Unmodified Catalyst Research Articles

Hydroformylation of propylene using unmodified cobalt carbonyl catalyst: selectivity studies

Isomer distribution and kinetics of the formation of n-butyraldehyde and isobutyraldehyde have been determined for the hydroformylation of propylene using unmodified cobalt carbonyl catalyst. Effects of the propylene and catalyst concentrations and the partial pressures of carbon monoxide and hydrogen on the n/iso ratio as well as on the individual reaction rates have been measured in a temperature range of 383-423K and a pressure range of 35-100 bar. An empirical rate model describing the intrinsic kinetics for each butyraldehyde has been proposed and its kinetic parameters evaluated. Such information is useful for the preferential production of n-butyraldehyde

Hydroformylation of propylene using an unmodified cobalt carbonyl catalyst: a kinetic study

The kinetics of hydroformylation of propylene using an unmodified cobalt carbonyl catalyst has been investigated in a temperature range of 383-423K and a pressure range of 35-100 bar. Effects of the propylene and catalyst concentrations and the partial pressures of carbon monoxide and hydrogen on the rate of hydroformylation have been measured. Initial rates were found to be in the kinetic regime for the intensively stirred reactor used. An empirical rate model has been proposed, which was found to represent the rate data with a standard deviation of 7%. Its two kinetic parameters were evaluated, and the activation energy was found to be 77 kJ/mol

Promoting effect of fluorine on cobalt—molybdenum/ titania hydrodesulfurization catalysts

The effect of fluoride incorporation on the titania support on the surface structure of promoted cobalt-molybdenum catalysts and their catalytic activity for thiophene hydrodesulfurization (HDS) has been studied. The relative activity between fluoride-modified and unmodified catalysts was found to be maximum and close to 5 for a fluorine content of 0.8 wt.-%. From high-resolution electron microscopy (HREM) examination of sulphided samples, the increase in HDS could be partly explained by smaller molybdenum sulphide crystallites (increase in the dispersion of the active phase). Diffuse reflectance spectroscopy (DRS) of the oxidic precursors shows that the effect of fluoride incorporation is also to increase the amount of the Mo VI in tetrahedral surroundings and to enhance the part of cobalt involved in the generation of the “CoMoS” active phase (probably cobalt in octahedral symmetry).

A TPD and XPS investigation of palladium on modified alumina supports used for the catalytic decomposition of methanol

A series of modified palladium catalysts on alumina supports previously have been prepared and evaluated for selectivity, activity, and thermal stability in decomposing methanol into CO and H 2. In this investigation the modified palladium catalysts are characterized by X ray photoelectron spectroscopy (XPS) and CO and NH 3 temperature-programmed desorption (TPD). Average particle sizes of the palladium crystallites were also determined using chemisorption techniques. The XPS results indicate that the lithium-modified catalyst, which deactivated substantially during methanol decomposition testing, exhibited a significant build-up of carbon on the catalyst surface, while a similar accumulation was not observed for the lanthanum-modified catalyst under identical conditions. The CO TPD results show that the lithium-, sodium-, and barium-modified catalysts, which deactivate during methanol decomposition testing, produce a much greater amount of CO 2 relative to the amount of CO desorbed than do the potassium-, rubidium-, cesium-, and lanthanum-modified and the unmodified catalysts, which do not deactivate considerably under identical conditions. Ammonia TPD and chemisorption results indicate that no correlation exists between support acidity or particle size and the degree of CO dissociation. Finally, a correlation between the charge density of the modifier and the degree of CO disproportionation is presented which fits for all cases except one. This appears to support an electrostatic model for the promotion of CO bond cleavage by the alkali modifier.

Identifying the functions of nickel in the attenuation of H 2S emissions from three-way automotive catalysts

The design of new automotive catalyst formulations requires development of laboratory tests which mimic the vehicle exhaust-gas fluctuations encountered by a three-way converter. Under specific vehicle operating conditions, an unmodified three-way catalyst (comprising precious metals on CeO 2-Al 2O 3) can emit a ‘spike’ of hydrogen sulphide. A laboratory test to emulate these spike conditions requires a gas-feed that contains SO 2, a sudden change in gas composition from fuel-lean (oxidising) to fuel-rich (reducing), and an operating temperature > ca.500°C. The emission of H 2S can be prevented by adding a nickel-containing precursor to the catalyst. Using a simplified gas mixture (H 2S/N 2) it can be shown that surface NiO is capable of acting as an ‘H 2S getter’ and that it can be reactivated by exposure to an oxidising atmosphere. However, tests in which spike conditions have been emulated do not show a simple correlation between attenuation and sulphur retention by NiO. The results are considered in the light of a recent computational study which indicated that NiO should form NiSO 4 under lean conditions, and then release oxygen (or consume hydrogen) when the gas-stream becomes reducing. We conclude that nickel-containing automotive catalysts can attenuate H 2S in the following ways: 1. by preventing its formation; 2. by trapping it once it appears in the gas-phase.

Characterization of ZrO 2-SiO 2 unmodified or modified with H 2SO 4 and acid catalysis

A series of ZrO 2-SiO 2 catalysts with various molar ratios of ZrO 2/SiO 2 were prepared by a coprecipitation method. The characterization of catalyst unmodified or modified with H 2SO 4 was performed using XRD, IR and XPS methods, and by the measurement of surface area. Mixing with amorphous SiO 2 or modifying with H 2SO 4 shifted the transition of ZrO 2 from the amorphous to tetragonal phase to a higher temperature. The catalytic activities for 2-propanol dehydration and cumene dealkylation were correlated with both acidity and acid strength of the catalyst, and the modification of catalyst with H 2SO 4 enhanced the catalytic activities remarkably. The difference in catalytic activities between modified and unmodified catalysts increased with increasing ZrO 2 content.

ChemInform Abstract: Enhanced Oxygen Storage Capacity of Cerium Oxides in CeO2/La2O3/Al2O3 Containing Precious Metals.

AbstractPt/Rh‐modified CeO2/Al2O3 and CeO2/La2O3/Al2O3 catalysts prepared by impregnation with an aqueous solution of H4PtCl6 and RhCl3 are found to have larger oxygen storage capacities (OSC) than the corresponding unmodified catalysts.

The influence of TiO 2 on the speciation and hydrogenation activity of Co/Al 2O 3 catalysts

The influence of TiO 2 on the distribution of supported species in 3 wt% Co/Al 2O 3 catalysts has been examined by X-ray diffraction, X-ray photoelectron spectroscopy (ESCA), Raman spectroscopy (LRS), and gravimetric analysis. The results show that for unmodified catalysts with low Ti loadings (<4 wt% Ti) the Co phase is present primarily as Co 3O 4 with lesser amounts of surface octahedral and tetrahedral cobalt [Co(o); Co(t)]. For catalysts having high Ti contents, Co 3O 4 formation is suppressed with increasing Ti loadings in favor of a CoTiO 3-like surface phase. Benzene and CO hydrogenation activity measurements indicate that Ti addition decreases the catalytic activity for both reactions. This has been attributed primarily to site blocking which results from the migration of reduced Ti species.

Study of propene metathesis on MoO3−x/Al2O3 catalysts; effect of diazomethane decomposition

AbstractPropene metathesis has been studied at 295 K and 1 atm in He or in H2 with MoO3−x/Al2O3 catalysts which were reduced at 673 K. Some catalysts were modified by exposing them to diazomethane vapor prior to testing. The diazomethane was synthesized shortly before use; it was stored by dissolving its vapor in di‐n‐butyl phthalate. Metathesis of the unmodified catalysts revealed an induction period during which the activity increased; this period is markedly shorter in H2 than in He. In He, metathesis is the sole reaction, in H2 it is accompanied by a prevailing hydrogenolysis. No induction period is visible for catalysts modified with diazomethane in accordance with the assumption that surface carbenes are reaction intermediates. The activity is, however, lowered by this treatment, as catalyst deactivation is enhanced by the pretreatment with diazomethane.

Lead modified platinum on carbon catalyst for the selective oxidation of (2−) hydroxycarbonic acids, and especially polyhydroxycarbonic acids to their 2-keto derivatives

D-Gluconic acid has been oxidised with oxygen and air at 55 C in water, using Pt/C catalysts. The primary hydroxyl group is preferentially oxidised using an unmodified catalyst. Addition of a lead(II)salt changes the preference dramatically towards oxidation at the position α to the car☐yl group. Study of the kinetics of the reactions is complicated by catalyst deactivation caused by as well oxygen as by (side)product adsorption. For the oxidation of D-gluconic acid to 2-keto-D-gluconic acid a dehydrogenation mechanism is proposed in which the α-H is activated by Pb II-complexation of the car☐yl- and α-OH functions at the Pt-site.

The selective oxidation of aldoses and aldonic acids to 2-ketoaldonic acids with lead-modified platinum-on-carbon catalysts

Aldoses and aldonic acids have been oxidised with oxygen and air at 55° in water, using Pt/C catalysts. After oxidation of the reducing group, if available, the primary hydroxyl group is preferentially oxidised using an unmodified catalyst. Addition of a lead(II) salt changes the preference dramatically toward oxidation at the position α to the carboxyl group. Provided that oxygen transfer to the liquid phase is carefully controlled in order to prevent deactivation of the catalyst, 2-ketoaldonic acids can be prepared in high yields.

Ziegler‐type propene polymerization catalyst systems involving tributyl phosphite as modifier

AbstractTributyl phosphite (1) was studied as modifier of heterogeneous TiCl3/(C2H5)2AlCl propene polymerization catalyst systems. When used as the sole modifier, 1 was found to produce catalyst systems with substantially improved stereospecificity and only slightly depressed activity relative to the unmodified catalyst system. Binary modifier packages consisting of 1 and bis‐(tributyltin) sulfide lead, apparently through synergism, to catalyst activities surpassing that of the unmodified catalyst system and to excellent stereospecificity (hexane extractables; 1,6–2,1%). Catalyst systems modified with 1 and triphenylantimony sulfide were also demonstrated to exhibit activities approaching or even exceeding that of the unmodified catalyst system with 2,1–2,3% hexane extractables, while systems involving 1 and triethyl thiophosphate as modifiers are more stereospecific (hexane extractables: 1,80%), but somewhat less active than the preceding system. Possible interactions and reactions of 1 with the components of the catalyst system are discussed.

Polymerization of propylene with TiCl3–AlEt2Cl–trilauryltrithiophosphite catalyst

AlEt3Cl was modified with TLTTP (trilauryltrithiophosphite) in the catalyst system consisting of TiCl3 and AlEt2Cl. The effects of TLTTP on the polymerization of propylene were studied in comparison with those of alkyl homologues of TLTTP. The catalytic behavior of the TiCl3–AlEt2Cl-TLTTP catalyst system in the polymerization of propylene was also studied in comparison with that of the TiCl3–AlEt2Cl catalyst system. In the study of the effect of various alkylthiophosphites added, it is found that the bulkiness of the alkyl group affects the rate of propylene polymerization and the stereoregularity of the resultant polymers. The TiCl3–AlEt2Cl–TLTTP catalyst system gave different catalytic behavior in the propylene polymerization from that of the unmodified conventional catalyst system (TiCl3–AlEt2Cl). These effects of TLTTP were considered to be due to the bulkiness of the alkyl groups attached to the phosphorous atom and the higher reactivity to TiCl3 of the modified AlEt2Cl than of the unmodified AlEt2Cl.

Effects of substituents in aromatic amine N‐oxide and amine modifiers on ziegler‐type propylene polymerization catalyst performance

AbstractStudies of the effects of ring substituents in aromatic amine N‐oxide or amine modifiers on Ziegler‐type propylene polymerization catalyst performance are reported. Among sterically hindered amines or N‐oxides, the o,o‐dimethyl substituted derivatives provide the best stereospecificity with little loss in activity. On the other hand, m‐ or p‐substituted derivatives with electron‐withdrawing substituents were found to activate the catalyst, producing higher yields relative to the unmodified (TiCl3‐Al alkyl) catalyst system. The inductive and steric effects introduced by the modifiers in the catalyst system are discussed. Aromatic amine N‐oxides generally produce less active catalyst systems relative to their parent amines, owing presumably to a redox reaction between the N—O function and Ti3+.

Cu-Ni/aerosil catalysts modified with RR-(+)-tartaric acid

1. The catalytic and asymmetrizing properties of copper-nickel catalysts deposited on Aerosil in the hydrogenation of acetylacetone have been investigated. 2. The adsorption of acetylacetone on these catalysts modified with RR-(+)-tartaric acid and the unmodified catalysts has been studied by IR spectroscopy. 3. A synergistic effect of the catalytic, asymmetrizing, and adsorption properties of the copper-nickel catalysts has been found. 4. The results obtained are in harmony with the idea of the occurrence of the asymmetric hydrogenation of acetylacetone through a mixed-ligand complex of the [substrate-modifying agent-catalyst] type.

Acetaldehyde as Main Product of the Oxidation of Ethylene Oxide on a Silver Catalyst

False conclusions about the relevance of a process in heterogeneously catalyzed reactions can be drawn if this process is examined in isolation. Thus ethylene is oxidized on an unmodified Ag catalyst to ethylene oxide which can undergo “after‐combustion” to CO2 and H2O. In contrast, when examined in isolation under the same conditions, ethylene oxide isomerizes to acetaldehyde. Ethylene appears to block the catalyst sites necessary for this reaction.

The reduction of nitrogen monoxide with ammonia on the activated surface of steel plates. 2. Catalyst with high durability against sulfuric acid.

The resistance to the effects of SO3 on the activity of the catalyst prepared from a mild steel plate was improved by addition of a vanadium compound and by calcination at temperature above 600°C. The reaction kinetics of NO reduction with NH3 on the modified catalyst can also be expressed by the equation, -1/KNH3(PNH3in-PNOin)•ln(1-x)PNH3in/PNH3in-xPNOin-ln(1-x)=k'RPT√KO2inPO2in/1+KH2OPH2Oin+√KO2PO2in•A/Fwhich was originally proposed for the reaction kinetics on the unmodified catalyst.1)The durability of a modified catalyst of the honeycomb form was verified by the results of the catalyst life tests done with the flue gas from a heavy oil fired boiler.

Stereospecific polymerization of methacrylonitrile. IV. Polymerization by ate complex‐type catalysts

AbstractMethacrylonitrile was polymerized by a number of ate‐complex catalysts. The catalysts used were NaAlR4, LiAlR4, LiZnR3, Li2ZnR4, RMg[AlR4], and Mg[AlR4]2. It was found that the ate‐complex catalysts in which one of the alkyls is replaced by a diphenylamino group are capable of producing polymers with higher degrees of crystallinity than those of polymers obtained by unmodified catalysts. It was shown that the diphenylamide linkage in these catalytic systems must play an important role in the steric control in the propagation steps of this type of polymerization, although the mechanism is not clear at present. The crystallinity index used in this research gave a linear relation against I measured by NMR, and can be used as a measure of the stereo‐regularity of the polymer.

Studies on the Action of Promotors and Carriers of Cobalt and Nickel Catalysts for the Fischer-Tropsch Synthesis

The action of promotors and carriers of the Cobalt and Nickel catalysts for Fischer-Tropsch synthesis reaction was discussed. The experiments were carried out by an by an ordinary fixed bed-flow system reactor at 150-300° and 100, - 400 space velocity under atmospheric pressure. Co and Ni catalysts, unmodified metallic and variously modified with kieselguhr and ThO2 were examined. At 190°, unmodified metallic Co catalyst produces large amounts of gaseous hydrocarbons, above 98% of which is methane, but produces no liquid hydrocarbons. By some treatments, such as slight pre-carburization or addition of little amounts of various volatile substances into synthesis gas, the unmodified metallic Co catalyst gave higher homologs of hydrocarbon. It was also found that the higher the degree of modification is the higher the degree of unsaturation of products is. For nickel catalysts the same facts were observed. According to these experimental facts, it is concluded that, in the case of unmodified metallic catalysts the velocity of hydrogenation reaction (Vn) is too large comparing with the velocity of C-C bond formation (Vp) to produce liquid hydrocarbons, and that kieselguhr, ThO2 or little amounts of added substances act to establish a suitable relationship between Vp and Vh. A catalyst, which is not modified permanently but is controlled temporarily by a teat-ment, maintains a controlled activity to give liquid hydrocarbons during prolonged reaction.

Influence of donor‐type impurities on the polymerization of propylene catalyzed by a titanium trichloride‐triethylaluminum system

AbstractThe influence of some typical oxygen‐, sulfur‐, and nitrogen‐containing impurties on the polymerization of propylene in a hydrocarbon medium under the catalytic action of titanium trichloride and triethylaluminum was studied. Both these catalyst components used in polar‐coordinated polymerizations of α‐olefins are very reactive toward substances having atoms with a free electron pair. Triethyl aluminum forms complex compounds with these substances. Some of the complexes are so stable as to allow distillation; attempts to isolate the original components often lead to the destruction of the whole molecule. Donor‐type compounds do not attack triethylaluminum only; they also attack titanium trichloride which displays the properties of a strong sorbent. The transitional metal (Ti) with incompletely occupied d‐orbits and a lone electron gives ample opportunities for chemisorbing molecules of olefins as well as molecules containing atoms of the fifth and sixth groups of the periodic table. Donor‐type substances were studied on the one hand from the viewpoint of the interaction with the separate catalyst components (the influence of the so modified catalyst on the polymerization being studied) and on the other hand from the viewpoint of the influence of the donor‐type substance during the course of polymerization, i.e., the effect on both unmodified catalyst components (including the active complex) simultaneously. Changes of the principal characteristics of the polymerization process (viz., the overall rate of reaction, the molecular weight, and the percentage of amorphous matter) have been followed. It became evident that the interaction between the donors and the solid phase of the catalyst is governed by rules of adsorption (excluding cases involving deeper changes of the solid phase during the reaction, e.g., its dissolution). Compounds which are sorbed influence the polymerization process in a significant manner. They come into play more intensely than the products of the interaction of donor‐type substances with triethylaluminum which generally result in the formation of complex compounds not influencing the course of polymerization so strongly. It has been found that from among the characteristics studied the overall rate of polymerization is the one which is most affected by the presence of substances with free electron pairs. With minor exceptions the molecular weight was found to increase through the agency of the admixtures. A similar relationship has been found to hold for the percentage of amorphous matter as well.