Al Mixed Oxide Catalysts Research Articles

Oxidative dehydrogenation of propane using Ni–Mg–Al mixed oxide catalysts from hydrotalcite-type precursors

Oxidative dehydrogenation of propane using Ni–Mg–Al mixed oxide catalysts from hydrotalcite-type precursors

Template-induced mesoporous Ni–Al oxide catalysts with tuned physico–chemical properties for the oxidative dehydrogenation of ethane

Oxidative dehydrogenation of ethane is a potential industrial process to produce ethylene. In this work, the template-induced mesoporous Ni–Al mixed oxide catalysts synthesized by the template-assisted self-assembly method were investigated for the oxidative dehydrogenation of ethane to ethylene using O2 as an oxidant. The template-induced structure evolution is an effective means to modulate physico-chemical properties of the Ni–Al mixed oxide, thus, it further improves the catalytic performance. All the mesoporous Ni–Al–template catalysts present higher C2H6 conversions and C2H4 selectivities than bulk NiO and non-porous Ni–Al–O catalysts in the temperature range of 350–500 °C. Meanwhile, up to 49.6% C2H6 conversion and 75.3% C2H4 selectivity (37.3% of C2H4 yield) can be obtained over Ni–Al–F127 catalyst at 500 °C. And the mesoporous Ni–Al–F127 catalyst exhibits a superior stability after a long run. The structure–performance correlation indicates that the remarkable catalytic performance is ascribed to the synthesis driven structural effect. The strong interaction between Ni and Al cations caused by the addition of template promotes the formation of small NiO particles and the better dispersion of NiO, which decreases the content of non-selective oxygen species and increases the availability of lattice oxygen.

Amination of methanol for selective production of acetonitrile over Zn-Al mixed oxide catalysts synthesized at different pH

Zn–Al mixed oxides with different acidic and basic natures were synthesized under different pH (8.0–9.5) conditions and applied to the amination of methanol (MeOH). The physical and chemical properties of the samples were characterized using X-ray diffraction (XRD), N2 sorption, and X-ray photoelectron spectroscopy (XPS), as well as temperature-programmed desorption (TPD) with different probe molecules, such as NH3, CO2, iso-propanol (IPA), and MeOH. The conversion of MeOH and selectivity to acetonitrile (ACN) increased as the pH of the synthetic mixture increased to 9.5. The activity of the catalysts was in good accordance with the desorption temperatures of propylene in IPA-TPD and dimethyl ether in MeOH-TPD, while their selectivity to ACN was well correlated with the proportion of the weak base sites on the surface of the catalyst. Particularly, the changes in the acidity and basicity of the catalysts with the synthesis pH were mainly influenced by the degree of disorder of the ZnAl2O4 spinel structure. During the amination of MeOH, the catalytic activity, product selectivity, and deactivation behavior of the catalysts were affected by the reaction parameters. The Zn–Al mixed oxide catalyst was readily regenerated by via simple calcination, which removed the carbonitride and coke that were formed during the reaction.

Novel Cs -Mg- Al Mixed Oxide Catalysts with Superior Storage Capacity for Lean Nox Trap at Low Temperature

Novel Cs -Mg- Al Mixed Oxide Catalysts with Superior Storage Capacity for Lean Nox Trap at Low Temperature

Biodiesel production from wild olive oil using TPA decorated Cr–Al acid heterogeneous catalyst

In the present work, wild olive (Olea oleaster) plant oil was chosen as a hopeful feedstock for efficient biodiesel production. Mixed oxides of aluminium and chromium were modified with different amounts (10−40 wt.%) of 12-tungstophosphonic acid (TPA), used for biodiesel production from low cost local wild olive oil (WOO). Moreover, the physicochemical characteristics of the synthesized catalysts were elaborated with different analytical techniques such as XRD, SEM, EDX, BET. The biodiesel reaction was carried out in a single step via trans-esterification reaction using TPA impregnated Cr–Al mixed oxide catalyst. The maximum 93% biodiesel yield was obtained under the optimized conditions: oil/methanol molar ratio 1:21, reaction temperature 80 °C, catalyst dosage 4 wt% and reaction times 5 hrs with stirring speed of 600 rpm. Interestingly, the reusability experiments showed that the synthesized catalyst sustained remarkable stability and reusability up to 5 runs in the biodiesel production from wild olive oil. Furthermore, the synthesized biodiesel completely complied with international standards.

Oxygen effect in NO direct decomposition over K/Co-Mg-Mn-Al mixed oxide catalyst–Temperature programmed desorption study

• The role of oxygen in NO decomposition was studied over Co-Mg-Mn-Al mixed oxide. • Transition metals in octahedral coordination represent sites for NO chemisorption. • Potassium ensures NO oxidation to surface nitrite intermediates. • Oxygen inhibition was ascribed to formation of stable surface nitrate species. Co-Mg-Mn-Al mixed oxide with or without K was prepared and characterized by XPS, TPR H 2 , TPD NO, TPD O 2 and TPD NO+O 2 . NO decomposition was performed over catalyst activated in different atmosphere (N 2 , He, O 2 ). Presence of oxygen during activation changed the course of surface stabilization but did not affect NO conversion achieved at steady state. O 2 desorbed as a reaction product does not affect the reaction rate for NO inlet concentration of 400 - 8000 ppm, but presence of O 2 in inlet gas mixture (0.05 - 3 mol.%) has significant inhibiting effect. Transition metals in octahedral coordination represent sites for NO chemisorption, while potassium ensures NO oxidation to surface nitrites, which are indispensable reactive species. Oxygen desorption was the slowest reaction step, while N 2 desorption was fast. Oxygen inhibition was ascribed to oxidation of NO* species on the octahedral Co 3+ and Mn 3+ to more stable surface nitrates making NO* species as limiting reactant.

Oxidative Dehydrogenation of Propane over Ni–Al Mixed Oxides: Effect of the Preparation Methods on the Activity of Surface Ni(II) Species

4Ni–Al layered double hydroxide (LDH) precursors were prepared by the following three methods: constant pH coprecipitation, variable pH coprecipitation and urea hydrolysis. The 4Ni–Al mixed metal oxide (MMO) catalysts were obtained by the calcination of LDH precursors at 600 °C, and their catalytic performances in ODHP from 350 to 550 °C were tested. The 4Ni–Al MMO from the urea hydrolysis method showed a higher and more stable propylene selectivity of ca. 40% with propylene yield of ca.11% at 500 °C, and that from the constant pH coprecipitation method was followed, while oxidative cracking of propane occurred on the 4Ni–Al MMO from the variable pH coprecipitation method. It is considered to be closely related to the dispersion and stability of the surface Ni(II) species through comprehensive analysis of XRD, N2-adsorption-desorption, TEM, XPS, H2-TPR and In-situ electrical conductivity. The urea hydrolysis method with a low salt concentration, leading to an excellent stability of the surface Ni(II) species at high reaction temperature, should be selected to prepare Ni–Al MMO catalysts for ODHP instead of the traditional variable pH coprecipitation method with a high salt concentration.

Dehydrogenation of methylcyclohexane over Pt supported on Mg–Al mixed oxides catalyst: The effect of promoter Ir

To enhance the hydrogen release during hydrogen storage, several Pt–Ir supported on Mg–Al mixed oxide catalysts were prepared and then applied into the dehydrogenation of methylcyclohexane (MCH) in this study. The effects of iridium content, reduction temperature on the activity and stability of the catalysts were studied in detail. In the presence of Ir, metal particle size was decreased and electron transfer between Ir and Pt was observed. High reduction temperature increased the metallic Ir content but enlarged the particle size of active sites. During the dehydrogenation reaction on Pt–Ir bimetallic catalyst, MCH was efficiently converted into toluene and PtIr-5/Mg–Al-275 exhibited the highest activity. After prolonging the residence time and raising the reaction temperature to 350 °C, the conversion and hydrogen evolution rate were increased to 99.9% and 578.7 mmol·(g Pt) −1 ·min −1 , respectively. Moreover, no carbon deposition was observed in the spent catalyst, presenting a high anti-coking ability and good potential for industrial application. Hydrogen evolution rate reached up to 578.7 mmol·g Pt −1 ·min −1 in the dehydrogenation of methylcyclohexane on Pt–Ir supported on Mg–Al mixed oxide catalyst and no carbon deposition on the catalyst surface was observed after dehydrogenation reaction.

Influence of surface Lewis acid sites for the selective hydrogenation of levulinic acid to γ-valerolactone over Ni–Cu–Al mixed oxide catalyst

Al2O3 interacted Cu–Ni bimetallic catalysts derived from incorporation of Cu into Ni–Al hydrotalcite were found to be efficient in the selective transformation of levulinic acid (LA) to γ-valerolactone (GVL). The promotional effect of Cu on Ni hydrogenation activity was explained due to an increased ease of NiO reduction and also enhanced surface Lewis acid sites measured by DRIFT spectroscopy. An optimum composition of Ni–Cu–Al catalyst with a mole ratio of 44:22:33 (NCA-423) exhibited a higher Ni metal surface area which demonstrated superior performance in the hydrogenation of LA to GVL with a productivity of 1.68 kgGVL kg cat −1 h−1. The physicochemical properties of Ni–Cu–Al catalysts were rationalized by XRD, H2-TPR, XPS, EPR, BET surface area, H2 chemisorption and pyridine adsorbed IR spectroscopy.

Deactivation of Cu–Mg–Al mixed oxide catalysts for liquid transportation fuel synthesis from biomass-derived resources

A “platform molecule” (2-hexanol) obtained from the primary conversion of sugars was upgraded to liquid transportation fuel precursors under gas phase conditions at 573 K and 101.3 kPa. Reaction was promoted by Cu-Mg-Al mixed oxides with different copper loading (0.3–61.2%) and a Mg/Al = 1.5 (molar ratio). Products were mainly low oxygen content C9-C24 oxygenates and hydrocarbons. The product pool average molecular weight and the oxygenates/hydrocarbons ratio increase with the catalyst copper loading, but the latter might be diminished by augmenting the contact time. A slow catalyst deactivation process occurs in the first 2 h of reaction. Temperature-programmed oxidation, BET surface are measurements and X-ray photoelectron and Auger electron spectroscopies of the spent catalysts indicated that the main reasons for the activity decay during reaction are carbon deposition on the active sites and, to a lesser degree, partial oxidation of the surface copper particles. Oxygenates (reactant or products) are the chemical species responsible for deactivation. The initial deactivation rate (rd0) depends on the copper content and contact time. On catalysts with low Cu content, rd0 is higher at short contact times, which is consistent with coke formed directly from the reactant. Contrarily, at high Cu loadings rd0 increases with contact time and parallels formation of heavy unsaturated oxygenates. Oxidation/reduction/catalytic test cycles of spent Cu-Mg-Al mixed oxides were implemented to explore catalyst reusability.

Upgrading of glycerol from biodiesel synthesis with dimethyl carbonate on reusable Sr–Al mixed oxide catalysts

The high demand for renewable energy has led to the upsurge of methanol-assisted biodiesel synthesis. Therefore, glycerol as a byproduct entered the waste stream given the oversupply of biodiesel to the market. The dimethyl carbonate (DMC)-assisted transesterification of glycerol on a catalyst has been a popular approach for converting glycerol into valuable glycerol carbonate (GLC). The synthesis of GLC from the DMC-assisted transesterification of glycerol on mixed oxide catalysts (Srx–Al) with different Sr/Al ratios was examined in this study. A glycerol conversion of 99.4% and a GLC yield of 100% were achieved in a catalyst with Sr/Al=0.5 (Sr0.5–Al). Both values are higher than those in catalysts synthesized with Sr/Al=0.25 and 0.75. The Sr0.5–Al catalyst withstood five transesterification reaction cycles without a serious deactivation induced by the leaching of active SrO. Therefore, the Sr0.5–Al catalyst is suitable for consecutive uses in the DMC-assisted transesterification of glycerol with DMC into GLC.

Design of a technical Mg–Al mixed oxide catalyst for the continuous manufacture of glycerol carbonate

A Mg–Al oxide obtained by thermal activation of a hydrotalcite and extruded with bentonite enables the continuous manufacture of glycerol carbonate from glycerol and urea owing to its strong Lewis basicity and resistance to leaching.

K-Doped Co–Mn–Al Mixed Oxide Catalyst for N2O Abatement from Nitric Acid Plant Waste Gases: Pilot Plant Studies

The K-doped Co–Mn–Al mixed oxide deN2O catalyst was prepared by calcination of Co–Mn–Al layered double hydroxide, subsequent impregnation with KNO3, and shaping into tablets of 5 mm × 5 mm. Tablets were tested for N2O decomposition in pilot scale reactor connected at the bypassed tail gas from the nitric production plant downstream of the SCR NOx/NH3 catalyst with the aim to perform kinetic measurements. Special attention was paid to study the changes in the catalytic performance, which was monitored using both the long-term catalytic test and the comparison of physical–chemical properties of the fresh and used catalyst. The changes in the surface composition, caused by the time-on-stream operation for 112 days in the pilot reactor, provided stable catalytic performance; average value of N2O conversion of 90 ± 6% at 450 °C was kept (GHSV = 11 000 m3 mbed–3 h–1). The obtained kinetic data were applied in modeling of a full-scale reactor for the N2O emissions abatement and can be used for estimation of the ...

La-modified mesoporous Mg–Al mixed oxides: effective and stable base catalysts for the synthesis of dimethyl carbonate from methyl carbamate and methanol

The incorporation of a suitable amount of La into Mg–Al mixed oxide catalysts was beneficial for the production of dimethyl carbonate.

Cu–Al mixed oxide catalysts for azide–alkyne 1,3-cycloaddition in ethanol–water

Cu(Al)O mixed oxide promotes the formation of 1,2,3-triazoles from an alkyne–azide cycloaddition reaction with excellent yields using an EtOH–H2O mixture as the solvent under microwave heating.

Hierarchical flower-like Co–Cu mixed metal oxide microspheres as highly efficient catalysts for selective oxidation of ethylbenzene

The selective oxidation of alkanes and alkylaromatics to corresponding alcohols, ketones or carboxylic acids is of great importance for the production of high added-value raw materials in the fine chemical industry. The design and synthesis of cost-effective and recyclable heterogeneous oxidation catalysts has become one of the most active research areas. In this work, a series of novel Al2O3@Co–Cu–Al mixed metal oxide (Al2O3@CoCuAl-MMO) catalysts with hierarchical flower-like microstructure were successfully prepared via a Co–Cu–Al layered double hydroxide precursor route, and their catalytic performance was investigated in the liquid-phase selective oxidation of ethylbenzene using tert-butyl hydroperoxide as oxidant without the addition of any organic solvents. The characterization results revealed that the incorporation of copper into the MMO could induce the formation of the interactions between the Co–Cu species, and thus catalytic performance of as-formed Al2O3@CoCuAl-MMO catalysts was significantly promoted. In the selective oxidation of ethylbenzene, a high conversion of 92.8% with an acetophenone selectivity of 89.4% was achieved over the Al2O3@CoCuAl-MMO catalyst with a Cu/(Cu+Co) molar ratio of 0.25. The high catalytic efficiency was attributed mainly to the synergistic effect between highly dispersed active Co and Cu species. More importantly, the obtained catalysts having good recyclability and stability displayed good catalytic performance in the oxidation of other alkanes and alkylaromatics including 1,2,3,4-tetrahydronaphthalene, toluene, cumene, and methylcyclohexane.

Role of Cu–Mg–Al Mixed Oxide Catalysts in Lignin Depolymerization in Supercritical Ethanol

We investigated the role of Cu–Mg–Al mixed oxides in depolymerization of soda lignin in supercritical ethanol. A series of mixed oxides with varying Cu content and (Cu+Mg)/Al ratio were prepared. The optimum catalyst containing 20 wt % Cu and having a (Cu+Mg)/Al ratio of 4 yielded 36 wt % monomers without formation of char after reaction at 340 °C for 4 h. Comparison with Cu/MgO and Cu/γ-Al2O3 catalysts emphasized the excellent performance of Cu–Mg–Al oxides. These mixed oxides catalyze the reaction between formaldehyde and ethanol, which limits polymerization reactions between phenolic products and formaldehyde. The combination of Cu and basic sites catalyzes the associated Guerbet and esterification reactions. These reactions also protect lignin side-chains (e.g., aldehyde groups). Lewis acid sites of the catalyst, mainly Cu and Al cations, catalyze C- and O-alkylation reactions that protect phenolic products and phenolic moieties in lignin oligomers. Hydrogen produced by dehydrogenation reactions is in...

Supported Co–Mn–Al mixed oxides as catalysts for N2O decomposition

The Co–Mn–Al mixed oxide catalysts on different supports (TiO 2 , SBA-15, Al 2 O 3 , SiO 2 , MMT, steel slag, granular blast furnace slag) were prepared by pore filling impregnation, characterized by AAS, XRD, SEM–EDAX, TPR-H 2 and N 2 physisorption and tested for N 2 O catalytic decomposition in kinetic regime in an inert gas and in the presence of O 2 , H 2 O and NO. The catalytic properties were compared on the basis of specific activities ( mol N 2 O /g ( Co+Mn ) /s ). The highest specific activities were observed over the Co–Mn–Al mixed oxide supported on SBA-15 and TiO 2 and the lowest on slags; the same trend was maintained in the presence of H 2 O, O 2 and NO. The dependence of the specific activity on the catalyst reduction characteristics (amount of reducible species and easiness of reduction) was observed, which means that the tested supports affected the properties of the active components. Based on the values of the specific activities, the following order of the N 2 O catalytic decomposition activity was found: Co–Mn–Al/SBA-15 ≈ Co–Mn–Al/TiO 2 ≥ Co–Mn–Al/MMT ≈ Co–Mn–Al/SiO 2 > Co–Mn–Al/Al 2 O 3 ≈ Co–Mn–Al/S1 ≈ Co–Mn–Al/S2.

Co–Mn–Al mixed oxides as catalysts for ammonia oxidation to N2O

Mixed oxide catalysts containing Co, Mn, and Al in a molar ratio of 4:1:1 were prepared by heating precursors obtained by a mechanochemical method (when appropriate nitrates were milled with ammonium hydrogen carbonate) or by coprecipitation. The precursors and related mixed oxides obtained at 500 °C were characterized by XRD, TG/DTA, UV–Vis, IR spectroscopy, TPR and NH3-TPD, and were tested for activity and selectivity in ammonia oxidation to N2O. The precursors prepared by mechanochemical reaction showed very similar phase composition to that of the coprecipitated product. All examined mixed oxide catalysts were active in the low temperature range (100 % conversion of NH3 was achieved at 250 °C), but the selectivity was sensitive to catalyst composition and the method used for preparation of the precursors. Non-modified Co–Mn–Al mixed oxide catalyst obtained from the coprecipitated precursor exhibited higher selectivity towards N2O formation than the calcined product prepared by the mechanochemical method. Modification of the latter mixed oxide catalysts with cesium promoter (1 wt%) significantly increased their selectivity to nitrous oxide. The yield of N2O at 250 °C was close to 100 %.

Optimization of Cs content in Co–Mn–Al mixed oxide as catalyst for N2O decomposition

A series of Co–Mn–Al mixed oxide catalysts with different Cs contents (0.5–4.6 wt%) was prepared by calcination of Co–Mn–Al hydrotalcite (Co:Mn:Al = 4:1:1), followed by impregnation by cesium salt (CsNO3, Cs2CO3) using the pore filling method. Chemical analysis, N2 sorption, temperature programmed reduction (TPR)-H2, temperature programmed desorption (TPD)-CO2 and TPD-NH3 and X-ray photoelectron spectroscopy (XPS) were used to characterize the catalysts. All prepared catalysts were tested for N2O catalytic decomposition in inert gas and in the presence of oxygen, water vapor and nitric oxide. The influence of Cs salts used for catalyst preparation and cesium content on catalyst activity were studied. A significant increase in catalytic activity with increasing amount of cesium promoter was observed without respect to the Cs precursor. The strong promotional effect of cesium is electronic in nature and is discussed in term of changes in surface composition and catalyst reducibility.