M.J. Illán-Gómez

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.

On the Structure Sensitivity of deNOx HC-SCR over Pt-Beta Catalysts

Abstract In this paper, the integration of activity results for the selective catalytic reduction of NO x with C 3 H 6 with a thorough characterization of Pt-beta catalysts with different platinum dispersion has been accomplished. The parent zeolite NH 4 -beta (Si/Al = 11.4) was ion-exchanged with a Pt(II) precursor and activated by calcination and reduction in H 2 before reaction. The evolution and nature of the Pt phase during the different preparation stages and after catalytic tests were investigated by CO chemisorption, TEM, XRD, and XPS. By using different heating rates during activation of the ion-exchanged material and upon the deNO x HC-SCR, the average particle size of platinum in the final catalyst was varied in the range of 2–25 nm. It has been clearly shown that deNO x HC-SCR conditions produce a decrease in the metal dispersion of the catalysts by sintering of Pt particles. The increase in average particle size has a positive effect on the activity of the catalysts. Thus, the larger the platinum particles, the higher the NO x conversion and the lower the operation temperature. The XPS results show that both Pt(0) and Pt(II) species are present in the calcined samples, after H 2 reduction and during reaction. Coke deposits, formed during reaction on the zeolite support, were studied by XPS, DRIFT, and TPO-TPD/MS. The structure sensitivity of the lean deNO x reaction toward the platinum phase has been confirmed by the direct correlation established between platinum particle size and TOF. Based on previous results on a single crystal, it seems that the key steps are the NO dissociation on Pt(100) planes and PtO clean off which will be easily performed on large Pt particles. On the other hand, the independence of Pt(100)/Pt(111) ratios with particle size explains the similar N 2 and N 2 O selectivity values presented along all the samples.

NOx reduction by carbon supporting potassium-bimetallic catalysts

Abstract The activity of potassium-bimetallic catalysts (KFe, KCo, KNi and KCu) for NOx reduction by carbon has been studied. Temperature-programmed reactions and isothermal reactions have been carried out in a fixed bed flow reactor using a 0.5% NO/5% O2/He mixture. The addition of a transition metal to a potassium catalyst enhances its activity showing a synergetic effect. Temperature-programmed desorption experiment in helium reveals that the temperature for transition metal reduction by carbon decreases in the presence of potassium. Among the combination of metals analyzed, the KNi is most interesting because it combines a high NOx reduction capacity, at low temperatures, with the lowest loss of carbon by combustion.

Improvements in NOx reduction by carbon using bimetallic catalysts

Abstract The catalysis of the C–NO x reaction has been studied to optimize the composition of the catalysts in order to decrease the carbon consumption by oxygen. Both the metal content and the composition of the catalysts have been investigated. The activity of bimetallic (KNi, NiCo and NiCu) catalysts for NO x reduction by carbon has been studied using both isothermal reactions at 300°C and temperature programmed reaction up to 500°C. It has been found that the experimental variables (i.e. amount of catalysts and nature of the bimetallic catalysts) determine the selectivity against carbon combustion by oxygen. Thus, it has been observed that the amount of catalyst greatly affects the C–O 2 reaction but only lightly the C–NO x reaction and, consequently, modifies the selectivity of the catalyst for NO x reduction. Among the bimetallic catalysts tested, NiCu catalyst presents the best performance, at a temperature as low as 250°C, a high de-NO x activity and a high NO x selectivity due to a low carbon burn-off, with the additional advantage of the absence of N 2 O and CO in the reaction products. Thus, the results obtained in this study show, in comparison with our previous results, that better selectivities are achieved.

Copper doped BaMnO3 perovskite catalysts for NO oxidation and NO2-assisted diesel soot removal

The activity for NO oxidation and for NO2-assisted diesel soot removal of a BaMn1−xCuxO3 (x = 0, 0.1, 0.2, 0.3) perovskite-type catalyst has been tested by Temperature Programmed Reaction (TPR) and isothermal experiments at 450 °C. Fresh and used catalyst characterization by ICP-OES, N2 adsorption, XRD, XPS, IR spectroscopy and H2-TPR was performed. Results showed that: (i) manganese is partially substituted by copper in the perovskite structure leading to the formation of a manganese-deficient perovskite with a new hexagonal structure, (ii) in BaMn1−xCuxO3 catalysts, manganese seems to be mainly Mn(III) and, as a consequence, the amount of oxygen vacancies increases gradually with the copper content and (iii) the presence of copper into the perovskite structure enhances the reducibility of the catalyst and increases the mobility of lattice oxygen. BaMn0.7Cu0.3O3 is the most active catalyst for NO2 generation and, consequently, shows the lowest T50% value, the highest CO2 selectivity, the best performance during TPR cyclic experiments, and the highest soot oxidation rate at 450 °C. This behavior is a result of the enhancement of the redox properties of the catalyst due to the replacement of Mn(III)/Mn(IV) by Cu(II) in the perovskite structure.

Selective catalytic reduction of NOx with C3H6 under lean-burn conditions on activated carbon-supported metals

The Selective Catalytic Reduction of NO x with C 3 H 6 under excess of oxygen has been investigated using different transition metals supported on a carbonaceous material. For this purpose, 1 wt % Pt, Pd, Fe, Co, Ni and Cu supported on an activated carbon, ROXN, have been tested by Temperature Programme Reaction (TPR). A as mixture containing 1000 ppm of NO, 1500 ppm of C 3 H 6 and 5 vol. % of O 2 (SV = 3600 h -1 ) has been used to carry out the experiments. In terms of NOx conversion and N 2 selectivity, a diversity of behaviours have been obtained. Pt/ROXN presents the highest NO x conversion, almost 100%, but exhibits a moderate N 2 selectivity. On the other hand, Fe/ROXN presents a 100% N 2 selectivity, but exhibits low NO x conversions. The results have been discussed attending to the characteristics of the active phase and to the behaviour of the catalysts for C 3 H 6 combustion. Conventional alumina-supported catalysts have been used for comparative purposes: an identical activity trend has been obtained for the studied metals. Nevertheless, the activated carbon-supported metal catalysts show two advantages; i) higher NO x conversions at lower temperatures and ii) the achievement of their maximum values for N 2 selectivities, which are similar to the obtained for the alumina-supported catalysts, at lower temperatures.