Hydrotalcite-like Compounds Research Articles

CoAl composite catalysts derived from hydrotalcite-like compounds for CH4 efficient dry reforming

In this study, CoAlx-LDH hydrotalcite-like was used as the precursors to prepare the CoAlx-LD composite catalysts for the DRM reaction. The transition metal Co was the main catalytic active centers for the DRM reaction. The layered structure of the hydrotalcite-like CoAlx-LDH precursors promoted the highly dispersed Co0 active centers to be formed in the CoAlx-LD catalysts. In addition, synergistic effects between active sites, basic sites and oxygen vacancies can promote the DRM catalytic performances of CoAl composite catalysts. Meanwhile, the Co/Al mole ratio can regulate the active sites, basic sites and oxygen vacancies in the catalysts, thereby affecting its catalytic performances. The CoAl12-LD catalyst with a Co/Al mole ratio of 1/2 exhibited excellent DRM catalytic performances. The CH4 and CO2 conversions on the prepared CoAl12-LD catalyst achieved 86.8% and 53.4% at atmospheric pressure and 700 °C, respectively. In addition, the catalyst also showed excellent use stability in the DRM reaction.

Sheet-assembled Zn-based sorbents towards highly efficient desulfurization of hot coal gas: H2S-absorption/COS-release behavior and sulfur-release inhibiting mechanism

It is still challenging to obtain high-temperature sorbents with strong abilities of absorbing H2S and suppressing COS-release during coal-gas desulphurization process. Furthermore, the related inhibiting mechanism is unclear. Herein, functional Zn-based sorbents, with HTLCs (hydrotalcite-like compounds) as the precursor, were designed and fabricated via microwave-assisted co-precipitation method. Doping of metals (Mo/Ni/Co) with function of catalyzing COS-hydrogenolysis was proposed for sorbent modification. The resultant sorbents exhibit hierarchical structure self-assembled from nanosheets. As expected, Mo-, Ni-, and Co-doping result in significant decrease (by 78 %–85 %, 83 %–90 %, and 59 %–74 %, respectively) in the amount of released COS for sorbents. Moreover, Ni-doping generally causes the smallest negative effect on H2S-uptake behavior. It is related to a decline (by about 40 %) in the length of laminas unit and more porous structure of sorbents because of Ni-doping. Especially, the sorbent with the lowest Ni-doping ratio shows high sulfur capacity (27.1 g S/100 g sorbent, desulfurization efficiency: > 99.5 %) and low COS-release amount (1.5 × 10−3 g COS/100 g sorbent). More importantly, it also maintains relatively stable performance over successive sulfidation-regeneration cycles. In addition, the analysis of COS-hydrogenation behavior over individual components in desulfurizers reveals that the doped metals greatly accelerate the COS-hydrogenolysis reaction, responsible for less COS emission of modified sorbents.

Synthesis, structural analysis and photocatalytic ability of novel Mg-Al-Ag and Mg-Al-Ag-Zn hydrotalcite-like compounds

To date, various hydrotalcite HT (Mg-Al) compounds are investigated to expand hydrotalcite-like material’s applications, especially for dye treatment purposes. From the characteristics of silver together with zinc oxide (ZnO) such as antibacterial along with photocatalytic behaviors, the combination of Ag-ZnO with hydrotalcite Mg-Al is necessitous. Consequently, this work aimed to synthesize and characterize hydrotalcite Mg-Al doped with Ag(I) (HT-Ag) as well as doped with Ag(I) and Zn (II) (HT-Ag-Zn) by the co-precipitation method. Both Ag(I) and Zn(II) were doped simultaneously on hydrotalcite Mg-Al for the first time. The characteristics of synthesized HT-Ag and HT-Ag-Zn were identified using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), dynamic light scattering, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–Vis diffuse reflectance spectroscopy (UV-Vis DRS) methods. The total surface area and pore size of the samples were evaluated due to BET surface area measurement. The obtained results indicated that regular Mg-Al-Ag and Mg-Al-Ag-Zn hydrotalcite-like compounds were synthesized successfully. Furthermore, the HT-doped materials implied the capacity to inhibit the growth of gram-negative bacteria such as E. coli, and gram-positive bacteria such as S. aureus. Besides, these doped materials were applied to the photocatalysis of Remazol Midnight Black (RMB) dyes. The HT-Ag exhibited higher photocatalytic capacity than the HT-Ag-Zn. The optimization process for degrading RMB dye molecules was carried out using response surface methodology combined with a Box-Behnken design and a quadratic model. In addition, the catalytic repeatability of the HT-doped material was determined to give suggestions for the potential application of HT-Ag as a photocatalyst.

Mixed-Matrix Organo-Silica-Hydrotalcite Membrane for CO2 Separation Part 1: Synthesis and Analytical Description.

Hydrotalcite exhibits the capability to adsorb CO2 at elevated temperatures. High surface area and favorable coating properties are essential to harness its potential for practical applications. Stable alcohol-based dispersions are needed for thin film applications of mixed membranes containing hydrotalcite. Currently, producing such dispersions without the need for delamination and dispersing agents is a challenging task. This work introduces, for the first time, a manufacturing approach to overcoming the drawbacks mentioned above. It includes a synthesis of hydrotalcite nanoparticles, followed by agent-free delamination of their layers and final dispersion into alcohol without dispersing agents. Further, the hydrotalcite-derived sorption agent is dispersed in a matrix based on organo-silica gels derived from 1,2-bis(triethoxysilyl)ethane (BTESE). The analytical results indicate that the interconnection between hydrotalcite and BTESE-derived gel occurs via forming a strong hydrogen bonding system between the interlayer species (OH groups, CO32-) of hydrotalcite and oxygen and silanol active gel centers. These findings lay the foundation for applications involving incorporating hydrotalcite-like compounds into silica matrices, ultimately enabling the development of materials with exceptional mass transfer properties. In part 2 of this study, the gas separation performance of the organo-silica and the hydrotalcite-like materials and their combined form will be investigated.

Europium insertion into MgAl hydrotalcite-like compound to promote the photocatalytic oxidation of nitrogen oxides

Easy synthesis of efficient, non-toxic photocatalysts is a target to expand their potential applications. In this research, the role of Eu3+ doping in the non-toxic, affordable, and easily prepared MgAl hydrotalcite-like compounds (HTlcs) was explored in order to prepare visible light semiconductors. Eu doped MgAl-HTlcs (MA-xEu) samples were prepared using a simple coprecipitation method (water, room temperature and atmospheric pressure) and europium was successfully incorporated into MgAl HTlc frameworks at various concentrations, with x (Eu3+/M3+ percentage) ranging from 2 to 15. Due to the higher ionic radius and lower polarizability of Eu3+ cation, its presence in the metal hydroxide layer induces slight structural distortions, which eventually affect the growth of the particles. The specific surface area also increases with the Eu content. Moreover, the presence of Eu3+ 4f energy levels in the electronic structure enables the absorption of visible light in the doped MA-xEu samples and contributes to efficient electron-hole separation. The microstructural and electronic changes induced by the insertion of Eu enable the preparation of visible light MgAl-based HTlcs photocatalysts for air purification purposes. Specifically, the optimal HTlc photocatalyst showed improved NOx removal efficiency, ∼ 51% (UV–Vis) and 39% (visible light irradiation, 420 nm), with excellent selectivity (> 96 %), stability (> 7 h), and enhanced release of •O2− radicals. Such results demonstrate a simple way to design photocatalytic HTlcs suitable for air purification technologies.

LDH-Based Voltammetric Sensors.

Layered double hydroxides (LDHs), also named hydrotalcite-like compounds, are anionic clays with a lamellar structure which have been extensively used in the last two decades as electrode modifiers for the design of electrochemical sensors. These materials can be classified into LDHs containing or not containing redox-active centers. In the former case, a transition metal cation undergoing a reversible redox reaction within a proper potential window is present in the layers, and, therefore, it can act as electron transfer mediator, and electrocatalyze the oxidation of an analyte for which the required overpotential is too high. In the latter case, a negatively charged species acting as a redox mediator can be introduced into the interlayer spaces after exchanging the anion coming from the synthesis, and, again, the material can display electrocatalytic properties. Alternatively, due to the large specific surface area of LDHs, molecules with electroactivity can be adsorbed on their surface. In this review, the most significant electroanalytical applications of LDHs as electrode modifiers for the development of voltammetric sensors are presented, grouping them based on the two types of materials.

Supported highly dispersed molybdenum nitride derived from molybdate-intercalated Mg‒Al hydrotalcite-like compounds as a catalyst for ammonia decomposition

Molybdate-intercalated magnesium–aluminum hydrotalcite-like compounds (HTlc) were synthesized by anion-exchange and used as precursor to prepare supported molybdenum nitride catalyst for ammonia decomposition. The as-synthesized precursors and the derived mixed metal oxides and nitride catalysts were characterized by ICP, XRD, Raman spectroscopy, XPS, H2-TPR, and HAADF-STEM-EDX. The characterizations indicated that molybdate was well intercalated into the HTlc interlayer as MoO42– and the Mo content was tunable by altering the intercalation degree of molybdate. Upon calcination, molybdena was dominantly presented as isolated tetrahedrally coordinated MoOx species. Upon nitridation with ammonia at 700 ºC, highly dispersed and composition-uniform molybdenum nitride (Mo2±xN) was formed. The Mo0.5Mg3Al nitride catalyst showed good activity for ammonia decomposition, providing nearly full conversion of ammonia at 625 ºC under a space velocity of 5,000 mL gcat–1 h–1. The optimal catalyst also exhibited high catalytic stability during 100 h operation at 625 ºC, and no obvious aggregation took place, attributable to the strong metal–support interaction between molybdenum nitride and Mg–Al mixed oxide. It is suggested that the hydrotalcite-derived Mg–Al mixed oxide supported highly dispersed Mo2±xN species was active and stable for ammonia decomposition.

Arsenic removal by layered double hydroxides (LDH): A mini review

ABSTRACT The World Health Organization (WHO) has classified arsenic as the most toxic chemical with carcinogenic effects and WHO has established a value of 10 μg/L arsenic as the maximum contaminant level for arsenic in potable water. High selectivity and high removal capacity are one of the most important factors when choosing an adsorbent. Hydrotalcite and hydrotalcite-like compounds have received much attention for the remediation of As-contaminated waters. The most interesting properties of layered double hydroxides (LDHs) include a large surface area and high anion exchange capacity. In this study, the importance of double-layered hydroxides, which has gained importance with the increasing environmental pollution recently, in removing oxyanion pollutants from water has been emphasized. This review article focuses on LDH synthesis and characterization techniques and arsenic removal potential using LDHs, as well as the safe consumability of water obtained after removal. In this review, various factors such as pH, dosage, and temperature that affect oxyanion adsorption on LDHs are discussed. The reusability of LDHs has been discussed. In addition, it has been investigated whether double-layer hydroxides (FeHT) could be used successfully in the removal of arsenic from polluted waters. It was also discussed whether the adsorbent used was safe for health.

Unlocking high-performance HCl adsorption at elevated temperatures: the synthesis and characterization of robust Ca–Mg–Al mixed oxides

The presence of HCl and SO2 gas imposes limitations on syngas utilization obtained from household waste in a wide range of applications. The hydrotalcite-like compounds (HTLs) have been proved that could remove HCl efficiency. However, the research on impact of synthesis conditions of HTLs and SO2 on HCl removal was limited. In this study, a range of Ca–Mg–Al mixed oxide sorbents was synthesized by calcining HTLs, with variations in crystallization temperature, solution pH, and the Ca/Mg molar ratio. These sorbents were examined for their effectiveness in removing HCl at medium–high temperatures under diverse conditions. The adsorption performance of selected sorbents for the removal of HCl, SO2, and HCl-SO2 mixed gas at temperature of 350 °C, 450 °C, and 550 °C, respectively, was evaluated using thermogravimetric analysis (TGA). It was observed that the HTL synthesis parameters significantly influenced the HCl adsorption capacity of Ca–Mg–Al mixed oxides. Notably, HTLs synthesized at 60 °C, a solution pH of 10–11, and a Ca/Mg ratio of 4 exhibited superior crystallinity and optimal adsorption characteristics. For individual HCl and SO2 removal, temperature had a minor effect on HCl adsorption but significantly impacted SO2 adsorption rates. At temperatures above 550 °C, SO2 removal efficiency substantially decreased. When exposed to a mixed gas, the Ca–Mg–Al mixed oxides could efficiently remove both HCl and SO2 at temperatures below 550 °C, with HCl dominating the adsorption process at higher temperatures. This dual-action capability is attributed to several mechanisms through which HTL sorbents interacted with HCl, including pore filling, ion exchange, and cation exchange. Initially, HCl absorbed onto specific sites created by water and CO2 removal due to the surface’s polarity. Subsequently, HCl reacted with CaCO3 and CaO formed during HTL decomposition.Graphical abstract

Simultaneous removal of arsenic and cadmium in aqueous solution by a novel hydrotalcite-like absorbent FeMnCa-LDHs

As(III) and Cd(II) pose a significant threat to the ecological environment and human health due to their high toxicity and carcinogenicity, the simultaneous removal of hazardous anions and cations in wastewater has always been a challenging problem. This study employed the co-precipitation method to synthesize FeMnCa-LDHs, a novel ternary metal material devoid of toxic metals, enabling simultaneous removal of As(III) and Cd(II) from aqueous solutions. The XRD patterns and SEM-EDS images showed that the prepared FeMnCa-LDHs exhibited characteristic peaks and a typical layered structure of hydrotalcite-like compounds with high crystallinity. In the composite adsorption system, FeMnCa-LDHs showed synergistic sorption of As(III) and Cd(II) in water, and their adsorption kinetics conformed to the quasi-secondary kinetic model, with adsorption rates of 0.31 and 0.136 g·(mg·h)−1, respectively, and the isothermal adsorption curves conformed to the Langmuir model, with the maximum adsorption amounts of 216.08 and 193.18 mg·g−1 (pH = 5.0, 25 °C), respectively, higher than those of the other LDHs. In the pH range of 3–6, FeMnCa-LDHs exhibited excellent adsorption performance on As(III) and Cd(II), and the adsorption capacity can reach 89.0 and 82.9 mg·g−1, respectively. The coexistence of both PO43− and CO32– ions in water had a competitive effect on the adsorption of As(III) but had little effect on Cd(II) adsorption. The main adsorption mechanism between Cd(II) and FeMnCa-LDHs was found to be isomorphic substitution and surface precipitation, as revealed by XRD, XPS, and FT-IR analyses. On the other hand, the adsorption mechanism that bonded As(III) involved oxidation, ion exchange, surface complexation, and surface precipitation. Furthermore, it maintains a specific adsorption capacity even after undergoing five adsorption cycles. This study demonstrates the potential of FeMnCa-LDHs in treating wastewater that contains As(III) and Cd(II).

Isomorphic Insertion of Ce(III)/Ce(IV) Centers into Layered Double Hydroxide as a Heterogeneous Multifunctional Catalyst for Efficient Meerwein-Ponndorf-Verley Reduction.

The development of highly active acid-base catalysts for transfer hydrogenations of biomass derived carbonyl compounds is a pressing challenge. Solid frustrated Lewis pairs (FLP) catalysis is possibly a solution, but the development of this concept is still at a very early stage. Herein, stable, phase-pure, crystalline hydrotalcite-like compounds were synthesized by incorporating cerium cations into layered double hydroxide (MgAlCe-LDH). Besides the insertion of well-isolated cerium centers surrounded by hydroxyl groups, the formation of hydroxyl vacancies near the aluminum centers, which were formed by the insertion of cerium centers into the layered double hydroxides (LDH) lattice, was also identified. Depending on the initial cerium concentration, LDHs with different Ce(III)/Ce(IV) ratios were produced, which had Lewis acidic and basic characters, respectively. However, the acid-base character of these LDHs was related to the actual Ce(III)/Ce(IV) molar ratios, resulting in significant differences in their catalytic performance. The as-prepared structures enabled varying degrees of transfer hydrogenation (Meerwein-Ponndorf-Verley MPV reduction) of biomass-derived carbonyl compounds to the corresponding alcohols without the collapse of the original lamellar structure of the LDH. The catalytic markers through the test reactions were changed as a function of the amount of Ce(III) centers, indicating the active role of Ce(III)-OH units. However, the cooperative interplay between the active sites of Ce(III)-containing specimens and the hydroxyl vacancies was necessary to maximize catalytic efficiency, pointing out that Ce-containing LDH is a potentially commercial solid FLP catalysts. Furthermore, the crucial role of the surface hydroxyl groups in the MPV reactions and the negative impact of the interlamellar water molecules on the catalytic activity of MgAlCe-LDH were demonstrated. These solid FLP-like catalysts exhibited excellent catalytic performance (cyclohexanol yield of 45%; furfuryl alcohol yield of 51%), which is competitive to the benchmark Sn- and Zr-containing zeolite catalysts, under mild reaction conditions, especially at low temperature (T = 65 °C).

Simultaneous catalytic removal of complex sulfur-containing VOCs over Mn-based hydrotalcite-like compounds: Active sites and oxidation mechanism

The biological fermentation industry faces a challenge in simultaneously purifying complex sulfur-containing volatile organic compounds (VOCs) and reducing tail gas emissions. This is due to the multi-step purification process required for sulfur-containing VOCs and the high energy usage involved. The adsorption performance and controllability of elements in hydrotalcite-like compounds are noteworthy and have the potential to enhance the catalytic purification of sulfur-containing VOCs. This study utilizes Mn-based hydrotalcite-like compounds as a highly efficient catalyst for the simultaneous catalytic removal of complex sulfur-containing VOCs such as ethanol (C2H5OH), acetaldehyde (CH3CHO), and diethyl sulfide (C4H10S). The study successfully achieves the simultaneous and efficient removal of sulfur-containing VOCs at a temperature of 325 °C. The removal rates of three types of gas pollutants can reach 100 % for 420 min, 450 min, and 360 min, respectively. Meanwhile, the VOCs breakthrough capacity is 426 mg/g. The competitive adsorption effect, adsorption sites, and reaction mechanism were investigated using experimental and theoretical calculation methods. The simultaneous adsorption of three gases resulted in competitive adsorption, with the priority order of adsorption being CH3CHO > C4H10S > C2H5OH. The various adsorption effects were attributed to the formation of Mg–O–H…O-C, O…O=C, and Mn–O–H…S-C, respectively. CH3CHO was initially adsorbed at the O-Top site, while C4H10S was adsorbed at the Mn-Top site. C2H5OH was adsorbed at the Mg-Top site. High-temperatures promote the oxidation of elemental S to sulfate. The primary reason for catalyst deactivation is the buildup and coating of sulfate on the surface of the catalyst. The main active sites responsible for the catalytic oxidation of C4H10S were Mn2+ and Mn3+. The oxygen defects act as active sites for the oxidation of C2H5OH and CH3CHO. C2H5OH undergoes gradual oxidation to form CH3CHO and CH3COOH (acetic acid), which are further oxidized to CO2 and H2O. C4H10S was oxidized to elemental S and eventually to sulfate. The experimental results in this work are consistent with the theoretical results, providing a theoretical basis for the simultaneous catalytic removal of sulfur-containing VOCs.

Supported Ni Catalysts from Ni-Mg-Al Hydrotalcite-like Compounds：Preparation and Catalytic Performance for Ammonia Decomposition

Supported Ni Catalysts from Ni-Mg-Al Hydrotalcite-like Compounds：Preparation and Catalytic Performance for Ammonia Decomposition

An Overview on (LDHs)

Layered Double Hydroxides are inorganic solid minerals with brucite-like structures. They are non-silicate minerals seen in the soil very rare in amount [1]. LDHs have brucite-like layers with an excess positive charge on their surface. The excess charges are balanced by anions that are present in the interlayer. Generally, LDHs are also known as Hydrotalcite-like compounds because Hydrotalcite is one of the LDHs seen commonly in soil. Due to their higher anion exchange capacity, they are also known by the name anionic clay. In nature, they generally occur as a clay mineral, but sometimes as the metabolic by-product of micro-organisms. Even humans can manufacture it at a low cost of production.

Efficient catalytic degradation of VOCs using Mn-based hydrotalcite-like compounds coupled with non-thermal plasma

Aiming to discover a novel catalyst that exhibits a high synergistic effect with plasma technology for the degradation of volatile organic compounds (VOCs), we employed manganese-based layered double hydroxides (LDHs), which are referred to as MMn-LDHs (M=Ni, Co, Fe). Comprehensive physicochemical characterization via catalyst characterization techniques such as XRD, SEM, XPS, BET, confirmed the successful synthesis of the catalysts. These analyses revealed excellent crystallinity, distinctive lamellar structure, and remarkable thermal stability for three synthesized catalysts. The experimental results demonstrate that post non-thermal plasma (post-NTP) catalytic system has significantly improved the degradation efficiency, CO2 selectivity, and carbon balance for toluene, while notably suppressing the formation of by-products (e.g., NOx and O3) compared to the NTP alone system. Among the three MMn-LDHs, NiMn-LDHs exhibited the best performance in the post-NTP-catalytic system, achieving a toluene degradation rate of 95.87%, a CO2 selectivity of 57.41%, a carbon balance of 79.86%, and an energy efficiency of 3.19 g·kWh−1 at a specific energy density (SED) of 930.45 J/L. The catalytic degradation mechanism of toluene was proposed based on a combination of catalyst characterization techniques, plasma emission spectroscopy, and gas chromatography-mass spectrometry (GC-MS). The findings revealed that plasma discharge generated a substantial amount of free radicals and active species, thereby promoting the decomposition of toluene. Subsequently, the residual toluene and intermediate products were adsorbed onto the catalysts, where they underwent further reacted with the abundant hydroxyl radicals and activate metal species on the catalyst surface, ultimately decomposing into CO2 and H2O. Additionally, the interaction of ozone with LDHs facilitated the generation of reactive oxygen species, consequently accelerating the decomposition of organic intermediates, formation of CO2, and the enhancement of toluene mineralization. The finding in this work offer valuable theoretical support for the plasma-catalytic degradation of VOCs.

New Sn-Mg-Al hydrotalcite-based catalysts for Baeyer-Villiger oxidation of β-cyclocitral

This study focuses on the Baeyer-Villiger (BV) oxidation of β-cyclocitral using tin-modified mixed oxides based on hydrotalcites as catalysts. Hydrotalcite-like compounds modified with tin were found to be promising catalysts capable of catalyzing both BV oxidation and subsequent hydrolysis of formed formate. The testing of catalytic activity and optimization of reaction conditions for achieving high conversion and selectivity to the desired product, 2,6,6-trimethylcyclohexanone, was carried out. The effects of the Mg/Al ions molar ratio, tin amount, catalyst amount, and form (hydrotalcite or mixed oxide) on the reaction course and selectivity to 2,6,6-trimethylcyclohexanone were studied. Optimal reaction conditions (temperature, reactant ratio, solvent type and amount) were determined. Additionally, different dosing methods, amounts and types of oxidizing agents were tested. The reaction was successfully scaled up, and the possibility of reusing the catalyst at least three times was confirmed. Gradual dosing of 6.4 molar equivalents of 50% hydrogen peroxide in 24 doses during 5-minute intervals over 115 min was determined as the most suitable method. The temperature of 115 °C, cyclohexanol in a mass ratio of 2:1 to the starting material as a solvent, and 15 wt% of the catalyst to the starting material was identified as optimal for the BV oxidation of ß-cyclocitral. The mixed oxide with a Mg/Al molar ratio of 2 impregnated with 3 wt% tin at room temperature (3Sn-MO2imp25) exhibited the highest activity and selectivity towards 2,6,6-trimethylcyclohexanone. Under these reaction conditions, total conversion and a 60% selectivity to the desired product were achieved after 5 h of reaction.

Enhancing catalytic hydrolysis activity of ZnNiAl hydrotalcite-like compounds-derived oxides using rare earth metals

Efficient catalysts are highly desirable for the simultaneous removal of hydrogen cyanide (HCN) and carbonyl sulfide (COS) to meet the increasingly stringent emission standards and achieve cleaner production. In this study, ZnNiAl hydrotalcite-like compounds (HTLCs)-derived oxides doped with a series of rare earth metals, such as cerium (Ce), gadolinium (Gd), and yttrium (Y), were synthesized and used for the simultaneous hydrolysis of HCN and COS. The results demonstrated that the chemical state and electronic structure of ZiNiAl were changed by Ce doping because of the incorporation of Ce into the nickel oxide (NiO) network. Thus, abundant active species for the adsorption and dissociation of HCN and COS, including chemically adsorbed oxygen and strong basic sites, were produced by Ce doping. Meanwhile, the well-developed mesoporous structure provided accessibility to the active sites. As a result, Ce doping significantly enhanced the catalytic performance of ZnNiAl. Furthermore, the mechanisms of HCN and COS hydrolysis over Ce-ZnNiAl and their deactivation were proposed. This study provides a novel route for efficiently eliminating HCN and COS in diverse industrial processes.

Excellent adsorption properties of Mg/Al/Fe LDOs for Cr(VI) in water

Cr(VI), a common wastewater pollutant discharged from metallurgical, electroplating and other industries poses a threat to human health and the ecological environment. Layered double hydroxides (LDHs), which have a strong anion exchange capacity and memory effect, are excellent adsorbents that are widely used for heavy metal adsorption. In this study, we found that Mg-Al-Fe ternary metal oxides (MAF-LDOs) obtained by the calcination of Mg-Al-Fe hydrotalcite-like compounds (MAF-LDHs) had great potential for the treatment of Cr(VI)-containing wastewater. The influences of the adsorption time, Cr(VI) concentrations, pH value and coexisting metal ions were also considered. By using batch adsorption experiments and various characterization tools, it was found that the mechanism of Cr(VI) adsorbed by MAF-LDO involved the use of a memory effect that involved HCrO4- in the reconstruction of laminates. In addition, some laminate -OH groups were protonated to electrostatically attract HCrO4-. The -OH groups in the laminate acted as electron donors to reduce Cr(VI) to Cr(III) that then underwent complexation for the effective removal of Cr(VI). The maximum theoretical adsorption capacity of MAF/LDOs for Cr(VI) was 122.85 mg/g at 20 °C. Furthermore, the MAF-LDO demonstrated excellent stability and reusability. In conclusion, the MAF-LDO exhibited a simple synthesis process, superior adsorption capacity with a short contact time, and a wide pH range of application. Hence, it is well-suited for industrial wastewater treatment and provides new insights for treating Cr(VI)-containing wastewater.

Flower-like spherical ZnCdS/Bi2WO6/ZnAl-LDH with dual type II heterostructure as a photocatalyst for efficient photocatalytic degradation and hydrogen production

One of the effective strategies for improving the photocatalytic activity of composite materials is to construct a heterostructure using layered double hydroxide (LDH) as the main photocatalytic material in order to accelerate photogenerated charge transfer. We report herein the preparation of a novel flower-like spherical photocatalytic composite, ZnCdS/Bi2WO6/ZnAl-LDH, with a dual type II heterostructure, by a hydrothermal method. ZnAl-LDH in the composite has the characteristic structure of a good hydrotalcite-like compound, and ZnCdS and Bi2WO6 are loaded on its surface to form flower-like spherical particles of uniform size. Compared with ZnAl-LDH, a ZnCdS/Bi2WO6/ZnAl-LDH composite has a significantly broader light absorption range and a more uniform pore size distribution. Electrochemical impedance, transient photocurrent, and photoluminescence results for ZnCdS/Bi2WO6/ZnAl-LDH composites have shown that the composition with 20% ZnCdS displayed the highest photocurrent density, the lowest electron-transfer resistance, and the lowest electron–hole recombination efficiency. Multi-mode photocatalytic degradation experiments showed all ZnCdS/Bi2WO6/ZnAl-LDH composites to exhibit good photocatalytic degradation ability. Meanwhile, ZnCdS/Bi2WO6/ZnAl-LDH showed enhanced hydrogen production of 79.20 μmol g−1 h−1, more than eight times that for ZnAl-LDH, and its photocatalytic activity remained stable after three experimental cycles. Through trapping experiments, the active species involved in the photocatalytic reaction has been identified, and the presence of a dual type II heterostructure in the ZnCdS/Bi2WO6/ZnAl-LDH composite is postulated. Rapid separation and migration of photogenerated charge carriers in the composite is achieved due to the close association of ZnCdS, Bi2WO6, and ZnAl-LDH.

Anti-coking Cu-Ni bimetallic catalyst for hydrogen production: Thermodynamic and experimental study of methanol autothermal reforming

Autothermal reforming has emerged as a promising route for hydrogen production from bio-methanol, offering a balance between hydrogen production and the energy demand of the process. To address the low catalytic performance of non-precious metal catalysts, one of the approaches is to introduce a second metal. In this work, a series of Cu-Ni bimetallic catalysts derived from Ca-Al hydrotalcite-like compounds were prepared by the urea hydrolysis method combined with hydrothermal treatment, featuring well-dispersion with a size of 3-5 nm. The electron redistribution triggered by the incorporation of Cu enhances the absorption of methanol at the electron-poor surface, leading to maintained catalytic activity at 450°C for 96 hours with few carbon-deposition observed for methanol autothermal reforming. The boundary conditions of the thermal-neutrality system are analyzed by thermodynamic calculations and similar trends to the simulation results were also obtained from experiments.