M. Khristova

Conversion of NO on Co-impregnated active carbon catalysts

Abstract The NO conversion in a NO+ Ar gas mixture has been investigated on Coimpregnated active carbon catalysts in the absence of any added gasphase reducing agents. The catalysts obtained are very promising with respect to NO conversion because they are active at low temperatures (below 200 °C) and the only resulting product is N2. Up to 200 °C the pure active carbon used as a support exhibits no activity towards the process investigated. It has been found that the ratecontrolling step of NO conversion over active carbon supported Co catalysts is NO adsorption. NO conversion is catalysed by the cobaltoxide active phase. The mechanism of this process up to 200 °C presumably differs from that above this temperature where NO reduction proceeds with the participation of the active carbon. The surface oxides evolve as CO above 200 °C, playing the role of added gasphase reducing agent.

Conversion of NO on a Ni impregnated-active carbon catalyst in the presence of oxygen

Abstract The conversion of NO in the presence and absence of oxygen in the gas mixture has been investigated on Ni-impregnated active carbon (AC) catalysts. No reducing agent has been added to the gas mixture. The AC plays the role of a reducing agent in the system. The active phase (Ni) is of considerable importance for the catalytic conversion of NO at low temperatures in the presence of oxygen and the resulting product is N2 alone. The AC is oxidized by NO (C–NO) and O2 (C–O2) from the gas phase. The C–NO reaction is activated by the presence of O2 in the gas mixture. The oxygen from the gas phase oxidizes the supported active phase and NO. This type of catalysts may be used for purification of waste gases from nitrogen oxide.

Reduction of nitric oxide with carbon monoxide on the surface of copper-containing catalysts based on aluminophosphates, silicoaluminosulphates and ZSM-5 zeolite

Abstract The interaction of nitric oxide with carbon monoxide on the surface of the Cu-containing catalysts Cu-AlPO4, Cu-AlPO-5, Cu-MnAlPO-5, Cu-SAPO-5, Cu-CoAPSO-11 and Cu-ZSM-5 has been studied by the transient response technique. In the temperature region studied (60–300°C), the catalysts Cu-AlPO4, Cu-MnAlPO-5, Cu-CoAPSO-11, Cu-AlPO-5 and Cu-SAPO-5 start to interact first with carbon monoxide above a definite temperature. High reduction degrees (over 30%) for the supported CuO are attained after treatment with a NO + N2O + CO + Ar gas mixture at 60–300°C. Nevertheless, only the last two catalysts exhibit activity towards conversion of nitric oxide to nitrogen (above 100°C) which is comparable to that of aCuO/γ-Al2O3 catalyst. The heat-treated in an inert (agron) atmosphere Cu-ZSM-5 catalyst exhibits activity towards the reduction of NO by CO to N2O and N2. A competition between the CO + NO and CO + O(surface) interactions is observed at a definite temperature under the conditions of a NO + N2O + CO + Ar gas mixture. Competitive carbon monoxide adsorption occurs, depending on the temperature and degree of surface reduction, which poisons the catalyst surface with respect to the reduction of nitric oxide to nitrogen. The surface of heat-treated Cu-ZSM-5 catalyst possesses centres active in the decomposition of nitrous oxide and nitric oxide to nitrogen from a NO + N2O + Ar gas mixture. During temperature-programmed desorption (TPD) experiments, a nitric oxide desorption peak with Tmax = 180°C is observed. The species to which this peak belongs are suggested as precursors for the nitric oxide decomposition reactions. The difference in catalytic behaviour of the catalysts studied is explained by the hypothesis (proposed by W.K. Hall) about the dependence of the catalyst activity on the ability of the catalyst surface to stabilize various intermediates during adsorption of nitric oxide and its interaction with carbon monoxide.

Copper oxide supported on carbon modified alumina as catalyst for reduction of NO with CO.

Carbon-modified alumina-supported copper oxide catalysts have been investigated. The samples have been prepared by modified incipient techniques. The gamma-Al(2)O(3)-supported carbon phase permits sufficient modification of the chemical nature of the support surface in the region of low carbon contents without changing the specific surface area and the mesoporous character of the samples as compared to those of initial gamma-Al(2)O(3). In addition, the surface oxygen groups of the carbon phase, similar to the hydroxyl groups of the alumina surface, affect the formation and type of copper oxide phase. It has been established that the catalysts investigated have high activity in the reduction of NO with CO, the highest activity belonging to the Cu17AC/AL catalyst, which contains the largest amount of carbon. This sample is also active with respect to the direct decomposition of NO.

Catalytic reduction of NO with decomposed methanol on alumina-supported Mn-Ce catalysts.

A series of manganese-ceria supported on alumina catalysts with various Mn/Ce ratios are investigated in both methanol decomposition to CO and hydrogen and SCR of NO(x) with CO. The study is aimed at the potential application of both reactions in integrated devices, where NO(x) is reduced with the products of the decomposed methanol. The samples are characterized by nitrogen physisorption, XRD, TEM, XPS, UV-Vis, and TPR. It was established that manganese-ceria supported on alumina catalysts are perspective in both methanol decomposition and NO reduction at temperatures above 723 K, which are typical for exhausted gases from the vehicles and some stationary stations. The best catalytic activity and selectivity to the desired products under these conditions was found for the samples with Mn/Mn+Ce ratio of 0.5 and 0.7. This superior catalytic performance is related to the formation of mixed valence Mn(3+)/Ce(4+) and Mn(4+)/Ce(3+) active sites.

NOVEL APPLICATION OF DEPLETED FULLERENE SOOT (DFS) AS SUPPORT OF CATALYSTS FOR LOW-TEMPERATURE REDUCTION OF NO WITH CO

Depleted fullerene soot (DFS) with fullerene residue content of about 2.2-3.2% are investigated in order to elucidate the possibility for their use as support of catalysts in low-temperature reduction of NO with CO. Bimetalic copper-cobalt and copper-manganese oxides supported on DFS are prepared. All samples are characterized by chemical analysis, XRD, SEM, IR spectroscopy, XPS, nitrogen adsorption measurements. The two DFS supported bimetallic catalysts manifest a high activity towards the reduction of NO with CO at temperatures below 150 degrees C, the CuCo/DFS being the more active one. The peculiarity of the support DFS predetermines the porous texture of the catalysts. The occurrence of a specific metal-support interaction favors the formation of the mixed oxide spinels CuCo2O4 and Cu1.5 Mn1.5 O4 that are responsible for the enhanced activity.

Influence of Ce addition on the catalytic behavior of alumina-supported Cu-Co catalysts in NO reduction with CO.

The effect of Ce addition to alumina-supported copper, cobalt, and copper-cobalt oxides with low loadings on the catalysts efficiency in NO reduction with CO was studied. The attention was focused on varying the impregnation procedure in the ternary-supported catalysts in order to determine the best catalyst as well as the reasons for the enhanced catalytic activity. Ternary Co-Cu-Ce and binary Co-Ce, Cu-Ce, and Cu-Co-supported alumina were prepared and characterized by ICP, XRD, TEM, adsorption studies, XPS, H(2)-TPR, and catalytic investigations. The high activity of the ternary and the binary catalysts was determined by the favorable influence of the added cerium on the dispersion of the copper and cobalt active phases. The presence of ceria contributes to the formation of appropriate active phases, resulting in catalytic sites on the surface of the samples that promote the reduction of NO with CO.

Interactions NO—CO and O2—NO—CO on CuCo2O4/γ-Al2O3 and on γ-Al2O3- and CuCo2O4/γ-Al2O3-supported Pt, Rh and Pt—Rh catalysts, a transient response study

Abstract The interactions NO—CO and O 2 —NO—CO have been studied onCuCo 2 O 4 γ-Al 2 O 3 and on γ-Al 2 O 3 - and CuCo 2 O 4 γ-Al 2 O 3 -supported Pt, Rh and Pt—Rh catalysts. The deposition of noble metals (Pt, Rh and Pt—Rh) on CuCo 2 O 4 γ-Al 2 O 3 instead of γ-Al 2 O 3 is beneficial in: lowering the temperature at which maximum N 2 O is formed and decreasing the maximum N 2 O concentration attained; lowering the onset temperature of NO to N 2 reduction, and increasing the N 2 selectivity; preserving the activity towards NO to N 2 reduction on a higher level following the concentration step NO + COO 2 + NO + CO and changing the conditions from stoichiometric to oxidizing (50% excess of oxidants). The reason for this behaviour of the CuCo 2 O 4 γ-Al 2 O 3 -based noble metal catalysts is the formation (reversible) of a reduced surface layer on the CuCo 2 O 4 supported spinel under the conditions of a stoichiometric NO + CO mixture.

Catalytic reduction of NO with CO over CuxCo3−xO4 spinels

The interaction between NO and CO over CuxCo3−xO4 spinels (0≤x≤1) has been studied. It has been found that the two reactions of NO reduction, to N2O and N2, respectively, are accelerated by the increase of Cu content (x). With the second reaction acceleration occurs only at x>0.5. This is attributed to the presence of different centers on which N2O and N2 are formed.AbstractИзучено взаимодействие между NO и CO на шпинелях CuxCo3−xO4 (0≦x≦1). Найдено, что обе реакции восстановления NO до N2O и N2 ускоряются с увеличением содержания Cu (x). Вторая реакция ускоряется лишь при x>0,5. Это приписывают присутствию различных центров, на которых образуются N2O и N2.

Catalytic reduction of NO by CO over Pd — doped Perovskite-type catalysts

The perovskite type oxides (nominal formula LaTi0.5Mg0.5O3) with addition of Pd were prepared by annealing the ethanol solution of precursors in nitrogen flow at 1200°C and characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption of NO (NO-TPD). Their activity was evaluated for NO reduction by CO under stoichiometric and oxidizing conditions and for direct decomposition of NO. Pd substituted samples exhibited high NO reduction activity and selectivity towards N2. Nearly complete elimination of NO was achieved at 200°C. Two simultaneous reactions, NO reduction by CO and direct decomposition of NO as well as two forms of NO adsorption were observed on the surface of Pd substituted perovskite samples. The distribution of Pd in different catalytically active sites or complexes on at the catalyst surface may be responsible for the proceeding of two reactions: NO reduction with CO and direct NO decomposition.