Resumen:

La emisión de óxidos de nitrógeno (NOx), hidrocarburos sin quemar (HCs) y óxidos de carbono (COx), provienen principalmente de fuentes móviles (medios de transporte) y centrales de potencia. En este trabajo se estudiaron sistemas catalíticos capaces de entrampar los hidrocarburos durante la etapa de baja temperatura, para luego eliminarlos cuando se alcanzan las condiciones óptimas del motor. Para ello, se emplearon como soportes catalíticos, una zeolita microporosa NaMordenita comercial y materiales mesoporosos MCM-41 y AlMCM-41 sintetizados mediante el método sol-gel. Los metales Ag o Co fueron incorporados por intercambio iónico, impregnación húmeda incipiente o mediante CO2 supercrítico. Los catalizadores preparados mediante intercambio iónico mostraron una pequeña fracción de óxido altamente disperso, en coexistencia con iones intercambiados en los sitios de la mordenita. La deposición con CO2 supercrítico representó un método eficaz para incorporar nanopartículas de óxido de cobalto dispersas en los sustratos mesoporosos. Estas especies resultaron activas para la oxidación preferencial de CO en atmósfera reductora. Los catalizadores Ag- o Co-Mordenita fueron activos y selectivos en la RCS-NOx con tolueno o butano. El agua mantiene la superficie limpia de depósitos carbonosos. Sólo los materiales AgMordenita mostraron una elevada capacidad de adsorción y retención de HCs. El tolueno interacciona con el catión a través de los electrones pi y mediante los grupos metilo con los oxígenos de la red próximos al catión. El butano sólo lo hace mediante los grupos C-H. De este modo, los catalizadores de Ag intercambiada en NaMOR permiten acoplar la adsorción de hidrocarburos con la RCS-NOx.

The emission of nitrogen oxides (NOx), unburned hydrocarbons (HCs) and carbon oxides (COx), mainly from mobile sources (vehicles) and power plants. In this work, catalytic systems capable of trapping hydrocarbons during low-temperature stage, and then delete them when they reach optimum engine conditions are studied. Thus, were used as catalyst supports, a microporous zeolite and mesoporous materials commercial NaMordenita MCM-41 and AlMCM-41 synthesized by the sol-gel method. Ag or Co metals were incorporated by ion exchange or incipient wet impregnation using supercritical CO2. The catalysts prepared by ion exchange showed a fraction of highly dispersed oxide, in coexistence with ion exchanged mordenite sites. The supercritical CO2 deposition represented an effective method to incorporate cobalt oxide nanoparticles dispersed in mesoporous substrates. These species were active for the preferential oxidation of CO in a reducing atmosphere. Ag, Co-Mordenite catalysts were active and selective in NOx-SCR with toluene or butane. Water keeps the clean surface of carbon deposits. Only materials AgMordenita showed high adsorption capacity and retention of HCs. The toluene interacts with the cation via pi electrons and by the methyl groups with the oxygens of the net near the cation. Butane only done by C-H groups. Thus, the catalysts of Ag exchanged NaMOR allow coupling the adsorption of hydrocarbons with the RCS-NOx

Consejo Nacional de Investigaciones Científicas y Técnicas

Resumen:

Silver catalysts were prepared by ion exchange of NaMordenite with 5, 10 and 15 wt% Ag. Various characterization techniques such as TPR, UV-vis and XPS indicated the presence of small particles of highly dispersed Ag2O together with isolated Ag+ cations located in α, β and γ exchange sites of NaMOR. The formation of clusters of cationic silver (Agnm+) was also considered. The prepared samples were active in the Selective Catalytic Reduction of NOx in the presence of toluene or butane as reducing agents, excess oxygen and 2% H2O. The solid with 15 wt% Ag was the most active one in the presence of water, reaching a maximum conversion of NOx to N2 of 47.5% or 51.2% when butane or toluene were respectively used. Under dry conditions, the maximum conversion of NO had an optimum between 5 and 10 wt% Ag for both hydrocarbons. The NaMOR support showed a higher adsorption capacity than the exchanged samples with both hydrocarbons. For the silver loaded solids, the toluene adsorption capacity at 100 °C increased with the increase of the metal content. In contrast, the amount of butane adsorbed was similar for the different contents of Ag. Consequently, silver has two opposite effects: one is the partial obstruction of the mordenite channels, as seen by the loss of crystallinity and the decrease of surface area and pore volume; and the other effect is the chemical interaction that depends on the nature of the adsorbed hydrocarbon. The interaction between toluene and Ag+ ions is stronger with the π-electrons of the aromatic ring of the toluene molecule than with the σ-electrons of the linear chain of butane. For this reason, toluene is retained at higher temperatures than butane. In addition, between 300 and 500 °C, the appearance of signals corresponding to H2, CO2 and H2O is observed during the TPD of toluene. This indicates that the toluene decomposition occurs, producing coke and hydrogen. Most probably, the generation of CO2 and H2O is a consequence of the reduction of Ag2O particles with toluene.

Afiliación de los autores: Aspromonte, Soledad Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Afiliación de los autores: Serra, Ramiro Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Afiliación de los autores: Miro, Eduardo Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Afiliación de los autores: Boix, Alicia Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Resumen:

Co/MCM41 catalyst with 4.3 wt % Co (Co/sc) has been prepared by supercritical CO2 reactive deposition (‘scfrd’) and characterized by different physicochemical techniques. This synthesized method was compared with others conventional methodologies such as template-ion exchanged (Co/tie) and incipient wet impregnation (Co/iwi) with similar cobalt content. All the samples were studied as catalysts on the CO total oxidation (COTox) and preferential oxidation of CO on H2-rich streams (COProx). Incorporating cobalt with supercritical CO2 leads to a catalyst which produces values of CO conversion similar to those obtained by conventional methods such as incipient wetness impregnation (Co/iwi) or template-ion exchanged (Co/tie). It has been possible to identify different cobalt species present in catalysts depending on their synthesis methods by Temperature-Programmed Reduction (TPR), X-ray Photoelectronic (XPS), Laser Raman (LRS) and X-ray Absorption (XANES/EXAFS) spectroscopic studies. All samples containing a main cobalt species of cobalt (II) coordinated with Si tetrahedral sites form part of mesoporous structure and lesser extent, cobalt orthosilicate on the surface. In addition, Co3O4 species dispersed over the MCM41 support were detected for the Co/iwi and Co/sc catalysts. Thus, the combination of Co3O4 nanoparticles and Co(II) sites interacting with the siliceous structure, highly dispersed on the surface and inside the mesoporous support obtained by the ‘scfrd’ method resulted in a more active and selective catalyst for the COProx reaction.

Afiliación de los autores: Aspromonte, Soledad Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Afiliación de los autores: Mizrahi, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina

Afiliación de los autores: Alonso, Esther. Universidad de Valladolid; España

Afiliación de los autores: Ramallo Lopez, Jose Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina

Afiliación de los autores: Boix, Alicia Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Resumen:

CoO and Co3O4 nanoparticles were uniformly dispersed inside mesoporous MCM-41 and Al-MCM-41 supports using supercritical CO2 reactive deposition. This method represents a one-pot reproducible procedure that allows the dissolution of the organocobalt precursor and supports impregnation in supercritical CO2 at 70 °C and 110 bar, followed by the precursor thermal decomposition into cobalt species at 200 °C and 160 bar. By the relative concentration of the cobalt precursor [cobalt (II) bis (η5-ciclopentadienil)], the load of cobalt nanoparticles was controlled and then determined by Inductively Coupled Plasma (ICP-OES). The synthesis of CoO and Co3O4 species inside the MCM-41 and Al-MCM-41 substrates was confirmed by X-ray Photoelectron (XPS) and Laser Raman Spectroscopies (LRS). By N2 adsorption and Small Angle X-ray Scattering (SAXS), it was determined that the hexagonal arrangement as well as the surface area and pore size of the substrates changed after the addition of cobalt. By means of X-ray mapping from SEM images, a homogeneous distribution of cobalt nanoparticles was observed inside the mesopores when the cobalt loading was 1 wt.%. In addition, spherical cobalt nanoparticles of average diameter close to 20 nm were detected on the outer surface of MCM-41 and Al-MCM-41 supports when the cobalt content was higher. On the other hand, by Transmission Electron Microscopy (TEM), it was possible to measure the interplanar distance of the crystalline plane of the outer nanoparticles, which was later compared with the theoretical distance values which allowed identifying the CoO and Co3O4 phases.

Afiliación de los autores: Aspromonte, Soledad Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Afiliación de los autores: Sastre, Alvaro. Universidad de Valladolid; España

Afiliación de los autores: Boix, Alicia Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Afiliación de los autores: Cocero, María José. Universidad de Valladolid; España

Afiliación de los autores: Alonso, Esther. Universidad de Valladolid; España

Resumen:

A study of the lean NOx reduction activity with butane and toluene in the presence of water over bimetallic and monometallic Ag, Co exchanged on Na-mordenite catalysts was performed. The Ag-Co interactions were analyzed through X-ray photoelectron spectroscopy (XPS) and Temperature-programmed reduction (TPR) techniques. It is shown that the metal silver particles formed at low temperature during the TPR experiment improve the dissociation of hydrogen thus facilitating the reduction of Co2+ species. The incorporation of 3.2 wt. % of silver to CoM catalyst, significantly improved the NOx to N2 conversion with butane, which reached 95 % under wet conditions (2 % H2O). However, this effect was not observed when toluene was the reducing agent.

Afiliación de los autores: Aspromonte, Soledad Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Afiliación de los autores: Miro, Eduardo Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentina

Afiliación de los autores: Boix, Alicia Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica ; Argentina

Resumen:

 Catalysts based on Na-mordenite (symbolized as M) exchanged with 5, 10, and 15 wt % of Ag were characterized by X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine line structure (EXAFS), X-ray absorption near edge spectroscopy (XANES) and UV-vis diffuse reflectance spectroscopy (DRS) to investigate the effect of different treatments on the chemical state and surface concentration of the silver species. The AgxM catalysts were analyzed in oxidizing (O2) or reducing (H2/Ar) atmospheres and also after being used in the selective catalytic reduction of NOx or in successive cycles of toluene adsorption/desorption. In calcined samples, EXAFS profiles showed two types of AgO spheres of coordination, one due to a dispersed phase of silver oxide and the other due to Ag+ ions in interaction with the oxygen of the zeolite framework. The UV-vis DRS spectra showed the coexistence of isolated Ag+, Agn(delta)+ (n < 10) cationic clusters and AgxO particles. In addition, through the modified Auger parameter (alpha), calculated from XPS measurements, it was possible to identify Ag+ ions at exchange sites (alpha = 722 eV) and AgxO ( alpha = 725 eV) highly dispersed on the surface. Both species constitute stable active centers for the selective catalytic reduction of NOx under severe reaction conditions. However, during the adsorption-desorption of toluene, the reduction of silver oxides produces Ag(0) due to thermal hydrocarbon decomposition.   

Afiliación de los autores: Aspromonte, Soledad Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Investigaciones En Catálisis y Petroquímica; Argentina. Universidad Nacional del Litoral; Argentina

Afiliación de los autores: Mizrahi, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; Argentina

Afiliación de los autores: Schneeberger, Florencia A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Investigaciones En Catálisis y Petroquímica; Argentina

Afiliación de los autores: Ramallo Lopez, Jose Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; Argentina

Afiliación de los autores: Boix, Alicia Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Investigaciones En Catálisis y Petroquímica; Argentina. Universidad Nacional del Litoral; Argentina