E.M. Ezzo

Catalytic conversion of alcohols on Al2O3-Cr2O3 catalysts I: The catalytic decomposition of ethanol

Abstract The catalytic conversion of ethanol on Cr 2 O 3 -Al 2 O 3 catalysts was studied using a flow technique. The catalytic activity was measured in the temperature range 280–350 °C at a space velocity of 0.37–0.63 min -1 under normal pressure. Three catalyst samples containing 13.62, 16.66 and 39.50 wt.% Cr 2 O 3 were prepared by coprecipitation of mixed hydroxides using NH 4 OH at 70 °C. The gels obtained were dried at 140 °C and were calcined at 400, 600 and 750 °C. The gaseous and liquid products of the conversion reaction were analysed using chromatography. The gaseous product was mainly ethylene. Water, ether and traces of acetaldehyde and acetone constituted the liquid products, together with unreacted ethanol. The proportion of each liquid depended on the composition of the catalyst and on its calcination temperature. The kinetics of ethylene formation revealed a zero order reaction in all cases and the apparent activation energy was calculated to be 12.5 ± 1.0 kcal mol -1 independent of both the chemical composition and the calcination temperature of the catalyst employed. The catalytic activity and selectivity, however, did depend on catalyst composition and calcination temperature. The formation of acetone and the significant gain in the mass of each catalyst sample after participation in ethanol conversion are explained in terms of the formation of condensation products on the catalyst surface; the conversion may proceed via decomposition of these condensation products or it may follow the polymolecular mechanism proposed by Rudenko.

Studies on the mixed oxide catalyst Al2O3-Cr2O3 I. Surface properties

Abstract The surface properties of pure alumina and its calcination products and of alumina-chromia mixed gels calcined in the temperature range 300–750 °C were studied by the adsorption of nitrogen at -195 °C. The surface areas, micropore volumes and the pore volume distributions were evaluated for the calcination products. With the rise of calcination temperature above 500 °C, the surface areas decreased considerably while the mean pore radius increased. Sintering at temperatures higher than 500 °C resulted in pore widening. Chromia inhibited the sintering of alumina when present in amounts of 5 or 15 mol.%.

Studies of the mixed oxide catalyst Al2O3-Cr2O3 III: The catalytic conversion of isopropanol

Abstract The heterogeneous catalytic process of ethanol conversion on a Cr 2 O 3 catalyst was studied using a flow technique. The catalytic activity was measured in the temperature range 300–480 °C at space velocities of 57.01–95.02 min -1 . The Cr 2 O 3 catalyst was prepared by the precipitation of hydroxide using NH 4 OH at 70 °C. The gel obtained was dried at 140 °C and was calcined at 400, 500, 600 and 750 °C. The surface areas, mean pore radii and crystallite sizes were determined for the heat-treated samples. Thermogravimetric and X-ray analyses were also carried out. The gaseous and liquid products of the conversion reaction were analysed chromatographically. The kinetics of ethylene formation revealed a zero-order reaction in all cases and the apparent activation energy was calculated to be 16.7 kcal mol -1 . The effect of the chemical composition of the mixed catalyst Al 2 O 3 -Cr 2 O 3 on its activity and selectivity was discussed. The Al 2 O 3 -Cr 2 O 3 catalyst containing 5–15 wt.% Cr 2 O 3 had surface areas of 180–200 m 2 g -1 and after calcination at 400 °C showed the highest activity in the conversion of ethanol. The results are discussed in terms of the different decomposition mechanisms for the polymolecular catalytic complex. These mechanisms depend on the kinetic conditions.

Conversion of hydrocarbons over an NiAl2O3 catalyst I: Surface and catalytic studies of the NiAl2O3 catalyst

Abstract 17.99%NiAl2O3 was prepared by the coprecipitation of mixed hydroxides from their nitrate solutions. The surface area SBET, the mean pore radius and the crystallite size of the sample were determined. Thermogravimetric and X-ray analyses were also carried out. The analysis of nitrogen adsorption data gave a value of 322 m2 g−1 for SBET and a value of 11.1 A for the average pore radius, indicating microporosity. The values of the d spacing obtained from the X-ray analysis were examined and the catalyst type was determined at 400, 600 and 750 °C. The crystallite size increased as the calcination temperature increased from 400 to 750 °C. The catalytic conversion of cyclohexane on an NiAl2O3 catalyst was studied using a flow technique. The catalytic activity was measured in the temperature range 400–480 °C at a space velocity of (11.93−48.13) × 10−4 min−1 under normal pressure. The gaseous and liquid products of the conversion reaction were analysed chromatographically. The gaseous products were methane, ethane and hydrogen, and the liquid products were benzene and cyclohexene together with unreacted cyclohexane. The kinetics of the gaseous products and of cyclohexene and cyclohexane revealed a zero-order reaction, but that of benzene did not. The apparent activation energy was calculated to be 21.08±0.5 kcal independent of space velocity. The formation of different products and the significant gain in the mass of the catalyst after its participation in the cyclohexane conversion are explained in terms of the formation of condensation products on the catalyst surface; the conversion may proceed via decomposition of these condensation products or it may have a polymolecular mechanism.

High temperature adsorption of cumene on decationated zeolite as influenced by the adsorbent crystallinity

Abstract The adsorption of cumene at 200–400 °C on decationated zeolite was carried out using a dynamic micropulse technique. The crystallinity of the zeolite sample was modified by treating it with water at room temperature and then heating it in a current of air at 450 °C. The degree of crystallinity was found to decrease considerably when the amount of water brought into contact with the zeolite sample reached 2.5 × 10 −2 mol g −1 . The retention volumes of cumene at 200–400 °C on zeolite treated with different amounts of water were calculated. The data obtained permitted us to compute the initial heat of adsorption of cumene. The heat of adsorption of cumene was found to decrease gradually when the number of hydration-dehydration cycles was increased. It was 21 kcal mol −1 for a fresh sample and 4.3 kcal mol −1 for the water-treated sample. These results are explained in terms of the collapse of the crystal structure of zeolite on being treated with water.

Conversion of hydrocarbons over cobalt oxide catalysts I: Surface and catalytic studies of the cobalt oxide catalysts

Abstract A cobalt oxide catalyst was prepared by precipitation of cobalt hydroxide from its nitrate solution. It was activated by passing dry air or pure hydrogen through it. Thermogravimetric analyses and X-ray diffraction analyses were carried out and the crystalline size and the surface area for the cobalt oxide catalysts were determined. The cobalt oxide catalyst lost its water of crystallization and water of hydroxylation at 250 °C. The results obtained from the X-ray diffraction measurements were compared with those given in the ASTM cards and the type of crystal was determined at 400, 500 and 750 °C. The crystallite size increased over the temperature range from 400 to 750 °C. From nitrogen adsorption measurements, the specific surface area for the cobalt oxide catalyst was found to be 6.5 m 2 g -1 . The catalytic conversion of cyclohexane on the cobalt oxide catalysts was studied using a flow technique. The catalytic activity was measured in the temperaturee range 420 × 490 °C at a space velocity of 6.97 × 10 -2 - 12.11 × 10 -2 min -1 under normal pressure. The gaseous and liquid products of the conversion reaction were analysed using chromatography. The gaseous products were hydrogen and methane. Benzane and cyclohexene were the liquid products, together with unreacted cyclohexane. The kinetics for the gaseous products, cyclohexene and cyclohexene revealed a zero-order reaction. The apparent activation energy was calculated to be 30.8 kcal mol -1 for cyclohexane independent of the space velocity. The formation of different products and the significant gain in the mass of the catalyst after participation in cyclohexane conversion are explained in terms of the formation of condensation products on the catalyst surface; the conversion may proceed via decomposition of these condensation products or it may follow the polymolecular mechanism.

A polymolecular mechanism of conversion of cyclohexene on Pd-Al2O3 catalyst☆

Abstract The kinetics of conversion of cyclohexene on Pd-Al 2 O 3 in a flow system at temperatures from 70 to 300 °C and under various partial pressures of reactive substance in the range 760 - 20 mmHg were studied. The presence of methyl groups in the structure of condensation products on the catalyst surface was established. The effect of pretreatment with different gases on the activity and selectivity of the catalyst was observed using an impulse technique. The main product and the composition of the condensation products were analysed. The condensation products were intermediate substances in the main process. During the process the labile part of the condensation products was able to decompose giving benzene, cyclohexane, cyclohexadiene and methyl cyclopentane at elevated temperatures. The labile condensation products contained more dehydrogenated substances than were present in the reaction product. The net content of benzene in these condensation products was greater than the absorption capacity of the catalyst by a factor of 2.4. The relative amount of labile condensation products decreased with increase in working time of the catalyst. The results obtained provide evidence of the effective contribution of the labile condensation products in the conversion of cyclohexene via a polymolecular mechanism.

Conversion of hydrocarbons over an Ni-Al2O3 catalyst II: Study of the mechanism of the conversion of cyclohexene

Abstract The catalytic conversion of cyclohexene on an Ni-Al2O3 catalyst was studied using a flow technique. The catalytic activity was measured in the temperature range 360–450 °C at space velocities of 11.93 × 10-4 − 48.13 × 10-4 min-1 under normal pressure. The gaseous and liquid products of the disproportionation reaction were analysed chromatographically. The gaseous products were methane, ethane, propane and hydrogen, and the liquid products were cyclohexane, methylcyclopentane, cyclohexadiene, benzene, toluene and p-xylene together with unreacted cyclohexene. The kinetics of the gaseous products and of cyclohexadiene, toluene, p-xylene and cyclohexane revealed a zero-order reaction. However, this was not the case for benzene. The apparent activation energy was calculated to be 16.39±0.5 kcal mol-1 independent of the space velocity. Artificial cyclohexene-benzene and cyclohexene-cyclohexene mixtures were prepared. It was shown that benzene can be obtained directly from cyclohexene and/or indirectly from the cyclohexane produced by the disproportionation reaction. The formation of different products and the gain in the mass of the catalyst after participation in cyclohexene conversion are explained in terms of the formation of condensation products on the catalyst surface which may decompose in different ways giving reaction products.

The influence of water treatment on the relation between the adsorptive and catalytic properties of ScY zeolite

Abstract The high temperature adsorption of cumene as well as its cracking on ScY zeolite were investigated using a pulse chromatographic technique. 12.3% of sodium ions were substituted by scandium ions. The effect of water on both the adsorptive and catalytic properties was investigated. Treatment of 20 mg of catalyst with a small amount of water (10-2 ml) was found to decrease the catalytic activity considerably. The degree of deactivation was dependent on both the temperature of treatment with water and the mode of activation of each catalyst sample. In contrast, neither the heat of adsorption nor the retention volume of cumene was found to vary appreciably with water treatment. These results may point to the absence of a direct relation between adsorption and catalysis in this case.

Study on the dependence of the activity of the conversion of hydrocarbons on the metal content of the catalyst

Catalysts with different contents of nickel are used in studying the effect of changing the metal content on the conversion of cyclohexane using a flow technique under normal pressure. An increase in the catalytic activity is observed with the increase in nickel content which is explained by the difference in the chemical composition and different types of active centres of the different catalysts produced after the thermal treatment.