Showing papers on "Selective reduction published in 2012"

Nickel(II) macrocycles: highly efficient electrocatalysts for the selective reduction of CO2 to CO

Abstract: A series of molecular materials that are structurally similar to the NiII macrocycle [Ni(cyclam)]2+ (cyclam = 1,4,8,11-tetraazacyclotetradecane) have been used as electrocatalysts for the reduction of CO2 at a mercury pool working electrode in aqueous solution. At pH 5, with an applied potential of −0.96 V vs. NHE (overpotential of −0.55 V), the complexes are highly efficient, having both high rate constants and Faradaic efficiencies (F.E.s) for the selective reduction of CO2 to CO. When the pH is below the pKa (pH < 2) of the Ni(H) species (pKas: 0.5–2), the F.E.s are still high but product selectivity changes to yield predominantly H2 from the reduction of water. At least two of the complexes investigated are better electrocatalysts than [Ni(cyclam)]2+, probably due to: (i) surface geometries that are suitable for adsorption onto the mercury electrode surface, and (ii) electronic effects of methyl groups or cyclohexane rings on the cyclam backbone. Mechanistic studies by pulse radiolysis show evidence of Ni(CO2) adducts for two of the catalysts, with KCO2 ∼ 10 M−1 for the reaction of NiI with CO2 in aqueous solution.

A review of selective catalytic reduction of nitrogen oxides with hydrogen and carbon monoxide

Abstract: The selective reduction of NO with hydrogen (H2-SCR) and CO (CO-SCR) over platinum group metal catalysts in the presence of O2 is overviewed. In the case of H2-SCR, Pt and Pd show high activity at low temperatures. The acidity of the support material greatly affects NO reduction activity and selectivity to N2/N2O. Although the activity of Ir and Rh for H2-SCR is low, coexisting SO2 in the reaction gas considerably promotes NO reduction. The best support for Ir and Rh is SiO2. Li and Zn additives improve the activity of Ir/SiO2 and Rh/SiO2, respectively, by maintaining the active reduced metal state. For CO-SCR, on the other hand, Ir is almost the only active metal species. Coexisting SO2 is also essential for CO-SCR on Ir/SiO2 to occur. The role of SO2 for both H2-SCR and CO-SCR on Ir/SiO2 is to keep Ir in the form of the catalytically active Ir metal state. The additions of WO3 and Nb2O5 considerably promote the activity of Ir/SiO2 for CO-SCR, catalyzing CO-SCR even in the absence of SO2. Ir metal interacting strongly with W oxide is the active species on WO3-promoted Ir/SiO2. Furthermore, the addition of Ba improves the performance of Ir/WO3/SiO2 catalyst.

Novel microwave synthesis of ruthenium nanoparticles supported on carbon nanotubes active in the selective hydrogenation of p-chloronitrobenzene to p-chloroaniline

Abstract: Carbon nanotubes (CNTs) have been employed for the preparation of supported ruthenium nanoparticles using, for the first time, a low boiling alcohol or a mixture ethanol/water as solvent/reducing agent under microwave irradiation as heating source. These systems were employed as catalysts in the selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) and resulted efficient systems for the selective reduction of the nitro group in p-CNB under mild reaction conditions (60 °C and 4 MPa of H 2 ), while the C Cl bond remains intact, thus allowing the almost complete substrate conversion with total selectivity to the target product. These supported ruthenium nanoparticles are characterized by small average diameters and narrow particle size distributions, even if synthesized in the absence of any additional stabilizing agents and appear very promising systems also for other catalytic applications.

Selective reduction of phenol derivatives to cyclohexanones in water under microwave irradiation

Abstract: Selective reduction of phenol to cyclohexanone over the Pd/C catalyst in the presence of a hydrogen source of HCOONa/H2O has been studied. Surprisingly, phenol was transformed efficiently to cyclohexanone in an excellent yield of above 98% under microwave irradiation. The influence of some parameters like reaction temperature, time and amount of hydrogen donor, as well as the reaction pathway has been discussed. The combination of microwave irradiation and HCOONa/H2O was certified to be effective for the reduction of phenol as well as its derivatives to their corresponding cyclohexanones.

Selective Reduction of Nitroarenes by using Zeolite‐Supported Copper Nanoparticles with 2‐Propanol as a Sustainable Reducing Agent

Abstract: Aromatic amines are key intermediates in the synthesis of pharmaceutical products, polymers, agrochemicals, dyes, photographic rubber materials, and biologically active compounds. Various methods have been developed for the preparation of aromatic amines from different starting materials, such as the reduction of nitrobenzene, the hydrogenation of azides, and the amination of aryl halides into aniline. Among these methods, the selective reduction of the nitro group in the presence of other reducible functionalities is a challenging task. A plethora of methods have been reported for the hydrogenation of nitroarenes with various transitionmetal catalysts and reducing agents, such as Mo/DBU (DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene), Pd/PMHS (PMHS = polymethylhydrosiloxane), Sm/1,1’-dioctyl-4,4’-bipyridinium dibromide, Re/PMHS, Se/CO/H2O, [9] Ru/HCOOH, In/Et3SiH, [11] Au/CO/H2O, [12] Pd/PSF (PSF = polymer-supported formate), Fe/PhSiH3, [14a] Fe/HCOOH, and Ce-zeolite/HCOOH. However, most of these methods suffer from several drawbacks, such as a lack of chemoselectivity, toxicity, highly sensitive or pyrophoric reagents, cost of the metal catalyst, incomplete conversion, and lower yields; thus, these drawbacks have led to the demand for more-sustainable methods. Moreover, these conventional methods that require strong reducing reagents often produce undesirable by-products. Recently, the hydrogenation of nitrobenzene has been reported with various metaland metal-oxide nanoparticles, such as FeO, Ni, Pd, Rh, Au, Pt, and bimetallic Pt–Ni nanoparticles. Although these noble metals are frequently employed, the use of lessexpensive Cu nanoparticles for hydrogenation reactions is very limited. A variety of reagents have been employed in reduction of nitroarenes, namely H2, [23] NaBH4, [24] formic acid, sodium trimethylsilanethiolate, and hydrazine hydrate. These systems involve more-powerfuland hazardous reducing agents, many of which are expensive. Thus, a simpleand inexpensive alternative reducing agent that offers more-environmentally friendly reaction conditions and higher efficiency is desirable. 2-Propanol is a very popular hydrogen donor because it is less expensive, non-toxic, volatile, possesses good solvent properties, and is readily transformed into acetone, which is environmentally friendly and easy to remove from the reaction system. Zeolites are considered to be valuable catalysts with various advantages, such as shape-selectivity and thermal stability, which enable them to be used for the highly selective synthesis of commodityand fine chemicals. Selvam and co-workers reported the reduction of nitrobenzene by using 2-propanol on mesoporous catalysts, such as Ni and Pd-MCM-41. These systems offer several advantages with respect to easy recoveryand recycling of catalysts, as well as the minimization of undesired toxic waste, although these heterogeneous procedures required a strong base and the flammable Raney-Ni catalyst presents hazards during handling. The synthesis of zeolite-supported metaland metal-oxide nanoparticles would prevent further aggregation of the nanoparticles through the confined void spaces of the microporous structure. Recently, Ranu and co-workers reported the chemoselective reduction of aromatic azides and nitrobenzene into aniline by using copper nanoparticles with ammonium formate. These systems needed additional solvent, longer reaction times, and higher temperatures. We are interested in heterogeneous catalysts, the development of simple syntheses of metaland metal-oxide nanoparticles, and the use of zeolites/clays as solid supports, 33] which offer several advantages, such as the fast and simple isolation of the products by filtration, recyclability, and minimization of the metallic wastes. We recently developed zeolite-supported copper nanoparticles (Cu NPs) as a heterogeneous and reusable catalyst for the transfer hydrogenation of carbonyl compounds and C C multiple bonds. Herein, we report the selective reduction of nitrobenzene by using zeolite-supported copper nanoparticles with 2-propanol in the absence of base and additional solvents. This system, which exhibits superior activity in terms of yields, selectivity, and reaction time compared to other reported hydrogen sources, and the observed results are discussed below. Cu nanoparticles are prepared from Cu-exchanged Y-zeolite (Cu–Y). These nanoparticles are characterized by UV/DRS (DRS = diffuse reflectance spectroscopy), powder XRD, XPS, and HRTEM (see the Supporting Information, Figures S1–S6). The as-prepared Cu nanoparticles exhibit an average diameter of 8 nm. HRTEM images are also recorded for the recycled catalyst (after the fifth cycle) ; these images show that the aggregation of the CuNPs/zeolite is not significant and that the average diameter of the nanoparticles is 6 nm (see the Supporting Information, Figures S6 a–c). Subsequently, the synthesized zeolite-supported Cu nanoparticles are used for the reduction of nitroarenes under two sets of reaction conditions. In the first set of conditions, the reduction is performed in an oil bath (Table 1). Nitrobenzene is chosen as a model substrate to optimize the reaction conditions. No appreciable reduction takes place in the absence of 2-propanol, which acts as both a reducing agent and as a solvent (Table 1, entry 1). Only moderate conversion is obtained [a] T. Subramanian, Prof. K. Pitchumani School of Chemistry, Madurai Kamaraj University Madurai-625021, Tamil Nadu (India) Fax: (+ 91) 452-2459181 E-mail : pit12399@yahoo.com Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201200443.

Selective Reduction of Carboxylic Acids to Aldehydes by a Ruthenium-catalyzed Reaction with 1,2-Bis(dimethylsilyl)benzene

Abstract: Novel transformation of carboxylic acids to aldehydes is achieved by a one-pot procedure consisting of a ruthenium-catalyzed hydrosilane reduction with 1,2-bis(dimethylsilyl)benzene (2) followed by...

Spectroscopic IR, EPR, and operando DRIFT insights into surface reaction pathways of selective reduction of NO by propene over the Co–BEA zeolite

Abstract: Interaction of a Co–BEA catalyst with individual components (NO, C3H6, CO, O2) and mixtures simulating the real feed of the selective catalytic reduction (SCR) of nitric oxide in static and pulse experiments at variable temperatures was investigated by means of IR, EPR, and operando DRIFT spectroscopy coupled with QMS/GC analysis of the products. Speciation of cobalt active sites into Co(II), mono- and polynuclear oxo-cobalt species as well as CoO clusters was quantified by IR using CO and NO as probe molecules. The key intermediates, by-products, and final products of the SCR reaction were identified and their spectroscopic signatures ascertained. Based on the spectroscopic operando results, a concise mechanistic scheme of the selective catalytic reduction of nitric oxide by propene, triggered by a two-electron Co(II)/Co(0) redox couple, was developed. It consists of a complex network of the sequential/parallel selective reduction steps that are interlocked by the rival nonselective oxidation of the intermediates and their thermal decomposition. It has been shown that the SCR process is initiated by the chemoselective capture of NO from the reaction mixture by the cobalt active sites leading to the cobalt(II) dinitrosyls, which in the excess of oxygen are partially oxidized to surface nitrates and nitrites. N2O is produced by semi-decomposition of the dinitrosyl intermediates on the mononuclear centers, whereas NO2via NO oxidation on the polynuclear oxo-cobalt sites. Cyanide and isocyanate species, formed together with propene oxygenates in the course of the CC bond scission, are the mechanistically pivotal reaction intermediates of C3H6 interaction with the dinitrosyles and NO3−/NO2− surface species. Dinitrogen is produced by three main reaction routes involving oxidation of cyanides by NO/NO2, reduction of dinitrosyls, nitrates, and nitrites by propene oxygenates (medium temperature range) or their reduction by carbon monoxide (high temperature range).

Dependence of the catalytic activity of Ag/Al 2 O 3 on the silver concentration in the selective reduction of NO x with n -hexane in the presence of H 2

Abstract: The activity of 0.25–5% Ag/Al2O3 catalysts in the selective catalytic reduction of nitrogen oxides with n-hexane under the conditions of promotion with a small amount of H2 was studied. It was found that, upon the introduction of ∼1000 ppm of H2 into the reaction mixture, the Ag/Al2O3 samples containing 1–2% Ag exhibited optimum activity and selectivity. It was established that, in the presence of 1000 ppm of H2, the rate of the selective catalytic reduction of NO x was higher by a factor of 10–13, and the onset temperature of the reaction was lower by approximately 100°C. It was found by X-ray photoelectron spectroscopy, temperature-programmed reduction, and UV spectroscopy that the high activity of 1–2% Ag/Al2O3 catalysts was due to the presence of small Ag δ+ and Ag 0 clusters on their surface. A decrease in the concentration of Ag below the optimum value resulted in the predominance of an inactive ionic form on the catalyst surfaces. As the concentration of Ag was increased (>2%), large particles of Ag2O and Ag0, which facilitate the oxidation of n-C6H14, were formed to lead to a decrease in selectivity and in the degree of reduction of nitrogen oxides.

Selective reduction of ketones using water as a hydrogen source under high hydrostatic pressure

Abstract: A selective reduction of a broad variety of ketones is described. The method is based on the combination of a Ni–Al alloy and high hydrostatic pressure (HHP, 2.8 kbar) in an aqueous medium. The reaction of the Ni–Al alloy with water provides in situ hydrogen generation and the high pressure ensures that the H2 formed remains in the solution, thus the CO reduction readily occurs. The application of the HHP resulted in selective formation of the desired products and the common problem of non-selective overhydrogenation could be avoided. In most cases the reductions resulted in high yields and excellent selectivities without the use of any base.

Preparation of activated carbon-based catalyst used for selective reduction desulphurization of flue gas

Abstract: Belonging to the technical field of sulfur recovery, the invention relates to a catalyst for selective reduction desulphurization, its preparation method and application. The catalyst is characterized in that: a catalyst active component is loaded on a carrier by means of an isometric immersion method, a multiple immersion method and an immersion precipitation method so as to obtain the catalyst; the catalyst carrier consists of coconut-shell activated carbon, fruit-shell activated carbon and coal-based activated carbon; the oxidation modifier of the catalyst carrier is one or a mixture of any of chloric acid, nitric acid, hydrogen peroxide or concentrated sulfuric acid; the active component of the catalyst is one or a mixture of any of CuO, NiO, Fe2O3, ZnO, Cr2O3, Co2O3, MnO2, and V2O5. The desulfurizer of the invention employs a selective reduction desulphurization technology to convert SO2 in flue gas into elemental sulfur. The preparation technology of the catalyst has the advantages of simplicity, easy control, low cost and long service life. Adoption of the activated carbon-based catalyst prepared in the invention for selective reduction desulphurization not only realizes high efficiency SO2 conversion rate and sulfur selectivity, but also effectively prevents secondary pollution.

Efficient and Selective Reduction of Aromatic Nitro Compounds to Aromatic Amines by NbCl5/Indium System

Abstract: However, most methods still lack the desired chemoselec-tivity when other reducible functional groups are present inthe nitroarene and often require long reaction times, or harshreaction conditions. Consequently, efficient and selectivemethods for the reduction of aromatic nitro compoundscontinue to be developed. It has been reported that NbCl

Structural functional design of catalysts for conversion of nitrogen(I, II) oxides

Abstract: The results of structural functional design of catalysts for the reduction of nitrogen(I) and nitrogen(II) oxides and the simultaneous conversion of NO and N2O are reviewed. Catalysts based on metals of the platinum group on structured supports for the reduction of nitrogen oxides (NOx) by carbon monoxide and methane and three-component transformations (CO/NO/CnHm) are presented together with complex oxide catalysts (Cu,Cr,Fe/γ-Al2O3) for the selective reduction of NOx with ammonia. Bifunctional metal-oxide (Co, Cr, Ce, In, Fe) catalysts and those doped with Rh (Pt) and deposited on ZrO2,Al2O3, and H-ZSM-5 and their binary composites for the reduction of NO and N2ObyC1-and C3-C4 hydrocarbons are examined.

Role of active components of an Ag/Al2O3/cordierite catalyst in selective reduction of NO by ethanol

Abstract: We show that the activity of silver/aluminum oxide catalysts in selective reduction of nitrogen oxides by ethanol increases as the Al2O3 content increases, and is determined by the optimal silver content for which Ag+ cations and $ {\mathrm{Ag}}_n^{\updelta + } $ nanoclusters form on the Al2O3 surface. The role of silver in Ag/Al2O3/cordierite is to regulate the redox and acid–base properties of the surface of the catalyst.

Highly Efficient and Selective Reduction of Nitroarenes with Hydrazine over Supported Rhodium Nanoparticles.

Abstract: A rhodium/porous ionic copolymer nanocatalyst can be used at low loading (0.1-1.0 mol%) for the selective reduction of the nitro group of nitroarenes in the presence of halide (F, Cl, Br, I), CN, NH2, OH, amide, ester, and alkene substituents to give the corresponding anilines quantitatively.

Selective reduction of NO by photo-SCR with ammonia in an annular fixed-film photoreactor

Abstract: Gaseous NO was photocatalytically reduced at room temperature by photo-assisted selective catalytic reduction (photo-SCR) with ammonia over TiO2 in this study. NO reduction efficiency and N2 selectivity were determined from gases composition at the outlet stream of photoreactor. Effect of operating conditions, e.g. light intensity and inlet concentrations of ammonia and oxygen, on the NO reduction efficiency and N2 selectivity were discussed to determine the feasible operating condition for photocatalytic reduction of NO. Experimental results showed that selective catalytic reduction of NO with ammonia over TiO2 in the presence of oxygen was a spontaneous reaction in dark. The photoirradiation on the TiO2 surface caused remarkable photocatalytic reduction of NO to form N2, NO2, and N2O under 254 nm UV illuminations, while almost 90% of N2 selectivity was achieved in this study. The ammonia and oxygen molecules played the roles of reductant and oxidant for NO reduction and active sites regeneration, respectively. The reduction of NO was found to be increased with the increase of inlet ammonia and oxygen concentrations until specific concentrations because of the limited active sites on the surface of TiO2. The kinetic model proposed in this study can be used to reasonably describe the reaction mechanism of photo-SCR.

Catalyst composition and method for use in selective catalytic reduction of nitrogen oxides

Abstract: Catalyst composition for selective reduction of nitrogen oxides and soot oxidation comprising a physical mixture of one or more acidic zeolite or zeotype components with one ore more redox active metal compounds and a method for selective reduction of nitrogen oxides and soot oxidation by use of the catalyst composition.

Catalyst for selective reduction of NOx with NH3 and preparation method thereof

Abstract: The invention belongs to the technical field of catalysts, in particular to a load-type LaBO3 (B=Mn, Fe) perovskite selective reduction of NOx with NH3 and a preparation method thereof. In the invention, a citric acid sol-gel method is combined with a wet process dipping method to prepare a carrier-loaded citric acid complex precursor, and the precursor is roasted at high temperature to obtain the load-type perovskite catalyst. The catalyst can be used for selective reduction of NOx with NH3, the good effect is obtained, the higher conversion rate at lower reaction temperature is achieved andthe defect of the high reaction temperature of the traditional catalyst is eliminated.

Catalyst for eliminating nitrogen oxide through low temperature selective reduction under high oxygen-rich condition and application thereof

Abstract: The invention belongs to the fields of polyphase catalysis, catalyst research technology and environmental protection. Provided is a catalyst for eliminating nitrogen oxide through low temperature selective reduction under high oxygen-rich condition and application thereof. A catalyst carrier mainly containing ZSM-5 molecular sieve is supported with precious metals Pt and / or Pd as well as modification a component of tungsten and / or molybdenum. The typical catalyst Pt (0.1wt%).W(1wt%) / HZSM-5 can realize a NO selective reduction rate higher than 90% at about 110 DEG, under reaction condition of GHSV being 35000 h , tail gas simulation gas being 1000 ppm NO, 5000 ppm H2, 10% of O2 and N2 as balance gas, wherein more than 63% of NO is reduced and eliminated into N2. The catalyst has characteristics of (1) low elimination temperature and wide window on nitrogen oxide and substantial catalysis effect on nitrogen oxide reduction elimination at 80-200 DEG C; (2) low precious metal usage amount; and (3) high selectivity of nitrogen oxide elimination into N2.