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Co-B catalyst, W-modified Co-B (Co-W-B) catalyst, and Mo-modified Co-W-B (Co-W-Mo-B) catalyst powders were synthesized via chemical reduction of metal salt solutions at room temperature. The optimal hydrogen production rate was obtained when the ratio of the reducing agent (NaBH4) to the metal solution was 4:1. Among the ternary catalysts, the Co0.1-W0.9-B catalyst showed the optimal hydrogen production rate when the content of W doping was 0.9. Furthermore, the hydrogen production rate of the quaternary catalyst was enhanced when the content of Mo doping was 0.075, denoted as Co0.1-W0.9-Mo0.075-B. The catalyst powders were characterized by SEM, XRD, XPS, and BET. The hydrogen production rates of the Co-B catalyst, Co0.1-W0.9-B catalyst, and Co0.1-W0.9-Mo0.075-B catalyst were investigated for the decomposition of alkaline sodium borohydride (NaBH4) in a water–ethanol mixture solution. The Co0.1-W0.9-Mo0.075-B catalyst exhibited the highest hydrogen production rate compared to Co-B and Co0.1-W0.9-B catalyst powders. The optimal hydrogen production rate of the Co0.1-W0.9-Mo0.075-B catalyst is 4600 ml·min−1·g−1, which is nearly 1.9 times higher than that of the Co-B catalyst. Moreover, the Co0.1-W0.9-Mo0.075-B catalyst exhibited good stability, retaining 73% of its catalytic activity after five cycles, and had a low apparent activation energy of 41.51 kJ·mol−1. [ABSTRACT FROM AUTHOR]

In this study, TiO2-supported Ni-Mo-Ru–B (TiO2@Ni-Mo-Ru–B) catalyst was synthesized by chemical reduction method for hydrogen production from the hydrolysis of potassium borohydride (KBH4) solution. The characterizations of the synthesized catalysts were carried out with BET, XRD, and SEM. In hydrolysis experiments, the effects of parameters such as KOH concentration, KBH4 concentration, catalyst amount, metal/TiO2 ratio, and temperature on hydrogen production rate were investigated. The optimum metal/TiO2 ratio was determined as 10% and the hydrogen production rate of the catalyst at 30 °C was calculated as 2410.28 mL/min.gcat. In addition, the reaction rate order was found to be 0.8 (nth order); accordingly, the value of the activation energy was obtained from the Arrhenius equation as 51.807 kJ/mol. [ABSTRACT FROM AUTHOR]

In this work, via the method of wet impregnation and chemical reduction, low-cost and available bentonite modified by cetyltrimethylammonium bromide (CTAB) was utilized as support to synthesize a novel organobentonite-supported Pd composite catalyst used for the catalytic transfer hydrogenation (CTH) of polyunsaturated fatty acid methyl ester (FAME). According to the results of characterization analysis, the organic modifier of CTAB was intercalated into the interlayer of bentonite, and the active metal Pd was immobilized and uniformly dispersed in the prepared composite catalyst. The possible formation mechanism of composite catalyst was proposed. The synthesized composite catalyst presented higher hydrogenation activity and selectivity compared with the pure nano-Pd catalyst. Moreover, the excellent stability remained for the composite catalyst after five catalytic runs in FAMEs hydrogenation. Hence, bentonite, as an economical and promising feedstock, could be used to synthesize a high-efficient and stable supported Pd composite catalyst successfully for the CTH of FAME. Low-cost bentonite, used as raw material, was modified by cetyltrimethylammonium bromide (CTAB) through the cation exchange process, forming organobentonite (OB) with an increased interlayer spacing. The cations of CTAB might be absorbed into the interlayers and on the surface of bentonite. The Pd ions were introduced through the impregnation of precursor solution of Pd (H2PdCl4) and bound to the cations of CTAB via electrostatic interactions. After the chemical reduction process by using NaBH4, the anionic PdCl42− could be reduced to metal Pd, which was immobilized and dispersed in the interlayers and on the surface of organobentonite, and then a novel Pd/OB composite catalyst formed. According to the result of TEM measurement, Pd particles showed the spheroidal shapes and dispersed uniformly in the synthesized composite catalyst. [ABSTRACT FROM AUTHOR]

The purpose of this work is activity evaluation of optimized Pd–Cu/rGO as an anode catalyst for electrooxidation of low ethanol concentrations (5–50 mM) in order to use in fuel cell-based breath alcohol analyzer. Accordingly, a simple and one-step synthesis of Pd/rGO and Pd–Cu/rGO with an optimized Pd/Cu ratio was performed via the chemical reduction method and evaluated for ethanol oxidation reaction (EOR). According to the transmission electron microscopy (TEM) and cyclic voltammetry (CV), the particle size and electrochemical active surface area (ECSA) of Pd0.9–Cu0.1/rGO were 4.5 nm and 181.5 m2 g−1, respectively. The ratio of If/Ib was measured to be 0.7 and 2.6 for Pd/rGO and Pd0.9–Cu0.1/rGO in the 0.5 M KOH solution containing 50 mM ethanol, thus indicating that the presence of Cu in the alloyed catalyst structure improved the catalytic activity by removing carbonaceous intermediates from the catalyst surface. Obtained results revealed that the onset potential (Eonset) of Pd0.9–Cu0.1/rGO was negatively shifted to 240 mV, as compared to Pd/rGO and no carbonate blockage of Pd–Cu/rGO sites happened in the presence of K2CO3. Therefore, Pd0.9–Cu0.1/rGO could be regarded as a superior anode catalyst for use in the anion exchange membrane fuel cell-based breath alcohol analyzer. [ABSTRACT FROM AUTHOR]

A low-cost Ni-B alloy catalyst was prepared by chemical reduction method and used for partial hydrogenation of fatty acid methyl esters. The conditions for catalyst preparation, including Ni to B ratio, pH of NaBH4 solution, types and quantity of metal modifiers were optimized. Ni-La-B, prepared by modification of Ni-B with La, showed significantly high catalytic partial hydrogenation activity. The optimum textural properties (small particle size, high specific surface area and well-defined pore structure) and electron enrichment of active Ni sites were the favorable factors for the high hydrogenation activity of Ni-La-B catalyst, which showed reasonable stability in catalyst recycle experiments. [ABSTRACT FROM AUTHOR]

The electrodeposition of tin and tin-nickel on a highly dispersed carbon material is used to obtain composite supports. These composite supports were used in the Pt(0) nanoparticles deposition from Pt(IV) solution by chemical reduction. The composition, structure, and activity of the obtained Pt(SnO2/C) and PtSnNi/C catalysts in the oxygen reduction and alcohol electrooxidation reactions were studied. The composite-support-based platinum catalysts exhibit higher activity in the reactions of alcohols electrooxidation in comparison with the commercial Pt/C analogue. Trimetallic PtSnNi/C catalysts are the most promising materials for the electrooxidation of alcohols. [ABSTRACT FROM AUTHOR]

We have synthesized catalysts for the hydrogen reduction of germanium tetrachloride: a catalyst based on multiwalled carbon nanotubes and a hybrid catalyst based on multiwalled carbon nanotubes whose surface was decorated with copper-containing nanoparticles. The hybrid catalyst has been characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results demonstrate that it consists of multiwalled carbon nanotubes whose surface is decorated with copper nanoparticles in a cuprous oxide shell (Cu2O/Cu/MWCNTs). The catalytic activity of the hybrid catalyst exceeds that of the as-prepared MWCNTs. The use of the Cu2O/Cu/MWCNT hybrid catalyst as a catalyst for the hydrogen reduction of germanium tetrachloride allows the reaction temperature to be lowered and ensures 95.7% germanium tetrachloride conversion at 873 K. [ABSTRACT FROM AUTHOR]

Recent developments in catalytic reduction with H2 of glycerol, which is a by-product of biodiesel manufacture, and the involved chemistry are summarized and reviewed. There are more than ten potential C3 products of glycerol reduction. Among them, 1,2-propanediol can be obtained in very high yield and the production from glycerol is now commercialized. Production of 1,3-propanediol, allyl alcohol and propylene are now possible in > 60%, > 90% and > 80% yield, respectively. Key reaction steps are metal-catalyzed dehydrogenation/hydrogenation, acid-catalyzed dehydration, carbonyl-induced dehydration, metal-catalyzed direct hydrogenolysis and deoxydehydration. The 2-Propanol and small-ring compounds (oxetane, propylene oxide) cannot be produced from glycerol by combinations of these key reaction steps, and no catalytic system is known at present, although the conversion reactions have minus ∆G°. [ABSTRACT FROM AUTHOR]

New materials based on electric arc furnace (EAF) dust have been produced via temperature-programmed reduction using hydrogen gas at different temperatures. Scanning electron microscopy, thermal analysis, X-ray diffraction, and Mössbauer spectroscopy suggested that the EAF dust is reduced by hydrogen at 600 and 700 °C producing reduced iron, e.g., iron (II) and iron metallic, magnetics and more active catalytic phases. The new materials show magnetic behavior as well as EAF starting material. Electron paramagnetic resonance studies using N-t-butyl-α-phenylnitrone as a trapped radical agent were performed showing characteristic signals related to paramagnetic species produced exclusively by the interaction of catalysts with hydrogen peroxide (H2O2). The new magnetic materials were successfully used for pollutant removal by adsorption followed by oxidation of model dyes such as methylene blue and indigo carmine. In addition, the great advantage of these materials is that they may be easily recovered magnetically and reused. [ABSTRACT FROM AUTHOR]

Fe@FeO core-shell nanowires were synthesized via the reduction of Fe ions by sodium borohydride in an aqueous solution with a subsequent heat treatment to form FeO shell and employed as a cathode catalyst for non aqueous Li-air batteries. The synthesized core-shell nanowires with an average diameter of 50-100 nm manifest superior catalytic activity for oxygen evolution reaction (OER) in Li-O batteries with the charge voltage plateau reduced to ∼3.8 V. An outstanding performance of cycling stability was also achieved with a cutoff specific capacity of 1000 milliampere hour per gram over 40 cycles at a current density of 100 mA g. The excellent electrochemical properties of Fe@FeO as an O electrode are ascribed to the high surface area of the nanowires' structure and high electron conductivity. This study indicates that the resulting iron-containing nanostructures are promising catalyst in Li-O batteries. [ABSTRACT FROM AUTHOR]

We describe herein the synthesis of solid Au@Pd and hollow AgPd nanoflowers displaying controlled sizes and compositions in order to investigate how their size, composition, and the presence of Au in the core of the nanoparticles influence their catalytic performance toward both liquid and gas-phase transformations. While the size and composition of Au@Pd and AgPd the nanoflowers could be controlled as function of growth time, their structure (solid or hollow) was dependent on the nature of the seeds employed for the synthesis, i.e., Au or Ag nanoparticles. Moreover, Au@Pd and AgPd nanoflowers were successfully supported onto commercial silica displaying truly uniform dispersion. The catalytic activities of Au@Pd and AgPd nanoflowers were investigated toward the 4-nitrophenol reduction and the benzene, toluene, and o-xylene (BTX) oxidation. The catalytic activities for the reduction of 4-nitrophenol decreased as follows: Au@Pd > Au@Pd > AgPd and AgPd > Au@Pd > AgPd, suggesting that the Au core enhanced the catalytic activity relative to the hollow material when for Pd at.% was up to 80. Regarding the BTX oxidation, supported Au@Pd displayed higher catalytic activities than AgPd nanoflowers, also illustrating the role of the Au cores in the nanoflowers for improving catalytic performance. We believe these results may serve as a platform for the synthesis of Pd-based bimetallic nanomaterials that enable the correlation between these physical/chemical parameters and properties and thus optimized catalytic activities. [ABSTRACT FROM AUTHOR]

In situ EPR spectroscopy proved to be a versatile tool to identify active sites for photocatalytic hydrogen generation in modified YTiO and CsTaWO catalysts of pyrochlore structure, in which the metal cations are located in two different positions A and B. It was found that the B-sites exclusively occupied by titanium (YTiO) and tantalum/tungsten (CsTaWO) act as electron traps on the surface. From these sites, electron transfer to the co-catalysts proceeds. Thus, the B-sites are responsible for photocatalytic water reduction. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel superparamagnetic gold/halloysite nanotubes/FeO (Au/HNTs/FeO) nanocomposite with coaxial structure was designed and fabricated by selective decoration of the inner lumen and the external wall of halloysite nanotubes (HNTs) based on the difference inside/outside surface charges. The structure and composition of Au/HNTs/FeO were characterized by transmission electron microscope, powder X-ray diffraction, and X-ray fluorescence. The results indicated that Au nanorods selectively generated within the lumen of HNTs, while FeO nanoparticles uniformly deposited on the external wall. It was particularly worth mentioning that the structure of HNTs was not destroyed in the preparation process of Au/HNTs/FeO nanocomposites. The catalytic activity of the as-prepared Au/HNTs/FeO was investigated for the reduction of 4-nitrophenol in the presence of NaBH. The Au/HNTs/FeO nanocomposites exhibited excellent catalytic activity and cycling stability according to the kinetic data of the catalytic reduction reaction. In addition, the Au/HNTs/FeO catalysts can be easily manipulated by an external magnetic field for recycling. [ABSTRACT FROM AUTHOR]

Several NOx reduction technologies under development in recent years have now been commercialized, including selective catalytic reduction (SCR) with NH or hydrocarbons, and Lean NOx Trap. The aim of the present study is to investigate characteristics on NOx adsorption according to the oxygen concentration, de-NOx performance according to lean/rich injection cycle and toxic intermediates at LNT downstram for lean-burn gasoline engine. Under oxygen of 6%, NOx storage capacity was the highest, showed the highest NOx conversion of 98%. The reason for this phenomena is because the excited oxygen atoms at high oxygen concentration increased oxidizing power of NO. Under low temperature of 205°C, LNT catalyst showed the least NOx conversion of 14% because its activity became lower, while the generation rate of toxic HNCO was highest as CO which is generated during the rich condition, reacts with NOx stored on Ba site. [ABSTRACT FROM AUTHOR]

We have reported a LaMnO-based, Pt free lean NO trap (LNT) catalyst shows promising NO reduction activities, but the mechanism of NO reduction or the role of the perovskite over this catalyst has not been addressed. This paper presented our investigation on the mechanistic aspects of NO adsorption and reduction over several LaMnO-based LNT catalysts. NO can be effectively oxidized to NO on LaMnO at 350 °C, while little NO (NO + NO) can be stored verified by the following temperature programmed desorption experiment; under the same conditions, a significant amount of NO (41 μmol NO/g washcoat) were stored over BaO/AlO/LaMnO indicating NO are adsorbed mainly on the BaO/AlO. The temperature programmed surface reaction with CO demonstrated that although it can store NO during the lean period, failed to reduce NO by CO over the BaO/AlO/LaMnO catalyst. After adding Pd into BaO/AlO/LaMnO, NO can not only be stored during the lean conditions but also reduced. It could be concluded that the Pd catalyst, not perovskite, is responsible for NO reduction during the rich conditions. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This review focuses on the importance of coupling of catalytic reactions which involves dehydrogenation and hydrogenation simultaneously and the study of catalytic materials that are designed, adopted and/or modified for these reactions. The special features of these reactions are minimization of H utilization and reduction in production cost. Structural and textural properties also play a decisive role in this kind of coupled reactions. This particular review although not comprehensive discusses the significant progress made in the area of coupled reactions and also helps future researchers or engineers to find out the improvements required in areas such as advancements in catalytic material preparation, design of the new reactors and the application of new technologies. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This study provides insight into the mechanistic and performance features of the cyclic reduction of NO by CO in the presence and absence of excess water on a Pt-Rh/Ba/AlO NO storage and reduction catalyst. At low temperatures (150-200 °C), CO is ineffective in reducing NO due to self-inhibition while at temperatures exceeding 200 °C, CO effectively reduces NO to main product N (selectivity >70 %) and byproduct NO. The addition of HO at these temperatures has a significant promoting effect on NO conversion while leading to a slight drop in the CO conversion, indicating a more efficient and selective lean reduction process. The appearance of NH as a product is attributed either to isocyanate (NCO) hydrolysis and/or reduction of NO by H formed by the water gas shift chemistry. After the switch from the rich to lean phase, second maxima are observed in the NO and CO concentrations versus time, in addition to the maxima observed during the rich phase. These and other product evolution trends provide evidence for the involvement of NCOs as important intermediates, formed during the CO reduction of NO on the precious metal components, followed by their spillover to the storage component. The reversible storage of the NCOs on the AlO and BaO and their reactivity appears to be an important pathway during cyclic operation on Pt-Rh/Ba/AlO catalyst. In the absence of water the NCOs are not completely reacted away during the rich phase, which leads to their reaction with NO and O upon switching to the subsequent lean phase, as evidenced by the evolution of N, NO and CO. In contrast, negligible product evolution is observed during the lean phase in the presence of water. This is consistent with a rapid hydrolysis of NCOs to NH, which results in a deeper regeneration of the catalyst due in part to the reaction of the NH with stored NO. The data reveal more efficient utilization of CO for reducing NO in the presence of water which further underscores the NCO mechanism. Phenomenological pathways based on the data are proposed that describes the cyclic reduction of NO by CO under dry and wet conditions. [ABSTRACT FROM AUTHOR]

The diminished surface-area-normalized catalytic activity of highly dispersed Pt nanoparticles compared with bulk Pt is particularly intricate, and not yet understood. Here we report on the oxygen reduction reaction (ORR) activity of well-defined, size-selected Pt nanoclusters; a unique approach that allows precise control of both the cluster size and coverage, independently. Our investigations reveal that size-selected Pt nanoclusters can reach extraordinarily high ORR activities, especially in terms of mass-normalized activity, if deposited at high coverage on a glassy carbon substrate. It is observed that the Pt cluster coverage, and hence the interparticle distance, decisively influence the observed catalytic activity and that closely packed assemblies of Pt clusters approach the surface activity of bulk Pt. Our results open up new strategies for the design of catalyst materials that circumvent the detrimental dispersion effect, and may eventually allow the full electrocatalytic potential of Pt nanoclusters to be realized. [ABSTRACT FROM AUTHOR]

SO uptake, thermal regeneration and the reduction of SO via H(g) over ceria-promoted NSR catalysts were investigated. Sulfur poisoning and desulfation pathways of the complex BaO/Pt/CeO/AlO NSR system was investigated using a systematic approach where the functional sub-components such as AlO, CeO/AlO, BaO/AlO, BaO/CeO/AlO, and BaO/Pt/AlO were studied in a comparative fashion. Incorporation of ceria significantly increases the S-uptake of AlO and BaO/AlO under both moderate and extreme S-poisoning conditions. Under moderate S-poisoning conditions, Pt sites seem to be the critical species for SO oxidation and SO storage, where BaO/Pt/AlO and BaO/Pt/CeO/AlO catalysts reveal a comparable extent of sulfation. After extreme S-poisoning due to the deactivation of most of the Pt sites, ceria domains are the main SO storage sites on the BaO/Pt/CeO/AlO surface. Thus, under these conditions, BaO/Pt/CeO/AlO surface stores more sulfur than that of BaO/Pt/AlO. BaO/Pt/CeO/AlO reveals a significantly improved thermal regeneration behavior in vacuum with respect to the conventional BaO/Pt/AlO catalyst. Ceria promotion remarkably enhances the SO reduction with H(g). [ABSTRACT FROM AUTHOR]

The effect of the acidity (p K) of the source of protons on the rate and selectivity of acetylene reduction has been investigated in order to elucidate the mechanism of protonation of substrate molecules coordinated to the reduced FeMoco cluster. A number of compounds whose p K in DMF varies between 6 and 20 have been examined as protonating agents. The rate of the reaction is almost independent of the acidity of the proton donor in a wide p K range. This can be explained in terms of the specific features of substrate protonation catalyzed by iron-sulfur clusters. Active protonating agents in the system are those which react with the catalyst to form hydrogen-bonded association species or those which are ligands reversibly binding to the cluster and are capable of donating protons, likely with simultaneous electron transfer. [ABSTRACT FROM AUTHOR]

Novel synthesis of amine-stabilized Au-Ag alloy nanoparticles with controlled composition has been devised using poly(ethylenimine) (PEI) as a reducing and a stabilizing agent simultaneously. The composition of Au-Ag alloy nanoparticles was readily controlled by varying the initial relative amount of HAuCl and AgNO. Due to the presence of abundant amine functional groups in PEI, which could act as the dissolving ligand for AgCl, the precipitation problem of Ag in the presence of Cl from the gold salt was avoided. On this basis, the relatively high concentrations of HAuCl and AgNO salts were used for the fabrication of Au-Ag alloy nanoparticles. The PEI thus plays triple roles in this study that include the co-reducing agents for HAuCl and AgNO, the stabilizing agents for Au-Ag alloy nanoparticles, and even the dissolving agents for AgCl. As a novel material for use in catalysis, the Au-Ag alloy nanoparticles including pure Au and Ag samples were exploited as catalysts for the reduction of 4-nitrophenol in the presence of NaBH. As the Au content was increased in the Au-Ag alloy nanoparticles, the rate constant of the reduction was exponentially increased from pure Ag to pure Au. [ABSTRACT FROM AUTHOR]

It is shown that palladium-cobalt oxide-cerium catalyst deposited on cordierite catalyzes the reduction of nitrogen(II) oxide with carbon monoxide, and cobalt-iron catalysts in simultaneous reduction of NO + NO with C-C alkanes retained high activity in the presence of water vapor and sulfur dioxide. The Pd-CoO/cordierite catalyst exceeds the Pt-CoO/codierite catalyst in the conversion of NO and CO in the reaction mixture CO + NO + O + HO + SO. Modification of the Pd-CoO/cordierite with cerium oxide considerably increases its sulfur resistance. [ABSTRACT FROM AUTHOR]

Metallic palladium nanoparticles (<5 nm) have been spontaneously obtained from an acid solution of palladium chloride salt on silica-rich substrates (sepiolite, microfibrous silica, fumed silica, and milled silica glass) without any additional reduction treatment. Variable proportions of metallic palladium were straightforwardly obtained, depending on the nature of the substrate. The presence of a large amount of silanol groups acting as nucleation centers, seem to be a requisite to obtain small Pd nanoparticles. Additionally, an absorbance maximum associated to a surface plasmon resonance corresponding to the spherical particles of metallic palladium has been identified at a wavelength of 238 nm. The large specific surface of the employed substrates with the palladium nanoparticles suggest that these materials could be used for gas catalysis. [ABSTRACT FROM AUTHOR]

Tin and titanium dioxides and their compositions were studied as catalysts for the reaction of complete oxidation of methane. The catalytic activity of the test samples was compared in terms of first-order reaction rate constants with reference to the unit surface area of a catalyst. The crystal structures and specific surface areas of the obtained compositions were characterized. The thermal stability of SnO was investigated. Data on the temperature-programmed reduction of SnO and the composition SnTiO in hydrogen were given. [ABSTRACT FROM AUTHOR]

Ti-SBA-15 and Ti-MCM-41 were synthesized and evaluated as possible photocatalysts for the reduction of CO, and for the photo-Kolbe decomposition of acetic acid. UV-Raman was used to study the adsorption of carbon dioxide, water, formic acid, and acetic acid over Ti-MCM-41 by monitoring the UV enhanced resonance peak of the totally symmetric stretching band of the grafted Ti species at 1,085 cm. Acetic and formic acid dissociate on Ti-SBA-15 and Ti-MCM-41 to form acetate and formate, respectively. The conjugate bases subsequently interact strongly with Ti sites. Water interacts with the Ti sites, while no change in the amplitude of the 1,085 cm band is observed in the presence of CO. Photocatalysis experiments indicate that these mesoporous silicalites are active in the photo-Kolbe decomposition of acetic acid. CO is formed by reaction of a hole with the acetate carboxylate groups. The methyl radical co-products react with a surface proton and an electron to form methane. No products resulting from the dimerization of methyl radicals are observed, presumably because of the highly dispersed active sites. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The results of the study of microstructural parameters and the data on the electrochemically active surface area of Pt/C and PtM/C (M = Ni, Cu, Ag) catalysts in 1 M HSO solutions are compared. The metal-carbon nanomaterials were prepared by the method of chemical reduction of metals from the organoaqueous solutions of their compounds. The loading of metal component in them was 30-33 wt %. It is found that actual composition of metal component in the synthesized binary systems fits best the theoretically expected one (1: 1) for the PtAg/C catalyst whereas in the PtNi/C and PtCu/C systems, a considerable fraction of alloying component is present in the form of the corresponding oxides. A decrease in the average size of crystallites of metal component from 3.8 to 1.6 nm in the series of studied materials PtAg/C > Pt/C ≥ PtCu/C s> PtNi/C does not correspond to the character of the variation of electrochemically active surface area of the catalysts: PtNi/C ≈ PtCu/C < Pt/C ≪ PtAg/C increasing from 16-20 to 62-69 m/g(Pt). The contradiction can be caused by the preferential segregation of platinum on the surface of nanoparticles of PtAg alloy, a higher degree of agglomeration of smaller nanoparticles, and, in the case of PtNi/C and PtCu/C materials, also by the insulation of a fraction of nanoparticle surface area by the corresponding oxides. [ABSTRACT FROM AUTHOR]

Direct carbonyl reduction to methylene has been achieved by mild reductant system obtained from the combination of organosilane and gallium (III) trifluoromethanesulfonate {Ga(OTf)}, a water tolerant, recyclable, catalyst. Among a series of organosilanes studied, dimethylchlorosilane (MeSiHCl, DMCS) showed the highest efficiency. Both aromatic and aliphatic ketones were effectively reduced to the corresponding methylene products with high functional groups tolerance, under very mild conditions in a relatively short period of time with good to excellent yields. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

This study gives an overview of zeolites used for hydrocarbon trapping, selective catalytic reduction of nitrogen oxides (NO) with NH (NH-SCR) and hydrocarbon NO reduction applications. We also discuss challenges for the use of zeolites in these applications and the material properties that require improvement. [ABSTRACT FROM AUTHOR]

The slow rate of the oxygen reduction reaction in the phosphoric acid fuel cell is the main factor limiting its wide application. Here, we present an approach that can be used for the rational design of cathode catalysts with potential use in phosphoric acid fuel cells, or in any environments containing strongly adsorbing tetrahedral anions. This approach is based on molecular patterning of platinum surfaces with cyanide adsorbates that can efficiently block the sites for adsorption of spectator anions while the oxygen reduction reaction proceeds unhindered. We also demonstrate that, depending on the supporting electrolyte anions and cations, on the same CN-covered Pt(111) surface, the oxygen reduction reaction activities can range from a 25-fold increase to a 50-fold decrease. This behaviour is discussed in the light of the role of covalent and non-covalent interactions in controlling the ensemble of platinum active sites required for high turn over rates of the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

A polyethylene glycol (PEG)-supported NADH model as a novel organic reductant was designed and synthesized. The reductions of various α, β-unsaturated ketones by the PEG-supported NADH model were examined, and the results showed that the reductions completely and quickly proceed with no catalyst at ambient temperature. The main advantages of this liquid-like PEG-supported NADH model are easy workup, and an optimal potential for recycling use and solvent-free for use in reactions. [ABSTRACT FROM AUTHOR]

The addition of gold, by deposition precipitation, to a mixed copper manganese oxide catalyst (Hopcalite) has been studied for ambient temperature carbon monoxide oxidation. The deposition of gold on the catalyst surface enhanced the activity of the Hopcalite. The catalyst containing 1 wt% gold was the most active and showed higher activity than Hopcalite containing 0.5 and 2 wt% gold. It is expected that the introduction of gold will introduce new active sites to the Hopcalite that are associated with the gold nanoparticles. However, gold addition also increased the reducibility of the catalyst significantly compared to unmodified Hopcalite, and the most easily reduced catalyst was the most active, indicating that the lability of lattice oxygen was an important factor influencing activity. Graphical Abstract: The activity of a copper-manganese oxide catalyst for ambient temperature CO oxidation is significantly promoted by the addition of gold using deposition precipitation.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Pd/CeO2, Pd/ZrO2 and Pd/CeO2–ZrO2, were prepared by impregnation on a well defined alumina support. The oxides are finely dispersed over alumina support. TPR results on promoted Zr and Ce catalysts indicate partial reduction of CeO4 and ZrO2. The dispersions for Pd/Al2O3 and Pd/Zr/Al2O3 are similar but very different on Pd/Ce/Al2O3 and Pd/Ce/Zr/Al2O3, increasing 4 and 7 times in relation to the Pd/Al2O3, suggesting re-dispersion of Pd, mainly due to the promoting effect of Ce. EPR signals of Pd/Ce/Al2O3 are related with O2− species of Ce4+–O2−. DRIFTS studies with NO and CH4 reaction showed that the Pdδ+ species interacts with Ce+δ, modifying significantly the NO + CH4 reaction route. Pd/CeO2, Pd/ZrO2 and Pd/ CeO2–ZrO2, were prepared on a well defined alumina support. The structural and surface properties were studied under different characterization analyses in situ. EPR signals of Pd/Ce/Al2O3 are related with O2- species of Ce4+–O2. The NO reduction by CH4 was also studied by DRIFTS. It shows that the Pdδ+ species interacts with Ce+δ and that Ce and Zr modifies significantly the NO + CH4 reaction route.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The data on the cathodic PdCo/C catalyst prepared by high-temperature synthesis from 20 wt % Pd/C (E-TEK) are shown. According to XRD data, the catalyst represents an alloy with the preferential composition of Pd2Co. The kinetics and mechanism of oxygen reduction on the PdCo/C catalyst are studied by the methods of rotating disk electrode, rotating ring-disk electrode, and electrochemical impedance. It is shown that oxygen is reduced preferentially to water ( k1) but in the potential range more negative than 0.6 V, the ratio of constants k1/ k2 decreases, which suggests that the contribution of the reaction that proceeds through the formation of H2O2 ( k2) increases. The activity of PdCo/C catalyst under model conditions in 0.5 M H2SO4 was assessed to be 15 mA/mgcat at a potential of 0.7 V. [ABSTRACT FROM AUTHOR]

The carbon support (C) is modified by its functionalized surface with Ti species and used as a support of Pt catalyst for oxygen reduction reaction (ORR). Anatase TiO2 nanoparticles with the size of 3–5 nm are uniformly dispersed on the modified carbon support (C-Ti). It is shown that the C-Ti is well dispersed in the solution of Pt precursor due to the hydrophilic TiO2 nanoparticles. This causes a uniform distribution of Pt nanoparticles on C-Ti support. The average particle sizes are 2.9, 2.6, and 3.1 nm, respectively, for Pt/C, Pt/C-Ti, and Pt-commercial. The ORR performance is evaluated in terms of both mass-activity and specific activity. It is found that the Pt/C-Ti revealed the highest performance. The enhancement factors of ORR performance on the Pt/C-Ti at the potentials of 0.75, 0.8, and 0.85 V was more than two for both mass activity and specific activity compared to those on the Pt/C. The large surface area of Pt with a favorable electronic structure would be responsible for a superior performance of the Pt/C-Ti in ORR. Carbon support (C) was modified by reacting Ti species with its functionalized surface and used as a support of Pt catalyst for oxygen reduction reaction (ORR). Due to the hydrophilic TiO2 nanoparticles, the modified support (C-Ti) revealed enhanced dispersion in the solution of Pt precursor, which made Pt nanoparticles highly dispersed on its surface. The enhancement factors of ORR performance on Pt/C-Ti was more than two for both mass activity and specific activity compared to those on the Pt supported on unmodified carbon (Pt/C).[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A fluidizable, Ni/Mg/K/AD90(90% α-Al2O3) catalyst was evaluated in a pilot-scale study with oak-derived syngas for tar and methane reforming at 900 °C. The catalyst was operated in a semi-batch mode for ten individual reaction cycles, each separated by a regeneration protocol consisting of steaming followed by H2 reduction. During the experiment, subsequent reaction cycles showed a decrease in activity as indicated by decreased initial methane conversion. During each reaction cycle, H2S poisoning was the dominant deactivation mechanism, while coking was deemed to be minor in comparison. Catalyst characterization by XRD and TPR suggest that the loss of activity for subsequent reaction cycles coincides with the formation of a NiAl2O4 species that is not fully reduced under process conditions, which in turn results in a decreased number of potential metallic nickel (Ni0) sites available for hydrocarbon steam reforming. An increase in nickel crystallite size with time-on-stream was also observed using XRD, indicating that sintering may also play a role in loss of catalyst activity, although this is not considered the primary deactivation mechanism because activity loss was observed even when nickel crystallite sizes remained nearly constant. [ABSTRACT FROM AUTHOR]

The NO x reduction with n-C6H14 was studied over a 3% Ag/Al2O3 catalyst in the presence of hydrogen. The catalyst performance was evaluated by varying the H2 concentration from 0 to 1600 ppm and by comparing the results with blank runs in which an empty reactor with no catalyst was used. Two distinct reaction pathways were revealed: one at low-temperature (Treact < 370 °C) and another one at high-temperature (Treact > 370–390 °C). Co-feeding of H2 promotes the reaction within the 150–360 °C interval. The high-temperature pathway (Treact > 370–390 °C) seems to be almost independent of hydrogen co-feeding. The homogeneous gas-phase NO x oxidation initiated by NO presumably plays an important role in this high-temperature pathway. [ABSTRACT FROM AUTHOR]

Ba doped Ir/WO3–SiO2 catalysts in monolithic form showed good catalytic performance for the selective reduction of NO with CO in laboratory investigations. The addition of WO3 to SiO2 widened the active temperature range, and the role of Ba was to stabilize catalytically active Ir species. The catalyst also showed activity for NO reduction with about 45% conversion under the condition of SV <6,000 h−1 for real diesel exhaust. [ABSTRACT FROM AUTHOR]

Single-crystalline La0.6Sr0.4MnO3+ δ microcubes of cubic perovskite phase were prepared hydrothermally. The adopted temperature and time of hydrothermal treatment and the amount of KOH used had great effects on the low-temperature reducibility of La0.6Sr0.4MnO3+ δ. The initial H2 consumption rate of La0.6Sr0.4MnO3+ δ played a vital role in determining its catalytic activity for toluene combustion. It is concluded that the perovskite-type oxide catalyst with a higher initial H2 consumption rate displayed a higher catalytic activity for the addressed reaction. [ABSTRACT FROM AUTHOR]

In NO/CO reaction, there is a competition between NO reduction by CO and Mo2C oxidation by oxygen generated during NO dissociation. A complete equality of NO conversion and NO reduction degree can be achieved after increasing CO concentration in the system, which makes establishing a catalytic cycle on Mo2C catalyst possible. [ABSTRACT FROM AUTHOR]

Copper catalysts supported on magnesia promoted ceria are synthesized and used for NO reduction by CO. The supports and the subsequent Cu catalysts are prepared by citric acid sol–gel and impregnation methods, respectively. The results of N2-physisorption, XRD, EPR and TPR measurements indicate that the Mg addition promotes not only the dispersion of CuO, but also the formation of Cu–O–Ce solid solution. The highest amount of Cu–O–Ce solid solution is found in catalyst modified with 5 wt.% MgO. Based on the catalytic performance, two active sites for the reduction NO by CO are proposed: copper matrix and Cu–O–Ce solid solution. The former does not require the involvement of oxygen vacancy and is more active at low temperature range (T < 200 °C), while the latter shows higher NO conversion at temperature above 200 °C, due to the easy regeneration of oxygen vacancy. Also, it is found that the NO conversion over copper matrix is suppressed, while that over Cu–O–Ce solid solution is stimulated in high CO concentration. [ABSTRACT FROM AUTHOR]

Alumina supported 5% Co catalyst was prepared, by the controlled nanocrystal deposition method using oleic acid as a capping agent, and tested for its activity and selectivity in Fischer–Tropsch synthesis. The catalyst exhibited facile reducibility of the cobalt species. The CO conversion and C5+ selectivity obtained on this size-controlled catalyst were higher than those observed on the catalysts prepared by impregnation and precipitation techniques. Decrease in the mobility of the nanoparticle towards the tetrahedral sites of alumina could be the reason for high reducibility, as the formation of cobalt aluminate was found to be considerably reduced during temperature programmed reduction. [ABSTRACT FROM AUTHOR]

An amorphous Co-B catalyst was prepared by chemical reduction method and characterized by isothermal N2 adsorption/desorption, XRD, ICP-AES and HR-TEM. The catalytic activity of the Co-B catalyst in the hydroformylation of 1-octene was evaluated in a 100 mL stainless autoclave. Fresh amorphous Co-B catalyst showed a relatively high activity in the hydroformylation of 1-octene. The thermal stability of fresh Co-B catalyst was also examined. When fresh Co-B catalyst was thermally treated in N2 or H2 atmosphere at 200–500 °C for 2 h, the specific surface area and the catalytic activity of the Co-B catalyst decreased. When Co-B was supported on SiO2, the activity of the catalyst increased obviously. Compared with conventional supported Co/SiO2 catalyst, Co-B/SiO2 showed much higher activity than Co/SiO2. The influences of solvents and reaction conditions on the catalytic activity of the amorphous Co-B catalyst were also studied. The recycle test of the amorphous Co-B catalyst was done. [ABSTRACT FROM AUTHOR]

Iron-containing zeolites are known to be promising catalysts for the NH3-SCR reaction. Here, we will investigate the catalytic activity of iron-based BEA catalysts, which was found to exhibit improved activities compared to previously described iron-containing zeolite catalysts, such as ZSM-5 and ZSM-12. Series of Fe-BEA zeolite catalysts were prepared using a range of different preparation methods. Furthermore, we found that an iron concentration around 3 wt% on BEA showed a small optimum in SCR activity compared to the other iron loadings studied. [ABSTRACT FROM AUTHOR]

The influence of syntheses parameters of zeolite ZSM-5 on the lean NO x reduction activity and hydrothermal stability of Cu-ZSM-5 has been investigated. The hydrothermal stability of Cu-ZSM-5 was found to depend on the aluminium source used and on the presence of Ca(OH)2 in the synthesis mixture for ZSM-5. [ABSTRACT FROM AUTHOR]

This study tested the selectivity and sustainability of an alumina-supported Pd–In bimetallic catalyst for nitrate reduction with H2 in a continuous-flow packed-bed reactor in the presence of: (i) dissolved oxygen (DO), an alternative electron acceptor to nitrate, (ii) variable NO3 −:H2 influent loadings, and (iii) the presence of a known foulant, sulfide. The sustainability of the catalyst was promising, as the catalyst was found to be stable under all conditions tested with respect to metal leaching. The presence of DO at concentrations typical of treatment conditions will increase H2 demand for NO3 − reduction, but has no negative impact on the selectivity of the catalyst. Under optimal conditions, i.e., a pH of 5.0 and a high NO3 −:H2 influent loading, low NH3 selectivity (5%) was achieved for extended periods (36 days), resulting in sustained levels of NH3 that approached the European legal limit. The biggest challenge to the sustainability of the catalyst was the addition of sulfide, that initially increased NH3 selectivity and ultimately resulted in complete deactivation of the catalyst. Further work is required to identify regeneration methods to restore sulfide-fouled catalyst activity and selectivity; however, the most effective use would be to remove sulfide prior to catalytic treatment. [ABSTRACT FROM AUTHOR]

Cobalt silicate formation reduces the activity of the catalyst in Fischer–Tropsch synthesis (FTS). In this article, the effects of calcination temperature and support surface area on the formation of cobalt silicate are explored. FTS catalysts were prepared by incipient wetness impregnation of cobalt nitrate precursor into various silica supports. Deionized water was used as preparation medium. The properties of catalysts were characterized at different stages using FTIR, XRD and BET techniques. FTIR-ATR analysis of the synthesized catalyst samples before and after 48 h reaction identified cobalt species formed during the impregnation/calcination stage and after the reduction/reaction stage. It was found that in the reduction/reaction stage, metal-support interaction (MSI) added to the formation of irreducible cobalt silicate phase. Co/silica catalysts with lower surface area (300 m2/g) exhibited higher C5+ selectivity which can be attributed to less MSI and higher reducibility and dispersion. The prepared catalysts with different drying and calcination temperatures were also compared. Catalysts dried and calcined at lower temperatures exhibited higher activity and lower cobalt silicate formation. The catalyst sample calcined at 573 K showed the highest CO conversion and the lowest CH4 selectivity. [ABSTRACT FROM AUTHOR]

The effects of using NO or NO2 as the NO X source on the performance of a NO X storage/reduction catalyst were investigated from 200 to 500 °C. The evaluation included comparison with constant cycling times and trapping the same amount of NO X during the lean phase. With NO2 as the NO X source, better trapping and reduction performance was attained in comparison to NO, at all operating temperatures except 300 °C. This exception, under the conditions tested, was likely due to high NO oxidation activity and rapid trapping of NO2, although it is expected that extending the trapping time would lead to consistent differences. Several reasons for the observed improvements at 200, 400 and 500 °C with NO2 relative to NO are discussed. One that can explain the data, for both trapping and release improvement, is treating the monolith as an integral reactor. With NO2, more NO X is trapped at the very inlet of the catalyst, whereas with NO, the maximum in trapping during cycling occurs slightly downstream. Thus more of the catalyst can be used for trapping with NO2 as the NO X source. The decreased release during catalyst regeneration is similarly explained; with more being released at the very inlet, there is more residence time and therefore contact with downstream Pt sites, but more importantly more interaction between reductant and stored NO X. NH3 and N2O measurements support this conclusion. [ABSTRACT FROM AUTHOR]

Redox reactions catalyzed by cobalt nitrides should be carried out below the critical temperature at which bulk oxidation of the nitrides occurs. Then, a catalytic redox cycle could be established by introducing a reducing agent into the system below this temperature so that the oxygen could be removed prior to the occurrence of bulk oxidation. [ABSTRACT FROM AUTHOR]

Ag/SBA-15 catalysts have been prepared by means of in situ reduction methods using hexamethylenetetramine and formaldehyde as reducing agents, respectively, and characterized by N2 adsorption/desorption, XRD, TEM and XPS. Presence of nanoparticles of silver in SBA-15 were confirmed by high angle X-ray diffraction data (peaks between 2 θ = 35–80º) and XPS, and transmission electron microscopy confirmed the diameter of the nanoparticles. When hexamethylenetetramine was used as reducing agent, uniform Ag nanoparticles inside the channels were formed, and diameter of nanoparticles is found to be ~6.0 nm which is coincident with channel diameter of SBA-15. The catalysts were subjected to CO oxidation in a flow reactor at atmospheric pressure and temperatures up to 300 °C. Studies revealed that catalysts prepared with different reducing agents strongly influence their catalytic performance in the CO oxidation, what prepared with hexamethylenetetramine as mild reducing reagent shows a certain low temperature catalytic activity. [ABSTRACT FROM AUTHOR]