Avelina García-García

Catalytic NOx reduction by carbon supporting metals

Abstract Catalytic NOx reduction by carbon supporting transition metals (Fe, Co, Ni, Cu) and potassium has been studied. The effect of oxygen on the catalytic properties of the metals has been analyzed. Temperature-programmed reactions and isothermal reactions have been conducted in a fixed bed flow reactor. Temperature-programmed reduction in hydrogen, XRD and XPS have been used to characterize the catalysts. All the metals studied catalyze the NOx reduction by carbon in the presence of oxygen, but also the O2–carbon reaction. Metal catalytic activity is the result of two factors, the tendency of the metal to be oxidized by NO and the easiness of the resulting oxide to be reduced by carbon. Among the metals studied, nickel exhibits the highest selectivity for NOx reduction. The results of this study strengthen the possible benefit of the lack of a gaseous reducing agent (such as ammonia or hydrocarbons) since the reduction of NOx is performed by the carbon support itself.

Potassium-containing briquetted coal for the reduction of NO

Abstract The reduction of NO by potassium-containing activated carbons and briquettes prepared from a bituminous coal was investigated. Partial washing of KOH activated carbons produced samples with different potassium contents. Briquetting with a binder containing potassium, at different binder/coal ratios, also allowed carbons with different potassium contents to be obtained. The NO-carbon reaction was studied with a fixed-bed flow reactor at atmospheric pressure in two types of experiment: (1) isothermal reaction at 300–600°C; (2) temperature-programmed reaction (TPR) in an NO-He mixture. The reaction products were monitored in both cases, allowing detailed oxygen and nitrogen balances to be determined. Both the potassium remaining in the activated carbons and that present in the briquettes act as a catalyst for the NO-carbon reaction. Therefore, the briquettes are active for NO reduction with the advantage of being produced by a much simpler process with no KOH consumption and no washing process. Furthermore, the briquettes can be moulded in the desired form with appreciable mechanical strength. The final potassium loading controls the capacity of the potassium-carbon samples for NO reduction. The reduction of NO by the potassium-containing briquettes is enhanced by the presence of oxygen.

Contributions of surface and bulk heterogeneities to the NO oxidation activities of ceria–zirconia catalysts with composition Ce0.76Zr0.24O2 prepared by different methods

The study of the catalytic activity towards NO oxidation to NO(2) was approached by using ceria-zirconia mixed oxides with the same nominal composition (Ce(0.76)Zr(0.24)O(2)) but prepared by different routes of synthesis: coprecipitation, solid combustion synthesis with urea, citrate complexation route, reversed microemulsion and template synthesis. The characterisation of the catalysts was performed by N(2) adsorption at -196 °C, XRD, Raman Spectroscopy, H(2)-TPR and XPS in order to ascertain the relationships between their catalytic activities and their bulk and surface properties. The results showed that the preparation method is critical for the physico-chemical properties of the mixed oxides, exhibiting very different BET surface areas, crystalline phase/s contributions and bulk oxygen mobility. The distribution of Ce and Zr on the surface with regard to the bulk is very much influenced by the preparation method as well. The NO(2) production from NO oxidation was shown to be mostly correlated with the Ce/Zr surface atomic ratio and the proportion of Ce(4+) (presumably in a doped cubic phase) in the uppermost layers.

Thermal treatment effect on NO reduction by potassium-containing coal-briquettes and coal-chars

This communication reports the NO reduction activity of potassium containing coal-briquettes prepared at different pyrolysis temperatures. For comparative purposes coal-chars prepared at the same temperatures have also been analyzed. NO reduction experiments were performed in a fix-bed flow reactor at atmospheric pressure using two types of experiment: (i) temperature programmed reaction in a NO/He mixture; and (ii) isothermal reactions at 600°C. The reaction products were monitored in both cases, thus allowing detailed oxygen and nitrogen balances to be determined. It has to be pointed out that a previous in situ heat treatment in He before reaction is necessary for the low temperature activity of potassium containing coal-briquettes. For fresh briquettes, NO direct attack in addition to NO conversion by the catalytic action of potassium is observed at high temperatures. The NO direct attack, both in potassium containing samples and coal-chars, is clearly manifested by a nitrogen imbalance.

Catalytic performance of CuO/Ce0.8Zr0.2O2 loaded onto SiC-DPF in NOx-assisted combustion of diesel soot

This work presents a comparative study between the catalytic performance of the 2% CuO/ceria-zirconia powder catalyst and the same catalyst supported on silicon carbide DPF (Diesel Particulate Filter) towards NO oxidation reaction and soot combustion reaction. The ceria-zirconia catalyst was prepared by the co-precipitation method and 2 wt% copper was incorporated by the incipient wetness impregnation method. The catalyst was incorporated onto the ceramic support using a simple and organic solvent-free procedure by a simply dipping the DPF into an aqueous solution of the catalyst. The powder catalyst has been characterized using N2 adsorption at −196 °C, XRD and Raman Spectroscopy; whereas the catalytic coating morphology has been evaluated by SEM and the mechanical stability by an adherence test. Both catalyst configurations were tested for NO oxidation to NO2 and for soot combustion under NOx/O2. The results revealed that incorporation of the very active copper/ceria-zirconia catalyst onto SiC-DPF has been successfully achieved by a simple coating procedure. Furthermore, the catalytic coating has shown suitable mechanical, chemical and thermal stability. A satisfactory catalytic performance of the catalytic-coated filter was reached towards the NO oxidation reaction. Moreover, it was proved that the catalytic coating is stable and the corresponding coated DPF can be reused for several cycles of NO oxidation without a significant decrease in its activity. Finally, it was verified that the loose-contact mode is a good choice to simulate the catalytic performance of this active phase in a real diesel particulate filter.

NOx reduction by potassium-containing coal pellets. Discussing lifetime test profiles

The activity of potassium-containing coal pellets for NOx reduction in an oxygen-rich environment was investigated at 350 °C, during lifetime tests, until the sample was completely consumed. A complex reaction profile is exhibited by the samples, consisting of four different steps. As the potassium content increases, the selectivity towards NOx reduction, the amounts of NOx reduced per gram of sample (ash-free basis), and the maximum NOx conversion reached progressively increase. The highest potassium content sample can remove a considerable amount of NOx, 3.1 g/g free-ash sample.

Potential of Cu–saponite catalysts for soot combustion

H– and Na–saponite supports have been prepared by several synthesis approaches. 5% Cu/saponite catalysts have been prepared and tested for soot combustion in a NOx + O2 + N2 gas flow and with soot and catalyst mixed in loose contact mode. XRD, FT-IR, N2 adsorption and TEM characterization results revealed that the use of either surfactant or microwaves during the synthesis led to delamination of the saponite support, yielding high surface area and small crystallite size materials. The degree of delamination affected further copper oxide dispersion and soot combustion capacity of the Cu/saponite catalysts. All Cu/saponite catalysts were active for soot combustion, and the NO2-assisted mechanism seemed to prevail. The best activity was achieved with copper oxide supported on a Na–saponite prepared at pH 13 and with surfactant. This best activity was attributed to the efficient copper oxide dispersion on the high surface area delaminated saponite (603 m2 g−1) and to the presence of Na. Copper oxide reduction in H2-TPR experiments occurred at lower temperature for the Na-containing catalysts than for the H-containing counterparts, and all Cu/Na–saponite catalysts were more active for soot combustion than the corresponding Cu/H–saponite catalysts.

NOX reduction by coal briquets.

Publisher Summary This chapter examines the possibility of using bindered carbons to reduce NO x emissions. The novel manufacture method in the chapter presents the advantage of using binder agent––humic acid containing potassium––that will act as an inherent catalyst. The system-catalyst-binder coal stays intimately joined by a molding stage and subsequent pyrolysis. The objectives are to analyze the effect of pyrolysis temperature and potassium content in the NO reduction in the presence of oxygen. The chapter analyzes the behavior of different coals and reactor type. Coal briquets prepared by humic acid impregnation, pressing, and pyrolysis have an adequate mechanical resistance and can be used as NO x reductants. The potassium introduced with the binder has catalytic effects. A larger amount of potassium added as potassium hydroxide (KOH) does not increase the reduction activity.