Perovskites free of critical raw materials (noble metals and rare earths) of the type Ba(1-y)SryMn(1-0.2-x)Mg(0.2)Cu(x)O(3) (y = 0.1, 0.5; x = 0.1, 0.2, 0.3) are developed for the abatement of pollutants in automotive exhaust, both gaseous (CO, NOx and HCs) and solid (carbon soot). The reactivity in oxidation and reduction is tuned through ad-hoc induced surface segregation phenomena and the promotion of specific Mn(III)/Mn(IV) and Cu/Mn atomic ratios. The insertion of Cu into the perovskitic cell, moves the crystalline structure from 2H-type toward a Mndeficient one, in which Mn(III) is prevalent. The catalytic capability in abatement of pollutants was studied comparing the activity in the following reactions: CO oxidation, CO assisted NO reduction, and with a complex mixture simulating the composition of automotive exhausts in stoichiometric and rich conditions. CO oxidation is favored by surface segregation of Mn, Mg may play a role in CO coordination. Copper enhances the NO reduction activity of the catalysts in the CO + NO reaction and Ba0.9Sr0.1Mn0.5Mg0.2Cu0.3O3 is the more active, whereas in the complex mixture Ba0.9Sr0.1Mn0.7Mg0.2Cu0.1O3 and Ba0.9Sr0.1Mn0.6Mg0.2Cu0.2O3 are the more active suggesting a less relevant role of surface composition and a more active contribution of bulk ion mobility.

In this contribution several La0.5Sr0.5CoO3 based nanocomposites have been prepared and tested for application as Three-Ways Catalysts (TWC), aiming to develop Platinum Group Metal (PGM)-free catalysts. To reach this objective we designed and realized nanocomposites in which active CuO nanoparticles are deposited on La0.5Sr0.5CoO3. This perovskite is active in oxidation and is characterized by high oxygen anion mobility; copper is active in reduction: catalytic bifunctionality is thus built-in via a tailor-made and controlled nano-composition. The supporting perovskite was prepared following the "citrate" route. The deposition was carried out by means of the Ammonium-Driving-Deposition precipitation (ADP) to highly disperse CuO on La0.5Sr0.5CoO3. In a precedent paper we focused on nanocomposites obtained using LaCoO3 as a support because this perovskite is active in oxidation. Sr-doped LaCoO3, in addition, is characterized by a more relevant presence of oxygen vacancies and mobility and the desire of comparing these systems is to better investigate the different role played by all these aspects on the interaction between highly dispersed CuO nanoparticles and perovskite and on the catalytic activity. The copper amount on the nanocomposite surface does not increase linearly with the nominal composition reaching a plateau: migration below the surface is observed for the nanocomposite with 30 wt.% of Cu. The surface composition of the perovskite is modified by the copper deposition which causes the decrease of A-cations surface segregation and enhances the presence of cobalt suggesting a certain synergy; the reducibility of the perovskite is also greatly favored by deposition. Both model reactions (CO oxidation and CO assisted NO reduction) and reactions with a synthetic automotive exhaust mixture, including 10% steam, and oxygen, were carried out. We compared the results with the ones obtained in similar reactions with CuO/LaCoO3. Different interaction and synergy were observed with respect to CuO/La0.5Sr0.5CoO3. Sr-doping, in fact, enhances oxygen mobility affecting the reducing character of the nanodispersed CuO and thus the reactivity under different conditions. The deposition of copper oxide significantly increases the activity of the nanocomposites in CO oxidation (about 100% conversion at 200 degrees C) and in CO + NO (50% conversion at 250 degrees C, more than 80% at 400 degrees C) reactions. When compared with the corresponding CuO/LaCoO3, the more significant difference has been observed in nanocomposites poorer in CuO, which became highly active at lower temperature. On simulated gasoline engine exhaust the nanocomposites always improve the oxidation activity compared to the parent perovskite, while the NO reduction is quantitative in the absence of O-2. The activity on a mixture simulating actual gasoline-engine exhaust proves that ADP synthesis provides materials with a higher activity compared to wet impregnation (WI), thanks to a higher dispersion of copper. NO reduction in fuel-rich conditions is activated at approx. 300 degrees C, (400 degrees C on WI sample), when significant amount of O-2 is still in the mixture. This feature completes the good performance in absence of noble critical metals that are promising facts to develop PGM-free catalysts for the automotive industry.

In this contribution several LaCoO3 based nanocomposites have been prepared and tested for application as Three-Way Catalytic Converters (TWC): the aim is in developing Platinum Group Metal (PGM)-free catalysts. To reach this objective we designed and realized nanocomposites in which active CuO nanoparticles are deposited on active LaCoO3. This perovskite is active in oxidation while copper is active in reduction: catalytic bi-functionality is thus built-in via a tailor-made and controlled nanocomposition. The deposition was carried out by means of an innovative Ammonium-Driving-Deposition precipitation (ADP) procedure allowing to obtain nanocomposites in which CuO is highly dispersed on LaCoO3. This increases the reducibility of the nano composites, as revealed by the TPR measurements. The deposition of copper does not alter significantly the surface composition which remains rich in lanthanum oxide/hydroxide, the main effect consisting in a slight increment of surface hydroxylation. Moreover, the copper amount on the LaCoO3 surface does not increase linearly with the nominal composition. Both model reactions (CO oxidation and CO assisted NO reduction) and tests with a synthetic automotive exhaust mixture, including 10 % steam, were carried out. Activity before and after high-temperature aging in steam was also evaluated. We compared the obtained results with the ones of CuO/nickelates of a previous work, to highlight the functionalities gained. In simple CO + NO and CO + O-2 mixtures, the deposition of copper oxide on LaCoO3 greatly increases the activity of the nanocomposites in NO reduction (100 % conversion at 350 degrees C) without significantly affecting the reactivity in CO oxidation. Results with the synthetic automotive exhaust mixture show that Cu loading on ADP prepared catalysts can significantly improve the NO reduction activity of LaCoO3. Still, NO reduction remains more relevant in O-2-poor mixtures (about 100 % conversion around 400 degrees C in the 10 wt.% Cu loaded), even slightly below the stoichiometric. Some deactivation on hydrocarbon oxidations occurs at low temperatures due to thermal aging, apparently due to coking and surface Cu depletion. Compared to CuO deposited by ADP on LaNiO3 of our earlier studies, cobaltites gain in oxidation activity, but NO reduction remains easier on nickelates. However, the promising performance and the absence of noble critical metals are promising features to develop PGM-free catalysts for the automotive industry.

Experiments and modelling were performed to investigate CO oxidation over a Pd-Rh monolith. We focused on thermal effects and hysteresis, to validate by modelling a thermal explanation of the results. Different feed composition (0.07-4% vol. CO) and heating rates (0.5-5 degrees C/min) have been used to reproduce both ignition and extinction stages, up to 300 degrees C, thus measuring the catalyst activity under transient conditions. The heating rate plays a marginal role in producing hysteresis, whereas the reactants concentration appears the real cause, because of its effect on the rate of heat production. A significant increase of the monolith temperature compared to the inlet gas is measured after ignition. The local overheating of the catalyst surface explains the hysteresis observed. When the reactor thermal control is based on the internal temperature, instead of the inlet one, the hysteresis appears dramatically different. The choice of the temperature used to control the oven, and report the activity results, may induce very misleading indications, including inexistent multiple steady-states. A model accounting for the thermal dynamics of the solid predicts the observed hysteresis, even with simple rate equations. That supports the thermal explanation for the direct hysteresis. The estimated activation energy is quite reasonable and compare well with literature. Preexponential factors accommodate for the weakening of the adiabatic channel critical assumption, less and less realistic as the reaction heat increases. The overall conclusion is that the local temperature can vary widely, in time and space, and any kinetic study not accounting for a precise knowledge of that will inevitably produce poorly representative parameter estimates. The limitation can be overcome with spatially-resolved measurements.

Several perovskites of the type La(1-x)A(x)Co(0.5)O(3) (A = K, Sr, Ba; x= 0, 0.25, 0.5)and a Sr-doped understoichiometric one, have been prepared by citrate method aiming at application as noble metals free catalysts for automotive application. The catalysts have been characterized by BET, X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), X-Ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM) and the effect of A-doping has been investigated. The catalytic activity was studied in model reactions (CO oxidation, CO assisted NO reduction), and in a complex three way catalysts (TWC) mixture approaching automotive exhaust composition at both stoichiometric and 02-limiting conditions and the obtained results are discussed in relation with characterization results. A-doping induces the formation of highly dispersed cubic CuO particles, as observed in the understoichiometric samples. Doping also influences the surface segregation. La segregation is observed in the undoped LaCo0,5Cu0.5O3 sample whereas K is surface segregated in La0.75K0.25Co0.5O3; Co segregates in the Ba-doped perovskite and Sr in the understoichiometric La0.35Sr0.35Co0.5O3. The reducibility (TPR) is altered by A-doping. The reactivity results suggest that in simple CO + O-2 and CO + NO mixtures the activation temperature is increased by any doping, but at 400 degrees C the conversion in the CO assisted NO reduction is not significantly different with respect to the one obtained in the undoped catalyst. Activity with a more complex mixture, simulating actual engine exhaust, reveals the interesting activity of the Sr-doped catalysts, that outperform LaCo0.5Cu0.5O3 at both stoichiometric and O-2-lean conditions. NO reduction can be achieved at lean O-2 conditions, where it is quantitative from 400 degrees C. The possibility to reach similar or better activity by replacing the use of La, which is a Rare Earth Element, by using Sr is particularly interesting. Stability at high temperatures and at fast fluctuations of O-2 in inlet stream for 50% Sr-doped catalyst confirms these results.

Several nanocomposites of the type CuO/LaNiO3 (Cu@LaNiO3) have been developed for application as noble metal free catalysts in TWC. The nanocomposites have been obtained by depositing copper oxide on lanthanum nickelate. The supporting perovskite has been prepared by means of the citrate route; copper, in contrast, was deposited by means of an innovative procedure: ammonia driven deposition precipitation method (ADP) optimized for deposition on perovskites. The nanocomposites have been developed based on the catalytic activity of LaNiO3 in oxidation and reforming reactions and of copper in reduction reactions. Nanocomposition is thus used to deposit a highly dispersed active specie ( CuO) on an active support (LaNiO3) with the aim of building catalytic functionality.The obtained nanocomposites have been characterized by means of XRD, XPS, SEM, TPR, BET, EDX, and ICP and the obtained results are correlated to the amount of copper deposited and to the reactivity. The reactivity was studied first in two model reactions, CO oxidation and CO assisted NO reduction, in order to investigate the role played by the different species. Moreover, the reactivity under real conditions, i.e. with a complex mixture reflecting the actual automotive exhaust composition, was considered to evaluate the real applicability. Finally, high-temperature deactivation was investigated. XPS reveals that the deposition of copper oxide affects the surface composition of the nanocomposites; the XRD, SEM, and TPR results confirm that CuO is deposited on the LaNiO3 surface and no diffusion below surface is observed. CuO species are deposited both as highly dispersed phase and as bigger particles; the relative amount of these phases depends on the total amount of copper deposited. The reactivity in the CO oxidation reaction is not significantly affected by the copper deposition. In contrast the reactivity in NO reduction is strongly enhanced by the presence of highly dispersed copper species. Activity tests with mixture reflecting actual automotive exhaust, reveal an enhancement in CO oxidation, but no NO decomposition at stoichiometric conditions. Complete NO reduction is achieved at rich conditions; also, hydrocarbons reforming reactions typically occurring at substoichiometric O-2, with CO and H-2 production, are less supported, preserving the activity in NO reduction. Finally, the high-temperature aging test confirmed an interesting stability of catalytic activity. (C) 2017 Elsevier B.V. All rights reserved.