Silver Catalyst Research Articles

Biosynthesized silver supported catalysts for disinfection of Escherichia coli and organic pollutant from drinking water

Presence of Escherichia coli in water is mainly responsible for contamination of drinking water. Currently, organic materials are being used for disinfection of drinking water. However, antimicrobial inorganic materials have more potential due to their thermal resistance, chemical stability, and long lasting action period. In this work silver nanoparticles (AgNPs) were synthesized by chemical and biological methods and then impregnated with different support materials including Activated carbon, Zeolite and Magnesium oxide. Formation of nanoparticles was confirmed by UV/visible spectrophotometer due to their surface plasmon resonance, in which AgNPs showed a peak at 445 nm. XRD patterns gave characteristic patterns to AgNPs on support. AgNPs on support material were further verified by FE-SEM and EDX analyses. AgNPs supported catalysts were more active and all the bacteria were inhibited in drinking water. Beside antibacterial activity, the prepared catalysts shows excellent activity in the reduction of azo dye methyl orange. Among all, MgO impregnated silver catalysts show an outstanding methyl orange reduction with the rate constant of 7.48 × 10−3 s−1. So, it indicates that different supported AgNPs have the potential to be used for removal of microbial and organic pollutants from drinking water.

Catalytic oxidation of ethyl acetate over silver catalysts supported on CeO2 with different morphologies

Abstract In this study, the Ag/CeO2 catalysts with three different morphologies of ceria nanocubes (CeO2-c), nanorods (CeO2-r) and nano-octahedra (CeO2-o) as supports were prepared by wet impregnation. Various characterizations such as XRD, BET, TEM/HRTEM, HAADF-STEM, XPS and H2-TPR were conducted, and a four step catalytic transformation was accordingly proposed. It was found that Ag/CeO2-c showed much more metallic Ag, active oxygen species and higher reducibility than those of Ag/CeO2-r and Ag/CeO2-o mainly due to the morphology effect. Ag/CeO2 and CeO2 catalysts were evaluated in the oxidation of ethyl acetate, and their catalytic activities were in the sequence of Ag/CeO2-c > Ag/CeO2-r > CeO2-r > CeO2-c > Ag/CeO2-o > CeO2-o. Besides, in-situ FTIR results revealed that the organic species on the catalyst surface were mainly acetates and adsorbed ethyl acetate for Ag/CeO2-c and CeO2-c, respectively, suggesting that addition of Ag promoted the complete oxidation of ethyl acetate.

Core-shell metal-organic frameworks and metal functionalization to access highest efficiency in catalytic carboxylation

A core-shell metal-organic frameworks (MOF@MOF) based on the Zr-MOFs assembly from core-structure UiO-66 combined with shell-structure UiO-67-BPY were explored. The synthesized materials were characterized via XRD, FTIR, SEM, TEM, and surface area analysis, etc. indicating the presence of a core-shell structure of UiO-66@UiO-67-BPY. Furthermore, incorporation of the bipyridinic (BPY) group in the linker used to construct the shell layer (UiO-67-BPY) could coordinate with active metal species and thus create an advantage for site-selective metal incorporation in the core-shell structure. Silver (Ag) was selected for the selective metal incorporation and an excellent Ag-dispersion via coordination with the bipyridinic groups in the UiO-67-BPY layer of the core-shell material was obtained. The synthesized material (UiO-66@UiO-67-BPY-Ag) was successfully applied as a heterogeneous catalyst for the CO2 fixation via carboxylation of terminal alkynes. The catalytic material showed excellent yields using at a low Ag-loading under mild reaction condition (50 °C, 1 bar). Moreover, the catalyst can be recycled for at least 5 times maintaining a stable catalytic performance. Interestingly, the high catalytic activity of the synthesized material demonstrated clearly the beneficial advantage of the metalated core-shell structure over the reported routes to synthesize silver catalysts such as encapsulated Ag nanoparticles (AgNP@MOF) or Ag-bidentately coordinated on traditional MOFs applying the same reaction model.

Catalytic oxidation of diesel particulate matter by using silver and ceria supported on alumina as the oxidation catalyst

To enable passive regeneration of a diesel particulate filter (DPF), this work seeks to study the potential of silver and ceria for the catalytic oxidation of diesel particulate matter (PM). Different contents of silver and ceria supported on alumina and silver loaded on ceria are synthesised by the incipient wetness impregnation method. The catalysts are characterised via XRD, SEM, and EDX. Catalytic PM oxidation performance for different PM/catalyst weight ratios and contact conditions is examined by using TGA. Removal of light soluble organic fraction (SOF) occurs between 110 and 350 °C through the vaporisation process. For the PM/catalyst weight ratio of 1/5, the silver compositions do not improve the depletion of light SOF but promote the combustion of both heavy SOF and soot, and the enhancement increases with silver content. For 16 wt% of silver supported on alumina, the PM/catalyst weight ratio of 1/20, and tight contact, oxidative activity is improved throughout the temperature window for light and heavy SOF and soot. The silver catalyst shows good stability for five runs. Active oxygen adspecies generated by ceria are different from those produced by silver. Enhanced performance for light SOF oxidation at a relatively low temperature is obtained using pure ceria. With the addition of alumina into ceria, light SOF removal ability of ceria is negatively affected. The positive effect on heavy SOF and soot reduction gained from the presence of silver is suppressed when ceria is mixed with silver.

Synthesis of methyl glycolate from the hydrogenation of dimethyl oxalate on Ag/SiO2 catalyst: the effects of Ag contents and promoters

A series of silica supported silver catalysts (Ag/SiO2) with Ag loading ranging from 5% to 15% were fabricated by the ammonia-evaporation deposition–precipitation method. The effect of Ag contents on the catalytic performance of the catalysts in the selective hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) was investigated. The result indicates that the catalyst with a 10 wt% silver loading exhibits the best catalytic activity and excellent long-term stability of more than 150 h. Characteristic studies by N2 adsorption, TPR, XRD, and XPS show that the Ag content has a significant impact on the physicochemical properties of the Ag/SiO2 catalyst. Furthermore, the influence of some additives (B, Ni, La, Ce, and Mo) on the catalytic performance of the most active 10%Ag/SiO2 catalyst in the DMO hydrogenation to MG was also studied.

Optimizing mesostructured silver catalysts for selective carbon dioxide conversion into fuels

Mass transport is responsible for the substantial rise in reaction selectivity with increasing thickness of mesostructured silver catalyst films.

Operando EXAFS study reveals presence of oxygen in oxide-derived silver catalysts for electrochemical CO2 reduction

Grazing incidence operando EXAFS measurements allow observation of oxygen in oxide-derived silver catalysts, its effect on CO2 reduction is explained.

Re- and Cs-copromoted silver catalysts for ethylene epoxidation: A theoretical study

The effect of Re and Cs co-promotion of Ag catalysts for ethylene epoxidation is studied computationally using density functional theory approach. The models reflecting Re involvement in the form of oxyanion and as a component of Ag—Re alloys are considered. The synergistic effect of Cs and Re is caused by the formation of the CsReOx species, with Cs stabilizing the Re oxyanion to promote ethylene epoxidation over Ag catalysts. The role of Re is proposed to be related to altering the electron density distribution, compensating oxygen vacancies, co­vering non-selective sites, and providing the optimal retention time for initial compounds, pro­ducts, and oxametallacycles on the catalyst surface.

Silver nanoparticles by atomic vapour deposition on an alcohol micro-jet.

We achieved sputter deposition of silver atoms onto liquid alcohols by injection of solvents into vacuum via a liquid microjet. Mixing silver atoms into ethanol by this method produced metallic silver nanoparticles. These had a broad, log-normal size distribution, with median size between 3.3 ± 1.4 nm and 2.0 ± 0.7 nm, depending on experiment geometry; and a broad plasmon absorption band centred around 450 nm. We also deposited silver atoms into a solution of colloidal silica nanoparticles, generating silver-decorated silica particles with consistent decoration of almost one silver particle to each silica sphere. The silver–silica mixture showed increased colloidal stability and yield of silver, along with a narrowed size distribution and a narrower plasmon band blue-shifted to 410 nm. Significant methanol loss of 1.65 × 10−7 mol MeOH per g per s from the mature silver–silica solutions suggests we have reproduced known silica supported silver catalysts. The excellent distribution of silver on each silica sphere shows this technique has potential to improve the distribution of catalytically active particles in supported catalysts.

Ethylene Epoxidation on Ag(100), Ag(110), and Ag(111): A Joint Ab Initio and Kinetic Monte Carlo Study and Comparison with Experiments

Ethylene epoxidation is commercially one of the most important selective oxidation reactions. Despite extensive research into different catalytic materials, silver catalysts remain unrivaled in industrial applications, albeit with significant doping. Experiments have already shown that different silver facets exhibit different catalytic performance in terms of turnover frequencies as well as selectivity. In this work, we present extensive first-principles simulations and kinetic Monte Carlo (KMC) modeling of the reaction on the three pristine silver surfaces Ag(100), Ag(110), and Ag(111) and on the missing-row reconstructed Ag(110). To better understand the kinetics on different surfaces and veraciously describe the surface coverages, we explicitly take into account the lateral interactions between the adsorbates and their effect on the activation barriers. We show that the most stable Ag(111) surface maintains very low oxygen coverage while being the least active surface and only moderately selective. Ag...

Silver‐Catalyzed Hydrogenation of Ketones under Mild Conditions

AbstractThe silver‐catalyzed hydrogenation of ketones using H2 as hydrogen source is reported. Silver nanoparticles are generated from simple silver (I) salts and operate at 25 °C under 20 bar of hydrogen pressure. Various aliphatic and aromatic ketones, including natural products were reduced into the corresponding alcohols in high yields. This silver catalyst allows for the selective hydrogenation of ketones in the presence of other functional groups.magnified image

Synthesis of a Bimetallic Catalyst in a Static CO2-Impregnation Process

The synthesis of palladium and palladium–silver catalysts using supercritical fluid CO2-impregnation (static conditions) was studied. It was shown that the highest amount of metal is impregnated onto a support in a temperature range of 318–323 K and a pressure range of 19.0–23.0 MPa. The activities of palladium catalysts prepared according to the proposed procedure were comparable with those of currently produced industrial samples.

Reversible Restructuring of Silver Particles during Ethylene Epoxidation

The restructuring of a silver catalyst during ethylene epoxidation under industrially relevant conditions was investigated without and with vinyl chloride (VC) promotion. During non-VC-promoted ethylene epoxidation, the silver particles grow and voids are formed at the surface and in the bulk. Electron tomography highlighted the presence of voids below the Ag surface. A mechanism is proposed involving reconstruction of the silver lattice and defect sites induced by oxygen adsorption on the external surface and grain boundaries, which finally create pores. Promotion of the catalytic reaction by VC suppresses to a significant extent void formation. The use of VC also redisperses silver particles, initially grown during ethylene epoxidation without VC. This process is rapid as the average size decreased from 172 to 136 nm within 2 h. These insights emphasize the dynamic nature of the silver particles during the ongoing ethylene epoxidation reaction and indicate that particle size and morphology strongly depend on reaction conditions.

Oxygen Reduction Reaction on Silver Catalysts in Alkaline Media: a Minireview

AbstractThe development of efficient platinum‐free catalysts for electrocatalytic oxygen reduction reaction (ORR) is one of the main challenges in the fuel cell research. Silver‐based materials are highly active towards ORR in alkaline conditions and recent achievements in improving the performance of anion exchange membrane fuel cells (AEMFCs) have provoked many scientists to study these catalysts. This minireview is focused on the ORR performance of monometallic Ag catalysts and Ag‐based composites, the electrochemical oxygen reduction behaviour of Ag‐containing alloys is outside the scope of this review. The effect of the morphology of Ag nanostructures on catalysts’ ORR activity and pathway is discussed and the role of the support material is described. The performance of AEMFCs using Ag‐based cathode catalysts is also reviewed.

Catalytic Effect of a Combined Silver and Surfactant Catalyst on Cobalt Ore Bioleaching

The effects of Ag+, surfactants, and their combination on cobalt ore bioleaching were investigated in this article. Ag+ ions and surfactants, either individually or in combination, can significantly accelerate mineral dissolution and increase metal leaching efficiencies. When 20 mg L−1 Ag+ was added, the cobalt and copper leaching efficiencies increased from 67.8% and 58.5% to 94.3% and 80.7%, respectively. In addition, in the presence of 150 mg L−1 Tween-20, the cobalt and copper leaching efficiencies increased by more than 25% and 11%, respectively. A similar trend was observed with Tween-60 and Tween-80. When a combined catalyst of Ag+ ions and surfactant was employed, the cobalt and copper leaching efficiencies increased by more than 23% and 10%, respectively. Moreover, the leaching time decreased by one quarter. The catalytic effect of the combined catalyst was more significant than that of a single catalyst.

Modifying catalytically the soot morphology and nanostructure in diesel exhaust: Influence of silver De-NOx catalyst (Ag/Al2O3)

The influence of an Ag/Al2O3 HC-SCR catalyst on the morphological and nanostructural aspects of the exhaust particulate matter (PM) generated during the combustion of diesel fuel and a glycol ether–diesel fuel blend was addressed in this research work. In addition, the impact of in-cylinder fuel post injections (FPI) on the particulate formation pathway and on the catalytic de-NOx efficiency was also studied.The tests were carried at low exhaust temperatures in the absence and presence of small amounts of hydrogen (H2). It is concluded that in the absence of H2, the catalyst does not modify the primary particle size (dp0) of the soot aggregates, while the aggregation of the soot particles throughout the catalyst channels is the main governing mechanism. The catalyst influence on the particulate structure was evident when H2 was introduced, with smaller dp0 seen downstream of the catalyst, indicating that despite the short residence time of the PM within the catalyst bed, the soot particles were partially oxidised. The use of late FPI reduces the exhaust PM level and delivers sufficient HC:NOx ratios that improves the catalyst activity up to a maximum of 80% NOx conversion, with no sign of catalyst deactivation when H2 (500 ppm) was injected. Furthermore, it is suggested that along with oxidising part of the particles produced during the main fuel injection phase, late FPI can also produce, to a lesser extent, some additional soot with a less matured structure, resulting on average in less ordered particles being emitted into the exhaust stream.This work shows that in modern diesel engines, a silver catalyst can alter the soot structure in the exhaust in a way that can ease the diesel particulate filter (DPF) regeneration cycles, improve its filtration efficiency and help in effectively reducing the tailpipe NOx emissions. For the catalyst to perform these functions, multiple in-cylinder fuel injection strategies (late FPI) combined with small amounts of hydrogen addition to the exhaust are required.

Synergistic interaction of metal–acid sites for phenol hydrodeoxygenation over bifunctional Ag/TiO2 nanocatalyst

Abstract The use of silver metal for hydrodeoxygenation (HDO) applications is scarce and different studies have indicated of its varying HDO activity. Several computational studies have reported of silver having almost zero turnover frequency for HDO owing to its high C O bond breaking energy barrier and low carbon and oxygen binding energies. Herein this work, titania supported silver catalysts were synthesized and firstly used to examine its phenol HDO activity via experimental reaction runs. BET, XRD, FESEM, TEM, EDX, ICP–OES, Pyridine-FTIR, NH3-TPD and H2-TPD analyses were done to investigate its physicochemical properties. Phenomena of hydrogen spillover and metal–acid site synergy were examined in this study. With the aid of TiO2 reducible support, hydrogen spillover and metal–acid site interactions were observed to a certain extent but were not as superior as other Pt, Pd, Ni-based catalysts used in other HDO studies. The experimental findings showed that Ag/TiO2 catalyst has mediocre phenol conversion but high benzene selectivity which confirms the explanation from other computational studies.

Moderation of chlorine coverage and ethylene epoxidation kinetics via ethane oxychlorination over promoted Ag/α-Al2O3

Optimal ethylene oxide selectivity during steady-state ethylene oxidation over Cs and Re-promoted Ag/α-Al2O3 catalysts is attained only if co-fed alkyl chlorides deposit chlorine adatoms and co-fed alkanes moderate surface chlorine coverages. Surface chlorine coverage under reaction conditions was measured in chemical transient studies immediately after reaching steady-state by removing reactants in flowing helium and recirculating ethane and oxygen in a gas-phase batch reactor; this resulted in removal of chlorine from the catalyst as ethyl chloride and enabled assessment of the total number of moles of chlorine desorbed per surface silver atom, which varied from 0.10 to 0.45 depending on the process conditions employed. Batch recirculation experiments demonstrated that oxygen is required to remove chlorine from silver catalysts, suggesting molecular events akin to those involved in oxychlorination of alkanes moderate chlorine coverage during steady-state catalysis. The chlorine content was largely unperturbed by changes in ethylene (20–40 mol%), carbon dioxide (1–5%), or oxygen (2–7%) concentrations during steady-state catalysis. Increasing temperature resulted in a monotonic decrease in chlorine coverage. A power law model accurately describes trends in chlorine coverage as a function of steady-state ethane (0.1–15 mol%) or ethyl chloride (0.5–6.3 ppmv) concentrations. The carbon selectivity for ethylene oxide increases with chlorine coverage, in agreement with expectations from steady-state measurement of rates and selectivity as a function of co-fed alkyl chloride promoters. These results explicate the critical role of oxygen-containing species in moderating Cl coverage during ethylene epoxidation catalysis, include a model that describes chlorine coverage across a broad concentration range of alkyl chloride promoter and alkane moderators, and enable correlation between kinetic parameters measured as a function of process conditions and the predicted chlorine coverage.

Atomic Force Microscopy Topographic and Phase-Contrast Imaging of Silver Catalyst Supported on CaCO3

Atomic Force Microscopy Topographic and Phase-Contrast Imaging of Silver Catalyst Supported on CaCO₃

Identifying the True Catalyst in the Reduction of 4-Nitrophenol: A Case Study Showing the Effect of Leaching and Oxidative Etching Using Ag Catalysts

The fundamental understanding of liquid-phase catalytic reactions is unavoidably complicated when the catalyst is prone to leaching since questions inevitably arise as to the true nature of the catalyst. While the catalytic reduction of 4-nitrophenol by borohydride is widely accepted as a trusted model reaction, it has faced little scrutiny concerning the potential impact of leached species or the appropriateness of assigning catalytic activity to the inserted nanostructures without rigorous experimental verification. Here, we present results from a spectroscopically monitored split test in which supported silver catalysts are physically separated from the reactants midway through the reaction. It is unambiguously demonstrated that the influence of leaching is far from benign, instead acting to extinguish the catalytic activity of the inserted nanostructures while giving rise to an unsupported heterogeneous catalyst that is the true catalytic entity. With only submonolayer quantities of silver leached fro...