping amount of Ce species leads to a decline in catalytic performance, indicating a size-dependent catalytic behavior. Density functional theory (DFT) calculation results indicate that the formation of oxygen vacancies in the Fe-O-Ce sites is more favorable than that in the Fe-O-Fe sites in the Ce-free α-Fe2O3 catalyst. The Fe-O-Ce sites can promote the oxidation of NO to NO2 on the Fe0.93Ce0.07Ox catalyst and further facilitate the reduction of NOx by NH3. In addition, the decomposition of NH4HSO4 can occur at lower temperatures on the Fe0.93Ce0.07Ox catalyst containing atomically dispersed Ce species than on the α-Fe2O3 reference catalyst, resulting in the good SO2/H2O resistance ability in the NH3-SCR reaction.

Mechanism of iron complexes catalyzed in the N-formylation of amines with CO2 and H2: the superior performance of N-H ligand methylated complexes.

CO2 hydrogenation into value-added chemicals not only offer an economically beneficial outlet but also help reduce the emission of greenhouse gases. Herein, the density functional theory (DFT) studies have been carried out on CO2 hydrogenation reaction for formamide production catalyzed by two different N-H ligand types of PNP iron catalysts. The results suggest that the whole mechanistic pathway has three parts: (i) precatalyst activation, (ii) hydrogenation of CO2 to generate formic acid (HCOOH), and (iii) amine thermal condensation to formamide with HCOOH. The lower turnover number (TON) of a bifunctional catalyst system in hydrogenating CO2 may attribute to the facile side-reaction between CO2 and bifunctional catalyst, which inhibits the generation of active species. Regarding the bifunctional catalyst system addressed in this work, we proposed a ligand participated mechanism due to the low pKa of the ligand N-H functional in the associated stage in the catalytic cycle. Remarkably, catalysts without the N-H ligand exhibit the significant transfer hydrogenation through the metal centered mechanism. Due to the excellent catalytic nature of the N-H ligand methylated catalyst, the N-H bond was not necessary for stabilizing the intermediate. Therefore, we confirmed that N-H ligand methylated catalysts allow for an efficient CO2 hydrogenation reaction compared to the bifunctional catalysts. Furthermore, the influence of Lewis acid and strong base on catalytic N-formylation were considered. Both significantly impact the catalytic performance. Moreover, the catalytic activity of PNMeP-based Mn, Fe and Ru complexes for CO2 hydrogenation to formamides was explored as well. The energetic span of Fe and Mn catalysts are much closer to the precious metal Ru, which indicates that such non-precious metal catalysts have potentially valuable applications.

Engineering the Nucleophilic Active Oxygen Species in CuTiOx for Efficient Low-Temperature Propene Combustion.

Industrialization has resulted in the rapid increase of volatile organic compound (VOC) emissions, which have caused serious issues to human health and the environment. In this study, an extensive Cu incorporating TiO2 induced nucleophilic oxygen structure was constructed in the CuTiOx catalyst, which exhibited superior low-temperature catalytic activity for C3H6 combustion. Thorough structural, surface characterization and density functional theory (DFT) calculations revealed that the Cu-O-Ti hybridization induced nucleophilic oxygen initiates C3H6 combustion by abstracting the C-H bond. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results indicated that incorporated copper species acted as the major adsorbent site for the propene molecule. In combination of the DRIFTS and DFT results, the promotion effect of the nucleophilic O on the C-H bond abstraction and CO2 formation pathway was proposed. The surface doping induced nucleophilic oxygen as strong Brønsted basic sites for low-temperature propene combustion exemplified an efficient strategy for rational design of next-generation environmental catalysts.

Study on Propagation Depth of Ultrasonic Longitudinal Critically Refracted (LCR) Wave.

The accurate measurement of stress at different depths in the end face of a high-pressure compressor rotor is particularly important, as it is directly related to the assembly quality and overall performance of aero-engines. The ultrasonic longitudinal critically refracted (LCR) wave is sensitive to stress and can measure stress at different depths, which has a prominent advantage in stress non-destructive measurements. In order to accurately characterize the propagation depth of LCR waves and improve the spatial resolution of stress measurement, a finite element model suitable for the study of LCR wave propagation depths was established based on a wave equation and Snell law, and the generation and propagation process of LCR waves are analyzed. By analyzing the blocking effect of grooves with different depths on the wave, the propagation depth of the LCR wave at seven specific frequencies was determined in turn. On this basis, the LCR wave propagation depth model is established, and the effects of wedge materials, piezoelectric element diameters, and excitation voltages on the propagation depth of LCR waves are discussed. This study is of great significance to improve the spatial resolution of stress measurements at different depths in the end face of the aero-engine rotor.

A Computational Mechanistic Study of Pd(II)-Catalyzed Enantioselective C(sp3)-H Borylation: Roles of APAO Ligands.

A computational mechanistic study has been performed on Pd(II)-catalyzed enantioselective reactions involving acetyl-protected aminomethyl oxazolines (APAO) ligands that significantly improved reactivity and selectivity in C(sp3)-H borylation. The results support a mechanism including initiation of C(sp3)-H bond activation generating a five-membered palladacycle and ligand exchange, followed by HPO42--promoted transmetalation. These resulting Pd(II) complexes further undergo sequential reductive elimination by coordination of APAO ligands and protonation to afford the enantiomeric products and deliver Pd(0) complexes, which will then proceed by oxidation and deprotonation to regenerate the catalyst. The C(sp3)-H activation is found to be the rate- and enantioselectivity-determining step, in which the APAO ligand acts as the proton acceptor to form the two enantioselectivity models. The results demonstrate that the diverse APAO ligands control the enantioselectivity by differentiating the distortion and interaction between the major and minor pathways.

Ligands and Bases Mediate Switching between Aminocarbonylations and Alkoxycarbonylations in Coupling of Aminophenols with Iodoarenes.

The mechanisms of aminocarbonylations and alkoxycarbonylations in coupling of aminophenols with iodoarenes catalyzed by the bidentate phosphorus ligand Pd complexes were explored with theoretical calculations. The origins of chemoselective carbonylation mediated by ligands and bases were disclosed. According to our calculations, the bifurcation points of reaction pathways caused by different ligands and bases combinations are L1/L2Int5, a [DPPP/DIBPP]benzoylpalladium(II)iodide complex. The affinity of L1/L2Int5 and adducts (K2CO3 and DBU), as well as the substrate itself, are the predominant factors of switching from aminocarbonylation to alkoxycarbonylation. The results reveal that K2CO3 directly exchanges iodine with L1Int5 and assists in hydrogen transfer in the DPPP-K2CO3 combination, in which alkoxycarbonylation is more favorable than aminocarbonylation, while for the DIBPP-DBU combination, iodine exchange is achieved by means of the hydrogen bond formed between the carbonyl group on L2Int5 and the substrate amino H due to the influence of the ligand, and then iodine exchange occurs; subsequently DBU-assisted amino H transfers to complete the aminocarbonylation. The proton transfer is the step that determines the chemoselectivity in the DPPP-K2CO3 combination. The iodine exchange determines the chemoselectivity between aminocarbonylation and alkoxycarbonylation in the DIBPP-DBU one. These results would be helpful to deeply understand the roles of each component in a chemoselective reaction in a multicomponent complex system.

Mechanistic Exploration of the Competition Relationship between a Ketone and C═C, C═N, or C═S Bond in the Rh(III)-Catalyzed Carbocyclization Reactions.

The introduction of a C═O, C═C, C═S, or C═N bond has emerged as an effective strategy for carbocycle synthesis. A computational mechanistic study of Rh(III)-catalyzed coupling of alkynes with enaminones, sulfoxonium ylides, or α-carbonyl-nitrones was carried out. Our results uncover the roles of dual directing groups in the three substrates and confirm that the ketone acts as the role of the directing group while the C═C, C═N, or C═S bond serves as the cyclization site. By comparing the coordination of the ketone versus the C═C, C═N, or C═S bond, as well as the chemoselectivity concerning the six- versus five-membered formation, a competition relationship is revealed within the dual directing groups. Furthermore, after the alkyne insertion, instead of the originally proposed direct reductive elimination mechanism, the ketone enolization is found to be essential prior to the reductive elimination. The following C(sp2)-C(sp2) reductive elimination is more favorable than the C(sp3)-C(sp2) formation, which can be explained by the aromaticity difference in the corresponding transition states. The substituent effect on controlling the selectivity was also discussed.

Comprehensive Mechanistic Insight into Cooperative Lewis Acid/Cp*CoIII-Catalyzed C-H/N-H Activation for the Synthesis of Isoquinolin-3-ones.

The mechanism of B(C6F5)3 promoted Cp*CoIII-catalyzed C-H functionalization was investigated in detail employing density functional theory (DFT). The formation free energy of every possible species in the multicomponent complex system was explored and the optimal active catalyst was screened out. The results uncover the role of B(C6F5)3 played in forming active catalyst is from the coordination with OAc-, but not from the formation of [I(C6F5)3B]-, and no acceleration effect is found in C-H activation as well as the formation of CoIII-carbene intermediate. Moreover, present theoretical results elucidate the Cp*CoIII-catalyzed C-H activation is mediated by imine N-coordination other than general proposed the sequence of N-deprotonation directed C-H activation. The metal-controlled C-H/N-H selectivity was then elucidated by insighting into [Cp*CoIIIOAc]+/[Cp*RhIIIOAc]+-catalyzed C-H and N-H activations, respectively.

Mechanistic Exploration of Cp*CoIII/RhIII-Catalyzed Carboamination/Olefination of N-Phenoxyacetamides with Alkenes.

A computational study of Cp*CoIII/RhIII-catalyzed carboamination/olefination of N-phenoxyacetamides with alkenes was carried out to elucidate the catalyst-controlled chemoselectivity. The reaction of the two catalysts shares a similar process that involves N-H and C-H activation as well as alkene insertion. Then the reaction bifurcates at the generated seven-membered metallacycle. For Cp*CoIII catalyst, the resulting metallacycle undergoes oxidation addition, reductive elimination, and protonation to yield the carboamination product exclusively. However, the Cp*RhIII catalyst could promote the subsequent olefination pathway via sequential ß-H elimination, reductive elimination, oxidation addition, and protonation, which enables the experimentally observed mixtures of both carboamination and olefination products. Our results uncover that the higher propensity for the ß-H-elimination of the Cp*RhIII than the Cp*CoIII catalyst in the olefination pathway could be responsible for the different selectivity and reactivity of the two catalysts.

Theoretical insights into the structural and fluorescence properties of DNA containing fluorescent nucleobases.

Fluorescent base analogues are of great importance as sensitive probes to detect the dynamic structures of DNA. In this research, the structural and photophysical properties of 13-mer oligonucleotides containing 4-aminophthalimide:2,4-diaminopyrimidine (4AP:DAP) (4AP0, 4AP') were characterized using both molecular dynamics simulations and quantum mechanics methods. The results indicate that the 4AP:DAP pair is well adapted to the overall B-DNA structure with higher stability and π-stacking abilities. The structural overlap of 4AP' and 4AP0 with the neighboring adenines only lies in the 5'-direction which results in the structure distortion from native B-DNA. Furthermore, the photophysical properties of the fluorescent base monomers and the B-DNA duplex were explored in detail. A very important result is that the hydrogen bond interaction does not have more effect on the fluorescence band apart from the slight red-shifts. In particular, the identity of the neighboring bases stacked with 4AP has an important effect on the fluorescence band. How the local environment can alter the photophysical features of the nucleobases when they are incorporated into the DNA duplex is elucidated.

Simultaneous Fluorescence and Chemiluminescence Turned on by Aggregation-Induced Emission for Real-Time Monitoring of Endogenous Superoxide Anion in Live Cells.

Biological sensors with simultaneous turn-on signals of fluorescence (FL) and chemiluminescence (CL) triggered by one single species are supposed to integrate spatiotemporally resolved FL imaging with dynamic CL sensing into one luminescent assay. Efficiently increased accuracy can be expected based on complementary information simultaneously obtained from two independent modes, which is crucial in disease detection and diagnosis. However, very few examples can be found to date because of the key challenges in the rational design of sensing structures. Herein, aggregation-induced emission (AIE) was employed to develop a novel organic platform TPE-CLA with simultaneous turn-on FL/CL signals specifically modulated by O2•- in cells, which can be attributed to the activation of AIE resulted from the decreasing solubility after recognition. Using imidazopyrazinone (CLA) as the reactive motif and tetraphenylethene (TPE) as FL/CL enhancing skeleton, TPE-CLA is sensitive enough to image native O2•- in Raw264.7 cells and lipopolysaccharide stimulated O2•- in mice. Endogenous O2•- in HL-7702 cells induced by acetaminophen (APAP) was uninterruptedly monitored for 7200 s with CL and the results were further confirmed by FL imaging. Accordingly, TPE-CLA turns out to be a reliable candidate for real-time and continuous monitoring of endogenous O2•- in live cells. The strategy utilizing AIE to accomplish the FL/CL dual detection is expected to extend the application of AIE as reaction-activated biosensors.

A Mechanistic Insight into the Ligand-Controlled Asymmetric Arylation of Aliphatic α-Amino Anion Equivalents: Origin of Regio- and Enantioselectivities.

The reaction mechanism and the origins of regio- and enantioselectivities for Pd-catalyzed asymmetric arylation of aliphatic α-amino anion equivalents were investigated computationally. The results indicate that the reaction proceeds via mainly six sequential steps: deprotonation at α'-site of imine, coordination of α-amino anion to Pd-catalyst, oxidative addition, transmetalation, reductive elimination, as well as the final dissociation to release the product and regenerate the catalyst. The transmetalation is a key step on which both enantioselectivity and regioselectivity depend. The charge inversions of α- and α'-C atoms and the orbital interaction between Pd center and α-C in transmetalation step are responsible for the regioselectivity. Additionally, the intermediates before the dissociation step are critical in controlling the enantioselectivity. Noncovalent interactions analyses indicate that the enantioselectivity primarily arises from the CH···π interactions of isopropyl (iPr) groups with the fluorene and the benzene rings for PdL1-catalyzed reaction.

Solvent Mediating a Switch in the Mechanism for Rhodium(III)-Catalyzed Carboamination/Cyclopropanation Reactions between N-Enoxyphthalimides and Alkenes.

Recently, a new synthetic methodology of rhodium-catalyzed carboamination/cyclopropanation from the same starting materials at different reaction conditions has been reported. It provides an efficient strategy for the stereospecific formation of both carbon- and nitrogen-based functionalities across an alkene. Herein we carried out a detailed theoretical mechanistic exploration for the reactions to elucidate the switch between carboamination and cyclopropanation as well as the origin of the chemoselectivity. Instead of the experimentally proposed RhIII-RhI-RhIII catalytic mechanism, our results reveal that the RhIII-RhV-RhIII mechanism is much more favorable in the two reactions. The chemoselectivity is attributed to a combination of electronic and steric effects in the reductive elimination step. The interactions between alkene and the rhodacycle during the alkene migration insertion control the stereoselectivity in the carboamination reactions. The present results disclose a dual role of the methanol solvent in controlling the chemoselectivity.

A theoretical insight into the formation mechanisms of C/N-ribonucleosides with pyrimidine and ribose.

The detailed formation mechanisms of C-ribonucleoside and N-ribonucleoside via the reaction of 2,4,6-triaminopyrimidine (TAP) with (d)-ribose in aqueous solution were explored using density functional theory (DFT). The calculations indicate that five isomers (α,ß-furanose, α,ß-pyranose and open-chain aldehyde) of (d)-ribose can exist in equilibrium in aqueous solution. In contrast to cyclic isomers, an open-chain aldehyde is most feasible to react with TAP. In general, the formation pathways of C-nucleoside and N-nucleoside proceed in three steps including nucleophilic addition, dehydration and cyclization. The calculated apparent activation energies are 28.8 kcal mol-1 and 29.2 kcal mol-1, respectively. It suggests that both C- and N-nucleoside can be formed in aqueous solution, which is in good agreement with the experimental results. The water molecule plays an important "H-bridge" role by the hydrogen atom relay. Finally, a model structure of nucleobase, which will be beneficial for the C-C glycosidic bond formation, is proposed.

Theoretical characterization of the conformational features of unnatural oligonucleotides containing a six nucleotide genetic alphabet.

The addition of the unnatural P:Z base pair to the four naturally occurring DNA bases expands the genetic alphabet and yields an artificially expanded genetic information system (AEGIS). Herein, the structural feature of oligonucleotides containing a novel unnatural P:Z base pair is characterized using both molecular dynamics and quantum chemistry. The results show that the incorporation of the novel artificial base pair (P:Z) preserves the global conformational feature of duplex DNA except for some local structures. The Z-nitro group imparts new properties to the groove width, which widens the major groove. The unnatural oligonucleotides containing mismatched base pairs exhibit low stability. This ensures efficient and high-fidelity replication. In general, the incorporation of the P:Z pair strengthens the stability of the corresponding DNA duplex. The calculated results also show that the thermostability originates from both hydrogen interaction and stacking interaction. The Z-nitro group plays an important role in enhancing the stability of the H-bonds and stacking strength of the P:Z pair. Overall, the present results provide theoretical insights in the exploration of artificially expanded genetic information systems.