Dimitar A. Panayotov

Interaction between NO, CO and O2on γ−Al2O3-supported copper-manganese oxides

The activity of γ−Al2O3-supported CuxMn3-xO4 catalysts towards the reduction of NO with CO has been investigated at temperatures of 150–500°C. It was established that the most active sample is Cu1.01Mn1.99O4/γ−Al2O3,i.e. the sample where the CuMn2O4 spinel is formed. In the presence of oxygen and the reducing agents CO and HC (a propane-butane mixture) oxygen has no blocking effect on the NO+CO reaction. Under oxidative conditions the reactions NO+CO and O2+CO are competitive.

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.

Effect of methanol on the Lewis acidity of rutile TiO2 nanoparticles probed through vibrational spectroscopy of coadsorbed CO.

Infrared spectroscopy of adsorbed CO has been used to characterize the effect of adsorbed methanol on the Lewis acidity of 4 nm rutile TiO(2) nanoparticles. Measurements of CO absorbance and vibrational frequency have revealed that CO adsorbs primarily at one class of Lewis acid sites on clean TiO(2) particles, where evidence for lateral interactions between neighboring molecules suggests dense coverage occurs near saturation. The response of the CO infrared intensities and frequencies to methanol exposure has shown that methanol uptake occurs primarily at the Lewis acid sites and through hydrogen bonding to surface OH groups. These surface sites appear to be responsible for driving both molecular and dissociative adsorption of methanol on the titania. Most importantly, these studies have revealed that the parent methanol and associated methoxy products lower the Lewis acidity of neighboring sites on TiO(2) nanoparticles.

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.

Chapter 2:Isotopes in the FTIR investigations of solid surfaces

In this chapter the recent achievements in the use of isotopically labelled molecules for characterization of surfaces by FTIR and other vibrational spectroscopy techniques is reviewed. A brief theoretical background is provided where special attention is paid on the deviations of the experimental results from the theory. Then the application of D-, 13C-, 15N- and 18O-labelling is consecutively considered. For deuterium we first discuss the properties of surface OD groups and then the use of deuterated molecular probes (D2, CHD2OH, C2D5OH, C6D12). When describing 13C-labelled compounds the application of 13CO and 13C18O is compared and then other labelled compounds (13CO2, D13CN, 13CH3OH, etc.) are considered. In the next section 15N2, NO isotopologues, (15NH2)2CO and aminoacids are discussed. For 18O-labelling we first consider the use of surfaces enriched to 18O, then different O2 adsorption and finally, H218O and C18O. In all cases the application of isotopic labelling for clarifying the mechanisms of catalytic reactions is also considered.

Isotopic Labelling in Vibrational Spectroscopy: A Technique to Decipher the Structure of Surface Species

The purpose of this paper is to provide a clear and simple introduction to the application of isotopically labelled molecules in the characterization of various surfaces by vibrational spectroscopies. Although the possible applications are multifarious, we have tried to systematize the most important of them in several groups. Initially we provide a brief theoretical background on the effect of isotopic substitution on the vibrational spectra and then consider the practical application of the technique for establishing the structure and composition of surface species, determination of the origin of particular atoms in these species and obtaining details on the interaction between adsorbed molecules. The second part of the paper describes three purpose-designed surface studies exemplifying the use of isotopically labelled molecules in order to: (i) determine of the maximal number of CO molecules than can be simultaneously bound to one Na+ cation from the NaY zeolite; (ii) measure the dynamic and static shift of CO molecules adsorbed on Ru/ZrO2; (iii) prove the H2 dissociation on Ru/ZrO2.