Effect Of Potassium Promotion Research Articles

Preparation of alumina-supported CuCo catalysts from cyanide complexes and their performance in CO hydrogenation

Alumina-supported CuCo catalysts were prepared in several impregnation conditions by free adsorption from solutions of various cyanide complexes. The species in the impregnating solutions and the kinetics and extent of the adsorption of metal complexes were determined by UV-visible spectrometry. A simple electrostatic model is used to explain the incorporation of metal complexes as a function of their nature and the impregnation conditions. After impregnation, samples were dried and reduced under hydrogen flow at 673 K with no intermediate calcination step. Infrared spectra of CO chemisorbed on reduced samples showed that CO is coordinated mainly to Cu interacting with Co atoms. The reduction to metallic copper and partial reduction of Co 3+/Co 2+ ions occur in parallel on H 2-reduced samples, as evidenced by X-ray photoelectron spectroscopy and X-ray induced Cu LMN Auger emission. Quantitative Cu(Co)/Al atomic ratios in reduced catalysts also revealed that copper and cobalt exposure strongly depends on the precursor used in the preparation. The catalysts were tested in CO hydrogenation at 553–593 K under CO : H 2 1 : 1 at 0.8 MPa and the product distribution described by an Anderson–Shultz–Flory kinetics. Ex-cyanide catalysts showed a slightly higher alcohol production than the conventionally prepared bimetallics. Moreover, for the ex-cyanide catalysts, the promoter effect of potassium produced an increase in both, higher alcohol synthesis and the olefin/paraffin ratio.

Promotion effect of potassium on the catalytic property of CuFe 2O 4 for the simultaneous removal of NO x and diesel soot particulate

Modification of CuFe 2O 4 catalyst for the simultaneous NO x -soot removal has been studied by doping alkali metals (Li, Na, K, Cs), vanadium and platinum. In pre-doped catalysts, designated as Cu 1− x A x Fe 2O 4 (A : dopant), potassium was superior to the other alkali metals and vanadium with respect to enhancing the activity and selectivity to NO x reduction into N 2, and the optimum doping level of potassium was x=0.05. Such a promotion effect of potassium was also observed with the impregnated 5 mol% K/CuFe 2O 4 catalyst. The impregnation of platinum to CuFe 2O 4 and Cu 0.95K 0.05Fe 2O 4 resulted in a decrease in the selectivity to N 2 formation with the activity being almost unchanged. The high catalytic performance, especially high selectivity, was realized only when the proper amount of potassium is doped in the Cu–Fe spinel catalyst. XPS analysis showed the segregation (enrichment) of potassium on the surface, and too much doping of potassium might cause the covering of active sites of the Cu–Fe spinel oxide.

The Effect of Potassium Promoter on Ni-Co-O and Zn-Co-O Spinel Composite Oxide Catalysts

The Effect of Potassium Promoter on Ni-Co-O and Zn-Co-O Spinel Composite Oxide Catalysts

Catalytic combustion of diesel soot particles on copper catalysts supported on TiO 2. Effect of potassium promoter on the activity

We have prepared a TiO 2 supported copper catalyst and studied the effect of potassium on its activity in the oxidation of soot particles. The catalysts, with a K/Cu atomic ratio varying between 0 and 2, were calcined at 1073 K. They were characterized by BET surface area measurements, X-ray diffraction and temperature-programmed reduction under hydrogen. The catalytic activity was measured in a microbalance by means of temperature-programmed oxidation in air or argon. The catalytic activity of copper was enhanced by the presence of potassium. This effect was attributed to the formation of mixed KTi oxides which inhibit the sintering of the TiO 2 support and thus increases the surface area of the catalyst. Although a redox mechanism can explain the catalytic combustion, no correlation could be established between the reducibility of the different solids and their activity in soot combustion.

Carbon monoxide hydrogenation using cobalt-manganese oxide catalysts: The influence of potassium as a promoter

The effect of potassium promoter on the CO hydrogenation reaction over precipitated cobalt manganese oxide catalysts was studied in a plug flow laboratory microreactor (220°C, 540 kPa, GHSV = 250 h −1, CO/H 2-ratio 1/1). On addition of low levels of the promoter (0.01-0.5%), significant increases in alkene/alkane ratios and higher hydrocarbon formation were observed, coupled with decreased methanation activity. Furthermore, the results showed that the presence of promoter favored the formation of longer chain alcohols, accompanied by decreases in the C 1OHC 4OH fraction. Maximum C 5+-hydrocarbon selectivity commensurate with high CO conversion and low methane formation was observed at between 0.1 and 0.2% potassium. C 2- and C 3-olefin selectivity was studied as a function of reactor operating conditions, and the selectivity was found to decrease with increasing temperature, pressure (constant conversion), reciprocal space velocity (space-time), and conversion. Bulk catalyst characterization by XRD and DSC suggested that the promoter did not influence the bulk structure of the catalyst. The potassium promoter concentrated on the surface as demonstrated from BET surface area measurements and XPS studies. BET measurements showed the catalyst surface area to initially decrease at low levels of promoter (0% potassium, 13.2 m 2/g; 0.01% potassium, 10.1 m 2/g), and then to increase with increased promoter loadings (1% potassium, 17.0 m 2/g). XPS studies on a 0.25% potassium promoted catalyst showed a surface aggregation of the potassium promoter from the bulk to occur during stages of calcination (6%), reduction (10%) and subsequent CO hydrogenation (2–4%). The data from the study suggest that the role of potassium is to modify the concentration of cobalt active sites and simultaneously to assist in the breakdown of the CO reactant.

Activation and promotion studies in a mixed slurry reactor with an iron-manganese Fischer-Tropsch catalyst

Synthesis gas was reacted over a coprecipitated iron-manganese Fischer-Tropsch catalyst in a slurry reactor. The effect of various activation parameters - temperature, pressure, and gas composition - on subsequent catalyst activity and product selectivity was investigated. The gas composition had the most dramatic effect on the catalyst activation and the ensuing synthesis gas conversion. The effect of potassium promotion on catalyst activity and product selectivity was also studied in slurry reactor tests.

The short range of the electronic promoter effect of potassium

The short range of the electronic promoter effect of potassium

The short range of the electronic promoter effect of potassium

Photoemission of Adsorbed Xenon atoms (PAX) as a local work function probe is used to investigate the range of the electronic promoter effect of potassium submonolayers on a Ru(001) surface. Three Xe states on these bimetallic K/Ru surfaces are clearly distinguishable by their 5p photoemission and are associated with Xe probe atoms at basically unmodified Ru sites, at “mixed” K.Ru sites next to K ions, and on top of potassium, respectively. From the relative intensities of these three states as well as from their 5p electron binding energies as a function of potassium coverage it is concluded that the radius of the “sphere” of modified charge density around one K ion is ∼ 6 Å.

Alkali promoters on supported nickel: Effect of support, preparation, and alkali concentration

The effect of potassium promoter for CO hydrogenation on supported nickel catalysts was studied in a differential reactor. The influences of the support (SiO 2, SiO 2 · A1 2O 3), the promoter concentration (0.05–4% K), the alkali salt (KC1, K 2CO 3, K 2C 2O 4, KOH, KNO 3), and the method of preparation (pre- and coimpregnation, and calcination) were studied. The activity and selectivity of promoted catalysts are shown to depend on the support; modifications in catalytic properties are not just due to a KNi interaction. On Ni SiO 2 an exponential decrease in total activity with increased promoter concentration is seen; this decrease is not due to a decrease in percentage nickel exposed (dispersion). A large increase in olefin/paraffin ratios is seen on Ni SiO 2 as the promoter decreases hydrogenation rates. In contrast, on Ni SiO 2 · A1 2O 3, the rate of paraffin formation, including methane, increases and exhibits a maximum with increased promoter concentration. Olefin selectivities decrease and higher paraffin selectivities increase. Much of the potassium salt may react with the silica-alumina support to modify the catalytic properties. The method of preparation has a lesser influence on the catalyst than the potassium concentration. The use of different potassium salts resulted in similar catalytic properties, indicating that for a given support the same potassium compound formed during preparation. A good correlation was found between C 2 and C 3 olefin/paraffin ratios and inverse total activity, showing that olefin selectivities increase as hydrogenation rates decrease.

Activation of dinitrogen molecule on the surface of iron (or ruthenium) based catalysts

Supported iron (or ruthenium) catalysts prepared by different methods were tested in the ammonia synthesis reaction. A promoter effect of potassium was observed in these catalysts. By means of infrared spectroscopy, the activation of dinitrogen species was observed on the surface of a highly dispersed 3.2 wt. % Ru-alumina non-promoted catalyst.

Effect of Potassium Promoter on Iron Oxide Catalysts for Dehydrogenation of Ethylbenzene to Styrene

Abstract The catalytic activity and the sintering property of iron oxide catalysts with and without potassium additives have been studied. The potassium oxide acts as a promoter and is effective under given conditions in increasing the activity of the catalyst from four to ten times. The effects of the promoter can be classified thus: (1) Structural promoter: The increase in the apparent bulk density and the shrinkage of the catalyst tablet upon calcination during the preparation of the catalyst are prevented by potassium additives. The differences in the specific surface area and in the pore volume of the catalyst between with and without potassium promoter are slight. These effects on iron oxide appear to be caused largely by the formation of K2Fe22O34. (2) Synergetic promoter: The potassium promoter changes the apparent energy of activation of the dehydrogenation reaction from 28 to 43 kcal/mol. The increase in the catalytic activity is due to the increase in the pre-exponential factor. The increase in the factor can be explained in terms of the higher concentration of the active center produced by the interaction of the potassium promoter with iron oxide. (3) Selectivity promoter: The formation of benzene by a side reaction is retarded by potassium additives.

Effect of potassium promoter on sintering of iron oxide in catalyst preparation

Catalytic activity of the Co–Mn–Al mixed oxide catalyst (Co:Mn:Al molar ratio of 4:1:1) modified with various amounts of potassium (0–3 wt%) was examined in total oxidation of toluene and ethanol. The prepared catalysts were characterized by chemical analysis (AAS), powder X-ray diffraction (XRD), surface area measurements, temperature programmed techniques (TPR, TPD), voltammetry of microparticles, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The non-modified catalyst was composed of spinel-like Co–Mn–Al mixed oxide as the only XRD crystalline phase. The surface concentrations of metal components obtained by XPS were different from the bulk ones determined by chemical analysis and the segregation of the metal components depended on the actual potassium content. The low K additions changed mainly the surface acid–base properties of the catalyst. According to XRD and voltammetry measurements, Mn oxides segregated from the original spinel-like phase at high concentration of potassium (2.7 and 3.0 wt%); XPS showed an enrichment of the catalysts surface with Mn. The K addition caused significant changes in the catalyst efficiency. The highest conversion in toluene oxidation was achieved with the catalyst containing about 1 wt% K; no reaction by-products were observed beside H2O and CO2. In ethanol oxidation, the catalysts activity gradually increased with increasing potassium content up to about 3 wt% K, but the presence of excess potassium in the Co–Mn–Al catalyst negatively affected formation of reaction by-products: acetaldehyde production steeply increased with potassium concentration higher than 1 wt%.

The oxidation and leaching of some chromia-alumina and chromia-silica-alumina preparations

The oxidation and leaching of some chromia-alumina and chromia-silica-alumina preparations have been studied. A correlation has been found between ionic potential of a number of ions used as promoters on a chromia-alumina, and the amount of equivalent CrO 3 leached from these preparations after oxidation at 500 °. The correlation is good for ions having inert gas electron configurations. Those ions having pseudo-inert gas configurations fit the correlation as well. A study of extended oxidation and leaching shows that a limit of oxidizability of chromia on alumina can be reached. However, this limit is closely approached while much of the clump chromia is still present. This is shown by electron spin resonance spectra. The presence of dispersed phase chromia is also shown. The loss of oxidizability is related to activity in dehydrocyclization of n-hexane and is explained in terms of accumulated surface acidity. The effect of potassium promotion on oxidizability and dehydrocyclization activity has also been studied.