Catalytic regeneration of Diesel Particulate Filters: Comparison of Pt and CePr active phases

Diesel Particulate Filters (DPFs) have been loaded with the same amount (0.6 wt.%) of either Pt or an optimized CePr active phase, and an experimental set-up has been designated and used to investigate the catalytic combustion of soot under realistic reaction conditions. Both active phases were stable under reaction conditions, with no evidences of deactivation in consecutive combustion experiments. The presence of H2O and CO2 together with NOx and O2 in the gas mixture slightly delays soot combustion to higher temperatures, but the effect is equal for the Pt and CePr active phases. The mass of soot loaded into the filters had no effect in the catalytic regeneration of the DPFs for soot:catalyst weigh ratios below 0.4, while it was hindered above this ratio. The Pt and CePr active phases behave equal until 0.6 soot:catalyst weigh ratio and Pt performance was slightly better for higher soot loading. This difference is explaining according to the main soot combustion mechanisms occurring during Pt–DPF (NO2-assited) and CePr–DPF regeneration (active oxygen). The CO2 selectivity is near 100% for both catalysts in all the experimental reaction conditions evaluated. According to this study, the CePr active phase seems to be a promising candidate to replace Pt in real applications.The financial support of Generalitat Valenciana (Project PROMETEOII/2014/010)), Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703) and European Union (FEDER funding) is acknowledged

Effect of RhOx/CeO2 Calcination on Metal-Support Interaction and Catalytic Activity for N2O Decomposition

The effect of the calcination conditions on the catalytic activity for N2O decomposition of 2.5% RhOx/CeO2 catalysts has been investigated. Ramp and flash calcinations have been studied (starting calcinations at 25 or 250/350 °C, respectively) both for cerium nitrate and ceria-impregnated rhodium nitrate decomposition. The cerium nitrate calcination ramp has neither an effect on the physico-chemical properties of ceria, observed by XRD, Raman spectroscopy and N2 adsorption, nor an effect on the catalysts performance for N2O decomposition. On the contrary, flash calcination of rhodium nitrate improved the catalytic activity for N2O decomposition. This is attributed to the smaller size of RhOx nanoparticles obtained (smaller than 1 nm) which allow a higher rhodium oxide-ceria interface, favoring the reducibility of the ceria surface and stabilizing the RhOx species under reaction conditions.The authors thank the financial support of Generalitat Valenciana (Project Prometeo 2009/047), the Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703), and the UE (FEDER funding)

Effect of the CeZrNd mixed oxide synthesis method in the catalytic combustion of soot

Ce0.64Zr0.27Nd0.09Oδ mixed oxides have been prepared by three different methods (nitrates calcination, coprecipitation and microemulsion), characterized by N2 adsorption, XRD, H2-TPR, Raman spectroscopy and XPS, and tested for soot combustion in NOx/O2. The catalyst prepared by microemulsion method is the most active one, which is related to its high surface area (147 m2/g) and low crystallite size (6 nm), and the lowest activity was obtained with the catalyst prepared by coprecipitation (74 m2/g; 9 nm). The catalyst prepared by nitrates precursors calcination is slightly less active to that prepared by microemulsion, but the synthesis procedure is very straightforward and surfactants or other chemicals are not required, being very convenient for scaling up and practical utilization. The high activity of the catalyst prepared by nitrates calcination can be attributed to the better introduction of Nd cations into the parent ceria framework than on catalysts prepared by coprecipitation and microemulsion, which promotes the creation of more oxygen vacancies.The authors thank the Spanish Catalyst Society-SECAT for the grant of J.G.M. and both the Spanish Ministry of Economy and Competitiveness and the FEDER funding of UE for the financial support to the Project CTQ2012-30703

Preparation of RhOx/CeyPr1−yO2 N2O decomposition catalysts by rhodium nitrate impregnation with different solvents

The effect of the solvent (water, ethanol or acetone) used to impregnate CeyPr1−yO2 (y = 1, 0.9 or 0.5) supports with rhodium nitrate, in order to prepare N2O decomposition catalysts, has been studied. RhOx/CeyPr1−yO2 catalysts were prepared and characterized by N2 adsorption at −196 °C, XRD, Raman spectroscopy, TEM, XPS and H2-TPR. The activity for N2O decomposition of the catalysts studied was related with the RhOx-support interaction, and both the nature of the ceria support and of the solvent used for rhodium impregnation affected such interaction. Ceria doping with 10% praseodymium had a positive effect in the RhOx-support interaction, but the benefit on the catalytic activity was only obtained for water impregnation because the temperature peaks created during calcination of ethanol and acetone-impregnated catalysts promoted Ce0.9Pr0.1O2 and RhOx sintering. The interaction between RhOx and Ce0.5Pr0.5O2 was not as good as that with Ce0.9Pr0.1O2. The best catalyst was obtained by impregnating Ce0.9Pr0.1O2 with a water solution of rhodium. However, if acetone or ethanol must be used for any reason the pure ceria support is more suitable (under the calcination conditions of this study; 250 to 500 °C at 10 °C/min) because do not sinters during solvents combustion.Financial support of Generalitat Valenciana (Project Prometeo 2009/047), The Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703), and the UE FEDER funding

The influence of promoters (Zr, La, Tb, Pr) on the catalytic performance of CuO-CeO2 systems for the preferential oxidation of CO in the presence of CO2 and H2O

CuO supported on CeO2 and Ce0.9X0.1O2, where X is Zr, La, Tb or Pr, were synthesized using nitrate precursors, giving rise ceria based materials with a small particle size which interact with CuO species generating a high amount of interfacial sites. The incorporation of cations to the ceria framework modifies the CeO2 lattice parameter, improving the redox behavior of the catalytic system. The catalysts were characterized by X-ray fluorescence spectrometry (XRFS), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, thermoprogrammed reduction with H2 (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The catalysts were tested in the preferential oxidation of CO under a H2-rich stream (CO-PROX), reaching conversion values higher than 95% between 115 and 140 °C and being the catalyst with 6 wt.% of Cu supported on Ce0.9Zr0.1O2 (sample 6CUZRCE) the most active catalyst. The influence of the presence of CO2 and H2O was also studied simulating a PROX unit, taking place a decrease of the catalytic activity due to the inhibitor effect both CO2 and H2O.The projects CTQ2012-37925-C03-03 and CTQ2012-30703 of Ministerio de Economía y Competitividad (Spain), the project of Excellence P12 RNM 1565 (Junta de Andalucía, Spain), the project of Excellence PROMETEUII/2014/010 (Generalitat Valenciana) and the UE (FEDER funding) are acknowledged for the financial support

Simultaneous catalytic oxidation of carbon monoxide, hydrocarbons and soot with Ce–Zr–Nd mixed oxides in simulated diesel exhaust conditions

Ce0.73−xZr0.27NdxO2 mixed oxides (x ≤ 0.3) were prepared, characterized by XRD, Raman spectroscopy, N2 adsorption isotherms and H2-TPR, and tested for simultaneous CO, propylene, benzene and soot oxidation in a gas mixture containing O2, NOx, H2O, CO2, CO, propylene (model aliphatic hydrocarbon) and benzene (model aromatic hydrocarbon) that simulates a diesel exhaust. Ce–Zr mixed oxide doping with a low atomic fraction of neodymium (0.01 ≤ x ≤ 0.09) promotes the creation of oxygen vacancies, has a minor effect in the BET specific surface areas of the oxides, increases the surface ceria reducibility and has a positive effect in the catalytic activity. On the contrary, higher neodymium atomic fractions (x = 0.2 and 0.3) promote sintering, with a drastic decrease of the BET specific surface area, surface reducibility and catalytic activity. The Ce0.73−xZr0.27NdxO2 catalysts with x ≤ 0.09 are able to accelerate simultaneously soot, propylene and benzene combustion, and as a general trend, the catalytic behavior of Ce0.73Zr0.27O2 is improved by low atomic fraction neodymium doping (0.01 ≤ x ≤ 0.09). These Ce0.73−xZr0.27NdxO2 mixed oxides with 0.01 ≤ x ≤ 0.09 are also able to accelerate CO oxidation in a certain extent, but there is a net production of CO during soot combustion because the oxidation capacity of these oxides is not high enough to oxidize all CO released as soot combustion product.The authors thank the financial support of CNPq – National Counsel of Technological and Scientific Development (Brazil), of the Spanish Ministry of Economy and Competitiveness (ProjectCTQ2012-30703) and of the UE (FEDER funding)

Strong dispersion effect of cobalt spinel active phase spread over ceria for catalytic N2O decomposition: The role of the interface periphery

A series of Co3O4/CeO2 catalysts with increasing cobalt spinel loading in the range of 1–20 wt.% was prepared by incipient wetness impregnation of CeO2. The obtained catalysts were thoroughly examined by XRD, XPS, XRF, RS, TEM/EDX/EELS, TPR and BET techniques. The catalytic tests in deN2O reaction revealed that the 10 wt.% of cobalt spinel in supported system is able to reproduce the activity of bare Co3O4 catalyst. However, it was found that the catalyst with the lowest content of Co3O4 equal to 1 wt.% exhibits the highest apparent reaction rate per mass of the spinel active phase. The observed activity was explained basing on the transmission electron microscopy analysis in terms of the dispersion of spinel phase over ceria support. A simple model that accounts for the observed strong dispersion effect is proposed. It consists in a two-step mechanism, where N2O is dissociated on the spinel nanograins and the resultant oxygen species are preferentially recombined at the Co3O4/CeO2 interface periphery.The authors would like to acknowledge the Polish National Centre for Research and Development funding awarded by the decision number PBS2/A5/38/2013. On the Polish part the research was partially carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Polish Innovation Economy Operational Program (contract no.POIG.02.01.00-12-023/08)

Evidences of the Cerium Oxide-Catalysed DPF Regeneration in a Real Diesel Engine Exhaust

The active phase Ce0.5Pr0.5O2 has been loaded on commercial substrates (SiC DPF and cordierite honeycomb monolith) to perform DPF regeneration experiments in the exhaust of a diesel engine. Also, a powder sample has been prepared to carry out soot combustion experiments at laboratory. Experiments performed in the real diesel exhaust demonstrated the catalytic activity of the Ce–Pr mixed oxide for the combustion of soot, lowering the DPF regeneration temperature with regard to a counterpart catalyst-free DPF. The temperature for active regeneration of the Ce0.5Pr0.5O2-containing DPF when the soot content is low is in the range of 500–550 °C. When the Ce0.5Pr0.5O2-containing DPF is saturated with a high amount of soot, pressure drop and soot load at the filter reach equilibrium at around 360 °C under steady state engine operation due to passive regeneration. The uncoated DPF reached this equilibrium at around 440 °C. Comparing results at real exhaust with those at laboratory allow concluding that the Ce0.5Pr0.5O2-catalysed soot combustion in the real exhaust is not based on the NO2-assisted mechanism but is most likely occurring by the active oxygen-based mechanism.The authors thank the financial support of Generalitat Valenciana (Project Prometeo 2009/047), Spanish Ministry of Science and Innovation (project CIT-420000-2009-48) and EU (FEDER funding)

Proof of concept of the SCR of NOx in a real diesel engine exhaust using commercial diesel fuel and a full size Pt/beta zeolite/honeycomb monolith

The Selective Catalytic Reduction (SCR) of NOx has been performed in a real diesel exhaust stream with commercial diesel fuel by using a full size home-made Pt/beta zeolite/honeycomb prototype catalyst. Fuel was injected upstream the catalyst to achieve total hydrocarbons concentrations between 1000 and 5000 ppm, and the SCR behaviour observed was similar to that typically reported in laboratory experiments performed with model hydrocarbons. Typical NOx removal volcano-shape profiles, with maxima at 250 °C for all THC inlet concentrations, were obtained, with an optimum THC concentration of 3000 ppm.The authors thank the financial support of Generalitat Valenciana (Project Prometeo 2009/047), the Spanish ministries of Economy and Competitiveness (Project CTQ2012-30703) and Science and Innovation (Project CIT-420000-2009-48), and EU for the FEDER resources

Pt/CexPr1−xO2 (x = 1 or 0.9) NOx storage–reduction (NSR) catalysts

Model Pt/Ce0.9Pr0.1O2 and Pt/CeO2 NOx storage–reduction catalysts were prepared via nitrate calcination, co-precipitation and carbon-templating routes. Raman spectroscopic data obtained on the catalysts indicated that the introduction of praseodymium into the ceria lattice increased the concentration of defect sites (vacancies), arising from the higher reducibility of the Pr4+ cation compared to Ce4+. For the Pr-promoted samples, H2-TPR profiles contained high temperature bulk reduction peaks which were less pronounced compared with their ceria analogs, indicating that the presence of praseodymium enhances oxygen mobility due to the creation of lattice defects. Under lean-rich cycling conditions, the cycle-averaged NOx conversion of the Pt/Ce0.9Pr0.1O2 samples was in each case substantially higher than that of the Pt/CeO2 analog, amounting to a difference of 10–15% in the absolute NOx conversion in some cases. According to DRIFTS data, a double role can be assigned to Pr doping; on the one hand, Pr accelerates the oxidation of adsorbed NOx species during the lean periods. On the other hand, Pr doping destabilizes the adsorbed NOx species during the rich periods, and the kinetics of nitrate decomposition are faster on Pt/Ce0.9Pr0.1O2, leading to improved catalyst regeneration. These results suggest that ceria-based mixed oxides incorporating Pr are promising materials for NOx storage–reduction catalysts intended for low temperature operation.The financial support of Generalitat Valenciana (predoctoral stay BEFPI/2012), the Spanish Ministry of Economy and Competitiveness (Project CTQ2012-30703), and co-financing by FEDER resources is acknowledged. Partial financial support was also provided by the National Science Foundation and the U.S. Department of Energy (DOE) under award no. CBET-1258742