Ni-Al Hydrotalcite Research Articles

Structural and catalytic properties of supported Ni–Ir alloy catalysts for H2 generation via hydrous hydrazine decomposition

Iridium modified Ni/Al2O3 catalysts were prepared using Ni–Al hydrotalcite as precursor and tested in the selective decomposition of hydrous hydrazine for H2 generation. Compared to Ni/Al2O3, NiIrx/Al2O3 catalysts exhibited an increase of the reaction rate up to 6-fold and the H2 selectivity from 93% to above 99%. The XRD and EXAFS analysis confirmed that Ir and Ni were present in the form of Ni–Ir alloy; and the H2 differential heat of adsorption is appreciably lowered with increasing the amount of Ir in Ni–Ir alloy. High-temperature reduction, e.g. 700°C, induced the migration of Ir atoms into the Ni bulk and produced a Ni-skin surface. This structural modification is associated with a strongly decrease of activity and selectivity. EXAFS measurements were also performed on different noble metals (NM, Ir, Pt, and Au) modified Ni/Al2O3 catalysts in order to verify the extent of NM-Ni bimetallic bond formation, which was found to correlate with the catalytic performance.

Characterization of nano-crystalline Mg–Ni–Al hydrotalcite derived mixed oxides as hydrogen adsorbent

A promising energy storage material containing magnesium, nickel and aluminum metals has been synthesized using conventional coprecipitation method. The physio-chemical properties, morphology and microstructure of hydrotalcite based mixed oxides (MNAM) have been characterized using ICP-MS, XRD, BET, FESEM and TEM techniques. The characterizations revealed that the adsorbent are highly dispersed, poly crystalline, homogenously distributed and interactive. Temperature programmed techniques have been used to explore the sorption capacities of mixed oxides. Nano-crystalline mesoporous and interactive reduced mixed oxides exhibit a 3.9 wt% H2 adsorption capacity at ambient conditions. Temperature programmed desorption study predicted a desorption capacity of 1.9 wt% H2. Different hydrogen adsorbed phases of magnesium and nickel have been characterized using HRTEM, Raman and FT-IR techniques.

Surface modification of Ni/Al2O3 with Pt: Highly efficient catalysts for H2 generation via selective decomposition of hydrous hydrazine

Hydrous hydrazine, such as hydrazine monohydrate (N2H4·H2O), is a promising hydrogen carrier material due to its high content of hydrogen (8.0wt%). The decomposition of hydrous hydrazine to H2 with a high selectivity and a high activity under mild conditions is the key to its potential usage as a hydrogen carrier material. Platinum-modified Ni/Al2O3 catalysts (NiPtx/Al2O3) were prepared starting from Ni–Al hydrotalcite and tested in the decomposition of hydrous hydrazine. Compared with Ni/Al2O3, the TOF was enhanced sevenfold over NiPt0.057/Al2O3; meanwhile, the selectivity to H2 was increased to 98%. Characterization results by means of HAADF-STEM, XRD, and EXAFS revealed the presence of surface Pt–Ni alloy in this Pt-promoted catalyst. The formation of Pt–Ni alloy could significantly weaken the interaction between adspecies produced (including H2 and NHx) and surface Ni atoms, which is confirmed by microcalorimetry and TPD results. The weakening effect could account for the greatly enhanced reaction rate, as well as H2 selectivity on NiPtx/Al2O3 catalysts.

Decavanadate-intercalated Ni–Al hydrotalcites as precursors of mixed oxides for the oxidative dehydrogenation of propane

Two nickel–aluminum hydrotalcite type precursors were synthesized with molar ratio Ni/Al=3, using hydroxyl and carbonate as compensation anions. These precursors were intercalated by 30% (theoretical) decavanadate anion. The catalysts were obtained after calcination at 550°C and their performance was evaluated in propane oxidative dehydrogenation at 400°C using space velocities of 100, 150, 200 and 400mlg−1min−1 under conditions of oxygen deficiency and oxygen excess. Catalysts derived from nickel–aluminum-hydroxyl precursors attained an excellent performance under oxygen deficiency conditions promoting high propene selectivity and conversion. Under oxygen excess conditions the catalyst was more active but its selectivity was lower. Vanadium-containing catalysts showed improved selectivity under this operation condition. The formation of the hydrotalcite phase in precursors and mixed oxides in the catalysts was evidenced by X-ray diffraction (XRD). Analyses of textural and reduction properties were carried-out with nitrogen adsorption and temperature programmed reduction techniques respectively. Structural studies were performed by X-ray absorption spectroscopy for materials that showed best performance in the oxidative dehydrogenation reaction.

Catalytic wet peroxide oxidation of phenol over Cu–Ni–Al hydrotalcite

Liquid phase catalytic oxidation of phenol was carried out over Cu–Ni–Al hydrotalcite at ambient temperature and pressure using hydrogen peroxide as oxidant. The results showed that the hydrotalcite catalyst had high catalytic activity, where phenol could be completely oxidized by H 2O 2 into oxalic acid, formic acid and CO 2 within 2 h at 30 °C. The catalytic oxidation process was zero-order kinetics with an activation energy of 61.5 kJ mol − 1 . A feasible reaction system could be proposed as follows: 0.8 g L − 1 of catalyst, n (H 2O 2)/n (phenol) = 15, temperature of 40 °C, 2.66 mM of phenol and time of 2 h. Furthermore, it was found that the presence of inorganic chlorides promoted markedly the oxidation rate of phenol, probably due to the formation of intermediate products containing chlorine such as quinones and/or radicals.

Study of structural transformations and phases formation upon calcination of Zn–Ni–Al hydrotalcite nanosheets

In this paper, we describe a general process for the synthesis of highly crystalline Zn–Ni–Al hydrotalcite-like materials. The structure and thermal decomposition of the prepared samples are studied by XRD, FT–IR, TG–DSC, SEM, TEM and N2 adsorption/desorption. The morphology of large-sized, porous and hexagonal platelike Zn–Ni–Al hydrotalcite is affected by calcination temperature. BET specific surface area and pore volume are observed to increase with increase of the calcination temperature up to 700°C followed by a further decrease with increasing temperature.

STRUCTURE, CHARACTERIZATION AND APPLICATION OF NI HYDROTALCITE AS SOLID BASE CATALYSTS FOR ORGANIC TRANSFORMATIONS

Ni hydrotalcites with different kinds of metals, ions exhibit considerable activity for organic transformations. Various ratios of Ni-Al hydrotalcites are prepared by using different compositions are characterized by XRD, IR and TPR analysis. Carbonate in the brucite sheets is active for selective oxidation reactions. Upon calcination the dehydroxylation of the hydrotalcite and concurrent decomposition of the carbonate ions produce mixed oxides which exhibits activity for variety of organic transformations.

ChemInform Abstract: NiO-Al2O3 Prepared from a Ni-Al Hydrotalcite Precursor as an Efficient Catalyst for Transfer Hydrogenation Reactions.

Abstract NiO-Al2O3 catalyst prepared by calcining a Ni-Al hydrotalcite precursor efficiently reduces nitroarenes and carbonyl compounds in presence of propan-2-ol and KOH. Presence of two different reducible groups in the substrate leads to chemoselective reduction.

Influence of Copper on the Isomerization of Eugenol for as-Synthesized NiCuAl Ternary Hydrotalcites: An Understanding Through Physicochemical Study

Catalysts with the hydrotalcite-like structure and general formula NiCuAlyz-HT having (Ni + Cu)/Al atomic ratio of 3.0 with varying Ni:Cu atomic compositions (100:0–50:50) were synthesized, characterized and tested for isomerization of eugenol to isoeugenol. The decrease in the activity upon addition of copper to NiAl lattice is investigated through temperature programmed reduction and phenol adsorption. Conversion of eugenol over active NiAl hydrotalcite significantly decreased upon incorporation of Cu2+ in the NiAl binary lattice wherein substitution of 25 at% of Ni2+ by Cu2+ annihilated the isomerization activity. The decrease in the activity upon addition of copper to NiAl lattice is investigated through physiochemical studies.

Partial hydrogenation of propyne over copper-based catalysts and comparison with nickel-based analogues

The partial hydrogenation of propyne was studied over copper-based catalysts derived from Cu–Al hydrotalcite and malachite precursors and compared with supported systems (Cu/Al 2O 3 and Cu/SiO 2). The as-synthesized samples and the materials derived from calcination and reduction were characterized by XRF, XRD, TGA, TEM, N 2 adsorption, H 2-TPR, XPS, and N 2O pulse chemisorption. Catalytic tests were carried out in a continuous flow-reactor at ambient pressure and 423–523 K using H 2:C 3H 4 ratios of 1–12 and were complemented by operando DRIFTS experiments. The propyne conversion and propene selectivity correlated with the copper dispersion, which varied with the type of precursor or support and the calcination and reduction temperatures. The highest exposed copper surface was attained on hydrotalcite-derived catalysts, which displayed C 3H 6 selectivity up to 80% at full C 3H 4 conversion and stable performance in long-run tests at T ⩾ 473 K. Both activated Cu–Al hydrotalcites (this work) and Ni–Al hydrotalcites [S. Abelló, D. Verboekend, B. Bridier, J. Pérez-Ramírez, J. Catal. 259 (2008) 85] exhibited a relatively high alkene selectivity under optimal operation conditions, but they present a markedly distinctive catalytic behavior with respect to temperature and hydrogen-to-alkyne ratio. The product distribution was assigned through Density Functional Theory (DFT) simulations to the different stability of subsurface phases (carbides, hydrides) and the energies and barriers for the competing reaction mechanisms. The behavior of Cu in partial alkyne hydrogenation resembles that of Au nanoparticles, while Ni is closer to Pd.

Preparation and characterization of new Ni-aluminosilicate catalysts and their performance in the epoxidation of (Z)-cyclooctene

Abstract This work reports the preparation of two series of Ni-aluminosilicates by the sol–gel and the co-precipitation methods. The main difference between the two processes of synthesis is the pH of the initial mixture, 2 for the sol–gel and 11 for the co-precipitation method, respectively. The obtained solids are heat-treated at various temperatures in the range of room temperature to 1000 °C, and the resulting materials are characterized by X-ray diffraction, thermogravimetric and differential thermal analysis, ultraviolet–visible spectroscopy, nitrogen adsorption, and transmission electron microscopy. Various nickel compounds crystallize under the sol–gel reaction conditions, as well as, amorphous silica and crystalline 2NaAlO 2 ·3H 2 O. Ni–Al hydrotalcite, takovite, and amorphous silica are obtained when the samples from the co-precipitation method are analysed. A maximum of 302 m 2 /g of specific surface area shows the co-precipitation samples series, with only 32 m 2 /g in the case of the sol–gel samples series. The catalytic performance in the epoxidation of ( Z )-cyclooctene at room temperature and atmospheric pressure is evaluated using aqueous hydrogen peroxide as oxidant.

NiAl hydrotalcite as an efficient and environmentally friendly solid catalyst for solvent-free liquid-phase selective oxidation of ethylbenzene to acetophenone with 1 atm of molecular oxygen

NiAl hydrotalcites with Ni/Al molar ratios of 2–5 and prepared using C O 3 2 − , Cl −, N O 3 − , or S O 4 2 − as a guest inorganic anion, were evaluated for the liquid-phase selective oxidation of a methylene group of ethylbenzene to carbonyl functionality with atmospheric pressure of oxygen as the sole oxidant under solvent-free and mild reaction conditions. Among the different NiAl hydrotalcites, the catalyst with a Ni/Al ratio of 5 mol mol −1 prepared in the presence of C O 3 2 − anion exhibited the greatest catalytic activity for the ethylbenzene oxidation reaction. NiAl hydrotalcite prepared with C O 3 2 − as a guest inorganic anion also showed very high acetophenone selectivity (>99%) compared with those prepared using Cl −, N O 3 − , or S O 4 2 − anions. Compared with other transition metal–containing hydrotalcite-like solid catalysts (e.g., CuAl-, ZnAl-, CoAl-, MgFe-, MgCr-), with similar molar compositions and prepared in the presence of the C O 3 2 − anion, the catalytic activity of NiAl hydrotalcite was much higher in the above oxidation reaction. The active NiAl hydrotalcite also exhibited good catalytic performance for the oxidation of a wide range of alkylaromatics to their corresponding benzylic ketones under similar experimental conditions. The NiAl hydrotalcite can be easily prepared from cheap, commercially available reagents and is stable and reusable for the ethylbenzene oxidation even in the absence of solvents and reducing reagents.

Selective reduction of aldehydes to alcohols by calcined Ni-Al hydrotalcite

Several aromatic and heterocyclic aldehydes are reduced at atmospheric pressure by calcined Ni-Al hydrotalcite and the catalyst is reused for several cycles with consistent activity and selectivity.

In situ Fourier transform infrared and laser Raman spectroscopic study of the thermal decomposition of Co–Al and Ni–Al hydrotalcites

In situ infrared spectra and in situ laser Raman spectra of Co–Al and Ni–Al hydrotalcites (HTlcs) have revealed several novel aspects of the structure, and physico-chemical transformations upon thermal decomposition of these materials in air. The infrared spectra of the Co–Al-HTlc at room temperature show the presence of a fraction of the carbonate in a low symmetry, which was not observed for Ni–Al-HTlc. Furthermore, compared to Co–Al-HTlc, a relatively smaller ratio of carbonate over hydroxyls is present in the as-synthesized Ni–Al-HTlc, as revealed by the infrared and Raman spectra. This is in agreement with a mass spectrometric analysis of the as-synthesized materials upon thermal decomposition, and the relatively small c-parameter determined from the X-ray diffraction (XRD) pattern of the as-synthesized Ni–Al-HTlc. An extraordinary stability of interlayer water in Ni–Al-HTlc was found, which was only completely removed above 300°C, a temperature of 100°C higher than found for Co–Al-HTlc. Dehydroxylation of the octahedral layers and carbonate reorganization and decomposition also require higher temperatures for Ni–Al-HTlc (300–350 and >550°C) than for Co–Al-HTlc (150–200 and 450–500°C). Raman spectra indicate the presence of an intermediate cobalt oxide (CoO x ) phase upon decomposition of Co–Al-HTlc in the temperature range of 175–250°C, before formation of a solid solution of cobalt spinels (Co(Co, Al) 2O 4) occurs. Highly dispersed NiO strongly interacting with the Al 2O 3 support was identified after decomposition of Ni–Al-HTlc at 550°C. The spectroscopically determined transition temperatures are in excellent agreement with XRD, thermogravimetric, and mass spectrometric analyses.

ChemInform Abstract: The First Example of Activation of Molecular Oxygen by Nickel in Ni—Al Hydrotalcite: A Novel Protocol for the Selective Oxidation of Alcohols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The First Example of Activation of Molecular Oxygen by Nickel in Ni-Al Hydrotalcite: A Novel Protocol for the Selective Oxidation of Alcohols

NiO in association with aluminum oxide has been identified by temperature-programmed reduction as the active species in the Ni–Al hydrotalcite catalyst that oxidizes α-ketols as well as benzylic and allylic alcohols to their corresponding carbonyl compounds in oxygen in quantitative yields under mild reaction conditions (see scheme).

The First Example of Activation of Molecular Oxygen by Nickel in Ni-Al Hydrotalcite: A Novel Protocol for the Selective Oxidation of Alcohols

NiO in Verbindung mit Aluminiumoxid wurde durch Temperatur-programmierte Reduktion als die aktive Spezies in Ni-Al-Hydrotalcit-Katalysatoren bestimmt. Diese Katalysatoren können α-Ketole sowie benzylische und allylische Alkohole zu den entsprechenden Carbonylkomponenten quantitativ und unter milden Reaktionsbedingungen oxidieren (siehe Schema).

The First Example of Activation of Molecular Oxygen by Nickel in Ni-Al Hydrotalcite: A Novel Protocol for the Selective Oxidation of Alcohols

NiO in association with aluminum oxide has been identified by temperature-programmed reduction as the active species in the Ni–Al hydrotalcite catalyst that oxidizes α-ketols as well as benzylic and allylic alcohols to their corresponding carbonyl compounds in oxygen in quantitative yields under mild reaction conditions.

NiO-Al2O3 Prepared From A Ni-Al Hydrotalcite Precursor As An Efficient Catalyst For Transfer Hydrogenation Reactions

NiO-Al2O3 catalyst prepared by calcining a Ni-Al hydrotalcite precursor efficiently reduces nitroarenes and carbonyl compounds in presence of propan-2-ol and KOH. Presence of two different reducible groups in the substrate leads to chemoselective reduction.

Comparative Study of Sol-Gel and Coprecipitated Ni-Al Hydrotalcites

Hydrotalcite is an anionic clay mineral (layered double hydroxide) whose general formula is [M(II)1−x M(III) x (OH)2] x+X / − ·mH2O. Anionic clays with a hydrotalcite-type are widely used as useful precursors of multicomponent catalysts. Hydrotalcites with Ni/Al molar ratio 2.5 have been synthesised both by the coprecipitation method, starting with nickel and aluminium nitrates and by the sol-gel method, using nickel acetylacetonate and aluminium isopropylate as precursors. The NiO-Al2O3 oxidic forms have been obtained by the thermal treatment of the precursors at 450°C and 900°C, respectively, and were characterised by DTA, XRD, IR spectroscopy and temperature programmed reduction (TPR). TPR clearly demonstrated a higher reducibility of the oxidic forms derived from the sol-gel synthesised precursors.