Sten T. Lundin

Activities of Vanadium Oxides in Ammoxidation of 3-Picoline

Ammoxidation of 3-picoline to nicotinonitrile was studied on V2O5, V6O13, and V2O4 catalysts in a fixed-bed integral reactor. The activity studies showed that V6O13 was the most active and selective catalyst of the pure oxides, with a maximum yield of 76% nicotinonitrile at 365 °C. The maximum yield on V2O5 catalyst was 34%, and was obtained at a higher temperature, 458 °C. V2O4 was found to be inactive under the conditions studied. The activities and selectivities of the oxides changed rapidly with reaction time when V6O13 and V2O4 were studied. By means of X-ray diffraction and a titrimetric method, the average oxidation number of vanadium was determined, V6O13 was both oxidized and reduced during the reaction; V2O4 was oxidized, while a relatively smaller reduction of V2O5 could be detected. The experiments showed that the V6O13 catalyst used, with both V2O5 and V6O13 phases present, was more selective than any of the pure oxides. This may be explained by active boundary surfaces. Also a mechanism of formation of nicotinonitrile is proposed, which includes a step in which an adsorbed aldehyde complex reacts with ammonia.

Catalytic Reduction of Nitrogen Oxides, 1. The reduction of NO

Abstract The selective catalytic reduction of NO with NH3 has been studied over V205/SiO2-TiO2 catalyst. The influence of side reactions has bee

Activities of V-Ti-O catalysts in the ammoxidation of 3-picoline

Ammoxidation of 3-picoline was studied on reduced V-Ti-O catalysts with V6O13 as the major vanadium oxide. The results showed that the initial activity as a function of the TiO2 content reached a maximum at 50–60 mole% TiO2. It is proposed that there is maximum contact between the vanadium and titanium phases at this composition, which results in a weakening of the (VO)3+ surface bond. The selectivity of formation of nicotinonitrile exhibited a maximum of 83% at 10 mole% TiO2 and minima of 73 and 75% at 0 and 30 mole% TiO2, respectively. At higher TiO2 concentrations the selectivity increased continuously to 83% at 90 mole% TiO2. The variation of the selectivity of formation of nicotinonitrile depends on the View the MathML source ratio in the TiO2 phase. It was also found that the conversion and yields varied with the reaction time, which could be explained by the fact that reduced vanadium oxides were oxidized to V2O5 during the ammoxidation process. This oxidation leads to the formation of active and highly selective boundary surfaces between the TiO2-promoted vanadium oxides V6O13 and V2O5. (Less)

Catalytic Reduction of Nitrogen Oxides, 2. The reduction of NO2

Abstract The selective catalytic reduction of NO2 with NH3 has been studied over a V2O5/SiO-TiO2 catalyst. The activity for the main reaction was measured between 420 and 670 K. Also reported are activities for the decomposition of NO2 to NO and O2 and the influence of O2 in that reaction. The reaction system NO2-O2-NH3 in N2 has been investigated in detail and activities in single as well as composed reaction media are reported.

Activity measurements and spectroscopic studies of the catalytic oxidation of toluene over V2O5/Al2O3-C catalysts

Vanadium oxide catalysts based on Al2O3-C (γ-Al2O3) as support contain at least four different forms of vanadium. The distribution between these depends on the vanadium loading. The activity (per gram of vanadium) of these catalysts for toluene oxidation increases with increasing loading. The selectivity for benzene formation decreases from 2% for the support to 0% for 0.5 wt% V, while the selectivity for benzaldehyde formation first appears at this concentration and rises to 29% for 10 wt% V. It is suggested that benzene is formed at Lewis acid sites on the support, whereas benzaldehyde is formed on vanadium sites. At low loadings (0.1 and 0.2 wt% V) single vandium species with tetrahedral coordination are formed. The oxidised forms have u.v. bands at 35 500 and 42000 cm–1 and the reduced forms have i.r. bands of adsorbed CO at 2200 cm–1(room temperature) and at 2190 and 2158 cm–1(133 K). At medium loadings, vanadium surface clusters with varying degrees of agglomeration are formed in addition to the other species. These are suggested to be single chain species with vanadium in tetrahedral coordination, double chain species with vanadium in square pyramidal coordination and aggregates of octahedral vanadium formed by the coupling of double chains. The oxidised forms have u.v. bands at 34 500 and 43000 cm–1 and the reduced forms have i.r. bands of adsorbed CO at 2178 cm–1(room temperature) and at 2178 and 2158 cm–1(133 K). The agglomerates are more active than the isolated species and show some selectivity for benzaldehyde. Both the activity and the selectivity appear to increase with the degree of agglomeration. At high vanadium loadings (10 wt% V), surface crystallites of vanadium oxide are formed in addition to the other species. The oxidised forms have u.v. bands at 30 000 and 43 000 cm–1 and the reduced forms have i.r. bands of adsorbed CO at 2181 cm–1(room temperature) and at 2181 and 2145 cm–1(133 K). These crystallites are more active and selective than other species with less agglomeration. It is suggested that the increased activity for the larger species is due to the possibility of a transition from corner to edge sharing octahedra at the release of oxygen, which increases the activity of the double-bonded oxygen.

An ESCA study of metal deposition on cracking catalysts

Abstract Equilibrium and fresh samples of FCC catalysts impregnated with V and Ni naphthenates have been analysed both by ESCA and atomic absorption spectrophototmetry. The samples were heated in air and in steam atmospheres. It was found that Ni may exist as Ni3+ or Ni2+ and the V as V5+ after the regenerator of the FCCU. It was also found that Ni was homogeneously distributed throughout the catalyst up to a concentration of at least 2% Ni. Higher loadings of Ni (3.7%) gave a surface enrichment. Further it was concluded that V is segregated in three different ways in an FCC catalyst: (i) Vanadium is deposited in the outer part of the catalyst particle during the cracking stage because of the polar nature of the V porphyrin complex. (ii) Vanadium migrates to the surface of the catalyst particles during the regeneration stage because of the low melting point of V2O5 (690°C). (iii) Vanadiun migrates from the matrix surface where it was originally deposited, to the zeolite, and reacts destructively with the zeolite [7].