Water‐Promoted Kinetic Separation of trans‐ and cis‐Limonene Oxides

The efficient hydrolytic kinetic separation of trans/cis‐(R)‐(+)‐limonene oxides was realized in a 1:1 mixed solvent of water and 1,4‐dioxane without additional catalyst. Optically pure trans‐(R)‐(+)‐limonene oxide was recovered in high yield (77%).     

Highly Active Aluminium Catalysts for the Formation of Organic Carbonates from CO2 and Oxiranes

Al^III complexes of amino‐tris(phenolate) ligand scaffolds have been prepared to attain highly Lewis acidic catalysts. Combination of the aforementioned systems with ammonium halides provides highly active catalysts for the synthesis of organic carbonates through addition of carbon dioxide to oxiranes with initial turnover frequencies among the highest reported to date within the context of cyclic carbonate formation. Density functional theory (DFT) studies combined with kinetic data provides a rational for the relative high activity found for these Al^III complexes, and the data are consistent with a monometallic mechanism. The activity and versatility of these Al^III complexes has also been evaluated against some state‐of‐the‐art catalysts and the combined results compare favorably in terms of catalyst construction, stability, activity, and applicability.     

Sign Reversal of a Large Circularly Polarized Luminescence Signal by the Twisting Motion of a Bidentate Ligand

This work demonstrates sign reversal of large circularly polarized luminescence (CPL) signal based on the hinge‐like twisting motion of a bidentate ligand, 3,3‐bis(diphenylphosphoryl)‐2,2‐bipyridine (BIPYPO), in a cis–trans isomerization of chiral europium(III) complexes. X‐ray diffraction analysis revealed that twisting motion of BIPYPO provides s‐cis and s‐trans geometries of a chiral Eu^III complex containing either tris[3‐(trifluoromethylhydroxymethylene)‐(+)‐camphorate] (D ‐ 1 ) or tris[3‐(heptafluoropropylhydroxymethylene)‐(+)‐camphorate] (D ‐ 2 ). The s‐cis Eu^III complexes show eight‐coordinate geometry around the Eu^III ion, in which the chelate between the phosphoryl oxygen and the Eu^III ion forces the s‐cis geometry of BIPYPO. In contrast, the phosphorus–nitrogen interaction provides a conformational lock for the s‐trans geometry of the BIPYPO ligand, inducing a quasi‐seven‐coordinate Eu^III complex. The difference in coordination geometry causes the sign change of the CPL signals between the s‐cis and s‐trans isomers, whereby the s‐cis and s‐trans isomers of Eu^III complexes exhibit the positive and negative CPL signals, respectively, for the ⁵D₀→⁷F₁ transition. The proportion of the s‐trans‐D ‐ 1 against s‐cis‐D ‐ 1 increases upon changing the solvent from [D₃]acetonitrile to [D₆]acetone, inducing a sign change of the CPL signals. The complexes D ‐ 1 and D ‐ 2 show a biexponential decay with two different lifetimes, suggesting two emitting species, that is, the s‐cis and s‐trans isomers of Eu^III complexes. In both cases, the proportions of the longer lifetime components (τ₁) decrease and instead the shorter lifetime components (τ₂) increase upon changing the solvent from [D₃]acetonitrile to [D₆]acetone.     

Influence of Central Metalloligand Geometry on Electronic Communication between Metals: Syntheses,Crystal Structures,MMCT Properties of Isomeric Cyanido‐Bridged Fe2Ru Complexes,and TDDFT Calculations

To investigate how the central metalloligand geometry influences distant or vicinal metal‐to‐metal charge‐transfer (MMCT) properties of polynuclear complexes, cis‐ and trans‐isomeric heterotrimetallic complexes, and their one‐ and two‐electron oxidation products, cis/trans‐ [Cp(dppe)Fe^IINCRu^II(phen)₂CN‐Fe^II(dppe)Cp][PF₆]₂ (cis/trans‐ 1 [PF₆]₂), cis/trans‐[Cp(dppe)Fe^IINCRu^II(phen)₂CNFe^III‐(dppe)Cp][PF₆]₃ (cis/trans‐ 1 [PF₆]₃) and cis/trans‐[Cp(dppe)Fe^IIINCRu^II(phen)₂CN‐Fe^III(dppe)Cp][PF₆]₄ (cis/trans‐ 1 [PF₆]₄) have been synthesized and characterized. Electrochemical measurements show the presence of electronic interactions between the two external Fe^II atoms of the cis‐ and trans‐isomeric complexes cis/trans‐ 1 [PF₆]₂. The electronic properties of all these complexes were studied and compared by spectroscopic techniques and TDDFT//DFT calculations. As expected, both mixed valence complexes cis/trans‐ 1 [PF₆]₃ exhibited different strong absorption signals in the NIR region, which should mainly be attributed to a transition from an MO that is delocalized over the Ru^II‐CN‐Fe^II subunit to a Fe^III d orbital with some contributions from the co‐ligands. Moreover, the NIR transition energy in trans‐ 1 [PF₆]₃ is lower than that in cis‐ 1 [PF₆]₃, which is related to the symmetry of their molecular orbitals on the basis of the molecular orbital analysis. Also, the electronic spectra of the two‐electron oxidized complexes show that trans‐ 1 [PF₆]₄ possesses lower vicinal Ru^II→Fe^III MMCT transition energy than cis‐ 1 [PF₆]₄. Moreover, the assignment of MMCT transition of the oxidized products and the differences of the electronic properties between the cis and trans complexes can be well rationalized using TDDFT//DFT calculations.     

Preparation and Characterization of Dinuclear Chromium(III) Complexes of a Hexadentate Tetraaza‐Dithiophenolate Ligand

The ability of the tetraaza‐dithiophenolate ligand H₂L² (H₂L² = N,N′‐Bis‐[2‐thio‐3‐aminomethyl‐5‐tert‐butyl‐benzyl]propane‐1,3‐diamine) to form dinuclear chromium(III) complexes has been examined. Reaction of Cr^IICl₂ with H₂L² in methanol in the presence of base followed by air‐oxidation afforded cis,cis‐[(L²)Cr^III₂(μ‐OH)(Cl)₂]⁺ ( 1a ) and trans,trans‐[(L²)Cr^III₂(μ‐OH)(Cl)₂]⁺ ( 1b ). Both compounds contain a confacial bioctahedral N₂ClCr^III(μ‐SR)₂(μ‐OH)Cr^IIIClN₂ core. The isomers differ in the mutual orientation of the coligands and the conformation of the supporting ligand. In 1a both Cl^? ligands are cis to the bridging OH function. In 1b they are in trans‐positions. Reaction of the hydroxo‐bridged complexes with HCl yielded the chloro‐bridged cations cis,cis‐[(L²)Cr^III₂(μ‐Cl)(Cl)₂]⁺ ( 2a ) and trans,trans‐[(L²)Cr^III₂(μ‐Cl)(Cl)₂]Cl ( 2b ), respectively. These bridge substitutions proceed with retention of the structures of the parent complexes 1a and 1b .     

Monomer sequencing and microstructural analysis on polymers of dimethyl norbornene dicarboxylate and 7‐oxanorbornene dicarboxylic derivatives employing ruthenium catalysts by ring‐opening metathesis polymerization

The physiochemical properties, comonomer sequencing, and regiospecificity of the linkages between monomeric units within homo/copolymers based on 5,6‐di‐substituted norbornene and 7‐oxanorbornene type monomers by ring‐opening metathesis polymerization are reported and correlated to their primary and secondary structural elements. In general, first‐generation Grubbs‐ I1 ruthenium catalyst generates polymers with high trans content that exhibits an extended secondary structure with exo,exo substituents, whereas second‐generation Grubbs‐ I2 catalyst produces polymers with high cis content that forms tight turns, resulting in a compact structure. Furthermore, I2 ‐produced polymers exhibit a high level of alternating cis–trans double bonds along their polymeric backbone. In stark contrast, both first‐ and second‐generation Grubbs catalysts display complete reversal in cis/trans selectivity when an oxygen atom is in position‐7 of the norbornene‐ring along with mono‐endo‐substitution in position‐5 or 6, and hence highlighting the importance of stereoelectronic complexation by the catalyst with the next incoming monomer for cis/trans selectivity. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2477–2501     

Synthesis and characterization of polymers of 1,4-hexadienes

The homopolymerization of trans-1,4-hexadiene, cis-1,4-hexadiene, and 5-methyl-1,4-hexadiene was investigated with a variety of catalysts. During polymerization, 1,4-hexadienes undergo concurrent isomerization reactions. The nature and extent of isomerization products are influenced by the monomer structure and polymerization conditions. Nuclear magnetic resonance (NMR) and infrared (IR) data show that poly(trans-1,4-hexadiene) and poly(cis-1,4-hexadiene) prepared with a Et₃Al/α-TiCl₃/hexamethylphosphoric triamide catalyst system consist mainly of 1,2-polymerization units arranged in a regular head-to-tail sequence. A 300-MHz proton NMR spectrum shows that the trans-hexadiene polymer is isotactic; it also may be the case for the cis-hexadiene polymer. These polymers are the first examples of uncrosslinked ozone-resistant rubbers containing pendant unsaturation on alternating carbon atoms of the saturated carbon-carbon backbone. Polymerization of the 1,4-hexadienes was also studied with VOCl₃- and β-TiCl₃-based catalysts. Microstructures of the resulting polymers are quite complicated due to significant loss of unsaturation, in contrast to those obtained with the α-TiCl₃-based catalyst. In agreement with the literature, there was no discernible monomer isomerization with the VOCl₃ catalyst system.     

Catalysis for One‐step Synthesis of Dimethyl Ether from Hydrogenation of CO

In this paper, a new catalyst system Cu‐Mn‐(M)/γ‐Al₂O₃ was developed for the directly synthesis dimethyl ether (DME) from synthesis gas in a fixed‐bed reactor. The catalysts with different n (Cu) : n (Mn) ratios, several promoter M (M is one of Zn, Cr, W, Mo, Fe, Co or Ni) were prepared and tested. The results showed the catalysts have a high conversion of CO and a high DME selectivity. The DME yield in tail gas reached 46.0% (at 63.27% conversion of CO) at 2.0 MPa, 275°C, 1500 h^?1 with the Cu₂Mn₄Zn/γ‐Al₂O₃ catalyst.     

Characterization and Activity of Cu‐MnOx/γ‐Al2O3 Catalyst for Hydrogenation of Carbon Dioxide

The effect of manganese on the dispersion, reduction behavior and active states of surface of supported copper oxide catalysts have been investigated by XRD, temperature‐programmed reduction and XPS. The activity of methanol synthesis from CO₂/H₂ was also investigated. The catalytic activity over CuO‐MnO_x/γ‐Al₂O₃ catalyst for CO₂ hydrogenation is higher than that of CuO/γ‐Al₂O₃. The adding of manganese is beneficial in enhancing the dispersion of the supported copper oxide and make the TPR peak of the CuO‐MnK_x/γ‐Al₂O₃ catalyst different from the individual supported copper and manganese oxide catalysts, which indicates that there exists strong interaction between the copper and manganese oxide. For the CuO/γ‐Al₂O₃ catalyst there are two reducible copper oxide species; α and β peaks are attributed to the reduction of highly dispersed copper oxide species and bulk CuO species, respectively. For the CuO‐MnO_x/γ‐Al₂O₃ catalyst, four reduction peaks are observed, α peak is attributed to the dispersed copper oxide species; β peak is ascribed to the bulk CuO; γ peak is attributed to the reduction of high dispersed CuO interacting with manganese; δ peak may be the reduction of the manganese oxide interacting with copper oxide. XPS results show that Cu⁺ mostly existed on the working surface of the Cu‐Mn/γ‐Al₂O₃ catalysts. The activity was promoted by Cu with positive charge which was formed by means of long path exchange function between Cu? O? Mn. These results indicate that there is synergistic interaction between the copper and manganese oxide, which is responsible for the high activity of CO₂ hydrogenation.     

Asymmetric Epoxidation of cis/trans‐β‐Methylstyrene Catalysed by Immobilised Mn(Salen) with Different Linkages: Heterogenisation of Homogeneous Asymmetric Catalysis

Immobilised Mn(salen) catalysts with two different linkages were studied in the asymmetric epoxidation of cis/trans‐β‐methylstyrene using NaClO as oxidant. The immobilised Mn(salen) complexes inside nanopores can lead to different catalytic behaviour compared with that of homogeneous Jacobsen catalyst. The rigidity of the linkage was found to be a key factor affecting the catalytic performance of immobilised catalysts. The immobilised catalyst with a rigid linkage exhibited comparable chemical selectivity, enantioselectivity and cis/trans ratio of product formation to that obtained with homogeneous Jacobsen catalysts. In contrast, the immobilised catalyst with a flexible linkage gave remarkably lower chemical selectivity, enantioselectivity and inverted cis/trans ratio compared with the results obtained with the homogeneous Jacobsen catalyst and the immobilised catalyst with rigid linkage. Thus, for immobilised Mn(salen) catalysts, a rigid linkage connecting active centres to the support is essential to obtain activity and enantioselectivity as high as those obtained in homogeneous systems.     

Asymmetric Hydrogenation of Maleic Acid Diesters and Anhydrides

Asymmetric hydrogenation of maleic and fumaric acid derivatives with iridium catalysts based on N,P ligands provides an efficient route to chiral enantioenriched succinates. A new catalyst derived from a 2,6‐difluorophenyl‐substituted pyridine‐phosphinite ligand was developed and enables the conversion of a wide range of 2‐alkyl and 2‐arylmaleic acid diesters into the corresponding succinates in high enantiomeric purity. Mixtures of cis/trans substrates can be hydrogenated in an enantioconvergent fashion with high enantioselectivity, and further enhances the scope of this transformation. The products are valuable chiral building blocks with a structural motif found in many bioactive compounds, such as metalloproteinase inhibitors.     

Synthesis,characterization and catalytic application of a new organometallic oligomer based on polyhedral oligomeric silsesquioxane

Although homogeneous catalysts provide high performance and selectivity, the difficulty of separation and recycling of these catalysts has bothered the scientific community worldwide. Therefore, the demand for heterogeneous catalysts that possess the advantages of homogeneous ones, with ease of separation and recyclability remains a topic of major impact. The oligomeric catalyst synthesized in this work was characterized using elemental analysis, Fourier transform infrared, ¹³C NMR, ²⁹Si NMR and energy‐dispersive X‐ray spectroscopies, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy and Brunauer–Emmett–Teller analysis and compared to its homogeneous counterpart [W(CO)₃Br₂(ATC)] in the epoxidation of 1‐octene, cyclooctene, (S )‐limonene, cis ‐3‐hexen‐1‐ol, trans ‐3‐hexen‐1‐ol and styrene. The results showed that the percentage conversion for the homogeneous species [W(CO)₃Br₂(ATC)] was slightly higher than for the oligomeric catalyst (POSS‐ATC‐[W(CO)₃Br₂]). Furthermore, the selectivity for epoxide of the oligomeric catalyst was greater than that of the homogeneous catalyst by about 25% when (S )‐limonene was used. Great conversions (yields) of products were obtained with a wide range of substrates and the catalyst was recycled many times without any substantial loss of its catalytic activity.     

Copolymerization of isoprene with ethylene catalyzed by cationic half‐sandwich fluorenyl scandium catalysts

Isoprene polymerization and copolymerization with ethylene can be carried out by using cationic half‐sandwich fluorenyl scandium catalysts in situ generated from half‐sandwich fluorenyl scandium dialkyl complexes Flu'Sc(CH₂SiMe₃)₂(THF)_n, activator, and AlⁱBu₃ under mild conditions. In the isoprene polymerization, all of these cationic half‐sandwich fluorenyl scandium catalysts exhibit high activities (up to 1.89 × 10⁷ g/mol_Sc h) and mainly cis?1,4 selectivities (up to 93%) under similar conditions. In contrast, these catalysts showed different activities and regio‐/stereoselectivities being significantly dependent on the substituents of the fluorenyl ligands in the copolymerization of isoprene with ethylene under an atmosphere of ethylene (1 atm) at room temperature, affording the random copolymers with a wide range of cis?1,4‐isoprene contents (IP content: 64 ? 97%, cis?1,4‐IP units: 65 ? 79%) or almost alternating copolymers containing mainly 3,4‐IP‐alt‐E or/and cis?1,4‐IP‐alt‐E sequences. Moreover, novel high performance polymers have been prepared via selective epoxidation of the vinyl groups of the 1,4‐isoprene units in the IP‐E copolymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2898–2907     

Molecular weight and configurational stability of poly[(fluorophenyl)acetylene]s prepared with metathesis and insertion catalysts

Series of high‐cis and cis/trans poly[(fluorophenyl)acetylene]s (PFPhA) have been prepared by polymerization of (2‐fluorophenyl)acetylene, (3‐fluorophenyl)acetylene, and (4‐fluorophenyl)acetylene with catalysts: [Rh(1,5‐cyclooctadiene) OCH₃]₂ (high‐cis PFPhAs) and tungsten(VI) oxychloride/tetraphenyltin (cis/trans PFPhAs). The molecular weight and configurational stability under various conditions at room temperature were studied for both PFPhAs series by means of size exclusion chromatography, ¹H‐NMR, and UV‐vis techniques. All samples exhibited slow degradation when exposed to the atmosphere in the solid state; the rate of degradation was independent on the F‐position on the Ph ring. The rate of degradation increased up to three orders of magnitude in the tetrahydrofuran solution where it was higher for high‐cis polymers compared with their cis/trans counterparts. The degradation of high‐cis PFPhAs was accompanied by significant cis‐to‐trans isomerization in aerated tetrahydrofuran solution. Rate of degradation and isomerization exhibited the same dependence on the F‐position on the Ph ring. The hypothesis was postulated that the degradation of high‐cis PFPhAs in solution was accelerated by cis‐to‐trans isomerization due to which the content of unpaired electrons on the main chains is enhanced. In both high‐cis and cis/trans series of polymers the ortho‐substituted isomers exhibited an enhanced stability compared with meta‐ and para‐substituted isomers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4296–4309, 2010     

Epoxide polymers: Synthesis,stereochemistry, structure,and mechanism

Epoxide polymerization studies have yielded technically important catalysts and polymers. The polymers were studied by cleaving them with Group IA organometallics to monomer, dimer, and trimer glycol fragments. The identification of these glycol fragments has established that the crystalline polymers from the cis- and trans-2,3-epoxybutanes are respectively racemic and meso-diisotactic and that the amorphous polymer from the cis-oxide is disyndiotactic. These studies also showed that the amorphous fraction from propylene oxide polymerization with coordination catalysts contains substantial head-to-head and tail-to-tail segments. This work has led to a much better understanding of the mechanism of epoxide polymerization. These facts were established: (1) epoxides polymerize with inversion of configuration of the ring-opening carbon atom; (2) monosubstituted epoxides polymerize largely by attack on the primary carbon with a coordination catalyst; and (3) two or more metal atoms must be involved in the coordination polymerization of epoxides.     

High yield synthesis of biodegradable poly(propylene carbonate) from carbon dioxide and propylene oxide

A novel SalenCo^III (2,4‐dinitrophenoxy) (Salen = N,N'‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamino) and 1,10‐phenanthroline monohydrate catalyst system was designed and employed for the copolymerization of CO₂ and propylene oxide (PO). The perfectly alternating copolymerization of CO₂ and PO proceeds effectively under middle temperature and pressure to yield poly(propylene carbonate) with a high yield and a high number average molecular weight of polymer. The structure of polymer was characterized by the IR and NMR measurements. The perfectly alternating copolymer was confirmed. The MALDI‐TOF spectrum insinuates that the copolymerization of CO₂ and PO was initiated by H₂O. Copyright © 2016 John Wiley & Sons, Ltd.     

Alternating copolymerization of carbon dioxide and propylene oxide catalyzed by (R,R)‐SalenCoIII‐ (2,4‐dinitrophenoxy) and Lewis‐basic cocatalyst

A binary catalyst system of a chiral (R,R)‐SalenCo^III(2,4‐dinitrophenoxy) (salen = N,N‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐diphenylethylenediimine) in conjunction with (4‐dimethylamino)pyridine (DMAP) was developed to generate the copolymerization of carbon dioxide (CO₂) and racemic propylene oxide (rac‐PO). The influence of the molar ratio of catalyst components, the operating temperature, and reaction pressure on the yield as well as the molecular weight of polycarbonate were systematically investigated. High yield of turnover frequency (TOF) 501.2 h^?1 and high molecular weight of 70,400 were achieved at an appropriate combination of all variables. The structures of as‐prepared products were characterized by the IR, ¹H NMR, ¹³C NMR measurements. The linear carbonate linkage, highly regionselectivity and almost 100% carbonate content of the resulting polycarbonate were obtained with the help of these effective catalyst systems under facile conditions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5050–5056, 2007     

Neutral Nickel Ethylene Oligo‐ and Polymerization Catalysts: Towards Computational Catalyst Prediction and Design

DFT calculations have been used to elucidate the chain termination mechanisms for neutral nickel ethylene oligo‐ and polymerization catalysts and to rationalize the kind of oligomers and polymers produced by each catalyst. The catalysts studied are the (κ²‐O,O)‐coordinated (1,1,1,5,5,5‐hexafluoro‐2,4‐acetylacetonato)nickel catalyst I , the (κ²‐P,O)‐coordinated SHOP‐type nickel catalyst II , the (κ²‐N,O)‐coordinated anilinotropone and salicylaldiminato nickel catalysts III and IV , respectively, and the (κ²‐P,N)‐coordinated phosphinosulfonamide nickel catalyst V . Numerous termination pathways involving β‐H elimination and β‐H transfer steps have been investigated, and the most probable routes identified. Despite the complexity and multitude of the possible termination pathways, the information most critical to chain termination is contained in only few transition states. In addition, by consideration of the propagation pathway, we have been able to estimate chain lengths and discriminate between oligo‐ and polymerization catalysts. In agreement with experiment, we found the Gibbs free energy difference between the overall barrier for the most facile propagation and termination pathways to be close to 0 kcal mol^?1 for the ethylene oligomerization catalysts I and V , whereas values of at least 7 kcal mol^?1 in favor of propagation were determined for the polymerization catalysts III and IV . Because of the shared intermediates between the termination and branching pathways, we have been able to identify the preferred cis/trans regiochemistry of β‐H elimination and show that a pronounced difference in σ donation of the two bridgehead atoms of the bidentate ligand can suppress hydride formation and thus branching. The degree of rationalization obtained here from a handful of key intermediates and transition states is promising for the use of computational methods in the screening and prediction of new catalysts of the title class.     

Bistability of an iron-cobalt binuclear complex

Bistability of the four cis/trans isomers of the proposed iron-cobalt binuclear complex [(CO)₂(benzoate-)Fe^II/III(-terephthalate-)Co^III/II(-benzoate)(CO)₂]¹⁺, arising from the Fe^II/III ↔ Co^III/II intramolecular charge transfer (IMCT) is investigated computationally at (TD)DFT-B3LYP/LanL2DZ level of theory. Energies, geometries, atomic charges, and the UV-Vis spectra are considered in this investigation. Results approve IMCT bistability of all cis/trans isomers by locating two stable states with distinctly different structures and charge distributions (Fe^II-Co^III and Fe^III-Co^II oxidation states). Also, well-defined first-order saddle points between these two IMCT states are found and characterized using QST2/QST3 method. Based on the analysis of the calculated charge distributions and the 0.35-1.66 eV activation (barrier) energies of the Fe^II-Co^III ↔ Fe^III-Co^II IMCT reactions, it can be predicted that electric field or NIR radiation may be used to switch between the two IMCT states of this bistable binuclear complex. It is also found that the cis/trans isomerization has significant effects on the energetics of this IMCT reaction, and that the trans-Fe^II/III-trans-Co^III/II isomer is the best candidate for prospective switching application due to having the least energy dissipation and the largest charge transfer.     

Carbon Dioxide Reforming of Methane over Ni Catalysts Supported on Al2O3 Modified with La2O3, MgO, and CaO

The preparation of synthesis gas from carbon dioxide reforming of methane (CDR) has attracted increasing attention. The present review mainly focuses on CDR to produce synthesis gas over Ni/MO_x/Al₂O₃ (X = La, Mg, Ca) catalysts. From the examination of various supported nickel catalysts, the promotional effects of La₂O₃, MgO, and CaO have been found. The addition of promoters to Al₂O₃-supported nickel catalysts enhances the catalytic activity as well as stability. The catalytic performance is strongly dependent on the loading amount of promoters. For example, the highest CH₄ and CO₂ conversion were obtained when the ratios of metal M to Al were in the range of 0.04–0.06. In the case of Ni/La₂O₃/Al₂O₃ catalyst, the highest CH₄ conversion (96%) and CO₂ conversion (97%) was achieved with the catalyst (La/Al = 0.05 (atom/atom)). For Ni/CaO/Al₂O₃ catalyst, the catalyst with Ca/Al = 0.04 (atom/atom) exhibited the highest CH₄ conversion (91%) and CO₂ conversion (92%) among the catalysts with various CaO content. Also, Ni/MgO/Al₂O₃ catalyst with Mg/Al = 0.06 (atom/atom) showed the highest CH₄ conversion (89%) and CO₂ conversion (90%) among the catalysts with various Mg/Al ratios. Thus it is most likely that the optimal ratios of M to Al for the highest activities of the catalysts are related to the highly dispersed metal species. In addition, the improved catalytic performance of Al₂O₃-supported nickel catalysts promoted with metal oxides is due to the strong interaction between Ni and metal oxide, the stabilization of metal oxide on Al₂O₃ and the basic property of metal oxide to prevent carbon formation.