Active Form Of Catalyst Research Articles

Catalytic Synthesis of Butene-1 and Hexene-1 in the Homogeneous Oligomerization of Ethylene in the Presence of Nickel Complexes Based on N-Heteroaryl-Substituted α-Diphenylphosphinoglycines

It has been experimentally shown that N-heteroaryl-substituted α-diphenylphosphinoglycines N-(pyrazin-2-yl)-α-diphenylphosphinoglycine, N-(pyridin-2-yl)-α-diphenylphosphinoglycine and N-(pyrimidin-2-yl)-α-diphenylphosphinoglycine obtained by the reaction of three-component condensation of diphenylphosphine, the corresponding primary amine and glyoxylic acid monohydrate are capable in combination with Ni(COD)₂, where COD is cyclooctadiene-1,5, to form active forms of catalysts for selective homogeneous dimerization and trimerization of ethylene with the formation of butene-1 and hexene-1 as the main products. It has been established that the obtained organo-nickel catalytic systems provide a yield of short-chain (C₄–C₆) olefins at the level of 90% with a selectivity for linear α-olefins of 97%. The study of the influence of temperature on the process of homogeneous ethylene oligomerization using the obtained compounds made it possible to establish that the optimal temperature for ethylene oligomerization, providing the highest selectivity to butene-1 and hexene-1, is 80–105°C at the optimum pressure of ethylene is 20–35 atm. Under these conditions, the selectivity for butenes is 71.4–72.6% (selectivity for butene-1 – 69.3–71.1%), for hexenes 20.6–21.2% (selectivity for hexene-1 – 19.2–19.5%), and the optimal duration of the oligomerization process at a temperature 105°C is 1.5 h, which provides the rate of formation of butene-1 equal to 168.1 golig gNi⁻¹h⁻¹) and the rate of formation of hexene-1 – 47.3 golig gNi⁻¹h⁻¹).

Structural subtleties and catalytic activity of sodium aminophenolate complexes in polylactide degradation: towards sustainable waste management solutions.

This study explores the intricate coordination chemistry of sodium aminophenolate species and their significant role in the depolymerization of polylactide (PLA), offering novel insights into catalytic degradation processes. By examining sodium coordination entities, including dimers and larger aggregates such as tetramers, we reveal how structural modifications, particularly the manipulation of steric hindrances, influence the formation and stability of these complexes. The dimers, characterized by a unique four-center core (Na-O-Na-O), serve as a foundational motif, which is further elaborated to obtain complexes with varied coordination environments through strategic ligand design. Our research delves into the lability of the amino arm in these complexes, a critical factor that facilitates the coordination of PLA to the sodium center, thereby initiating the depolymerization process. Moreover, DFT studies have been pivotal in identifying the most energetically favorable structures for catalysis, highlighting a distinct preference for an eight-membered ring motif stabilized by intramolecular hydrogen bonds. This motif not only enhances the catalyst's efficiency but also introduces a novel structural paradigm for sodium-based catalysis in PLA degradation. Experimental validation of the theoretical models was achieved through NMR spectroscopy, which confirmed the formation of the active catalyst forms and monitored the progress of PLA degradation. The study presents a comprehensive analysis of the influence of ligand structure on the catalytic activity, underscoring the importance of the eight-membered ring motif. Furthermore, we demonstrate how varying the steric bulk of substituents on the amino arm affects the catalyst's performance, with benzyl-substituted ligands exhibiting superior activity. Our findings offer a profound understanding of the structural factors governing the catalytic efficiency of sodium aminophenolate complexes in PLA degradation. This research not only advances the field of coordination chemistry but also presents a promising avenue for the development of efficient and environmentally friendly catalysts for polymer degradation.

Ferrocene-based catalysts for in-situ hydrothermal upgrading of heavy crude oil: Synthesis and application

In this work, the effect of synthesized Ferrocene-based ligand catalysts, including Mono-, Di- and Tri-Ferrocene, as additives for promoting the catalytic in-situ hydrothermal upgrading of Tatarstan (Russia) heavy crude oil was studied. In addition, the changes in composition of upgraded oil samples as well as the in-situ transformation and characteristics of used catalysts were evaluated in detail using comprehensive analyzing techniques. All of the catalytic and non-catalytic hydrothermal upgrading experiments were carried out under the steam stimulation conditions at 300 °C, 72 bar (1044.27 psi) and 24 h of reaction time. The results show that introducing Ferrocene-based ligand catalysts to the upgrading system promotes the in-situ upgrading of heavy crude oil and improves the physical and chemical properties of upgraded oil samples. The maximum viscosity reduction was observed in presence Tri-Ferrocene and reached around 40% compared to non-catalytic hydrothermal upgrading. In addition, the upgrading performance also reflects in increase of H/C ratio, reduction of sulfur content, increase of saturates and aromatics, and decrease of the content of resins and asphaltenes as well as a noticeable change (increase) in the light fractions of C10-C20 are observed for all upgraded oil samples. Mono-Ferrocene as an oil-soluble catalyst mainly transformed to the particles of Fe3O4 (Magnetite) and FeS, which can act as active forms of catalysts and accelerate the hydrothermal conversion of heavy crude oil and its heavy fractions including resins and asphaltenes. These transformations were confirmed using XRD, SEM-EDX and Mössbauer analyzing techniques. Generally, the good catalytic performance of used ferrocene-based ligand catalysts as well as their low cost and commercial availability makes them great potential catalysts for improving the efficiency of steam injection for heavy oil production and in-situ upgrading.

Surface properties of wustite based iron-cobalt catalysts for ammonia synthesis reaction

In this work, surface properties of wustite-based iron and iron‑cobalt catalysts were investigated. Measurements of hydrogen temperature-programmed desorption (TPD-H2) and surface area of active forms of catalysts were conducted after reduction of catalyst precursors (16 h) in pure hydrogen at various temperatures (450, 475, 500, 550 and 600 °C). The amount of cobalt in the catalyst structure and the number of adsorption sites relative to hydrogen were correlated with the activity for ammonia synthesis reaction. The presence of cobalt increased thermal resistance of the catalysts and at the same time their activity in ammonia synthesis reaction.

Catalyst for Selective Hydrogenolysis of Glycerol, Prepared from Hydrotalcite-Like Structures

A process of transforming hydrotalcite, containing Cu–Zn–Al (2:1:1) to a catalysts for selective hydrogenolysis of glycerol to 1,2-propanediol has been studied. A two steps process, consisted of the calcination at increased temperature and subsequent reduction with hydrogen, as well as a one step process, in which the hydrotalcite was heated at hydrogen atmosphere so the calcination and reduction were joined to one operation, were verified experimentally. The influence of the temperature in the calcination step in the two steps process on composition, texture and catalytic properties of the active form of catalyst has been studied in detail. X Ray diffraction, thermogravimetric analyses, nitrogen physisorption, mercury porosimetry, temperature-programmed reduction and high-resolution transmission electron microscopy were used for the catalysts characterization. A study of calcination of a Cu–Zn–Al containing hydrotalcite at different temperatures showed, that at temperature ending with 350 °C, predominantly amorphous, mixed oxides containing phase was formed. The most active and most selective catalyst was obtained by the reduction of this amorphous oxide phase. In contrary, highly crystalline material was obtained at higher calcination temperatures, i.e at 450 or 700 °C respectively, but the activity of the reduced form of these crystalline oxides was lower. It was also proven, that by simultaneous calcination and reduction, a catalyst of the same activity and even better selectivity towards 1,2-propanediol could be prepared, comparing with the catalyst prepared by the two steps method.

Erratum to: Modified hydrotalcites as precursors for catalysts effective in the hydrogenolysis of glycerol to 1,2-propanediol

A series of hydrotalcite-like materials containing Al, Cu and one other bivalent metal, selected from the group Ni, Fe, Co and Zn, were prepared in the frame of this study. These hydrotalcite-like structures were used as precursors of the catalysts for the hydrogenolysis of glycerol. The hydrotalcites were converted to active forms of catalysts by calcination at a programmed temperature, increasing with the speed of 2 °C/min, up to 350 °C and reduction by hydrogen at 350 °C and 7 MPa. The catalysts were characterized by XRD, TGA, TPR, TPD, HRTEM, Hg porosity and N2 physisorption. The catalyst containing Zn exhibited the highest activity and selectivity to 1,2-propanediol in the hydrogenolysis of glycerol despite the fact that it had lowest internal surface area from all the catalysts studied. Its activity was attributed to its specific pore volume distribution with highest fraction of wider macropores in the range between 1 and 10 µm, remarkably distinguishing this catalyst from all the other catalysts studied.

Mechanistic implications in the phosphatase activity of Mannich-based dinuclear zinc complexes with theoretical modeling.

An "end-off" compartmental ligand has been synthesized by an abnormal Mannich reaction, namely, 2-[bis(2-methoxyethyl)aminomethyl]-4-isopropylphenol yielding three centrosymmetric binuclear μ-phenoxozinc(II) complexes having the molecular formula [Zn2(L)2X2] (Zn-1, Zn-2, and Zn-3), where X = Cl(-), Br (-), and I (-), respectively. X-ray crystallographic analysis shows that the ZnO3NX chromophores in each molecule form a slightly distorted trigonal-bipyramidal geometry (τ = 0.55-0.68) with an intermetallic distance of 3.068, 3.101, and 3.083 Å (1-3, respectively). The spectrophotometrical investigation on their phosphatase activity established that all three of them possess significant hydrolytic efficiency. Michaelis-Menten-derived kinetic parameters indicate that the competitiveness of the rate of P-O bond fission employing the phosphomonoester (4-nitrophenyl)phosphate in 97.5% N,N-dimethylformamide is 3 > 1 > 2 and the kcat value lies in the range 9.47-11.62 s(-1) at 298 K. Theoretical calculations involving three major active catalyst forms, such as the dimer-cis form (D-Cis), the dimer-trans form (D-Trans), and the monoform (M-1 and M-2), systematically interpret the reaction mechanism wherein the dimer-cis form with the binuclear-bridged hydroxide ion acting as the nucleophile and one water molecule playing a role in stabilizing the leaving group competes as the most favored pathway.

Mechanistically Driven Development of Iridium Catalysts for Asymmetric Allylic Substitution

Enantioselective allylic substitution reactions comprise some of the most versatile methods for preparing enantiomerically enriched materials. These reactions form products that contain multiple functionalities by creating carbon-nitrogen, carbon-oxygen, carbon-carbon, and carbon-sulfur bonds. For many years, the development of catalysts for allylic substitution focused on palladium complexes. However, studies of complexes of other metals have revealed selectivities that often complement those of palladium systems. Most striking is the observation that reactions with unsymmetrical allylic electrophiles that typically occur with palladium catalysts at the less hindered site of an allylic electrophile occur at the more hindered site with catalysts based on other metals. In this Account, we describe the combination of an iridium precursor and a phosphoramidite ligand that catalyzes enantioselective allylic substitution reactions with a particularly broad scope of nucleophiles. The active form of this iridium catalyst is not generated by the simple binding of the phosphoramidite ligand to the metal precursor. Instead, the initial phosphoramidite and iridium precursor react in the presence of base to form a metallacyclic species that is the active catalyst. This species is generated either in situ or separately in isolated form by reactions with added base. The identification of the structure of the active catalyst led to the development of simplified catalysts as well as the most active form of the catalyst now available, which is stabilized by a loosely bound ethylene. Most recently, this structure was used to prepare intermediates containing allyl ligands, the structures of which provide a model for the enantioselectivities discussed here. Initial studies from our laboratory on the scope of iridium-catalyzed allylic substitution showed that reactions of primary and secondary amines, including alkylamines, benzylamines, and allylamines, and reactions of phenoxides and alkoxides occurred in high yields, with high branched-to-linear ratios and high enantioselectivities. Parallel mechanistic studies had revealed the metallacyclic structure of the active catalyst, and subsequent experiments with the purposefully formed metallacycle increased the reaction scope dramatically. Aromatic amines, azoles, ammonia, and amides and carbamates as ammonia equivalents all reacted with high selectivities and yields. Moreover, weakly basic enolates (such as silyl enol ethers) and enolate equivalents (such as enamines) also reacted, and other research groups have used this catalyst to conduct reactions of stabilized carbon nucleophiles in the absence of additional base. One hallmark of the reactions catalyzed by this iridium system is the invariably high enantioselectivity, which reflects a high stereoselectivity for formation of the allyl intermediate. Enantioselectivity typically exceeds 95%, regioselectivity for formation of branched over linear products is usually near 20:1, and yields generally exceed 75% and are often greater than 90%. Thus, the development of iridium catalysts for enantioselective allylic substitution shows how studies of reaction mechanism can lead to a particularly active and a remarkably general system for an enantioselective process. In this case, a readily accessible catalyst effects allylic substitution, with high enantioselectivity and regioselectivity complementary to that of the venerable palladium systems.

Aging Studies of Voltammetrically Dealloyed Pt-Cu Nanoparticle ORR Electrocatalysts

Voltammetrically dealloyed Pt-Cu alloy nanoparticles show significantly improved Pt-mass and specific activities for the oxygen reduction reaction in acidic media in both RDE and MEA configurations. The active phase of the catalyst is prepared from very Cu-rich precursor materials which are formulated into catalyst inks and electrode layers. The high Cu content of the precursor materials raises fundamental and practical questions as to the molecular stability / oxidation state of the Cu rich catalyst surface and the shelf-life of precursor powders, inks and electrode layers. Here we present aging studies of a carbon-supported Pt25Cu75 nanoparticle catalyst precursor. We monitored how the surface area (ECSA) and the oxygen electroreduction (ORR) reactivity of dealloyed precursors (active form of catalyst) change as a function of the exposure time to air of the Pt25Cu75 precursor at room temperature. Similarly, we aimed to investigate how ECSA and ORR of the active catalyst changed with the time the liquid catalyst ink was exposed to air. We find little detrimental effect of air aging of the precursor on ORR activity over the time scales investigated. The effect of air aging of the catalyst inks is more complex, however. Initially, aged inks show increased ORR reactivity, that is, aged inks result in more active catalyst layers. After about 4-5 days of aging of the inks in air, however, we observed a drop in ORR activity of the resulting catalyst layers. This complex aging behavior of the inks seems independent of prior air aging of the dry powder precursor.

A study of molybdenum catalysts in the polymerization of 2,5-didodecyl-1,4-dipropynylbenzene

The reaction of 2,5-didodecyl-1,4-dipropynylbenzene with different molybdenum sources (Mo(CO) 6, norbornadiene-Mo(CO) 4, cyclooctadiene-Mo(CO) 4, cycloheptatriene-Mo(CO) 3, (PhC CPh) 3Mo(CO), (acac) 2MoO 2/AlEt 3) was investigated in the presence of 4-chlorophenol or 2-fluorophenol. Upon heating to 105–130 °C, the formation of didodecyl-PPE resulted. The degree of polymerization of the PPE is dependent on the used phenol and to the utilized molybdenum precursor. The most active catalyst forms from (acac) 2MoO 2, AlEt 3 and 2-fluorophenol. This catalyst combination gives high molecular weight PPEs after 6 h at 105 °C.

N,N,N-Tridentate iron(II) and vanadium(III) complexes

UV-Visible spectroscopic studies on methyl aluminoxane activated N,N,N-tridentate Iron(II) and Vanadium(III) complexes. The ethene oligomerization and polymerization activity of N , N , N -tridentate pyridine-diimine vanadium(III)- and iron(II)-complexes showed a remarkable time and temperature dependence after their activation with methyl aluminoxane (MAO). It was observed that the complex/MAO ratio and the time elapsed after MAO-addition to the catalyst precursor are critical factors for its overall performance. Different results were obtained from the same catalyst depending on the time that had passed from the time the catalyst was prepared until it was tested. Similarly. It was also found that an increase in reaction temperature decreased the catalytic activity. In order to investigate these observations, we employed UV–vis absorption spectroscopy on two representative vanadium(III)- and two iron(II)-based N , N , N -tridentate pyridine-diimine complexes activated with MAO. On time-scales of minutes to days, we have observed growths and decays of spectral band-systems, some of which are presumably related with chemical changes leading to active catalyst forms for ethene polymerization/oligomerization. Tentative explanations of the spectral changes that were observed for one of the vanadium systems under varying conditions of relative MAO concentrations are proposed. While the chemistry of the reactions of the complexes with MAO has still remained ill understood, the kinetic data based on spectral changes would be of empirical value to monitor and possibly correlate catalyst performances. This is the first glance into causes due to changes in the activated catalyst depending on concentration and time.

N,N,N-Tridentate iron(II) and vanadium(III) complexesPart III. UV–vis spectroscopic studies of reactions of ethene-oligomerization and polymerization catalysts with methyl aluminoxane cocatalyst

UV-Visible spectroscopic studies on methyl aluminoxane activated N,N,N-tridentate Iron(II) and Vanadium(III) complexes. The ethene oligomerization and polymerization activity of N , N , N -tridentate pyridine-diimine vanadium(III)- and iron(II)-complexes showed a remarkable time and temperature dependence after their activation with methyl aluminoxane (MAO). It was observed that the complex/MAO ratio and the time elapsed after MAO-addition to the catalyst precursor are critical factors for its overall performance. Different results were obtained from the same catalyst depending on the time that had passed from the time the catalyst was prepared until it was tested. Similarly. It was also found that an increase in reaction temperature decreased the catalytic activity. In order to investigate these observations, we employed UV–vis absorption spectroscopy on two representative vanadium(III)- and two iron(II)-based N , N , N -tridentate pyridine-diimine complexes activated with MAO. On time-scales of minutes to days, we have observed growths and decays of spectral band-systems, some of which are presumably related with chemical changes leading to active catalyst forms for ethene polymerization/oligomerization. Tentative explanations of the spectral changes that were observed for one of the vanadium systems under varying conditions of relative MAO concentrations are proposed. While the chemistry of the reactions of the complexes with MAO has still remained ill understood, the kinetic data based on spectral changes would be of empirical value to monitor and possibly correlate catalyst performances. This is the first glance into causes due to changes in the activated catalyst depending on concentration and time.

Hydroconversion of resids with dispersed molybdenum catalysts derived from phosphomolybdates

Phosphomolybdic acid (PMA) and cobalt, nickel and potassium phosphomolybdates have been found very active catalyst precursors for the conversion of coal- and petroleum-derived resids when they are impregnated onto coal and Al 2O 3. They are mostly stable up to 400–450°C in the presence of He and H 2, but significant change in stability occurs in the presence of H 2S, transforming these materials into an active form of catalyst. Their solubility in water provides highly dispersed catalysts in the reaction media. PMA and these bimetallic materials were tested at the concentration of 15, 150 and 1500 mg Mo per kg feed for reaction times of 30 and 90 min, and compared to a commercial NiMo/Al 2O 3 catalyst (AKZO-60). In the 30 min reactions, increasing Mo concentration did not provide a significant improvement in resid conversions compared to the non-catalyzed case. However, in the 90 min reactions, improvements were observed in conversion of coal and Mayan resids to distillate boiling below 525°C. The results indicate that thermal reactions play an important role in the 30 min reactions, and catalytic reactions resulting in increased resid conversions become more important in the 90-min reactions. Higher conversions with nickel phosphomolybdate supported on Al 2O 3 were observed with Mayan resid compared with coal resid. Nickel phosphomolybdate has been found to have promising catalytic activity for hydroconversion processes.

Transformation of phosphomolybdic acid into an active catalyst with potential application in coal liquefaction

Since phosphomolybdic acid (PMA) is known to be transformed into an active catalyst for liquefying coal and converting the residual product to distillate material, its conversion under conditions similar to those used in liquefaction has been investigated. The form of active catalyst formed from PMA under conditions of liquefaction is unknown. This paper reports the reaction of PMA observed in He, H 2 and H 2S–H 2 at temperatures up to 450°C. PMA is stable in both He and H 2 up to 200°C. However, when H 2S is present, sulfur is incorporated rapidly into the structure. The amount of incorporated sulfur increases both with temperature and exposure to H 2S. At temperatures up to 300°C, the maximum incorporation of sulfur was approximately 5 wt.% to give a material having a S/Mo atomic ratio of 0.27. Exposure to a large excess of H 2S did not further increase incorporation of sulfur. At 450°C, which is the temperature required for liquefaction of coal, approximately 20 wt.% sulfur was incorporated to give a S/Mo atomic ratio of 0.88. In this sample, the remaining oxygen was present as P 2O 3. IR and Raman spectra showed the presence of MoS 2, although insufficient sulfur was present to completely convert Mo to its disulfide. When H 2S is present, even at 125–150°C, the crystalline structure collapses destroying the Keggin structure. The rate of sulfur addition to PMA is much faster for MoO 3, than for MoO 2.

Partial oxidation of methane to carbon monoxide and hydrogen over NiO/La 2O 3/γ-Al 2O 3 catalyst

The production of H 2 and CO by catalytic partial oxidation of CH 4 at atmospheric pressure has been examined over NiO γ- Al 2O 3 and NiO/La 2O 3/γ-Al 2O 3 catalysts. When NiO loading increased to 17.5 wt.-%, the syngas production over NiO γ- Al 2O 3 is found to increase consistently. In that case, the addition of La 2O 3 can improve the catalytic activity significantly, with a NiO content of more than 17.5 wt.-%, a very small extent of change in the catalytic activity and the selectivity for the methane oxidation to syngas as well as a little effect of La 2O 3 on the activity and the selectivity are observed. Under the condition of high space velocity, the CO 2 and H 2O reforming of CH 4 occurs to a very small extent over reduced 12.5 wt.-% NiO/0.5 wt.-% La 2O 3 γ- Al 2O 3 catalyst. This fact and the results of the effect of space velocity on the methane partial oxidation to syngas suggest that both H 2, CO and CO 2, H 2O are the primary products of the methane oxidation. The results of characterizing 12.5 wt.-% NiO/0.5 wt.-% La 2O 3 γ- Al 2O 3 catalyst reveal that the active form of catalyst is metallic Ni and the promoter La 2O 3 facilitate the reduction of the oxidative nickel.

Kinetics of addition of acetic acid to epichlorohydrin in the presence of DMF or DMSO

AbstractThe kinetics of reaction between acetic acid and epichlorohydrin carried out in the presence of DMF or DMSO was studied. In addition, the conductivity of the reaction mixture was measured. The conductivity was found to increase considerably as the reaction proceeded. This was explained in terms of the formation of new effective forms of catalysts: the ammonium salt (in case of DMF) or sulphonium salt (for DMSO). A reaction scheme has been proposed, taking into account the active catalyst forms. The set of kinetic equations describing the reaction has been developed and the appropriate rate constants evaluated.

Thermocatalytic hydroconversion of heavy petroleum cuts with dispersed catalyst

This report concerns the use of unsupported dispersed catalysts in upgrading heavy feeds. The conversion of heavy crudes and resids into valuable products requires an efficient hydrogen activation. A method recently investigated deals with the use of metallic or organometallic (water- or oil-soluble) compounds, which under a thermal treatment decompose and give rise to a slurry of fine solid particles. This active form of catalyst promotes locally the spill-over of the hydrogen and therefore enhances the conversion of resids to distillate, reducing the coke formation. The primary objective of this report is to assess the current state of knowledge on this field, in order to identify new directions and strategies for Research.