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Mesoporous silica gel doped with dysprosium, lanthanum and modified with silver (Dy-Ag/MPS, La-Ag/MPS) was obtained by the template method. The physicochemical characteristics of the obtained catalyst were studied by scanning electron microscopy, X-ray fluorescence and X-ray diffraction analysis, inductively coupled plasma mass spectrometry and temperature-programmed reduction. In addition, the possibility of using obtained materials as an efficient and selective catalysts in the hydrogenation of a 1-heptyne/1-heptene mixture (with 30% of alkyne content) in a temperature range of 140–160 °C and a hydrogen pressure of 3 atm was studied. It was found that after 15 min from the start of the hydrogenation reaction at 140 °C on the La-Ag/MPS catalyst, total conversion of 1-heptyne was observed and selectivity for 1-heptene was 84%. Moreover, it was shown that on a Dy-Ag/MPS at 150 °C 1-heptyne conversion was 84%, the selectivity for alkene was 79%. Furthermore, with an increase in temperature to 160 °C, the conversion of 1-heptyne reaches 95%, the selectivity for 1-heptene—84%. [ABSTRACT FROM AUTHOR]

The efficient SBA-15 supported silver catalysts(Ag/SBA-15) were prepared and characterized by ICP-OES, XRD, TEM, SEM, XPS and N2 adsorption–desorption techniques. The catalysts exhibited an excellent catalytic activity for the aerobic oxidation of toluene to benzaldehyde under solvent-free conditions. Conversion of toluene and selectivity of benzaldehyde were 50% and 89% respectively over catalyst with 9.1 wt% Ag loading (10Ag/SBA-15). A wide range of substrates were tolerated under the selected reaction conditions. The kinetic study shows that the oxidation of toluene over 10Ag/SBA-15 is pseudo-first-order reaction and the activation energy Ea is 45.1 kJ/mol. A plausible mechanism involving oxygen free radicals was proposed for the aerobic oxidation reaction. Compared with the traditional method, the newly designed heterogeneous catalytic system shows better economic applicability, environmental friendliness and broader application prospects. [ABSTRACT FROM AUTHOR]

La1−xAgxFeO3 (x = 0.05–0.25) perovskites deposited on a honeycomb-shaped monolithic metallic support were used as catalysts for the total oxidation of hydrocarbons. Monolithic catalysts were prepared by washcoating honeycomb substrates with lanthanum-stabilized γ-Al2O3, on which La1−xAgxFeO3 was deposited. Catalysts with La1−xAgxFeO3 perovskites show higher activity for methane oxidation at x ≥ 0.05 and hexane oxidation at x ≥ 0.1 than LaFeO3 catalyst. The perovskite catalysts were characterized by XRD, XPS, SEM, TEM, TPR-H2, O2-TPD and BET specific surface area measurement. Ag forms solid solutions with the La1−xAgxFeO3 perovskite lattice for x = 0.05–0.1. In La1−xAgxFeO3 perovskites (x ≥ 0.1), Ag0 particles with average crystallite sizes from 31 to 41 nm were also identified. When Ag is introduced into the LaFeO3 perovskite, both the changes occurring after some Ag is incorporated into its structure and the presence of large crystallites of metallic silver contribute to the catalysts' activity increase. [ABSTRACT FROM AUTHOR]

Mesoporous Fe-N-C supported Ag nanoparticles (AgNPs) with different metal loadings (Fe-N-C/AgNPs-n, n = 1, 2, 3) were prepared by a facile method. The as-prepared Fe-N-C/AgNPs-n catalysts were demonstrated to be the excellent electrocatalysts for oxygen reduction reaction (ORR) in alkaline media. The Fe-N-C/AgNPs-2 exhibited the highest electrocatalytic activity with onset potential of 1.03 V and half-wave potential of 0.88 V for ORR, which were higher than commercial Pt/C (20 wt%) and Fe-N-C catalysts reported in the literature. Moreover, the prepared Fe-N-C/AgNPs-2 material possessed intrinsic long-time stability and the excellent methanol resistance toward the ORR in alkaline media. The Tafel slope and Tafel curve shape for ORR on Fe-N-C/AgNPs-n and Fe-N-C and the decrease of N's binding energy in the Fe-N-C/AgNPs-n testify that the active sites for ORR in Fe-N-C/AgNPs-n are on Fe-N-C rather than on AgNPs. The AgNPs enhance the electrocatalytic activity of Fe-N-C for ORR as cocatalyst by inducing a more negative charge on the adjacent N to C, which may be the important reason for improving ORR performance of Fe-N-C. Graphical Abstract: [ABSTRACT FROM AUTHOR]

BiFeO nanoparticles have been synthesized by hydrothermal method. Ag nanospheres (1 wt%) have been successfully decorated on the surface of BiFeO nanoparticles by photo-deposition method. XPS study confirms the decoration of Ag on the surface of BiFeO. Synthesized nanoparticles have been characterized by studying their morphological, structural, optical and photocatalytic properties. It has been found that the photocatalytic properties of Ag decorated BiFeO nanoparticles to decompose methylene blue in visible light are far better than those of bare BiFeO nanoparticles. The mechanism of enhanced photocatalytic activities of Ag-decorated BiFeO nanoparticles has been disclosed. Graphical Abstract: [ABSTRACT FROM AUTHOR]

The present work highlights for the first time that a thermal treatment of γ-AlO in water at 80 °C for 24 h prior to Ag deposition (Ag/AlO-OH) leads to a drastic enhancement of H-CH-SCR performance at low temperature. This enhancement is attributed to the higher NO coverage on Ag/AlO-OH compared with that of Ag/AlO. The higher NO adsorption capacity of the sample prepared from the γ-AlO thermally-treated in water is proposed to result from the preferential interaction of Ag with newly-created AlO anchoring sites (Al(OH) bayerite domains), which were not available on the untreated pristine support. Graphical Abstract [ABSTRACT FROM AUTHOR]

Au/SBA-15 nano catalysts were synthesized from four different methods, viz., homogeneous deposition-precipitation, micro-emulsion, impregnation and polyol, and their catalytic activities were investigated for the vapor phase oxidation of benzyl alcohol to benzaldehyde. The physico-chemical properties of the catalysts were characterised by XRD, TEM, BET surface area, pore size distribution, CO-chemisorption and XPS techniques. The structural data of the catalysts along with their catalytic studies indicate that the presence of very small metallic Au species with particle size of 7-8 nm, was responsible for the higher activity observed in the vapor phase oxidation of benzyl alcohol reaction. The title reaction, though industrially important, was used as a test reaction to investigate firstly, the influence of different preparation methods on the uniform dispersion of gold particles on the support SBA-15 and to understand the metal-support interaction in Au/SBA-15 catalysts, and secondly, to study the catalytic performance of the catalyst (Au/SBA-15) in terms of activity, selectivity and stability over a period of reaction time. The conversion of benzyl alcohol was found to increase with decrease in the size of gold particles. Smaller gold particles with higher percentage of dispersion on the support SBA-15 had a beneficial effect on the catalytic activity. Among the four methods used for the preparation of gold on SBA-15 support, the catalyst prepared by homogeneous deposition-precipitation method showed the best performance in terms of conversion, selectivity for benzaldehyde and longer catalyst life. Graphical Abstract: Vapor phase oxidation of benzyl alcohol over nano Au/SBA-15 catalysts. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this theoretical work sequential adsorption of H and O on a Ag cluster surface is first studied and AgHO cluster co-complex thereby obtained is used for the NO reduction process. This cationic charged silver nano cluster simulates small Ag crystals experimentally detected on γ-AlO support. For NO reduction, three different mechanisms and intermediate steps of these mechanisms reported in experimental literature are examined. Energy profiles, activation barriers and transition states of the reaction steps involved are studied. Some intermediate steps turned out to have high activation barriers. Hence a combined mechanism selected from the favorable steps found in these three mechanisms is proposed. By using this combined mechanism, reduction of NO to N is achieved. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Silver/alumina catalysts are known to be highly active for hydrogen-assisted selective catalytic reduction (SCR) of nitrogen oxides. A comparison of silver/alumina and pure alumina catalysts shows that hydrogen conversion occurs on the silver. Subsequently formed NO is crucial for NH-SCR and in addition products from the hydrogen conversion influence nitrates on the alumina by spill-over. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Today ethylene oxide can be produced industrially with ~90 % selectivity through the epoxidation of ethylene over silver catalyst. The past decades there has been a substantial increase in the understanding of the molecular chemistry that leads to high selectivity catalysis. Especially the discovery of an oxometallacycle intermediate that produces ethylene epoxide in competition with acetaldehyde can be considered a major advancement. The state of the surface at reaction conditions causes different reaction paths to compete. At high oxygen coverage also a direct epoxidation channel opens. We will also review recent progress on the understanding of promotion and coverage dependent reactivity. The contributions in our understanding of this reaction from computational catalysis will be emphasized. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Ag-based catalysts on different nanocrystalline perovskite supports (MgTiO, CaTiO, SrTiO, and BaTiO), and nanocrystalline TiO support prepared by a sol-gel method and on a commercial α-AlO support were comparatively studied for catalytic activity of the ethylene epoxidation reaction. The dependence of ethylene oxide production performance on calcination temperature of the support, type of titanate nanocrystal supports, Ag loading, and reaction temperature was systematically investigated. The catalysts were analytically characterized by a Brunauer-Emmett-Teller (BET) surface area, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Among studied catalysts, the 17.2 wt% Ag/SrTiO catalyst exhibited the highest catalytic activity towards ethylene epoxidation reaction. Graphical Abstract: The long-term stability of the dominant catalysts (which exhibited a high catalytic activity to produce ethylene oxide) was studied at 48 h of time on stream. As shown in the figure, the 17.2 wt% Ag/SrTiO catalyst with the support calcination temperature of 923 K is the most effective catalyst for the ethylene epoxidation reaction, giving not only the highest EO selectivity but also providing the highest long-term stability.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A new preparation of silver supported alumina catalysts, with highly dispersed and stable silver particles, is reported. The preparation, performed from a mixture of silver oxide and alumina, consists simply of heating this mixture under an oxidizing gas containing a water vapour concentration higher than 5.0 mol% in a temperature range between 903-948 K. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A heterogeneous silver catalyst was prepared and applied efficiently for the selective bromination of aromatics with NBS. The silver nanoparticles combined with the acidic support HMB can activate both the aromatic ring and NBS, and the synergistic effects between the silver nanoparticles and the HMB highly enhanced the efficiency of the bromination reaction. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations were employed to study epoxidation of ethylene on a [AgO] cluster model representing silver oxide (001) surface. Theoretical results obtained in this study showed that formation paths of acetaldehyde and vinyl alcohol have higher activation barriers than that of ethylene oxide formation path on silver oxide (35 and 35 vs. 20 kcal/mol). Formation of the ethylene oxometallocycle intermediate is found to have a low probability on AgO(001) surface. The essential reason for this may be lower basicity of surface oxygen atom on silver oxide surface and the absence of a surface vacancy position to activate ethylene. Adsorbed EO is formed on AgO surface cluster without an activation barrier. The activation barriers of the rate-limiting steps for the production of EO mechanisms (via ethyleneoxy and non-activated paths, 20 vs. 14 kcal/mol) are in relatively good agreement with the experimental activation energy values (14, 17 and 22 kcal/mol) reported for EO formation on silver catalyst. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The role of Ag in simultaneously catalyzing NO reduction and C3H6 oxidation was shown to be strongly dependent on the redox properties of its local environment. Under an atmosphere of 1,000 ppm NO, 3,000 ppm C3H6, and 1% O2 and a GHSV of 30,000 h−1, a perovskite La0.88Ag0.12FeO3 prepared by reactive grinding is active giving a complete NO conversion and 92% C3H6 conversion at 500 °C. These values are much higher than the NO conversion of 55% and C3H6 conversion of 45% obtained over a 3 wt.% Ag/Al2O3 catalyst under the same conditions. Under an excess of oxygen (10% O2) a good SCR performance with a plateau of N2 yield above 97% over a wide temperature window of 350–500 °C along with C3H6 conversion of 90% at 500 °C was observed over Ag/Al2O3, while minor N2 yields (∼10% at 250–350 °C) and high C3H6 conversions (reaching ∼100% at 450 °C) were obtained over La0.88Ag0.12FeO3. Abundant molecular oxygen is desorbed from Ag substituted perovskite after 10% O2 adsorption as verified by O2- temperature programmed desorption (TPD). This reflects the strongly oxidative properties of La0.88Ag0.12FeO3, which lead to a satisfactory NO reduction at 1% O2 due to the ease of nitrate formation but to a significant C3H6 combustion above that value. The formation of nitrate species over the less oxidizing Ag/Al2O3 was accelerated under an excess of oxygen resulting in an excellent lean NO reduction behavior. The redox properties of silver catalysts could be adjusted via mixing perovskite with alumina for an optimal elimination of both NO and C3H6 over the whole range of oxygen concentration between 0 to 10%. [ABSTRACT FROM AUTHOR]

The Ag/α-Al2O3 catalyst modified with rare earth metal oxide (Y2O3) and alkali metal oxide (K2O) for the epoxidation of propylene by molecular oxygen were prepared and characterized by TG-DTA, XRD and XPS. The results show that a small quantity of Y2O3 added plays a role of electron and structure-type promoters, and can change the binding energies of Ag3d and restrain the sintering of Ag crystallites during catalyst preparation. The effects of promoters loading, Ag loading, reaction temperature, and calcination atmosphere on the performance of Ag catalyst were investigated. The results show that the loadings of K2O, Y2O3 and Ag, and reaction temperature affect obviously the catalytic performance of Ag–Y2O3–K2O/α-Al2O3 for the epoxidation of propylene to propylene oxide. Under the reaction conditions of 0.1 MPa, 245 °C, GHSV of 2000 h−1 and the feed gas of 20%C3H6/8%O2/N2, the conversion of propylene of 4% and the selectivity to propylene oxide of 46.8% were achieved over the 20%Ag–0.1%Y2O3–0.1%K2O/α-Al2O3 catalyst. Y2O3 plays a role of electron and structure-type promoters in the Ag–Y2O3–K2O/α-Al2O3 catalyst, which can change the binding energies of Ag3d and restrain the sintering of Ag crystallites, resulting in obvious improvement of the catalytic performance of Ag–Y2O3–K2O/α-Al2O3 for the epoxidation of propylene to propylene oxide by molecular oxygen.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Nitromethane (NM) is a very efficient reductant for converting NO2 to N2 over Ag/Y: Between 140 °C and 400 °C, the N2 yield is close to 100%. This high N2 yield results from the ability of Ag/Y to effectively catalyze the reaction between NM and NO2. This high catalytic activity of Ag/Y is minimally affected by surface bound CN−, NC−, or acetate, all of which are stable at temperatures below ∼300 °C. At T ≥ 400 °C, there is a reaction path that yields N2 from NM even in the absence of NO2. However even at 400 °C, under typical deNO x conditions, most N2 molecules are formed as a result of the reaction of NM and NO2. [ABSTRACT FROM AUTHOR]

The role of the Al2O3 support on the activity of supported Ag catalyst towards the selective catalytic reduction (SCR) of NO with decane is elucidated. A series of Ag/Al2O3 catalysts were prepared by impregnation method and characterized by N2 pore size distribution, XRD, UV–Vis, in-situ FT-IR and acidity measurement by NH3 and pyridine adsorption. The catalytic activity differences of Ag/Al2O3 are correlated with different properties of Al2O3 supports and the active Ag species formed. 4wt% Ag supported on sol-gel prepared Al2O3 (Ag/Al2O3 (SG), showed higher NO x conversion (65% at 400 °C), compared with the respective catalysts made from commercial Al2O3 (Ag/Al2O3 (GB), Ag/Al2O3 (ALO), (∼26 and 7% at 400 °C). The higher surface area, acidity and pore size distribution in sol–gel prepared Al2O3 (SG) results in higher NO and hydrocarbon conversion. Based on the UV–vis characterization, the activity of NO reduction is correlated to the presence of Ag clusters and acidity of Al2O3 support was found to be one of the important parameter in promoting the formation and stabilization of Ag clusters. Furthermore from pyridine adsorption results, presence of more number of Bronsted acid sites in Ag/Al2O3 (SG) is confirmed, which could also contribute to low temperature hydrocarbon activation and improve NO conversion. In situ FT-IR measurements revealed the higher rate of –CN and –NCO intermediate species formation over 4wt% Ag/Al2O3 (SG). We conclude that the physico–chemical properties of Al2O3 play a crucial role in NO x conversion over Ag/Al2O3 catalysts. Thus, the activity of the Ag/Al2O3 catalyst can be tailored by using a proper type of Al2O3 support. [ABSTRACT FROM AUTHOR]

Commercial activated carbon (AC) was used as a support either in its original form or after various modifications, giving diverse textural and surface chemical characteristics. The changes of these properties were monitored by N2 adsorption–desorption isotherms, temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). Ag catalysts were prepared over the AC supports by a conventional wet impregnation method. The catalytic performances of supported Ag/AC catalysts in the selective oxidation of CO in excess H2 were tested. The results indicate the textural and surface chemical characteristics are responsible for the different catalytic performances. [ABSTRACT FROM AUTHOR]

Nano-scale silver supported mesoporous molecular sieve Ag/MCM-41 was directly prepared by one-pot synthesis method. The prepared sample was characterized by XRD, TEM, and N2 sorption. The results showed that the sample of Ag/MCM-41 had no appreciable incorporation of silver into the mesoporous matrix of MCM-41 with good crystallinity, and silver nanoparticles were dispersed inside or outside of the channels in the mesoporous host. The catalytic performance of the sample for the cyclohexane liquid-phase oxidation into cyclohexanone and cyclohexanol by oxygen in the absence of solvents without inducing agents was investigated. The 83.4% selectivity to cyclohexanol and cyclohexanone at 10.7% conversion of cyclohexane was obtained over Ag/MCM-41 catalyst at 428 K for 3 h. The turn over numbers (TONs) of Ag/MCM-41 was up to 2946. The catalytic activity of Ag/MCM-41 was also compared with Ag/TS-1 as well as Ag/Al2O3. The results indicated that Ag/MCM-41 showed superior activity to both Ag/TS-1 and Ag/Al2O3. A calcined Ag/MCM-41 was found to be an efficient catalyst for the cyclohexane oxidation into cyclohexanol and cyclohexanone using oxygen as oxidant. [ABSTRACT FROM AUTHOR]

In situIR measurements for CO adsorption and preferential CO oxidation in H2-rich gases over Ag/SiO2 catalysts are presented in this paper. CO adsorbed on the Ag/SiO2 pretreated with oxygen shows a band centered around 2169 cm-1, which is assigned to CO linearly bonded to Ag+ sites. The amount of adsorbed CO on the silver particles (manifested by an IR band at 2169 cm-1) depends strongly on the CO partial pressure and the temperature. The steady-state coverage on the Ag surface is shown to be significantly below saturation, and the oxidation of CO with surface oxygen species is probablyviaa non-competitive Langmuir-Hinshelwood mechanism on the silver catalyst which occurs in thehigh-rate branchon a surface covered with CO below saturation. A low reactant concentration on the Ag surface indicates that the reaction order with respect to Pco is positive, and the selectivity towards CO2 decreases with the decrease of Pco. On the other hand, the decrease of the selectivity with the reaction temperature also reflects the higher apparent activation energy for H2 oxidation than that for CO oxidation. [ABSTRACT FROM AUTHOR]

Catalytic reaction was performed in theunregardedtemperature region over silver catalysts with long catalytic lifetime for the conversion of methanol to methyl formate. Oa-saturated or O?-saturated silver catalysts were studied individually to identify the roles of Oa, O? in the oxidative esterification of methanol over an unsupported polycrystalline silver catalyst. A synergic process is proposed based on the coexistence of a-oxygen species and ?-oxygen species on the surface of polycrystalline silver at about 573 K. [ABSTRACT FROM AUTHOR]

The polycrystalline silver after pre-treated with oxygen at high temperature was found to show excellent activity and selectivity in the process of direct dehydrogenation of methanol to anhydrous formaldehyde and the active oxygen species for this reaction was observed and proposed as the active centeres within situRaman scattering. [ABSTRACT FROM AUTHOR]

The mixed copper-silver oxide, Cu2Ag2O3, has been prepared by co-precipitation and tested for ambient temperature carbon monoxide oxidation. The catalyst demonstrated appreciable low temperature oxidation activity and the catalyst aged for 4 h was the most active. Carbon monoxide conversion increased with time-on-stream, reaching steady state after ca. 1000 min. A?comparison of the catalytic activity has been made with a representative sample of a high activity hopcalite, mixed copper/manganese oxide catalyst. On the basis of CO oxidation rate data corrected for the effect of catalyst surface area the Cu2Ag2O3, aged for 4 h was at least as active as the hopcalite. [ABSTRACT FROM AUTHOR]