Giovanni Manara

Oxidation of propene in the absence of gaseous oxygen: II. Bismuth molybdates and iron antimonates

Propene oxidation in the absence of gaseous oxygen has been studied on unsupported bismuth molybdate with atomic ratio MoBi = 2.66, and on unsupported iron antimonates prepared according to various procedures. The study was carried out in a flow reactor: the distribution of the products and the oxygen consumption were followed. The experimental conditions were: temperature, 450–550 °C; C3H6 WHSV, 0.1–0.2 hr−1; and C3H6 partial pressure, 108 mbar. On bismuth molybdate and iron antimonate with ratio SbFe = 2 the main oxidation product was acrolein, whereas for SbFe = 1 deep oxidation products were obtained. The structural modifications occurring during the reduction of bismuth molybdate are pointed out and the structure of the intermediate phase was elucidated. The chemical composition of this intermediate is close to 2Bi2O3 · MoO3 and the structure is monoclinic pseudo-tetragonal (a = b = 5.58 A; c = 11.62 A; γ = 89.00 °). The different behavior of iron-antimony catalysts obtained varying the chemical composition and the thermal treatment of the samples supports the hypothesis that the two phases of the catalyst, FeSbO4 and Sb2O4, cooperate in producing acrolein with a higher selectivity than on each phase alone. A mechanism has been proposed to explain the phenomenon.

Oxidation of propene in the absence of gaseous oxygen: I. Single metal oxides

Abstract The oxidation of propene in the absence of gaseous oxygen has been studied on unsupported antimony, bismuth, iron, molybdenum and tin oxides. The study was carried out in a flow reactor by following the distribution of the products and the oxygen consumption. The experimental conditions were: temperature, 450–600 °C; C 3 H 6 WHSV, 0.05–4 hr −1 ; C 3 H 6 partial pressure, 60–1000 mbar. The main oxidation products were 1,5-hexadiene, benzene, acrolein and, of course, carbon monoxide and dioxide. The above-mentioned oxides can be classified according to their catalytic behavior as follows: (a) highly active, not selective-Fe 2 O 3 ; (b) active and selective —Bi 2 O 3 , MoO 3 ; (c) weakly active and selective-Sb 2 O 4 , SnO 2 . The highest selectivity to 1,5-hexadiene was obtained on Sb 2 O 4 , to benzene on Bi 2 O 3 and to acrolein on MoO 3 . The influence of operative parameters, reduction of the catalyst and the trend towards the different allylic products on the various oxides are discussed.

Sieving effects of hormites in gas-adsorption chromatography

Abstract Sepiolite, a clay mineral of the hormite group characterized by a porous lattice, was tested as a stationary phase in gas chromatography. The adsorbent is homogeneous and is able to separate molecules on the basis of steric factors. Oxygen, nitrogen, methane and carbon monoxide are easily separated at −78°; carbon dioxide is eluted with a symmetric peak at room temperature. A simple ballistic programme is able to perform the complete resolution of all the above components with a short column (80 cm long). As the specific interactions are weak, sepiolite may be applied to the separation of liquid hydrocarbons on the basis of their geometric configurations. The elution order for the paraffins is: doubly branched alkanes, singly branched alkanes, straightchain alkanes. The resolution between cis and trans forms of disubstituted cycloalkanes is very high. The values for the efficiency and symmetry are such that the use of sepiolite in gas-solid chromatography is considered to be practical.

Selective adsorption properties of the surfaces of attapulgite and sepiolite

Abstract Representative samples of sepiolite and attapulgite, clay minerals of the hormite group characterized by a porous lattice, were tested as stationary phases in gas—solid chromatography. The selectivity and efficiency of such adsorbents are largely dependent upon differences in surface geometry and homogeneity. In gas analysis, the most interesting application of hormites appears to be the possibility of separating O 2 , N 2 , CO, CH 4 , CO 2 and light hydrocarbons by using a single short column. Configurational and steric isomers are easily resolved on hormites. The selectivity towards isomeric alkanes may be related to the different sizes of the open channels on the external surface of such minerals. The resolution between cis and trans forms of disubstituted cycloalkanes is very high. For instance, there is a complete separation of all the dimethylcyclopentane isomers, and very high relative volatilities are shown by the cis and trans forms of dimethylcyclohexanes. Efficiency values are such that the use of hormites in gas—solid chromatography has proved to be practical.