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Remediation of dense non-aqueous phase liquids (DNAPLs) contaminants in groundwater has received considerable attention in the environmental field. Generally, DNAPLs can flow with groundwater and further infiltrate down to deeper aquitard zone that is difficult to be removed by pumping. The DNAPLs may also contaminate the soil and groundwater concurrently in the duration of flowing with groundwater slowly. In this study, remediation of 1,2-dichloroethane (1,2-DCE) in DNAPL contaminated groundwater was studied by a reductive reaction with polyethylenimine (PEI) surface-modified zero-valent iron nanoparticles (PEI-nZVI). The prepared PEI-nZVI was injected into upstream wells and reach the plume of DNAPLs down with the flowing groundwater. Moreover, nZVI was further characterized after field injection and 1-day reaction with the contaminants to assess its effectiveness for the on-site reduction of 1,2-DCE. After direct injection of PEI-nZVI into the contaminated plume, the concentrations of 1,2-DCE was significantly reduced. Moreover, the plume was decontaminated to nontoxic species onto the highly active nZVI. By using resistivity image profiling (RIP), the conductivity data of modified nZVI solution and sampled groundwater were similar. In addition, RIP can reveal complex subsurface DNAPLs structures by dense sampling of resistivity variation at shallow depth. Additionally, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy studies indicated that after the reductive reaction, nZVI and PEI-nZVI were oxidized to Fe3O4. The interatomic distances for the reacted samples were 1.95 Å and 1.93 Å, respectively. The combined technique of floating surface-modified nZVI and RIP method would be economically and environmentally attractive.Graphical Abstract: [ABSTRACT FROM AUTHOR]

The formation of N2O has been studied by means of isothermal lean-rich experiments at 150, 180 and 250 °C over Pt-Ba/Al2O3 and Pt/Al2O3 catalysts with H2 and/or C3H6 as reductants. This allows to provide further insights on the mechanistic aspects of N2O formation and on the influence of the storage component. Both gas phase analysis and surface species studies by operando FT-IR spectroscopy were performed. N2O evolution is observed at both lean-to-rich (primary N2O) and rich-to-lean (secondary N2O) transitions. The production of both primary and secondary N2O decreases by increasing the temperature. The presence of Ba markedly decreases secondary N2O formation. FT-IR analysis shows the presence of adsorbed ammonia at the end of the rich phase only for Pt/Al2O3 catalyst. These results suggest that: (i) primary N2O is formed when undissociated NO in the gas phase and partially reduced metal sites are present; (ii) secondary N2O originates from reaction between adsorbed NH3 and residual NOx at the beginning of the lean phase. Moreover, N2O reduction was studied performing temperature programming temperature experiments with H2, NH3 and C3H6 as reducing agents. The reduction is completely selective to nitrogen and occurs at temperature higher than 250 °C in the case of Pt-Ba/Al2O3 catalyst, while lower temperatures are detected for Pt/Al2O3 catalyst. The reactivity order of the reductants is the same for the two catalysts, being hydrogen the more efficient and propylene the less one. Having H2 a high reactivity in the reduction of N2O, it could react with N2O when the regeneration front is developing. Moreover, also ammonia present downstream to the H2 front could react with N2O, even if the reaction with stored NOx seems more efficient. [ABSTRACT FROM AUTHOR]

The development of highly active and durable nonprecious metal catalysts that can replace expensive Pt-based catalysts for the oxygen reduction reaction (ORR) is of pivotal importance in polymer electrolyte membrane fuel cells. In this line of research, metal and nitrogen codoped carbon (M-N/C) catalysts have emerged as the most promising alternatives to Pt-based catalysts. This review provides an overview of recently developed synthetic strategies for the preparation of M-N/C catalysts to enhance the catalytic activity of the ORR. We present five major strategies, namely the use of metal-organic frameworks as hosts or precursors, the use of sacrificial templates, the addition of heteroelements, the preferential generation of active sites, and a biomimetic approach. For each strategy, the advantages capable of boosting catalytic activity in the ORR are summarized, and notable examples and their catalytic performances are presented. The ORR activities and measurement conditions of high-performing M-N/C catalysts are also tabulated. Finally, we summarize this review with some suggestions for future studies. [ABSTRACT FROM AUTHOR]

Vanadia supported on ceria shows particularly high catalytic reactivity. To elucidate its reduction site, cationic cerium-vanadium oxide clusters, CenVmOx+ (n = 1-6, m = 0-5), were generated in the gas phase and their thermal response, such as reduction by oxygen release, was investigated by gas phase thermal desorption spectrometry. Stoichiometric and near-stoichiometric CenVmOx+ clusters were dominantly formed, suggesting that Ce and V atoms in thermally stable clusters at 310 K have the oxidation states of + 4 and + 5, respectively. An oxygen molecule O2 was found to desorb from the clusters, resulting in formation of CenVmOx−2+, upon heating. Presence of more than two Ce atoms in the clusters for odd values of m, or more than three Ce atoms for even values of m lowered the desorption temperature, indicating that not V atoms (+ 5 to + 4) but Ce atoms (+ 4 to + 3) in CenVmOx+ tend to be reduced. [ABSTRACT FROM AUTHOR]

The temperature used in the chemical reduction of graphene oxide (GO) with hydroiodic acid has a significant influence on the removal of surface oxygenated functional groups, on the residual iodine species and on the rupture, stacking and graphitization of the graphene sheets in the reduced graphene oxides. The modification in the characteristics of the reduced graphene oxides induces changes in the surface area, the exposition of reduced graphene oxide entities and in the concentration of small CdS nanocrystals with strong confinement effect on the CdS-reduced graphene oxide hybrids. The hybridization of the reduced graphene oxide with CdS modifies in different way their photocatalytic behavior for hydrogen production from aqueous solutions of NaS and NaSO under simulated sunlight irradiation. Only the hybrid formed between the CdS and the reduced graphene oxide treated at higher temperature showed improved hydrogen production rate respect to the bare CdS reference associated with the better conductivity of the reduced graphene oxide and with the increase in the concentration of small CdS nanocrystals sith strong confinement effect observed in the hybrid. [ABSTRACT FROM AUTHOR]

Manganese (IV) oxide (MnO) nanoparticles were synthesized, via a plasma-chemical route by using a gliding arc discharge at atmospheric pressure. α-MnO nanorods were obtained from the chemical reduction of KMnO. The synthesis yield was 96.8% after 4.5 min of exposure of the solution to the plasma. Further increase of the exposure time induced a decrease of MnO yield because of its reductive transformation into Mn ions. Particles were characterized by X-ray powder diffraction, scanning electron microscopy, Fourier Transform Infrared spectroscopy, and nitrogen physisorption. The plasma-catalytic properties of the synthesized material were tested in the bleaching of amaranth red (AR). AR bleaching efficiencies of 17 and 44% were respectively obtained when the plasma and plasma-catalyst processes were applied for 30 min with initial pH 10. The influence of the initial pH, and catalyst concentration were investigated: the AR bleaching efficiency increased linearly with the catalyst concentration and increased markedly when the pH of the solution decreased. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the release and reduction of NO (nitrates) stored on Rh-Ba/AlO and Pt-Rh-Ba/AlO catalysts and compared with Pt-Ba/AlO. It is shown that the release occurs at the interface between the PGM sites and the storage sites, can be probed by isotopic exchange experiments and is governed by the rate of oxygen removal from the metallic PGM sites. Accordingly the presence of a reductant, that keeps the PGM sites in a reduced state by scavenging oxygen adatoms formed upon nitrate decomposition, greatly favors the release of NO and its subsequent reduction. In these steps, not much differences have been observed considering either Pt- or Rh-based samples. [ABSTRACT FROM AUTHOR]

Cu migration into *BEA zeolite in the course of NH-faciliated solid-state ion exchange (SSIE) was studied using $${\text{Cu}}^{\text{II}} {\text{O}}$$ and $${\text{Cu}}^{\text{I}}_{ 2} {\text{O}}$$ as the Cu sources. It was found that $${\text{Cu}}^{\text{II}} {\text{O}}$$ and $${\text{Cu}}^{\text{I}}_{ 2} {\text{O}}$$ are equally effective when SSIE is carried in the presence of 500 ppm NO and 500 ppm NH. Removal of NO significantly reduces the efficiency of SSIE for [ $${\text{Cu}}^{\text{II}} {\text{O }} + {\text{ NH}}_{ 4} {\text{-}}^{*}{\text{BEA}}$$ ] since the process becomes limited by $${\text{Cu}}^{\text{II}} {\text{O}}$$ → $${\text{Cu}}^{\text{I}}_{ 2} {\text{O}}$$ reduction. When $${\text{Cu}}^{\text{I}}_{ 2} {\text{O}}$$ is used as the Cu source the rate of SSIE is no longer limited by the reduction, but becomes limited by the formation and migration of mobile [Cu(NH)] complexes. A time-resolved study of SSIE with NH and a $${\text{Cu}}^{\text{I}}_{ 2} {\text{O }} + {\text{ NH}}_{ 4} {\text{-}}^{*}{\text{BEA}}$$ mixture at 200 and 250 °C reveals two distinctly different stages during Cu migration, which are tentatively attributed to non-random occupation of different cationic positions that the Cu-species occupy upon consecutive exposure to the atmosphere in the selective catalytic reduction of nitrogen oxides with ammonia. [ABSTRACT FROM AUTHOR]

A series of sponge-like NiM (M = Cu, Co, Cr, Fe; x = 0.00-0.10) alloys was prepared via synthetic routes with subsequent reduction in H atmosphere at 800-1000 °C. Formation of Ni-based solid solutions with face-cantered cubic (fcc) lattice of nickel was proven by X-ray diffraction analysis for all prepared samples. NiM alloys were explored as precursors for self-organizing catalysts active in processing of 1,2-dichloroethane into carbon nanomaterial (CNM). According to kinetic studies of CNM growth performed at 600 °C, the catalytic activity of NiM samples changes as follows: Cr > Co-Cu ≫ Fe. Ni-Cr sample showed rather stable performance during 4 h whereas Ni-Co, Ni-Cu and Ni (reference) samples underwent rapid deactivation after ~150 min of reaction. The presence of the residual amount of Cr (0.5 at.%) found by energy dispersive X-ray microanalysis method in the composition of active Ni particles responsible for the growth of CNM is considered to be a key factor providing the stable catalytic performance. The obtained carbon product is represented by well-ordered segmented fibers (0.4-0.8 μm in diameter) and characterized with comparatively high textural parameters (surface area 290-330 m/g, pore volume 0.43-0.57 cm/g). [ABSTRACT FROM AUTHOR]

The effect of a reduction step on the catalytic activity of Pd supported doped ceria catalysts was investigated for the propane combustion. Two different oxides based on ceria zirconia (CZ), as a reference three-way catalyst support, and Gadolinia doped ceria (GDC), a mixed ionic electronic conductor, have been used to support Pd nanoparticles. The samples were characterized by H-CO chemisorption, temperature programmed reduction, and XPS. In addition, the reduction step in H was in situ observed by environmental transmission electron microscopy. It was found that the catalytic activity of Pd supported on ceria-based supports can be strongly promoted by a reduction step whereas it does not change on alumina. This effect was attributed, in particular on GDC, to the reduction of a surface interaction phase, PdCeO, which induces a re-dispersion of metallic Pd nanoparticles. [ABSTRACT FROM AUTHOR]

The activity of cobalt-boron catalysts in sodium borohydride hydrolysis has been correlated with change of structure in the active component of the catalysts upon their thermal treatment. It was shown that at temperatures to 300 °C there takes place loss of water and hydrogen from the catalysts without noticeable changes in activity. At temperatures above 300 °C the amorphous cobalt boride particles undergo crystallization to produce metallic cobalt with a hexagonal structure and this is seemingly the cause of the substantial fall in the rate of hydrogen generation in the presence of cobalt-boron catalysts. [ABSTRACT FROM AUTHOR]

Methanation of CO by H can be in the future an important reaction to store the surplus of renewable electricity during production peaks. The catalytic thermal CO methanation (the Sabatier reaction) can be carried out at temperatures above 250 °C using Ni supported on silica-alumina (Ni/SiO-AlO). Recently it has been observed that this exothermic reaction can be promoted by solar light irradiation of Ni/SiO-AlO at initial near ambient temperatures. In the present work we provide a study of the influence of the initial temperature on the photoassisted Ni/SiO-AlO methanation of CO, under conditions in which the dark reaction is not observed. An increase of the photoassisted methanation rate with the initial temperature in the range from ambient to 150 °C has been observed. The reaction kinetics for lower initial temperatures exhibited an induction period not observed for reactions performed at higher temperatures. The results are discussed in terms of the operation of plasmon photo activation in which the energy of photons is thermalised in a confined space of the active nanoparticles leading to locally high temperatures and the simultaneous photogeneration of electrons and positive holes. [ABSTRACT FROM AUTHOR]

Low temperature dry reforming of methane was studied over (0.13-0.51 wt%) Pd and (0.16-0.64 wt%) Pt doped 1.4 wt%Ni-1.0 wt%Mg catalysts on a ceria-zirconia oxide support, as well as control catalysts containing Pt or Pd, but not Ni and Mg. Temperature-programmed reduction studies showed Pd catalysts having initial reduction peaks at lower temperatures compared to Pt catalysts. Reaction studies showed the lowest 10 % conversion of methane at 383 °C for the 0.13%Pd-1.39%Ni-1.0%Mg/(CeZr)O catalyst. The same catalyst also had the lowest 10 % conversion temperature (366 °C) for carbon dioxide. Syngas ratios (H:CO) for Pd catalysts (0.24-0.41) were better than Pt catalysts (0.22-0.30) at 450 °C, however still not close to the stoichiometric ratio as a result of the RWGS reaction simultaneously occurring at the low operating temperatures studied. Turnover frequencies were calculated from steady-state reaction experiments done in the temperature range of 430-470 °C. Both catalysts' TOFs increased with increasing temperature, however overall Pt catalysts had marginally higher TOFs (2.69-4.74 s) compared to Pd catalysts (2.40-4.58 s). Although both Pd and Pt catalysts had comparable activities and rates, the 0.13 %Pd-1.39 %Ni-1.0 %Mg/(CeZr)O catalyst was selected as the most promising one because of its higher H:CO ratios, negligible changes during reaction as evidenced in post-reaction characterization, more basic sites that may decrease coking, and its lower cost. [ABSTRACT FROM AUTHOR]

The influence of hydrogen and silver loading on lean NO reduction with methanol over Ag-AlO are investigated by flow-reactor experiments, H-TPR, TEM and XPS. Reduction of silver at low temperatures over Ag-AlO with high silver loading, suggests involvement of silver species/particles that are large (which is supported by the TEM analysis) and/or loosely bound to the support. The silver species reduced by hydrogen cannot be directly associated with the activity for NO reduction under methanol-SCR conditions. Furthermore, the activity for NO reduction increases slightly at low temperatures when hydrogen is added to the feed. However, also without co-fed hydrogen, a high low-temperature activity is achieved for methanol assisted lean NO reduction over Ag-AlO. [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]

X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were used to probe the electronic and geometric structures of Rh-Pd/CeO catalysts before and after ethanol steam reforming (ESR) at 400 °C, as well as after heating in CO atmospheres as a function of time and temperatures. The O/Ce ratio determined by XPS for the as-prepared Rh-Pd/CeO catalysts (individual metal loadings of 0.5 or 2 wt%) were close to 2, with the Rh and Pd present primarily in oxidized form (as oxide and chloride surface species). After ESR at 400 °C the ceria support was heavily reduced to CeO (x = 0.3-0.4), with Rh (64 % of total Rh) and Pd (67 % of total Pd) being the dominant species. Heating the as-prepared Rh-Pd/CeO catalysts under a CO atmosphere at 200-400 °C while monitoring the Pd and Rh K edges by XAS was also conducted. XAS of the K edge of Pd and Rh indicated, as expected, reduction of Pd before that of Rh from 200 °C onward. The FCC order of Pd is however perturbed at 400 °C. On the contrary, Rh once reduced maintained a well ordered (FCC) structure. This observation is rationalised by the greater reduction effect of Pd on CeO compared to Rh and therefore at the interface Pd structure may be altered at high temperatures. [ABSTRACT FROM AUTHOR]

To overcome stability issues associated with the use of an aldehyde in a catalytic reductive amination reaction, a cyclic ketolactol (ω-hydroxylactone) was employed as an aldehyde surrogate to form a γ-aminoacid. The reaction proceeded most favorably over a Pt/C catalyst. The thermodynamics of each step were evaluated using density functional theory calculations, which correctly predicted the dominance of the ring-closed lactol reactant, yet suggested a preference for a ring-opened iminium intermediate upon the initial, slightly endoergic addition of amine substrate. Exoergic hydrogenation of this intermediate provided the thermodynamic driving force for the overall transformation. During development, the reaction was observed to depend significantly on the volumetric gas to liquid mass transfer coefficient (ka) and this parameter was optimized to ensure successful scale up in a 400 L stirred tank reactor. [ABSTRACT FROM AUTHOR]

We report here the results of density functional theory quantum mechanical (QM) studies of the detailed chemical mechanism underlying the n-butane selective oxidation to form maleic anhydride (MA) on vanadyl pyrophosphate [(VO)PO] and vanadyl phosphate [VOPO] surfaces. This QM-derived mechanism differs substantially from previous suggestions but is in excellent agreement with key experimental observations. We find that the O(1)=P bond of the oxidized X1 phase of the VOPO surface is the active site for initiating the VPO chemistry, by extracting the H from the n-butane C-H bond. This contrasts sharply with previous suggestions, all of which involved the V=O bonds. The ability of O(1)=P to cleave alkane C-H bonds arises from a new unique mechanism that decouples the proton transfer and electron transfer components of this H atom transfer reaction. We find that the juxtaposition of a highly reducible V next to the P=O bond but coupled via a bridging oxygen dramatically enhances the activity of the P=O bond to extract the proton from an alkane, while simultaneously transferring the electron to the V to form V. This Reduction-Coupled Oxo Activation (ROA) mechanism had not been known prior to these QM studies, but we believe that it may lead to a new strategy in designing selective catalysts for alkane activation and functionalization, and indeed it may be responsible for the selective oxidation by a number of known mixed metal oxide catalysts. To demonstrate the viability of this new ROA mechanism, we examine step by step the full sequence of reactions from n-butane to MA via two independent pathways. We that find that every step is plausible, with a highest reaction barrier of 21.7 kcal/mol. [ABSTRACT FROM AUTHOR]

Monodisperse RhCu bimetallic nanoparticles (NPs) with various compositions were prepared by the co-reduction of Rh and Cu ions in the presence of poly( N-vinyl-2-pyrrolidone) (PVP). Powder X-ray diffraction analysis of the PVP-stabilized RhCu NPs revealed the formation of a novel solid-solution structure in which the Rh and Cu atoms are randomly distributed. The catalytic properties of the colloidal RhCu NPs were studied using hydrogenation of 4-nitrobenzaldehyde as a test reaction. We found that the RhCu NPs efficiently reduced 4-nitrobenzaldehyde using atmospheric hydrogen at room temperature and that the selectivity to 4-aminobenzaldehyde was enhanced from ~70 % with monometallic Rh NPs to ~97 % with RhCu NPs with a Cu content of 50 %. [ABSTRACT FROM AUTHOR]

Low temperature ethanol steam reforming (ESR) was studied over a series of 1 wt% Rh-x % Fe catalysts with various Fe loading (x = 0-10 wt%) and on different supports (Ca-AlO, SiO and ZrO). The results show that close interaction between Rh and Fe is required to reduce the CO selectivity to almost negligible values. In addition, Rh-Fe supported on Ca-AlO exhibits the best performance in terms of CO selectivity and hydrogen yield as compared to other supports. Characterization by XPS and XANES indicates the presence of FeO species upon reduction, resulting in the formation of coordinatively unsaturated ferrous (CUF) active sites along the Rh-FeO interface. These CUF sites promote water-gas shift reaction during low temperature ESR. Temperature programmed oxidation and Raman spectroscopy of spent catalysts also indicate that the addition of iron oxide reduces coke deposition and forms more reactive coke. Hence, the catalyst lifespan is significantly extended. [ABSTRACT FROM AUTHOR]

The 'cathodic corrosion' method for nanoparticle synthesis has been used to produce Pt nano-crystals with a preferential (100) orientation. These particles are surfactant-free and electrochemically clean, featuring a significant percentage of (100) terrace sites, as confirmed by electrochemical characterization tests to establish the amount of (100) sites: blank voltammetry in HSO, adsorbed CO stripping, and Ge irreversible adsorption. The high catalytic activity of these preferentially oriented particles is confirmed for reactions preferring (100) sites, such as dimethyl ether oxidation, ammonia oxidation, and nitrite reduction in alkaline media. In the case of nitrite reduction it is demonstrated that, similarly to (100) terraces of a well-ordered Pt single crystal electrode, the (100) facets of the nano-crystals can steer the reaction towards the selective formation of N. The use of an inexpensive preparation method to obtain nano-electrocatalysts that can perform selective electrocatalytic reactions such as ammonia oxidation and nitrite reduction, can pave the way for a new generation of practical catalysts for environmental and energy purposes. [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 mechanism involved in the formation of N and of NO during the reduction of nitrates stored onto a Pt-Ba/AlO LNT catalyst is investigated using labeled NO and unlabeled ammonia, in the presence and in the absence of NO in the gas phase. The reduction of the stored NO species (labeled nitrates) with NH leads to the selective formation of N. Based on the isotopic distribution, it appears that N formation occurs primarily through the statistical coupling of N-atoms formed by dissociation of NO and NH at metal Pt sites. When the reduction of the stored nitrates is carried out in the presence of NO in the gas phase, NO is preferentially reduced. This implies that the rate determining step of the reduction of nitrates by ammonia is likely associated with the release of stored NO. Negligible amounts of nitrous oxide have been observed during the NH-TPSR with adsorbed nitrates, whereas relevant quantities of NO have been detected at low temperatures (below 180 °C) in the runs performed in the presence of NO in the gas phase. The data converge to indicate that NO formation involves the presence of gaseous NO and this suggests that the formation of nitrous oxide occurs either through the coupling of two adsorbed NO molecules or the recombination of an adsorbed NO molecule with an adsorbed NH species. [ABSTRACT FROM AUTHOR]

The nucleation and growth of Au and Ag nanoparticles on rutile TiO(110)-(1 × 1) surfaces in different oxidation states is studied by means of photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM). Au and Ag nanoparticles were found to bind much more strongly to oxidized TiO(110) model supports than to reduced TiO(110) surfaces, as directly revealed by STM. Detailed PES studies addressing small Au and Ag particles complete this picture and show that the PES core level spectra acquired on Au/TiO(110) and Ag/TiO(110) can be best described by fitting with two binding energy (BE) components. Particularly for coverages in the sub-monolayer regime and for depositions at low temperatures (100 K) the PES core level spectra must be fitted with at least two BE components. The higher BE component is attributed to atoms at the interface between the metal clusters and the TiO(110) support. For Au/TiO(110), the two BE components were evident in the core level spectra for higher coverage than for Ag/TiO(110), consistent with different growth modes for Au (initially 2D) and Ag (3D) on TiO(110). Finally, strong evidence for charge transfer from Ag nanoparticles to the TiO(110) support is presented, whereas the charge transfer between Au nanoparticles and the TiO(110) support is very small. [ABSTRACT FROM AUTHOR]

Defect sites in titania have a substantial effect on many thermal and photochemical reactions. Three common types of defects are titanium interstitials, oxygen vacancies and oxygen adatoms-all of which can react with organic molecules adsorbed on the surface. We look broadly at thermal reduction and photochemical oxidation reactions of oxygenates. In particular, we focus on the reductive coupling of benzaldehyde, the photo-oxidation of butyrophenone, the photostability of benzoic acid, and the photo-oxidative coupling of methanol to methyl formate. Methods used include temperature programmed reaction spectroscopy, scanning tunneling microscopy, and density functional theory. [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 detailed reaction mechanism of Di-Air, which showed the unprecedented high deNO performance at high temperature conditions, was studied in this work. Since the Di-Air phenomenon occurs with continuous short pulse injections of hydrocarbons over NSR (NO storage and reduction) catalyst, this study focused on the specific function of HC as an effective reductant for NO reduction reaction. As a first step, the deNO performance was compared with three different reductant gases including CO, H and CH in a modified synthetic gas bench equipped with a gas injector which enables continuous small amount of injections. At inlet gas temperature of 450 °C CH showed the best deNO performance whereas H was the best at 150 °C. Moreover the result of temperature programmed desorption showed that intermediate species represented by -NCO (isocyanates) produced from CH was thermally more stable than that produced from CO. These results confirmed that the injected HC reacts with adsorbed NO on NSR catalyst generating thermally stable intermediates, which could contribute the high deNO performance at high temperature conditions. [ABSTRACT FROM AUTHOR]

The three-way activity under complex feed-streams of a series of Pt/CeZrO catalysts, either fresh or submitted to different ageing treatments, both before and after reduction, has been studied and related to the species present on the catalysts in view of their characteristics and TPR behaviour. [ABSTRACT FROM AUTHOR]

This study is devoted to an operando study of Pt-Rh/AlO-BaO lean-NO trap catalyst during the regeneration with H/CO reaction mixture. Particular attention was paid to the influence of CO coexisting with H during the regeneration that can simulate the regeneration step by using reformate composed of CO and H. In rich H mixture ammonia predominantly forms. As expected, strongly chemisorbed CO molecules over noble metals lower the efficiency of the trap at 150 °C. Successive hydrogenation of N atoms to ammonia predominates in our conditions. However, the comparison of the outlet gas composition with infrared spectral features also suggests a minor participation of isocyanate species (NCO) as possible intermediates in the production of ammonia especially for long regeneration duration in the absence of water. Interestingly, ammonia formation as reducing agent for the selective reduction of NO can stimulate practical applications for further coupling lean-NO trap with SCR catalysts. [ABSTRACT FROM AUTHOR]

The number and type of copper species present in an under-exchanged Cu-Beta zeolite catalyst were characterized using temperature-programmed reduction mass spectrometry (TPR-MS). Both H consumption and HO evolution were tracked, yielding additional insights into the nature of Cu species. Prior to the TPR-MS tests, catalyst samples were subjected to various high- temperature aging treatments in the presence of O in He, in order to assist with interrogating and resolving different types of sites. Absence of reducible species in the precursor material was confirmed by subjecting the H-form of the same zeolite to the TPR. Upon aging at temperatures below 700 °C, the TPR pattern showed several distinct peaks of different intensities. Aging at 800 °C led to shifting and broadening of these H consumption peaks, as well as to some reduction of the integral amount of the reducible sites. The 900 °C exposure resulted in a drastic change of the TPR pattern, with several new well-resolved H consumption peaks, indicative of drastic changes in the catalyst structure. The integral amount of H consumed quantitatively matched the amount of Cu species present in the catalyst, assuming the $$ {\text{Cu}}^{ 2+ } \to {\text{Cu}}^{0} $$ stoichiometry. The combination of experimental findings in this work lends support to a hypothesis that different TPR peaks are indicative of different types of sites rather than of step-wise reduction of copper species. [ABSTRACT FROM AUTHOR]

A commercial copper exchanged zeolite was characterised and studied regarding the selective catalytic reduction of nitrogen oxides (NO) by ammonia using physicochemical analyses (XRF, XRD, NMR, BET, UV-Visible, IR) and synthetic gas bench test rig, respectively. As expected, two adsorption sites were identified for ammonia: Brönsted and Lewis acid sites, the latter retaining stronger ammonia. Furthermore, ammonia and water adsorb on the same sites, and competition phenomena decrease ammonia storage capacity. Concerning the NO conversion, in spite of a high efficiency, an important selectivity into NO is noticed, due to the formation of an ammonium nitrate by-product on the catalyst surface. The limited NO conversion efficiency at low temperature is due to the weak NO oxidation activity, whereas NH oxidation activity at high temperature involves a decrease in NO reduction. [ABSTRACT FROM AUTHOR]

As a continuation of our study of heat-integrated converters, we have fabricated a multifunctional converter that can treat all the components of emissions from diesel vehicles, namely CO, hydrocarbons, nitrogen oxides (NO), and particulate matter (PM). NO is reduced over a NH-SCR catalyst while PM is removed by a diesel particulate filter. The converter is also equipped with a self-heat exchanger that transfers heat from downstream to upstream of the converter, increasing the converter temperature and thereby substantially improving its performance. In an experiment using a 2.2-L engine vehicle operated at a constant speed of 60 km/h, the NO and PM reduction rates respectively reached 98 and 99.97 % due to efficient heating of the exhaust gas from 117 to 320 °C in the converter by the addition of H in the exhaust gas combined with the self-heat exchange function. Under transient driving conditions (Japanese 10-15 mode), the total NO reduction rate was 96 %. [ABSTRACT FROM AUTHOR]

Reduction of surface nitrates with CH on a Pt/AlO catalyst was investigated using diffuse reflectance infrared spectroscopy (DRIFTS) and a reactor system designed for monolith-supported catalysts. CH oxidation was inhibited by the presence of NO, and vice versa, and data indicate that adsorbed NO reacted with gas phase CH. DRIFTS results confirm reaction between CH and surface nitrates with linear nitrites as the reaction products. Data show that Pt is required for this reaction, which suggests the nitrates in proximity to the Pt particles are affected/relevant. [ABSTRACT FROM AUTHOR]

The oxidation state of palladium in a model Pd/ACZ three-way catalyst was monitored by synchronous XANES and mass spectrometry during two consecutive heating (to 850 °C) and cooling (to 100 °C) cycles under stoichiometric conditions simulating exhaust after treatment of a natural gas engine. During heating in the first cycle, PdO reduction occurred around 500 °C and the initial fully oxidized state of Pd was never recovered upon heating and cooling cycles. A mixed Pd/Pd oxidation state was at work in the second cycle. Hence, the operando XANES study reveals that the PdO/Pd pair exists in a working catalyst but is less active than the catalyst in its initial state of fully oxidized palladium. It is also evident from XANES spectra that ceria-zirconia promotes re-oxidation of metallic Pd, thus reasonably sustaining catalytic activity after exposure to high temperatures. [ABSTRACT FROM AUTHOR]

The effect of aging atmosphere on the sintering behavior of commercial Pd and Rh catalysts as well as the TWC performance thereof has been investigated under straight oxidizing, reducing and periodic cycling aging conditions, in search of useful guidance in the optimum design of thermally durable TWCs for advanced gasoline engines equipped with the deceleration fuel cutoff technology. Pd and Rh catalysts individually exhibit an opposite trend in the thermal sintering behavior with respect to the aging atmosphere. Under oxidizing conditions, the Pd catalyst becomes more resistant to sintering in higher O concentrations, whereas the Rh catalyst reveals the opposite behavior, regardless of the aging temperature. Physicochemical characterizations by using TGA and CO chemisorption have indicated that the state of Pd (PdO vs. Pd) and Rh (RhO vs. Rh) on the catalyst surface formed during the thermal aging plays an important role for determining the trend of thermal sintering; the positive effect of the O concentration on Pd sintering is attributable primarily to the formation of PdO, while the main cause for severe deactivation of the Rh catalyst under oxidizing conditions is the diffusion of RhO into the support along with the agglomeration of Rh particles. [ABSTRACT FROM AUTHOR]

Fuel consumption for NO trap regeneration depends on the regeneration frequency, which is a function of NO trap performance parameters. Hence, the impact of thermal aging must be considered in the operation strategy. For this purpose, the effect of thermal aging on the physical and chemical properties of a commercial NO storage/reduction catalyst containing Pt/Pd/Rh has been investigated. After thermal treatment under various conditions, the samples were characterized using CO chemisorption measurements, X-ray diffraction (XRD), N physisorption, and electron microscopy. It is shown that the major impact of lean hydrothermal treatment on the catalyst activity is the continuous decrease of the specific surface area with aging temperature due to collapse of smaller pores. The noble metal nanoparticles remained highly dispersed, even after lean aging at 800 °C. In contrast, noble metal sintering represents the main aging effect of lean/rich cycling at elevated temperatures. Furthermore, XRD and selected area electron diffraction revealed a significant loss of crystallinity for the barium component in consequence of lean/rich aging treatment. However, independent from the aging treatment, no formation of mixed oxides could be observed. [ABSTRACT FROM AUTHOR]

Catalysts with highly dispersed palladium on alumina, alumina doped with 20 wt% ceria and ceria have been prepared, characterized and examined for net-lean methane oxidation. In particular, the activity and selectivity were investigated during rich/lean cycling of the feed. The ceria content is found to influence both the general and the instantaneous activity responses. The results indicate that the active phase of palladium changes between reduced and oxidised Pd during the rich/lean cycling, and that the process is influenced by the presence of ceria. [ABSTRACT FROM AUTHOR]

Systematic studies of Co-Mo-B-P alloy catalysts, synthesized by chemical reduction methods, were conducted for H generation by hydrolysis of ammonia borane (AB). The molar concentrations of Mo and P were optimized in the alloy to obtain the best catalytic activity. The combined promoting effects induced by Mo and P in the quaternary alloy caused the H generation rate to increase by ~7.5 times as compared to the undoped-Co-B catalyst. XPS, XRD, SEM, and BET surface area analyses were carried out to understand the promoting role of each dopant element during AB hydrolysis. In the Co-Mo-B-P alloy catalyst, Mo in form of oxides acts as an atomic barrier to avoid Co-B particles agglomeration to preserve the effective surface area. These oxidized species also act as Lewis acid sites to enhance the absorption of reactant to further assist the hydrolysis reaction over alloy catalysts. The role of P in the alloy catalyst is to create a higher number of Co active sites on the catalyst surface as confirmed by XPS. These combined promoting effects provided by P and Mo doping in the Co-B catalyst reduce the activation energy to the lowest value (23 kJ/mol) in the hydrolysis of AB. [ABSTRACT FROM AUTHOR]

A low loading of Rh (0.5 wt%) was added to a MoO/ZrO sample with the objective of lowering the temperature at which the molybdena phase could be transformed in the presence of CH/H to produce an active carbide phase for the hydroisomerisation reaction of linear alkanes. The presence of Rh reduced the reduction temperature of the supported molybdena in hydrogen alone and reduced the temperature required for the onset of carburisation in hydrogen/methane. Pre-treatment cycles of reduction and oxidation further enhanced the extent of rhodium-molybdena interactions and further lowered the temperature required to form the carbidic phase. Although the presence of rhodium facilitated the formation of an active molybdenum carbide phase, the products formed in the hydroisomerisation reactions of both hexane and octane were mainly hydrogenolysis products due to the high activity of rhodium for these reactions under the conditions employed. The distribution of the fragments were different for sample carbided after calcination and sample carbided after a reduction-oxidation cycle suggesting a surface composition which was significantly different for the samples prepared by the two different routes. [ABSTRACT FROM AUTHOR]

Metal nitrides may be of interest as potential sources of activated nitrogen which can be reacted with target organic molecules. Accordingly, the reduction of nitrogen within NiN, CuN, ZnN and TaN under a 1/3 Ar/H flow at elevated temperature has been determined as a simple test of lattice nitrogen reactivity. As anticipated by consideration of their stability, NiN and CuN are reduced completely at 250 °C with up to 30 % of their total lattice nitrogen yielding ammonia. The elimination of N results in the formation of pores which are particularly pronounced in the case of the denitrided Cu system. In the case of ZnN, the lattice nitrogen is less reactive with incomplete denitridation being observed at 400 °C and the amount of ammonia produced being 15 % of the total nitrogen available. Although TaN contains the least reactive nitrogen of the four samples studied, it can be regenerated by ammonolysis which is an important consideration in any envisaged application. [ABSTRACT FROM AUTHOR]

Mesoporous Ni-P amorphous alloy nanospheres with controllable sizes and compositions were synthesized by chemical reduction of Ni(OH) colloidal particles co-assembling with surfactant hexadecyl-trimethyl-ammonium bromide in liquid crystal mesophase using hypophosphite as reductant. The effects of the synthesis conditions on the particle size, composition and mesostructure of the mesoporous Ni-P nanospheres were systematically studied. It was found that the size of the mesoporous Ni-P nanospheres could be tuned from 35 to 90 nm by changing the reduction temperature, and the phosphorus content of the Ni-P products could be adjusted in the range of 20.1 to 27.6 % by changing the molar ratio of HPO/Ni. The active surface area and the thermal stability of the mesoporous Ni-P nanosphere catalyst are much higher than those for the conventional nonporous Ni-P amorphous alloy. In the liquid phase hydrogenation of nitrobenzene, the typical mesoporous Ni-P nanosphere catalyst exhibits much higher activity and better selectivity than the conventional nonporous Ni-P. The correlation between the catalytic performance and the structural properties is discussed based on the results of detailed characterization. [ABSTRACT FROM AUTHOR]

Nitrous Oxide (NO), an ozone depleting greenhouse gas, is an observed intermediate in aqueous nitrate/nitrite reduction mediated by both natural microbial and synthetic laboratory catalysts. Because of our interest in catalytic nitrate/nitrite remediation, we have endeavored to develop a detailed concordant experimental/theoretical picture of NO reduction with H over a Pd catalyst in an aqueous environment. We use batch experiments in H excess and limiting conditions to examine the reduction kinetics. We use density functional theory (DFT) to model the elementary steps in NO reduction on model Pd(100), Pd(110), Pd(111) and Pd(211) facets and including the influence of adsorbed O, H, and of HO. Both experiments and theory agree that hydrogen is necessary for removal of adsorbed oxygen from the catalyst surface. The dissociation of NO to N(g) and O(ads) is facile and in the absence of H proceeds until the catalyst is O-covered. Water itself is proposed to facilitate the hydrogenation of surface O by transferring absorbed hydrogen to Pd-absorbed O and OH. We measure an apparent activation energy of 41.4 kJ/mol (0.43 eV) for NO reduction in the presence of excess H, a value that is within 0.1 eV of the barriers determined theoretically. [ABSTRACT FROM AUTHOR]

The present study aims at investigating the role of potassium (K) promoter on the surface and catalytic behavior of Pd/AlO catalysts during NO reduction by alkanes (CH, CH) or alkenes (CH). In this context, the surface properties of un-promoted and K-promoted catalysts were evaluated by means of X ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of CO adsorption and FTIR-pyridine adsorption. The results reveal that both the electronic and structural properties of Pd entities can be substantially modified by potassium ions, which are in close proximity with catalyst surface without exhibiting a tendency to accumulate. This in turn results in significant modifications on reactants/intermediates chemisorption bonds, affecting the catalytic performance of K-promoted catalysts. Indeed, it was found that potassium strongly promotes the NO reduction by propane or propene yielding notably lower NO light off temperatures (ca. 100 °C) as compared to those obtained over un-promoted catalysts. On the contrary, a slight inhibition upon K-promotion was observed, when using CH as reducing agent, implying that the action of the K-promoter is strongly related with the reducing agent used and its' relative interaction with the catalyst's surface. The results are discussed in terms of the correlation between the surface chemistry modifications induced by electropositive promoters and the de-NO performance of K-promoted catalysts. [ABSTRACT FROM AUTHOR]

Commercial Cu-ZSM-5- and Ag/AlO-based lean NO catalysts were evaluated in a synthetic exhaust gas bench with the fuels RME, B30, B15, Agrodiesel 15, GTL, NExBTL, and MK1 as reducing agents. The influence of reductant was larger for Ag/AlO, albeit moderate, whereas the Cu-zeolite showed the highest NO conversion at lower temperature for all alternative fuels tested. [ABSTRACT FROM AUTHOR]

A catalyst of Ni supported on alumina coated monolith has been prepared, characterized and tested in NH decomposition. The characterization of the catalyst by XPS and TPR showed that there is no formation of aluminates after catalyst use. It is studied the effect of the space velocity, by varying the feed flow rate and the catalyst's length. Some evidences are shown about the reaction inhibition by produced H and about the reasons for the better performance of the monolith than packed bed catalyst. [ABSTRACT FROM AUTHOR]

Hydrogen can be produced from a mixture of CH and CO, based on chemical looping techniques. A physical mixture of a Ni/AlO catalyst and FeO-CeZrO as oxygen storage material is used in the chemical looping. During the reduction step, CH/CO is converted over Ni/AlO into syngas, which then reduces iron oxide, giving CO and HO. During re-oxidation of the oxygen storage material by steam, H with ppm levels of CO is produced. [ABSTRACT FROM AUTHOR]

Nanostructured VO(B) was prepared by employing glycerol as reductant. Key parameters of the pH value of crystallization solution and the volume ratio of glycerol to water were optimized to prepare pure phase VO(B). The VO(B) could catalyze the aerobic oxidation of benzene to phenol with molecular oxygen in high selectivity. [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]

Effects of Pt and Ba content of Pt/Ba/Al2O3 on NO x storage reduction (NSR) catalyst were investigated by means of kinetic analysis of surface nitrates using in situ FT/IR. Turnover frequencies of both storage and reduction of nitrate were significantly enhanced at higher Ba content, while those were higher at lower Pt content below 0.2 wt%. [ABSTRACT FROM AUTHOR]

The role of hydrogen in H2-assisted HC–SCR of NO x over Ag–Al2O3 is investigated by XPS and in situ DRIFT spectroscopy. Hydrogen does not reduce the surface silver species to metallic silver, however direct reduction of surface nitrates by hydrogen is observed. It is proposed that one important role of hydrogen is the removal of nitrates from the Ag–Al2O3 surface. [ABSTRACT FROM AUTHOR]