Layered Double Hydroxide Precursor Research Articles

Topotactic reduction of layered double hydroxides for atomically thick two-dimensional non-noble-metal alloy

Layered double hydroxides (LDHs) have been widely used as catalysts owing to their tunable structure and atomic dispersion of high-valence metal ions; however, limited tunability of electronic structure and valence states have hindered further improvement in their catalytic performance. Herein, we reduced ultrathin LDH precursors in situ and topotactically converted them to atomically thick (~2 nm) two-dimensional (2D) multi-metallic, single crystalline alloy nanosheets with highly tunable metallic compositions. The as-obtained alloy nanosheets not only maintained the vertically aligned ultrathin 2D structure, but also inherited the atomic dispersion of the minor metallic compositions of the LDH precursors, even though the atomic percentage was higher than 20%, which is far beyond the reported percentages for single-atom dispersions (usually less than 0.1%). Besides, surface engineering of the alloy nanosheets can finely tune the surface electronic structure for catalytic applications. Such in situ topotactic conversion strategy has introduced a novel approach for atomically dispersed alloy nanostructures and reinforced the synthetic methodology for ultrathin 2D metal-based catalysts.

Enhanced photocatalytic ability of Cu, Co doped ZnAl based mixed metal oxides derived from layered double hydroxides

Cu, Co doped mixed metal oxides (MMOs) were synthesized from their ternary layered double hydroxides (LDHs) precursors, ZnCu(or Co)Al-CO3via simple calcination at different temperatures. Interestingly, MMO prepared at 400°C (MMOs-400) showed only weakly crystallized ZnO phase, suggesting that other metals such as Al, Cu(or Co) remain as amorphous phase around ZnO nanoparticles. Moreover, by increasing Cu(or Co) substitution content into ZnAl-LDHs framework, the amorphous phase on the surface of MMOs was clearly observed as ‘hole’-like structure by transmission electron microscopy (TEM). This amorphous phase composed of Co(or Cu) Al would play a crucial role, as doping agent of ZnO, in the improvement of photocatalytic ability towards orange II degradation, as only MMOs-400 showed significantly fast degradation rate. However, no meaningful improvement was observed for MMOs-600 or 800 that contain lower amounts of amorphous phase. Furthermore, the optimal substitution ratio of Zn/Cu(or Co) was also found to be of 19 (Zn1.9Cu0.1Al1-400), giving the best performance for dye degradation. Therefore, this report would provide a facile approach for the synthesis of efficient photocatalysts based on LDHs and their MMOs.

CuTi LDH derived NH3-SCR catalysts with highly dispersed CuO active phase and improved SO2 resistance

Dispersed CuyTi1Ox catalysts derived from Cu-Ti-CO3 layered double hydroxides (LDHs) were successfully prepared. Due to the better dispersion of active CuO phase, the optimal catalyst Cu1Ti1Ox reached a high NOx conversion of 88.9% at 200°C, which is significantly higher than that of the control catalyst 10wt% CuO/TiO2 (29.5%). Cu1Ti1Ox catalyst also showed improved SO2 resistance, with a very stable NOx conversion of 76.4% at 200°C after 8h running with 50ppm SO2, much higher than that of 10wt% CuO/TiO2 (3.3%). The reaction mechanism was discussed with NH3-TPD and H2-TPR analyses, which indicated that Cu1Ti1Ox has more surface acidic sites and higher redox property than 10wt% CuO/TiO2. In all, CuyTi1Ox prepared from Cu-Ti LDH precursor can work as highly efficient and SO2 resistant low-temperature NH3-SCR catalyst for NOx removal.

Theoretical and experimental study on the topotactic transformation mechanism of Zn-Al layered double hydroxides

Layered double hydroxides (LDHs) are a class of minerals with nanoscale two-dimensional layered structure. The topotactic transformation of LDHs under calcination and the reconstruction behavior (memory effect) of the calcined LDHs in aqueous solution play a key role in the fabrication of high dispersed metal nanocatalysts. The thermal topotactic transformation mechanism of ZnAl-layered double hydroxides (LDHs) and memory effect of LDHs were investigated by density functional theory based molecular dynamics (MD) simulation, combined with thermogravimetric/differential thermal analysis (TG-DTA). TG-DTA results reveal that the LDH phase undergoes two key endothermic events at 273 and 800 °C. The results show that the anion in LDHs decomposes to CO2 and H2O via a monodentate intermediate at 273 °C, and H2O releases prior to CO2. After the decomposition of interlayer CO32− at 273 °C, the distribution of metal cations in LDH matrix changed heavily along both LDH(001) facet and the c -axis direction perpendicular to the (001) facet. The dehydrated products cannot reconstruct back to the hydroxide phase, showing no memory effect. At 800 °C, a complete collapse of layered structure occurs, resulting in a totally disordered cation distribution and plenty of holes in the final product. This work will be helpful for the design and preparation of highly dispersed nanocatalysts derived from LDHs precursors.

<italic>In-situ</italic> conversion and catalytic properties of mixed-metal oxide catalysts for photosynthesis of hydrogen peroxide

Titanium-based mixed-metal oxide (MMO), acting as a catalyst for light-driven generation of hydrogen peroxide (H2O2), was obtained by calcining a titanium-based layered double hydroxide precursor. The findings indicated that the ZnO phase within the MMO was etched and the MMO was transformed into TiO2-ZnTiO3 heterostructure during the synthesis of H2O2. Both the MMO and TiO2-ZnTiO3 are superior to the commercial TiO2 (P25: 80% anatase and 20% rutile) for photosynthesis of H2O2. The generation of H2O2 was determined by both the formation rate and the decomposition rate. The kinetic studies revealed that the formation rate constant ( K f) is 3.581 μM/min on the TiO2-ZnTiO3, 3.65 times larger than that on the MMO ( K f=0.982 μM/min) and also 4.2 times larger than that on P25 ( K f=0.852 μM/min). And the decomposition rate constant ( K d) of H2O2 on the TiO2-ZnTiO3 is 0.0472 min−1, 3.97 times larger than that on the MMO ( K d=0.0119 min−1) and 1.26 times larger than that on P25 ( K d=0.0374 min−1). The in situ generated TiO2-ZnTiO3 possessed larger K f and K d values. Consequently, the yield of H2O2 reached the same level on the TiO2-ZnTiO3 and the MMO with a longer reaction period, although the former catalyzed a higher yield of H2O2 at the beginning of the reaction. This result hinted that the reaction kinetics was affected by the phase change of the catalyst whereas the final yield of H2O2 was hardly impacted. The key way to enhance the yield of H2O2 could be the inhibition of H2O2 decomposition on the surface of catalyst. This work intensified the understanding of reaction kinetics regarding the photosynthesis of H2O2 on the Ti-based MMO and directed the structural design of the oxide photocatalyst to some extent.

ZnO/ZnGaNO heterostructure with enhanced photocatalytic properties prepared from a LDH precursor using a coprecipitation method

Wurtzite Zinc-gallium oxynitrides (ZnGaNO) particles were synthesized by nitridation of Zn/Ga/CO3 layered double hydroxides (LDHs) using three different coprecipitation methods, called Decreasing-pH method, Constant-pH method, and Increasing-pH Method, respectively. The obtained particles were found to be a ZnO/ZnGaNO composite, a single-phase ZnGaNO, and a porous ZnGaNO/ZnGa2O4 composite, respectively, as characterized by X-ray diffraction, scanning electron microscope, scanning and transmission electron microscope, Raman Spectroscopy, UV–vis diffuse refection spectra, and room temperature photoluminescence (PL). Photocatalytic activities of the obtained particles were evaluated under visible-light irradiation against the photodegradation of methylene blue (MB) and phenol. The ZnO/ZnGaNO heterostructure, which was formed due to sequential precipitation of Zn and Ga ions in the Decreasing-pH method, exhibited significant advance in the photocatalytic activity compared to other ZnGaNO particles. The enhanced photoactivity of ZnO/ZnGaNO particles was attributed to efficient separation of photogenerated electron-hole pairs driven by the matched band edges. The predominant active species for the phenol photodegradation over the ZnO/ZnGaNO particles were determined to be superoxide radicals and holes. The facile synthesis of the ZnO/ZnGaNO heterostructure makes it as a potential efficient visible-light responsive photocatalyst for water pollutant degradation.

In situ synthesis of polyelectrolyte/layered double hydroxide intercalation compounds

Intercalation is usually achieved through the insertion of guest species into a pre-formed layered compound. Herein, we report our exploration of the formation of intercalation compounds through a direct growth method using cationic layered double hydroxide (LDH) and anionic polyelectrolytes. LDH precursors and intercalant molecules were used as the raw materials to directly grow layered intercalation compounds through a hydrothermal method. Three poly(sodium 4-styrene-sulfonate) (PSSNa) with different molecular weights (i.e., 70000, 200000, and 500000) were systematically studied as an intercalant in terms of their effect on the growth of intercalation compounds. The mass ratio of PSSNa and LDH was also varied to study how the formulation ratio of the raw materials influences the growth of the PSSNa/LDH intercalation compounds. These directly synthesized PSSNa/LDH intercalation compounds were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy, based on which their growth mechanism was discussed. This direct growth method offers an alternative for large-scale production of intercalation compounds for potential commercial applications.

Adsorption of Acid Yellow 42 dye on calcined layered double hydroxide: Effect of time, concentration, pH and temperature

The adsorption of textile dyes onto Layered Double Hydroxides (LDH) and their thermally decomposed products is a promising strategy for the treatment of contaminated effluents - combining high removal efficiency with reasonable cost. The main purpose of this paper was to investigate the adsorption of textile azo dye Acid Yellow 42 (AY) onto calcined and uncalcined Mg-Al-CO3-LDH. A set of analytical techniques was used to characterize the materials, namely X-ray diffraction (XRD), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), thermogravimetric analyses (TGA), N2 adsorption-desorption isotherms and Scanning Electron Microscopy (SEM). In the study of azo dye adsorption, the following factors were assessed: kinetics, adsorption capacity, effect of temperature, initial pH value, and recyclability of the adsorbent material. The adsorption capacity of calcined LDH (CLDH) was almost four times greater than that of the LDH precursor: 1266mg·g−1 (1.669mmol·g−1) and 330.0mg·g−1 (0.4350mmol·g−1), respectively, at pH equal to 7.0 and 25°C. The greater adsorption capacity for CLDH is related to the recovery property of these materials in light of the so called “memory effect”, which allows an intercalation process of the anionic dye, as demonstrated by XRD data.

Influence of Mn content on the catalytic properties of Cu-(Mn)-Zn-Mg-Al mixed oxides derived from LDH precursors in the total oxidation of methane

Cu-(Mn)-Zn-Mg-Al mixed oxides with Cu/Zn atomic ratio of 1 and different Mn contents were synthesized by thermal decomposition of layered double hydroxides (LDHs) precursors. They were characterized using X-ray diffraction, textural measurements, EDX, TEM, H2-TPR and XPS techniques, and their catalytic properties in the total oxidation of methane were evaluated. The precursors consisted in nitrate-interlayered multicationic LDH phase with additional Mn3O4 side phase for Mn-containing systems. Their thermal decomposition resulted in complex mixed oxides containing periclase-like, CuO and different spinel (Cu1.5Mn1.5O4, CuMn2O4, and MnAl2O4) phases. XPS analysis confirmed the existence of copper and manganese with different valence states in the Cu,Mn-containing mixed oxides. The catalytic activity expressed as the intrinsic rate of CH4 conversion increased by adding Mn to the CuZnMgAl mixed oxide calcined at 650°C and by increasing its content. The intrinsic activity also strongly increased when the calcination temperature increased from 650 to 800°C. The increased activity was correlated to enhanced catalyst reducibility due to the favorable Cu-Mn interaction. Among the different catalytic active phases, i.e. CuO, Cu1.5Mn1.5O4 and CuMn2O4, the Cu1.5Mn1.5O4 spinel seems to be the most active one.

Foam‐Structured NiO‐MgO‐Al2O3 Nanocomposites Derived from NiMgAl Layered Double Hydroxides In Situ Grown onto Nickel Foam: A Promising Catalyst for High‐Throughput Catalytic Oxymethane Reforming

AbstractCatalytic oxymethane reforming is an effective and efficient route to produce syngas, but the commonly used Ni catalysts suffer from coke deposition, Ni sintering, and heat‐transfer limitations. A Ni‐foam‐structured NiO‐MgO‐Al2O3 nanocomposite catalyst was developed by thermal decomposition of NiMgAl layered double hydroxides (LDHs) in situ hydrothermally grown onto the Ni‐foam. Originating from the lattice orientation effect and topotactic decomposition of the LDH precursor, NiO, MgO, and Al2O3 are highly distributed in the nanocomposite, and thus, this catalyst shows enhanced resistance to coke and sintering. At 700 °C and a gas hourly space velocity of 100 L g−1 h−1, 86.5 % methane conversion and selectivities of 91.8/88.0 % to H2/CO are achieved with stability for at least 200 h. We believe this type of tailoring strategy and the as‐obtained materials can open up new opportunities for future applications in other high‐throughput and high‐temperature reactions.

Improvement of catalytic stability for CO2 reforming of methane by copper promoted Ni-based catalyst derived from layered-double hydroxides

Copper-promoted nickel-based metal nanoparticles (NPs) with high dispersion and good thermal stability were derived from layered-double hydroxides (LDHs) precursors that were facilely developed by a co-precipitation strategy. The copper-promoted Ni-based metal NPs catalysts were investigated for methane reforming with carbon dioxide to hydrogen and syngas. A series of characterization techniques including XRD, N2 adsorption and desorption, H2-TPR, XPS, CO2-TPD, TEM, TGA and in situ CH4-TPSR were utilized to determine the structure-function relationship for the obtained catalysts. The copper addition accelerated the catalyst reducibility as well as the methane activation, and made the Ni species form smaller NPs during both preparation and reaction by restricting the aggregation. However, with higher copper loading, the derived catalysts were less active during methane reforming with CO2 to syngas. It was confirmed that the catalyst with 1wt% Cu additive gave the higher catalytic activity and remained stable during long time reaction with excellent resistance to coking and to sintering. Furthermore, the mean size of metal NPs changed minimally from 6.6 to 7.9nm even after 80h of time on stream at temperature as high as 700°C for this optimized catalyst. Therefore, this high dispersed anti-coking copper-promoted nickel catalyst derived from LDHs precursor could be prospective catalyst candidate for the efficient heterogeneous catalysis of sustainable CO2 conversion.

DFT-Based Simulation and Experimental Validation of the Topotactic Transformation of MgAl Layered Double Hydroxides.

The thermal topotactic transformation mechanism of MgAl layered double hydroxides (LDHs) is investigated by a combined theoretical and experimental study. Thermogravimetric differential thermal analysis (TG-DTA) results reveal that the LDH phase undergoes four key endothermic events at 230, 330, 450, and 800 °C. DFT calculations show that the LDH decomposes into CO2 and residual O atoms via a monodentate intermediate at 330 °C. At 450 °C, the metal cations almost maintain their original distribution within the LDH(001) facet during the thermal dehydration process, but migrate substantially along the c-axis direction perpendicular to the (001) facet; this indicates that the metal arrangement/dispersion in the LDH matrix is maintained two-dimensionally. A complete collapse of the layered structure occurs at 800 °C, which results in a totally disordered cation distribution and many holes in the final product. The structures of the simulated intermediates are highly consistent with the observed in situ powder XRD data for the MgAl LDH sample calcined at the corresponding temperatures. Understanding the structural topotactic transformation process of LDHs would provide helpful information for the design and preparation of metal/metal oxides functional materials derived from LDH precursors.

Magnesium-aluminum mixed metal oxide supported copper nanoparticles as catalysts for water-gas shift reaction

Mg(Al)O mixed metal oxide (MMO) supported Cu nanoparticles catalysts have been prepared by calcination and reduction of Cu-Mg-Al layered double hydroxides (LDHs). By adjusting the chemical compositions of LDHs precursors, various catalysts with 10–40wt% Cu content and molar ratio of (Cu+Mg)/Al=1–4 were prepared. The catalysts were characterized by ICP, N2 physical adsorption, XRD, TEM, H2-TPR, and N2O chemisorption, and tested for the water-gas shift (WGS) reaction. The characterization results suggested that upon calcination Cu-Mg-Al LDHs were converted to Mg(Cu, Al)O MMOs, where both Cu2+ and Al3+ were incorporated into the MgO framework to form a solid solution; reduction of Mg(Cu, Al)O gave highly dispersed and uniform Cu metal nanoparticles. The Cu metal dispersion was as high as 22–78% and the particle size varied from 1.5 to 5nm depending on the chemical compositions. The WGS activity of the Cu catalysts increased with the increase of Cu0 surface area. Among the prepared catalysts, the 30%Cu/Mg2Al catalyst exhibited the highest Cu surface area and the highest WGS activity. The optimized catalyst also showed superior activity, thermal stability, and steady-state stability than a commercial Cu/ZnO/Al2O3 catalyst under the present reaction conditions. The characterization on the spent catalysts showed that the LDHs-derived Cu nanoparticles remained highly dispersed, suggesting that the Mg(Al)O supported Cu nanoparticles were stable and possessed good resistance against sintering.

Stoichiometric synthesis of Fe/CaxO catalysts from tailored layered double hydroxide precursors for syngas production and tar removal in biomass gasification

A series of bi-functional Fe/CaxO catalysts with different Ca/Fe molar ratios (2/1, 3/1, 4/1, 5/1) were prepared from tailored single-source CaxFe-LDHs precursors and applied to the thermo-chemical catalytic conversion of biomass. The results of catalyst characterization using XRD, SEM and CO2-TPD techniques indicate that the Fe load has a significantly influence on the composition, particle size, alkalinity and CO2 adsorption capacity of resulting Fe/CaxO materials. As catalysts, the selectivity of H2 was increased and the selectivity of CO was reduced with increasing Fe load. The highest gasification yield of 48.3wt.%, H2 yield of 37.48vol.% and H2/CO ratio of 1.36 were obtained at an optimized composition of Ca/Fe=2/1, with the gasification efficiency as high as 76.4%. GC–MS analysis of the condensable tar indicated that the as-synthesized Fe/CaxO catalysts were capable for selective phenolics production from biomass gasification, with the maximum phenolics yield as high as 90.06%. Moreover, based on the results of structure characteristics and catalytic activities, a synergistic catalytic mechanism was proposed that the Ca2Fe2O5 and Fe3O4 formed by partial reduction of Ca2Fe2O5 during biomass gasification are the main active site for catalytic cracking of tar, which can be further promoted by the in-situ CO2 absorption of CaO.

Aluminum doped nickel oxide thin film with improved electrochromic performance from layered double hydroxides precursor in situ pyrolytic route

Electrochromic materials with unique performance arouse great interest on account of potential application values in smart window, low-power display, automobile anti-glare rearview mirror, and e-papers. In this paper, high-performing Al-doped NiO porous electrochromic film grown on ITO substrate has been prepared via a layered double hydroxides(LDHs) precursor in situ pyrolytic route. The Al3+ ions distributed homogenously within the NiO matrix can significantly influence the crystallinity of Ni-Al LDH and NiO:Al3+ films. The electrochromic performance of the films were evaluated by means of UV–vis absorption spectroscopy, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry(CA) measurements. In addition, the ratio of Ni3+/Ni2+ also varies with Al content which can lead to different electrochemical performances. Among the as-prepared films, NiO film prepared from Ni-Al (19:1) LDH show the best electrochromic performance with a high transparency of 96%, large optical modulation range (58.4%), fast switching speed (bleaching/coloration times are 1.8/4.2s, respectively) and excellent durability (30% decrease after 2000 cycles). The improved performance was owed to the synergy of large NiO film specific surface area and porous morphology, as well as Al doping stifled the formation of Ni3+ making bleached state more pure. This LDHs precursor pyrolytic method is simple, low-cost and environmental benign and is feasible for the preparation of NiO:Al and other Al-doped oxide thin film.

Rapid Synthetic Route to Nanocrystalline Carbon-Mixed Metal Oxide Nanocomposites with Enhanced Electrode Functionality

A rapid synthetic route to nanocrystalline carbon-incorporated mixed metal oxide nanocomposites with enhanced electrode performance for lithium ion batteries is developed by applying a very short heat-treatment of layered double hydroxide (LDH) precursor under C2H2 flow. Employing C2H2 atmosphere makes possible the rapid synthesis of nanocrystalline C–NiO–NiFe2O4 nanocomposite via the calcination of the Ni–Fe–LDH precursor at 300 °C in a very short period of 5 min. In the case of ambient atmosphere, a prolonged calcination time of several hours is demanded to induce a complete phase transformation from Ni–Fe–LDH to electrochemically active NiO–NiFe2O4 nanocomposite, highlighting the usefulness of C2H2 atmosphere in promoting the formation of mixed metal oxide nanocomposite. The present C–NiO–NiFe2O4 nanocomposite shows much better anode performance for lithium ion batteries with greater discharge capacity and better cyclability than do the NiO–NiFe2O4 nanocomposites prepared by the prolonged calcination of LDH under ambient atmosphere. The superior electrode activity of the present C–NiO–NiFe2O4 nanocomposite is attributable to the optimization of charge transfer induced by the enhanced electrical conductivity and a short diffusion length of Li ion. The present C2H2-assisted phase transition of LDH precursor provides a convenient, economic, and scalable synthetic way to carbon–mixed metal oxide nanocomposites with promising electrode performance for lithium ion batteries.

Facile synthesis of highly efficient nano-structured gallium zinc oxynitride solid solution photocatalyst for visible-light overall water splitting

Gallium-zinc oxynitride (GaZnON) solid solution is a photocatalyst capable of effective overall water splitting under visible light. In order to address the inefficiencies of the synthesis of GaZnON solid solution (e.g., 10+ h at 850°C under 250mlmin−1 NH3 flow), a facile technique is proposed. The technique utilizes crystalline Ga3+ and Zn2+ layered double hydroxides (LDHs) material as an atomic-level uniform precursor, and urea as the nanotemplated source of nitrogen. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis confirm the formation of wurtzite GaZnON in a 12min process through distribution of the uniform Ga3+ and Zn2+ LDHs precursor within the nanotemplate formed through urea pyrolysis. The structural, optical, and electrochemical properties of the prepared samples were characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy, and photoluminescence (PL) analysis. The newly synthesized photocatalyst consists of nanopores distributed uniformly through the surface and bulk of the solid solution particles; the presence of these nanopores improves the active surface area of the photocatalyst up to seven times, as compared to the one for traditionally prepared solid solution photocatalyst. The proposed technique is capable of controlling the composition of the final photocatalyst in a wide range of ZnO content ([Zn]/[Zn+Ga] up to 0.66). Apparent quantum yield (AQY) up to 2.5% at 420–440 was achieved by the photocatalyst with bulk [Zn]/[Zn+Ga]=0.32, loaded with 1wt% Rh nanoparticles. The effect of crystal defects and Zn content of the solid solution on the PL emission of the samples revealed that the GaZnON samples prepared with the LDHs precursor contain fewer crystal imperfections, which aids their water-splitting performance. The performance of the newly synthesized photocatalyst is among the highest reported in the open literature for photocatalysts loaded with a single co-catalyst. This photocatalyst has potential for future improvement through enhancement of the crystalline structure and improvement of the charge separation.

Rich surface Co(iii) ions-enhanced Co nanocatalyst benzene/toluene oxidation performance derived from Co(II)Co(III) layered double hydroxide.

A hierarchical CoCo layered double hydroxide (LDH) nanostructure was constructed through a facile topochemical transformation route under a dynamic oxygen atmosphere. Self-assembled coral-like CoAl LDH nanostructures via the homogeneous precipitation method were also inspected under different ammonia-releasing reagents and solvents. Benzene and toluene were chosen as probe molecules to evaluate their catalytic performance over the metal oxide CoCoO and CoAlO calcined from their corresponding LDH precursors. Nanocatalyst of trivalent Co ions replaced Al(3+) ions in the bruited-like layer had a higher catalytic activity (T99(benzene) = 210 °C and T99(toluene) = 220 °C at a space velocity = 60 000 mL g(-1) h(-1)). Raman spectroscopy, XPS and H2-TPR demonstrated the existence of abundant high valence Co ions that serve as active sites. TPD verified the types of active oxygen species and surface acid properties. It was concluded that the high valence Co ions induced excellent low-temperature reducibility. Surface Lewis acid sites and the surface Oads/Olatt molar ratio (0.61) played relevant roles in determining its catalytic oxidation performance. Our design in this work provides a promising approach for the development of nanocatalysts with exposed desirable defects.

Influence of the preparation route on the basicity of La-containing mixed oxides obtained from LDH precursors

A series of La-containing Mg(Al)O mixed oxide catalysts were obtained from layered double hydroxide (LDH) precursors following different La3+ incorporation methods, i.e., coprecipitation, impregnation and intercalation. Structural and textural properties investigated by XRD and N2 physisorption revealed a large range of specific surface areas of the materials and different ordering of the structures. The surface areas were between 18 and 230m2g−1 for the coprecipitated and intercalated samples, respectively, and rose to 330m2g−1 for the intercalated sample treated by sonication. The base properties of these samples, and for the sake of comparison of Mg(Al)O and Mg(La)O mixed oxides, were investigated by TPD of CO2 and by performing the highly demanding isomerization reaction of 2,3-dimethyl-1-butene (1). Strong base sites are introduced in the mixed oxide, when La3+ is incorporated by coprecipitation or intercalation in the Mg/Al LDH precursor. Finally, the relative values of the catalytic activities of the different mixed oxide found in the isomerization reaction of (1) showed that not only the densities of strong base sites, but also their accessibility was controlling the catalytic activities.

Ni–Co catalyst derived from layered double hydroxides for dry reforming of methane

Ni/Co monometallic and bimetallic layered double hydroxides (LDH) were in-situ synthesized on the surface of γ-Al2O3 by urea precipitation method. Then they were decomposed and reduced by H2/Ar atmospheric plasma jet at 400 °C for 15 min to become into catalysts. The LDH precursors were verified by XRD, SEM, FT-IR and Raman, while the catalysts were characterized by N2 adsorption-desorption, XRD, TEM and H2-TPR. After that their catalytic activity and stability were evaluated in dry reforming of methane (DRM) reaction. Both Ni and 2Ni–1Co showed better catalytic performance than other catalysts. Finally, the weight and species of carbon deposition on spent catalyst were tested by TG-DTA analysis. The deposition of inert carbon was the main reason for deactivation of catalysts in DRM. Moreover, a highly uniform dispersion and small particle size of active component are achieved by in situ co-precipitation method, and γ-Al2O3 provided large specific surface area for these Ni/Co catalysts.