Catalysts Of Various Compositions Research Articles

Copolymerization of ethylene and a-olefins by highly active, supported catalysts of various compositions

Copolymerization of ethylene and a-olefins by highly active, supported catalysts of various compositions

Surface reactions of hydrocarbons as a probe for the characterization of rhodium-copper/silica catalysts

RhCu/SiO{sub 2} catalysts of various compositions were prepared from nitrate precursors and characterized by transmission electron microscopy and chemisorption. The catalytic properties were determined in a flow microreactor, at low conversion, for the hydrogenation of benzene, poisoned or not by thiophene, and the conversion of a series of alkanes: n-hexane (n-H), 2-methylpentane (2MP), 2,2-dimethylbutane (22DMB), 2,2,3,3-tetramethylbutane (2233TMB), methylcyclopentane (MCP). The conversion of alkanes at 493 K gives mainly hydrogenolysis of C-C bonds. The rate of cleavage depends on the degree of substitution of the carbon atoms and on the Cu/Rh ratio. Cu inhibits all reactions; however, the magnitude of this effect depends on the structure of the reactant. The comparison of the alloying effect with the effect of Rh particle size on the same set of reactions (Coq et. al.) shows that on the one hand 2233TMB has a lower sensitivity to alloying than to particle size; the selectivity to i-C{sub 4} remains high and characteristic of large particles of rhodium up to Cu/Rh = 1. On the other hand n-H, 2MP, and MCP are more sensitive to alloying than to change of particle size. These results suggest that Cu occupies preferentially the sites of low coordination, edges, and corners,more » and Rh the sites of high coordination on dense planes. This set of reactions, therefore, probes the extent of surface segregation on RhCu-supported particles.. By addition of thiophene a monotonic decrease of activity in the hydrogenation of benzene occurs due to sulfurization of the surface. The rate of poisoning is faster when the local density of states at the Fermi level of Rh surface atoms is higher. Dilution of Rh by Cu has little effect on the thioresistance which remains low even at high Cu content. Very likely little electronic interaction occurs between Rh and Cu.« less

Structure and activity of chromium-promoted raney copper catalysts for carbon monoxide oxidation

Chromium promoted Raney copper catalysts of various compositions were prepared and their activity for carbon monoxide oxidation measured. The surface areas of the Raney catalysts were found to be directly related to Al content in the precursor alloy and to a lesser extent to the presence of chromium. Crystalline Al, in excess of the amount required to form Al 2Cu in the alloy, appeared to lead to the formation of a structure of channels observed by scanning electron microscopy of the Raney catalysts. Bulk CuO and Cu 2O were detected by X-ray diffraction in the Raney catalysts. The presence of chromium appeared to inhibit the formation of CuO but not of Cu 2O. The activity was found to decrease as chromium content increased. However, when catalysts were prereduced with carbon monoxide prior to reaction, an optimum was found at low values of chromium concentration. A relation between deactivation by carbon monoxide pretreatment and temperature-programmed reduction spectra was established.

ChemInform Abstract: An in situ Moessbauer Spectroscopic Investigation of Titania‐supported Iron‐Ruthenium Catalysts.

AbstractThe 57Fe Mößbauer spectroscopic results obtained for Fe/TiO2 and Fe‐Ru/TiO2 catalysts of various compositions exposed to argon, H2, and H2‐CO atmospheres indicate that the surface area of the TiO2 support and the Ru concentration influence the metal‐support interactions and consequently the nature of the solids formed in air and their reduction products.

A study on BiFeMo oxide catalysts by means of 57Fe Mössbauer spectroscopy and electron microscopy

BiFeMo oxide catalysts of various compositions have been investigated using X-ray diffraction, 57Fe Mössbauer measurements, and analytical electron microscopy. When a BiFeMo oxide catalyst with a composition of Bi/Fe/Mo = 3/1/2 is calcined at 523–773 K, two kinds of tetragonal Bi 3FeMo 2O 12 particles are generated, their average diameters being different from each other. Paramagnetic doublets in the Mössbauer spectra of these tetragonal particles are identical to those in an earlier report analyzed as monoclinic Bi 3FeMo 2O 12. In the case of a BiFeMo oxide catalyst of a composition, Bi/Fe/Mo = 1/1/1, calcined at 523–773 K, fine particles 15 nm in diameter are produced along with tetragonal Bi 3FeMo 2O 12 particles. The fine particles are found to be superparamagnetic α-Fe 2O 3 and/or small crystallites of tetragonal Bi 3FeMo 2O 12. During calcination at 823 K, the tetragonal Bi 3FeMo 2O 12 phase decomposed to a mixture of monoclinic Bi 3FeMo 2O 12, Bi 2O 3 MoO 3, Fe 2(MoO 4) 3, and ferromagnetic α-Fe 2O 3. Their particle sizes were from 15 to 50 nm in diameter. The Mössbauer spectrum of the BiFeMoO 6 phase reported by T. Notermann, G. W. Keulks, A. Skliarov, Yu. Maximov, L. Ya. Margolis and O. V. Krylov ( J. Catal. 39, 286 (1975)) was not observed but the pattern detected was interpreted to be the superposition of the spectra of the Bi 3FeMO 2O 12 and α-Fe 2O 3 phases. This was also confirmed by analytical electron microscopy.

Comparative study of alumina-supported CuO and CuCr 2O 4 as catalysts for CO oxidation

Alumina-supported CuO and CuCr 2O 4 catalysts of various compositions were prepared and their activity for CO oxidation measured. Fresh, pretreated with CO, and reoxidized catalysts were studied. In general, the activity increased with the CO pretreatment. The extent of the activation depended on the catalyst composition. Thus, copper catalysts were more active than copper chromite at low metal concentrations (<12 wt%), but the opposite was observed at concentrations higher than about 12 wt%. The results on activity behavior, together with TPR and XRD spectra, suggest that the active species are related to copper cations. In the low concentration copper catalysts, the most active surface is generated after CO pretreatment, followed by a fast reoxidation occurring at the first stages of the reaction. In the high concentration copper catalysts, the CO pretreatment produced an induction period as a result of excessive reduction. It is suggested that the role of chromium is to limit the extent of reduction through the formation of the CuCr 2O 4 phase. The presence of this phase also resulted in catalysts less prone to deactivation, as compared to copper on alumina catalysts.

Propene polymerization on titanium‐magnesium catalysts, 4. ESR study of TI3+ ions

AbstractThe role of Ti3+ ions in titanium‐magnesium catalysts of various composition, TiCl4/MgCl2 + AlR3, TiCl4/MgCl2 + Al(i‐Bu)3 + EB, TiCl4/EB/MgCl2 + Al(i‐Bu)3 and TiCl4/EB/MgCl2 + Al(i‐Bu)3 + EB, was studied by means of ESR. The ESR data and the catalytic properties were compared. It could be shown that the introduction of ethyl benzoate (EB) leads to an increase of stereospecificity, to a considerable increase of the portion of Ti3+ ions which can be observed by ESR, to the appearance of several new signals in the ESR spectra and to an increase of the portion of titanium in solution, removed from the solid catalyst during the interaction with the organoaluminium cocatalyst. Titanium ions are found mainly in the particles or surface associates whose Ti3+ ions produce no signals in the ESR spectra, Ti3+ ions observed by ESR are found to be inactive centers of polymerization. The active centers appear to be localized in highly dispersed particles or surface associates of TiCl3, formed on the MgCl2 surface and are not revealed in the ESR spectra. Increasing stereospecificity in the presence of EB is assumed to be caused by deactivation of non‐stereospecific active centers with ethyl benzoate.

Performance of combined cobalt—nickel—zirconia and HZSM‐5 catalyst systems for carbon monoxide hydrogenation

AbstractThe synthesis of hydrocarbons via hydrogenation of carbon monoxide was investigated over cobalt—nickel—zirconia catalysts of various compositions in combination with zeolite HZSM‐5 in “mixed bed” and “follow bed” arrangements. These combinations resulted in the formation of aromatics in amounts as high as 30‐35 wt% under relatively mild operating conditions (1 atm, 250–280°C). Although the olefinicity of C2 and C3 fractions in the product stream was higher in the mixed bed compared to the follow bed arrangement, the selectivities to aromatics were comparable in the two bed arrangements. The aromatic selectivity was found to be sensitive to operating conditions. The formation of aromatics was favored at high HZSM‐5/metal catalyst ratios, low space velocities and high reaction temperatures. The product distributions obtained using various metal/zeolite bifunctional catalysts have been discussed.

Study of the state of titanium ions and the composition of the active component in titanium‐magnesium catalysts for ethylene polymerization

AbstractThe state of Ti3+ ions formed at various steps of preparation and activation of highly active titanium‐magnesium catalysts of various composition (dry milling of TiCl3 with MgCl2; reduction of TiCl4 by nonsolvated magnesium dialkyl; interaction of the TiCl4/MgCl2 system with an organoaluminium compound) was studied by the ESR method. It was found that in all systems studied the same three types of Ti3+ ions in the chlorine environment are formed, differing in coordination and localization sites in MgCl2. The content of these ions depends on the composition and preparation conditions of the catalysts, and does not exceed 20% of the total content of titanium. Most of the Ti3+ ions formed in all systems enter the composition of particles or surface aggregates of TiCl3 and appear in the ESR spectra only after dissolution of the sample in pyridine. The active centers of titanium‐magnesium catalysts are supposed to be constituents of these particles or of surface aggregates.

Transition Periods of the Activity of Co‐Mo/Al2o3 Catalysts in Thiophene Hydrodesulfurization

AbstractHydrodesulfurization (HDS) of thiophene was studied over Co‐Mo/Al2O3 catalysts of various composition. Sulfidation was carried out by the reactant itself, alternating with dimethylsulfoxide. Mo‐rich catalysts reached their maximum activity level when the upper limit of sulfidation was not higher than 15%. From 50–60% sulfidation, a slow activity decrease appeared. Co‐rich catalysts reached very rapidly (2–3% sulfidation) a very low, very stable activity level. The C4‐selectivity was 80–96% at the quasi‐constant activity level. Butane yields were roughly proportional to the HDS activity. The predominance of cis‐2‐butenes permitted us to suggest a mechanism for thiophene HDS.

Electron microscopic and chemisorption studies of the dispersity of supported rhodium catalysts of various compositions

The dispersity and size distribution of metal particles in mono- and bimetallic rhodiumcontaining catalysts prepared via decomposition of SiO2- and Al2O3-supported complexes and impregnation of the support by inorganic metal compounds have been studied.

Study of copolymerization of ethylene with hex-1-ene on applied catalysts

A study was made of copolymerization of ethylene with hex-1-ene on applied catalysts of various compositions which, according to activity at temperatures of 80–90° occupy the following order: Zr(C 3H 5) 3Cl : SiO 2 ⪡ CrO 3 : SiO 2−Al 2O 3 ⪡ TiCl 4 : : MgCl 2 + Al(C 2H 3) 3. It was found that with low concentrations (up to 2–3 mole %) of hex-1-ene in the reaction mixture the rate of copolymerization is 2·5–3·0 times higher than in homopolymerization of ethylene on chromic oxide and titanium-magnesium catalysts. It was shown that other α-olefin monomers of linear structure have a similar effect on the rate of copolymerization with ethylene. The α-olefins examined occupy the following order, according to their effect on the rate of copolymerization with ethylene on a chromic oxide catalyst: 3-methylpent-1-ene<4-methylpent-1-ene<hept-1-ene<hex-1-ene<pent-1-ene<propylene. The main properties of homo- and copolymers of ethylene were investigated.

Acid-base and catalytic properties of Al 2O 3ZnO

Alumina-zinc oxide catalysts of various compositions were prepared from their nitrates by coprecipitation and the acidic and basic properties were measured by titrations with n-butylamine and benzoic acid using various indicators. The acidities (the numbers of acid sites) at H 0 = −3.0 and H 0 = −5.6 of Al 2O 3ZnO catalysts prepared from their nitrates, were found to be lower than those of Al 2O 3ZnO catalysts prepared from their chlorides by the same method. With the increase in ZnO content, the acidities per unit surface area decreased monotonously, whereas a maximum basicity was observed on Al 2O 3ZnO (1:1), the highest base strength (p K a ) being 12.2. The activity change for alkylation of phenol with methanol was correlated well with the acidity change and the highest selectivity (almost 100%) for formations of ortho products, o-cresol and 2,6-xylenol, was observed on Al 2O 3ZnO (1:9). Isomerization of 1-butene was suggested to proceed on basic sites on Al 2O 3ZnO catalysts. In isomerization of 3-carene (I), the selectivity for formation of 2-carene (II) was more than 90% over Al 2O 3ZnO (1:9). From poisoning experiments with CO 2 and pyridine, the active sites for formation of 2-carene were concluded to be both acidic and basic sites.

Selectivities of bismuth vanadate catalysts for toluene oxidation

Oxidation of toluene vapors over fused bismuth vanadate catalysts of various compositions in fixed bed has been studied. The optimum conversion of toluene to benzaldehyde is related to the Bi2O3 content of the catalyst. The composition Bi2O3−V2O5(25∶75) and Bi2O3−V2O5 (40∶60) are highly active and selective for the oxidation of toluene to benzaldehyde.

Effect of composition on the activity of aluminum-chromium-potassium isopentane dehydrogenation catalysts

1. A study has been made of the catalytic properties of aluminum-chromium-potassium catalysts of various compositions as exhibited in the dehydrogenation of isopentane to isoamylenes. 2. A comparison has been made between the catalytic and some other properties of the ACP catalysts and their surface features and structure. 3. The most active ACP catalysts were the ones which contain 9–17% chromium oxide and 2–3% by weight of potassium oxide and had the smallest pore diameters (38–45 A) and the largest specific surface (175–183 m2/g). 4. The spinel structure phase is catalytically more active than the corundum phase in dehydrogenating isopentane to isoamylenes. 5. The maximum activity of ACP catalysts in the dehydrogenation of isopentane to isoamylenes occurs for the composition which gives maximum strength.