Hydrotalcite Precursors Research Articles

Oxidative steam reforming of ethanol (OSRE) over stable NiCo–MgAl catalysts by microwave or sonication assisted coprecipitation

The present paper reports the physicochemical and catalytic characterization of NiCo–MgAl mixed oxides prepared from hydrotalcite (HT) precursors using ultrasound (US) or microwave radiation (MW)-assisted coprecipitation. The US or MW use reduces the preparation time and enhance both basicity and redox properties of the material compared to the solid obtained by the conventional method (coprecipitation).The oxidative steam reforming of ethanol (OSRE) was performed during 100 h (stability test) with or without solid pre-reduction in order to understand some aspects of the OSRE mechanism when transition metal catalysts are used without activation. The results demonstrate the potential of using 1Ni1Co mixed oxides obtained by MW or US assistance which exhibited better properties and catalytic stability employing shorter synthesis times. Furthermore, experiments conducted without material pre-reduction indicate the sensitivity of OSRE to the basic strength of the surface. A marked increase in basicity decrease H2 yield because of the formation of C3 byproducts.

Syngas production by the CO2 reforming of CH4 over Ni–Co–Mg–Al catalysts obtained from hydrotalcite precursors

The catalytic performance of the Ni, Co, Mg, and Al mixed-oxide solids, synthesized via hydrotalcite route, was investigated towards the dry reforming of methane for hydrogen production. The hydrotalcite structure was successfully obtained upon the synthesis. After calcination at 800 °C under an air flow, this structure was completely decomposed and the resulting oxides (CoxNiyMgzAl2800, x and y = 0; 1; 2; 3; 4, z = 2; 4, x + y + z = 6, x, y, and z are the molar ratios) were used as catalysts and were characterized using X-ray diffraction and Temperature-Programmed Reduction. The dry reforming of methane was carried out using a mixture of CH4:CO2 (1:1) after 2 h of reduction under an H2 flow at 800 °C. Co2Ni2Mg2Al2800 showed the highest catalytic activity in the studied series, ascribable to an interaction between Ni and Co, which is optimal for such Co/Ni ratio. The post-reaction characterization of the catalytic samples by X-ray diffraction and Differential Scanning Calorimetry evidenced a better resistance towards carbon deposition for the catalysts where Co molar ratio is higher than Ni.

A Short Review on the Catalytic Activity of Hydrotalcite-Derived Materials for Dry Reforming of Methane

Nickel-containing hydrotalcite-derived materials have been recently proposed as promising materials for methane dry reforming (DRM). Based on a literature review and on the experience of the authors, this review focuses on presenting past and recent achievements on increasing activity and stability of hydrotalcite-based materials for DRM. The use of different NiMgAl and NiAl hydrotalcite (HT) precursors, various methods for nickel introduction into HT structure, calcination conditions and promoters are discussed. HT-derived materials containing nickel generally exhibit high activity in DRM; however, the problem of preventing catalyst deactivation by coking, especially below 700 °C, is still an open question. The proposed solutions in the literature include: catalyst regeneration either in oxygen atmosphere or via hydrogasification; or application of various promoters, such as Zr, Ce or La, which was proven to enhance catalytic stability.

Hydrodeoxygenation of furfuryl alcohol over Cu/MgAl and Cu/ZnAl catalysts derived from hydrotalcite-like precursors: A reaction for bio-oil upgrading

The aqueous phase hydrodeoxygenation (HDO) of furfuryl alcohol over Cu/MgAl and Cu/ZnAl catalysts with different Mg/Al and Zn/Al molar ratios, were investigated. Mg-Al and Zn-Al mixed oxides derived from hydrotalcites precursors were used as supports, which were impregnated with an aqueous solution of copper nitrate by incipient wetness impregnation. The HDO reaction was carried out in a typical batch reactor at 5 MPa of H2 and 200 °C for 4 h. Among the catalysts studied, the Cu/MgAl-0.5 catalyst exhibited the higher furfuryl alcohol conversion (86%) and yield of cyclopentanol (35%), which is the reaction product with the highest hydrogen-carbon (H/C) ratio. With the Cu/MgAl-3 catalyst a high cyclopentanone yield (67%) was achieved. The results obtained, showed that copper supported on mixed oxides catalysts derived from hydrotalcite precursors are a promising alternative to improve the bio-oil quality.

Efficient Catalytic Conversion of Ethanol to 1-Butanol via the Guerbet Reaction over Copper- and Nickel-Doped Porous

The direct conversion of ethanol to higher value 1-butanol is a catalytic transformation of great interest in light of the expected wide availability of bioethanol originating from the fermentation of renewable resources. In this contribution we describe several novel compositions of porous metal oxides (PMO) as highly active and selective catalysts for the Guerbet coupling of ethanol to 1-butanol in the temperature range 180–320 °C. The novel PMO catalysts that do not contain any noble metals are obtained by calcination of a series of hydrotalcite precursors synthesized through modular procedures. In particular, catalyst compositions simultaneously containing Cu and Ni dopants have shown excellent catalytic activities. Up to 22% 1-butanol yield at 56% ethanol conversion was reached in a batch mode; recycling and leaching tests showed excellent robustness of the new catalysts. An extensive characterization by means of several techniques such as powder XRD, SEM, TEM, BET, and NH3- and CO2-TPD was performed...

CO2 reforming of CH4 over a highly active and stable Ni[sbnd]Mg[sbnd]Al catalyst

Although the catalytic systems containing the NiOMgO solid solution possess excellent catalytic performance in CO2 reforming of CH4 reaction, a serious drawback was that the higher than 10 wt% Ni loadings would increase the burden on the environment and finance. A NiMgAl catalyst with 3 wt% Ni loadings derived from a hydrotalcite precursor was prepared in order to study the CO2 reforming of CH4 reaction. For comparative purpose, a NiOMgO catalyst and a Ni/γ-Al2O3 catalyst containing NiAl2O4, were also synthesized. Analysis showed that the NiMgAl catalysts had high catalytic activity due to the improved reducibility which was caused by the presence of Al3+ ions in the NiOMgO cubic lattice. Moreover, the NiMgAl catalyst showed ultra-stability without carbon formation for 320 h period due to the small Ni particles and the suitable Ni-support interaction which effectively prevented the sintering of Ni particles.

Methanol and ethanol reactivity in the presence of hydrotalcites with Mg/Al ratios varying from 2 to 7

Mg-Al mixed oxides, prepared from hydrotalcite precursors with Mg/Al ratio varying from 2 to 7, were tested in the Guerbet reaction of methanol and ethanol to heavier products. Acidic-basic properties were followed by the adsorption calorimetry of SO2 and NH3 molecules and correlated with the catalytic activity. The results showed that the selectivity to higher alcohols is increasing with the increase of both kinds of active sites.

Catalytic Conversion of Glucose into Sorbitol Over Ni/Cu/Al/Fe Catalysts Derived from Hydrotalcite Precursors

Catalytic Conversion of Glucose into Sorbitol Over Ni/Cu/Al/Fe Catalysts Derived from Hydrotalcite Precursors

The effects of thermal treatment of ZnO–ZnCr2O4 catalyst on the particle size and product selectivity in dehydrocyclization of crude glycerol and ethylenediamine

The ZnO–ZnCr2O4 (Zn–Cr–O) sample obtained by decomposition of Zn-Cr hydrotalcite precursor was subjected to the thermal treatment at different temperatures and the physico-chemical properties of the Zn–Cr–O system were compared with its catalytic behavior in dehydrocyclization of crude glycerol and ethylenediamine (EDA). Upon high temperature treatment of Zn–Cr–O the Cr6+ ions underwent autoreduction to form stable Cr3+ species and the particle size of both ZnO and ZnCr2O4 increased dramatically. Thermal effect did not influence the intermolecular cyclisation of EDA to form pyrazine. By contrast, an inversely proportional dependence was found between the rate of formation of 2-methylpyrazine and the particle size of Zn–Cr–O whereas the rate of 2-pyrazinylmethanol was directly proportional to the particle size.

Gold promoted Cu/ZnO/Al2O3 catalysts prepared from hydrotalcite precursors: Advanced materials for the WGS reaction

Outstanding catalysts for the water was shift reaction are reported in this work. The combination of gold nanoparticles with Cu/ZnO/Al2O3 prepared from hydrotalcite-like precursors leads to very promising systems for pure hydrogen production. Full CO conversion is reached at temperatures as low as 180°C. The key point seems to be the cooperation of Au and Cu and the optimal metal-oxide contact derived from the synthesis method. The high activity of gold for low temperature CO oxidation and the suitability of copper for the WGS results in a perfect synergy. Moreover the materials developed in this work present good stability and tolerance towards start/stop cycles an indispensable requisite for a realistic application in an integrated hydrogen fuel processor.

Insight into the function of base-promoted Cu-containing catalysts for highly efficient hydrogenolysis of cellulose into polyols

The Cu-containing catalysts were synthesized via thermal treatment of the CuMgAl hydrotalcite with a fixed metal ratio at various calcination temperatures. The bi-functional solid base catalysts exhibited high activity for the hydrogenolysis of highly concentrated cellulose. The hydrotalcite precursors and the calcined samples were characterized by means of X-ray diffraction (XRD), thermogravimetric analysis (TG), N2 adsorption–desorption, temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption of CO2 (CO2-TPD) and dissociative N2O adsorption. The characterization results indicated that the transformation of structure was caused by the increasing calcination temperature, which could further influence the numbers of the base sites and metal active sites in the CuMgAl catalysts. The hydrogenolysis of cellulose was systematically investigated over different catalytic systems. With the CuMgAl-600 catalyst, complete conversion of cellulose can be accomplished and the highest yield obtained is 81.4%, with total polyols yields obtained are 59.1% for the C2–C3 polyols. In addition, either the in-situ hydroxyl or the hydrated OH− due to the “memory effect” of hydrotalcite as Brønsted bases, was proved to exhibit promotional effect on the hydrogenolysis of cellulose, which could effectively substitute the effect of ionizing alkali. Furthermore, it is noteworthy that the conversion of cellulose could maintain up to 90.2% with unobvious formation of coke-like precipitates when the cellulose concentration reached a high level of 18%.

Storage capacity and oxygen mobility in mixed oxides from transition metals promoted by cerium

The oxygen mobility and storage capacity of Ce-Co/Cu-MgAl or Ce–MgAl mixed oxides, obtained by hydrotalcite precursors, were evaluated using Toluene-temperature-programmed-reaction, 18O2 isotopic exchange and O2-H2 titration. The presence of oxygen vacancies-related species was evaluated by means of Electron Paramagnetic Resonance. A correlation was found between the studied properties and the catalytic activity of the oxides in total oxidation processes. It was evidenced that catalytic activity depends on two related processes: the facility with which the solid can be reduced and its ability to regenerate itself in the presence of molecular oxygen in the gas phase. These processes are enhanced by Cu-Co cooperative effect in the mixed oxides. Additionally, the incorporation of Ce in the Co-Cu catalysts improved their oxygen transport properties.

Synthesis and characterization of Co–Al–Fe nonstoichiometric spinel-type catalysts for catalytic CO oxidation

CoAlFe nonstoichiometric spinel-type oxides derived from hydrotalcites precursors exhibit high activities for catalytic CO oxidation.

Metal Phosphides Derived from Hydrotalcite Precursors toward the Selective Hydrogenation of Phenylacetylene

We report a new synthetic strategy for the fabrication of several supported nickel phosphides (Ni12P5, Ni2P, and NiP2) with particle size ranging from 5 to 15 nm via a two-step procedure: preparation of supported Ni particles from layered double hydroxide precursors, followed by a further reaction with a certain amount of red phosphorus. The selective hydrogenation of phenylacetylene over these metal phosphides was evaluated, and the as-prepared Ni2P/Al2O3 catalyst shows a much higher selectivity to styrene (up to 88.2%) than Ni12P5/Al2O3 (48.0%), NiP2/Al2O3 (65.9%), and Ni/Al2O3 (0.7%) catalysts. EXAFS and in situ IR measurements reveal that the incorporation of P increases the bond length of Ni–Ni, which imposes a key influence on the adsorption state of alkene intermediates: as the Ni–Ni bond length extends to 0.264 nm, the alkene intermediate undergoes di-π(C═C) adsorption, facilitating its desorption and the resulting enhanced selectivity. Moreover, electron transfer occurs from Ni to P, as confirmed...

Effect of precursor synthesis on the physicochemical properties of Zn–Mg–Al mixed oxides

In this work, the influence of the zinc content and synthesis methodology on the physicochemical properties of mixed oxide derivatives from the hydrotalcite precursor MgZnAl-HT were evaluated. Layered double hydroxides (LDH) were prepared by co-precipitation, ultrasound and urea hydrolysis methods followed by calcination at 500°C. The materials were studied by such techniques as inductively coupled plasma, X-ray powder diffraction, Raman spectroscopy and 27Al solid-state NMR spectroscopy. The textural and morphological properties of mixed oxides were evaluated through the adsorption/desorption of N2 and scanning electron microscopy (SEM). Different textural and morphological properties were observed for the samples.

Effect of Mg/Al Ratio on Catalytic Behavior of Fischer–Tropsch Cobalt-Based Catalysts Obtained from Hydrotalcites Precursors

Layered double hydroxides of the hydrotalcite (HT)-type materials have been considered as promising supports for Co-based Fischer–Tropsch synthesis (FTS) catalysts. In this work the effect of the Mg/Al ratio on the catalytic behavior of cobalt-based catalysts obtained from HTs precursors have been studied. Cobalt supported on Mg–Al oxides obtained from HTs Mg–Al precursors were prepared by wet impregnation method and calcined at 300 °C. The textural, structural and reducibility properties of the samples were characterized using different techniques. FTS was evaluated in a down-flow fixed-bed reactor at 20 bar, 250 °C and H2/CO ≈ 2 molar ratio. All catalysts were active and stable during 72 h testing time. The stability was improved by the presence of magnesium in the alumina support; however the CO conversion was negatively affected by increasing the Mg/Al ratio. The reducibility of cobalt decreased as the Mg/Al ratio increased, probably due to the strong Co–O–Mg interaction as evidenced by the formation of CoxOy–MgO mixed oxide. Furthermore, the activity of the catalysts was correlated with the H2-chemisorption measurements. The results suggest that HTs as Co-based catalysts were highly stable in FTS.

Effect of Mg/Al ratio of NiMgAl mixed oxide catalyst derived from hydrotalcite for carbon dioxide reforming of methane

How to stabilize Ni during the carbon dioxide reforming of methane (DRM) reaction is crucial for practical use of Ni catalysts for the DRM reaction. It is revealed in the present paper that there are two points that play key role in stabilization of Ni: one is formation of hydrotalcites precursors, and the other is formation of MgNiO2. Therefore, the NiMgAl mixed oxides with higher Mg/Al ratio exhibits better catalytic activity and coke resistance, and the NiMgAl with Mg/Al ratio of 1 gives the best activity and stability for the DRM reaction.

Effective Upgrade of Levulinic Acid into γ-Valerolactone over an Inexpensive and Magnetic Catalyst Derived from Hydrotalcite Precursor

A low-cost and magnetic catalyst derived from a hydrotalcite precursor was developed for selective hydrogenation of levulinic acid (LA) into γ-valerolactone (GVL) in a methanol solvent. An excellent GVL yield of 98.1% with full LA conversion was achieved at 415 K over a magnetic and recyclable Ni4.59Cu1Mg1.58Al1.96Fe0.70 catalyst. The specific textural and chemical characteristics of prepared samples were identified by ICP-AES, XRD, XPS, NH3-TPD, Py-IR, and nitrogen physisorption. Various parameters such as Ni/Cu molar ratio, reduction temperature, and reaction solvent played a great role in LA hydrogenation. The recycling experiments revealed that reactivated Ni4.59Cu1Mg1.58Al1.96Fe0.70 maintained excellent activity, stability, and magnetism after being used five times, which made Ni4.59Cu1Mg1.58Al1.96Fe0.70 a potential catalyst for the production of GVL in industry.

Influence of Rare Earth (La, Pr, Nd, Gd, and Sm) Metals on the Methane Decomposition Activity of Ni–Al Catalysts

Rare earth (RE = La, Pr, Nd, Gd and Sm) metal-doped Ni-Al (Ni-RE-Al) hydrotalcite precursors were obtained by coprecipitation and calcined to form mixed oxide catalysts. The physicochemical characteristics of calcined and reduced Ni-RE-Al samples were determined by X-ray powder diffraction, Brunauer–Emmett–Teller surface area, H2 temperature-programmed reduction, O2 pulse chemisorption, UV-diffuse reflectance spectroscopy, electron spin resonance spectrometry, and Fourier transform infrared spectroscopy. The catalysts were evaluated for CH4 decomposition at 550 °C until their complete deactivation. The deactivated catalysts were examined by transmission electron, scanning electron, and Raman spectroscopy and elemental analysis. The Raman spectra indicated the presence of both ordered and disordered carbon in deactivated catalysts. A correlation is drawn between H2 production rates and the Ni metal surface area of catalysts. The addition of La to Ni-Al dramatically changed the Ni behavior, leading to highe...

Transition metal-modified mesoporous Mg-Al mixed oxides: Stable base catalysts for the synthesis of diethyl carbonate from ethyl carbamate and ethanol

A series of transition metal-modified hydrotalcite precursors (HT-M, M=Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+ and Zn2+) were prepared by using the “memory effect” of Mg-Al hydrotalcite. Then, the mixed oxides with different composition were obtained by thermal decomposition of as-prepared hydrotalcite precursors at 773K, and their physicochemical properies were characterized by thermogravimetry and differential thermogravimetry (TG-DTG), X-ray diffraction (XRD), N2 adsorption–desorption, X-ray photoelectron spectroscopy (XPS), scanning electron micrograph (SEM) and CO2 temperature-programmed desorption (CO2-TPD) technique. It was found that the mesoporous structure was formed during calcination. More important, the basicity of the calcined hytrotalcites (HTC-M) samples was depended on the type of transition metal. Simultaneously, they were used as solid base catalysts and evaluated for the synthesis of diethyl carbonate (DEC) from ethyl carbamate and ethanol. Among them, HTC-Mn exhibited maximum activity with the DEC yield of 56.7% under optimum reaction conditions. Then, the correlation between their basic properties and catalytic performance was studied in detail for the HTC-M catalysts. Furthermore, HTC-Mn catalyst could be readily recycled while maintaining high catalytic activity toward this reaction.