Magnesium Catalyst Research Articles

Oxidative methylation of organic compounds with methane over alkali promoted MgO catalysts

The oxidative methylation of acetone, acetophenone and diphenylmethane with methane has been investigated over sodium, cesium and sodium-cesium promoted magnesia catalysts at 750°C and under normal atmospheric pressure. All these compounds do react with methane and produce their corresponding methane coupling products. The bialkali (5 mol-% Na-5 mol-% Cs) promoted MgO catalyst provided higher product yields than the individual mono-alkali promoted MgO catalysts at the same alkali content of 10 mol-%.

ChemInform Abstract: Intrinsic Surface Structures and Their Roles in the Catalysis and Photocatalysis of Microcrystalline Magnesium Oxide Catalysts

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

Improvement of Stereospecificity of an MgCl2-Supported Titanium Catalyst upon Treatment with Al(C2H5)3

Magnesium dichloride supported titanium catalysts were prepared by solubilizing anhydrous magnesium dichloride in 2-ethyl-1-hexanol followed by treatment with titanium tetrachloride. 2,2-Dimethoxypropane was used as an internal Lewis base. Solid products were characterized by compositional analysis, and specific surface area. Titanium magnesium catalysts (Ti-Mg) in conjunction with triethylaluminium showed high activity (5110 g PP/g Ti) and high stereospecificity (I.I = 92) for propylene polymerization. The variation in the amount of 2,2-dimethoxypropane during catalyst synthesis governs the productivity of the catalyst. Furthermore, the increase in the chain length of the alkyl group from ethyl to hexyl of trialkylaluminum cocatalyst retards the activity of the catalyst system, with minor variation in the isotactic index of polypropylene. The addition of diphenyldimethoxysilane into triethylaluminum further improves the stereospecificity of the catalyst system.

Aromatization of n-Octane over Pt-Based Catalysts: Influence of the Support on the Product Distribution Among C8 Aromatics

Oxidative dehydrogenation (ODH) of n-octane was carried out over a vanadium–magnesium oxide catalyst in a continuous flow fixed bed reactor. The catalyst was characterized by ICP–OES, powder XRD and SEM. The catalytic tests were carried out at different gas hourly space velocities (GHSVs), viz. 4000, 6000, 8000, and 10,000 h−1. The best selectivity for octenes was obtained at the GHSV of 8000 h−1, while that for C8 aromatics was attained at the GHSV of 6000 h−1 at high temperatures (500 and 550 °C). The catalytic testing at the GHSV of 10,000 h−1 showed the lowest activity, while that at the GHSV of 4000 h−1 consistently showed the lowest ODH selectivity. Generally, the best ODH performance was obtained by the catalytic testing at the GHSVs of 6000 and 8000 h−1. No phasic changes were observed after the catalytic testing.

Catalytic and electrocatalytic oxidation of propane on V-Mg-O and V-Mg-O (Ag) catalysts

Vanadium magnesium oxide catalysts prepared in this work were found active in selective oxidation of propane to propene. A selectivity as high as 79% was obtained at 10% conversion (813 K). No oxygenated or C2 products were detected and the catalysts were found to undergo no change in activity over many weeks of operation. Under electrochemical pumping of oxygen (EOP) towards the catalyst (with oxygen present in the feed gas), both conversion and selectivity were found to increase slightly as external current increased, indicating the effect of electrical current can be exhibited by an oxide catalyst. However, in the absence of oxygen in the feed gas, EOP could lead to an even higher selectivity: 84 and 86.9% respectively for a 24 V-Mg-O and a 24 V-Mg-O (Ag) (1/2) catalyst. The overall results obtained suggest that electrochemically supplied oxygen is more selective towards C3H6. Mechanisms of both catalytic and electrocatalytic oxidation of propane were tentatively suggested, with surface oxygen ion vacancy identified as active surface species and the rate determining step involving heterolytic splitting of the C3H8 molecule to form a surface bonded C3H7− ion and a surface hydroxyl ion. The higher selectivity towards C3H6 in case of EOP was explained on this basis. While mixing with Ag powder was found to improve significantly the electrocatalytic performance of vanadium magnesium oxide, its role appears to be non-chemical: it simply gives rise to a larger area of the gas/catalyst/Ag electrode interface.

Oxidative methylation of ?-, ?- and ?-picolines with methane vinylpyridines and ethylpyridines over mono- and bialkali promoted magnesia catalysts

The oxidative methylation of α-, β- and γ-picolines with methane to the corresponding vinyl- and ethylpyridines was carried out at 750°C and under normal atmospheric pressure, over sodium, cesium or sodium-cesium promoted magnesia catalysts. Among the three picolines, the γ-picoline was the most reactive, followed by α- and β-picolines. The (5 mol% Na-5 mol% Cs)/MgO catalyst provided higher yields than the individual promoters, at the same total alkali content of 10 mol%.

Thermal and X‐ray investigations of ethylene–α‐olefin copolymers obtained with highly active supported Ti–Mg and V–Mg catalysts

AbstractCopolymers of ethylene with propylene, butene‐1 and hexene‐1 were prepared using a titanium–magnesium (TMC) or a vanadium–magnesium catalyst (VMC). The copolymers were examined for thermal stability by TGA, melting and crystallization behaviour by DSC and crystallinity by XRD. Fractionated samples of ethylene–hexene‐1 copolymers were also similarly characterized. Results indicate that VMC produces copolymers with a higher degree of crystallinity and greater compositional homogeneity than TMC.

The oxidative coupling of methane and the oxidative dehydrogenation of ethane over a niobium promoted lithium doped magnesium oxide catalyst

The promoting effect of niobium in a Li/MgO catalyst for the oxidative coupling of methane (OCM) and for the oxidative dehydrogenation of ethane (ODHE) has been studied in some detail. It has been found that a Li/Nb/MgO catalyst with 16 wt % niobium showed the highest activity for the C 2 production in the OCM reaction; the activity at 600 °C was ten times that of the Li/MgO catalyst at the same temperature. The Li/Nb/MgO catalyst was also slightly more active for the ODHE reaction than was the Li/MgO catalyst. However, the Li/Nb/MgO catalyst produced considerably more carbon dioxide in the both reactions. Structural investigation of the catalyst showed that the addition of niobium to the Li/MgO catalyst increased the surface area and gave an increase in the lithium content of the calcined catalysts. Two niobium phases, LiNbO 3 and Li 3NbO 4, were formed; it is shown that the first of these probably causes the increased activity. Ageing experiments showed that the activity of the catalyst was lost if the catalyst was used above 720 °C, the melting point of the lithium carbonate phase. The catalyst showed a decrease of surface area after ageing and a sharp decrease of the amount of the two niobium phases. The addition of carbon dioxide to the feed could not prevent the deactivation of the Li/Nb/MgO catalyst.

Origin of kinetic isotope effects during the oxidative coupling of methane over a lithium(1+)/magnesia catalyst

Kinetic isotope effects (KIEs) during the oxidative coupling of methane over a Li + /MgO catalyst at 700 o C have been determined using several different experimental methods and by a reaction model that includes both heterogeneous and homogeneous reactions. By maintaining a constant partial pressure of methane of 190 Torr and changing the partial pressure of oxygen, a variation in the H/D KIE, based on differing rates of CH 4 and CD 4 conversion, was observed

The preparation and properties of magnesia catalyst supports

AbstractThe preparation of magnesia has been investigated with the object of preparing a catalyst support material that maintained high surface area after heating to high temperatures. The effect of precipitation, ageing, washing, drying and calcining on the surface area and porosity of magnesia has been studied. It was found possible to produce stable magnesia by washing with methanol or acetone, but the surface area was low for most catalytic applications.

Role of F centers in the oxidative coupling of methane to ethane over lithium-promoted magnesium oxide catalysts

We report a study of the partial oxidation of methane to ethane over a model MgO catalyst prepared under well-controlled, ultrahigh vacuum (UHV) conditions using a combination of surface science techniques and elevated pressure kinetics measurements.

Hydrogen activation by magnesia catalysts

Hydrogen activation by magnesia catalysts was investigated by studying H 2D 2 exchange. The number of active sites, surface composition, rate, and mechanism of the reaction were investigated as a function of the activation temperature. Behavior of a commercial magnesia and a catalyst synthesized from Mg(OH) 2 were similar, although the latter catalyst had a much larger surface area. The upper limit for the number of active sites was determined in the classical manner by using selective poisoning by CO. A novel technique involving monitoring the stoichiometric reaction between magnesia and D 2(g) enabled the very unusual determination of the lower limit for the number of active sites. Thus, the true number of active sites is bracketed within the upper and lower limits. Maximal activity occurred after activation at 700°C. The number of active sites is about 10 12/cm 2, which is 103-fold higher than formerly reported on the basis of EPR data. The turnover frequency at 273 K and a partial pressure of 20 Tort of an equimolar mixture of H 2D 2 is 4 s −1, roughly 10 3-fold less than previously reported. The site density and activity are now consistent with expected values, rather than the anomalous values previously reported. The hydroxyl coverage of the surface was determined in a novel manner using thermogravimetric analysis over the temperature range of 300 to 1400 K. The catalysts are of low activity when the surface is either of very high or very low hydroxyl content. A mechanism in which the active site includes an ensemble consisting of a Mg 2+ center and neighboring surface OH and O 2− is proposed.

The relationship between catalyst morphology and performance in the oxidative coupling of methane

A detailed study of the oxidative coupling of methane over magnesium oxide and lithium-doped MgO catalysts is presented. The morphology of a number of different catalysts has been examined by detailed transmission electron microscopy and the results have been correlated with catalyst performance, in particular selectivity to C 2 hydrocarbons. Three samples of magnesium oxide have been prepared by different methods. Magnesium oxides prepared from the hydroxide, (ex OH), and from burning magnesium ribbon in air show similar morphology, exposing largely {100} planes; they also show very similar catalytic selectivity and specific activity. The ribbon residue material, however, has a cube length which is greater than that of the ex OH material by a factor of 5–10. Steps and corner sites are therefore present in much greater density on the ex OH sample than on the ribbon residue, and, since catalyst performance is unchanged, it is clear that these sites play no significant part in the catalysis over these materials. The active site is therefore located on the planar {100} surfaces. The most selective magnesium oxide catalyst was prepared by thermal decomposition of magnesium hydroxycarbonate and exposed a greater proportion of higher index mean crystal planes, e.g., {l11}, than the less selective forms of magnesium oxide. It is suggested that an additional selective site is present in this form of magnesium oxide, with density related to morphology but not directly to surface area, perhaps a “bottom step” site. The morphology/performance relationship has also been examined for lithium-doped magnesium oxide catalysts. In agreement with previous studies, addition of lithium causes a loss of surface area and of the morphology characteristic of the precursor magnesium oxide; the grain size also increases, grain boundary dislocations become evident, and dislocations are also observed in the bulk of the grains. These are immobile and of the type 1 2 〉110〈 , pinned by the presence of lithium ions. The emergence of a dislocation at the surface of the crystallite provides a locus for [Li +O −] centres, thought to be the active site in methyl radical generation in methane coupling. Similar dislocations are observed in Au/MgO catalysts, which are much less selective to C 2 hydrocarbons than is pure MgO.

Selective synthesis of liquid hydrocarbons from carbon dioxide and methane

The synthesis of liquid hydrocarbons from carbon dioxide and methane was studied under pressurized conditions using two stage reactor process composed of methane reforming by CO 2 and Fischer-Tropsch reaction. A nickel supported magnesia catalyst gave the equilibrium conversion of CH 4 and CO 2 above 850 °C. On a Co-La/SiO 2 catalyst the CO conversion was 20 % at 250 °C and 0.7 MPa and the selectivity to C5+ hydrocarbon was 70%. The major by-product in the second reactor was CH 4, which can be recycled into the first reforming reactor.

The effect of addition of a third component on the behaviour of the lithium doped magnesium catalysts for the oxidative dehydrogenation of ethane

The oxidative dehydrogenation of ethane was studied with the use of promoted Li/MgO catalysts at temperatures of 600–650°C. The addition of known promoters, cobalt and tin, gave a slight Increase In activity but a strong decrease in selectivity to ethylene under the conditions used. The addition of sodium improved the selectivity to ethylene and suppressed the formation of carbon monoxide. Using a feed of 12 vol% ethane and 6 vol% oxygen, the U/Na/MgO catalyst with 3.2wt% sodium showed a selectivity of 86 % to ethylene at 38 % conversion of ethane; the Li/MgO catalyst showed a selectivity of 80 % at similar conversions Thermal Investigations of the Li/Na/MgO catalyst showed that an eutectic melt of LINaCO 3 is formed at 490°C; the existence of this molten phase is probably the cause of the Increased selectivity.

Relationship between morphology and catalytic performance of lithium and gold doped magnesium oxide catalysts for the oxidative coupling of methane

A detailed study is presented of the relationship between morphology and catalytic performance of Li and Au doped MgO prepared by the thermal decomposition of the hydroxide. Addition of Li to MgO causes a loss of the characteristic morphology of the precursor MgO due to grain growth via agglomeration of crystallites and grain boundary dislocations are evident. In contrast, Au doping of MgO does not lead to an increase in grain size. For both Li and Au doped MgO, dislocations are observed that are immobile and are proposed to be of the type a 2 (110) which are probably pinned by Li or Au ions segregating to the line of the defect. The importance of these dislocations is discussed with respect to the catalytic performance of Li and Au doped MgO catalysts for the oxidative coupling of methane.

Ketones from carboxylic acids over supported magnesium oxide and related catalysts

Silica-supported alkaline earth oxides revealed excellent activity to convert acetic acid selectively into acetone in a vapor-phase fixed-bed flow system. Acetone was obtained through the cyclic formation of alkaline earth acetate followed by decomposition. Magnesium oxide should be supported on the silica surface without formation of magnesium silicate, which was inactive for the present reaction. Attempted syntheses of benzophenone and acetophenone are also described.

Structural aspects of magnesium oxide catalysts for the oxidative coupling of methane

A study of the structure and catalytic performance of Li doped MgO catalysts is presented. The addition of Li to MgO causes a loss of the characteristic morphology of the precursor MgO due to agglomeration of crystallite grains. Growth of MgO grains leads to the formation of grain boundary dislocations. In addition, dislocations are also observed in the bulk of the grains. These dislocations are immobile and are suggested to be of the type a/2(110) and are probably pinned by Li + segregating to the line of the defect. The importance of these dislocations is discussed with relevance to the partial oxidation of methane.

Hydrogenation of 1,3-butadiene over magnesium oxide prepared by the decomposition of magnesium oxalate

In order to find the cause of the high activity for hydrogenation of 1,3-butadiene over a magnesium oxide catalyst prepared by thermal decomposition of magnesium oxalate, ESR and poisoning techniques were used. The cause of the high activity was attributed to large surface area and electron donating properties, which might be related to the surface basicity.

Former ACS president Albert Zettlemoyer dies

Albert C. Zettlemoyer, 75, president of the American Chemical Society in 1981 and former Lehigh University provost and vice president, died Jan. 27 in Bethlehem, Pa. Well known as a surface and colloid chemist, Zettlemoyer reportedly was still doing research until two weeks ago at Sinclair Laboratory—a Lehigh building for which he led fund-raising two decades ago. Zettlemoyer began his association with Lehigh by earning a B.S. degree in chemical engineering in 1936 and an M.S. degree in 1938. He received a Ph.D. degree in physical chemistry from Massachusetts Institute of Technology in 1941, and then joined Armstrong Cork as a research chemist. Soon after, he returned to Lehigh as an instructor. In 1950, he became a full prof essor, and in 1983 Distinguished Professor Emeritus of Chemistry. His activities at Lehigh ranged from directing research projects and teaching to starting a surface chemistry lab to work on active magnesia catalysts for the World War ...