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In this paper, fundamental issues of the NSR technology are addressed. The reaction paths and the mechanism involved in the storage of NO and the relevance of the proximity between the noble metal and the alkali or alkaline-earth component of the catalyst are discussed first. Then the release of NO, the reaction pathways of NO reduction by different reducing agents, and the mechanisms involved in the formation of N, NH and NO are illustrated. The use of the combined technologies LNT + SCR and DPNR is addressed next and key aspects that highlight the synergies of the individual technologies are discussed. Finally, the perspectives of the NSR technology are outlined. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Mechanistic aspects involved in the formation of N and of NO during the reduction of NO, stored nitrites and stored nitrates in the presence of NO are investigated in this work by means of isotopic labeling experiments over a model PtBa/AlO NSR catalyst. The reduction of gaseous labeled NO with unlabelled NH leads to the formation of NO at low temperature (below 180 °C), and of N at high temperature. All N possible isotopes are observed, whereas only labeled molecules have been detected in the case of NO. Hence the formation of nitrous oxide involves undissociated NO molecules, whereas that of N can be explained on the basis of the statistical coupling of N- and N-adatoms on Pt. However, due to a slight excess of the mixed NN isotope, a SCR-like pathway likely operates as well. The reduction of the stored labelled nitrates is very selective to N and all isotopes are observed, confirming the occurrence of the recombination pathway. However also in this case a SCR-like pathway likely occurs and this explains the abundance of the NN species. When the reduction of the stored nitrates is carried out in the presence of NO, this species is preferentially reduced pointing out the higher reactivity of gaseous NO if compared to the nitrates. [ABSTRACT FROM AUTHOR]

The effect of soot on the NO storage-reduction performances of a Pt-K/AlO catalyst is analysed in this work by performing lean-rich cycles at constant temperature. The interaction between soot and the stored NO has been also investigated by temperature programmed methods. It has been found that the presence of soot reduces the NO storage capacity of the catalyst; besides the presence of soot favours the decomposition of the stored nitrates. A direct reaction between the stored nitrates and soot is suggested, that has been explained on the basis of the surface mobility of the adsorbed nitrates. [ABSTRACT FROM AUTHOR]

The reduction of NO stored over a Pt-Ba/AlO Lean NO Trap is analysed when H, CO or heptane are used as reductants. In all cases, the reduction proceeds via a Pt-catalyzed process involving the formation of intermediate species like ammonia and isocyanates in the case of H and CO, respectively. No specific intermediates have been observed when heptane is used as reductant. It is claimed that the role of the reductant is to keep Pt in a reduced state; this favours nitrate decomposition and reduction over the Pt sites. The effect of water on the reaction is also investigated. [ABSTRACT FROM AUTHOR]

Mechanistic aspects involved in the formation of N2andof N2O during the reduction of gas-phase NO and of NOxstored over a model PtBa/Al2O3NSR catalyst are investigated using unlabeled ammonia andlabeled NO. The reduction of the stored NOxspecies (labeled nitrites and nitrates) with NH3leadsto the selective formation of N2as a major product andof small amounts of nitrous oxide. Based on the nitrogen isotopicdistribution, it appears that N2formation occurs primarilythrough the statistical coupling of N-atoms formed by dissociationof NOx- and NH3-related surfaceintermediates, although an SCR-pathway (involving the coupling ofNH3- and NO-derived ad-species) is also likely to occur.It appears as well that the formation of nitrous oxide involves eitherthe coupling of two adsorbed NO molecules or the recombination ofan adsorbed NO molecule with an adsorbed NHxfragment. [ABSTRACT FROM AUTHOR]

The article discusses the use of Operando Fourier transform infrared spectroscopy (FTIR) to examine the critical role of the nitrite route in the NOx adsorption mechanism over Pt-Ba/AI2O3 NOx storage reduction catalysts. It mentions the emergence of lean-burn engines due to the growing need for fuel consumption reduction and carbon dioxide emissions. It notes that the nitrite route is the unique passage responsible for the storage of NOx.

The nature of stored NOx and mechanistic aspects of the reduction of NOx stored over a model Pt—K/Al2O3 catalyst sample are investigated in this paper, and a comparison with a model Pt—Ba/Al2O3 catalyst is also made.It is found that at 350 °C on both the catalysts the storage proceeds with the initial formation of nitrites, followed by the oxidation of nitrites to nitrates. A parallel pathway involving the direct formation of nitrates species is also apparent; at saturation, only nitrates are present on the catalyst surface over both Pt—K/Al2O3 and Pt—Ba/Al2O3. However, whereas bidentate nitrates are present in remarkable amounts on Pt—K/Al2O3, along with ionic nitrates, only very small amounts of bidentate nitrates were observed on Pt—Ba/Al2O3.Under nearly isothermal conditions, the reduction of the stored NOx with H2 occurs via an in series two-steps Pt-catalysed molecular process involving the formation of ammonia as an intermediate, like for the Pt—Ba/Al2O3 catalyst sample. However, higher N2 selectivity is observed in the case of the Pt—K/Al2O3 catalyst due to the similar reactivity of the H2 + nitrate and NH3 + nitrate reactions. Accordingly ammonia, once formed, readily reacts with surface nitrates to give N2, and this drives the selectivity of the reduction process to N2. Notably, a strong inhibition of H2 on the reactivity of NH3 towards nitrates is also pointed out, due to a competition of H2 and NH3 for the activation at the Pt sites. Finally, the effect of water and CO2 on the reduction process is also addressed. Water shows a slight promotion effect on the reduction of the nitrates by H2, and no significant effect on the reduction by ammonia, whereas CO2 has a strong inhibition effect due to poisoning of Pt by CO formed upon CO2 hydrogenation. [Copyright &y& Elsevier]

Abstract: A kinetic study for the reduction of NO x stored onto a Pt-Ba/Al2O3 LNT catalyst is developed, based on previous experimental work where regeneration of stored NO x was accomplished under isothermal wet conditions using ammonia and hydrogen as reducing agents [L. Lietti, I. Nova, P. Forzatti, J. Catal. 257 (2008) 270–282]. The kinetic model developed in the present paper differs from those available in the literature because it considers the most relevant physico-chemical features of regeneration of LNT catalysts under nearly isothermal conditions. It is based exclusively on a consecutive reaction scheme with ammonia as intermediate, as proposed in the previous study, and on a mechanism which considers only surface reactions of stored NO x . The model includes the elementary-like steps of adsorption–desorption of hydrogen, ammonia and water at Pt sites, and the lumped steps of reduction of stored nitrates by hydrogen to give ammonia and of reduction of residual stored nitrates by ammonia to give nitrogen. A surface dependent energy of activation for the reduction of nitrates with ammonia is required to describe the data in the T interval 150–300°C. This is due to the presence of nitrates with high and low reactivity that are envisaged as close and far from the noble metal crystallites, respectively. A low energy of activation (22.94kJ/mol) is estimated for the reduction of nitrates by hydrogen to give ammonia. This applies above a consumption of 1.5–2×10−4 mol of stored NO x /gcat, where the residual NO x species are expectedly stored far from the Pt crystallites and the rate of their consumption is limited by surface diffusion. Before this consumption level the reaction is limited by the concentration of hydrogen at any temperature in the T interval 150–350°C. The model is shown to capture the major features of the isothermal experiments performed under wet conditions over Pt-BaO/Al2O3 LNT catalyst with hydrogen and ammonia as reducing agents in the T interval 150–350°C and is able to describe nicely on a purely predictive basis independent NH3-TPSR experiments. However the model underestimates H2 consumption and net NH3 production during independent H2-TPSR experiments below 100°C, where the consumption of stored NO x is less than 1×10−4 mol/gcat and is associated with fast regeneration of Ba sites in close proximity to the Pt crystallites. The model is also used to simulate the axial concentration profiles in the reactor for gas and surface species as function of time during regeneration with ammonia. [Copyright &y& Elsevier]

Abstract: A detailed analysis of the catalytic behaviour in the storage/reduction of NOx of single Pt–Ba/Al2O3 LNT and FeZSM-5 SCR systems and of combined LNT+SCR configurations is analyzed and compared in this work under clean conditions (i.e. in the absence of CO2 and H2O in the feed stream). By working under dilute conditions (i.e. with low reductant concentrations) and with an inert purge between the lean and the rich phases, nearly ideal isothermal conditions could be attained and the chemical pathways operating in the each step of the NSR cycle could be analyzed for the investigated catalysts configurations. It is found that when the SCR catalyst is placed downstream the NSR catalyst bed (double-bed configuration), ammonia released from the LNT sample during the rich phase is stored on the SCR catalyst placed downstream and is then converted to N2 in the subsequent lean phase according to the occurrence of a SCR reaction. This has a benefit on both the NOx removal efficiency and the N2 selectivity. If the zeolite SCR catalyst is mixed with the LNT sample (physical mixture), during the rich phase the SCR catalyst traps ammonia which being intermediate in N2 formation leads to a decrease in the evolution of nitrogen at the reactor outlet. Ammonia stored on the SCR catalyst then reacts with NOx during the subsequent lean phase, leading to a significant N2 evolution: this increases the NOx removal efficiency and the N2 selectivity if compared to the single Pt–Ba/Al2O3 catalyst sample. [Copyright &y& Elsevier]

Abstract: In this paper the reactivity of NO x stored at 350°C onto Pt–Ba/Al2O3 LNT catalyst in the reduction by H2, CO and CO/H2O mixture is investigated by means of transient experiments and complementary FT-IR analyses. Hydrogen is found to be the best reductant, being characterized by the highest NO x removal efficiency in the range 150–350°C. It is proposed that the reduction by hydrogen proceeds according to a dual-steps mechanism in which NO x are first reduced to ammonia, which in turn further reacts with other nitrate species leading selectively to N2. Conversely, when CO is used as reducing agent under dry conditions only a part of the initially stored NO x is removed as N2, the other fraction being reduced to adsorbed cyanates/isocyanates species. It is proposed that the cyanate/isocyanate ad-species lead to the formation of nitrogen by oxidation involving other nitrate species; this reaction is self-poisoned by CO. In the presence of water, CO reduced nitrates into cyanates/isocyanates ad-species that were readily hydrolyzed to ammonia; this species is hence precursor in N2 formation upon reaction with residual nitrate species. Alternatively, stored nitrates are reduced by H2 formed via the water gas shift (WGS) reaction. [Copyright &y& Elsevier]

The reduction of NO x stored over a Pt–K/Al2O3 Lean NO x Trap is analyzed when H2 is used as reductant. An in series 2-steps process is herein proposed, involving at first the formation of NH3 upon reaction of nitrates with H2 (step 1), followed by the reaction of NH3 with residual nitrates to give N2 (step 2). [ABSTRACT FROM AUTHOR]

In this study, mechanistic aspects of NO adsorption/desorption over a home-made Pd/SSZ-13 passive NOx adsorber (PNA) catalyst are investigated. Operando FT-IR spectroscopy and microreactor experiments are performed to envisage the performance of the catalyst and the pathway involved in NO adsorption, with particular emphasis to the impact of species such as C3H6 and CO. In the absence of C3H6 and CO, NO is observed to adsorb as nitrosyls (anhydrous and hydrated) over both Pd2+ and Pd+ species, and as nitrates. 80 μmolNOx/gcat (NO/Pd molar ratio of 0.8) are adsorbed. The stability of nitrosyls is higher in comparison to the nitrates in that the former initially dehydrate and further decompose at elevated temperatures (> 300 °C) leading to the evolution of NO. The presence of CO and C3H6 negatively affects the amounts of NO adsorbed (53 and 45 μmolNOx/gcat, respectively) due to the reduction of Pd sites. CO admission to the catalyst forms a variety of carbonyl species over Pd2+, Pd+ and Pd0 sites which upon NO admission are readily displaced and NO is adsorbed as hydrated/anhydrous nitrosyls of Pdn+. The nitrosyls so formed exhibit lower thermal stability in comparison to nitrosyls observed in the absence of CO and decompose below 300 °C. The addition of C3H6 leads to the apparent formation of oxidized species like acetone, acrolein and acetates, besides propylene adsorption. The NO adsorption in the presence of C3H6 leads to the formation of Pdn+(NO)(X) complexes; upon heating the decomposition of this complexes is observed at low temperatures along with propylene and water desorption. Formation of organic nitro-compounds is also observed that decompose at higher temperatures. [ABSTRACT FROM AUTHOR]

The combustion of model soot (i.e. Printex U) by NO 2 and O 2 in the presence of water was investigated in a fixed bed micro reactor under isothermal conditions. A wide range of experimental conditions (e.g. 250–350 °C, 0–5 vol% O 2 , 0–500 ppmv NO 2 , 0–5 vol% H 2 O) were considered in order to investigate the role of NO 2 , O 2 and H 2 O in the combustion process. It was found that the oxidation of soot is initiated by NO 2 at temperatures where oxygen is unreactive. In addition, a synergistic effect between NO 2 and O 2 on soot combustion was observed in the presence of the NO 2 -O 2 mixture. Both the direct reaction between soot and NO 2 and also the contribution of gaseous oxygen on the combustion process appeared to rise with the increasing temperature and in the presence of water. Finally, the kinetic analysis of the experimental results showed a non-negligible dependence of the kinetic parameters on carbon conversion and in particular the poor accuracy of the shrinking-core model at low conversion degree. [ABSTRACT FROM AUTHOR]

Abstract: The NO x storage-reduction over the single Pt–Ba/Al2O3 and Fe-ZSM-5 systems and over the hybrid Pt–Ba/Al2O3 +Fe-ZSM-5 systems, both physically mixed and in dual bed configuration with the SCR catalyst placed downstream of the LNT catalyst, is systematically investigated by Isothermal Step Concentration (ISC) experiments and FTIR spectroscopy. The study is accomplished using H2 as the reductant, in the presence and absence of CO2 and H2O and in a wide temperature interval (150–350°C). The results are explained at the quantitative level by applying a scheme of the reduction of stored NO x , which implies at first the reduction of nitrates to give NH3, followed by the reaction of ammonia with NO x stored downstream in the reactor to give N2. The following main points have been clarified: (1) the storage of NO x occurs primarily onto Pt–Ba/Al2O3 and is lower in the presence of CO2 and H2O because BaCO3 is formed which retards NO x adsorption; (2) NH3 formed as intermediate in the reduction of stored NO x is trapped onto the Fe-ZSM-5 catalyst. The trapping of NH3 is most favoured when the particles of Pt–Ba/Al2O3 and of Fe-ZSM-5 are extensively in contact, as in the LNT/SCR physical mixture, and at low temperature. NH3 trapped onto Fe-ZSM-5 reacts during the subsequent lean phase with gaseous NO x slipped from the Pt–Ba/Al2O3 particles to give N2 via SCR; (3) the NO x removal efficiency is always higher for both LNT/SCR dual bed and physical mixture compared to single LNT, due to the additional contribution of SCR over Fe-ZSM-5 during the lean phase; (4) in the case of the LNT/SCR physical mixture, NH3 trapped onto the Fe-ZSM-5 particles can be oxidised over the LNT particles upon admission of oxygen to give N2, N2O and NO. The selectivity to nitrogen is almost complete at any temperature in the presence of CO2 and H2O, while in the absence of CO2 and H2O, it increases significantly with temperature and is almost complete at 350°C; (5) the ammonia slip is low to the best over the LNT/SCR dual bed at any temperature in the absence of CO2 +H2O. In the presence of CO2 and H2O, the ammonia slip is nil at any temperature over the LNT/SCR dual bed. [Copyright &y& Elsevier]

The effect of NO x storage on the soot combustion activity when alkaline- and alkaline/earth-containing model DPNR catalysts are used is investigated in this work. The influence of different experimental conditions (NO concentration, temperature, and particulate loading) is addressed and discussed in relation to the NO x storage efficiency and soot oxidation activity as well. [ABSTRACT FROM AUTHOR]

Abstract: The activity in the soot combustion of K- and Ba-based catalysts in “loose” and “full” contact is investigated in this study. Under loose contact systems (obtained by mechanically mixing the soot and catalysts), the K-containing samples are very active in the oxidation of soot, as opposite to the Ba-containing samples. Also, a synergistic effect in this reaction is seen between K and Pt for the case of the K-containing samples. Under full contact conditions (obtained by impregnation of the soot with aqueous metal solutions), the reactivity of soot increases; in these conditions the performance of the poorly reactive Ba-containing samples becomes similar to the very active K-based system. This result points out the key-role played by both the selected alkaline or alkaline earth metal oxides in the soot combustion, and suggests that the poor activity of Ba under loose conditions is possibly due to the low mobility of the Ba surface species. Finally, it is found that the presence of NO favors the soot oxidation under loose contact, specifically over noble metal-containing samples, due to the oxidation of NO to NO2. However the presence of the alkaline and alkaline earth oxide also affects the soot oxidation activity in the presence of NO. This has been ascribed to the formation of Ba- and K-nitrite/nitrate species which participate in the soot combustion process by giving rise to NO x upon nitrite/nitrate decomposition and/or by directly reacting with soot. [Copyright &y& Elsevier]

The potentiality of a Pt-K/Al2O3 catalyst in the simultaneous removal of particulate matter (soot) and NO x is investigated in this work by means of Temperature Programmed Oxidation (TPO) experiments and Transient Response Method (TRM), and compared with Pt-Ba/Al2O3. The results point out the higher performances of K-based sample in the soot combustion as compared to the Ba-based catalyst, and similar behaviour in the NO x -storage. [ABSTRACT FROM AUTHOR]

The study of the gas-phase NO reduction by H2 and of the stability/reactivity of NO x stored over Pt–Ba/Al2O3 Lean NO x Trap systems allowed to propose the occurrence of a reduction process of the stored nitrates occurring via to a Pt-catalyzed surface reaction which does not involve, as a preliminary step, the thermal decomposition of the adsorbed NO x species. [ABSTRACT FROM AUTHOR]

A series of Pt–Ba/Al2O3 NOx storage-reduction (NSR) catalysts having different Ba loadings (in the range 0–30%, w/w) have been prepared, characterized and tested in the NOx adsorption-reduction under realistic operating conditions. Accordingly, the role of the Ba loading on the storage of NOx and on their subsequent reduction has been addressed.The results indicated that the presence of Ba negatively affects both the catalyst morphological properties and the Pt dispersion in the samples with Ba loading higher than 10%, while a strong increase of the NOx adsorption capacity is observed. This effect has been associated to the involvement in the NOx storage process of Pt–Ba neighboring species. The analysis of the storage phase also showed that the highest the Ba content, the lowest the NO2 concentration at catalyst saturation: this effect has been related to the decrease in the Pt content of the catalyst following Ba addition to the samples and/or to a possible masking of Pt sites when the Ba coverage approaches and exceeds the monolayer capacity of the support.Concerning the reduction phase, the data pointed out that for all the investigated catalysts the stored NOx species are readily reduced upon H2 admission: nevertheless, the reduction process resulted very complex and it can lead to nitrogen and/or ammonia depending on the formulation and properties of the catalysts. [Copyright &y& Elsevier]

In this study a Pd-doped SSZ-13 zeolite sample is synthesized, characterized and evaluated for potential use in the low-temperature NO x adsorption. TEM/HR-TEM and in-situ CO/NO adsorptions followed by FT-IR spectroscopy are used to gain information on the nature and accessibility of the Pd sites. It is found that over the calcined sample Pd is present as isolated Pd+ and Pd2+ cations formed by ion exchange with the Brønsted acid sites of the zeolite, and as Pd+ and Pd2+ species belonging to PdO x particles on the external surface of the zeolite. Isolated Pd2+ ions prevail on the calcined fresh sample. The NO x adsorption/desorption performances, investigated by microreactor studies and operando FT-IR under relevant operating conditions, indicate that significant amounts of NO are stored on the catalyst (i.e. ca. 80–95 μmol/g cat of NO x in the temperature range 50–150 °C) which suggests the participation in the NO x uptake of both isolated Pdn+ sites and PdO x particles. NO is adsorbed as nitrosyls (anhydrous and hydrated) over both Pd2+ and Pd+; at low temperatures the formation of nitrates is also observed. The NO uptake as nitrosyls occurs with evolution of NO 2 according with a NO storage mechanism which implies (i) the initial adsorption of NO on Pd2+, followed by (ii) the reduction of Pd2+ to Pd+ by NO accompanied by NO 2 release and eventually (iii) the adsorption of NO on Pd+. The suggested interconversion of Pd2+ into Pd+ during NO adsorption is herein discussed based on FT-IR evidences. The stored NO x species are decomposed upon heating; nitrates are responsible for low temperature NO x desorption (below 200 °C), whereas nitrosyls show much higher stability and lead to a high temperature NO desorption (above 200 °C). The presence of NO 2 in the feed stream increases the NO x adsorption capacity and results in the formation of mainly surface/bulk nitrates and nitro-compounds at the expense of nitrosyls. [Display omitted] • Pd/SSZ-13 passive NOx adsorbers for NO adsorption during cold start. • NOx adsorb over Pd cations in the form of nitrosyls. • The stability of the adsorbed NOx depends on the adsorption temperature. • NO adsorption is accompanied by NO 2 evolution. • Nitrate formation is seen at low temperatures. [ABSTRACT FROM AUTHOR]

• The adsorption of NO/O 2 over Pt- and Rh-containing catalysts leads to nitrites at low T and of nitrates at high T. • Pt-based catalysts shows superior NO x storage properties. • Pt-based catalysts shows superior NO oxidizing properties. • Pt-based catalysts are more active that Rh/Al 2 O 3 in the reduction of stored NO x. • Rh- based catalysts show higher activity in the NH 3 decomposition reaction and steam reforming of propylene. In this work the reactivity of Pt-Rh NO x storage-reduction (NSR) catalysts in the reduction of NO x under lean conditions is investigated. It is found that significant amounts of NO x are stored on both Rh- and Pt-based samples at all the investigated temperatures (in the range 150–350 °C). Mostly chelating nitrites are adsorbed at the lowest investigated temperature (150 °C), while nitrates (both bidentate and ionic) at higher temperatures. However, at all temperatures nitrites prevail at the beginning of the storage phase, while nitrates represent the most abundant adsorbed species after prolonged contact. Pt-containing catalysts (either monometallic Pt or bimetallic Pt/Rh) show higher NO x storage capacity than the Rh monometallic sample, possibly due to the higher dispersion of Pt vs. Rh and/or to the higher oxidizing capability of Pt vs. Rh. The stored NO x species show relevant thermal stability, and decompose to NO x and O 2 upon heating. In particular, nitrites disproportionate to gaseous NO and nitrates; these latter then decompose to NO x and O 2. On the Rh-Ba/Al 2 O 3 catalyst the disproportionation reaction is observed with a higher temperature onset if compared to the Pt-based samples. The analysis of the reactivity of the stored NO x species (probed by isotopic labeling experiments and reduction with H 2 and NH 3) showed the lower reactivity of the Rh-Ba/Al 2 O 3 sample; however Rh shows activity in the ammonia decomposition reaction to N 2 and H 2 , unlike Pt. The lower reactivity of the Rh-Ba/Al 2 O 3 sample is also pointed out by experiments under cyclic lean-rich conditions. However, the presence of Rh increases the reactivity of the catalyst in the steam reforming of hydrocarbons, especially at high temperature, and accordingly the reactivity of the bimetallic Pt/Rh sample at high temperatures is higher than that of the Pt and Rh monometallic catalysts. [ABSTRACT FROM AUTHOR]

In this study, Ce/Zr-based materials without noble metals in their formulation have been prepared, characterized and tested in NOx adsorption at different temperatures. In particular, the effect of the presence of Ba and Cu in the catalytic formulation has been investigated. The catalyst characterization shows that the redox properties of the catalysts are enhanced by Cu and inhibited by Ba. Upon interaction with NO/O2, it is found that NOx are stored at low temperatures (150 °C) in the form of nitrites, without any relevant NO oxidation activity. This suggests a direct NO uptake. At higher temperatures (300 °C) a significant NO oxidation activity is observed, that is enhanced by Cu and depressed by Ba. In this case, NOx are stored in the form of nitrates; the samples containing both Ba and Cu exhibits the better performances in terms of NOx adsorption capacity. [ABSTRACT FROM AUTHOR]

In this study the pathways involved in N2O formation over a commercial LNT catalyst are addressed, when using H2 as a reductant. For this purpose, flow microreactor experiments coupled with FT-IR under operando conditions are used. The results indicate that N2O formation occurs both at the lean-to-rich (primary N2O) and rich-to-lean (secondary N2O) transitions. Primary N2O originates at the reduction front due to the presence of partially reduced PGM sites that do not readily dissociates NO released from the stored NOx. Undissociated NO couples with N-adatoms leading to the formation of N2O. At variance, secondary N2O originates upon oxidation with NO/O2 of reducing species left adsorbed on the catalyst surface (adsorbed CO, isocyanates and possibly NH3) during the rich phase, as pointed out by FT-IR spectroscopy. The concentration of such adsorbed species is however limited and hence the formation of secondary N2O is much smaller than that of primary N2O, when using H2 as reducing agent. The emissions of N2O reduce upon increasing the temperature, and above 250 °C N2O formation is negligible. Finally the reactivity of N2O with adsorbed NOx species (nitrites) and with the actual reductants (H2 and NH3) is also investigated, to provide further indications concerning the pathways leading to N2O emissions. It is found that N2O does not react with NOx species stored downstream the reduction front; at variance both H2 and NH3 may reduce N2O to N2 and water at rather low temperatures. The role of this reaction on N2O emission is herein discussed. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • NO can disproportionate to N 2 O over reduced metal sites. • N 2 O formation from NO is favored at low temperatures and with poorly reactive reducing agents. • Isocyanate species are involved in N 2 O formation. • Pt and Rh are the sites where N 2 O is formed. Abstract In this paper mechanistic aspects involved in the formation of N 2 O over model Pt-Ba/Al 2 O 3 and Rh-Ba/Al 2 O 3 LNT catalysts are discussed. The reactivity of both gaseous NO and of stored NO x (nitrates) has been studied, with simultaneous surface characterization by operando FT-IR spectroscopy, using different reductants (i.e. H 2 , CO, CO + H 2 , CO + H 2 O) both under isothermal conditions and temperature programming. The results show that N 2 O formation may occur during both the lean/rich and rich/lean switches (primary and secondary N 2 O, respectively). In particular: i) primary N 2 O formation involves the presence of gas-phase NO and partially reduced metal sites; ii) N 2 O formation increases in the presence of CO because the reduction of the metal sites is slower, thus favoring N 2 O formation upon the lean/rich transition; iii) residual reducing species onto the surface (i.e. NCO−, CO) can react with NO giving the secondary N 2 O peak. A reaction pathway for N 2 O formation is suggested where metal sites (Pt or Rh) catalyse the NO dissociation reaction into N- and O-adatoms; N-species further interact with undissociated NO molecules leading to the formation of N 2 O (primary N 2 O). In additions, isocyanates formed during the NO x reduction in the presence of CO may participate in the N 2 O formation upon reaction with NO during the lean phase (secondary N 2 O). Pt- and Rh-based catalysts show similar behavior even if Rh-based catalyst is less reactive than Pt-based sample likely due to the lower dispersion of the noble metal. [ABSTRACT FROM AUTHOR]

Abstract A thermal stability test-rig for organic Rankine cycles working fluids was designed and commissioned at the Laboratory of Compressible-fluid dynamics for Renewable Energy Applications (CREA Lab) of Politecnico di Milano, in collaboration with the University of Brescia. The set-up is composed by a vessel containing the fluid, heated for about 80 h at a constant stress temperature. During the test, the pressure is monitored to detect thermal decomposition of the fluid. After the test, the vessel is placed in a thermal bath, where the vapor pressure is measured at different values of temperature lower than the stress temperature and critical temperature and is compared to that obtained before the fluid underwent thermal stress. If departure from the initial fluid behavior is observed, thermal decomposition occurred and a chemical analysis of the sample is carried out on both liquid and vapor phase using gas chromatography and mass spectrometry. Experimental results are reported for the pure siloxane fluids MM (Hexamethyldisiloxane, C 6 H 18 OSi 2 ) and MDM (Octamethyltrisiloxane, C 8 H 24 O 2 Si 3 ), showing that limited but appreciable decomposition is occurring at 240 °C and 260 °C respectively. [ABSTRACT FROM AUTHOR]

In this work the one-pot conversion of CO 2 into lower olefins is investigated over a physical mixture of a methanol synthesis catalyst and a methanol-to-olefins (MTO) zeolite. First, the feasibility of the single reactions is tested at CO 2 to olefins conditions, i.e., high temperature and high H 2 /CO 2 pressure, providing insights on the reaction mechanism and catalyst stability. The effects of the operating conditions are then analyzed over the individual samples, starting from CO 2 /H 2 mixtures in the case of the methanol synthesis catalyst and from methanol in CO 2 /H 2 in the case of the zeolite. The In 2 O 3 -ZrO 2 catalyst exhibits very good selectivity to methanol and high activity, reaching thermodynamic equilibrium above 380 °C. The zeolite sample showed high activity as well and the presence of high H 2 partial pressure consistently increases the zeolite lifetime at high temperatures, but also the paraffin selectivity at the expense of the olefins, especially at low space velocity. It is therefore clear that a trade-off should be identified when testing the bi-functional catalytic samples in order to guarantee high methanol formation and good olefins production in the one-pot process. Finally, a comparison between methanol-mediated and modified Fischer-Tropsch (MFT) routes is presented, highlighting strengths and weaknesses of each reaction pathway. In particular, CO must be reduced in the methanol-mediated route, while methane and C 5 + hydrocarbons formation is the main issue for the MFT reaction. [Display omitted] • In 2 O 3 -ZrO 2 proved stable in methanol synthesis from CO 2 at high temperature. • SAPO-34 showed increased lifetime when working under high H 2 partial pressure. • CO 2 is effectively converted to lower olefins using a In 2 O 3 -ZrO 2 /SAPO-34 mixture. • CO is the main issue for MeOH-mediated route and CH4 and C 5 + for modified FT. [ABSTRACT FROM AUTHOR]

In this study mechanistic aspects related to the adsorption of NO x over alumina-supported Pt, Ba and PtBa catalysts are deepened, that are of interest for NO x Storage-Reduction (NSR) catalysts and other applications involving the adsorption of NO x (e.g. Passive NO x Adsorbers, PNAs). NO x adsorption is investigated at low and high temperatures (150 °C and 350 °C, respectively); the thermal decomposition and the reactivity with H 2 of the adsorbed species is also addressed. By coupling FT-IR spectroscopy and microreactor studies, new insights on the adsorption, decomposition and reactivity of the stored NO x are derived. In particular it is found that at 150 °C nitrites are formed on all surfaces when starting from NO/O 2 ; different species are formed onto the different storage sites (Ba vs. Al) that can be distinguished spectroscopically. Different routes for the storage of nitrites are highlighted, i.e. direct oxidative NO uptake and nitrite formation involving NO 2 produced by oxidation of NO. Clear and novel evidence is herein provided that the direct NO oxidative uptake is much faster than the route involving the NO to NO 2 oxidation. Both routes are catalyzed by Pt, although Ba is also able to store nitrites; the role of the interaction between Pt and the storage sites is discussed. When the NO x storage is carried out at higher temperatures (350 °C), both routes are greatly favored although nitrites can hardly be observed being readily transformed into nitrates. Besides NO 2 is also formed in significant amounts that may participate to the formation of nitrites/nitrates adspecies following a NO 2 disproportion pathway for which clear and new spectroscopic evidences are herein provided. The adsorbed species (nitrites or nitrates) start to decompose above the adsorption temperature, i.e. 150 °C and 350 °C, respectively. In the presence of Pt, the decomposition of the stored nitrites leads to the formation of nitrates and NO due to the occurrence of a nitrite disproportion reaction. The formed nitrates show high thermal stability and decompose only at high temperatures, thus making these systems unappropriated for PNA applications. In the presence of a reductant, Pt catalyzes the reduction of the stored NO x at much lower temperatures than the adsorption; the role of the interaction between Pt and the storage sites on this step is herein discussed. [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]

In this paper mechanistic aspects on the formation of NO over a model Pt-Ba/AlO NO storage and reduction catalyst are investigated. The data indicate that NO formation involves the coupling of N-adspecies with undissociated NO molecules: accordingly this requires the presence of partially reduced Pt sites, to catalyse the NO dissociation into N- and O-adspecies on one side and to prevent complete NO dissociation on the other side. In fact NO formation is observed at temperatures where the reductant leads to a partial reduction of the Pt sites, at increasing temperatures in the order CO > NH > H. [ABSTRACT FROM AUTHOR]

The effect of potassium on the oxidation of a model carbonaceous material (Printex U, namely, soot for brevity) has been investigated under isothermal conditions. For this purpose, Raman spectroscopy, Transmission Electron Microscopy (TEM), and Brunaure, Emmet, Teller surface area characterization have been applied to investigate structural changes occurring during soot oxidation both in the presence and in the absence of potassium. The Raman spectra of the model soot during combustion showed that oxidation preferentially involves the amorphous carbon fraction of the soot and only subsequently it affects the more orderedsp2domains. However, in the K-doped Printex U the oxidation of both the amorphous and more orderedsp2structures occurs concurrently. These findings have been confirmed by TEM analysis and explain the observed higher combustion activity of K-containing sample. Copyright © 2016 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

The release and reduction of NO x stored on Pt–Ba/Al 2 O 3 is here investigated under nearly isothermal conditions. It is shown that the release driven by adsorption–desorption equilibrium of stored NO x is negligible. It is also shown that NO isotopic exchange between stored 14 NO x and 15 NO in absence of O 2 , which implies the release of stored NO x and has the potential to decouple NO x release from its further reduction, is catalyzed by Pt and is observed from temperatures well below that of the NO x thermal desorption. It is suggested that reduced Pt sites activate stored NO x that are destabilized and eventually released as NO x in the gas phase or adsorbed onto Pt. Therefore, under nearly isothermal conditions, the NO x release is a chemical reaction catalyzed by Pt occurring at the Pt/Ba interface. In the presence of reductants, the release of stored NO x and its further reduction cannot be decoupled. The higher is the reducing power the more effective is the reduction of Pt and activation of stored NO x by metal Pt that represent the first step of release and reduction of stored NO x . [ABSTRACT FROM AUTHOR]

Highlights: [•] The effect of CO2 and H2O on the NOx storage on PtBa/Al2O3 is investigated. [•] NOx are stored on PtBa catalysts as nitrites and nitrates. [•] CO2 inhibits nitrite formation mostly at high temperatures. [•] The dead time for NOx breakthrough is significantly shortened. [•] Nitrite and carbonate thermal stability as key to the reading CO2 inhibition effect. [ABSTRACT FROM AUTHOR]

Highlights: [•] The soot decreases the NO x storage activity of Pt-K/Al2O3 catalyst at any temperature in the range 250–350°C. [•] The stability of the species stored over Pt-K/Al2O3 catalyst is lower in the presence of soot. [•] Nitrates ad-species directly interact with soot and participate to the soot combustion. [•] Aged catalyst shows a lower storage capacity and a lower soot oxidation activity attributed to the volatile nature of K-active species. [ABSTRACT FROM AUTHOR]

Abstract: The effect of cerium addition to a model Pt-Ba/Al2O3 lean NO x trap catalyst (LNT) is investigated in this paper by a combination of characterization techniques and reactivity experiments. It is found that the presence of Ce does not alter the morphological and structural characteristics of the catalyst, although slight changes in the Ba-carbonate phase are apparent. On the other hand, the presence of Ce does not seem to affect significantly the characteristics of Pt, in particular its redox state. CO adsorption experiments pointed out the presence of Pt° particles presenting different coordination degree, whose characteristics are however not significantly affected by the presence of Ce. The storage capacity of the PtBa/Al sample is hardly affected by the presence of Ce; however Ce favours the thermal decomposition of the stored NO x species. The Ce-doped sample also shows a slightly higher reactivity in the reduction of the stored NO x by H2: in fact the reaction is monitored at lower temperatures. A slightly higher selectivity towards the formation of N2 is also observed. [Copyright &y& Elsevier]

Abstract: The effect of soot on the storage-reduction performances of a PtBa/Al2O3 catalyst is investigated in this work. It is found that the presence of soot reduces the NO x storage capacity of the catalyst, evaluated in presence of water and CO2 in the feed stream in the range 200–350°C and with different values of the NO inlet concentration. Besides the presence of soot favors the decomposition and the reduction of the stored nitrates, while soot is being oxidized. A direct reaction between the stored nitrates and soot is suggested, that has been explained on the basis of the surface mobility of the adsorbed nitrates. This soot oxidation pathway involves surface species and parallels the NO2-soot oxidation that occurs in the presence of gas-phase NO2. Finally, the presence of soot does not influence appreciably the behavior of the PtBa/Al2O3 catalyst in the reduction by H2 of the stored nitrates: in all cases N2 is the main reaction product and ammonia is observed in minor amounts. [Copyright &y& Elsevier]

Abstract: The storage of NO2 and NO/O2 in the presence and in the absence of CO2 was investigated at 350°C on Pt-Ba/Al2O3 LNT catalysts and on the reference Ba/Al2O3 system, by coupling in situ FT-IR spectroscopy and transient response method (TRM). Experiments were performed by admitting NO2/CO2 or NO/O2/CO2 mixture (CO2/NO x ratios in the range 1–7) or, in alternative, by admitting NO2 or NO/O2 on catalysts previously saturated by flowing CO2. In the case of NO2/CO2 adsorption, it was found that NO2 was efficiently stored as nitrate species according to a disproportion reaction, which occurs with evolution of NO, as in the absence of CO2. In the case of NO/O2/CO2 adsorption it was confirmed that two pathways operated simultaneously as in the absence of CO2: the “nitrite route”, involving the initial formation of surface nitrite and their subsequent evolution to nitrates, and the “nitrate route”, involving NO oxidation to NO2 over Pt and its subsequent adsorption on Ba in the form of nitrates. The presence of CO2 inhibits to some extent the “nitrite route”, whereas the “nitrate route” proceeds as in the absence of CO2. [Copyright &y& Elsevier]

Abstract: The storage-reduction of NO x over Pt–Ba/Al2O3 samples is analyzed in this work. It is pointed out that the storage of NO in the presence of excess oxygen proceeds through two parallel routes: (i) the “nitrate route” where NO is oxidized to NO2 on Pt sites followed by NO2 disproportionation on Ba sites to form nitrates with evolution of gaseous NO; (ii) the “nitrite route”, where NO is oxidized on Pt sites and directly stored on Ba neighbouring sites in the form of nitrites that are then oxidized to nitrates. The latter route possibly dominates at high Ba loadings. Concerning the reduction of the stored NO x , the bulk of data indicates that the process under isothermal conditions is not initiated by the release of NO x in the gas phase but occurs through a Pt-catalysed reduction of adsorbed NO x species. This route requires the co-presence of Pt and Ba on the same support. It is speculated that H2 is activated on Pt sites and spills on the alumina support towards nitrate ad-species where it operates the reduction, although alternative explanations are possible. [Copyright &y& Elsevier]

The NOx storage process over Ba/Al2O3 and Pt–Ba/Al2O3 NSR catalysts has been analyzed in this study by performing experiments at 350 °C with NO2 and NO/O2 mixtures using different complementary techniques (Transient Response Method, in situ FT–IR and DRIFT spectroscopies). The collected data suggest that over the Pt–Ba/Al2O3 catalyst the NOx storage process from NO/O2 mixtures occurs forming at first nitrite species, which progressively evolve to nitrates. In addition, a parallel nitrate formation via disproportionation of NO2 (formed upon NO oxidation) cannot be excluded. [ABSTRACT FROM AUTHOR]

• The presence of copper in the ceria-based catalysts promotes the formation of oxygen vacancies. • High conversions of NO to N 2 and N 2 O can be achieved under these experimental conditions. • Catalysts' surface transformations, monitored by in situ DRIFTS, are crucial to elucidate the pathways. • The NO reduction is interpreted as the progressive catalysts' oxidation (consumption of oxygen vacancies). In this work, a fundamental and systematic study was conducted, leading to a better understanding of the phenomena occurring on the catalyst's surface during the NOx reduction process in NSR systems. For this purpose, ceria-based catalysts, with Cu in substitution of noble metal, have been synthesized and deeply characterized by means of XRF, XPS, in situ (XRD, Raman spectroscopy and DRIFTS), temperature-programmed reduction under H 2 (H 2 -TPR) and under NO reaction (NO isothermal reaction + NO-TPR). The whole results show the key role of copper to promote the reducibility and the creation of oxygen vacancies, allowing a high NO consumption and fast kinetics of N 2 O and N 2 formation, until the oxygen vacancies consumption takes place. The study of the surface reactions taking place in the formation of adsorbed NO x species and the oxygen vacancies consumption with NO uptake is complex; however, a hydroxyl consumption route is found to be involved. The reduction of NO provided higher levels of N 2 at higher temperatures; also, a very high efficiency of the previously created oxygen vacancies was found for this process. [ABSTRACT FROM AUTHOR]

Introduction: The etiology of bipolar disorder (BD) is poorly understood, involving genetic, epigenetic mechanisms and environmental contributions. Aim: Among the candidate genes associated with major psychoses, the present study investigated the degree of DNA methylation at brain-derived neurotrophic factor (BDNF) gene promoter in peripheral blood mononuclear cells (PBMCs) isolated from bipolar patients. Methods: DNA was isolated from the blood of 94 BD patients (49 BD I and 45 BD II) and 52 controls and converted with sodium bisulfite. Real Time Methylation Specific PCR was performed to quantify promoter methylation. Results: A significant BDNF gene expression down-regulation was observed in BD II 0.53±0.11%; p<0.05), but not in BD I (1.13±0.19%) patients compared with controls (CONT: 1±0.2%). Consistently, an hypermethylation of the BDNF promoter region was specifically found in BD II patients (CONT: 24.0±2.1%; BDI: 20.4±1.7%; BDII: 33.3±3.5%, p<0.05). Of note, higher levels of DNA methylation were observed in BD subjects on pharmacological treatment with mood stabilizers plus antidepressants (34.6±4.2%, predominantly BD II) compared with those exclusively on mood stabilizing agents (21.7±1.8%; p<0.01, predominantly BD I). Moreover, among the different pharmacological therapies, lithium (20.1±3.8%, p<0.05) and valproate (23.6±2.9%, p<0.05) were associated with a significant reduction of DNA methylation compared to other drugs (35.6±4.6%). Conclusions: Present findings suggest selective changes in DNA methylation of BDNF promoter in subjects with BD type II and highlight the importance of epigenetic factors in mediating the patophysiology an treatment response of BD. [ABSTRACT FROM AUTHOR]

Introduction: Few questionnaires on the psychopathological onset and latency to treatment in psychiatric patients are currently available. Objectives: In this perspective we developed a brief questionnaire: the Psychopathological Onset Latency and Treatment Questionnaire (POLQ). Methods: The questionnaire was administered to 265 patients with any psychiatric diagnosis. Statistical analyses were performed using SPSS. Results: The sample showed the following demographic variables in terms of age (48±15 years), occupation (17% unemployed) and familiarity (54%). Clinical variables included: age at onset (30.66±15 years), age at first diagnosis (36±19 years) and age at first drug treatment (35±14 years). The most common symptoms at onset were related to the anxiety spectrum (41.2%), mood spectrum (24.5%) or both (25.3%). Stressful life-events in relation to onset occurred in 63% of patients (12.1% familiar issues, 11.3% work problems, bereavement or end of a relationship in 16.6%). Most frequent first diagnoses were major depressive episode (26.8%), manic/hypomanic/mixed episode (13.6%) and anxiety disorders (11.7%). Average latency to the first visit was 34 months. In the 76.2% of the sample, the first contact was with a psychiatrist, a psychologist in 15.8%; 78.1% were treated with drugs as a first treatment, 11.7% with psychotherapy, 7.2% with both. The average duration of first treatment was 23 months (4 weeks - 360 months) and reasons for discontinuation were: lack of efficacy (23.8%) or complete remission (21.9%). Conclusions: POLQ resulted to be a useful and reliable instrument in the collection of information on the psychopatological onset and latency to treatment. [ABSTRACT FROM AUTHOR]