Synthesis, Characterization and Catalytic Activity of Supported NiMo Catalysts

A study of NiMo catalysts supported on MCM41 modified with alumina prepared by the sol?Cgel method is presented. Ni?CMo phases were impregnated on the supports using the solution method with the purpose to obtain a material whose hexagonal structure of the MCM41 would not be affected with the addition of these active phases. The impregnation of the metals method used in the present work was outstanding, the textural properties of the catalysts decreased from 42 to 67%. There was a diminution in the textural properties of the catalysts with respect to the supports, nevertheless the prepared materials had more significant textural properties that the conventional catalysts of HDS. The adsorption?Cdesorption isotherms of the catalysts did not change considerably with the support source. By DRX was determined the structural properties of the metallic phases present in the material where phases such as NiMoO₄, MoO₃ and NiO were observed. Support wall thickness was increased with the incorporation of Ni and Mo metals into the materials. By means of Raman spectroscopy, the presence of MoO₃ and Mo₈O₂₆ ^4? species was corroborated. Through UV?Cvis where determined NiO of octahedral symmetry as well as Mo of tetrahedral and octahedral symmetry. The main reaction products were biphenyl (BP), cyclohexylbenzene (CHB) and bicyclohexyl (BCH) when the materials were tested in the HDS of DBT.     

A Comparison of Catalytic Oxidative Dehydrogenation of Ethane Over Mixed V-Mg Oxides and Over Those Prepared via a Mesoporous V-Mg-O Pathway

The catalytic oxidative dehydrogenation of ethane was investigated in a fixed-bed tubular microreactor at 500, 550 and 600 °C and a space velocity of 35 027ml g^-1h^-1. Two kinds of V-Mg oxides catalysts containing various V/Mg atomic ratios were employed. One group of catalysts was prepared by the solid reaction between fine powders of vanadium pentoxide and magnesium nitrate and the other ones were obtained from mesostructured V-Mg-Os. For the former catalysts, it was found that the selectivity to ethene increased and the conversion of ethane passed through a maximum with increasing V/Mg atomic ratio. For the catalysts obtained from the mesoporous materials, an optimum V/Mg atomic ratio was found, for which the conversion of ethane and the selectivity to ethene were maxima. Compared with the mixed-oxide catalysts, those obtained from the mesoporous materials exhibited much higher yields to ethene. Several new phases, such as pyro-Mg₂V₂O₇, ortho-Mg₃(VO₄)₂ and meta-MgV₂O₆, formed between magnesia and vanadia, were identified by XRD in the mixed V-Mg oxide catalysts; they may be responsible for the catalytic activity. In the catalysts prepared from mesoporous V-Mg-O, a V₂O₃ phase, which may contain highly dispersed magnesium, was identified and suggested to be responsible for the higher catalytic performance.     

Role of Pt in the Activity and Stability of PtNi/CeO2–Al2O3 Catalysts in Ethanol Steam Reforming for H2 Production

Hydrogen production from ethanol reforming was investigated on bimetallic PtNi catalysts supported on CeO₂/Al₂O₃. Pt content was varied from 0.5 to 2.5 %. Physico-chemical characterization of the as-prepared and H₂-reduced catalysts by TPR, XRD and XPS showed that Pt phase interacted with the Ni and Ce species present at the surface of the catalysts. This interaction leads to an enhancement of the reducibility of both Ni and Ce species. Loadings of Pt higher than 1.0 wt% improved the activity and stability of the Ni/CeO₂–Al₂O₃ catalyst in ethanol steam reforming, in terms of lower formation of coke, C₂ secondary products and a constant production of CO₂ and H₂. The amount and type of carbon deposited on the catalyst was analyzed by TG–TPO while the changes in crystalline phases after reaction were studied by XRD. It was found that for Pt contents higher than 1 wt% in the catalysts, a better contact between Pt and Ce species is achieved. This Pt–Ce interaction facilitates the dispersion of small particles of Pt and thereby improves the reducibility of both Ce and Ni components at low temperatures. In this type of catalysts, the cooperative effect between Pt⁰, Ni⁰ and reduced Ce phases leads to an improvement in the stability of the catalysts: Ni provides activity in C–C bond breakage, Pt particles enhance the hydrogenation of coke precursors (C_xH_y) formed in the reaction, and Ce increases the availability of oxygen at the surface and thereby further enhances the gasification of carbon precursors.     

Methane Combustion Over Copper Chromites Catalysts Prepared by the Sol–Gel Process

Abstract  

Methane combustion was performed over a series of copper chromites (CuCr₂O₄) catalysts prepared by the sol–gel process (SG). The results were compared with those obtained over commercial CuCr₂O₄. The samples were characterised by elemental analysis, thermal analysis, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The as-synthesised CuCr₂O₄ sample exhibited higher specific surface area (248 m² g⁻¹) with respect to commercial solids (42 m² g⁻¹). The surface properties were established using XPS. Simultaneously, an increase in the atomic Cr⁶⁺/Cr³⁺ ratio (0.56 for SG catalyst vs. 0.39 for commercial sample) and a decreasing surface copper concentration (8.3%, for SG specimen vs. 17.6% for commercial catalyst) are observed. XPS study revealed also that Cu²⁺/(Cu° + Cu⁺) ratio of copper species remained constant (ca. 5) in both catalysts. Structure transformations of CuCr₂O₄ under reduction-reoxidation conditions showed that the reduction of copper and/or chromium cations from the CuCr₂O₄ and from delafossite (CuCrO₂) structure (CuCr₂O₄↔CuCrO₂ + Cu + Cr₂O₃↔Cu + Cr₂O₃) were different. This has lead to a difference in catalytic properties of the catalysts. Catalytic activity of SG catalysts was superior to that of commercial CuCr₂O₄ tested under the same conditions. Complex hysteresis behaviour for CuCr₂O₄ catalysts ramped over a temperature range of 220–850 °C where the stables active phases were obtained only after the first ramp of heating under reactants. No catalysts deactivation was further observed after several cycles of heating and cooling. The stabilisation of catalytic activity was attributed to the formation of mixed crystalline phases containing both copper and chromium species.     

Methane combustion over copper chromite catalysts

A study of the activity and durability of two different copper chromite catalysts in methane combustion is presented. The catalysts, a massive (CAT-E) and a supported (CAT-I) copper chromite, were characterized by different techniques in order to investigate morphological properties (N₂ adsorption), crystalline structure (X-ray diffraction, XRD) and surface composition (X-ray photoelectron spectroscopy, XPS). Among the different crystalline phases identified, CuCr₂O₄ spinel represented the common phase in both the catalysts. The Cr^VI/Cr^III surface ratio was almost the same for the two catalysts, while the Cu^II/Cu^I surface ratio was much higher on the massive catalyst than on the supported one. The activity for CH₄ combustion was studied in the temperature range 300-700°C at constant CH₄:air ratio of 1:30 and constant methane content, 1.2%. The activity was higher for CAT-I and CAT-E showed better stability. A kinetic study from the catalytic data, collected at different contact times in the interval 0.047-0.315 s as a function of temperature, provided a value of about 110 kJ/mol for the activation energy. This value was obtained for various degrees of methane converted for the two catalysts. The reaction rates were between 10^-3 and 10^-4 (mol_CH4)_conv/(g h) in the temperature interval 550-700°C, for both the catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ammoxidation of 3-picoline to nicotinonitrile over vanadium phosphorus oxide-based catalysts

Ammoxidation of 3-picoline to nicotinonitrile was investigated on vanadium phosphorus oxide (VPO), VPO/SiO₂ and additive atom (Cu, Zr, Mn and Co) incorporated VPO catalysts under atmospheric pressure and at 673 K. For the purpose of comparison a conventional V₂O₅–MoO₃/Al₂O₃ catalyst was also studied under identical conditions. These catalysts were characterized by means of X-ray diffraction, electron spin resonance, infrared, ammonia chemisorption and BET surface area methods. The VPO-based catalysts show better performance than the V₂O₅–MoO₃/Al₂O₃ catalyst. Further, the VPO/SiO₂ and VPO catalysts exhibit better conversion and product selectivities than the additive-containing VPO catalysts. Better activity of VPO and VPO/SiO₂ catalysts was related to their high active surface area, higher surface acidity and lower oxidation state of vanadium. The redox couple between (VO)₂P₂O₇ (V⁴⁺) and α_I-VOPO₄ (V⁵⁺) phases appears to be responsible for the ammoxidation activity of VPO catalysts. © 1998 SCI.     

Oxidative dehydrogenation of ethanol over AgLi–Al2O3 catalysts containing different phases of alumina

Oxidative dehydrogenation of ethanol over the AgLi–Al₂O₃ catalysts having different phase compositions of alumina was investigated. The pure gamma (CHI00), pure chi (CHI100) and equally mixed phases (CHI50) derived from the solvothermal synthesis can play important roles on the physicochemical properties of AgLi–Al₂O₃ catalysts. Especially, the amount of weak basic sites, the oxidation state of Ag, and the reduction behaviors of catalysts are crucial in determining the ethanol conversion and product selectivity. It was found that increased amounts of weak basic sites and Ag_n^δ + clusters enhanced the catalytic activity as seen for the AgLi–CHI50 catalyst.     

On the La–Cr–O Phase Change During Methane Catalytic Combustion Investigated with in situ HT-XRD

La₂CrO₆ (Cr6), LaCrO₃ (Cr3), LaCrO₃–La₂CrO₆ (Cr6–Cr3) and LaCrO₃–La₂O₃ (Cr3-L) catalysts were synthesised and investigated with in situ X-ray diffraction (ISXRD) during methane catalytic combustion in order to characterise the solid phases present under reactants and to determine the effect of chromium oxidation state on the catalytic activity. Methane conversion was evaluated over a temperature range of 300–800 °C, using oxygen-to-methane ratio of 4 and GHSV of 8,000 h^?1. The TPR provided information about the oxygen depletion temperatures characteristic of lattice oxygen mobility in the samples and ISXRD results evidenced a cooperative effect of Cr3 and Cr6 phases at low temperatures (<725 °C) and of Cr3 and LaCrO₄ (Cr4) phases at high temperatures (>750 °C). The relative phase composition determined the oxygen activation capability and hence the corresponding activity for the oxidation of methane. It was observed that while direct and back Cr6 ? Cr4 transition temperatures were unaffected by Cr6 content in the samples, the methane conversion was strongly modified. This suggests that Cr³⁺/Cr⁶⁺ and Cr³⁺/Cr⁵⁺ species involved substantial modification of the surface chemistry which affected the catalytic activity. These results provide the first direct evidence of the presence of Cr4 metastable phase during methane combustion over La–Cr–O catalysts.     

Methanol selectivity of silica-supported PtFe

Adding Fe to Pt/SiO₂ catalysts improves activity for methanol synthesis from 3H₂/CO at 523 K and 3.19 MPa. Over 90% methanol selectivity can be achieved at low conversion, depending on the metal composition and dispersion.In situ Mössbauer measurements after reduction in hydrogen at 673 K and during steady-state reaction show the presence of PtFe alloy and Fe³⁺ phases only. The amount of PtFe alloy increases as catalysts activate to produce methanol with higher activity and selectivity.     

COMPARATIVE STUDY OF Ag2O/CO3O4 CATALYSTS PREPARED BY THE SOL-GEL AND CO-PRECIPITATION TECHNIQUES: CHARACTERIZATION AND CO ACTIVITY STUDIES

In this study effects of the preparation method on the characteristic properties and CO oxidation activities of Ag₂O/Co₃O₄ catalysts were investigated. Catalysts were prepared by two different methods: sol gel and co-precipitation. N₂ physisorption measurements, X-ray diffraction, and scanning electron microscopy measurements were used to characterize the catalysts. CO oxidation activity tests were carried out under 1% CO, 21% O₂, and the remainder He feed condition between 20° and 200°C. According to the N₂ physisorption measurements, catalysts prepared by the co-precipitation method have a higher surface area than the catalysts prepared by the sol-gel method. Co₃O₄ and AgCoO₂ phases were obtained from catalysts prepared by both techniques. In addition to these phases, metallic silver peaks were obtained by increasing calcination temperature. SEM micrographs of the catalysts showed that catalysts have uniform particles. Increasing the calcination temperature caused the formation of different-sized agglomerates and an increase in the gaps between agglomerates. The best activity was obtained from the Ag₂ O/Co₃ O₄ catalyst calcined at 200°C and prepared by the co-precipitation method. This catalyst gave 50% CO conversion at 106°C. The other two catalysts gave 100% CO conversion at a higher temperature of 200°C.     

TPR and XPS study of cobalt–copper mixed oxide catalysts: evidence of a strong Co–Cu interaction

In this work the results of a TPR and XPS investigation of Co_xO_y–CuO mixed oxides in the range of composition Co : Cu=100:0–8:92 are reported and compared. The final catalysts were obtained by thermal decomposition in air and N₂ at 723 K for 24 h of singlephase cobalt–copper hydroxycarbonates prepared by coprecipitation at constant pH. The Co : Cu=100 : 0 specimen calcined in air formed the Co²⁺[Co³]₂O₄ (Co₃O₄) spinel phase. The coppercontaining catalysts (Co : Cu=85 : 15–8 : 92) showed mainly two phases: (i) spinels, like Co²⁺[Co³⁺]₂O₄, Co _1-x ²⁺ Cu _x ²⁺ [Co³⁺]₂O₄ and (ii) pure CuO, the relative amount of each phase depending on the Co : Cu atomic ratio. The results of the XPS study are consistent with the bulk findings and revealed the presence of Co²⁺, Co³⁺ and Cu²⁺ species at the catalyst surface. Moreover, the surface quantitative analysis evidenced a cobalt enrichment, in particular for the most diluted cobalt samples. The TPR study showed that the catalyst reduction is affected by a strong mutual influence between cobalt and copper. The reducibility of the mixed oxide catalysts was always promoted with respect to that of the pure Co₃O₄ and CuO phases and the reduction of cobalt was markedly enhanced by the presence of copper. Cobalt and copper were both reduced to metals regardless of the catalyst composition. On the other hand, the Co : Cu=100 : 0 specimen calcined in N₂ formed, as expected, CoO. The initial addition of copper resulted in the formation of the Cu⁺Co³⁺O₂ compound, besides CoO, up to a Co/Cu=1 atomic ratio at which the CuCoO₂ phase was the main component. A further addition of copper led to the formation of CuCoO₂ and CuO phases. The XPS results were in good agreement with these findings and the surface quantitative analysis revealed a less enrichment of cobalt with respect to the catalysts calcined in air. The TPR analysis confirmed that the reduction of the N₂calcined catalysts was also remarkably promoted by the presence of copper. Also in this case cobalt and copper metal were the final products of reduction.     

Selective oxidation of propane over PMoV?M/α‐Al2O3 (M: Co,Fe, or Ni)

Alumina supported phosphovanodomolybdic acid and alumina supported phosphovanodomolybdic acid‐transition metal ions (M: Fe³⁺, Co²⁺, or Ni²⁺) were prepared by impregnation. The thermal decomposition, in situ at 400°C, of supported catalysts showed the formation of V₂O₅, P₂O₅, MoO₃ and MoO₃, CoMoO₄, (Mo_0.3V_0.7)₂O₅ phases, on the alumina surface, in the presence of H₄PMo₁₁VO₄₀/α‐Al₂O₃ and H₄PMo₁₁VO₄₀? Co/α‐Al₂O₃, respectively. The catalytic activity of alumina‐supported catalysts was evaluated in the reaction of propane oxidation at 380 and 400°C. The addition of transition metal increases the conversion and changes the reaction products distribution. The reaction conditions (temperature and propane/oxygen ratio) have also modified the behaviour of the studied catalysts.     

Conventional and wet proofed CuO/Al2O3 catalysts for phenol oxidation: deactivation studies in a trickle bed reactor

A large variety of catalytic systems have been studied for the catalytic wet air oxidation of phenolic solutions. Most of them show good activity, but serious stability problems. In this contribution, stability studies were performed over CuO/Al₂O₃ conventional (CNT) and polytetrafluorethylene coated (C3T) catalysts used for the oxidation of 5 g L^?1 phenol solutions in a trickle bed reactor (140 °C and 7 atm of oxygen pressure). For the hydrophilic catalyst, phenol conversion decreased with usage due to the formation of Cu₂O and copper oxalate phases. For the wet proofed catalyst, the hydrophobic layer prevented the appearence of those phases, and conversion levels remained practically constant with reaction time. After usage, both catalysts were oxidized at 400 °C and tested for reaction: in the case of the C3T catalyst, the phenol conversion was increased over its initial level; for CNT catalyst, the phenol conversion was also increased, but initial levels were not completely restored. The deactivation mechanism of the CNT catalyst is associated with the formation of the Cu₂O and copper oxalate phases during reaction. For catalyst C3T, practically no deactivation was observed. Copyright © 2007 Society of Chemical Industry     

Bimetallic Au–Cu, Ag–Cu/CrAl3O6 Catalysts for Methanol Synthesis

The influence of silver and gold addition on the activity and physicochemical properties of supported Cu/CrAl₃O₆ catalysts was the aim of this work. The reduction of CrAl₃O₆ support shows only one reduction stage attributed to Cr (VI) species reduction originating from previously oxidized binary oxide. Supported copper catalysts reduce in one or two stages depending on copper concentration representing the reduction of copper oxide—CuO, copper oxide chemically combined with Cr(III) oxide as copper chromite—CuCr₂O₄ and Cr(VI) species originating from surface chromate ions CrO₄ ^2?. Additionally, the introduction of silver into supported copper catalysts Cu/CrAl₃O₆ can led to the appearance of silver chromate phase. XRD investigations of support CrAl₃O₆ alone, supported copper and gold and silver promoted copper supported catalysts calcined at 400, 700 and 900 °C indicated the presence of highly amorphous alumina γ-Al₂O₃ like structure network in which some of cationic locations of aluminum were occupied by chromium atoms and small quantities of α-Cr₂O₃ phase. Additionally, for copper, silver–copper, and gold–copper supported catalysts the following oxide phases were distinguished: monometallic oxides CuO, Ag₂O, binary oxides CuAl₂O₄, Ag₂CrO₄, CuCr₂O₄ and even ternary oxide CuAlCrO₄. In the case of gold promoted copper supported catalysts metallic gold phase was detected. Activity tests carried out for these catalysts show that the most active was 20 wt.% Cu/CrAl₃O₆ catalyst. Promotion of copper catalysts by silver improves the activity in methanol synthesis, what can be assigned to silver chromate formation. The analogical gold chromate like formation was not confirmed.     

Investigation of palladium interaction with cerium oxide and its state in catalysts for low-temperature CO oxidation

Palladium catalysts supported on nanosized CeO₂ supports were synthesized by different methods. The catalysts showed high low-temperature activity (LTA) in CO oxidation. The synthesized palladium–ceria catalysts for low-temperature CO oxidation were investigated by a complex of physicochemical methods, and their catalytic performance was determined in the light-off regime. It was shown using high-resolution transmission electron microscopy (HRTEM) and EDX microanalysis that the catalysts with high LTA are characterized by exceptionally high dispersity of palladium on the surface of the supports. Two different states of palladium were observed by XPS. They correspond to the surface interaction phases (SIPs) as Pd_xCeO_2−δ and small metal clusters (<10 Å). According to diffraction images obtained by HRTEM, the latter have flattened shape due to epitaxial binding between (1 1 1) facets of palladium and CeO₂. Two types of CO adsorption sites (Pd²⁺ and Pd⁰) were distinguished by FTIR. They can be attributed to SIP (Pd²⁺) and palladium in flat metal clusters (Pd^δ+ and Pd⁰). The drop of LTA in CO oxidation is related to the loss of the palladium chemical interaction with the surface of the support and palladium sintering to form PdO nanoparticles. The formation of PdO particles is stimulated by crystallization of CeO₂ particle surface due to the calcination of support at temperatures above 600 °C. The XPS, HRTEM and FTIR data give reliable evidence that PdO particles are not responsible for LTA in CO oxidation.In this work, the structure of the active sites consisting of two phases: atomically dispersed palladium within the SIP and palladium metal nanoclusters is proposed. The catalyst pretreatment in hydrogen was found to improve significantly its catalytic (LTA) properties. The effect of the hydrogen pretreatment was supposed to be related to the formation of hydroxyl groups and their effect on the electronic and geometrical state of the surface active sites and their possible direct participation in CO oxidation.     

Methanol Decomposition to Synthesis Gas Over Supported Pd Catalysts Prepared from Hydrotalcite Precursors

Supported Pd catalysts were prepared by solid-phase crystallization (spc) starting from MgAl hydrotalcite anionic clay minerals as the precursors, and were tested for the methanol decomposition to synthesis gas. The precursors based on [Mg₆Al₂(OH)₁₆CO₃ ^2-] · 4H₂O were prepared by coprecipitation from raw materials containing Pd²⁺, Mg²⁺ and Al³⁺ ions as the components of hydrotalcite. The precursors were thermally decomposed and reduced to afford supported Pd catalysts on MgAl mixed oxide. Pd-supported catalysts as a reference were also prepared by the impregnation (imp) method. The spc-Pd catalysts thus prepared afforded highly dispersed Pd metal particles and showed higher activity as well as lower activation energy than the imp-Pd catalysts. When the precursor was prepared under mild conditions, finer particles of Pd metal were formed over the catalyst, resulting in a high activity. In the case of spc-Pd catalysts, carbon monoxide adsorbed on Pd easily desorbed, compared with imp-Pd catalysts. It is likely that the high activity is due to the highly dispersed and stable Pd metal particles and the easy desorption of carbon monoxide.     

Hydrotalcite derived Cu-Zn-Cr catalysts admixed with γ-Al2O3 for single step dimethyl ether synthesis from syngas: Influence of hydrothermal treatment

The Cu-Zn-Cr catalysts derived from hydrotalcite (HT) structures were prepared by the hydrothermal and non-hydrothermal methods. The catalysts were admixed with Al₂O₃ to synthesize DME (dimethyl ether) from syngas. XRD analysis revealed the presence of hydrotalcite (HT)-like structures in the oven dried form was decomposed to disperse copper species in the calcined conditions. ESR spectra of the fresh calcined catalysts disclosed both the isolated and clustered copper species and bulk Cr³⁺ species are seen in used catalysts. The TPR analysis indicated that the Cu²⁺ ions are reduced in two stages. DME synthesis experiments showed that the CO conversion and DME yield were linearly correlated with Cu metal surface areas of Cu-Zn-Cr catalysts admixed with γ-Al₂O₃. Activity results indicated that hydrothermal treatments have pronounced influence on the dispersion of copper species and consequently on DME synthesis rates.     

High Pressure Desorption of K+ from Iron Ammonia Catalyst – Migration of the Promoter Towards Fe Active Planes

The thermal desorption of potassium ions from industrial iron catalysts was studied in situ in the wide pressure range of 10^?8–10 bar of Ar, N₂ and synthesis gas mixture of N₂:3H₂. While high activation energy of 284 ± 1 kJ/mol, for K⁺ was determined for the catalyst precursor, in the reaction conditions it drops down to 231 ± 5 kJ/mol, corresponding well to that found for iron single crystals in UHV studies. The results are rationalized in terms of potassium migration from oxide storage phases towards the iron facets developed during the catalyst activation.     

WP/γ-Al2O3催化剂的制备、表征及加氢脱硫和加氢脱氮活性

Two series of WP/Al2O3 catalyst precursors with WP mass loading in the range 18.5%-37.1% were prepared using the impregnation method and mixing method, respectively, and the catalysts were then obtained by temperature-programmed reduction of supported tungsten phosphate (precursor of WP/Al2O3 catatlysts) in H2 at 650℃ for 4h. The catalysts were characterized by XRD, BET, TG/DTA, XPS and 31p MAS-NMR. The activities of these catalysts were tested in the hydrodenitrogenation (HDN) of pyridine and hydrodesulfurization (HDS) of thiophene at 340℃ and 3.0MPa. The results showed that owing to the stronger interaction of the support with the active species, the precursor of WP/Al2O3 catalyst was more difficultly phosphided and a greater amount of W species was in a high valence state W6 on the surface of the catalyst prepared by the impregnation method than that by the mixing method. 31p MAS-NMR results indicated that 31p shift from 85% H3PO4 of 2.55 × 10-4 for WP and 2.57 × 10-4 for WP/γ-Al2O3 catalysts prepared by mixing method. Such WP/Al2O3 catalysts showed higher HDN activities and lower HDS activities than those prepared by the impregnation method under the same loading of WP.WP/γ-Al2O3 catalysts with weak interaction between support and active species were favorable for HDN reaction while the WP/γ-Al2O3 catalysts with strong interaction were favorable for HDS reaction.     

Surface Properties of CaO (or BaO)–La2O3–MgO Catalysts and Their Performance in Oxidative Coupling of Methane

CaO–La₂O₃–MgO and BaO–La₂O₃–MgO catalysts with different compositions have been studied for their bulk and surface properties (viz. crystal phases, surface area, acidity/acid strength distribution, basicity/base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) at different processing conditions (reaction temperature, 700–850°C; CH₄/O₂ ratio in feed, 3·0, 4·0 and 8·0 and GHSV, 102000 and 204000 cm³ g⁻¹ h⁻¹). The surface acidity and strong basicity of La₂O₃–MgO are found to be increased due to the addition of a third component (CaO or BaO), depending upon its concentration in the catalyst. The addition of CaO or BaO to La₂O₃–MgO OCM catalyst causes a significant improvement in its performance. Both the CaO- and BaO-containing catalysts show a high activity and selectivity at 800°C, whereas, the activity and selectivity of BaO-containing catalysts at 700°C is lower than that of CaO-containing catalysts. © 1997 SCI.