Hydrotalcite-derived Catalysts Research Articles

Selective hydrogenation of levulinic acid into γ-valerolactone over Cu/Ni hydrotalcite-derived catalyst

A highly efficient and selective Cu/Ni hydrotalcite-derived catalytic system has been developed for liquid phase hydrogenation of levulinic acid (LA) into γ-valerolactone (GVL) under mild reaction conditions. Full conversion of LA with 100% selectivity towards GVL has been achieved at 140°C, 30bar H2 pressure in 3h using dioxane as a solvent over activated Cu/Ni/Mg/Al catalyst with 0.75/0.5/1/1 molar ratios of metal cations in the synthesis mixture. It has been found that the catalytic activity increases with increasing copper content, while the selectivity towards GVL formation increases with increasing nickel content and surface Lewis basic sites (SLB) resulting from MgO promotes the hydrogenation of LA under mild reaction conditions by activating the CO group of LA for hydrogenation. Influence of various parameters such as reaction temperature, hydrogen pressure, reaction time and the nature of solvent have been studied. A series of Cu-based catalysts have been prepared by co-precipitation method and characterized using XPS, XRD, FEG-SEM, EDS, NH3-TPD, CO2-TPD, TPR and N2 physical adsorption techniques. Furthermore, the catalyst was easily reactivated and recycled for four times without significant loss in catalytic activity and selectivity towards GVL formation.

Promotion effect of zirconia on Mg(Ni,Al)O mixed oxides derived from hydrotalcites in CO2 methane reforming

Hydrotalcite-derived catalysts promoted with Zr species were prepared via co-precipitation method, resulting in materials with various Zr loading. Physicochemical properties of catalysts precursors and final catalysts were investigated via XRF, XRD, low temperature N2 sorption, H2-TPR, CO2-TPD, TG, SEM and TEM techniques. So characterized catalysts were subsequently tested in the dry methane reforming reaction at 550°C. Zr-loading introduced into brucite-like layers influenced the process of thermal decomposition of HTs and, as a result, their properties and performance in DRM. Although Zr promotion decreased activity, it strongly increased the stability and selectivity of the catalysts. The catalyst with Zr species present in the framework of periclase-like mixed oxide exhibited high resistance to coking due to the rearrangement of Ni particles upon DRM reaction.

The influence of lanthanum incorporation method on the performance of nickel-containing hydrotalcite-derived catalysts in CO2 methanation reaction

A series of hydrotalcite-derived mixed oxides containing Ni/Mg/La/Al and obtained by thermal decomposition, were characterized by XRD, H2-TPR, CO2-TPD, elemental analysis and low temperature nitrogen sorption techniques. The results confirm the formation of periclase-like structured materials. The catalysts containing lanthanum, incorporated by different methods, i.e. co-precipitation, impregnation and ion-exchange, showed outstanding catalytic activity at 300°C, with CO2 conversions around 36–87% and CH4 selectivity of 98–99%.

Hydrotalcite-derived Co-containing mixed metal oxide catalysts for methanol incineration

The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H2-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO2, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co3+ cations, formed during high-temperature treatment of the hydrotalcite-like precursor.

The influence of nickel content on the performance of hydrotalcite-derived catalysts in CO2 methanation reaction

A series of mixed oxides obtained by thermal decomposition of hydrotalcites containing different amounts of Ni and constant MII+/MIII+ molar ratio were characterized by XRD, XANES, XES, H2-TPR, CO2-TPD, elemental analysis and low temperature nitrogen sorption technique. The results confirm the formation of periclase-like structured materials after thermal treatment, with nickel present as NiO in octahedral coordination environment. As proven by H2-TPR with increasing Ni content the interaction between Ni and hydrotalcite matrix weakens, which has a positive influence on the catalytic performance. The catalysts containing different amounts of nickel (10.3, 16.2, 27.3, 36.8, 42.5 wt.%) showed at 300 °C a very good catalytic performance in carbon dioxide methanation, with CO2 conversion of 36 (Ni10.3)–82% (Ni42.5) and CH4 selectivity of 98–99%.

Catalytic activity of hydrotalcite-derived catalysts in the dry reforming of methane: on the effect of Ce promotion and feed gas composition

Ni/Al and Ni/Mg/Al hydrotalcite-derived materials containing various Ni loadings were synthesized and subsequently promoted with Ce-species via adsorption from [Ce(EDTA)]− complexes. The obtained materials were characterized by elemental analysis (ICP-MS), XRD, H2-TPR, CO2-TPD, TG and low temperature N2 sorption experiments. The amount of the introduced Ce was dependent on the nickel and magnesia content in catalysts precursors, and it influenced materials properties (i.e. basicity, reducibility of Ni species) in various ways and the catalytic performance in the dry reforming of methane (DRM). The promoted catalysts showed improved performance with CH4 and CO2 conversions at 550 °C in the range of 35–55 and 35–45%, respectively. The extent of the improvement was dependent on the nickel content and the presence of magnesia. In general, Ce promotion increased materials stability by changing of the type of carbonaceous deposits. Ce modification hindered the transformation of amorphous carbonaceous deposits to graphitic carbon. The former may be easier oxidized and contribute to syngas production. Two selected catalysts were additionally tested in DRM at elevated temperatures (650 and 750 °C) and over various feed gas compositions.

Influence of Ce/Zr molar ratio on catalytic performance of hydrotalcite-derived catalysts at low temperature CO2 methane reforming

Zr and Ce promoted hydrotalcite-derived materials were tested as a catalysts for dry reforming of methane. Zirconium species were introduced into hydrotalcite brucite-like layers, while cerium species were deposited on the external surfaces of crystallites. Three catalysts with Ce/Zr molar ratio of 1.2, 0.6 and 0.3 were synthesized, tested in dry reforming at 550 °C and subsequently characterized with the aid of XRD, XRF, FTIR, H2-TPR, CO2-TPD and TG techniques. Promotion with both Ce, Zr resulted in decrease catalytic activity, however, stability of materials was significantly increased, which could be attributed to increased concentration of strong basic sites. The effect of Ce/Zr molar ratio was mainly dependent on the position of Zr species in brucite-like layers or in mixed ceria–zirconia on catalyst surface and influenced materials basicity, reducibility and stability in DRM.

Oxidative amidation of benzaldehydes and benzylamines withN-substituted formamides over a Co/Al hydrotalcite-derived catalyst

A highly efficient synthetic strategy for amidesviaoxidative amidation of benzaldehydes or benzylamines withN-substituted formamides has been developed using cobalt based heterogeneous catalyst.

Ceria promotion over Ni-containing hydrotalcite-derived catalysts for CO2methane reforming

The catalytic activity in dry methane reforming of hydrotalcite-derived catalysts with ceria and/or nickel species introduced into hydrotalcite interlayer spaces was examined. The prepared materials were characterized (XRF, XRD, FT-IR, H2-TPR and N2 sorption) and subsequently tested in CO2 methane reforming at 550 °C. The obtained results showed that the incorporation of nickel species between hydrotalcite layers resulted in active catalyst with no sign of carbon deposition. Additionally, a beneficial effect of ceria promotion was observed. Ceria-promoted sample exhibited higher activity, stability and selectivity towards DRM, which may be explained by the formation of small Ni crystallites and prevention of the formation of inactive NiAl2O4 spinel phase.

Hydrogen production from ethylene glycol reforming catalyzed by Ni and Ni–Pt hydrotalcite-derived catalysts

In this work, we report a study of the steam reforming (SR) and the aqueous phase reforming (APR) of ethylene glycol (EG) with catalysts based on Ni, prepared from hydrotalcite-like compounds. The Pt–Ni bimetallic catalyst was synthesized using controlled techniques derived from Surface Organometallic Chemistry on Metals (SOMC/M). This methodology allows obtaining very well-defined active phases, with low atomic Pt/Ni bulk values (∼0.004) and a specific interaction between both metals.We demonstrate that in the APR of EG, in which the CO bond cleavage reactions are more favored than in SR, the Ni catalyst is more efficient than the bimetallic Pt–Ni. However, this Pt–Ni bimetallic catalyst is more active and selective to hydrogen in the SR at 450 °C.The interaction of ethylene glycol with the catalyst surface was studied combining diffuse reflectance infrared spectroscopy with mass spectrometry. Through these studies carried out on the Pt–Ni catalyst, we observed low stability of the formate and carboxylate intermediate species, which would explain its higher activity to produce H2 and CO2 through the water gas shift reaction.

La-promoted Ni-hydrotalcite-derived catalysts for dry reforming of methane at low temperatures

La-promoted Ni-containing hydrotalcite-derived catalysts were prepared and tested in dry methane reforming at low-moderate temperatures. The prepared materials were characterized by means of X-ray diffraction (XRD), temperature programmed reduction (H2-TPR) and CO2-temperature programmed desorption (TPD). The presence of lanthanum was found to enhance the reforming reaction, but also direct methane decomposition at low reaction temperatures. This fact was assigned to an increased presence of Ni0 sites as a consequence of improved reducibility of Ni-species in the La-promoted catalysts. Lanthanum can well contribute to the gasification of amorphous carbon deposits, resulting in lower overall carbon deposition at 550°C.

Low temperature hybrid plasma-catalytic methanation over Ni-Ce-Zr hydrotalcite-derived catalysts

The activity of Ceria and Zirconia-promoted Ni-containing hydrotalcite-derived catalysts was assayed in a hybrid plasma-catalytic process for the hydrogenation of carbon dioxide into methane at low temperatures and in the presence of a cold dielectric barrier discharge (DBD) plasma. High methane yields, around 80%, were measured under hybrid plasma-catalytic conditions, even at very low temperatures (110°C, adiabatic conditions). In the absence of plasma, acceptably high CO2 conversions and methane yields were only observed at temperatures higher than 330°C. The presence of completely reduced Ni-crystallites of intermediate size, more readily available on the non-promoted catalysts was found to enhance the methanation reaction. Ce and Zr addition did not result in a noticeable improvement of the catalytic activity.

Low temperature dry methane reforming over Ce, Zr and CeZr promoted Ni–Mg–Al hydrotalcite-derived catalysts

Hydrotalcite derived catalysts promoted with Ce, Zr and CeZr showed considerable activity in dry methane reforming (DMR) at low temperatures (550 °C). Direct methane decomposition resulting in the extensive formation of fishbone-type carbon nanofibers was substantially inhibited in the presence of Zr. Physicochemical characterization by means of N2 adsorption, XRD, TPR and CO2-TPD evidenced narrower porosity and higher surface areas for the Zr-containing catalysts, together with the presence of smaller Ni particles (around 4 nm) and CO2 preferential adsorption in weak basic sites. Such small Ni particles are inactive towards the direct methane decomposition reaction. The ability of the Zr-containing catalysts to adsorb CO2 on weak basic sites results in the formation of active carbonate species that are able to react with methane through the DMR route. The reverse Boudouard reaction occurs simultaneously to a certain extent in the presence of Zr-promoted catalyst, since carbon nanotube formations were visible on the catalyst surface upon its utilization.

Catalytic performance of Pd-promoted Cu hydrotalcite-derived catalysts in partial hydrogenation of acetylene: effect of Pd–Cu alloy formation

A highly dispersed PdCu nanoalloy catalyst derived from a CuMgAl-hydrotalcite precursor exhibited superior catalytic performance in partial hydrogenation of acetylene.

Methane dry reforming over hydrotalcite-derived Ni–Mg–Al mixed oxides: the influence of Ni content on catalytic activity, selectivity and stability

Ni-containing hydrotalcite-derived catalysts were prepared using different Ni loadings (from ca. 4 to 60 wt%) at the same MII/MIII ratio equal to 3.

Stable Rh particles in hydrotalcite-derived catalysts coated on FeCrAlloy foams by electrosynthesis

Rh-based structured catalysts for the Catalytic Partial Oxidation of CH4 to syngas were prepared by electrosynthesis of Rh/Mg/Al hydrotalcite-type compounds on FeCrAlloy foams and calcination. The effects of Rh content, total metal concentration, and partial replacement of Mg2+ by Ni2+ in the electrolytic solution on coating thickness, Rh speciation, metallic particle size, and catalytic activity were investigated by SEM/EDS, μ-XRF/XANES and tests under diluted and concentrated reaction conditions.The amount of Rh species, present as Mg (RhxAl1−x)2O4, depended on the thickness of the electrosynthesised layer as well as the Rh particle size and dispersion. Smaller and more dispersed particles were obtained by decreasing the Rh concentration in the electrolytic solution from Rh/Mg/Al=11/70/19 to 5/70/25 and 2/70/28 atomic ratio% (a.r.%) and in thinner rather than thicker layers. Despite the improvement in metallic particles features, the CH4 conversion was negatively affected by the low amount of active sites in the coating, the high metal support interaction and possibly the oxidation of metallic particles and carbon formation.A larger amount of solid containing well dispersed Rh particles was deposited by increasing the total metal concentration from 0.03M to 0.06M with the Rh/Mg/Al=5/70/25 a.r.%, and the catalytic performances were enhanced. The partial replacement of Mg2+ by Ni2+ gave rise to a very active bimetallic Rh/Ni catalyst, CH4 conversion and selectivity to syngas were above 90%, however, it slightly deactivated with time-on-stream.

Carbon monoxide oxidation using Zn–Cu–Ti hydrotalcite-derived catalysts

Multioxide catalysts of zinc, copper and titanium with different ratios obtained from layered double hydroxide (LDH) precursors were used in the oxidation of carbon monoxide. The catalysts were characterized by energy-dispersive X-ray spectrometry, X-ray diffraction, thermal analyses (TG, DTG and DTA) and scanning electron microscopy. X-ray diffraction showed different phases of double hydroxide structures. On increasing the percentage of zinc, hydrotalcite structure became the main phase in these samples. SEM images confirmed the presence of layered double hydroxide as plate-like structure. Experimental results indicated a sharp increase in the catalytic activities of the calcined samples towards the oxidation of carbon monoxide at temperatures in the range of 225–275∘C. High conversion of carbon monoxide (90 ∼ 95%) was achieved at reaction temperature of 275∘C by samples having ZnTiO3 as a main phase. These results suggested that hydrotalcite structure of Zn-Ti has a positive catalytic effect towards carbon monoxide oxidation. Multioxides catalysts of zinc, copper and titanium with different ratios obtained from layered double hydroxide (LDH) precursors were used in the oxidation of carbon monoxide. The experimental results indicated a sharp increase in the catalytic activities of the calcined samples towards the oxidation of carbon monoxide at the temperatures 225–275°C.

Clofibric acid degradation by catalytic ozonation using hydrotalcite-derived catalysts

The degradation of an aqueous solution of clofibric acid was investigated during catalytic ozonation. Mg/Al hydrotalcite (HT) catalysts containing Fe, Cu, and Ni, and spinel-type materials CuAl2O4 and CuMgAl2O4 were prepared by co-precipitation method, calcined and used for the ozonation reaction of clofibric acid. The combination of ozone and HT catalysts was effective for the removal of total organic carbon (TOC). MgCuAl HT and CuMgAl2O4 showed the highest activity, followed by MgFeAl and MgNiAl. The best result of clofibric acid mineralization concerning activity and stability was observed over Mg3Fe0.5Al1 HT catalyst calcined at 900°C with no leaching of Fe, and Cu0.75Mg0.5Al2O4 catalyst after pretreatment with 2% of oxalic acid calcined at 950°C, with which least leaching of Cu metal was detected. With these materials, up to 70 and 80% of mineralization degree, respectively, was achieved. These materials have shown to be stable after reuse. Also XRD analyses of used catalysts showed similar crystallographic structures than fresh materials. The efficiency of the process is mainly attained by a heterogeneous radical based mechanism, and not significantly affected by initial pH of solution.

Low temperature hydrolysis of carbonyl sulfide using Zn–Al hydrotalcite-derived catalysts

A series of Zn–Al hydrotalcite-like compounds (HTLCs) were synthesized by co-precipitation method. The mixed oxides derived from HTLCs were tested for the catalytic hydrolysis of carbonyl sulfide (COS) at relatively low temperatures of 50°C. These catalysts were characterized by X-ray diffraction (XRD) and Thermogravimetry/Derivative Thermogravimetry Analysis (TG-DTA) and the results can help us to understand the effect of preparation conditions. The results showed that the Zn–Al hydrotalcite-like compounds were efficient precursor in preparing active and stable catalysts for hydrolysis of COS. The catalyst performance was strongly related to the synthesis pH and calcination temperature. The optimum condition was pH of 10, and calcination temperature of 400°C. Although water was indispensable for hydrolysis of COS, the excess water would hinder the adsorption of COS. In general, COS was hydrolyzed to H2S, which is depending on the chemistry of the derived oxides. The end-products of hydrolysis were simple substance S and sulfate. The presence of oxygen will accelerate the formation of the final product.

Cobalt hydrotalcites as catalysts for bioethanol steam reforming. The promoting effect of potassium on catalyst activity and long-term stability

Cobalt hydrotalcite-derived catalysts, doped with potassium, are active materials for the ethanol steam reforming reaction. Potassium addition reduces the acid sites number and strength. It acts as a promoter of the ethanol steam reforming (ESR); ethanol conversion is higher at lower temperature, as the amount of potassium at the surface of the catalyst increases. The catalysts are stable for long-term experiments (300h) under high loads of ethanol and bioethanol (0.036gEtOHmin−1, H2O:CH3CH2OH=4:1 molar). Moreover, they generate a low amount of carbon (0.0067gCgcatalyst−1h−1). The catalysts after reaction contain almost exclusively high spin Co2+ in cobalt oxide (or in (Co,Mg)O); only traces of metallic cobalt are identified by magnetometry, <0.1wt.% Co0, suggesting that oxidized cobalt is an active species in ESR.