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Ag(3 wt%)-loaded gamma-Al2O3 (Ag/Al2O3) catalysts were prepared using four types of commercially available alumina powders (CTB, PUR, VGL, and CFF). Based on the support, the activity of these catalysts for the H-2-assisted selective catalytic reduction (SCR) of NO by NH3 or C3H6 decreased in the order CTB > PUR > VGL > CFF. After sintering treatment (H-2 reduction at 800 degrees C), the particle size of the Ag metal nanoparticles (NPs) changed and was found to be correlated with the catalytic activity (CTB < PUR < VGL < CFF). After re-oxidation of H-2-reduced Ag/Al2O3 at 500 degrees C, the in situ infrared (IR) spectra showed negative bands at 3762 cm(-1) due to the HO-mu(1)-Al-VI site, where the band intensity increased in the order CTB > PUR > VGL > CFF. IR study of pyridine adsorbed on Ag-free gamma-Al2O3 showed that the number of strong Lewis acid sites (unsaturated Al-IV(3+)) increased in the same order, CTB > PUR > VGL > CFF, and the number of strong Lewis acid sites decreased when Ag was loaded on the supports. In situ X-ray absorption near-edge structure (XANES) and UV-vis studies of Ag/Al2O3 sintered under NO + O-2 at 400 degrees C showed oxidative redispersion of the Ag metal NPs to regenerate atomic Ag(i) sites. The amount of redispersed Ag metal and the initial rates of redispersion estimated from the in situ UV-vis results changed in the following order: CTB > PUR > VGL > CFF. These results suggest that the HO-mu(1)-Al-VI site adjacent to the unsaturated Al-IV(3+) site on gamma-Al2O3 is the anchoring site of the atomic Ag species, and the sintering resistance of Ag/Al2O3 increases with the number of HO-mu(1)-Al-VI sites. During H-2-assisted SCR, where both H-2 and NO + O-2 were co-fed to the catalysts, the number of highly dispersed Ag species (active sites) increased with the number of HO-mu(1)-Al-VI sites; hence, NO conversion increased with the number of HO-mu(1)-Al-VI sites on the support. The present results provide molecular-level insights into the design of sintering-resistant Ag/Al2O3 catalysts for SCR.

Metal/oxide support perimeter sites are known to provide unique properties because the nearby metal changes the local environment on the support surface. In particular, the electron scavenger effect reduces the energy necessary for surface anion desorption, thereby contributes to activation of the (reverse) Mars-van Krevelen mechanism. This study investigated the possibility of such activation in hydrides, carbides, nitrides, and sulfides. The work functions (WFs) of known hydrides, carbides, nitrides, oxides, and sulfides with group 3, 4, or 5 cations (Sc, Y, La, Ti, Zr, Hf, V, Nb, and Ta) were calculated. The WFs of most hydrides, carbides, and nitrides are smaller than the WF of Ag, implying that the electron scavenger effect may occur when late transition metal nanoparticles are adsorbed on the surface. The WF of oxides and sulfides decrease when reduced. The surface anion vacancy formation energy correlates well with the bulk formation energy in carbides and nitrides, while almost no correlation is found in hydrides because of the small range of surface hydrogen vacancy formation energy values. The electron scavenger effect is explicitly observed in nanorods adsorbed on TiH2 and Ti2O3; the surface vacancy formation energy decreases at anion sites near the nanorod, and charge transfer to the nanorod happens when an anion is removed at such sites. Activation of hydrides, carbides, and nitrides by nanorod adsorption and screening support materials through WF calculation are expected to open up a new category of supported catalysts., Supplementary material available at https://doi.org/10.1039/D1CP02068D

Literature data based on the water gas shift (WGS) reaction have been analyzed using statistical methods based on machine learning (ML). Our ML approach, which considers elemental features as input representations rather than the catalyst compositions, was successfully applied, and new promising catalyst candidates for future research were proposed.

Systematic computational efforts aimed at calculating surface anion vacancy formation energies as important descriptors of catalytic performance are summarized.

Spinel oxides are an important class of materials for heterogeneous catalysis including photocatalysis and electrocatalysis. The surface O vacancy formation energy (EOvac) is a critical quantity on catalyst performance because the surface of metal oxide catalysts often acts as reaction sites, for example, in the Mars-van Krevelen mechanism. However, experimental evaluation of EOvac is very challenging. We obtained the EOvac for (100), (110), and (111) surfaces of normal zinc-based spinel oxides ZnAl2O4, ZnGa2O4, ZnIn2O4, ZnV2O4, ZnCr2O4, ZnMn2O4, ZnFe2O4, and ZnCo2O4. The most stable surface is (100) for all compounds. The smallest EOvac for a surface is the largest in the (100) surface except for ZnCo2O4. For (100) and (110) surfaces, there is a good correlation, over all spinels, between the smallest EOvac for the surface and bulk formation energy, while the ionization potential correlates well in (111) surfaces. Machine learning over EOvac of all surface sites in all orientations and all compounds to find the important factors, or descriptors, that decide the EOvac revealed that bulk and surface-dependent descriptors are the most important, namely the bulk formation energy, a Boolean descriptor on whether the surface is (111), and the ionization potential, followed by geometrical descriptors that are different in each O site., Comment: Supplementary material available at https://doi.org/10.1039/D1CP03657B

We have constructed and analyzed an updated dataset consisting of 4759 experimental datapoints for the oxidative coupling of methane (OCM) reaction based on literature data reported before 2020 (similar to 2019) using machine learning (ML) methods. Several ML methods, including random forest regression (RFR), extra trees regression (ETR), and gradient boosting regression with XGBoost (XGB), were used in conjunction with our proposed approach, in which elemental features are used as input representations rather than inputting the catalyst compositions directly. A recent research trend, namely, the extensive exploration of Mn/Na2WO4/SiO2 catalyst systems in recent years due to their high activity and durability, was clearly reflected in the dataset analysis. An ML model for the prediction of the reaction outcome (C-2 yield) was success- fully developed, and feature importance scores and SHapley Additive exPlanations (SHAP) values were calculated based on ETR and XGB, respectively, to identify the input variables with the greatest influence on the catalyst performance and observe how these important variables affect the C-2, yield in the OCM. The discovery and optimization of catalytic processes using ML as a "surrogate" model were explored, and promising catalytic system candidates for the OCM reaction were identified. Notably, the developed ML model predicted catalysts containing elements that do not appear in the OCM dataset. This clearly demonstrates desirably high potential of our ML model to enable extrapolative predictions for ML-aided future catalysis research.

The activity and stability of supported metal catalysts, which exhibit high efficiency and activity, are significantly influenced by the interactions between the metal and the support, that is, metal-support interactions (MSIs). Here, we report an investigation of the MSIs between supported rhenium (Re) and oxide supports such as TiO

Designing novel catalysts is key to solving many energy and environmental challenges. Despite the promise that data science approaches, including machine learning (ML), can accelerate the development of catalysts, truly novel catalysts have rarely been discovered by ML because of one of its most common limitations and criticisms—the assumed inability of the models to extrapolate and identify extraordinary materials beyond those present in the training data set. Herein, we demonstrate an extrapolative ML approach to develop new multi-elemental catalysts based on supported Pt as an active metal and TiO2 as a support for the low-temperature reverse water-gas shift (RWGS) reaction. Using 45 catalysts as the initial data points and performing 44 cycles of the closed loop discovery system (ML prediction + experiment), we experimentally tested a total of 300 catalysts and identified more than 100 catalysts with superior activity as compared to the previously reported high-performance catalysts. The composition of the optimal catalyst discovered by this approach was Pt(3)/Rb(1)-Ba(1)-Mo(0.6)-Nb(0.2)/TiO2. Notably, Nb was not included in the original dataset, and the catalyst composition identified was unpredictable even by human experts.

Synergistic nitrogen reduction and water oxidation process is significant to the photocatalytic fixation of nitrogen. However, the coupling mechanism remains ambiguous and lacks study. Herein, we r...

Photodriven nonoxidative coupling of CH 4 (NOCM) is an attractive potential way to use abundant methane resources. Herein, a n-type doped photocatalyst for NOCM is created by doping single-atom Nb into hierarchical porous TiO 2 -SiO 2 (TS) microarray, which exhibits a high conversion rate of 3.57 μmol g -1 h -1 with good recyclability. The Nb dopant replaces the 6-coordinated titanium on the (1 0 1) surface and forms shallow electron-trapped surface polarons along [0 1 0] direction as verified by the experimental analyses and the first-principle density functional theory calculation. The comparison of different models proves that the electron localization caused by the n-type doping is beneficial to both the methane activation and ethane desorption. The positive effect of n-type dopant on CH 4 conversion is further verified on Mo-, W- and Ta-doped composites. In contrast, the doping of p-type dopant (Ga, Cu, Fe) shows less active influence. This study provides an in-depth insight into the effect of dopant type and is expected to guide the smart photocatalyst design for CH 4 conversion.

The reverse water-gas shift (RWGS) reaction is a promising catalytic route for reducing CO2 emissions because its product, CO, is a key intermediate in various industrialized catalytic processes that produce fuels and chemicals. We describe herein a MoOx/TiO2-supported Pt catalyst (Pt(3)/MoOx(15)/TiO2; Pt loading = 3 wt%, MoO3 loading = 15 wt%) that promotes the RWGS reaction at low temperature (200–300 °C) with high activity and selectivity. The catalytic performance for both CO2 conversion and selectivity of Pt(3)/MoOx(15)/TiO2 is better than those of Pt catalysts on other supports and other metal catalysts supported on MoOx(15)/TiO2, as well as Cu– and Fe–Cr-based industrial catalysts. Moreover, results of operando X-ray absorption spectroscopy studies show that the reaction takes place via the reverse Mars–van Krevelen mechanism where H2 acts as a reducing agent to create oxygen vacancies on the supported Mo oxide species that are filled by CO2 as an oxidizing agent.

It is important to develop self-producing reactive oxygen species (ROSs) systems and maintain the continuous and effective degradation of organic pollutants. Herein, for the first time, a system of ultrasound-treated CoS2-x mixed with Fe2+ is constructed to sustainably release singlet oxygen (1 O2 ) for the effective degradation of various organic pollutants, including dyes, phenols, and antibiotics. Ultrasonic treatment produces defects on the surface of CoS2 which promote the production of ROSs and the circulation of Fe3+ /Fe2+ . With the help of Co4+ /Co3+ exposed on the surface of CoS2-x , the directional conversion of superoxide radical (. O2- ) to 1 O2 is realized. The CoS2-x /Fe2+ system can degrade organic pollutants efficiently for up to 30 days, which is significantly better than the currently recognized CuPx system (

Introduction of linker defects in a visible light responsive metal–organic framework (MOF) photocatalyst, MIL-125(Ti)–NH2, has been attempted to improve its reactivity. MIL-125(Ti)–NH2, composed of Ti-oxo cluster and 2-aminoterephthalic acid organic linker, was synthesized by a solvothermal method and then underwent photothermal treatments. XRD measurements and 1H NMR spectroscopy revealed that linker elimination from the MOF occurred by a simultaneous visible-light irradiation and mild heating at 313 K in water containing electron donor, while keeping its framework structure. The resultant defective MOF effectively promotes visible light-driven H2 evolution reaction from water containing electron donor without using any cocatalysts, and its activity is comparable to that of Pt cocatalysts-loaded crystalline MIL-125(Ti)–NH2. When pristine MIL-125(Ti)–NH2 without cocatalysts is used in the reaction, the reduction of Ti species in Ti-oxo clusters from Ti4+ to Ti3+ takes place instead of reducing protons to evolve H2; thereby, linker defect introduction caused by the photothermal treatment was concluded to play a role in creating effective reaction sites for proton reduction on Ti-oxo clusters.

3D-MoS2 can adsorb organic molecules and provide multidimensional electron transport pathways, implying a potential application for environment remediation. Here, we study the degradation of aromatic organics in advanced oxidation processes (AOPs) by a 3D-MoS2 sponge loaded with MoS2 nanospheres and graphene oxide (GO). Exposed Mo4+ active sites on 3D-MoS2 can significantly improve the concentration and stability of Fe2+ in AOPs and keep the Fe3+ /Fe2+ in a stable dynamic cycle, thus effectively promoting the activation of H2 O2 /peroxymonosulfate (PMS). The degradation rate of organic pollutants in the 3D-MoS2 system is about 50 times higher than without cocatalyst. After a 140 L pilot-scale experiment, it still maintains high efficiency and stable AOPs activity. After 16 days of continuous reaction, the 3D-MoS2 achieves a degradation rate of 120 mg L-1 antibiotic wastewater up to 97.87 %. The operating cost of treating a ton of wastewater is only US$ 0.33, suggesting huge industrial applications.

This work spotlights the facile method to deposit cobalt oxide (CoOx) nanoparticles as a cocatalyst on Fe-MOF-bpdc to enhance its photocatalytic activity for water oxidation reaction (WOR) under visible light irradiation to evolve gaseous O2. Due to the soft conditions needed for the process developed, the framework structure of Fe-MOF-bpdc was maintained even after the deposition of CoOx. The optimized CoOx@Fe-MOF-bpdc composite showed enhanced activity towards visible-light-driven WOR as compared to pristine Fe-MOF-bpdc, the amount of evolved O2 being increased by about 2 times at the maximum with CoOx loading of 2 wt% as Co metal. Investigations on the wavelength dependence of visible-light-driven WOR on CoOx@Fe-MOF-bpdc revealed that the direct photo-excitation of Fe-oxo clusters within Fe-MOF-bpdc plays an important role to initiate the reaction. Furthermore, it was found that the rate of 2-propanol oxidation reaction, which is a typical two-electron oxidation reaction, was hardly affected by CoOx deposition, suggesting that CoOx acts as a unique hole trapping site and more preferentially catalyse the four-electron oxidation reactions like WOR than the two-electron oxidation reaction.

Perovskite oxides comprise an important class of materials, and some of their applications depend on the surface reactivity characteristics. We calculated, using density functional theory, the surface O vacancy formation energy (

Metal/oxide support perimeter sites are known to provide unique properties because the nearby metal changes the local environment on the support surface. In particular, the electron scavenger effect reduces the energy necessary for surface anion desorption, and thereby contributes to activation of the (reverse) Mars-van Krevelen mechanism. This study investigated the possibility of such activation in hydrides, carbides, nitrides, and sulfides. The work functions (WFs) of known hydrides, carbides, nitrides, oxides, and sulfides with group 3, 4, or 5 cations (Sc, Y, La, Ti, Zr, Hf, V, Nb, and Ta) were calculated. The WFs of most hydrides, carbides, and nitrides are smaller than the WF of Ag, implying that the electron scavenger effect may occur when late transition metal nanoparticles are adsorbed on the surface. The WF of oxides and sulfides decreases when reduced. The surface anion vacancy formation energy correlates well with the bulk formation energy in carbides and nitrides, while almost no correlation is found in hydrides because of the small range of surface hydrogen vacancy formation energy values. The electron scavenger effect is explicitly observed in nanorods adsorbed on TiH2 and Ti2O3; the surface vacancy formation energy decreases at anion sites near the nanorod, and charge transfer to the nanorod happens when an anion is removed at such sites. Activation of hydrides, carbides, and nitrides by nanorod adsorption and screening support materials through WF calculation are expected to open up a new category of supported catalysts.

Generation of surface active sites with tailor-made structure is a promising way to enhance catalytic properties of inexpensive metal oxides, as a replacement to noble metals. In the abatement of N...

Photodriven nonoxidative coupling of CH

Charged domain walls and boundaries in ferroelectric materials display distinct phenomena, such as an increased conductivity due to the accumulation of bound charges. Here, we report the electron microscopy observations of atomic-scale arrangements at charged domain boundaries in the hybrid improper ferroelectric Ca2.46Sr0.54Ti2O7. Like in the prototype improper ferroelectric YMnO3, we find that charged domain boundaries in Ca2.46Sr0.54Ti2O7 correspond to out-of-phase boundaries, which separate adjacent domains with a fractional translational shift of the unit cell. In addition, our results show that strontium ions are located at charged domain boundaries. The out-of-phase boundary structure may decrease the polarization charge at the boundary because of the ferrielectric nature of Ca2.46Sr0.54Ti2O7, thereby promoting the stabilization of the charged state. By combining atomic-resolution imaging and density-functional theory calculations, this study proposes an unexplored stabilization mechanism of charged domain boundaries and structural defects accompanying out-of-phase translational shifts.

It is important to develop self-producing reactive oxygen species (ROSs) systems and maintain the continuous and effective degradation of organic pollutants. Herein, for the first time, a system of ultrasound-treated CoS

3D-MoS

In this chapter, the application of metal-organic framework (MOF) as a visible light–responsive photocatalyst for water-splitting reaction will be reviewed. The organic linker moieties as well as inorganic metal oxide clusters within MOF can act as the visible light–harvesting units where excited electrons and holes are produced. It will be demonstrated that the H2 evolution reaction on MOF photocatalysts are initiated by the photoexcitation of organic linker moieties and following electron transfer to metal oxides, that is the dye-sensitizing mechanism. On the other hand, the O2 evolution reaction on MOF is initiated by the water oxidation by the photoformed holes produced on metal oxide moieties under visible light irradiation.

Derivatives of malachite green, a well-known triphenylmethine dye, have been adapted for third-generation photovoltaic applications as dye-sensitized solar cells (DSSC). The solar cells were developed based on a concentrated Br3−/Br− liquid electrolyte coupled to different trifluoroacetate (TFA−), triflate (TfO−), bromide (Br−) and tetrafluoroborate (BF4−) malachite green salts as dye sensitizers and mesoporous TiO2 anatase as electron collector, and their optoelectronic properties were characterized. The adsorption patterns of such salts at the TiO2 nanoparticle surface were studied by zeta (ζ) potential measurements on colloidal suspensions under neat conditions, and compared to the desorption rates of the dyes when exposed to the DSSC electrolyte. The different affinities of the ionic pairs for the oxide surface and the bulk were found crucial for the stability of the self-assembled monolayer of carboxylic acid-anchored chromophores at the surface, and for the photoconversion efficiency associated ther...

Various triflate (TfO–), tetrafluoroborate (BF4–), and perchlorate (ClO4–) salts of (E)-9-(3-(4-(diphenylamino)phenyl)allylidene)-9H-carbazol-9-ium chromophores, asymmetrical streptocyanine blue dyes, were synthesized, and their structures and photochemical and electrochemical properties were characterized. Displaying a high absorption band in the wavelength range 620–640 nm in acidified benzonitrile, the dyes provide an intense absorption at longer wavelength thanks to their oxidized π-conjugated systems. The π-electronic structure underwent twisting and bending, counteracting the electron-donating/withdrawing induction of its different substituents with a propensity to cancel its dipole moment and HOMO–LUMO charge-transfer coefficient. Zeta potential measurements of colloidal suspensions of sensitized TiO2 anatase nanoparticles outlined the difference in electric behavior of the organic ionic pairs at the surface of the nanoparticles: The noncoordinating or coordinating characters of the counterions wer...

Anchoring titania on carbon sphere forms a core–shell structure (TiO2@CS) which shows high-performance visible light response photocatalysis. In order to further improve such photocatalysis, herein acrylic acid (AA) is employed to modify the surface chemistry of CS so as to craft the interfacial structure between CS and TiO2. It was found that AA addition leads to morphology change from smooth to rough surface or to aggregates of smaller primary nanoparticles which, however, do not impede formation of the close contact core–shell structure with TiO2. Detailed analysis demonstrates a complex change in surface functional groups of CS in which the acidic OH is the major type whose quantity shows a peak maximum and a continuous increase at small and large AA addition ranges, respectively. Photocatalysis, photocurrent, and DFT calculation certificate that rather than COOH, the acidic OH, particularly, that related to sufficiently conjugated backbone carbon contributes to the formation of the interfacial structure which facilitates better visible light responsive photocatalysis. Benefiting from the improved interfacial charge separation, the visible light photoactivity reaches the highest when the quantity of the conjugated carbon-related OH becomes the maximum. An explicit charge transfer mechanism is proposed based on both experimental and theoretical calculation results.

TiO 2 -encapsulated H-ZSM photocatalysts were prepared by physical mixing of TiO 2 and zeolites. Pt was immobilized on the surface of the TiO 2 -encapsulated zeolite (H-ZSM) catalysts by a simple photochemical reduction method. Different weight ratios of both TiO 2 and Pt were hybridized with H-ZSM and the catalytic performance of the prepared catalysts was investigated for 2-propanol oxidation in liquid phase and acetaldehyde in gas phase reaction. Around 5–10 wt% TiO 2 -encapsulated H-ZSM catalysts was found to be optimal amount for the effective oxidation of the organics. Prior to light irradiation, Pt-TiO 2 -H-ZSM showed considerable amount of catalytic degradation of 2-propanol in the dark, forming acetone as an intermediate. In this study, Pt has played a major and important role on the total oxidation of 2-propanol as well as acetaldehyde. As a result, no residual organics were present in the pores of the zeolites. The catalysts could be reused more than three times without losing their catalytic activity in both phases. The Pt-TiO 2 -H-ZSM photocatalysts could overcome the problem of strong adsorption of organics in the zeolite pores (after the reaction). Thus, Pt-TiO 2 -H-ZSM can be used as a potential catalyst for both liquid and gas phase oxidation of organic pollutants.