Influence of Pretreatment on the Interaction of Oxygen with Silver and the Catalytic Activity of Ag／SiO2 Catalysts for CO Selective Oxidation in H2

The interactions of oxygen with pre~reduced silver catalysts as well as their catalytic propertiesfor CO selective oxidation in H2 after oxygen pre-treatment are studied in this paper. It is found that the pretreatment exerts a strong influence on the activity and selectivity of the silver catalyst. A drop in activity and selectivity is observed after treating a pre-reduced catalyst with oxygen at low temperatures,whereas a converse result is obtained after an oxidizing treatment at high temperatures (T≥350℃). O2-TPD results show that surface oxygen species adsorbs on silver surface after the oxygen treatment at low temperatures. However, penetration of oxygen into the silver is enhanced by a high temperature treatment, meanwhile the surface oxygen species disappear. No other silver species except metallic silver are observed on all the catalysts by XRD, and the size of silver particle is not changed after the treatment with oxygen at low temperatures. The surface oxygen species formed by oxygen treatment can also be removed by hydrogen reduction. The strongly-adsorbed surface oxygen species prohibit the adsorption and diffusion of oxygen species in reaction gas on the surface of silver catalyst, causing the decrease in CO oxidation activity, in other words, it is important to obtain a clean silver surface for increasing the catalyst activity in CO removal from H2-rich feed gas. The differences in activity and selectivity due to the oxygen pretreatment at different temperatures axe discussed in terms of the changes in the surface/subsurface oxygen species of the silver particles.     

Differential Selectivity of Palladium–Phosphorus Catalysts in the Competitive Hydrogenation of Isomeric Chloronitrobenzenes

The competitive hydrogenation of сhloronitrobenzene isomers in the presence of different palladium- containing catalysts was studied. The nature of catalytic activity carriers for the Pd–P nanoparticles containing both Pd(0) clusters and palladium phosphides was determined by the method of phase trajectories. It was found that the hydrogenation of сhloronitrobenzene isomers under mild conditions occurred on the clusters of Pd(0), and the dependence of the differential selectivity of Pd–P clusters in the hydrogenation of o- and m-сhloronitrobenzene on the P/Pd ratio was related to the dispersity of the Pd(0) clusters.     

Influence of the Br?nsted and Lewis Acid Sites in Platinum/Solid Acid Catalysts on the Hydrogenation of Benzene and Toluene

The hydrogenation of benzene and toluene was investigated over US-SSY, -Al₂O₃, and Ha1-MCM-41 supported platinum catalysts. The acidity of catalyst supports was measured by IR spectra of pyridine adsorption. On the Brönsted acid supported catalyst, both the hexacyclic saturation product and the pentacyclic one, the hydroisomerization product, were observed, and these two products were revealed to be primary reaction products. The two products were proposed to be formed competitively on Brönsted acid sites with carbonium ions as the reaction intermediate. By contrast, no hydroisomerization product was found on Lewis acid supported catalysts. It was inferred that the electron-deficient reaction intermediate formed on Lewis acids could not undertake any skeletal isomerization process to give a pentacyclic saturation product.     

Fischer–Tropsch Synthesis in the Presence of Catalysts Based on Unmodified Iron Ores

Russian Journal of Applied Chemistry - The use of commercial magnetite-type iron ore and of ferriferous quartzite type ore as catalysts for low-temperature Fischer–Tropsch synthesis is...     

Purification Influence of Synthesis Gas Derived from Methanol Cracking on the Performance of Cobalt Catalyst in Fischer-Tropsch Synthesis

1. Introduction Fischer-Tropsch synthesis (FTS) has gained in- dustrial attention for converting synthesis gas to high- boiling points waxes that can be further converted to sulfur-free motor fuels by hydrogenation or hydroc- racking as alternative resour…     

Participation of Water in the Secondary Transformations of Hydrocarbons on Cobalt–Zeolite Catalysts for the Fischer–Tropsch Synthesis

This review is dedicated to the effect of water as the main by-product of the Fischer–Tropsch synthesis on the process. The reasons for the negative effect of water are analyzed and the possible versions of the control of its participation in the process are considered. As an optimal solution to the problem, the use of zeolites in the H form as the constituents of cobalt catalysts for the Fischer–Tropsch synthesis is proposed. Bibliography: 148 references.     

Influence of Aging Time on the Properties of Precursors of CuO／ZnO Catalysts for Methanol Synthesis

The aging process of pure copper precursors and copper-zinc binary precursors were studied by XRD, TG-DTG and TPR techniques. The catalytic activity and stability of CuO/ZnO were tested using fixed-bed flow reactor, and the physical properties of the catalysts and Cu species were characterized with N2 adsorption and N2O passivation method, respectively. For the Cu-Zn binary system prepared at the precipitating condition of pH=8.0 and temperature=80℃, the initial phase was a mixture of copper nitrate hydroxide Cu2(NO3)(OH)3, georgeite and hydrozincite Zn5(CO3)2(OH)6. By increasing the duration of its aging time, the phase of Cu2(NO3)(OH)2 first transited to georgeite, and then interdiffused into Zns(CO3)2(OH)6 and resulted in two new phases: rosasite (Cu,Zn)2CO3(OH)2 and aurichalcite (Zn,Cu)5(CO3)2(OH)6. The former phase was much easier to be formed than the latter one, while the latter phase was more responsible for the activity of methanol synthesis than the former one. It is found that the composition and structure of the precursors altered obviously after the colour transition point. The experimental results showed that methanol synthesis is a structure-sensitive catalytic reaction.     

Effect of the Acid–Base Properties of the Support on the Activity of Pd–Zeolite Catalysts for CO Oxidation

The effect of the acid–base properties of zeolite Y on the activity of palladium–zeolite catalysts for CO oxidation was studied. The modification of the support with basic additives was found to improve the catalyst activity. A linear correlation between the ratio between the amounts of O₂and CO adsorbed on the surface of palladium and the catalyst activity was established.     

Influence of the Feed Gas Composition on the Fischer-Tropsch Synthesis in Commercial Operations

Key technical challenges relating to the Fischer-Tropsch(F-T)synthesis applied in the commer- cialization of coal/gas-to-liquids(CTL/GTL)technolo- gies have been reviewed.Based on the experiences ac- cumulated from pilot plant,semi-work test and lab re- searches,the influences of the H_2/CO ratio and the CO_2 in the feed gas on the F-T process as well as on CTL/GTL complex in terms of product yields,energy efficiency and carbon utilization efficiency have been studied.Being contrary to the current design schemes for F-T process using the coat derived syngas and the iron-based cata- lyst,it is suggested to feed the F-T synthesis unit with a syngas having a H_2/CO ratio of 0.5 and then adjusting to 1.4 via the recycling process.As a result,the carbon efficiency of the whole plant could be reached to as high as 50%.For the issue of CO_2 addition to the feed gas, it is proved that only a diluting role is played under the current commercial slurry phase F-T process.     

Pretreatment of Alumina and Its Influence on the Properties of Co/Alumina Catalysts for Fischer-Tropsch Synthesis

16.6%Co/γ-Al_2O_3 catalysts prepared by incipient wetness impregnation method were used for Fischer-Tropsch synthesis.The support was pre-treated with different concentration of NH_4NO_3 aqueous solution.The effect of support pre-treatment on the properties of support and performance of supported- cobalt-based catalysts was investigated.To treat the support with NH_4NO_3 aqueous solution enlarged the pore ofγ-Al_2O_3,decreased the impurity Na_2O content,and weakened the surface acidity ofγ-Al_2O_3. The change in the properties of the support decreased the interaction between cobalt species and support, enhanced the CO hydrogenation rate and the C_(5 )selectivity.For all catalysts,increasing the reaction temperature increased the CO hydrogenation rate or the CO conversion,slightly decreased the total hydrocarbon selectivity,and favored the formation of methane and light hydrocarbons,while the chain growth probability decreased.For 16.6%Co/γ-Al_2O3 catalysts,prepared with the support treated with 100 g/L NH_4NO3 aqueous solution,the CO conversion,the CH_4 selectivity,and the C_(5 )selectivity were 83.13%,6.86% and 82.75% respectively,and the chain growth probability was 0.83 under the condition of 493 K,1.5 MPa,500 h~(-1)and the molar ratio of H_2 to CO being 2.0 in feed.     

Improving the Selectivity of the Phosphoric Acid β-Elimination on a Biotinylated Phosphopeptide

This study aims at improving the MALDI-TOF detection of a phosphorylated peptide containing a cysteine residue by ??-elimination of H₃PO₄ hardly enriched by classical methods. The experimental conditions were optimized on this phosphopeptide (biot-pAdd) and its nonphosphorylated counterpart (biot-Add). The major side-reactions were H₂S elimination on the cysteine residues and H₂O elimination on the non phosphorylated serine residue of biot-Add. The former dilutes the MALDI-TOF signal for the desired species. The latter gives a product similar to what is obtained by H₃PO₄ elimination and should prompt to caution when working with a mixture between phosphorylated and non phosphorylated peptides. Modifications on the solvent, the reaction temperature and time, the nature, and concentration of the base were made. Major improvement of the selectivity of the reaction was observed in 30?% ACN, at room temperature for 4?h. However, these optimizations are specific to these sequences and should be performed anew for different peptides. The selectivity of the reaction towards H₃PO₄ elimination is improved, but the persistence of side-reactions renders a previous sample fractionation necessary. In these optimized conditions, the ionization enhancement is 3-fold and the detection limits for biot-pAdd are similar to biot-Add (100?fmol).     

Influence of Carboxylic Acids on the Synthesis of Chlorohydrin Esters from 1,3‐Butanediol

The influence of diverse carboxylic acid on the preparation of chlorohydrin esters using a one‐pot esterification–chlorination reaction, in which one of the reagents (chlorotrimethylsilane) acts as solvent, is described. Whereas the acid with low pKa provided higher amounts of the 2‐chloro regioisomer, the ones with higher pKa rendered the 1‐chloro regioisomer in 80% yield. These results are in accordance with the mechanism proposed in a previous article.     

Influence of Ag additions on the activation energy for the reverse eutectoid reaction in Cu–Al alloys

The eutectoid transformation may be defined as a solid-state diffusion-controlled decomposition process of a high-temperature phase into a two-phase lamellar aggregate behind a migrating boundary on cooling below the eutectoid temperature. In substitutional solid solutions, the eutectoid reaction involves diffusion of the solute atoms either through the matrix or along the boundaries or ledges. The effect of Ag on the non-isothermal kinetics of the reverse eutectoid reaction in the Cu–9 mass%Al, Cu–10 mass%Al, and Cu–11 mass%Al alloys were studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The activation energy for this reaction was obtained using the Kissinger and Ozawa methods. The results indicated that Ag additions to Cu–Al alloys interfere on the reverse eutectoid reaction, increasing the activation energy values for the Cu–9 mass%Al and Cu–10 mass%Al alloys and decreasing these values for the Cu–11 mass%Al alloy for additions up to 6 mass%Ag. The changes in the activation energy were attributed to changes in the reaction solute and in Ag solubility due to the increase in Al content.     

The Influence of Alkali Treatment for Synthesizing Hierarchical Zeolite on Behavior of Cobalt Fischer–Tropsch Synthesis Catalysts

Hierarchical zeolites were synthesized by alkali treatment and their applications in Fischer–Tropsch (FT) synthesis were studied. It was found that alkali treatment not only created hierarchical structure but also could tune cobalt-support interaction. The dissolution of Si by alkali treatment became easier with the increase of Si/Al ratio, and thus the amount of mesopority increased. An optimal Si/Al molar ratio was identified over the zeolite with Si/Al ratio of 80, which was found to be superior to other catalysts in terms of better diesel selectivity and lower CH₄ selectivity due to its relatively narrow bimodal pore size distribution and moderate cobalt-support interaction. Meanwhile alkali treatment could enhance cobalt-support interaction via the formation of ɑ-SiO_2, Co/MZ-120 catalyst showed the lowest FT activity and higher CH₄ selectivity due to the increase of such new phase.     

The Influence of Temperature on the Heat Effects of Acid—Base Interaction in Aqueous Solutions of Citric Acid

The heat effects of interaction of a solution of citric acid with solutions of HNO₃ and KOH at 288.15, 298.15, and 308.15 K and ionic strength values 0.5, 1.0, and 1.5 (KNO₃) were measured calorimetrically. The heat effects of acid dissociation were calculated using the HEAT program. The standard thermodynamic characteristics of step dissociation of citric acid were determined.     

Influence of Method of Introduction of Cu- and Zn-Based Modifiers on the Properties of Chromia–Alumina Catalysts

Three methods of introduction of modifiers based on Cu and Zn compounds into the CrO_x/Al₂O₃ catalysts for dehydrogenation of light paraffin hydrocarbons are considered: Introduction from sol, introduction using successive impregnation technique and introduction of modifiers by impregnation along with precursor of chromium oxide. The obtained samples are studied by a complex of physical-chemical methods (XRD, UV-Vis spectroscopy, temperature-programmed reduction with hydrogen (TPR-H₂), X-ray fluorescent (XRF) spectrometry, low-temperature N₂ sorption). The catalytic properties of the samples are studied in kinetic mode in isobutane dehydrogenation. Cu- and Zn-modifiers are shown to influence on the peculiarities of reduction of Cr⁶⁺ and, hence, specify the state of active surface of CrO_x/Al₂O₃ catalysts formed in the reductive reaction medium. Not only do the states of modifiers influence on the initial activity of the catalyst, but also on its activity after oxidative regeneration. Introduction of modifiers by successive impregnation method results in formation of copper and zinc aluminates or defective spinels on the Al₂O₃ surface. When the active component is introduced, the modified surface of the support promotes formation and stabilization of Cr⁶⁺ sites that can undergo reversible reduction–oxidation and provide high activity and selectivity towards formation of isobutylene (>98%).     

Carbon Deposits Formed on the Surface of Ru–Ni Catalysts During the Mixed Reforming of Methane Process

Monometallic nickel and bimetallic ruthenium–nickel catalysts supported onto aluminum oxide without additives and aluminum oxide modified with MgO and CaO were prepared by an impregnation method. The catalysts were tested in the process of the mixed reforming of methane, and their properties were characterized by thermogravimetry, scanning electron microscopy, and X-ray diffractometry. The total organic carbon content of the catalysts was also measured. The promoting effect of ruthenium and structural promoters on the catalytic activity of Ni/Al₂O₃ was confirmed. The Ru–Ni/MgO–Al₂O₃ catalyst exhibited the highest stability and activity; this fact can be explained by the increased adsorption of methane on the surface of ruthenium–nickel clusters.     

Effects of Ag Atomic Segregation from Different Planes on the Size-Dependent Melting of Ag–Pd Clusters

This paper studies the effects of Ag atomic segregation from the inner (100) or (111) planes on the melting of Ag–Pd clusters with different sizes by a molecular dynamics simulation. The results show that Ag segregation leads to the atomic energy decreases with increasing the temperature. Furthermore, the effect of the (100) segregation is larger than that of the (111) segregation. Meanwhile, the influence of segregation on the energy decreases with increasing the cluster size. The melting points of the clusters without segregation are the largest, followed by the clusters with a (111) and (100) segregation.     

Influence of Solute–Solvent Interaction on Acid Strength of Some Substituted Phenols in Ethanol–Water Media

The solute–solvent interactions of some phenol derivatives were investigated potentiometrically in 0–60 % (v/v) ethanol–water mixtures. The acidity constants values were correlated with either macroscopic parameters such as molar fraction, permittivity and the solvating ability or microscopic parameters, such as the Kamlet–Taft solvatochromic parameters. Moreover, it is demonstrated that the pK _a values in any ethanol–water mixtures are linearly related to the pK _a values of the phenols in pure water. The slope and intercept parameters of the linear correlations are related with the mole fraction of ethanol. These equations permit accurate calculation of the pK _a values of the studied phenols at any ethanol–water composition.