Addition Of Alkali Metals Research Articles

Detailed Modeling of the Effects of K/Na Additives on the Thermal DeNOx Process

A reduced mechanism simplified from a detailed chemical kinetics mechanism containing N/H/O/K/Na elements was developed and validated in this paper. When the reduced mechanism was integrated into computational fluid dynamics (CFD) software, the effect of potassium and sodium additives on the selective non-catalytic reduction (SNCR) thermal DeNOx process was simulated. The simulation results were compared to those of experiments under different oxygen concentrations, normalized stoichiometric ratios (NSRs) of the N agent/NO, and alkali metal additive concentrations within the temperature range from 1023 to 1523 K, and the simulation results coincided qualitatively with those of the experiment in an entrained flow reactor. The alkali metal additives did not change the effects of the oxygen concentration and NSR on the SNCR process: a conversion temperature point exists at about 1173–1223 K; below the conversion temperature point, a higher oxygen concentration can promote the effect of SNCR, while above the conversion temperature point, the efficiency will be reduced; and a higher NSR is beneficial for NO reduction, but its effect becomes less obvious with the increase of the reducing agent. The alkali metal additives extend the “temperature window” toward a lower temperature by about 50–100 K with more OH and NH2 radical production, and the effect of K additives is less obvious than that of Na. However, the promoting effect of the K additive cannot be well-simulated because of the lack of a suitable mechanism. A K chemistry mechanism should be optimized on the basis of its effect on the SNCR process. The K or Na concentration almost has no influence on the effect of alkali metal additives on the thermal DeNOx process when the K or Na concentration is beyond a certain value.

The influence of support in the synthesis of dimethyl carbonate by Cu-based catalysts

The effects of various anions containing copper based catalysts were studied in regard to the preparation of dimethyl carbonate (DMC) through oxidative carbonylation of methanol under a liquid phase system. A copper compound providing the strong withdrawing power of halides as anion yielded excellent results with respect to the conversion of methanol and selectivity to DMC.However, copper homogenous catalysts suffer from separation of the catalyst after reaction. Thus, the development of a new reaction system using various supports including Y-zeolite was attempted. The conversion of methanol and selectivity to DMC were affected by the properties of the supports. In particular, Y-zeolite showed the best yield among various supports.The influence of various promoters was examined with the aim of increasing the yield of DMC from methanol. The yield of DMC was increased with the addition of alkali metal in the order Li+<Na+<K+, but with selectivity in the order of Li+>Na+>K+, respectively.Various analyses were conducted in order to elucidate these results. From a XRD analysis, the existence of crystal forms of copper chloride hydroxide of Cu/Na/Y-zeolite (dry) was observed. We confirmed the presence of peaks of CuO in Cu/Na/Y-zeolite (550°C). The CO-TPD analysis revealed that CO desorption is an important step to determine the formation of DMC. The addition of NaOH as a co-catalyst resulted in a lower desorption temperature of carbon monoxide in Cu catalyst. Also, XPS analysis results showed that Cu+ on the calcined Cu/Na/Y-zeolite catalyst was formed by the reduction of Cu2+. XANES results provided the difference of reactivity according to the state of the copper catalyst. Activity of this reaction in terms of DMC yields, obtained in the order of CuCl2>Cu/Na/Y-zeolite (dry)>Cu/Na/Y-zeolite (550°C)>Cu(OH)2 was in accordance with the maximum peak of the low photon energy position.

SO2 promoted alkali metal doped Ag/Al2O3 catalysts for CH4-SCR of NOx

A study of the lean NOx reduction activity in the presence of SO2 and water over alkali promoted Ag/Al2O3 catalysts has been done using methane as a reductant. The alkali doped materials are synthesized by the co-impregnation method. Their promotional behavior, existence of several silver species and improved adsorption properties have been thoroughly investigated by various techniques: XRD, XANES, TEM, UV–Vis DRS, SO2 TPD and NO TPD. The evaluated samples exhibited high surface area around 220m2g−1. TEM results demonstrated the presence of highly dispersed nano sized silver particles on surface, where the addition of alkali metals slightly enhanced the crystallization of silver. Moreover, standard XRD profiles of fresh and used samples indicate the high durability and mechanical strength of catalysts. These findings are in line with the time-on-stream studies. The XANES results revealed that the edge spectra of prepared materials are similar to that of the reference Ag2SO4. From XANES and UV–Vis DRS, the presence of crystalline Ag0 and Ag+ species were identified. Poor activity of Na promoted sample is attributed to absence of suitable amount of ionic silver compounds. However, the synthesized alkali doped materials showed the promotional deNOx conversions in the presence of SO2 and H2O stream. Among the investigated samples K–Ag/Al2O3 and Cs–Ag/Al2O3 exhibited higher NOx conversions and thermal stability. The higher SCR of NOx was explained by the NO adsorption properties identified from the NO TPD studies.

Absence of photoemission from the Fermi level in potassium intercalated picene and coronene films: Structure, polaron, or correlation physics?

The electronic structure of potassium intercalated picene and coronene films has been studied using photoemission spectroscopy. Picene has additionally been intercalated using sodium. Upon alkali metal addition core level as well as valence band photoemission data signal a filling of previously unoccupied states of the two molecular materials due to charge transfer from potassium. In contrast to the observation of superconductivity in K(x)picene and K(x)coronene (x ~ 3), none of the films studied shows emission from the Fermi level, i.e., we find no indication for a metallic ground state. Several reasons for this observation are discussed.

The Chameleon-Like Nature of Zwitterionic Micelles: Effect of Cation Binding

Addition of salts, especially perchlorates, to zwitterionic micelles of SB3-14, C(14)H(29)NMe(2)(+)(CH(2))(3)SO(3)(-), induces anionic character and uptake of H(3)O(+) by SB3-14 micelles. Thus, the addition of alkali metal perchlorates accelerates the acid hydrolysis of 2-(p-heptoxyphenyl)-1,3-dioxolane, HPD, in the presence of SB3-14 micelles, which depends on the local proton concentration at the micelle surface. The addition of metal chlorides to solutions of such perchlorate-modified SB3-14 micelles decreases both the negative zeta potential of the micelles and the observed rate constant for acid hydrolysis of HPD. The effect of the monovalent cations Li(+), Na(+), and K(+) is smaller than that of the divalent cations Be(2+), Mg(2+), and Ca(2+), and much smaller than that of the trivalent cations Al(3+), La(3+), and Er(3+). The major factor responsible for this cation valence dependence of these effects is shown to be electrostatic in nature, reflecting the strong dependence of the micellar surface potential on the cation valence. The fact that the salt effects are not identical after correction for the electrostatic effects indicates that additional secondary nonelectrostatic effects may contribute as well.

Enhanced reversibility of H2 sorption in nanoconfined complex metal hydrides by alkali metal addition

Complex metal hydrides, containing up to 18 wt% H2, are attractive candidates for on-board hydrogen storage. However, only limited reversibility of H2 desorption is achieved under mild conditions, especially in the absence of catalysts. Nanoconfining the materials in porous matrixes facilitates rehydrogenation, but still full reversibility has been rarely achieved. We reveal the factors that limit the reversibility using NaAlH4 in a porous carbon matrix as a model system. Relatively large Al crystallites (>100 nm) are formed after desorption, migrating out of the mesopores of the matrix. However, their formation does not fundamentally limit the reversibility, as these crystallites react with Na(H) and H2 reforming nanoconfined NaAlH4 under relatively mild conditions. We show for the first time that the main limiting factor for the decayed cycling capacity is the loss of active alkali metal species. Evaporation losses are minor, even when dehydrogenating at 325 °C in vacuum. Significant losses (30–40%) occur upon the first hydrogen desorption run, and are attributed to the reaction of Na species with impurities in the carbon matrix. A one-time addition of extra Na compensates for this loss, leading to close to full reversibility (>90%) at 150 °C under 55 bar H2 pressure. A similar effect is found when adding extra Li species to nanoconfined LiBH4. For nanoconfined complex metal hydrides irreversible loss of the reactive alkali metal species due to reaction with impurities can act as a major loss mechanism. However, the one-time addition of extra alkali metal species is very effective in resolving this issue, leading to close to full cycling reversibility under relatively mild conditions even in the absence of catalysts.

Synchrotron Radiation Studies of Additives in Combustion, II: Soot Agglomerate Microstructure Change by Alkali and Alkaline-Earth Metal Addition to a Partially Premixed Flame

Small-angle X-ray scattering (SAXS) has been used in a comparative study to characterize soot particle formation in a partially premixed ethylene−air flame into which plain water, and 0.1 mol/L solutions of potassium chloride, cesium chloride, barium chloride, and calcium chloride were aspirated. The plain water results are assumed to be the reference in this study. On the basis of previous findings, a two-level universal fitting function for the scattering intensity I(q), 0.04 nm−1 < q < 0.5 nm−1, is used to retrieve the size and concentration of both primary particles, which are the subunits of relatively large (∼100 nm) fractal aggregates, and smaller subprimary particles, which aggregate in turn to form primaries. It is found that CsCl addition produces ∼40% smaller primary particles at larger residence times, compared to plain water addition. CaCl2, BaCl2, and KCl addition have almost no effect on primary and subprimary sizes. Cesium chloride addition produces a dramatic reduction of the subprimary particle dimension, up to a factor of 2.2, while the concentration of primaries and subprimaries is increased by factors of up to 5 and 2, respectively, with respect to plain water. The contribution to the soot volume fraction (fv) from primary and subprimary particles is separately estimated for all the additives, with respect to the standard plain water addition. At larger residence times, CsCl addition leads to a reduction of the fv contribution from primaries, with larger rates compared to KCl. On the other hand, the effect of suppression by CsCl at smaller heights can be weaker than pure water, contrary to KCl, which is a better fv suppressor than water at all heights, even if a smaller rate than that for CsCl is in operation. The effect of CsCl and KCl is the same for the subprimary fv contribution. BaCl2 has the effect of yielding a primary fv contribution, which is a factor of 2 smaller than that for plain water, almost independently of the height in the flame and, moreover, it yields a large decrease (up to a factor of 4 at a height above the burner (HAB) of 28 mm) in the subprimary fv contribution, compared to plain water. CaCl2 addition has a negligible effect on both the primary and subprimary fv contribution, with respect to water.

Influence of alkali promoters on synthetic diesel production over Co catalyst

The effects of the addition of alkali metal and alkali-earth metal promoters over cobalt based catalyst on Fischer–Tropsch activity and on hydrocarbon product distribution were studied. The influence of promoters on the reducibility and cobalt particle size was studied by different techniques, including N2 adsorption, X-ray diffraction, temperature-programmed reduction, temperature-programmed desorption and acid–base titrations. Experiments were carried out on a bench scale fixed bed reactor and catalysts were prepared by incipient wetness impregnation. It was observed that the addition of small amounts of these promoters (0.5wt%) improved the cobalt oxide reducibility by reducing the formation of cobalt aluminate species. The interaction between cobalt oxide and promoted support was reduced and larger cobalt oxide particles were formed on the surface. A positive correlation between basicity and particle size was observed with the exception of K promoted sample. Furthermore, CO conversion and C5+ selectivity were found to be also influenced by the addition of promoters. An enhanced dispersion that provides abundant catalytically active sites was observed on promoted catalyst. The addition of Ca to the cobalt based catalyst greatly improved the diesel selectivity. However Ca promoted catalyst yield a higher amount of methane at 242°C than the Na sample.

Salt Effects on the Rates and Mechanisms of Solvolysis Reaction of Organic Halides and Water Structure Distortion in N,N-Dimethylformamide– and N,N-Dimethylacetamide–Water Mixed Solvents

Abstract In 50% (v/v) DMF– and DMA–H2O mixed solvents, salt effects on the solvolysis reaction rates of aliphatic halides and related compounds (RX) have been examined for further exploring. Compared with previous results obtained in other organic solvent systems, such as 50% (v/v) acetone–, 1,4-dioxane–, or sulfolane–H2O, no exceptional behavior was observed in the “pseudo” first-order rate constants (k/s−1) of all the typical SN1 and SN2 substrates by the addition of alkali metal and alkaline earth metal perchlorates or many kinds of tetraalkylammonium salts in 50% (v/v) DMF– and DMA–H2O mixed solvents. The detailed examination of Δlog(k/s−1)/Δ[LiClO4] for 1-adamantyl bromide vs. the contents of organic solvents (CH3CN, DMA, and DMSO) suggested that the observed different salt effects were caused by the different solvation abilities of the solvents toward the leaving-group anion as well as the metal cation. As a new highlight in the present paper, we were able to demonstrate a proportionality or correlation between the LiClO4 effects in the solvolysis rates and the carbocation stabilities expressed by the Gibbs free energy values (ΔGo) of RX in the gas phase. Based on the Raman spectra of DMA–H2O and DMA–D2O as well as DMF–D2O mixed solvents, we discuss the distortion of the bulk water structure.

Inhibition of methane formation in steam reforming reactions through modification of Ni catalyst and the reactants

Methane, a greenhouse gas and a main by-product in steam reforming reaction, can greatly diminish hydrogen yield. Modifications of both the catalyst and reactants were performed in this study to suppress methane formation. Ni/Al2O3 catalysts modified with a series of promoters (Li, Na, K, Mg, Fe, Co, Zn, Zr, La, Ce) were evaluated in acetic acid reforming reaction. The addition of Co, Zr, La, or Ce to Ni/Al2O3 promoted the methanation reaction, and consequently promoted methane formation. Conversely, alkali metal modified samples effectively inhibited methane formation, especially the Ni–K/Al2O3 catalyst. Moreover, the addition of alkali metal remarkably increased the number of metallic Ni sites on the catalyst surface by promoting the reduction of Ni oxides, which enhanced the catalytic activity. In addition, the presence of K on alumina also promoted stability of the Ni catalyst through suppression of coke formation. Type of fuels reformed also affected methane formation. Methane selectivity was much higher in steam reforming of the neutral fuels (ethanol, 1-propanol) than in steam reforming of the acidic fuels (acetic acid, propanoic acid). Acidification of neutral alcohols with nitric acid remarkably suppressed methane formation, which was accomplished through the suppression of the methanation reaction. Besides, the addition of nitric acid to ethanol can help eliminate coke deposition in ethanol reforming reactions, since production of the main carbon precursor, ethylene, is suppressed to a significant extent in the presence of nitric acid.

Catalytic combustion of soot. Effects of added alkali metals on CaO–MgO physical mixtures

The effect of adding alkali metals (Li, Na, K) to a CaO–MgO mixture, on the catalytic combustion of carbon black (CB), a model compound for soot, was studied. Catalysts were prepared by the Sol–Gel method and characterized by surface (BET surface area, XPS, DRIFTS) and bulk (AAS, XRD and TPR) techniques. Samples with a 4:1 catalyst-CB ratio were subjected to catalytic oxidation in a thermo-gravimetric apparatus and the temperature T m, at which combustion occurs at its maximum rate, was recorded for comparison of catalytic activity. The addition of alkali metals (Li, Na, K) over the CaO–MgO mixture significantly increased the catalytic activity, due to the formation of surface oxygenated species that enhanced the oxidizing properties of the catalyst surface. That activity for CB combustion increases with the atomic number of the alkali metal contained in the catalyst. The presence of alkali metals also diminished the amount and stability of carbonates formed on the catalyst. The K-containing catalyst showed the largest activity for the catalytic CB combustion, because it shows the largest capacity to enrich its surface with α-oxygen type and promotes best the surface dissociation of that oxygen. Furthermore, surface-adsorbed OH and carbonate groups that disable the active sites and prevent the oxygen adsorption and dissociation, were less abundant and desorbed at lower temperatures, showing to be less stable on this K-containing catalyst.

Preferential CO oxidation in hydrogen-rich stream over Pt catalysts modified with alkali metals

Abstract The addition of alkali metals over Pt/Al 2 O 3 has both promoting and negative effects on the catalytic performance in the preferential CO oxidation in H 2 -rich stream (PROX), therefore there is an optimum amount of alkali metal. The Pt/Al 2 O 3 catalysts modified with Na, K, Rb and Cs were characterized by means of transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), and Fourier transform infrared spectroscopy (FTIR). The results show that the addition of larger amount of alkali metals with stronger basicity causes the aggregation of Pt metal particles. The Pt particles on Pt/Al 2 O 3 modified with alkali metals are more electron-deficient than those on Pt/Al 2 O 3 , and this weakens the strength of CO adsorption on Pt/Al 2 O 3 modified with alkali metals, which is related to the enhancement of turnover frequency of the PROX. In addition, in situ FTIR observation suggests that the coadsorbed species originating from H 2 and O 2 (e.g., the OH species) under the PROX condition, which promote the CO oxidation, can be found on highly active catalysts.

Effect of temperature, steam-to-carbon ratio, and alkali metal additives on improving the sulfur tolerance of a Rh/La–Al2O3 catalyst reforming gasoline for fuel cell applications

2 wt% Rh/La–Al2O3 was tested for autothermal reforming (ATR) of S-free and 34 ppm-S-gasoline and characterized by scanning electron microscopy, elemental analyses, surface area, CO chemisorption, DRIFTS and X-ray absorption spectroscopy. The poisoning effect of S was more pronounced during ATR at 700 °C than at 800 °C. Complete recovery of the initial activity could be achieved when switching from S-containing gasoline to S-free gasoline at 800 °C, while only 50% of the activity could be recovered at 700 °C. Sulfur increased Rh sintering due to an increase in the catalyst temperature caused by a greater inhibition of steam reforming than partial oxidation. An increase in the H2O:C from 2.0 to 3.0, or the addition of K to Rh significantly enhanced the sulfur tolerance of the catalysts. The beneficial effect of temperature, steam, and alkali metal was attributed to the inhibition of coke, which was the major cause of catalyst deactivation.

Temperature dependences of wetting angles of steel 12Cr18Ni9Ti and ceramics by the melts with least additions of alkali metals

Temperature dependences of wetting angles of 12Cr18Ni9Ti steel and PZT ceramics by the melts with least additions of alkali metals were studied in a wide temperature range in helium atmosphere. The temperature thresholds of wetting were found on the dependences when In-Na melts wet the 12Cr18Ni9Ti steel. Observed thresholds have been studied versus the concentration of sodium in indium. The sudden decrease in wetting angles was also observed at 650-700°C if substrate used was the PZT piezo-ceramics. Similar features were not detected at wetting the same materials by Cd-Na and Pb-Li melts.

Vapor-phase Oxidation of Alkylaromatics over V/TiO2and VSb/Al2O3Catalysts: Effect of Alkali Metals

Oxidation of alkylaromatics including toluene and p-methoxytoluene has been carried out over alkali metal (AM)-containing catalysts such as AM-V/TiO2 and AM-VSb/Al2O3 in vapor-phase using oxygen as an oxidant. The selectivity for partial oxidations increases with incorporation of an alkali metal or with increasing the basicity of alkali metals (from Na to Cs), irrespective of the supports or reactants. However, the conversion is nearly constant or slightly decreasing with the addition of alkali metals in the catalyst. The increased selectivity may be related with the decreased acidity even though more detailed work is necessary to understand the effect of alkali metals in the oxidation. The AM-VSb/Al2O3 may be suggested as a potential selective catalyst for vapor-phase oxidations.

Characterization and Catalytic Performance of PtSn Catalysts Supported on Al2O3 and Na-doped Al2O3 in n-butane Dehydrogenation

PtSn/Al2O3 and PtSn/Al2O3–Na catalysts display important modifications of the metallic phase with respect to Pt/Al2O3 one. In this sense, TPR and XPS results show the presence of strong interactions between Pt and Sn, with probable alloy formation, which would be responsible for the decrease of the reaction rate and the increase of the activation energy in cyclohexane dehydrogenation. Besides the experiments of cyclopentane hydrogenolysis show that the alkali metal addition to bimetallic PtSn/Al2O3 catalysts completely eliminates the hydrogenolytic ensembles, which could be due to a geometric modification of the metallic phase. These important modifications in the nature of the metallic function due to the simultaneous addition of Na and Sn to Pt/Al2O3 are responsible for the excellent catalytic performance in the n-butane dehydrogenation, thus giving high conversions, selectivities to butenes higher than 95%, and lower deactivation capacity than those corresponding to bimetallic PtSn catalysts (with different Sn contents) supported on undoped alumina. The excellent stability of PtSn/Al2O3–Na catalysts would be due to a low carbon formation during the reaction, such as it was observed from pulse experiments.

Switching between Ligand‐to‐Ligand Charge‐Transfer, Intraligand Charge‐Transfer, and Metal‐to‐Ligand Charge‐Transfer Excited States in Platinum(II) Terpyridyl Acetylide Complexes Induced by pH Change and Metal Ions

A series of platinum(II) terpyridyl alkynyl complexes, [Pt{4'-(4-R1-C6H4)terpy}(C[triple chemical bond]C-C6H4-R(2)-4)]ClO4 (terpy=2,2':6',2''-terpyridyl; R1=R2=N(CH3)2 (1); R1=N(CH3)2, R2=N-[15]monoazacrown-5 (2); R1=CH3, R2=N(CH3)2 (3); R1=N(CH3)2, R2=H (4); R1=CH3, R2=H (5)), has been synthesized and the photophysical properties of the complexes have been examined through measurement of their UV/Vis absorption spectra, photoluminescence spectra, and transient absorptions. Complex 3 shows a lowest-energy absorption corresponding to a ligand-to-ligand charge-transfer (LLCT) transition from the acetylide to the terpyridyl ligand, whereas 4 shows an intraligand charge-transfer (ILCT) transition from the pi orbital of the 4'-phenyl group to the pi* orbital of the terpyridyl. Upon protonation of the amino groups in 3 and 4, their lowest-energy excited states are switched to dpi(Pt)-->pi*(terpy) metal-to-ligand charge-transfer (MLCT) states. The lowest-energy absorption for 1 and 2 may be attributed to an LLCT transition from the acetylide to the terpyridyl. Upon addition of an acid to a solution of 1 or 2, the amino group on the acetylide is protonated first, followed by the amino group on the terpyridyl. Thus, the lowest excited state of 1 and 2 can be successively switched from the LLCT state to the ILCT state and then to the MLCT state by controlling the amount of the acid added. Such switches in the excited state are fully reversible upon subsequent addition of a base to the solution. Sequential addition of alkali metal or alkaline earth metal ions and then an acid to a solution of 2 also leads to switching of its lowest excited state from the LLCT state, first to the ILCT state and then to the MLCT state. All of the complexes exhibit a transient absorption of the terpyridyl anion radical, which is present in all of the LLCT, ILCT, and MLCT states. However, the shape of the transient absorption spectrum depends on both the substitution pattern on the terpyridyl moiety and the nature of the excited state.

Chain structure and electronic states of liquid Rb-Se mixtures byab initiomolecular-dynamics simulations

The effects of excess electronic charges transferred from alkali metals to Se atoms on the chain structure in liquid ${\mathrm{Rb}}_{x}{\mathrm{Se}}_{1\ensuremath{-}x}$ for $x\ensuremath{\leqslant}0.5$ are investigated by means of ab initio molecular-dynamics simulations. It is found that the interaction between Se chains is enhanced by the transferred electrons, and that the average length of Se chains becomes shorter with increasing alkali-metal concentration. The shortening of Se chains is responsible for an increase of electronic states at the Fermi level, which explains the observed increase of the electrical conductivity on the addition of alkali metals. At the equiatomic concentration, there are almost no electronic states at the Fermi level due to the formation of $\mathrm{Se}_{2}{}^{2\ensuremath{-}}$ dimers. The alkali-metal-concentration dependence of the bonding properties between Se atoms is discussed in comparison with liquid alkali-metal tellurides based on a population analysis.

Catalytic Active Site for NO Decomposition Elucidated by Surface Science and Real Catalyst

Comprehensive studies combining surface science and real catalyst were performed to get further insight into catalytic active site and reaction mechanism for NO decomposition over supported palladium and cobalt oxide-based catalysts. On palladium single-crystal model catalysts, adsorption, dissociation and desorption behavior of NO was found to be closely related to the surface structures, the stepped surface palladium being active for dissociation of NO. In accordance with this result, the activity of powder Pd/Al2O3 catalysts for NO decomposition was directly related to the number of step sites exposed on the surface, suggesting that the step sites act as the catalytic active site for NO decomposition on Pd/Al2O3. NO decomposition over cobalt oxide was found to be significantly promoted by addition of alkali metals. Surface science study and catalyst characterization led to the same conclusion that the interface between the alkali metal and Co3O4 serves as the catalytic active site. From the results of in situ Fourier transform infrared (FT-IR) spectroscopy and isotopic transient kinetic analysis, a reaction mechanism was proposed in which the reaction is initiated by NO adsorption onto alkali metals to form NO 2 − species and then NO 2 − species react with the adsorbed NO species to form N2 over the interface between the alkali metal and Co3O4.

Effect of alkali metal additives on the activity and selectivity of structured silver catalysts in epoxidation of ethylene by nitrogen(I) oxide

We have shown that introducing Cs, K, or Na additives into the composition of silver catalysts (supported on ceramic honeycomb monoliths) for epoxidation of ethylene by nitrogen(I) oxide leads to an increase in the yield of the target product (ethylene oxide) by a factor of 1.5–2, while the presence of lithium in the composition of the composites inhibits the process. The optimal content of alkali promoters in the composition of the catalysts decreases in the series Na, K, Cs antibatically relative to the ionic radii of the elements.