Plasma Chemical Looping: Unlocking High-Efficiency CO2 Conversion to Clean CO at Mild Temperatures.

We propose a plasma chemical looping CO2 splitting (PCLCS) approach that enables highly efficient CO2 conversion into O2-free CO at mild temperatures. PCLCS achieves an impressive 84% CO2 conversion and a 1.3 mmol g-1 CO yield, with no O2 detected. Crucially, this strategy significantly lowers the temperature required for conventional chemical looping processes from 650 to 1000 °C to only 320 °C, demonstrating a robust synergy between plasma and the Ce0.7Zr0.3O2 oxygen carrier (OC). Systematic experiments and density functional theory (DFT) calculations unveil the pivotal role of plasma in activating and partially decomposing CO2, yielding a mixture of CO, O2/O, and electronically/vibrationally excited CO2*. Notably, these excited CO2* species then efficiently decompose over the oxygen vacancies of the OCs, with a substantially reduced activation barrier (0.86 eV) compared to ground-state CO2 (1.63 eV), contributing to the synergy. This work offers a promising and energy-efficient pathway for producing O2-free CO from inert CO2 through the tailored interplay of plasma and OCs.

Modifying the Charge-Density of Tetrahedral Cobalt(II) Centers through Carbon-Layer Modulation Promotes C-H Activation in the Propane Dehydrogenation Reaction (PDH).

The electronic structure of active metal centers plays an indispensable role in regulating catalytic reactivity in heterogeneous catalysis, developing other metals as promoters to decorate electronic state is a common strategy, while non-metal component of carbon as electronic additives to regulate d-band center has rarely been studied in thermal-catalysis field. Herein, we report electron-deficient tetrahedral Co(II) (Td-cobalt(II)) centers through carbon-layer modulation for propane dehydrogenation (PDH). It is indicated that bifunctional sites of both Td-cobalt(II) and metallic-cobalt are designed, and the in situ generated carbon through the disproportionation of CO on metallic-cobalt can cover the inactive metallic-cobalt and tailor d-band of active Td-cobalt(II) simultaneously. More importantly, the pre-deposited carbon-layer is proposed to decrease electron density of Td-cobalt(II) and make d-band center closer to Fermi level, consequently promotes C-H activation in PDH reaction. This study provides new perspective for the utilization of inactive carbon as electronic promoters and unlocks new opportunity to fabricate efficient PDH and other heterogeneous catalysts.

Preparation of nano-MFI zeolites doped with Al/Ti and their performance in VOC sorption.

Highly crystalline nano-MFI-type zeolites containing different elements were synthesized, and the sorption effects of the elements on volatile organic compounds (VOCs) were investigated. The results showed that the optimal toluene and acetone breakthrough time of the synthesized zeolites was 2.1 and 1.9 times as long as that of the commercial zeolite, respectively. For a weakly polar toluene molecule, MFI zeolites (aluminum-free) showed better adsorption properties than aluminum-containing zeolites. For the highly polar acetone molecule, zeolites with a Si/Al ratio of 87 showed the highest adsorption capacity, which was 7% higher than that of the all-silica zeolite and 1.4 times that of the commercial zeolite. Furthermore, MFI zeolites with Ti replacing part of Al proved to have better performance for highly polar molecules. In the adsorption process of VOCs, in addition to internal diffusion, diffusion on the external surface of the zeolite also played a remarkable role, and the adsorption data of all samples fitted better with the pseudo-first-order model. This study may provide a reliable structure-performance relationship for the synthesis of nanosized zeolite-based adsorbents and their use in the industrial recovery/treatment of VOCs.

A motif for B/O-site modulation in LaFeO3 towards boosted oxygen evolution.

Here, a series of transition metal (Ni) doped iron-based perovskite oxides LaFe1-xNixO3-δ (x = 0, 0.25, 0.5, 0.75, 1) were prepared, and then the perovskite oxide with the optimized nickel-iron ratio was doped with non-metallic elements (N). Experimental and theoretical investigations reveal that the co-doping breaks the traditional linear constraint relationship (GOOH - GOH = 3.2 eV) and the theoretical overvoltage is reduced from 0.64 V (LaFeO3-δ) to 0.44 V (LaFe0.5Ni0.5O3-δ/N). Specifically, Ni-doping can accelerate electron transfer and improve the conductivity. Moreover, N-doping can reduce the adsorption energy of *OH/*O and enhance the adsorption energy of *OOH. We demonstrated that the optimized cation and anion co-doped LaFe0.5Ni0.5O3-δ/N perovskite oxide exhibits an excellent OER performance, with a low overpotential of 270.6 mV at 10 mA cm-2 and a small Tafel slope of 65 mV dec-1 in 1 M KOH solution, markedly exceeding that of the parent perovskite oxide LaFeO3-δ (300.9 mV) and commercial IrO2 (289.1 mV). It also delivers decent durability with no significant degradation after a 35 h stability test. This work reveals the internal mechanism of perovskite oxide by doping cation and anion for water oxidation, which broadens the idea for the rational design of new perovskite-based sustainable energy catalysts.

Role of H2O in Catalytic Conversion of C1 Molecules.

Due to their role in controlling global climate change, the selective conversion of C1 molecules such as CH4, CO, and CO2 has attracted widespread attention. Typically, H2O competes with the reactant molecules to adsorb on the active sites and therefore inhibits the reaction or causes catalyst deactivation. However, H2O can also participate in the catalytic conversion of C1 molecules as a reactant or a promoter. Herein, we provide a perspective on recent progress in the mechanistic studies of H2O-mediated conversion of C1 molecules. We aim to provide an in-depth and systematic understanding of H2O as a promoter, a proton-transfer agent, an oxidant, a direct source of hydrogen or oxygen, and its influence on the catalytic activity, selectivity, and stability. We also summarize strategies for modifying catalysts or catalytic microenvironments by chemical or physical means to optimize the positive effects and minimize the negative effects of H2O on the reactions of C1 molecules. Finally, we discuss challenges and opportunities in catalyst design, characterization techniques, and theoretical modeling of the H2O-mediated catalytic conversion of C1 molecules.

Perovskites as oxygen storage materials for chemical looping partial oxidation and reforming of methane.

The traditional partial oxidation, dry reforming and steam reforming of methane technologies are separated into two reactors for execution by chemical looping technology, which can avoid the defects exposed in the traditional process (avoiding carbon accumulation, reducing costs, etc.). The key to chemical looping technology is to find suitable oxygen carriers (OCs), which can store and release oxygen to form a closed loop in the chemical looping. The purpose of this review is to summarize the current status of perovskite oxides for partial oxidation and reforming of methane in chemical looping, describe the structure, oxygen capacity, oxygen migration rate and common synthesis methods of perovskites in chemical looping. In addition, the effects of impregnation loading, ion doping, and structural morphology on the catalytic conversion of CH4 by perovskite OCs and the reaction mechanism on the OCs are also discussed.

Application of Fe-MOFs in Photodegradation and Removal of Air and Water Pollutants: A Review.

Photocatalytic technology has received increasing attention in recent years. A pivotal facet of photocatalytic technology lies in the development of photocatalysts. Porous metal-organic framework (MOF) materials, distinguished by their unique properties and structural characteristics, have emerged as a focal point of research in the field, finding widespread application in the photo-treatment and conversion of various substances. Fe-based MOFs have attained particular prominence. This review explores recent advances in the photocatalytic degradation of aqueous and gaseous substances. Furthermore, it delves into the interaction between the active sites of Fe-MOFs and pollutants, offering deeper insights into their mechanism of action. Fe-MOFs, as photocatalysts, predominantly facilitate pollutant removal through redox processes, interaction with acid sites, the formation of complexes with composite metal elements, binding to unsaturated metal ligands (CUSs), and hydrogen bonding to modulate their respiratory behavior. This review also highlights the focal points of future research, elucidating the challenges and opportunities that lie ahead in harnessing the characteristics and advantages of Fe-MOF composite catalysts. In essence, this review provides a comprehensive summary of research progress on Fe-MOF-based catalysts, aiming to serve as a guiding reference for other catalytic processes.

LaFe0.8Co0.15Cu0.05O3 Supported on Silicalite-1 as a Durable Oxygen Carrier for Chemical Looping Reforming of CH4 Coupled with CO2 Reduction.

Chemical looping reforming of CH4 coupled with CO2 reduction is a novel technology for the utilization of CH4 and CO2. Here, we report a durable and outstanding LaFe0.8Co0.15Cu0.05O3/S-1 oxygen carrier at lower operating temperature to efficiently convert CH4 and utilize CO2. LaFe0.8Co0.15Cu0.05O3 showed a high CH4 reaction rate (7.0 × 10-7 mol·(g·s)-1), CO selectivity (84.2%), and CO yield (0.045 mol·g-1) at 800 °C. However, the reactivity of LaFe0.8Co0.15Cu0.05O3 reduced quickly with the redox cycles. The introduction of Silicalite-1 promoted the performance of the LaFe0.8Co0.15Cu0.05O3 perovskite oxygen carrier during the redox cycles. It can be attributed to the fact that under heat treatment, the LaFe0.8Co0.15Cu0.05O3 particles grew along the edge of Silicalite-1 and the LaFe0.8Co0.15Cu0.05O3 nanoparticles were homogeneously dispersed on the Silicalite-1 surface, which improved the thermal stability and reactivity of the oxygen carrier. In addition, the interface between Silicalite-1 and LaFe0.8Co0.15Cu0.05O3 nanoparticles also played important roles because the porous structure of Silicalite-1 could reduce the mass transfer restriction of the interface. In addition, Silicalite-1 also possessed high CH4 and CO2 adsorption selectivity, leading to higher reactivity.

Density functional theory studies of transition metal carbides and nitrides as electrocatalysts.

Transition metal carbides and nitrides are interesting non-precious materials that have been shown to replace or reduce the loading of precious metals for catalyzing several important electrochemical reactions. The purpose of this review is to summarize density functional theory (DFT) studies, describe reaction pathways, identify activity and selectivity descriptors, and present a future outlook in designing carbide and nitride catalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), nitrogen reduction reaction (N2RR), CO2 reduction reaction (CO2RR) and alcohol oxidation reactions. This topic is of high interest to scientific communities working in the field of electrocatalysis and this review should provide theoretical guidance for the rational design of improved carbide and nitride electrocatalysts.

Highly effective remediation of high-arsenic wastewater using red mud through formation of AlAsO4@silicate precipitate.

High-arsenic wastewater derived from the metallurgical industry of nonferrous minerals is one of the most dangerous arsenic (As) sources that usually follow the emission of massive hazardous arsenic-bearing wastes. Considering the properties of red mud (RM), we propose an alternative and environmentally friendly method for the efficient remediation of high-arsenic wastewater using RM through formation of AlAsO4@silicate precipitate, aiming at ''zero-emission of hazardous solid waste''. The results show nearly 100% of arsenic could be stepwisely removed from high-arsenic wastewater and reduce the arsenic concentration from 6100 mg/L to 40 µg/L using RM at room temperature. The highest arsenic removal capacity of RM reaches 101.5 mg/g at a RM-to-wastewater ratio of 40 g/L due to the superior arsenic adsorption and the co-precipitation of arsenate and Al3+ to form insoluble aluminum arsenate. The silicate shell of arsenic-loaded RM created at an alkaline condition acts as an arsenic stabilizer, resulting in a leached arsenic concentration of 1.2 mg/L in TCLP tests. RM acts as a highly effective arsenic remover and stabilizer for the disposal of high-arsenic wastewater. It shows great potential for the remediation of wastewater containing heavy metals with varying concentrations to produce clean water available for industrial purpose.

Ultra-Fine CeO2 Particles Triggered Strong Interaction with LaFeO3 Framework for Total and Preferential CO Oxidation.

Interactions between the active components with the support are one of the fundamentally factors in determining the catalytic performance of a catalyst. In contrast to the comprehensive understanding on the strong metal-support interactions (SMSI) in metal-based catalysts, it remains unclear for the interactions among different oxides in mixed oxide catalysts due to its complexity. In this study, we investigated the interaction between CeO2 and LaFeO3, the two important oxygen storage materials in catalysis area, by tuning the sizes of CeO2 particles and highlight a two-fold effect of the strong oxide-oxide interaction in determining the catalytic activity and selectivity for preferential CO oxidation in hydrogen feeds. It is found that the anchoring of ultra-fine CeO2 particles (<2 nm) at the framework of three-dimensional-ordered macroporous LaFeO3 surface results in a strong interaction between the two oxides that induces the formation of abundant uncoordinated cations and oxygen vacancy at the interface, contributing to the improved oxygen mobility and catalytic activity for CO oxidation. Hydrogen spillover, which is an important evidence of the strong metal-support interactions in precious metal catalysts supported by reducible oxides, is also observed in the H2 reduction process of CeO2/LaFeO3 catalyst due to the presence of ultra-fine CeO2 particles (<2 nm). However, the strong interaction also results in the formation of surface hydroxyl groups, which when combined with the hydrogen spillover reduces the selectivity for preferential CO oxidation. This discovery demonstrates that in hybrid oxide-based catalysts, tuning the interaction among different components is essential for balancing the catalytic activity and selectivity.

Ultrahigh photo-stable all-inorganic perovskite nanocrystals and their robust random lasing.

Photo-instability has prevented further commercialization of all-inorganic perovskite nanocrystals (NCs) in the field of high-power optoelectronics. Here, an accelerated transformation process from non-luminescent Cs4PbBr6 to CsPbBr3 NCs with bright green emission is explored with irradiation at 365 nm during water-triggered structural transformation. The photoelectric field provided by the photon energy of 365 nm promotes the rapid stripping of CsBr and atomic reconstruction, contributing to the production of ultrahigh photo-stable defect-free CsPbBr3 NCs. The robust emission output of the as-obtained CsPbBr3 NCs is well preserved even when recorded after 160 min. Moreover, a long-term stable random lasing could be achieved when excited using an ∼800 nm femtosecond laser for at least 8.6 × 107 laser shots. Our results not only elucidate the photo-induced accelerated phase transformation process of the all-inorganic perovskites, but also open up opportunities to synthesize highly stable CsPbBr3 NCs for their practical application in photovoltaics and optoelectronics.

Enhanced CH4 and CO Oxidation over Ce1- xFe xO2-δ Hybrid Catalysts by Tuning the Lattice Distortion and the State of Surface Iron Species.

CeO2-Fe2O3 mixed oxides are very attractive as catalysts for catalytic oxidation. Herein, we report the structural dependence of the Ce1- xFe xO2-δ catalysts for CH4 combustion and CO oxidation via changing lattice distortion degrees, surface Fe2O3 states, and oxygen vacancy concentrations. The lattice distortion degree and oxygen vacancy concentration of Ce-Fe-O solid solution can be tuned by changing the contents of Fe and the precipitation temperatures in the preparation process. The precipitation at relatively high temperature (70 °C) promotes the lattice distortion, whereas a lower temperature (0 °C) helps the formation of surface oxygen vacancies. The in situ diffuse reflectance infrared/Raman experiments and the physicochemical characterization suggest that both the CO and CH4 oxidations mainly follow a Mars-van Krevelen mechanism. Both the lattice distortion and the surface iron species play a crucial role in determining the catalytic activity by affecting the redox property of the catalysts. The surface iron species, combined with the oxygen vacancies, improve the catalytic performance by enhancing the adsorption capacity of reactants and reducibility of catalysts. The lattice distortion of CeO2 contributes to the catalytic activity by tuning the oxygen mobility in the bulk, which promotes the re-oxidation rate of catalysts.

Self-enhanced and efficient removal of arsenic from waste acid using magnetite as an in situ iron donator.

High arsenic-containing waste acid from the heavy nonferrous metallurgical sector (Cu, Pb, Zn, Ni, Sn, etc.), one of the most dangerous arsenic hazardous wastes with extremely high arsenic concentrations, has presented enormous challenges to the environment and caused severe environmental pollution over the past few decades due to the lack of affordable and environmentally friendly disposal technologies. Here, we report a green process for the self-enhanced and efficient removal of arsenic from waste acid using magnetite as an in situ iron donator. Firstly, the room-temperature predissolution of magnetite in waste acid provides initial iron ions as a starting precipitator of arsenic, simultaneously providing a suitable pH range and an active surface that are ready for the nucleation and growth of scorodite. Afterwards, arsenic is precipitated in form the of scorodite, which is driven by a mutually improved cycle composed of arsenic precipitation and magnetite dissolution on the surface of magnetite particles. This cycle creates a low supersaturation of iron and constant pH in the waste acid, ensuring the continuous precipitation of arsenic as well-crystallized and environmentally stable scorodite by using magnetite as an in situ iron donator via the reaction of 2Fe3O4 + 6H3AsO4 + H2O2 = 6FeAsO4 + 10H2O. Under optimal conditions, including a 6-h room-temperature predissolution, a 12-h atmospheric reaction at 90 °C and a pH of 2.0 with a magnetite dosage at the Fe3O4/As molar ratio (the molar ratio of Fe3O4 in magnetite to As in waste acid) of 1.33, 99.90% of arsenic was successively removed from waste acid with an initial arsenic concentration of 10300 mg/L. In combination with the good adaptability of this process, the performed case study and prospective process show the successful removal of arsenic from waste acid as well as great potential for large-scale applications.

Sn separation from Sn-bearing iron concentrates by roasting with waste tire rubber in N2 + CO + CO2 mixed gases.

The waste tire rubber releases CO, H2S, SO2 and COS during pyrolysis process in N2+CO+CO2 mixed gases, which can reduce and sulfurize SnO2 to SnS thermodynamically. Correspondingly, a new process to separate Sn from Sn-bearing iron concentrates through roasting with waste tire rubbers at a relative low temperature (1273 K) is put forward in the present paper. The formation of Fe-Sn alloy restricts Sn volatilization obviously during the roasting process, and its formation mechanism differs related to roasting temperature and CO content in the mixed gases. The Fe-Sn alloy formation could be weakened and the Sn residual content is decreased to 0.020 wt % at a roasting temperature of 1273 K and waste tire rubber amount of 10 wt %. Meanwhile, the Fe content in the roasted residue increases to 72.25 wt % through a reduction of Fe3O4 to FeO under a mixed gas of 58%N2+21%CO+21%CO2, realizing the tin removal and iron resource utilization from Sn-bearing concentrates. Besides, the zinc which originated from waste tire rubber in the roasted residue is low to 0.015 wt %, implying that it is concentrated in the dust and could be recovered using a dust collection process.

Exploring the ternary interactions in Cu-ZnO-ZrO2 catalysts for efficient CO2 hydrogenation to methanol.

The synergistic interaction among different components in complex catalysts is one of the crucial factors in determining catalytic performance. Here we report the interactions among the three components in controlling the catalytic performance of Cu-ZnO-ZrO2 (CZZ) catalyst for CO2 hydrogenation to methanol. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements under the activity test pressure (3 MPa) reveal that the CO2 hydrogenation to methanol on the CZZ catalysts follows the formate pathway. Density functional theory (DFT) calculations agree with the in situ DRIFTS measurements, showing that the ZnO-ZrO2 interfaces are the active sites for CO2 adsorption and conversion, while the presence of metallic Cu is also necessary to facilitate H2 dissociation and to provide hydrogen resource. The combined experiment and DFT results reveal that tuning the interaction between ZnO and ZrO2 can be considered as another important factor for designing high performance catalysts for methanol generation from CO2.

Disposal of high-arsenic waste acid by the stepwise formation of gypsum and scorodite.

The typical disposal of high-arsenic waste acid is at the expense of discharging a large quantity of hazardous solid waste, resulting in secondary pollution of arsenic. We propose a modified lime/ferric salt method for high-arsenic waste acid disposal by the stepwise formation of gypsum and scorodite at atmospheric pressure. The sulfuric acid in the high-arsenic waste acid is first removed by calcium carbonate generating gypsum, and then the arsenic in the solution is precipitated in form of scorodite. Gypsum with an arsenic leaching concentration below 5 mg L-1 is obtained at a final pH of 0.5 in the calcium carbonate neutralization stage. In the second stage, the optimal conditions including a starting pH of 2.0, an Fe/As ratio of 1.5, a reaction temperature in the range of 80-90 °C and a reaction time equal to or longer than 8 hours provide an arsenic removal efficiency of 95.34% by the formation of well-crystallized and environmentally stable scorodite with grain sizes in a range of 1-5 µm. The proposed process offers a promising and facile solution for the low-cost disposal of high-arsenic waste acid in the nonferrous metallurgical industry, which enables an efficient arsenic removal with the good accessibility of chemical reagents and facilities.

DFT insights into oxygen vacancy formation and CH4 activation over CeO2 surfaces modified by transition metals (Fe, Co and Ni).

The effects of transition metal (Fe, Co and Ni) modification (adsorption, insertion and substitution) of CeO2 surfaces on oxygen vacancy formation and CH4 activation are studied on the basis of first principles calculations. The results indicate that the hollow, O-O-bridge and Ce-O-bridge sites are the most stable sites for Fe, Co and Ni atom adsorption on the CeO2(111) surface, and the double O-bridge, O-top and double O-bridge sites are the corresponding most favorable sites for the CeO2(110) surface. Most of the configurations that are generated by the transition metal modification of CeO2(111) and (110) surfaces are accompanied by the reduction of Ce4+ to Ce3+. Based on the calculated subsurface (SS) and sublayer (SL) oxygen vacancies of the CeO2(111) surface, the results show that the substitution of transition metals on the CeO2(111) surface can promote SS oxygen vacancy formation spontaneously, whereas the most stable adsorption of transition metal Fe and Ni atoms on the CeO2(111) surface can promote SL oxygen vacancy formation spontaneously. For the CeO2(110) surface, the substitution of transition metals can facilitate plain (P) and spilt (S)-type oxygen vacancy formation spontaneously. With respect to CH4 activation, the results show that Co atom substitution on the CeO2(110) surface can greatly facilitate the first C-H bond activation step, with an energy barrier of 0.783 eV and a reaction energy of 0.229 eV. However, Co atom substitution on the CeO2(110) surface with P and S-type oxygen vacancies is not conducive to C-H activation. The obtained results could provide new insights into the structural features of transition metal-modified CeO2 at the atomistic level, leading to the more efficient design of oxygen carriers and the optimization of the activation pathways of methane over this type of catalyst.